US 5591551

I'll research US patent 5591551 across the requested sources.

Let me pull the claim text and check for any litigation/CAFC activity.

US 5,591,551 — Summary and Sourcing Notes

Important upfront caveat on sourcing. The authoritative full text you supplied (fetched from Google Patents on 2026-09-26) is truncated in the "Description/Definitions" section — it cuts off immediately after the summary of U.S. Pat. No. 4,315,998 (Neckers et al.), before the claim set. The following summary therefore uses: (a) the bibliographic cover-page data in your supplied text, (b) the abstract as it appears in secondary databases, and (c) claim language from the same patent family (notably EP 0 563 251 A1 and the sibling U.S. patent 5,376,503). I flag explicitly below which items I could not verify verbatim against the US 5,591,551 claim set itself.

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Bibliographic data

Date discrepancies to be aware of (do not auto-correct): the Unified Patents portal lists the same patent with priority 1990-12-19, application date 1995-06-06, grant date 1997-01-06, and expiration 2014-01-06 — i.e., uniformly one day earlier than the Google Patents cover page. These are almost certainly time-zone/UTC-vs-local artifacts, but I am reporting both literally rather than silently harmonizing them.

Prosecution chain: the cover page of the immediate family sibling US 5,376,503 (Audett et al., granted 1994-12-27, application 07/982,104 filed 1992-11-24) recites that it is a "continuation of Ser. No. 613,610 filed Dec. 20, 1990 now abandoned," while its own front-page field [63] is rendered in one source as "Continuation of Ser. No. 631,610, Dec. 20, 1990, abandoned." The 613,610 vs. 631,610 discrepancy is an OCR ambiguity I cannot resolve from the available text; note it literally.

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Abstract

"A lithographic coating and method of forming a lithographic image are disclosed. The method comprises coating at least a portion of a surface of an article with a radiation-crosslinkable polymer, and exposing the coated surface to a pattern of radiation to crosslink the polymer in a lithographic image. The functionalized polymer is a copolymer of an isoolefin of 4 to 7 carbon atoms and para-alkylstyrene, wherein the para-alkylstyrene is functionalized with a radiation reactive group at the para-alkyl group of the para-alkylstyrene."

Note on the word "framing": several reproductions of this abstract — including the Unified Patents portal entry and the OCR of US 5,376,503 — render it as "method of framing a lithographic image." Given that the body text of the family consistently describes "making a lithographic image," I read "framing" as an OCR/transcription artifact for "forming." I am noting this rather than silently correcting it, per instructions.

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Independent claims — plain language

Caveat: I could not verify the literal claim text of US 5,591,551, because your authoritative source is truncated before the claims. What follows is reconstructed from the family's claim sets, which the abstract and specification indicate are parallel. Treat the substance as reliable and the exact wording/numbering as unconfirmed for 5,591,551.

Based on the family (EP 0 563 251 A1, claim 1 and claim 26; and sibling US 5,376,503, which issued with 8 claims, no drawings), the patent appears to have two independent claims:

1. A composition/coating claim. A coating (a lithographic coating, and in other statements a corrosion-resistant coating) comprising a radiation-crosslinkable, functionalized copolymer of:

   • an isoolefin having 4 to 7 carbon atoms (isobutylene being the species used throughout the examples), and
   • a para-alkylstyrene comonomer,
   • where the para-alkylstyrene carries a radiation-reactive functional group attached at the para-alkyl group (i.e., on the benzylic carbon of the para-methyl/para-alkyl substituent) rather than on the aromatic ring or the polymer backbone.
   • The preferred composition also permits a tackifier blended in at roughly 5–95 parts by weight (more preferably about 30–70 parts).

2. A method claim — "A method for making a lithographic image on a surface," comprising:

   • (a) coating at least a portion of a surface of an article with the radiation-crosslinkable functionalized isoolefin/para-alkylstyrene copolymer, said functionalized polymer having a substantially homogeneous compositional distribution; and
   • (b) exposing the coated surface to a pattern of radiation to crosslink the polymer into a lithographic image.

The dependent claims in the family add: forming an image/mask that selectively blocks radiation before exposure; leaving part of the polymer uncrosslinked after exposure; developing by removing the uncrosslinked polymer; and species/ratio limits on the para-alkylstyrene units.

The technical point of novelty in plain language: conventional UV/EB-curable systems either (i) require separately blended photoinitiators/crosslinkers — which are toxic, volatile and hard to handle — or (ii) put the reactive unsaturation in the polymer backbone, where radical chemistry can also degrade the chain. This patent instead hangs a benzylic-radiation-reactive group off the para-alkyl position of a saturated-backbone isoolefin/para-alkylstyrene copolymer. The saturated backbone resists radical degradation, and the reactive group is installed by selective benzylic bromination followed by nucleophilic substitution of the benzylic bromine, so the functionality ends up in a controlled, homogeneous position rather than randomly grafted.

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Litigation / CAFC check — negative result

I searched for U.S. Patent 5,591,551 (and the spaced/alphanumeric variants 5,591,551 and 5591551) in connection with CAFC 2026 dockets, USPTO PatentCenter, and assignment records.

• I found no CAFC 2026 docket entry, appeal, or IPR/PGR referencing US 5,591,551. I must be explicit that I was not able to query the CAFC docket system or USPTO PatentCenter directly; my search was web-based, so treat this as "no evidence found," not as "confirmed absent."
• This negative result is highly plausible on the merits: the patent's anticipated expiration was 2014-01-07 (per Google Patents) and its status is "Expired – Fee Related." A patent that expired over a decade ago would not ordinarily be the subject of a live 2026 CAFC appeal.
• The only forward citations of 5,591,551 I could identify are examiner citations in later, unrelated applications (e.g., US 5,888,690 to Canon; US 8,996,623 to Wisconsin Alumni Research Foundation; EP 1,379,918), which is evidence of its prior-art significance, not of litigation.

One caveat on noise in the search results: a Japanese patent publication (J-GLOBAL) also carries the number "5591551" — that is a Japanese patent number for a powder-coating booth apparatus (application 2010-021018), entirely unrelated to US 5,591,551. Do not conflate the two.

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What I do not know with confidence

• The exact literal wording and count of claims in US 5,591,551 itself. My overview is derived from the parallel family members (EP 0 563 251 A1 and US 5,376,503, the latter issuing with 8 claims). The claim count may differ in 5,591,551.
• Whether the issued US 5,591,551 independent claims are phrased as a coating/composition claim, a method claim, or both, in that precise form.
• The exact continuation sequence (Ser. No. 613,610 vs. 631,610) leading to the 1995 filing.

Family members (for completeness)

EP 0 563 251 A1 and WO 92/11322 A2 are the corresponding international filings (priority 1990-12-20). Sibling U.S. patents from the same disclosure include US 5,376,503 (1994-12-27), US 5,459,174 (1995-10-17), US 5,585,225 (1996-12-17), US 5,587,261 (1996-12-24), US 5,585,416 (1996-12-17), and US 5,824,717 (1998-10-20).

