Synthesis and characterization of a hydrogen-bonded nematic network based on 4-propoxybenzoic acid side groups grafted onto a polysiloxane

Abstract

A polymethylsiloxane with 4-propoxybenzoic acid side groups was prepared by hydrosilylation of polymethylhydrosiloxane and methyl 4-allyloxybenzoate followed by hydrolysis. The existence of strong hydrogen bonding interactions in this polymer due to dimerization of the carboxylic acid groups was demonstrated by FTIR. The polymer exhibits a nematic mesophase at elevated temperatures due to the self-assembly of hydrogen-bonded mesogens (dimers). After cooling from its nematic melt, a stable hydrogen-bonded nematic network structure was formed, as demonstrated by differential scanning calorimetry, polarizing optical microscopy, and X-ray diffraction. Temperature-variable FTIR analysis presents a convincing interpretation for the DSC thermogram of the polymer, and furthermore assists in understanding the process of formation of the nematic network and the reversibility of such hydrogen-bonded networks.