ELUCIDATING THE STRUCTURE OF HYPERBRANCHED SIDE-CHAIN LIQUID CRYSTALLINE POLYACRYLATES

Side-chain liquid crystalline polymers (SCLCPs) prepared by non-living polymerizations generally exhibit very broad phase transitions, in contrast to low molar mass liquid crystals. The broad phase transitions were immediately dismissed in the SCLCP literature as being due to polydispersity in molecular weight. For example, when poly[11-(4\u27-cyanophenyl-4 -phenoxy)undecyl acrylate] was prepared by a conventional radical polymerization and then fractionated,1 each of the fractions underwent a narrower smectic A to isotropic transition (full widths at half maximum peak intensity (fwhm) = 6.25 – 10.71 o C) than the unfractionated polymer (fwhm = 17.0 o C).2 However, we have provided evidence that the broad smectic A to isotropic (sA - i) phase transition of this polymer is due to the limited miscibility of a mixture of linear and variously branched structures, which is consistent with its chain transfer constant to polymer (Cp = 5.48 x 10-3).3 The fwhm of the isotropization biphasic region of 1:1 binary blends of individual molecular architectures of poly[11-(4\u27-cyanophenyl-4 -phenoxy)undecyl acrylate]s increases relatively linearly with the difference in end group densities of the two components, regardless of the combination of topologies or the type of end groups