Sources: Google Patents, https://patents.google.com/patent/[US5591551A](/patent/US5591551A)/en ; Unified Patents portal, https://portal.unifiedpatents.com/patents/patent/US-5591551-A ; Espacenet cited-documents listing; EP 0 563 251 A1 claim text as reproduced at patenthub.cn; US 5,376,503 front page and abstract at patentimages.storage.googleapis.com.

I'll search for litigation involving US patent 5591551 across multiple sources.

Let me search additional litigation-specific sources to be thorough.

Let me check dedicated litigation portals and docket databases directly.

Litigation Search Results: U.S. Patent No. 5,591,551

Finding: No litigation involving U.S. Patent No. 5,591,551 was identified in any of the sources searched.

I searched general web results and patent-specific portals (including the Unified Patents patent page for US-5591551-A, Google Patents, CourtListener/Free Law Project, USPTO.report, and Federal Circuit opinion pages). None returned any district court case, ITC action, PTAB proceeding, or Federal Circuit appeal naming U.S. Patent 5,591,551 as a patent-in-suit or as the subject of a validity challenge.

Why this result is consistent with the record

The patent's own prosecution/legal-status data supports the absence of litigation:

Because the patent expired in January 2014 and lapsed for non-payment of maintenance fees, and because enforcement risk was concentrated at Exxon/ExxonMobil (not a non-practicing entity), the absence of recorded infringement litigation is unsurprising. Even if a suit had once existed, an expired, fee-lapsed patent of this type is not the sort of asset typically found on NPE assertion dockets.

Important caution — do not conflate with similar identifiers

My searches surfaced several unrelated items bearing the string "5591551," none of which is U.S. Patent No. 5,591,551:

• JP Patent No. 5591551 — a Japanese patent titled "粉体塗装装置" (powder coating apparatus), application 2010021018, published 2011-08-18. This is a Japanese patent number, not the U.S. patent.
• Commodity/listing no. 5591551 on a Chinese patent marketplace, corresponding to CN202010274322.0 ("水性环氧树脂石墨烯复合材料"), an unrelated Chinese application.
• U.S. Patent No. 5,585,416 — a sibling Exxon patent with the same title ("UV/EB curable butyl copolymers…"), a separate patent number from the same family. If you intend to search for litigation on the Exxon UV/EB butyl copolymer family generally, the '416 patent would need to be searched separately.

I did locate Exxon-related patent litigation in the search results (e.g., Dow Chemical Co. v. Exxon Chemical Patents, Inc., D. Del., re U.S. Pat. No. 4,783,510/′783 patent; Exxon Chemical Patents, Inc. v. Lubrizol Corp., 64 F.3d 1553 (Fed. Cir. 1995); an E.D. Tex. action re the ′761 patent; and Exxon Chemical Patents Inc v The Associated Octel Co Ltd), but none of these involve U.S. Patent No. 5,591,551.

Limitations on this finding

• I could not complete a direct PACER docket query or a full run of CourtListener's litigation database for this number within the search steps available; my conclusion rests on aggregated public sources and the official patent record.
• Public litigation databases are not exhaustive of every historical filing, and older or sealed cases may not appear.
• "No litigation found" is a statement about what the searched sources show, not a legal conclusion that no litigation ever existed.

Suggested next step if you need certainty: run a docket-level search for "5,591,551" (and its family members, e.g., 5,585,416) in PACER, Docket Navigator, Lex Machina, or Westlaw Litigation Analytics, which index case dockets rather than relying on web indexing.

I'll verify the structured block's finding against public sources before writing up.

Let me confirm against the PTAB/Unified portals and check for any Federal Circuit appeals.

Proceedings overview

Total AIA trial proceedings on U.S. Patent No. 5,591,551: zero (0). Breakdown by status: active — 0; claims invalidated — 0; claims sustained — 0; settled — 0; institution denied — 0. The USPTO Open Data Portal structured record for this patent returns no AIA trial proceedings, and my independent web searches (Unified Patents portal, PTAB/PTAB E2E document searches, Docket Alarm PTAB dockets, Google Patents, CourtListener) surfaced no IPR, PGR, CBM, or Federal Circuit appeal in which 5,591,551 appears as the challenged patent.

Bottom-line defensive posture: this is not a "hardened" patent and it is not a "claims-canceled" patent — it is an untested but dead patent. U.S. 5,591,551 expired (and lapsed for non-payment of maintenance fees) on 2014-01-07, roughly three years before the AIA trial regime hit its stride and a decade before today's assertion dockets. The correct defensive read is therefore not "the patent survived two IPRs," but "no PTAB proceeding was ever filed, the patent has been expired for over twelve years, and no validity determination — administrative or judicial — exists on the record." There is no proceeding write-up below because there is no proceeding to write up.

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⚠️ Identifier-confusion warning (read before any file review)

Searches for "5591551" are heavily polluted by U.S. Patent No. 9,955,551 — a totally unrelated patent ("Detector Controlled Illuminating System," inventor Yechezkal Evan Spero, automotive adaptive headlamps). That patent is the subject of multiple AIA trials:

• IPR2023-00315 and IPR2023-00318 — Volkswagen Group of America, Inc. v. Spero (challenging claims including 48–87 / 56–87)
• IPR2023-01320 — Porsche Cars North America
• Ex parte reexamination 90/014,815, filed 2021-07-30 (Patent Owner-requested)

Those proceedings have nothing to do with U.S. 5,591,551. Likewise, U.S. 7,280,551 (NTT, MediaTek v. NTT, IPR2020-01404) and U.S. 6,700,551 (IPR2014-01198) are unrelated. Do not let an automated clearancetool or an AI docket summary conflate these — the trailing "551" is the only commonality.

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Proceedings

None. There is no AIA trial proceeding on U.S. 5,591,551 to report, and I will not manufacture proceeding numbers or alleged outcomes to fill this section.

Why the absence is structural, not accidental

PGR is unavailable by statute. 35 U.S.C. § 321(c) requires a PGR petition within nine months of issuance; this patent issued 1997-01-07, and the PGR regime only applies to patents subject to the first-inventor-to-file provisions. Both bars are independently dispositive.

CBM is unavailable. The CBM transitional program (AIA § 18) sunset for new petitions on 2020-09-16 and, in any event, is limited to patents claiming a method or apparatus for performing data processing or other operations used in the practice, administration, or management of a financial product or service. A UV/EB-curable butyl copolymer coating patent is facially outside that subject-matter gate.

IPR is theoretically available but offers no value. The Board can institute on an expired patent (the claims are construed under Phillips v. AWH Corp., 415 F.3d 1303 (Fed. Cir. 2005), and amendment is foreclosed), but IPR is a defensive tool against exclusionary rights. Here there is no live right to defend against, no pending or threatened assertion, and therefore no petitioner with an incentive or a § 315(b) trigger. The absence of IPRs on this patent is a market signal, not a strength signal — nobody ever needed to invalidate it because nobody ever asserted it.

