Synthesis and characterization of new segmented copolymers with side chain liquid crystalline soft segments

Liquid crystalline polyurethane thermoplastic elastomers with cyano-biphenyl mesogens pendant on the soft segment have been synthesized for the first time. These materials offer a unique opportunity to study the interplay between the liquid crystalline ordering of the elastomer and the morphology of the segmented copolymer. We present the synthesis of carbinol end-capped hydromethylsiloxane oligomers, which can be functionalized with mesogen via a hydrosilylation technique. These side chain liquid crystalline (LC) siloxane macromonomers are then converted to segmented polyurethanes using traditional urethane chemistry. Structural analysis and characterization of the resulting polymers is provided, along with a comparison study of the thermal and optical behavior of these urethanes as the spacer length is increased from 3 to 8 methylene units. Polymers with a high degree of decoupling (spacer length = 8) are above the soft segment T-g at room temperature with a stablized smectic phase. Less decoupled polymers (spacer length = 3) are harder, flaky materials which exhibit a nematic phase at high temperatures. Discussions of the effects of the hard segment mobility on the phase behavior of these liquid crystalline polyurethanes is offered. These materials show promise as elastomers with mechanooptic and electrooptic behavior.