prov:value
| - t group chosen from oxygen, sulphur, alkylene with one to three carbon atoms, or a group of formulae IIIa to IIIj ##STR13## the radicals R1, R2, R3, R4, being alkyl groups with one to five carbon atoms, R5 being an alkylene group or an arylene group and B is a group which is capable of addition polymerization selected from the group consisting of radicals of formula IVa, IVb, IVc and IVd ##STR14##
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