Spherulite growth rate as a function of temperature and fit to the LH theory with a single regime.

1. A B Polymer CrystallizationHervé Marand, Virginia Polytechnic Institute and State University, DMR 0706210 This work focuses on the crystallization mechanism of highly stereoregular poly(L-lactic acid) (PLLA), an important polymer with biodegradable and biocompatible properties. Crystal growth studies between 130 and 175oC using spherulites initiated at lower temperatures show no evidence for a change in crystallization mechanism or morphology in this temperature range. The stark contrast between our results and these reported in the literature either suggest that crystal growth data in previous studies were incorrectly analyzed or that previously reported changes in crystallization mechanism are closely associated with morphological changes, at least in the case of PLLA. Spherulite growth rate as a function of temperature and fit to the LH theory with a single regime. Spherulitic (A) and hedritic (B) morphologies formed by crystallization at 135 C, respectively with and without self-seeding.

2. ln Stick regime Marginal regime N4 Rouse regime N VrouseN-1 lnV V*N-4 Polymer CrystallizationHervé Marand, Virginia Polytechnic Institute and State University, DMR 0706210 International collaborations have been initiated with the groups of Yves Grohens (Université Bretagne-Sud) andLiliane Léger (Université Paris-Sud) to prepare and characterize PEO samples for the study of friction regimes. These studies will allow us to probe whether changes in crystallization mechanism can be explained by a transition between the Marginal and the Rouse viscoelastic regimes. Correlations between the melting and the crystallization behavior of polymers, an important aspect of the determination of the equilibrium melting temperature, are investigated using the new rapid heating- cooling DSC from TA Instruments for which our group is one of the four beta sites world-wide.