US 4387186

I'll search for the specific patent number and check for any litigation activity.

Let me run more targeted searches for the exact patent number.

Let me run a couple more checks for litigation/CAFC activity and the family members.

US Patent 4,387,186 — Summary

Important search note on the identifier: My searches for the bare string "4387186" also surfaced JP4387186B2, an unrelated Japanese patent (dual-transfected cell lines, Daiichi/Boeringer). That is a different patent in a different jurisdiction and should not be conflated with the US number. All content below pertains specifically to US 4,387,186.

Litigation / CAFC check: I could not find any CAFC 2026 docket, district-court case, or PTAB proceeding involving US 4,387,186. Searches returned no litigation records at all. Given the patent's status (see below), it is highly unlikely to be in active 2026 appellate litigation. I do not have authoritative confirmation of zero litigation — only the absence of any hits — so treat this as "no evidence found," not as a certified negative.

Bibliographic Data

Abstract (as issued)

"Water swellable monovalent alkali metal salt of crosslinked interpolymer of maleic anhydride, monovinyl alkyl ether and 1-5 mole percent crosslinking agent comprising divinyl ether of aliphatic diol."

Prior Art Cited

• US 3,448,088 (GAF Corp) — "Crosslinked interpolymers" (the water-soluble viscosity-improver precursors the patent builds on)
• US 3,514,419 (ICI Ltd) — "Cross-linked vinyl/dicarboxylic anhydride copolymers"

Plain-Language Claim Overview

The patent has 9 claims, only one of which is independent (claim 1); claims 2–9 are dependent.

Claim 1 (the only independent claim): A composition that swells in water but does not dissolve in it. It is defined as a monovalent alkali-metal salt of a crosslinked interpolymer (a copolymer network) made of:

• Maleic anhydride and a monovinyl alkyl ether (alkyl of 1–4 carbons), in substantially equimolar (roughly 1:1 alternating) amounts; and
• About 1 to about 5 mole percent (relative to the vinyl ether) of a divinyl-ether crosslinking agent, of either formula:
  • H₂C=CH–O–X₁–OCH=CH₂, where X₁ is an alkylene of 2–12 carbons, or
  • H₂C=CH₂–(OX₂)ₙ–OCH=CH₂, where X₂ is an alkylene of 2–4 carbons and n is 2–100. (Note: the second formula is printed with "H₂C=CH₂" in the patent text/claim — a likely typographical artifact; read literally, it is the divinyl ether of a polyalkylene glycol. I am flagging this rather than silently correcting it.)

In plain terms: take an alternating maleic-anhydride/vinyl-ether polymer, lightly crosslink it with a divinyl ether, then neutralize the acid groups with an alkali-metal base. The result is a superabsorbent gel (the patent's examples report ~52 g of simulated urine absorbed per gram of polymer).

Dependent claims (narrowing the above):

• Claim 2 — vinyl ether is methyl vinyl ether.
• Claim 3 — vinyl ether is ethyl vinyl ether.
• Claim 4 — crosslinker is the first formula where X₁ is butylene (i.e., butanediol divinyl ether).
• Claim 5 — crosslinker is the second formula where X₂ is ethylene and n = 2 (diethylene glycol divinyl ether).
• Claim 6 — alkali metal is sodium.
• Claim 7 — alkali metal is potassium.
• Claim 8 — combination: methyl vinyl ether + sodium or potassium + butylene-linked crosslinker (first formula).
• Claim 9 — combination: ethyl vinyl ether + sodium or potassium + ethylene-linked crosslinker with n = 2 (second formula).

Significance / Utility

The specification states the compositions are useful as superabsorbents in diapers, sanitary napkins, tampons, adult-incontinent products, and as horticultural/agricultural aids. The key inventive distinction over US 3,448,088 is that the same class of interpolymer, when suitably crosslinked and converted to the alkali-metal salt, becomes water-swellable but water-insoluble (a gelling superabsorbent) rather than water-soluble.

Confidence / Uncertainty

• Bibliographic data, abstract, claims, and examples are authoritative (taken from the full Google Patents text for US 4,387,186).
• No CAFC 2026 docket activity was found, and I did not retrieve a verified USPTO PatentCenter record directly; the assignment and maintenance-fee/expiration details come from the Google Patents legal-events listing.
• I did not independently verify the current USPTO assignment chain beyond the June 29, 1981 assignment to GAF Corporation.

I'll search for litigation involving US patent 4387186 across patent litigation sources.

Let me search more targeted litigation sources.

Let me check CourtListener and other litigation databases directly.

Litigation Search Report — U.S. Patent No. 4,387,186

Bottom line

No litigation involving U.S. Patent No. 4,387,186 was found. Based on the searches available to me, there is no record of any district court action, Section 337/ITC investigation, PTAB proceeding, or Federal Circuit appeal in which U.S. 4,387,186 was asserted, challenged, or otherwise at issue.

Patent identification (as confirmed in the record)

The patent is directed to water-swellable (but not water-soluble) monovalent alkali metal salts of crosslinked maleic anhydride / monovinyl alkyl ether interpolymers crosslinked with a divinyl ether of an aliphatic diol, and claims priority to a single U.S. application.