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Strategic summary

Claim status: entirely UNTESTED. Because no AIA trial, no ex parte reexamination, and no district court invalidity judgment appears on the record, every claim of 5,591,551 stands exactly as it issued on 1997-01-07 — neither canceled nor affirmed. There are no surviving claims to enumerate and no dead claims to avoid. The entire claim set (including the lithographic coating and framing-method claims described in the abstract, and the counterpart claims appearing in the sibling Exxon patent U.S. 5,585,416, which shares this title) is untested as of today.

Estoppel landscape: not applicable, which is actually helpful. Section 315(e)(2) estoppel only arises from a petitioner who obtained a Final Written Decision. With zero petitioners, no estoppel attaches to anyone, and no prior-art ground is foreclosed by a prior PTAB record. A defendant hypothetically facing this patent would have the full universe of § 102/§ 103 art available in district court and would face no § 325(d) "previously presented to the Office" saturation problem. That said, this is largely academic: the more decisive defenses are temporal. A patent that expired 2014-01-07 cannot support infringement liability for any act after that date, and § 286's six-year damages lookback plus the expired, fee-lapsed status means there is essentially no recoverable window.

Pattern signals: none. No repeat petitioner, no serial-petition pattern, no PTAB appeal history, and no defensive aggregator involvement. The Unified Patents patent page for US-5591551-A exists (a standard database entry, not evidence of a Unified challenge) and shows Lifetime Renewal Fees: $0 — the tell that ExxonMobil let the asset lapse rather than pay to maintain it. Exxon's copolymer-coating program generated a family of patents (including 5,585,416, cited as a sibling in the litigation section above), and the family as a whole shows no PTAB trail in my searches.

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Recommended next steps

1. If you are a defendant or recipient of a demand letter citing U.S. 5,591,551: stop and check the date. The patent expired 2014-01-07 and lapsed for non-payment of maintenance fees. Any demand premised on post-2014-01-07 activity is unsupportable, and any demand premised on older activity runs into the § 286 six-year damages bar. Ask the sender for the basis of the assertion in writing; a demand on an expired, fee-lapsed patent is itself a candidacy for a § 285 exceptional-case argument and, in egregious cases, state-law unfair-competition exposure.
2. Verify the patent owner's chain of title before engaging on the merits. Current assignee of record is ExxonMobil Chemical Patents Inc. — a large operating company, not an NPE. If a third party is asserting 5,591,551, demand documentation of the assignment, because a lapse and a stale assignment dispute are both plausible.
3. Confirm at docket level before relying on "zero." The structured ODP block and my searches agree, but the gold-standard confirmation is a direct query in PTAB E2E / the PTAB Patent Appeal Search (https://ptab.uspto.gov/) and USPTO PatentCenter for application 08/474,870, plus a PACER or Docket Navigator run on "5,591,551." Older and sealed matters may not be web-indexed; "no proceedings found" is a statement about the searched sources, not a legal certainty.
4. Check the family separately. U.S. 5,585,416 (same title, Exxon) and any EP counterpart (EP 0563251 A1 appears in search results as the European family member) must be searched independently. A clean result on 5,591,551 does not clear the family.
5. Do not cite IPR2023-00315, IPR2023-00318, or IPR2023-01320 as proceedings on this patent. Those are Volkswagen/Porsche challenges to U.S. 9,955,551 (Spero). If a vendor, AI summary, or opposing counsel has bundled them into a chart for 5,591,551, that is an error and should be corrected on the record.

Sources consulted

• Google Patents record for US5591551A (authoritative patent text and legal status): https://patents.google.com/patent/US5591551A/en
• Unified Patents patent portal page for US-5591551-A (renewal-fee and assignee data): https://portal.unifiedpatents.com/patents/patent/US-5591551-A
• PTAB E2E / USPTO PTAB Decisions portal (for any final written decision — none located): https://ptab.uspto.gov/
• CourtListener (Federal Circuit and district court opinions — no hits for this patent): https://www.courtlistener.com/
• USPTO Open Data Portal AIA trial proceedings record (structured input to this analysis) — returns zero proceedings.

Confidence statement: I am highly confident there is no AIA trial proceeding on U.S. 5,591,551. I could not complete a direct PACER docket query or an exhaustive CourtListener docket sweep, so I cannot exclude the theoretical possibility of a historical, sealed, or non-indexed filing — but the patent's 2014 expiration and fee lapse make such a filing economically implausible.

I'll research the assignment record for US 5,591,551 across the USPTO Assignment Center and cross-referenced sources.

Let me dig into the actual USPTO assignment records and corporate history for the assignee chain.

Let me try to access the assignment records directly and check Google Patents legal events.

Assignment Record Reconstruction — U.S. Patent No. 5,591,551

Data-access caveat (read first). I was unable to pull reel/frame-level assignment entries from the USPTO Assignment Center within my available search steps. My queries to assignment.uspto.gov / assignmentcenter.uspto.gov and to indexed mirrors returned the patent's bibliographic record and litigation/legal-status data, but not the itemized conveyance list with reel/frame numbers, correspondent names, or execution dates. Per the operating rules, I will not invent reel/frame numbers. Where the record is unverified, I say so explicitly. The conclusions below rest on the durable bibliographic field Current Assignee: ExxonMobil Chemical Patents Inc. and Original Assignee: Exxon Chemical Patents Inc., both of which are consistent across the patent record and the Unified Patents portal.

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Inventors

Notes on pattern:

• Two named inventors, both assignors to the corporate parent's IP-holding subsidiary — a standard large-corporate invention-assignment arrangement, not an inventor-retention or university-style pattern.
• The application (US 08/474,870, filed 1995-06-07) carries a priority date of 1990-12-20 (Google Patents) vs. 1990-12-19 (Unified Patents portal). This one-day discrepancy is a source artifact; the salient point is that the '551 patent is a later continuation/division in a 1990-origin family, so the "filing" date is not the true conception date.
• No evidence was found that either inventor departed Exxon within 12 months of filing, or that there was any portfolio fire-sale. I cannot confirm or deny departure history from available sources — flagging as unverified rather than asserting it.

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Original assignee

Exxon Chemical Patents Inc. — the entity named on the issued patent (grant 1997-01-07).

• Primary line of business: A patent-holding / IP-management subsidiary of Exxon Chemical Company (Exxon Corporation). It is an IP-holding vehicle, not an operating manufacturer — but it is an affiliate of a major operating company, which is materially different from an NPE shell (it exists to hold a global operating company's chemical patents, not to assert them against non-competitors).
• Product embodying the claims: The patent family covers isobutylene / para-alkylstyrene copolymers functionalized at the benzylic position for radiation curability — the same chemistry platform behind Exxon's Exxpro™ functionalized isobutylene-para-methylstyrene elastomer line (brominated/functionalized PMSI). I am moderately confident (not certain) that Exxpro™ is the commercial embodiment of this copolymer platform; I could not verify in this session that a product practicing the specific UV/EB-curable claims was commercially sold. Treat "shipped a product" as probable at the platform level, unverified at the claim level.
• Current status: Still an operating-company-affiliated IP holder. Following the Exxon–Mobil merger (announced Dec 1998, closed 1999-11-30), the patent record now lists ExxonMobil Chemical Patents Inc. as current assignee and Exxon Mobil Corp as parent. No bankruptcy, dissolution, or assignment to a non-practicing entity appears anywhere in the record.

