Abstract
Stereo-diblock copolymers of high molecular weight polylactide (PLA) were synthetized by the one pot-sequential addition method assisted by a heteroscorpionate catalyst without the need of a co-initiator. The alkyl zinc organometallic heteroscorpionate derivative (Zn(Et)(κ3-bpzteH)] (bpzteH = 2,2-bis(3,5-dimethylpyrazol-1-yl)-1-para-tolylethoxide) proved to assist in the mechanism of reaction following a coordination-insertion process. Kinetic studies along with the linear correlation between monomer and number average molecular weight (Mn) conversion, and the narrow polydispersities supported the truly living polymerization character of the initiator, whereas matrix-assisted laser desorption/Ionization-time of flight (MALDI-TOF) studies showed a very low order of transesterification. The high stereo-control attained for the afforded high molecular weight derivatives was revealed by homonuclear decoupled 1H NMR spectra and polarimetry measurements. The nanostructure of the PLA derivatives was studied by both wide-angle X-ray scattering (WAXS) and differential scanning calorimetry (DSC) and the stereocomplex phase of the PLA stereo-diblock copolymers was successfully identified.
Highlights
IntroductionPolyesters, and polylactide (PLA), are largely investigated in the bioplastic field due to the low cost production, the remarkable physicochemical properties, and the biodegradability (under industrial compostable controlled conditions [1])
PLA stereocomplexation has typically been achieved by the blend of the PLA enantiomers with detrimental phase separation at a high molecular weight that diminishes the promising physicochemical properties featured by the SC phase
The enhancement of the mechanical properties, as well as the thermal and hydrolysis degradation resistance of PLA derivatives, is still required, which could potentially be attained by the generation of stereo-diblock PLA copolymers
Summary
Polyesters, and polylactide (PLA), are largely investigated in the bioplastic field due to the low cost production, the remarkable physicochemical properties, and the biodegradability (under industrial compostable controlled conditions [1]). PLA is a semicrystalline polymer with bio-assimilate characteristics thanks to the hydrolysis of the polymer chain ester bond in physiological media, yielding lactic acid [2]. PLA is the bio-based polymer most widely employed in diverse industrial fields such as food handling, fibre manufacturing, textile industry or biomedical area [3].
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