Effect of end groups on the thermotropic behavior of linear poly[11-(4′-cyanophenyl-4"-phenoxy)undecyl acrylatels prepared by ATRP and their topological blends

Linear poly[11-(4'-cyanophenyl-4"-phenoxy)undecyl acrylate]s with 9-77 (GPC relative to linear polystyrene) or 7-101 (GPC(L8)) repeat units were synthesized by atom transfer radical polymerization of 11-(4'-cyanophenyl-4"-phenoxy)undecyl acrylate using a mesogenic initiator, 11-(4'-cyanophenyl-4"-phenoxy)undecyl 2-bromopropionate. The biphasic regions of the smectic A to isotropic (s(A)-i) transition of the linear polymers are extremely narrow, with full widths at half of the maximum peak intensity (fwhm) = 4.52-7.74 degreesC, in contrast to that of the corresponding polymer prepared by conventional radical polymerization (fwhm = 17.0 degreesC). The breadths of this transition do not vary with chain length, in contrast to the corresponding linear polymers with methyl propionate end groups. The breadth of the sA-i biphasic region of 1:1 binary blends of poly[11-(4'-cyanophenyl-4"-phenoxy)undecyl acrylate]s increases relatively linearly with the difference in end group (and therefore branching) density of the two components, regardless of the combination of molecular architectures (linear, three-arm star, or comb) or the type of end groups (bromine and hydrogen or methyl propionate).