ich each group R18 is the same or different and is hydrogen or alkyl of 1 to 4 carbon atoms, or aralkyl, for example benzyl or phenethyl, each group R19 is alkyl of 1 to 4 carbon atoms, qq is from 1 to 6 and pp is from 0 to 49 [0082] Most preferably R13 is a straight alkyl having 8 to 18, preferably 12 to 16 carbon atoms. [0083] The reactive monomer to which provides crosslinkability preferably ha