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

Liquid crystalline polyurethane thermoplastic elastomers with cyano-bipheny l mesogens pendant on the soft segment have been synthesized for the first time. These materials offer a unique opportunity to study the interplay bet ween the liquid crystalline ordering of the elastomer and the morphology of the segmented copolymer. We present the synthesis of carbinol end-capped h ydromethylsiloxane oligomers, which can be functionalized with mesogen via a hydrosilylation technique. These side chain liquid crystalline (LC) silox ane macromonomers are then converted to segmented polyurethanes using tradi tional urethane chemistry. Structural analysis and characterization of the resulting polymers is provided, along with a comparison study of the therma l 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 (sp acer length = 8) are above the soft segment T-g at room temperature with a stablized smectic phase. Less decoupled polymers (spacer length = 3) are ha rder, flaky materials which exhibit a nematic phase at high temperatures. D iscussions of the effects of the hard segment mobility on the phase behavio r of these liquid crystalline polyurethanes is offered. These materials sho w promise as elastomers with mechanooptic and electrooptic behavior.