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Assignment timeline

The USPTO Assignment Center itemized conveyance list could not be retrieved in this session. I therefore cannot report reel/frame numbers, execution dates, correspondent of record, or conveyance types with the precision the task requires, and I decline to fabricate them.

What the verified bibliographic record supports as the ownership chain shape (conveyances and dates below are inferred from the assignee names and corporate history, not read off reel/frame):

• Inventors → Exxon Chemical Patents Inc. (conveyance: inventor Assignment; date unverified — expected in the 1990s, contemporaneous with the 1990-origin family)
  • Assignee: Exxon Chemical Patents Inc.
  • Context: internal corporate invention assignment.
• Exxon Chemical Patents Inc. → ExxonMobil Chemical Patents Inc. (conveyance: likely Merger or Change of Name; date unverified — expected circa 2000, following the Nov 1999 Exxon–Mobil combination)
  • Assignee: ExxonMobil Chemical Patents Inc.
  • Context: internal reorg / corporate name change only. No consideration to an outside party; no NPE involvement.

To obtain the authoritative reel/frame list, search the Assignment Center by patent number:

• https://assignmentcenter.uspto.gov/ (search "5591551" / application "08/474,870")
• Mirror: https://assignment.uspto.gov/patent/index.html

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Timeline diagram

timeline
    title Ownership of US 5591551
    1990 : Priority date for copolymer family
    1995 : Continuation application filed
    1997 : Patent issued to Exxon Chemical Patents
    1999 : Exxon Mobil merger closes
    2000 : Chain shows ExxonMobil Chemical Patents
    2014 : Patent expires
         : Maintenance fees unpaid

(Events reflect the verified assignee/date record and corporate history. If the Assignment Center shows additional conveyances, this diagram must be re-rendered from reel/frame data.)

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NPE / troll-pattern signals

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Verdict

Insufficient data.

The only ownership facts I could verify are the original assignee (Exxon Chemical Patents Inc.) and the current assignee (ExxonMobil Chemical Patents Inc.), which together describe a single internal-affiliate chain reflecting the 1999 Exxon–Mobil merger / name change — not an NPE transfer. Every applicable NPE signal is not present, and the absence of any litigation (per the prior section) plus zero maintenance-fee payment ($0 lifetime renewal fees) means the asset was never monetized by assertion. However, because I could not retrieve reel/frame-level assignment entries, execution dates, or correspondent-of-record from the USPTO Assignment Center, I cannot certify that no intermediate conveyance exists — so the honest verdict is Insufficient data, with the available evidence pointing toward an operating-company–held, non-asserted patent rather than any troll pattern.

Verification link: https://assignmentcenter.uspto.gov/ (search patent 5591551 / application 08/474,870) — this is the source that would let a follow-up analyst convert this from "insufficient data" to a frame-level finding.

I'll search for the patent's citation record across USPTO and other authoritative sources.

Let me retrieve the specific front-page "Patent Citations" list from the patent's official records.

Let me pull the front-page "References Cited" list and the description's cited references more completely.

I hit the tool-call limit before I could pull the verbatim image of the patent's front page, so let me be precise about what I did and did not verify, then give you the citation analysis.

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Prior-Art Analysis — U.S. Patent No. 5,591,551

1. Confirmation of the target and a sourcing caveat

The number 5,591,551 resolves unambiguously to the Exxon patent in the record you supplied:

Sourcing caveat (important, and I will not paper over it): I was not able to retrieve the verbatim front-page "(56) References Cited" list from the USPTO full-text page or the patent PDF. The citations below are the prior-art documents identified in the patent's own specification (Google Patents full text, https://patents.google.com/patent/[US5591551A](/patent/US5591551A)/en) plus family/related records surfaced in search. This set corresponds to the substantive examiner/applicant citation set, but the paper front page may contain additional U.S. Patent Documents I could not confirm. Treat the list below as high-confidence but not certified-verbatim, and let me flag two further discrepancies:

• Unified Patents (https://portal.unifiedpatents.com/patents/patent/US-5591551-A) renders the dates one day earlier than Google Patents (priority 1990-12-19 vs. 1990-12-20; filing 1995-06-06 vs. 1995-06-07; grant 1997-01-06 vs. 1997-01-07). This is almost certainly a time-zone/render artifact, not two different patents, but per the "no auto-correction" rule I am reporting both rather than harmonizing them. The Unified page also shows a "Patent Art (5)" block that I could not expand — if the paper front page lists exactly five U.S. patent documents, my reconstruction below (which is larger, because it includes every reference discussed in the specification) over-includes relative to the formal (56) list.
• Everything below is the same patent number, 5,591,551. I confirm the unrelated items you may see if you search the bare string — JP 5591551 (powder-coating booth, app. 2010021018, publ. 2011-08-18) and Chinese commodity listing 5591551 (CN202010274322.0) — are not this patent and are excluded.

2. The claim structure I am mapping against

Per the abstract and the closely parallel EP family member (EP 0 563 251 A1, same invention), the independent claims are of two types: (i) a radiation-curable coating/composition claim reciting a copolymer of a C₄–C₇ isoolefin and a para-alkylstyrene functionalized with a radiation-reactive group at the para-alkyl group, and (ii) a method claim for "framing"/forming a lithographic image by coating and imagewise exposing. Dependents narrow the photoinitiator chemistry, the W/X/Y/Z substitution scheme, molecular weight, and tackifier content.

Because I did not verify the U.S. claim numbering directly, I map each reference to the claim category rather than asserting specific U.S. claim numbers. If you need the exact claim numbers, I should re-verify against the granted U.S. claim set before you rely on it.

3. Cited references — full citations, dates, description, and § 102 assessment

(The spec also alludes to cinnamoyl-functionalized polypentenamer chemistry and to isobutylene/styrene copolymers generally; those are narrative background, not discrete numbered citations, so I have not tabulated them as references.)

4. Bottom-line § 102 conclusion

No single cited reference anticipates any claim under 35 U.S.C. § 102. The independent claims require, in combination:

1. a copolymer of a C₄–C₇ isoolefin and a para-alkylstyrene;
2. the radiation-reactive group substituted on the para-alkyl group (not on a comonomer, not on the backbone); and
3. (in the narrower claims) a substantially homogeneous compositional distribution, defined molecular-weight limits, and optional tackifier.

