Thermotropic comblike polymers with lipobiphenyl side chains: Factors governing nature of mesophases

Abstract

In this article we describe the thermotropic behavior of comblike polymers with three types of main chains (polyacrylamide, polymethacrylamide, and polystyrylamide ), two lengths of spacers ( 10 or five methylene groups ), and three types of mesogenic cores (biphenyl, carbonitrilbiphenyl, and 2-methyl-1-butoxybiphenyl). The spacers are always linked to the mesogens by an ester bond. All the polymers are smectic at room temperature and exhibit two different smectic phases as a function of temperature, except for the polymer with a styrylamide main chain and a carbonitrilbiphenyl mesogen that presents only one mesophase; but the type of smectic phases is governed by the nature of both the main chain and the substituent R of the biphenyl core. Polyacrylamide polymers exhibit only bilayer smectic phases whose type is determined by the nature of the substituent R of the biphenyl; the smectic phases are SI2 and SC2 for R = H, SC2 and SA2 for R = CN, and SF2 and SC2 for R =O-CH 2 -CH(CH 3 )-C 2 H 5 . On the contrary, polymethacrylamide and polystyryl-amide polymers exhibit two perpendicular monolayer smectic phases, SB1 and SA1, except for R = CN where a SAd phase replaces the SA1 phase.