Facile Preparation of Stereoblock PLA From Ring-Opening Polymerization of rac-Lactide by a Synergetic Binary Catalytic System Containing Ureas and Alkoxides.

Ze Kan,Dejuan Zheng,Shaofeng Liu,Chuanzhi Wei,Binghao Han,Tong Shi,Wenlong Luo

doi:10.3389/fchem.2018.00547

Ze Kan, Dejuan Zheng + Show 5 more

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https://doi.org/10.3389/fchem.2018.00547

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Abstract

Ring-opening polymerization (ROP) of cyclic esters/lactones by efficient catalysts is a powerful method for synthesis of biodegradable and biocompatible polyesters with well-defined structures. To develop catalytic systems that are fast, selective and controlled is a persistent effort of chemists. In this contribution, we report a binary urea/alkoxide catalytic system that could catalyze ROP of rac-LA in a fast (over 90% conversion within 1–2 min), stereoselective (Pi up to 0.93) and controlled manner, indicated by narrow MW distributions, linear relationship between the monomer conversions and Mns, end-group fidelity, and chain extension experiments. Remarkably, the catalytic system described here is simple, easily prepared, and structurally tunable and thus has versatile catalytic performances.

Highlights

Polylactide (PLA) is one of the most popular and commercial polymers in our daily lives (DechyCabaret et al, 2004; Rasal et al, 2010; Raquez et al, 2013)
Investigations were performed with a 3:1 ratio for urea/KOMe unless specified. These results are significant since the ROP of rac-LA with fast rate and high stereoselectivity has been achieved using a simple catalytic system under mild conditions
With comparative conditions, the degrees of stereoregularity (Pi) of PLA prepared by N-heterocyclic carbenes (NHCs) and dimeric phosphazene were 0.59 and 0.72, respectively (Dove et al, 2006; Zhang et al, 2007)

Summary

Introduction

Polylactide (PLA) is one of the most popular and commercial polymers in our daily lives (DechyCabaret et al, 2004; Rasal et al, 2010; Raquez et al, 2013). For one thing, it is derived from renewable resources and could completely degrade to metabolites by hydrolysis after several months of exposure to moisture,(Castro-Aguirre et al, 2016; Farah et al, 2016) which could immensely reduce consumption volume of fossil resources and environmental pollution and makes it being a perfect substituent for petroleum-based plastics (Auras et al, 2004; Ray and Bousmina, 2005). The stereocomplex of L-PLA and D-PLA in 1:1 ratio (Ikada et al, 1987; Tashiro et al, 2017) or Synergetic Catalysts for Stereoselective ROP stereoblock PLA prepared from rac-LA using stereoselective catalysts (Stanford and Dove, 2010; Thomas, 2010; Dijkstra et al, 2011) has an even higher Tm up to 230◦C and improved mechanical properties, due to cocrystallization of enantiomers (Ovitt and Coates, 2000; Fujita et al, 2008)

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