Effect of End Groups on the Thermotropic Behavior of Linear Poly[11-(4‘-cyanophenyl-4‘ ‘-phenoxy)undecyl acrylate]s Prepared by ATRP and Their Topological Blends

Abstract

Linear poly[11-(4‘-cyanophenyl-4‘ ‘-phenoxy)undecyl acrylate]s with 9−77 (GPC relative to linear polystyrene) or 7−101 (GPCLS) 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 (sA−i) transition of the linear polymers are extremely narrow, with full widths at half of the maximum peak intensity (fwhm) = 4.52−7.74 °C, in contrast to that of the corresponding polymer prepared by conventional radical polymerization (fwhm = 17.0 °C). 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).