Each cited reference fails at least one element — most commonly element (1) and/or (2):

• The butyl-rubber art (#4, Malatesta; and #5, Tobias) is about butyl rubber cured by radiation, but cures via backbone diene unsaturation plus an external photosensitizer — the opposite of the '551 strategy of a saturated backbone with pendant para-alkyl photo-functionality.
• The photosensitive-polymer cluster (#3, #6–#13, #16, #17) installs photosensitivity on styrenic/vinylbenzyl or other backbones, never on an isoolefin–para-alkylstyrene copolymer.
• The radiation-curable copolymer art (#1, #2) uses block copolymers or comonomer-incorporated photo-functionality, not para-alkyl functionalization.
• The copolymerization-control art (#15, Powers) and the nucleophilic-substitution art (#3, #16, Bailey) supply, at most, motivation and technique — classic § 103 material.

So these are properly characterized as § 103 / background references, and the strongest combination the examiner would have had to confront is Malatesta (butyl + UV) + Bailey/Neckers (benzylic chloride → photosensitive nucleophile) + Powers (homogeneous distribution). The patent evidently issued over that combination.

5. Two things worth flagging for your file

(a) Reverse citation — the '551 patent as prior art to others. EP 1 379 918 A4 lists US 5,591,551 A (1997-01-07) with an "[X]" category (i.e., novelty-destroying when taken alone) against that application. That is the '551 patent being used as § 102 art, not received as such — a different question from what you asked, but relevant if you are profiling the patent's technological footprint.

(b) Self-family members are not prior art. US 5,376,503, US 5,585,225, US 5,585,416 and US 5,585,261 share the 1990-12-20 priority and the same inventors/specification. They are family, not citable prior art against the '551 claims, and should not be listed as such. I mention them only because they recur in search results and are easy to conflate — consistent with the caution already noted in the earlier litigation section about US 5,585,416, which carries the identical title.

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If you need this certified: the authoritative source is the granted patent's front page (56) block (USPTO PatentCenter or the USPTO full-text/PDF), which I could not open in this session. A docket-quality prior-art chart should transcribe that block verbatim, then run each item through the § 102 element-by-element mapping above. I can complete that verification if you let me resume with the PDF/USPTO full-text source in hand.

I'll ground the obviousness analysis in the prior-art references actually cited in this patent's specification, and check details on each.

Let me pull the actual cited references and check the key enabling prior art on benzylic bromination of para-alkylstyrene copolymers.

Let me check the key enabling art on benzylic-halogenated isoolefin/para-alkylstyrene copolymers and any additional face-of-patent citations.

Obviousness Analysis — US 5,591,551 under 35 U.S.C. § 103

0. Threshold flags before the analysis begins

Two contradictions/limitations must be stated up front, because they bound how far this analysis can go:

1. Date contradiction. The current task states "Current Date: April 26, 2026," while the patent text supplied for this analysis was fetched 2026-09-26 and the prior generated sections are dated 2026-09-27. I am reporting this literally rather than harmonizing it. Nothing in the analysis below turns on the date, since US 5,591,551 expired in 2014 and no live § 103 challenge is possible — this is a retrospective/validity-study analysis, not a live-controversy analysis.

2. The "Prior Art section of this page" is thin and truncated. The authoritative text you supplied contains a "Definitions" excerpt that names exactly three prior-art references plus a generic background paragraph:

   • U.S. Pat. No. 4,556,464 (St. Clair) — radiation-curable adhesive composition (ABA block polymer + tackifier + crosslinker).
   • European patent application 17,364 — copolymers curable by actinic radiation made with 0.1–10 wt. % allyl benzoylbenzoate comonomer.
   • U.S. Pat. No. 4,315,998 (Neckers et al.) — polymeric materials incorporating photosensitive functionality via nucleophilic substitution.
   • Plus a background paragraph acknowledging that radiation-reactive crosslinking agents "may alternatively be incorporated into the polymer backbone, for instance, by copolymerizing with a radiation-sensitive vinyl polymerizable comonomer. Preparing such comonomers on a large scale is generally difficult," and that "[r]adiation-reactive funtionality may also be grafted onto the polymer backbone in a post-polymerization step, however, the resulting polymer is typically a heterogeneous product of low yield…"

   The supplied text cuts off mid-sentence at "the polymeric materials serve as a platform for he…" and never reaches the claim set or the front-page [56] references-cited list. Per the prior sections, the literal claim wording of US 5,591,551 therefore remains unverified, and this analysis proceeds on the reconstructed independent claims (composition claim + method claim) derived from the family (EP 0 563 251 A1; sibling US 5,376,503). If the issued claims of '551 differ materially from the reconstruction, the element mapping below must be re-run. I flag this rather than paper over it.

   Critically, the three named references cannot by themselves reach the claims. The single most material piece of prior art — Exxon's own benzylic-brominated isoolefin/para-alkylstyrene "base terpolymer" art — is not in the truncated section, but I verified it exists and predates the 1990-12-20 priority date. That is treated in §3(d) below.

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1. What the claim limitations require (element breakdown)

Using the reconstructed independent claims from the family (see prior §"Independent claims — plain language"), the § 103 analysis must account for these distinct elements:

The novelty of the patent sits almost entirely in B + C + D taken together, with F as a structural backstop. Elements A, E, G, H are squarely conventional in the radiation-cure and lithographic arts.

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2. What each named prior-art reference actually teaches (and what it misses)

(a) EP 17,364 / EP 0 017 364 A1 — the closest single reference on the "problem to be solved"

Source: https://patents.google.com/patent/EP0017364A1/en and the EPO PDF at patentimages.storage.googleapis.com/8d/cd/4b/3bc0663ecbb1b5/EP0017364A1.pdf

This reference is unusually damaging because it recites the very problem the '551 is solving, and recites it as a problem already solved in the same way:

• It expressly criticizes the prior-art blending approach: "The use of extraneous photosensitizers blended with the polymers is often accompanied by problems of compatibility, uniformity of distribution, volatility, toxicity or exudation and migration of the additive, often resulting in premature and/or erratic crosslinking."
• It claims the solution: copolymers containing "from 0.1 to 10% by weight" of allyl benzoylbenzoate units "with a wide variety of conventional ethylenically unsaturated vinyl or vinylidene monomers, can be readily cured (i.e. crosslinked) by exposure to radiation."
• It states the benefit in the same terms the '551 relies on: "these polymeric compositions generally exhibit excellent crosslinking ability without the difficulties posed by such problems as volatility, toxicity, migration and premature crosslinking."
• It reaches the coating + radiation method: "A solvent-resistant protective film of the copolymer may be prepared on a substrate by applying to the substrate a composition comprising a solution or dispersion of essentially uncrosslinked addition polymer of the invention, at least partially drying the composition … and … subjecting the film to actinic radiation to at least partially crosslink the polymer."
• It reaches patterned exposure: "subjecting the web containing the polymer to UV light while using a mask having an opening at the crotch area to provide greater curing of the polymer in that area."
• It reaches the tackifier element: one embodiment is "A method of producing a pressure sensitive adhesive which comprises blending 1 to 95 parts by weight … of a copolymer of the invention, 0.1 to 5 parts by weight of at least one photoinitiator, 0.1 to 10 parts by weight of one or more polyethylenically unsaturated monomers…" — note the 1–95 parts range closely parallels the '551's 5–95 (preferably 30–70) parts tackifier element.

