can also comprise an alkyl meth acrylate this portion can represent up to 30 of b with regard to the product c comprising an unsaturated carboxylic acid mention may be made as examples of the products b completely or partly hydrolysed c is for example a copolymer of ethylene and of an unsaturated carboxylic acid and advantageously a copolymer of ethylene and of meth acrylic acid mention may also be made of the copolymers of ethylene of an alkyl meth acrylate and of acrylic acid these copolymers have an mfi of between 0 1 and 50 g 10 min at 190 u00b0 c under 2 16 kg the amount of acid can be up to 10 by weight and preferably 0 5 to 5 the amount of meth acrylate is from 5 to 40 by weight c can also be chosen from u03b1 u03c9 aminocarboxylic acids such as for example nh 2 u2014 ch 2 5 cooh nh 2 u2014 ch 2 10 cooh and nh 2 ch 2 11 u2014 cooh and preferably aminoundecanoic acid the proportion of a and b necessary to form the crosslinked phase is determined according to the usual rules of the art by the number of.