What I found (and what I did not)

1. No litigation hits. Searches for the patent number in connection with infringement complaints, defendants, damages, and case citations returned only unrelated matters. No case caption, docket number, court, or filing date naming U.S. 4,387,186 was identified.
2. No PTAB/CAFC proceedings. Nothing tying this patent to an IPR/PGR/CBM or to a Federal Circuit appeal surfaced.
3. No Unified Patents litigation record. I could not retrieve a Unified Patents portal entry (or a comparable Docket Alarm / Docket Navigator / Justia docket entry) for this patent.

Important identifications to avoid (do not auto-correct or conflate)

• JP 4387186 B2 (Japanese Patent No. 4387186, "P4387186") — an unrelated Japanese patent (Deutsches Krebsforschungszentrum / Boehringer Ingelheim; double-transfected cell lines). This is a different jurisdiction and a different patent. It is not U.S. 4,387,186.
• Search noise such as the "'438 patent" references (Zytiga/abiraterone IPR) and various Realtime Data, Apple v. Samsung, and Honeywell/Litton materials are different patents and unrelated to U.S. 4,387,186.

Why no litigation is plausible (context, not proof)

The record shows the patent lapsed on June 7, 1987, just under four years after issuance and before the first maintenance-fee window closed. A patent that terminated for non-payment in 1987 had a very short enforceable window (mid-1983 to mid-1987), which is consistent with the absence of any recorded assertion. Additionally, the patent's own specification and prosecution history point to the superabsorbent-art context (diapers, sanitary napkins, horticultural aids), with cited prior art U.S. 3,448,088 (GAF) and U.S. 3,514,419 (ICI) — none of which appear here as litigation.

Caveats and limitations

• Google Patents' record for this patent lists "Cited By" and "Similar Documents" but no litigation section, and I found no third-party docket source reporting a case.
• I was not able to query PACER or the Unified Patents litigation portal directly within this session's search budget, and the public web search results did not surface any docket for this patent number. Accordingly, my conclusion is grounded in the searches performed and the patent's own record, not an exhaustive PACER/docket-database confirmation.
• Because the patent number search space overlaps with the unrelated JP 4387186, any future verification must confirm the US patent number (and ideally application no. 06/278,278) before attributing a case.

Recommended next steps for definitive confirmation

1. Search PACER's nationwide docket index and the Unified Patents litigation case list (https://portal.unifiedpatents.com/litigation/caselist) using both the patent number and application number 06/278,278.
2. Query Docket Navigator and Lex Machina by patent number (these index older cases and NPE activity better than free sources).
3. Cross-check the CAFC docket and the USPTO Patent Center assignment/legal-events history (which here shows only the 1981 assignment and the 1987 lapse).

Conclusion: On the information available, there is no known litigation involving U.S. Patent No. 4,387,186. I state this with the caveat that PACER/Unified Patents were not directly queryable in this session, so it should be treated as a negative finding from available sources rather than a certified "no cases ever filed" determination.

Proceedings overview

Total AIA trial proceedings on file for US 4,387,186: 0 — no IPRs, no PGRs, no CBM reviews, active or terminated (0 active / 0 claims invalidated / 0 claims sustained / 0 settled / 0 institution denials). The USPTO Open Data Portal returns an empty AIA-trial set for this patent, and my web checks surfaced no PTAB petition, FWD, or Federal Circuit appeal naming US 4,387,186 — the hits were unrelated patents (e.g., a different "’438" patent in IPR2016-00286, and JP 4387186 B2, a Boehringer Ingelheim cell-line patent). The bottom-line defensive posture is not "the patent has survived IPRs and is hardened" and not "claims 1–5 are canceled" — it is that this patent was never tested at the PTAB because it has been dead since 1987 (see below), which is the most useful fact a defendant can have.

No proceedings to list

There is no proceeding to format under the per-proceeding template. For completeness on why:

• The patent lapsed pre-AIA. Per the Google Patents legal events, US 4,387,186 expired 1987-06-07 for failure to pay maintenance fees ("PATENT EXPIRED DUE TO NONPAYMENT OF MAINTENANCE FEES UNDER 37 CFR 1.362"). Its statutory term would in any event have run out long before 2012.
• AIA trials did not exist during its life. IPR/PGR became available 2012-09-16, and CBM review (now sunset) was likewise post-2012. A patent that expired in 1987 could not have generated an AIA trial in the ordinary course. (Expired patents can be subject to IPR if still asserted, but there is no evidence of any such filing here — and a patent that lapsed for non-payment 39+ years ago has no assertion value.)
• No assertion activity is evident. Nothing in the record or search results indicates this patent was ever litigated or asserted, which is consistent with zero PTAB activity.

I cannot invent a proceeding number, panel, or FWD that does not exist, and I will not.

Strategic summary

Claim status: entirely untested at the PTAB — and moot. All nine claims of US 4,387,186 (independent claim 1; dependents 2–9) stand or fall as issued and were never subject to an AIA challenge. But they are not merely untested; they are unenforceable-through-expiry. The patent lapsed for non-payment of maintenance fees effective 1987-06-07, so as of today there is no enforceable claim term, no owner-in-interest with standing to assert it, and no live damages window. Any current demand letter citing US 4,387,186 is citing a patent that cannot support an infringement claim — this is a laches/expiry/standing defense on the face of the record, independent of any invalidity theory.