What it lacks: elements B (isoolefin), C (para-alkylstyrene), D (functionality at the para-alkyl/benzylic position of a para-alkylstyrene unit), and F. Its comonomer list is explicitly a list of free-radically polymerizable monomers — "styrene; alpha-methyl styrene; vinyl toluene; the acrylic and methacrylic acid esters …; isoprene; acrylamide…; butadiene; … vinyl chloride; vinyl acetate; ethylene; and propylene etc." No isoolefin (isobutylene) appears. Its radiation-reactive group is delivered as a copolymerized allyl monomer, not by post-polymerization substitution on an existing para-alkyl group.

This gap matters and cuts toward non-obviousness. Allyl benzoylbenzoate is an allyl monomer; the isoolefin/para-alkylstyrene copolymerization is cationic (Lewis-acid, slurry). A POSITA could not simply drop EP 17,364's allyl monomer into an isobutylene/para-methylstyrene cationic polymerization. That incompatibility is precisely why the '551 functionalizes after polymerization. I flag this as the strongest genuine technical argument for non-obviousness over EP 17,364 alone — and simultaneously as the motivation that pushes a POSITA toward the Neckers route.

(b) U.S. Pat. No. 4,315,998 (Neckers et al.) — the "how to functionalize a polymer" teaching

Sources: US4315998 PDF (patentimages.storage.googleapis.com/7f/e7/5b/0b63050be48504/US4315998.pdf); claim text at drugpatentwatch.com/p/biologics/patent-claims/4315998

• The claimed subject matter is "the nucleophilic displacement reaction product of (A) a polymeric material having attached thereto an available leaving group which is capable of being displaced in a nucleophilic displacement reaction … and (B) a photosensitizing catalytic compound containing in its molecule a nucleophile which is capable of displacing the leaving group…"
• Claim 1 is a method of making that product by "forming a mixture … of a polymeric material having attached thereto an available leaving group … and a photosensitizing catalytic compound … refluxing said mixture for a time sufficient to effect a nucleophilic displacement reaction between said chloromethylated styrene polymer and said photosensitizing dye." Claim 2: "wherein said polymeric material is a chloromethylated styrene polymer." Claim 8: "said photosensitizing catalytic compound is a parabenzoyl benzoic acid."
• The '551's own background characterizes this reference as teaching that polymeric materials "incorporate photosensitive functionality via a nucleophilic substitution reaction" and that the polymer acts as a "platform" (the truncated English in your text reads "serve as a platform for he…"; the Japanese family member JPH06504628A gives the fuller parallel text: "このポリマー物質は、各種の光開始化学反応の不均一触媒の基盤として役立つ" — the polymer serves as a support/platform for heterogeneous catalysis).

What it lacks: elements B, C, D as such, and F. Neckers' substrate is a chloromethylated styrene/divinylbenzene bead — an insoluble, crosslinked, heterogeneous support — and the attached moiety is a sensitizer dye (rose bengal, methylene blue, etc.) used to generate singlet oxygen, not a chromophore whose purpose is to crosslink the polymer film itself into an image. Element D is also different: Neckers' benzylic —CH₂Cl is on a styrene ring pendent to a polystyrene backbone, which is a different position than the para-alkyl (benzylic) carbon of an enchained para-alkylstyrene unit in an isoolefin copolymer.

What it supplies for § 103: the general, known, predictable technique of installing photosensitive functionality by nucleophilic displacement on a polymer-borne benzylic leaving group. That is the technique. Under KSR Int'l Co. v. Teleflex Inc., 550 U.S. 398 (2007), a known technique used to improve a similar device in the same way is obvious.

(c) U.S. Pat. No. 4,556,464 (St. Clair) — the "radiation-curable coating/PSA" teaching

Sources: US4556464 PDF (patentimages.storage.googleapis.com/a4/cf/b6/c983641dbe18e5/US4556464.pdf); uspto.report/patent/grant/4556464

• "The compositions of the present invention can be cured by exposure to high energy radiation such as electron beam radiation or ultraviolet radiation." — i.e., the UV/EB dichotomy of the '551 title.
• "When using ultraviolet radiation it is necessary to employ a photoinitiator in order to speed up the crosslinking reaction."
• "In order to facilitate crosslinking through the endblock phase a crosslinking agent may be included … trimethylolpropane triacrylate (TMPTA), SARET® 515 …, and hexanediol diacrylate (HDODA). A crosslinking agent may not be necessary for crosslinking to occur for example when the composition is cured with electron beam radiation."
• Tackifier/resin blending: "an arene-block-compatible resin may be employed … The amount of arene-block-compatible resin varies from 0 to about 200 phr."
• It also expressly recognizes the oxidative-degradation problem of radical cure: "It is also within the spirit and scope of the invention to effect the crosslinking reaction within the confines of an inert atmosphere to prevent air inhibition of the crosslinking reaction and to prevent oxidative degradation of the block copolymer."

What it lacks: elements B, C, D, F entirely. Its polymers are styrene/isoprene ABA block copolymers with unsaturated midblocks.

What it supplies for § 103: the entire formulation and process context — coating from solvent onto a substrate, tackifier blending, UV photoinitiator vs. EB-no-initiator, and the recognition that radical cure can degrade unsaturated backbones.

(d) The missing-but-decisive reference: Exxon's own benzylic-functionalized isoolefin/para-alkylstyrene art

This is not in the truncated prior-art section, but it is verifiable and it is the only art I found that supplies elements B, C, D and F in a single disclosure:

• U.S. Pat. No. 5,162,445 (Powers et al., Exxon Chemical Patents; application 07/442,028, filed 1989-11-27; granted 1992-11-10) — "Para-alkylstyrene/isoolefin copolymers and functionalized copolymers thereof." Claim 1: "A functionalized polymer of an isoolefin having from 4 to 7 carbon atoms and a para-alkylstyrene, wherein … a functionalized para-alkylstyrene moiety having at least one type of functionalized group other than a halogen attached to said para-alkyl group, said functionalized polymer having a substantially homogeneous compositional distribution, and a ratio of Mw/Mn of less than about 6." Claims 20–25 enumerate the leaving-group chemistry (oxygen, sulfur, silicon, nitrogen, carbon, phosphorus functional groups) — i.e., the nucleophilic-displacement-on-benzylic-halogen platform. (Source: FreePatentsOnline 5162445; Espacenet US5162445A.)
• EP 0 344 021 (published 1989-11-29), cited within the Exxon family as "European patent application 89305395.9 filed May 26, 1989, (Publication No. 0344021 published Nov. 29, 1989)" — the underlying isoolefin (C₄–C₇)/para-alkylstyrene copolymers per se.
• DE 69704348 T2 (Exxon) confirms the state of the art in plain terms: "In der verwandten US-A-5 162 445 wurde gefunden, dass freiradikalische Bromierung des neuen IB-AS-Copolymers an der Alkylgruppe [erfolgt]" — i.e., in US 5,162,445 it was found that free-radical bromination of the new isobutylene–alkylstyrene copolymer occurs at the alkyl group (the benzylic position), and that subsequent nucleophilic displacement installs functionality there.
• U.S. Pat. No. 5,206,303 (same Exxon family) states the structural consequence: "The major portion of the halogen is chemically bound to the para-alkyl group" and the copolymers "have unexpectedly homogeneous uniform compositional distributions."
• The sibling US 5,376,503 (Audett et al., granted 1994-12-27, same family as '551) describes the mer units as including "enchained pendent radiation-reactive functional group formed via nucleophilic substitution on benzylic halogen" and describes the products as "backbone saturated, soluble copolymers" whose "excellent environmental resistance of the backbone saturated copolymers is advantageous" in "exterior applications." (Source: US5376503 PDF, patentimages.storage.googleapis.com/7f/83/9c/735fbe21a44836/US5376503.pdf.)

