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Chapter 1

PLA Synthesis. From the Monomer to the Polymer

Among the bio-based polymers developed so far, PLA polymers and their derivatives stand at the forefront of practical use and are currently manufactured. PLLA obtained from naturally occurring l-lactic acid is generally produced and utilized on an industrial scale. Two synthetic routes to PLLA have been known: one is the ROP of l-lactide and the other is the direct polycondensation of l-lactic acid. In the former method, various polymerization mechanisms have been demonstrated. Among them, bulk polymerization of l-lactide monomer in the presence of tin octoate is favoured to avoid racemization and trans-esterification (chain scrambling). This ROP method is the most convenient for controlling the molecular weight of PLLA and attaining a high molecular weight polymer (Mw>1×106). NatureWorks LLC (USA) and other current manufacturers of PLLA depend on this ROP route for their production. Many other catalysts, based on organic, cationic and metal compounds, are also effective for ROP, although their process control has not yet been fully established. The alternative direct polycondensation of l-lactic acid has been less studied compared to the ROP method. Recently, much effort has been made to establish the direct polycondensation method. A key technology for its success is the melt/solid polycondensation, by which a high molecular weight of PLLA and sb-PLA can be produced at lower cost. Stereo-complexed PLA materials and PLA copolymers consisting of different macromolecular chains can also be synthesized for higher performance and specialties. The molecular weight, terminal groups, copolymer composition and functionalities must be precisely controlled for wider application of these PLA polymers.

Print publication date: 13 Nov 2014
Copyright year: 2015
Print ISBN: 978-1-84973-879-8
PDF eISBN: 978-1-78262-480-6
ePub eISBN: 978-1-78262-340-3
From the book series:
Polymer Chemistry Series