Estoppel landscape. § 315(e)(2) estoppel is irrelevant here: with zero petitioners, no party is estopped, and conversely there is no FWD to leverage. If you needed to knock the claims out on the merits, every prior-art ground would be available because none has been raised — but you almost certainly do not need to, given the 1987 lapse.

Pattern signals. No repeat petitioners, no patent-owner PTAB appeals, no defensive aggregator (Unified Patents, RPX, etc.) involvement — because there is no proceeding. The absence of PTAB activity is not here the usual "well-asserted patents eventually attract IPRs" signal; it reflects that the patent died in 1987 and was never a litigation target.

Recommended next steps

• If you are a defendant: do not spend IPR budget. The dispositive point is the 1987-06-07 lapse for non-payment of maintenance fees, documented in the patent's legal events at Google Patents — US4387186A. Confirm the lapse and the absence of any later reinstatement or reissue before responding to any assertion; there is no FWD to link because none exists.
• If you want claim-level paper: the only "challenge" record is the prosecution history and the two references cited on the face of the patent — US 3,448,088 (GAF, "Crosslinked interpolymers," cited by examiner) and US 3,514,419 (ICI, "Cross-linked vinyl/dicarboxylic anhydride copolymers") — not a PTAB decision. Note the specification itself concedes the present compositions are "essentially the same as the interpolymers described in U.S. Pat. No. 3,448,088," a helpful § 102/§ 103 admission if you ever needed it, though expiry makes it academic.
• Milestones: none — there is no pending trial, no institution deadline, and no FWD due date, because there is no proceeding.

If you have a document suggesting a specific proceeding number against this patent, send it and I'll verify against the PTAB E2E docket and CourtListener rather than speculate. Based on the canonical ODP data and my searches, the current and correct answer is: no PTAB proceedings on file.

I'll cross-check the assignment record and the original assignee's corporate history before writing this up.

Let me check for any litigation, portfolio transfers, and the current corporate fate of the original assignee.

I could not query assignmentcenter.uspto.gov directly (it is a JavaScript single-page app that my fetch tooling cannot render), so the reel/frame below is taken from the USPTO-derived assignment data transcribed in the Google Patents legal-events record for this patent, cross-checked against the cited-art and family records. That is flagged where it matters.

Inventors

Both were career GAF chemists, not one-shot filers. Williams appears as inventor on GAF-assigned patents spanning 1973–1983 (e.g. US 3,954,682; US 4,018,754; US 4,057,533; US 4,396,734), and Lorenz on GAF-assigned work including US 4,247,714, US 4,301,209 and US 4,375,398.

Pattern check — departures within 12 months of filing: not present. Williams filed at least one further GAF-assigned application (US 4,514,271, filed 1983-05-23, assigning to GAF Corporation of Wayne, NJ) and Lorenz filed GAF-assigned applications into 1982 (US 4,375,398, filed 1982-05-24). There is no cluster of post-filing assignor-side reunions, no abandonment of the GAF relationship, and therefore no inventor-departure precursor to a portfolio fire-sale. The 1983 change of the recorded GAF address from New York, NY to Wayne, NJ reflects Heyman-era relocation of headquarters, not an ownership change.

Original assignee

GAF Corporation, 140 West 51st Street, New York, NY (recorded assignee address on reel 003898/0359); later Wayne, NJ.

• Primary line of business at filing (1981): diversified speciality chemicals plus building materials (residential/commercial roofing). GAF was winding down a five-year divestment programme and by end-1982 had retained only chemicals and building materials. Its chemicals strengths included acetylene derivatives, butanediol, and vinylpyrrolidone/maleic anhydride polymer chemistry — the same chemistry family as the Gantrez-class MVE/MA copolymers referenced by this patent's own antecedent, US 3,448,088 (GAF).
• Product embodying the claims: I found no commercial GAF product identified as practising the crosslinked, alkali-metal-salt claims. The patent discloses only laboratory absorbency data (500 mg polymer absorbing 52 g of simulated urine per gram at pH 7.0, Examples 1–2) and identifies no product name. The claims are directed to crosslinked superabsorbents for diapers/sanitary products, whereas GAF's documented commercial MVE/MA business was the water-soluble thickener line (the US 3,448,088 subject matter). Treat "GAF shipped a superabsorbent product under these claims" as unverified.
• Current status of the entity: the "GAF Corporation" of this patent no longer exists under that identity. GAF was taken private in 1989 in a ~$1.4 billion management-led LBO; the chemicals business was spun off in 1991 as International Specialty Products (ISP), with GAF's remaining roofing arm operating as GAF Materials Corporation. ISP was in turn spun off under G-I Holdings and was acquired by Ashland Inc. for $3.2 billion in 2011; GAF roofing is now part of Standard Industries. Court filings in successor-liability litigation (D.N.J., CERCLA) describe a "Plan of Complete Liquidation" of the old GAF entity and refer to "New GAF" and to IES as a successor-in-interest. I have not independently verified the exact dissolution/bankruptcy dates for the GAF/G-I Holdings shell, so treat that element as moderate confidence only — but note it is moot for this patent, which lapsed in 1987 (below).

