Stereocomplex- and homo-crystallization of blends from 2-armed poly(l-lactide) and poly(d-lactide) with identical and opposite chain directional architectures and of 2-armed stereo diblock poly(lactide)

Abstract

Ethylene glycol (EG) and succinic anhydride (SA)-based 2-armed PLLA and PDLA correspondingly with tail-to-tail (T–T) and head-to-head (H–H) architectures, together with SA-based linear 2-armed stereo diblock copolymer, were synthesized and the SC crystallization and homo-crystallization behavior of blends of 2-armed PLLA and PDLA with various combinations of molecular architectures, together with that of neat polymers, were investigated. The crystallizability was higher for SC crystalline samples than for homo-crystalline samples during solvent evaporation and slow cooling from the melt. The hydrogen bonds of hydroxyl terminals and/or low molecular weight of EG-based polymer rather than specific chain directional architecture or its combination disturbed and delayed the crystallization, lowering the crystallization temperature (Tc), crystalline], the reciprocal of experimental crystallization half time [1/tc(1/2) (exp)], spherulite growth rate (G), enthalpy of crystallization (ΔHc) for 1st cooling, and total enthalpy of cold crystallization and melting [ΔH(tot)] for 2nd heating of both SC crystalline and homo-crystalline samples, the melting temperature (Tm) for 1st and 2nd heating, nucleus density and the degree of lamella orientation of spherulites of SC crystalline samples. The opposite chain directional architectures of polymers in blends should have increased ΔH(tot) for 1st heating, ΔHc for 1st cooling, ΔH(tot) for 2nd heating, and G of SC crystalline samples. The effects of hydrogen bonds of hydroxyl terminal groups, Mn (or Mn per one arm or block), and chain directional combination were determined by the crystallization temperature range and the presence or absence of a solvent. The Tm values of SC crystalline samples were determined by Mn (or Mn per one arm or block), whereas those of homo-crystalline samples did not show clear dependence on Mn (or Mn per one arm or block) values per one arm, hydroxyl terminal groups (hydrogen bonding), or chain direction. The intermolecular SC crystallization in the enantiomeric polymer blends was favored compared with intramolecular SC crystallization in the stereo diblock copolymer.