A polymer composition comprising a crosslinked network, the network comprising a) a plurality of repeating units derived from a first reagent, the first reagent comprising a monomer having the structure of Formula 1, Formula 1-A, Formula 1-B or Formula 1-C; wherein X is Br or I; m in Formula 1-C is 1-5; each R 11 is independently a substituted or unsubstituted C 2 -C 36 alkylene group; C 2 -C 36 cycloalkylene group; C 2 -C 36 alkenylene group; C 2 -C 36 cycloalkenylene group; C 2 -C 36 alkynylene group; C 5 -C 36 arylene group; or C 5 -C 36 heteroarylene group; each L 11 is independently a single bond; -(CH 2) q -; -(HCCH) q -; -O-; -S-; - SO-; -SO 2 -; -SO 3 -; -OSO 2 -; -NR 12 -; -CO-; -COO-; -OCO-; -OCOO-; -CONR 13 -; -NR 14 CO-; -OCONR 15 -, -NR 16 COO-, or -NR 17 CONR 18 -; each Ar 11 is independently an iodine-, bromine or bismuth-containing C 5 -C 36 aryl group containing one or more rings, or an iodine-, bromine or bismuth-containing C 5 -C 36 heteroaryl group containing one or more rings; each of R 12 - R 18 is independently hydrogen or a C 1 -C 10 alkyl group; each q is independently an integer selected from the range of 1 to 10; and b) a plurality of repeating units derived from a second reagent, the second reagent comprising a branched monomer or oligomer comprising at least three terminal polymerizable groups, but not comprising iodine, bromine or bismuth, wherein the branched monomer or oligomer of the second reagent comprises from 3 to 20 terminal acrylate groups and further comprises a central portion R 1 linked to at least two end portions, Y 1 and Y 2, at least one of the end portions being branched and wherein R 1 is C 6 -C 20 alkylene. a) a plurality of repeating units derived from a first reagent, the first reagent comprising a monomer having the structure of Formula 1, Formula 1-A, Formula 1-B or Formula 1-C; wherein X is Br or I; m in Formula 1-C is 1-5; each R 11 is independently a substituted or unsubstituted C 2 -C 36 alkylene group; C 2 -C 36 cycloalkylene group; C 2 -C 36 alkenylene group; C 2 -C 36 cycloalkenylene group; C 2 -C 36 alkynylene group; C 5 -C 36 arylene group; or C 5 -C 36 heteroarylene group; each L 11 is independently a single bond; -(CH 2) q -; -(HCCH) q -; -O-; -S-; - SO-; -SO 2 -; -SO 3 -; -OSO 2 -; -NR 12 -; -CO-; -COO-; -OCO-; -OCOO-; -CONR 13 -; -NR 14 CO-; -OCONR 15 -, -NR 16 COO-, or -NR 17 CONR 18 -; each Ar 11 is independently an iodine-, bromine or bismuth-containing C 5 -C 36 aryl group containing one or more rings, or an iodine-, bromine or bismuth-containing C 5 -C 36 heteroaryl group containing one or more rings; each of R 12 - R 18 is independently hydrogen or a C 1 -C 10 alkyl group; each q is independently an integer selected from the range of 1 to 10; and wherein X is Br or I; m in Formula 1-C is 1-5; each R 11 is independently a substituted or unsubstituted C 2 -C 36 alkylene group; C 2 -C 36 cycloalkylene group; C 2 -C 36 alkenylene group; C 2 -C 36 cycloalkenylene group; C 2 -C 36 alkynylene group; C 5 -C 36 arylene group; or C 5 -C 36 heteroarylene group; each L 11 is independently a single bond; -(CH 2) q -; -(HCCH) q -; -O-; -S-; - SO-; -SO 2 -; -SO 3 -; -OSO 2 -; -NR 12 -; -CO-; -COO-; -OCO-; -OCOO-; -CONR 13 -; -NR 14 CO-; -OCONR 15 -, -NR 16 COO-, or -NR 17 CONR 18 -; each Ar 11 is independently an iodine-, bromine or bismuth-containing C 5 -C 36 aryl group containing one or more rings, or an iodine-, bromine or bismuth-containing C 5 -C 36 heteroaryl group containing one or more rings; each of R 12 - R 18 is independently hydrogen or a C 1 -C 10 alkyl group; each q is independently an integer selected from the range of 1 to 10; and b) a plurality of repeating units derived from a second reagent, the second reagent comprising a branched monomer or oligomer comprising at least three terminal polymerizable groups, but not comprising iodine, bromine or bismuth,