Assignment timeline

There are no post-issuance assignments of record. The Assignment Center record for US 4,387,186 contains exactly one recorded assignment — the original inventor-to-company assignment — and nothing since.

• 1981-06-17 to 1981-06-22 (executed) / recorded 1981-06-29 — Reel 003898 / 0359
  • Conveyance: Assignment of assignors' interest (original assignment)
  • Assignor: Earl P. Williams; Donald H. Lorenz
  • Assignee: GAF Corporation, 140 West 51st St., New York, NY
  • Correspondent: Not determinable from the available record. The USPTO-derived transcription of reel 003898/0359 carries the reel/frame, conveyance, parties and signing dates, but no correspondent/correspondent-address field; because I could not open the Assignment Center UI itself I cannot state the recording attorney or agent. This is a data gap, not a negative finding — do not read it as "no correspondent."
  • Context: Ordinary corporate take-up of employee invention — filed essentially contemporaneously with (same day as) the application.

Related non-assignment legal events (from the same USPTO-derived record — these are fee/status events, not conveyances):

• 1987-01-09 — maintenance-fee reminder mailed.
• 1987-06-07 — patent lapsed / expired for failure to pay maintenance fees under 37 CFR 1.362 (statutory 4-year window).
• 1987-08-25 — lapse event recorded, effective 1987-06-07. Status remains Expired – Fee Related.

Family note (no assignment data retrieved): the same subject matter was filed abroad — CA 1,183,994 A (Canadian filing date 1982-06-04) and EP 0 068 847 A1 (EP filing date 1982-06-25), both claiming the 1981-06-29 US priority. I did not obtain prosecution or assignment records for either, so I make no statement about their ownership history.

Because there is only the original assignment, per the brief's instruction the analysis below stops short of a full chain reconstruction — the empty chain is the finding.

Timeline diagram

timeline
    title Ownership of US 4387186
    1981 : Filed by GAF Corporation
         : Inventors assign to GAF reel 003898 frame 0359
    1983 : Patent issued
    1987 : Lapsed for unpaid maintenance fee
         : No assignment ever recorded after 1981
    1989 : GAF taken private in leveraged buyout
    1991 : GAF chemicals spun off as ISP
    2011 : ISP acquired by Ashland

NPE / troll-pattern signals

1. Shell-entity transfer — not present. The sole recorded assignee is GAF Corporation, a large operating company at a corporate headquarters address (140 West 51st St., New York, NY) on reel 003898/0359. No "IP / Holdings / Licensing / Ventures" entity appears anywhere in the record, and no registered-agent service address is present.
2. Known asserter in the chain — not present. The complete chain is inventors → GAF Corporation. No entity on the Acacia / Marathon / Intellectual Ventures / Wi-LAN / Conversant / Pendrell / Round Rock / Spangenberg lists — or any Unified Patents or RPX high-frequency plaintiff — appears as assignor or assignee.
3. Repeat correspondent across the chain — not present (and not evaluable). There is only one link, so recurrence is impossible by construction. Separately, the correspondent field is not exposed in the record I could retrieve (see timeline entry). No correspondent name can be cited, so no finding is made.
4. Cascading transfers — not present. Zero post-issuance assignments across the ~42 years since issuance, and the patent was already expired by 1987. There is no chained-LLC sequence, no shared correspondent address, and no sub-24-month transfer cluster to analyse.
5. Pre-litigation transfer — not present. No assignment within 6 months of any suit; no infringement action naming US 4,387,186 surfaced in searches. Because the patent lapsed 1987-06-07 for non-payment under 37 CFR 1.362, it could not have been asserted for the last ~39 years as a matter of law — any transferee would have acquired nothing but an expired right.
6. Bankruptcy fire-sale — not present as to this patent. Corporate-level stress at the original assignee is documented (1989 LBO; later G-I Holdings proceedings and a "Plan of Complete Liquidation"), but the patent lapsed in 1987 — roughly two years before the LBO — and therefore never travelled through the insolvency process. No patent-level sale occurred.
7. Privateering — not present. No transfer to a litigation vehicle, and no SEC or Patent Progress / EFF coverage connecting this patent to an assertion programme. GAF was private from 1989, and its 1991 ISP spin-off moved the chemicals business, not a licensing shell.
8. Defensive aggregator — not present. Chain does not terminate at RPX, AST, LOT Network, Unified Patents or OIN. It simply terminates at expiry.

Verdict

Insufficient data — only the original assignment is of record.

The chain for US 4,387,186 consists of a single conveyance, inventors Williams and Lorenz to GAF Corporation, executed 1981-06-17/22 and recorded 1981-06-29 at reel 003898/0359; there is no subsequent assignment of any kind, and the patent lapsed for unpaid maintenance fees effective 1987-06-07 per the 37 CFR 1.362 expiration entry. With no downstream transfers, no NPE-list entity, no correspondent recurrence and no assertion or litigation history, none of the eight signals is present, so the "NPE" branches are affirmatively unsupported — the correct label under the rubric is Insufficient data because the record contains only the founding assignment, not because the evidence is ambiguous. Substantively, this is a long-expired, never-reassigned operating-company patent, i.e. the inverse of a troll vehicle.

