Synthesis of Poly(Lactic Acid-co-Glycolic Acid) Copolymers with High Glycolide Ratio by Ring-Opening Polymerisation.

Alastair Little,David M Haddleton,Zhaoyang Sun,Yang Ji,Chaoying Wan,Bowen Tan,Alan M Wemyss

doi:10.3390/polym13152458

Abstract

The rise in demand for biodegradable plastic packaging with high barrier properties has spurred interest in poly(lactic acid-co-glycolic acid) (PLGA) copolymers with a relatively high glycolide content. In this work, we examined how reaction conditions affect the synthesis of PLGA25 (L:G 25:75) through the ring-opening polymerisation of d-l-lactide (L) and glycolide (G), using tin 2-ethylhexanoate (Sn(Oct)2) as the catalyst and 1-dodecanol as the initiator. The effects of varying the initiator concentration, catalyst concentration, reaction time, and temperature on the molecular weight, monomer conversion, and thermal properties of PLGA25 were investigated. Increasing the reaction temperature from 130 to 205 °C significantly reduced the time required for high monomer conversions but caused greater polymer discolouration. Whilst increasing the [M]:[C] from 6500:1 to 50,000:1 reduced polymer discolouration, it also resulted in longer reaction times and higher reaction temperatures being required to achieve high conversions. High Mn and Mw values of 136,000 and 399,000 g mol−1 were achieved when polymerisations were performed in the solid state at 150 °C using low initiator concentrations. These copolymers were analysed using high temperature SEC at 80 °C, employing DMSO instead of HFIP as the eluent.

Highlights

The use of biodegradable plastic packaging is regarded as an effective way to reduce the amount of plastic pollution in the natural environment
The ring-opening polymerisation (ROP) of cyclic esters is often initiated by hydroxyl compounds, where a reduction in the concentration of the initiator relative to the monomer increases the molecular weight of the product. 1-Dodecanol is frequently used as an initiator in the ROP of poly(lactic acid-co-glycolic acid) (PLGA), as its high boiling point prevents evaporation during polymerisation and its relatively high
When synthesising PLGA75, Wang et al varied the monomer to the 1-dodecanol ratio ([M]:[I]) from 20:1 to 300:1 and observed that the Mn increased from 3400 to 99,000 g mol−1 [24]

Summary

Introduction

The use of biodegradable plastic packaging is regarded as an effective way to reduce the amount of plastic pollution in the natural environment. Poly(lactic acid) (PLA) is the world’s most widely used biodegradable plastic [1]. PLA requires industrial composting facilities (>58 ◦ C) to undergo biodegradation and is slow to degrade in the ocean and other natural environments [7,8,9]. Poly(glycolic acid) (PGA) is a biodegradable aliphatic polyester that has biodegradation rates comparable to cellulose. It possesses a higher tensile strength, superior barrier properties, and higher thermal stability than most currently used packaging plastics [11,12]

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