The ranking covers 100 companies, with the leading assignee holding 220 of the 2,834 records in scope. The gap to the field is steep: fifth place holds 76 records and tenth place holds 52, so the top five together account for 22.8% of all records while the top ten reach 33.3%. That leaves a long tail of assignees with only a handful of filings each, meaning the field is concentrated at the top but still has substantial room for new entrants outside the leading group.

Filing peaked at 195 records in 2020 and had fallen to 90 by 2024, a -38% move from 2021's 144 filings over that three-year span. That is the most reliable read because 2024 is the last year with largely complete publication data. Figures for 2025 and 2026 are still incomplete due to the roughly 18-month lag between filing and publication, so they should not yet be read as confirmation of a continued decline.

Separation processes under IPC class B01D appear in 30.6% of the 2,834 records, making membrane and filtration applications the single largest claim area. Polymer composition claims (C08L) follow at 24.6%, with additive use, condensation polymer chemistry and polymer processing each around 13.5%. Sterilising-specific claims (A61L) are comparatively rare at 5.6%, which suggests most hydrolysis-resistance and steam-sterilization language is being claimed through membrane or molding property claims rather than as standalone sterilising methods.

US11578208B2, assigned to Sumitomo Chemical Company, claims an aromatic polysulfone resin built from two repeating units in a specific molar ratio range of 1:2,000 to 1:200, with defined substitution options on the phenylene hydrogens. It is a composition-of-matter claim rather than a process or application claim, so it constrains resin formulations that fall inside that stoichiometric window regardless of what the resin is ultimately used for. Anyone drafting a new polysulfone resin composition claim should check their monomer ratio and substitution pattern against this range before finalising claim language.

The technology composition data shows the densest claim activity sits in separation processes and general polymer composition, while adjacent branches such as fuel-cell membrane applications, solvent-casting process parameters, and transparent molding grades for medical housings carry comparatively thin coverage. These branches sit next to well-covered core claims rather than in an entirely unclaimed area, so a workable strategy is to file narrowly around a specific processing parameter or end-use combination rather than attempting a broad composition claim, which is more likely to collide with the concentrated top-ten portfolios.