Two verification notes for the file. First, please re-run the reel/frame and the "no further assignments" finding directly in USPTO Patent Assignment Search — https://assignmentcenter.uspto.gov/ (legacy index: https://assignment.uspto.gov/patent/index.html) — and retrieve the correspondent of record that I could not read from the transcribed data; the Google Patents legal-events page I relied on is at https://patents.google.com/patent/US4387186/en. Second, a drafting defect worth noting for any claim-strength work: claim 1 and the specification both write the polyalkylene-glycol crosslinker as H2C=CH2--(OX2)n--OCH=CH2 (an impossible saturated ethylidene start to a vinyl ether), while claim 5 and the abstract write the same genus as CH2=CH(OX2)n--OCH=CH2 — an internal inconsistency that would have made claim 1 vulnerable to a §112 challenge had the patent not lapsed in 1987.

I'll research this systematically. Let me search for the patent and its cited references.

I have solid data on the '419 reference. Let me get more detail on US3448088 and confirm the citation records.

I have the '419 details. Let me pull specifics on US3448088 (the closest reference) and the background water-absorbent patents.

Prior-Art Analysis — US Patent 4,387,186 (“Water Swellable Polymers”)

Patenting party: GAF Corporation (inventors Earl P. Williams and Donald H. Lorenz). Application US06/278,278; filed June 29, 1981; granted June 7, 1983; expired (fee-related) 1987. Family: CA1183994A (filed 1982-06-04), EP0068847A1 (filed 1982-06-25). Note: the EP sibling EP0068847A1 contains broader subject matter (partial amide-amine carboxylates or alkali-metal salts), which is relevant context below.

Verification note: The authoritative Google Patents record for US4387186 lists exactly two patent citations (both "cited by examiner"): US3448088A and US3514419A. All other documents on the page (e.g., US4818794, US4952558, US4366294, CA1183994A) are either "Cited By" (later art) or family members and are not prior art to the '186 patent. I did not auto-correct any identifiers.

CITATION 1 — US 3,448,088 A (the primary reference)

Brief description (as characterized in the '186 patent itself): "U.S. Pat. No. 3,448,088 describes water soluble crosslinked interpolymers which are useful as viscosity improvers." The '186 specification states the products are "essentially the same as the interpolymers described in U.S. Pat. No. 3,448,088," the asserted difference being that the '088 materials are water-soluble (viscosity improvers) whereas the '186 materials use much larger amounts of crosslinking agent so as to be water-swellable but not water-soluble. ⚠️ I do not have full confidence in the complete disclosure of the '088 specification from the retrieved record; the description above is drawn from the '186 specification's own characterization and should be confirmed against the '088 text.

Anticipation analysis (§ 102):

• Claims 1–9 — potentially significant, but not a clean § 102 anticipation. Because '088 is the same assignee/same monomer chemistry (maleic anhydride + alkyl vinyl ether) and is a crosslinked interpolymer, it is the closest prior art and bears on every independent claim. However, on the record the '088 polymers are water-soluble, which conflicts with the claim 1 negative limitation "water swellable but not water soluble." Under § 102 the reference must disclose each limitation; the solubility difference (attributable to crosslinker level) is the likely distinguishing feature. Recommendation: treat '088 as the primary § 102/§ 103 reference, but confirm (a) whether it discloses divinyl-ether crosslinkers of the claimed formulas, (b) the mole-percent crosslinker range, and (c) any alkali-metal-salt formation.

CITATION 2 — US 3,514,419 A

Brief description (from the '419 abstract): A cross-linked alternating copolymer of an α,β-unsaturated dicarboxylic anhydride and a vinyl monomer, water-soluble or water-swellable per se or in salt form. Explicitly the copolymer "may be derived from maleic anhydride and either ethylene, isobutylene, styrene or methyl vinyl ether." Cross-linking is effected by means of an epoxy compound (ethylene/propylene/styrene oxide, glycidol, glycidyl methacrylate, epichlorhydrin, epoxy resins), in an amount such that equivalents of epoxy groups do not exceed 30 per 100 equivalents of copolymer (i.e., ≯3:10 epoxy:anhydride). Polymerization is run in a solvent (e.g., benzene) with peroxide/azo catalysts (benzoyl peroxide, lauroyl peroxide, cumene hydroperoxide, diisopropyl peroxydicarbonate, AIBN); the cross-linked copolymer "may be treated with aq. potassium or sodium hydroxide to give the potassium or sodium salt which may be the half acid-half salt." URL: https://patents.google.com/patent/US3514419

Anticipation analysis (§ 102):

• Claim 1 (and dependent claims 2, 6, 7) — close but likely NOT anticipatory. The '419 reference teaches: (i) maleic-anhydride/methyl-vinyl-ether alternating copolymer; (ii) cross-linking; (iii) the product being water-swellable (or water-soluble) in salt form, including the Na and K salts produced by aqueous NaOH/KOH. These correspond to significant elements of claim 1 — the interpolymer, the sodium/potassium salt (claims 6, 7), and methyl vinyl ether (claim 2). The point of departure for § 102 is the crosslinker identity: claim 1 requires a divinyl ether of an aliphatic diol (formulas H₂C=CH–O–X₁–OCH=CH₂ or H₂C=CH–(OX₂)ₙ–OCH=CH₂), whereas '419 cross-links with an epoxy compound (an ether-free, epoxide-reactive crosslinker). Because the claimed crosslinker genus is absent, '419 should not be treated as an anticipating reference for the '186 claims; it is, however, strong § 103 art on the anhydride/vinyl-ether/salt/swelling concept. Note also that '419 uses an epoxy crosslink and states prior crosslinking via "a compound having two or three double bonds" (UK Pat. 715,412) — that UK reference is a lead worth pursuing for a divinyl-ether crosslinker.
• Claims 4, 5, 8, 9 (specific divinyl-ether crosslinkers / diethylene-glycol divinyl ether) — not anticipated; no corresponding disclosure identified in the '419 abstract.

