Preparation of multiblock copolymers via step-wise addition of l-lactide and trimethylene carbonate.

Mark Abubekerov,Qibing Pei,Kevin R Swartz,Junnian Wei,Paula L Diaconescu,Zhixin Xie

doi:10.1039/c7sc04507g

Abstract

Poly(l-lactide) (PLA) is a bioderived and biodegradable polymer that has limited applications due to its hard and brittle nature. Incorporation of 1,3-trimethylene carbonate into PLA, in a block copolymer fashion, improves the mechanical properties, while retaining the biodegradability of the polymer, and broadens its range of applications. However, the preparation of 1,3-trimethylene carbonate (TMC)/l-lactide (LA) copolymers beyond diblock and triblock structures has not been reported, with explanations focusing mostly on thermodynamic reasons that impede the copolymerization of TMC after lactide. We discuss the preparation of multiblock copolymers via the ring opening polymerization (ROP) of LA and TMC, in a step-wise addition, by a ferrocene-chelating heteroscorpionate zinc complex, {[fc(PPh2)(BH[(3,5-Me)2pz]2)]Zn(μ-OCH2Ph)}2 ([(fcP,B)Zn(μ-OCH2Ph)]2, fc = 1,1'-ferrocenediyl, pz = pyrazole). The synthesis of up to pentablock copolymers, from various combinations of LA and TMC, was accomplished and the physical, thermal, and mechanical properties of the resulting copolymers evaluated.

Highlights

We discuss the preparation of multiblock copolymers via the ring opening polymerization (ROP) of LA and trimethylene carbonate (TMC), in a step-wise addition, by a ferrocene-chelating heteroscorpionate zinc complex, {[fc(PPh2)(BH[(3,5Me)2pz]2)]Zn(m-OCH2Ph)}2 ([(fcP,B)Zn(m-OCH2Ph)]2, fc 1⁄4 1,10-ferrocenediyl, pz 1⁄4 pyrazole)
In the course of studying the redox switchable reactivity[32,33,34,35,36,37,38,39,40,41,42,43,44,45,46] of the ferrocene-chelating heteroscorpionate zinc complex {[fc(PPh2)(BH[(3,5-Me)2pz]2)]Zn(mOCH2Ph)}2 ([(fcP,B)Zn(m-OCH2Ph)]2)[37] toward various monomers, we discovered that it can perform the ring opening polymerization (ROP) of LA and TMC regardless of the addition order
The mechanical properties of the polymers were determined via dynamic mechanical analysis (DMA, Table 2 and Fig. S74– S81†) on multiple samples of each copolymer prepared via a solvent casting method

Summary

Introduction

Growing concerns over the environmental damage caused by petroleum-based plastic waste[1] and the associated health effects due to petroleum processing[2] necessitate a shi to environmentally benign commodity plastics.[3,4,5,6] As a result, biodegradable plastics obtained from bio-renewable sources, in particular poly(L-lactide) (PLA),[7,8] have received much attention in the past decades.[3,9,10,11] Currently, applications of PLA vary widely from specialty plastics in biomedical devices[12,13,14,15] to commodity plastics in food packaging.[14,15,16] The mechanical properties of PLA resemble those of polystyrene;[11] it is a hard material with good tensile strength and high modulus.[10]. We discuss the preparation of multiblock copolymers via the ring opening polymerization (ROP) of LA and TMC, in a step-wise addition, by a ferrocene-chelating heteroscorpionate zinc complex, {[fc(PPh2)(BH[(3,5Me)2pz]2)]Zn(m-OCH2Ph)}2 ([(fcP,B)Zn(m-OCH2Ph)]2, fc 1⁄4 1,10-ferrocenediyl, pz 1⁄4 pyrazole). The solid state molecular structure of [(fcP,B)Zn(m-OCH2Ph)]2 was determined using single-crystal X-ray diffraction (Fig. 1).

Results

Conclusion