DYNAMIC LIGHT-SCATTERING STUDY ON SOL-GEL TRANSITION OF POLY(GAMMA-BENZYL L-GLUTAMATE)-TOLUENE SOLUTIONS

The autocorrelation function (ACF) was measured at various temperature s using the dynamic light scattering (DLS) technique for two kinds of toluene solutions of poly(gamma-benzyl L-glutamate) (PBLG): one was a semidilute PBLG (M(W)=2.3x10(5)) solution far above the critical cross over concentration phi(2) (PBLG-23), and the other was also a semidil ute PBLG (M(W)=1.0x10(5)) solution near phi(2) (PBLG-10). Both of the PBLG solutions were sol at elevated temperatures and gelled with decr easing temperature. For PBLG-23, the ACF obtained in the sol phase cou ld be fit well by a double-exponential function: the fast mode was due to a cooperative diffusive motion in a transient entangled PBLG-23 ne twork; the slow mode was considered to be diffusive motion of aggregat ed PBLG-23 chains. On the other hand, the ACF of PBLG-10 was character istic and was modulated vibrationally near the gelation threshold. Thi s fact suggested strongly underdamped coupling between aggregated doma ins of PBLG-10 chains.