LIFETIME RENORMALIZATION IN CRITICAL-DYNAMICS AS APPLIED TO THE ISOTROPIC-NEMATIC TRANSITION IN SIDE-CHAIN LIQUID-CRYSTALLINE POLYMERS

We study the dynamic behavior near the isotropic-nematic transition in liquid crystalline sidechain polymers using a mode coupling technique as applied to the life-time. renormalization. To lowest order in mode coupling we find for the dynamical critical exponent z for the relaxa tion time of the order parameter the value z = 1.5, while in mean fiel d approximation one obtains z = 1. This result is in agreement with re cent experiments done in Martinoty's group on two different classes of sidechain liquid crystalline polymers using electric and acoustic bir efringence measurements. This qualitative difference in behaviour betw een low molecular weight systems and sidechain polymers can be traced back to nonlinear (cubic) cross coupling terms in the generalized ener gy between the order parameter and the strain associated with the tran sient network. The importance of such nonlinear cross coupling terms i s corroborated further by recent measurements of the dynamic stress-op tical coefficient in sidechain elastomers.