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

A polymethylsiloxane with 4-propoxybenzoic acid side groups was prepared by hydrosilylation of polymethylhydrosiloxane and methyl 4-allyloxybenzoate f ollowed by hydrolysis. The existence of strong hydrogen bonding interaction s in this polymer due to dimerization of the carboxylic acid groups was dem onstrated by FTIR. The polymer exhibits a nematic mesophase at elevated tem peratures due to the self-assembly of hydrogen-bonded mesogens (dimers). Af ter 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-variabl e FTIR analysis presents a convincing interpretation for the DSC thermogram of the polymer, and furthermore assists in understanding the process of fo rmation of the nematic network and the reversibility of such hydrogen-bonde d networks.