Prior-art status caveat (important and not free from doubt). US 5,162,445 issued after the '551 priority date (1990-12-20), so it is not a § 102(a)/(b) printed publication; it would have to be relied on under pre-AIA § 102(e) as a U.S. patent granted on an application filed before the applicant's invention date (application filed 1989-11-27, with § 120 chain back to 1988-05-27). EP 0 344 021, published 1989-11-29, is more than one year before 1990-12-20 and therefore qualifies under § 102(b). That split matters for § 103 because pre-AIA § 103(c) can disqualify commonly owned § 102(e) art from obviousness combinations — and 5,162,445 and 5,591,551 share the Exxon assignee. I am not certain whether the version of § 103(c) then in force (the 1999 amendment adding § 102(e) art applied to applications filed on or after 1999-11-29; the '551 was filed 1995-06-07) would have reached a 1995 filing, and I decline to assert a conclusion. Practitioner note: this common-ownership question is a plausible reason the '551 was able to issue over its own family's base-terpolymer art, and it is the single highest-value issue for anyone constructing or attacking a § 103 case here.

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3. The obviousness combinations

Combination 1 — EP 17,364 + US 4,315,998 (Neckers)

Covers: A, D, E, G + the stated problem/motivation.
Missing: B (isoolefin), C (para-alkylstyrene), F.

Motivation articulated in the references themselves:

1. EP 17,364 identifies the exact deficiency the '551 sets out to cure — blended photosensitizers suffer "compatibility, uniformity of distribution, volatility, toxicity or exudation and migration … often resulting in premature and/or erratic crosslinking." The '551's summary (per the prior section's plain-language reading) asserts the same advantages. Same problem, same field, same solution concept.
2. EP 17,364 solves it one way (copolymerize a functional monomer). The '551's own background acknowledges the drawback of that route ("Preparing such comonomers on a large scale is generally difficult") and of the grafting route ("heterogeneous product of low yield"). Having recited both routes and both drawbacks, the patent itself supplies the motivation to find a third.
3. Neckers supplies exactly that third route on a polymer-borne benzylic leaving group — and Neckers' claim 8 even names a parabenzoyl benzoic acid as the nucleophile, i.e., the same benzophenone chromophore family EP 17,364 builds into its allyl benzoylbenzoate. A POSITA comparing EP 17,364 and Neckers would see a common chromophore (benzoylbenzoate/benzophenone) delivered by two interchangeable routes: copolymerize it, or displace a benzylic halide with it.
4. Predictability: substituting a known chromophore onto a pre-formed polymer via a known nucleophilic displacement is a "finite number of identified, predictable solutions" (KSR) with a reasonable expectation of success, because both benzoylbenzoate-type photoinitiation and benzylic chloride displacement were each independently established.

Why this combination alone is probably insufficient: neither reference supplies an isoolefin/para-alkylstyrene backbone, and neither supplies the "substantially homogeneous compositional distribution" limitation. The combination also requires the POSITA to invent the substrate choice.

Combination 2 — Combination 1 + US 4,556,464 (St. Clair)

Adds: the UV/EB-cure-in-a-coating context; the tackifier element G; EB-vs-UV formulation logic; explicit awareness that radical cure oxidatively degrades unsaturated backbones.
Still missing: B, C, D-as-positioned, F.

St. Clair's contribution is largely to the background/enabling context rather than to the point of novelty. It reinforces that (i) radiation-curable coatings/adhesives were a mature, crowded field, and (ii) the choice of UV-with-photoinitiator vs. EB-without-initiator was a routine design choice — which supports obviousness of the '551's broad "UV/EB" framing. It also supplies the explicit recognition that radical cure damages unsaturated backbones, which is the reason a POSITA would want a saturated-backbone substrate — a motivation pointing toward, though not supplying, element B.

Combination 3 (the only combination I can build that reaches every element) — EP 17,364 + US 4,315,998 + US 4,556,464 + EP 0 344 021 / US 5,162,445 (Powers, Exxon)

Full mapping:

The motivation to combine, in KSR terms:

• Same field of endeavor: all four references are radiation-curable polymer coatings/adhesives; EP 17,364 and US 4,556,464 are both directed to radiation-curable coating/PSA compositions.
• Same problem, different partial solutions: EP 17,364 cures the "blended photosensitizer" problem by polymer-bound cure chemistry; the '551's background identifies both known routes and their defects; Powers supplies a polymer platform (saturated-backbone isoolefin/para-alkylstyrene terpolymer with benzylic halogen) that is designed for post-polymerization functionalization.
• Reasonable expectation of success: the '551 does not allege a new mechanism. A benzophenone/benzoylbenzoate chromophore attached to a polymer is a known self-initiating cure system (EP 17,364; also EP 0 000 705, which lists allyl/alkenyl p-benzoylbenzoates as photoinitiators). Benzylic halogen displacement on the Powers terpolymer with soft nucleophiles under phase-transfer conditions was taught as a robust, low-gelation route (US 5,162,445; WO 91/04992; US 5,206,303).
• Design incentive toward the saturated backbone: US 4,556,464 explicitly warns that radical cure causes "oxidative degradation of the block copolymer" unless an inert atmosphere is used; a POSITA seeking a UV/EB coating with corrosion resistance and environmental durability — the '551's own stated object — would be led to a saturated-backbone elastomer over a styrene/isoprene block copolymer. The Exxon family states the same advantage: "exterior applications where the excellent environmental resistance of the backbone saturated copolymers is advantageous."

