Thermal, Dynamic Mechanical and Dielectric Behavior of Liquid-Crystalline Linear and Crosslinked Polyurethanes with Mesogenic Group in Side Chains

Abstract

This paper describes DSC, dielectric and dynamic mechanical behavior of linear and crosslinked liquid crystalline (LC) polyurethanes based on LC diols with a mesogenic group in the side chain, diisocyanates of various flexibility and two triols. From our investigations it follows: a) Linear polymers prepared from diols with simple end side chain substituents (as hydrogen, nitro and nitril group) exhibit only amorphous behavior regardless of the structure of used diisocyanate; generally, the most pronounced LC behavior exhibited polymers prepared from a diol with phenyl substituent. b) Investigation of the curing reaction showed that rheological power-law parameters, which are characteristic of the structure at the gel point, are dependent on the initial ratio of the reactants (amount of LC diol in EANCs). c) Strong physical interactions between the mesogens support the cyclization in the course of crosslinking reaction. d) Introduction of chemical junctions (amount of triols) suppresses LC ordering in the networks.