کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
5191657 1381236 2005 11 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Spherulite growth of l-lactide copolymers: Effects of tacticity and comonomers
موضوعات مرتبط
مهندسی و علوم پایه شیمی شیمی آلی
پیش نمایش صفحه اول مقاله
Spherulite growth of l-lactide copolymers: Effects of tacticity and comonomers
چکیده انگلیسی

The spherulite growth behavior and mechanism of l-lactide copolymers, poly(l-lactide-co-d-lactide) [P(LLA-DLA)], poly(l-lactide-co-glycolide) [P(LLA-GA)], and poly(l-lactide-co-ε-caprolactone) [P(LLA-CL)] have been studied using polarization optical microscopy in comparison with poly(l-lactide) (PLLA) having different molecular weights to elucidate the effects of incorporated comonomer units. The incorporation of comonomer units reduced the radius growth rate of spherulites (G) and increased the induction period of spherulite formation (ti), irrespective of the kind of comonomer unit. Such effects became remarkable with the content of comonomers. At a crystallization temperature (Tc) of 130 °C, the disturbance effects of comonomers on the spherulite growth decreased in the following order: d-lactide>glycolide>ε-caprolactone, when compared at the same comonomer unit or reciprocal of averaged l-lactyl unit sequence length (ll). The ti estimation indicated that the glycolide units have the lowest disturbance effects on the formation of spherulite (crystallite) nuclei. The PLLA having the number-average molecular weight (Mn) exceeding 3.1×104 g mol−1 showed the transition from regime II to regime III at Tc=120 °C, whereas PLLA with the lowest Mn of 9.2×103 g mol−1 crystallized solely in regime III kinetics and the copolymers excluding P(LLA-DLA) with 3% of d-lactide units crystallized solely according to regime II kinetics. The nucleation and front constant for regime II and III [Kg(II), Kg(III), G0(II), and G0(III), respectively] estimated with each Tm0 (not with a fixed Tm0 for high-molecular-weight PLLA) decreased with increasing the amount of defects per unit mass of the polymer for crystallization, i.e. with increasing the comonomer content and the density of terminal group through decreasing the molecular weight.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Polymer - Volume 46, Issue 13, 17 June 2005, Pages 4917-4927
نویسندگان
, , , , ,