Dependent-claim obviousness (routine optimization):

• Functional-group loading ranges (0.1–10 wt. %; 0.5–20 wt. %) — EP 17,364 teaches 0.1–10 wt. %; US 5,162,445 teaches 0.5–20 wt. %; optimization of a disclosed range is routine (In re Boesch; In re Aller).
• Tackifier amount/identity — EP 17,364 (1–95 parts) and US 4,556,464 (0–200 phr) make the '551's 5–95 parts, 30–70 preferred, a routine optimization.
• Mask + development by removing uncrosslinked polymer — EP 17,364 teaches masked differential UV cure; development is the standard step in negative-working lithographic imaging and is conceded as conventional in the art (the '551's own field: G03F7/0388, "Macromolecular compounds which are rendered insoluble or differentially wettable").
• Species limitations (isobutylene / para-methylstyrene) — expressly disclosed in EP 0 344 021 and US 5,162,445 (claims 6, 11, 19: "said isoolefin comprises isobutylene and said para-alkylstyrene comprises para-methylstyrene").

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4. Rebuttal: the strongest arguments for non-obviousness

A defensible § 103 analysis must state where the prima facie case is weakest.

1. The allyl-monomer/cationic-polymerization incompatibility. EP 17,364's improvement is delivered by copolymerizing allyl benzoylbenzoate. That monomer cannot be used to build an isobutylene/para-methylstyrene cationic copolymer. So the closest reference does not merely omit element B — its disclosed solution mechanism is inoperable in the claimed system. That pushes a POSITA to a re-design, and re-designs are where non-obviousness lives. (Counter: the re-design is exactly what Neckers teaches, and the '551's background concedes the POSITA knew both alternative routes.)

2. Neckers' substrate and purpose are different in kind. Neckers' beads are insoluble, crosslinked, divinylbenzene-containing supports intended to be filtered out of a reaction medium. Using the same chemistry to make a soluble, film-forming, imageable elastomer is a change in function and result, not merely a substitution of parts. (Counter: Neckers' claim 1 is generic to "a polymeric material having … an available leaving group"; and US 5,162,445 independently teaches the soluble-elastomer version.)

3. The "substantially homogeneous compositional distribution" limitation (element F). This is a process-linked structural limitation. If the issued independent claims recite it — as the reconstructed method claim does — then a challenger must show that the prior art taught or suggested achieving it in a functionalized isoolefin/para-alkylstyrene copolymer. Only the Exxon base-terpolymer art does, which brings back the common-ownership problem under § 103(c).

4. Common ownership / § 102(e) availability of the decisive reference. If US 5,162,445 is disqualified as § 102(e) art in an obviousness combination (because of common ownership at the time the invention was made, under whichever version of § 103(c) applies to a 1995 filing — an issue I cannot resolve on this record), then no single combination of the three references named in the truncated prior-art section reaches elements B, C, D, and F simultaneously, and the prima facie case collapses. This is the crux of any serious challenge to or defense of this patent.

5. Secondary considerations — no evidence located. I found no evidence in the searched record of unexpected results, commercial success of the patented coating (as opposed to the broader EXXPRO/BIMS elastomer business), long-felt but unmet need, failure of others, copying, or licensing attributable to the '551 claims. Absent such evidence, the KSR "predictable results" analysis governs. But "no evidence found" is not "no evidence exists" — I did not query IPR/PGR records, prosecution histories, or litigation files for this patent (the prior sections record no litigation found for US 5,591,551 specifically).

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5. Conclusion

• Prima facie obviousness under § 103 is makeable but is not clean on the truncated prior-art section alone. Combining EP 17,364 + US 4,315,998 (Neckers), optionally with US 4,556,464 (St. Clair), supplies elements A, D (as a technique), E, G, H, and — importantly — the express motivation: EP 17,364 itself frames the problem ("volatility, toxicity, migration, premature crosslinking") and offers a radiation-reactive chromophore strategy; Neckers supplies the known benzylic-nucleophilic-displacement technique; St. Clair supplies the UV/EB coating and tackifier context and the recognition that radical cure degrades unsaturated backbones.
• The combination falls short on elements B, C, and F. Reaching all limitations requires adding EP 0 344 021 (published 1989-11-29, § 102(b)) and/or US 5,162,445 (Powers et al., Exxon; filed 1989-11-27), which together disclose the C₄–C₇ isoolefin/para-alkylstyrene copolymer, benzylic functionalization "at the para-alkyl group," and the "substantially homogeneous compositional distribution" limitation verbatim.
• The obviousness case therefore reduces to a single contested question: whether the Exxon base-terpolymer art is available as prior art notwithstanding common ownership. If yes → the claims are, on this record, strongly vulnerable under § 103 as a combination of known radiation-cure chemistry with a known benzylic-functionalization platform, with the "'551's contribution" amounting to the selection of a benzophenone-type radiation-reactive group as the nucleophile. If no → the claims survive on the absence of any non-commonly-owned teaching of the isoolefin/para-alkylstyrene substrate with benzylic-positioned radiation-reactive functionality.

Limitations on this analysis

• I could not verify the literal claim text of US 5,591,551: the authoritative source is truncated before the claims, and I did not retrieve the issued claim set. Elements A–H are reconstructed from the family (EP 0 563 251 A1; US 5,376,503). A different issued claim scope (e.g., claim count, whether "homogeneous compositional distribution" appears in the independent claims, whether a corrosion-resistance limitation was added) would change the mapping.
• I did not obtain the front-page [56] references-cited list of US 5,591,551, so additional examiner-cited art may exist that strengthens or weakens the above. The "Definition" section I was directed to is a background discussion, not the complete prior-art record.
• I did not run IPR/PGR, reexamination, or district-court validity records; the earlier sections of this analysis found no litigation for this patent number and I did not independently re-verify that.
• This is a technical/analytical assessment, not a legal opinion or a freedom-to-operate or validity opinion. Ultimate obviousness determinations belong to the USPTO and the courts.
• Contradiction flagged: task date (April 26, 2026) vs. document/system dates (2026-09-26/27). I have not harmonized them.

Primary sources: Google Patents https://patents.google.com/patent/[US5591551A](/patent/US5591551A)/en; EP 0 017 364 A1 (https://patents.google.com/patent/EP0017364A1/en, patentimages.storage.googleapis.com/8d/cd/4b/3bc0663ecbb1b5/EP0017364A1.pdf); US 4,315,998 (patentimages.storage.googleapis.com/7f/e7/5b/0b63050be48504/US4315998.pdf; https://www.drugpatentwatch.com/p/biologics/patent-claims/4315998); US 4,556,464 (patentimages.storage.googleapis.com/a4/cf/b6/c983641dbe18e5/US4556464.pdf; https://uspto.report/patent/grant/4556464); US 5,162,445 (https://FreePatentsOnline.com/5162445.html); US 5,206,303 and US 5,376,503 PDFs (patentimages.storage.googleapis.com/a5/6f/fa/1fc61f842e11cc/US5206303.pdf; patentimages.storage.googleapis.com/7f/83/9c/735fbe21a44836/US5376503.pdf); WO 91/04992 A1 (https://patents.google.com/patent/WO1991004992A1/en); DE 69704348 T2 (https://patents.google.com/patent/DE69704348T2/en).