Patent ID: 8252878

Claim:
A polymer obtained by copolymerizing a monomer mixture comprising (i) 5 to 40wt % of a hydrophilic monomer of the general formula (I) Y—B—X (I) wherein B is a straight or branched alkylene, oxaalkylene or oligo-oxaalkylene chain optionally containing one or more fluorine atoms up to and including perfluorinated chains or, if X contains a carbon-carbon chain between B and the centre of permanent positive charge or if Y contains a terminal carbon atom bonded to B, a valence bond; X is a zwitterionic group and Y is an ethylenically unsaturated polymerisable group of the general formula (II) where: R 1 is hydrogen or a C 1 -C 4 alkyl group; A 1 is —O— or —NR 2 — wherein R 2 is hydrogen or C 1-4 alkyl group or R 2 is BX where B and X are as defined above; (ii) 5 to 40wt % of styrene or a substituted styrene; (iii) 10 to 89wt % of a monomer (a) or mixture of monomers a), b) etc, which when polymerised form a polymer having a calculated Tg as calculated using 1 Tg = Wa Tga + Wb Tgb + … wherein Tg=glass transition temperature in Kelvins Tga and Tgb=glass transition temperature of a homopolymer of a and b respectively in Kelvins Wa and Wb=weight fraction of component a and b respectively which is lower than the Tg of a homopolymer formed by polymerizing monomer (ii); and (iv) 0.5 to 10wt % of a monomer having a crosslinkable group wherein after crosslinking the polymer has (a) a Tg (dry) in the range from 15 of 90° C.; (b) a hydrated modulus at room temperature of at least 5 MPa; (c) hydrated elongation at break of at least 50%; (d) a water content in the range from 10 to 60%; and (v) wherein monomer (i) is 2-methacryloyloxyethyl-2′-trimethylammoniumethyl phosphate inner salt, monomer (ii) is styrene, monomer (iii) comprises methyl methacrylate, butyl acrylate and hydroxybutyl acrylate and monomer (iv) is trimethoxysilyl propyl methacrylate.