Background art referenced in the specification (not in the formal citation list)

The '186 specification's "Background" paragraph cites, for the general concept of water-absorbing crosslinked polymers and their end uses (diapers, sanitary napkins, tampons, horticultural aids):

• US 3,997,484
• US 3,669,103
• US 3,670,731

These three are discussed only as general background for swellable (superabsorbent) polymers and as such are weaker than the two examiner citations; they are not identified as anticipating any specific claim. I have not separately verified their full disclosures.

Bottom line

1. Most relevant prior art: US 3,448,088 (GAF, 1969) — same assignee, same maleic-anhydride/vinyl-ether crosslinked chemistry, expressly acknowledged in the '186 specification as "essentially the same" interpolymer. It is the reference most likely to be asserted under § 102/§ 103, subject to the water-solubility vs. water-swellability distinction.
2. Second most relevant: US 3,514,419 (ICI, 1970) — anticipates the anhydride/vinyl-ether/salt/swelling platform and the Na/K-salt and methyl-vinyl-ether elements (claims 1, 2, 6, 7) but not the claimed divinyl-ether-of-aliphatic-diol crosslinker, which is the principal distinguishing claim limitation.
3. Caveats / recommended next steps: (a) Obtain and read the full text of US 3,448,088 to confirm its crosslinker chemistry (divinyl ether vs. other), its crosslinker mole-% range, and whether it discloses alkali-metal salts — this determines whether it is a true § 102 anticipation of claim 1. (b) Review UK Pat. 715,412 (cited within US 3,514,419) as potential § 102 art on divinyl/diunsaturated crosslinking of anhydride copolymers. (c) The negative limitation "water swellable but not water soluble" in claim 1 is the crux of patentability and the analytical dividing line from both cited references.

All patent numbers and dates are reported literally as they appear in the authoritative US4387186 record and the retrieved original references; no identifiers were auto-corrected.

I'll ground this analysis in the prior art cited on the patent page, with a few verification searches first.

Obviousness Analysis — U.S. Patent 4,387,186 ("Water Swellable Polymers")

Analyst note on scope. U.S. 4,387,186 (Williams & Lorenz, GAF Corp., filed and priority 1981‑06‑29, granted 1983‑06‑07) is pre‑AIA art, so pre‑AIA 35 U.S.C. § 103(a) governs; the substantive standard is unchanged by KSR Int'l Co. v. Teleflex Inc., 550 U.S. 398 (2007) ("subject matter as a whole would have been obvious"). I use only the references listed in the Prior Art section of the patent page (cited‑by‑examiner references plus the background references the patent itself identifies), as instructed. Where I could not read a reference's full text in this session, I say so explicitly. The patent is Expired – Fee Related (lapsed 1987‑06‑07 for non‑payment of maintenance fees), so this is a retrospective validity exercise, not an enforcement question.

1. Claim construction — what must be taught

Claim 1 is the genus: a water swellable but not water soluble composition consisting essentially of a monovalent alkali metal salt of a crosslinked interpolymer of

Dependent claims 2–9 are pure species/selection claims: MVE (2), EVE (3), 1,4‑butanediol divinyl ether (4), diethylene‑glycol divinyl ether where "X₂ is ethylene and n is 2" (5), Na (6), K (7), and two combinations (8, 9).

Literal-reading defects to flag (do not auto-correct). The second Markush structure in claim 1 is printed as "H₂C═CH₂–(OX₂)ₙ–OCH═CH₂," i.e., a saturated CH₂ terminus rather than the vinyl group shown in the specification ("H₂C═CH–(OX₂)ₙ–OCH═CH₂"). The same typo appears in the abstract/§112 description chain. Independently, claims 5 and 9 recite "CH₂═CH(OX₂)ₙ–OCH═CH₂," which omits the ether oxygen adjacent to the vinyl carbon. Taken literally, claim 1's formula (ii) may not even read on the claim‑5 species, and claim 5 may be indefinite as to how it depends from claim 1. This matters because it means the strongest obviousness case is against claims 1–4 and 6–8 (formula (i), butylene species, Na/K), and a literalist reading gives claims 5/9 an unintended scope that still does not save them from §103 (see §7).

Also note the claim/disclosure mismatch: the specification permits C₁–C₁₈ vinyl ethers (with <10 mole% of >C₃ ethers), while claim 1 caps the ether at C₄. The claims are narrower than the disclosure — there is no written‑description problem, but it confirms the C₁–C₄ selection is a claim‑drafting choice, not a discovered technical boundary.

2. The prior art of record

All of 3,448,088, 3,514,419, 3,669,103, 3,670,731 and 3,997,484 published more than one year before 1981‑06‑29 and are therefore § 102(b) prior art available for § 103.

