Synthesis of side-chain liquid crystal polymers by living ring-opening metathesis polymerization. 2. Influence of molecular weight, polydispersity, and flexible spacer length (n = 9-12) on the thermotropic behavior of the resulting polymers

Abstract

Abstract : The living ring opening metathesis polymerization of 5-carbo(n-(4'- methoxy-4-biphenylyl)oxy)alkyl)bicyclo(2.2.1)hept-2-ene (1-n, n=2-8) by Mo(CH-t- Bu)(NAr) (0-t-Bu)2(Ar=2,6-C6H3-t-Pr2) is described. Polymers with degrees of polymerization from 5 to 100 and narrow molecular weight distributions (Mw/Mn=1. 05-1.24) were obtained in high yield. All polymers exhibit an enantiomorphic nematic mesophase. Glass transition and isotropization temperatures increase with increasing molecular weight and become independent at approximately 30-50 repeat units. The change in enthalpy of isotropization is relatively independent of molecular weight. Using polymer blends, it was shown that polydispersity has no effect on either the transition temperatures or the temperature range of isotropization. Isotropization alternates in an odd-even manner up to spacer lengths of n=6, and then levels off. Living ring opening metathesis polymerization, Side chain liquid crystalline polymers (SCLCPs).