Polymers comprising repeating units of the formula I where the variables are defined as follows: a is an integer from 0 to 3, R1, R2, R3 are identical or different and are selected independently from among hydrogen, C1-C20-alkyl, C1-C20-alkyl containing one or more Si, N, P, O or S atoms, C6-C30-aryl, preferably C6-C14-aryl, C4-C14-heteroaryl, —N(C6-C14-aryl)2, and Y1, where Y1 may be identical or different and are selected from among —CH═CH2, trans- or cis-CH═CH—C6H5, acryloyl, methacryloyl, methylstyryl, O—CH═CH2 and glycidyl, where Y2 is selected from among —CH═CH2, trans- or cis-CH═CH—C6H5, acryloyl, methacryloyl, methylstyryl, —O—CH═CH2 and glycidyl, and one or more groups Y1 or Y2 may be crosslinked to one another.