A polymer of formula wherein: each of R a -R d, each of R a0 -R d0, each of R a1 -R d1, and each of R a2 -R d2 are respectively independently selected from the group consisting of H, halogen, C 1 -C 6 alkyl, halo C 1 -C 6 alkyl, C 1 -C 6 alkoxy, halo C 1 -C 6 alkoxy, C 3 -C 12 cycloalkyl and halo C 3 -C 12 cycloalkyl; n and n 0 are each independently a number from 0 to 40, and n+n 0 is a number from 20 to 40; and n 1 and n 2 are each independently a number from 0 to 2, and/or n 1 +n 2 is a number from 0 to 3; obtainable by a process which comprises reacting a polymer of formula with a compound of formula, wherein n'=n+n 0 +n 1 +n 2, R a -R d, n, n 0, n 1 and n 2 are each as defined_above, and X is a halogen, preferably chlorine or bromine, wherein the reaction of the polymer of formula with the compound of formula is carried out in the presence of an alkaline catalyst, which is preferably one or more selected from the group consisting of NaOH, KOH, Na 2 CO 3, K 2 CO 3, more preferably K 2 CO 3, wherein the polymer of formula and the compound of formula are used in an amount such that the molar ratio of the monomer unit contained in the polymer of formula to the compound of formula is from 1:1 to 1:3, preferably from 1:1.8 to 1:2.0; and wherein the reaction of the polymer of formula with the compound of formula is carried out at 0-30°C, preferably at 25-30°C. each of R a -R d, each of R a0 -R d0, each of R a1 -R d1, and each of R a2 -R d2 are respectively independently selected from the group consisting of H, halogen, C 1 -C 6 alkyl, halo C 1 -C 6 alkyl, C 1 -C 6 alkoxy, halo C 1 -C 6 alkoxy, C 3 -C 12 cycloalkyl and halo C 3 -C 12 cycloalkyl; n and n 0 are each independently a number from 0 to 40, and n+n 0 is a number from 20 to 40; and n 1 and n 2 are each independently a number from 0 to 2, and/or n 1 +n 2 is a number from 0 to 3; obtainable by a process which comprises reacting a polymer of formula with a compound of formula, wherein n'=n+n 0 +n 1 +n 2, R a -R d, n, n 0, n 1 and n 2 are each as defined_above, and X is a halogen, preferably chlorine or bromine, wherein the reaction of the polymer of formula with the compound of formula is carried out in the presence of an alkaline catalyst, which is preferably one or more selected from the group consisting of NaOH, KOH, Na 2 CO 3, K 2 CO 3, more preferably K 2 CO 3, wherein the polymer of formula and the compound of formula are used in an amount such that the molar ratio of the monomer unit contained in the polymer of formula to the compound of formula is from 1:1 to 1:3, preferably from 1:1.8 to 1:2.0; and wherein the reaction of the polymer of formula with the compound of formula is carried out at 0-30°C, preferably at 25-30°C. wherein the reaction of the polymer of formula with the compound of formula is carried out in the presence of an alkaline catalyst, which is preferably one or more selected from the group consisting of NaOH, KOH, Na 2 CO 3, K 2 CO 3, more preferably K 2 CO 3, wherein the polymer of formula and the compound of formula are used in an amount such that the molar ratio of the monomer unit contained in the polymer of formula to the compound of formula is from 1:1 to 1:3, preferably from 1:1.8 to 1:2.0; and wherein the reaction of the polymer of formula with the compound of formula is carried out at 0-30°C, preferably at 25-30°C.