Effect of blending ratio and oligomer structure on the thermal transitions of stereocomplexes consisting of a D‐lactic acid oligomer and poly(L‐lactide)

Abstract

Poly(lactic acid) (PLA) stereocomplexes have high potential as renewable materials for advanced polymer applications, mainly due to their high melting temperature (Tm, typically 230–240°C). The properties of PLA stereocomplexes consisting of linear high molar mass homopolymers have been studied extensively in the past, but the available information about the possibilities to affect the thermal properties of the stereocomplex by varying the structure of the blend components has not been sufficient. Novel stereocomplexes containing linear or star‐shaped D‐lactic acid (D‐LA) oligomers and high molar mass poly(L‐lactide) (L‐PLA) were thus prepared. The Tm and melting enthalpy (ΔHm) of the racemic crystallites were found to depend strongly on both the blending ratio and the arm‐length of the D‐lactic acid oligomer. The preparation method of the oligomers, i.e. step‐growth polymerization or ring‐opening polymerization (ROP), did not affect the Tm or ΔHm of the blends significantly. Slightly higher ΔHm values were, however, obtained, when linear oligomers were used. The results thus indicated that the Tm and ΔHm of PLA stereocomplexes could be optimized, simply by selecting a D‐LA oligomer having a suitable arm‐length and structure as the other blend component. The possibility to adjust the melting behavior of the stereocomplex blend is a significant advantage and could make PLA suitable for a wider range of products used at elevated temperatures. Copyright © 2010 John Wiley & Sons, Ltd.

Configurational Molecular Glue: One Optically Active Polymer Attracts Two Oppositely Configured Optically Active Polymers

“…In the case of PLA, the mechanical performance, thermal/hydrolytic degradation-resistance of stereocomplexed materials are higher than those of constituent polymers, L-PLA and D-PLA11121314151617. A variety of stereo block343536373839404142434445464748495051, star-shaped5253545556575859606162636465, star-shaped stereo block PLAs6667686970 were synthesized, and the effects of stereo block and star-shaped or branching architectures on crystallization were extensively investigated and found to have crucial effects on stereocomplex (SC) and homo-crystallization behavior.…”

Stereocomplex‐ and Homo‐Crystallization and Phase‐Transition Behavior of Relatively High‐Molecular‐Weight Linear One‐ and Two‐Armed and Star‐Shaped Four‐Armed Poly(l‐lactide)/Poly(d‐lactide) Blends

“…The melting temperature ( T m ) or crystalline thickness of PDLA/PLLA blends with different arm numbers or 1‐L/4‐D or 1‐L/six‐armed PDLA (6‐D) blends was determined by the mole­cular weight per one arm of branched polymer not by the overall molecular weight of branched polymer, regardless of the arm number. The enthalpy of melting (Δ H m ) of SC crystallites of linear one‐armed PLLA/branched PDLA (1‐L/4‐D or 1‐L/6‐D) blends can be optimized by selecting the molecular weight per one arm of branched PDLA . The critical mole­cular weight above which in addition to SC crystallization, homo‐crystallization occurs decreased in the following order: one‐armed/one‐armed > one‐armed/three‐armed > three‐armed/three‐armed .…”

Preparation and properties of multi-branched poly(D-lactide) derived from polyglycidol and its stereocomplex blends

“…The number and types of functional groups on these polymers can be modified to control their properties for specific applications [33]. Recently, multi-branched PLAs have been developed, and their possible applications have been assessed [34][35][36][37][38]. In this work, multi-branched poly(D-lactide)s (mbPDLAs), with different structures and properties, are prepared by employing polyglycidol (PG) as a macro-initiator.…”