3. Element‑by‑element: what each reference supplies, and what it leaves open

Caveat on US 3,448,088. I could not retrieve the full text of this reference in this session. My statement that it discloses MA/vinyl‑ether interpolymers crosslinked with divinyl ethers of aliphatic diols at about 1–5 mole percent rests on (a) the '186 specification's own admission that the two polymers are "essentially the same… except for the use of much larger amounts of crosslinking agent" (language appearing in the EP 0 068 847 family member), and (b) the fact that the identical passage — "the amount of crosslinking agent generally varied from about 1 to about 5 mole percent based on monovinyl alkyl ether… the divinyl ethers of 1,2‑ethanediol… 1,4‑butanediol… and further polyalkylene glycols up to a molecular weight of about 5900" — is attributed to the GAF prior art (expressly citing U.S. 3,448,088) in later GAF/ISP documents (see WO 91/10689 and EP 0 510 002 B1, Google Patents). Those later documents are not prior art to '186; they are used only as evidence of what 3,448,088 discloses. If 3,448,088's text is confirmed to contain the 1–5 mole% divinyl‑ether disclosure, the § 103 case below is strong; if it contains only a narrower crosslinker disclosure, the case weakens and additional art would be needed.

4. The obviousness case

Combination 1 (primary): US 3,448,088 + US 3,514,419

This combination maps every claim‑1 element:

• 3,448,088 supplies the backbone and the crosslinker: substantially equimolar maleic anhydride + C₁–C₄ monovinyl alkyl ether, crosslinked with the 1–5 mole% divinyl ether of an aliphatic diol (elements A and B). The '186 patent concedes the structural identity.
• 3,514,419 supplies the two remaining limitations. It (i) teaches reacting a crosslinked maleic‑anhydride/MVE copolymer with aqueous NaOH or KOH to give the sodium or potassium salt (element C), and (ii) expressly classifies the salt-form product as "water‑soluble or water‑swellable," and describes the well‑known consequence of higher crosslink density — highly crosslinked material "whose alkali metal salts remain as gelled lumps" in water (element D).

Motivation, articulated for the record:

1. Same field, same problem, recognized structural identity. Both references are crosslinked maleic anhydride/vinyl ether interpolymers used to thicken or gel aqueous systems; the applicant himself states the '186 polymers are "essentially the same" as 3,448,088's. KSR treats identity of art and predictability as strong indicators.
2. A finite set of known options with a predictable result. Given a known water‑soluble MA/MVE divinyl‑ether crosslinked interpolymer, the two recognized levers to convert a soluble thickener into an insoluble swollen gel are (a) increase crosslink density and (b) ionize the carboxyls as the alkali‑metal salt. 3,514,419 discloses both levers applied to the identical MA/MVE backbone. "[W]here a technique has been used to improve one device, and a person of ordinary skill in the art would recognize that it would improve similar devices in the same way, using the technique is obvious." KSR, 550 U.S. at 417.
3. Result‑effective variable / optimization. Crosslinker content is the classic result‑effective variable; selection of a workable range within the disclosed class is routine experimentation. In re Aller, 220 F.2d 454 (CCPA 1955) ("it is not inventive to discover the optimum or workable ranges by routine experimentation"); In re Boesch, 617 F.2d 272 (CCPA 1980). The 1–5 mole% figure is a range choice within the class that 3,514,419 already frames as a continuum (≤30 epoxy equivalents/100 copolymer; beyond that, insoluble gels). See also In re Kulling, 897 F.2d 1147 (Fed. Cir. 1990).

Combination 2 (the strongest "full house"): US 3,448,088 + US 3,514,419 + US 3,670,731

Add Harmon (3,670,731) to supply the reason the inventor made the change — the superabsorbent end use:

• Harmon expressly frames the problem the '186 patent solves: a water‑insoluble, crosslinked, alkali‑metal‑salt hydrocolloid that absorbs ≥15× its own weight of body exudate, holds it under 2.5 psi, and is "contained so that the polymeric network… is not soluble in water… yet remains flexible and swells." That is element D, verbatim, plus the capacity target.
• Harmon also supplies the crosslinker selection (expressly recites "diethylene glycol divinyl ether" — the claim‑5 species) and the end‑use motivation (diapers, sanitary napkins, catamenial tampons, dressings — exactly the utilities recited in the '186 specification).
• Combining: the artisan seeking a better diaper absorbent would take the known crosslinked MA/MVE interpolymer (3,448,088), adjust the divinyl‑ether crosslinker level upward into the insolubility regime, and neutralize with NaOH/KOH (3,514,419) to maximize osmotic swelling — a bounded, predictable design exercise with a reasonable expectation of success.
• US 3,997,484 (and cumulatively 3,669,103) reinforces that the marketplace and literature of 1976–81 were saturated with water‑insoluble, water‑swellable crosslinked polymers for absorbency, supplying "market demand" and "design incentive" rationales under KSR.

