Broadband DielectricInvestigaton of Amorphous and Semicrystalline L-Lactide/meso-Lactide Copolymers

摘要

The dynamics of crystalline and amorphous samples of poly(L-lactide) and three-locatide/meso-lactide random copolymers were investigated in the frequency domain using broadband dielectric spectroscopy(DRS).Two relaxations,the segmental(alpha)and (beta)processes,were observed in the temperature ragne between -100 and 105 deg C.Modification of the characteristics of the alpha process,i.e.,the relaxation strength(delta epilon),mean relaxaton time (tau_m) and shape parameters,as a function of crystal content was investigated on "fully crystallized"samples as well as real-time crystallization experiments.As expected,the strength of the alpha relaxationwas smaller and its distribution broader for materials with higher degrees of crystallinity.The relaxaton strenght of the alpha process of the amorphous samples increased with temperature,while that of the crystallien materials changece of a rigid amorphous components.Changes in tau_m and T_0 (the Vogel temperature)for the copolymers crystallized at various T_c are influenced by crystalline microsturuture as well as by crystalline content.A relaxation is also observed in higher temperature (125-155 deg C) experiments on amorphous and crystalline materials.The evidence at hand suggests that these processes are associated with the normal mode and alpha_c process,respectively.