Heterostereocomplex‐ and Homocrystallization and Thermal Properties and Degradation of Substituted Poly(lactic acid)s, Poly(l‐2‐hydroxybutanoic acid) and Poly(d‐2‐hydroxy‐3‐methylbutanoic acid)

Abstract

Heterostereocomplex‐ and homocrystallization behavior, thermal properties and degradation of neat poly(l‐2‐hydroxybutanoic acid) [P(l‐2HB)], poly(d‐2‐hydroxy‐3‐methylbutanoic acid) [P(d‐2H3MB)], and their equimolar blend are first investigated. Regime I and II kinetics are observed for neat P(l‐2HB), whereas regime II and III kinetics are seen for the blend. The growth geometry of the neat P(l‐2HB) is linear and circular while that of the blend is spherical, whereas that of the neat P(d‐2H3MB) changes from linear to spherical, depending on crystallization temperature (T c). The main crystalline species is heterostereocomplex (HTSC) in the blend for a wide T c range of 0–180 °C and a very small amount of P(d‐2H3MB) homocrystallites form for melt‐crystallization at T c below 70 °C and solution‐crystallization. The equilibrium melting temperature of P(l‐2HB)/P(d‐2H3MB) HTSC crystallites (234.5 °C) is higher than those of P(l‐2HB) and P(d‐2H3MB) homocrystallites (114.9 and 208.6 °C, respectively). The activation energy values for thermal degradation of the P(l‐2HB)/P(d‐2H3MB) blend (190–219 kJ mol−1) are between those of neat P(l‐2HB) and P(d‐2H3MB) (164–180 and 210–380 kJ mol−1, respectively), reflecting that the interaction between the polymers with opposite configurations is similar to or lower than that between the polymers with the same configurations at a high temperature in the melt.image