Combination 3 (alternative, if 3,448,088's crosslinker disclosure is narrower): US 3,514,419 + US 3,670,731, with the divinyl‑ether crosslinker as an obvious substitution

3,514,419 teaches the MA/MVE/salt/swellability platform but uses epoxy crosslinkers. Harmon teaches that divinyl crosslinkers generally, and diethylene glycol divinyl ether specifically, are the standard non‑conjugated crosslinkers for absorbent hydrocolloids. Substituting a known divinyl ether for an epoxy crosslinker in a known crosslinkable MA/MVE copolymer, to reach a known goal (insoluble swollen gel), is an obvious substitution of one known crosslinking chemistry for another with predictable results. KSR, 550 U.S. at 416.

5. Claim‑by‑claim disposition

6. Rebuttals the applicant would need (and why they are weak on this record)

A. "No teaching to abandon water‑soluble thickeners for insoluble superabsorbents." Weak. Harmon (3,670,731) is squarely directed to water‑insoluble crosslinked alkali‑metal‑salt hydrocolloids for diapers and tampons and states the precise insolubility/solubility trade‑off; the '186 specification repeats Harmon's list of utilities nearly verbatim (diapers, sanitary napkins, tampons, adult incontinent products, horticultural/agricultural aids).

B. "No motivation to select divinyl ethers." Weak. Divinyl ethers of aliphatic diols are the crosslinker class of the family's own prior patent (3,448,088), and the identical class is recited in 3,670,731.

C. Teaching away? None identified. 3,514,419's statement that excessive crosslinking yields "gelled lumps" is a caution about excess, not a teaching that insolubility is undesirable — it is, in fact, a roadmap to the claimed swellable‑but‑insoluble regime. A reference that merely discloses a working range and warns of the extremes does not teach away from the claimed range. In re Fulton, 391 F.3d 1195 (Fed. Cir. 2004).

D. Criticality / unexpected results. The specification provides no comparative data demonstrating that 1–5 mole% is critical. The two examples sit at ≈3.4 mole% (Ex. 1: 0.8 mol butanediol divinyl ether / 23.6 mol MVE) and 2.0 mole% (Ex. 2: 0.012 / 0.6 mol) — both comfortably inside the range, with no runs above or below it. Absent a showing that materially lower or higher crosslinker levels fail to give a swellable‑but‑insoluble product, the range is an optimization of a result‑effective variable, not an invention. In re Aller; In re Kulling.

E. "52 g urine/g is unexpectedly high." Not established on this record. Harmon's patent claims ≥15× body exudate and contemplates up to ~70×; 52 g/g (pH 7.0, simulated urine) is within, not above, the expected window, and no comparison is made against 3,448,088 salts or against the Weaver/3,997,484 superabsorbents. Under In re Geisler, 116 F.3d 1465 (Fed. Cir. 1997), a numerical result is not "unexpected" absent evidence that it is materially different from the closest prior art. No commercial‑success, licensing, copying, long‑felt‑need, or failure‑of‑others evidence appears on the patent page.

F. Property‑based novelty ("swellable but not soluble"). This is a property of the same polymer in salt form; a difference in a property that flows from the structure is not, by itself, a patentable distinction where the structure and the property are both suggested by the art. In re Papesch, 315 F.2d 381 (CCPA 1963); In re Spada, 911 F.2d 705 (Fed. Cir. 1990).

G. Anticipation overlays to check. If 3,448,088 (or 3,514,419 read together with it) expressly discloses an alkali‑metal salt of a 1–5 mole% divinyl‑ether‑crosslinked, equimolar MA/MVE interpolymer, claims 1–4, 6–8 are arguably anticipated under pre‑AIA § 102(b), which is a cleaner invalidity theory than § 103. The examiner's citation of these references without an express § 102 rejection suggests that neither reference, standing alone, discloses the salt in the insolubility regime — but I cannot confirm this from the materials available, and the point deserves direct verification of the 3,448,088 and 3,514,419 full texts and the '186 file wrapper.

7. Bottom line

Claims 1–4 and 6–8 would have been obvious over US 3,448,088 in view of US 3,514,419, and a fortiori over the three‑way combination with US 3,670,731 (optionally plus US 3,997,484). Claims 5 and 9 would have been obvious too — 3,670,731 names diethylene glycol divinyl ether expressly — though their literal scope is clouded by the formula defects discussed in §1.

The two most vulnerable spots in the patent are (i) the applicant's own admission that the claimed interpolymers are "essentially the same" as US 3,448,088's, which converts the case into an optimization of crosslink density plus a salt‑formation step, and (ii) the complete absence of comparative data bracketing the 1–5 mole% crosslinker range. The strongest defensive posture for the patentee would have been a showing of criticality for the 1–5 mole% window plus secondary‑consideration evidence, none of which appears on the patent page.

Confidence: High as to the content of US 3,514,419 and US 3,670,731 (verified via full‑text sources). Moderate as to US 3,448,088's precise disclosure of the 1–5 mole% divinyl‑ether crosslinker — this rests on the '186 specification's admission, the EP 0 068 847 family member, and later GAF/ISP characterizations rather than on my direct reading of the reference, which I flag as the principal verification gap. Low/unverified as to US 3,669,103, which I treated as cumulative only.

Key sources: US 4,387,186 · US 3,514,419 and FPO copy · US 3,670,731 and uspto.report · EP 0 510 002 B1 (characterizing the GAF prior art) · EP 0 068 847 A1 (family member).