Polyesters from p-Lactones

For all of these reasons, the chemistry of lactones polymerization is considered not only very complex but also delicate. Moreover, as has been reviewed by others. 

Handbook of Ring-Opening Polymerization. Edited by P. Dubois, O. Couiembier, and J.-M. Raquez Copyright 2009 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 978-3-527-31953-4 

In this chapter we review the basic principles of polyester synthesis produced from 2-oxetanone-type monomers (named P-lactones), including details of pertinent mechanistic aspects and the general properties of the resultant polymeric materials. Before discussing the ROP of P-lactones, however, we provide a brief overview of the synthesis of P-lactone key derivatives. 

The direct conversion of ketones and aldehydes to P-lactones in a single step has been successfully realized. For example, as ketenes have been shown to 

In the following sections, the polymerization of P-lactones will be discussed with regards to the nature of the active species, whether anionic, cationic, coordination-type or carbene-based. Finally, a brief overview will be provided of the enzymatic ROP of four-membered lactones. 

---

Part 2 includes chapters on specific classes of cyclic monomers and their polymerization mechanisms and kinetics, their main (co)polymer architectures and related products, as well as current and future applications. Hence, siloxane-con-taining and sulfur-nitrogen-phosphorus-containing polymers are described in Chapters 3 and 4, respectively, while the polymerization of cyclic depsipeptides, ureas and urethanes, of polyethers and polyoxazolines, and of polyamides are detailed in Chapters 5, 6 and 7, respectively. Chapters 9, 10, 11 and 12 include details of polyesters prepared from either P-lactones, from dilactones, from larger lactones and from polycarbonates, while the polymerization of cycloalkanes is described in Chapter 13. It should be noted that, slightly out of place . Chapter 8 covers the subject of ring-opening metathesis polymerizahon. 

An enantioselective polymerization of four-mem-bered lactones was demonstrated. Racemic a-methyl-/3-propiolactone was stereoselectively polymerized by Pseudomonas cepacia lipase (lipase PC) to give an optically active (S)-enriched polyester with enantiomeric excess (ee) of 50%.154 From racemic /3-BL, (P)-enriched PHB with 20—37% ee was formed by using thermophilic lipase as catalyst.155... 

Optically active lactones are valuable building blocks in organic synthesis (4) and in the preparation of optically active biodegradable polymers (7,5). Several chemical methods for producing these compounds and their corresponding polymers have been explored (6) but unfortunately all of these methods are either experimentally cumbersome or afford the lactones with only modest enantioselectivities. Examples of chemically prepared optically active polyesters include poly(a-phenyl-P-propiolactone) (7), poly(a-ethy(-a-phenyl-P -propiolactone) (S, 9), poly(a-methyl-a-ethyl-P-propiolactone) (70) and poly(lactic acid) (77, 72). Use of enantioselective polymerization catalysts to carry out stereoelective polymerizations of racemic lactones has produced mixed results. For example, stereoelective polymerization of [/ ,S]- P-methyl-P-propiolactone with a catalyst from Zn ( 2115)2 and [7 ]-(-)-3,3-dimethyl-l,2-butanediol showed only a small enantiomeric enrichment in the final polymer (75). Stereoselective copolymerizations of racemic (LL/DD monomers) and meso (LD monomer) lactides using chiral catalyst that gives heterotactic and syndiotactic PLA, respectively have also been studied (77). 

Finally chloropivalic acid obtained by K. E. Moller from methallyl chloride is of interest as intermediate in the a,a-dimethyl-p-propiolactone synthesis. This lactone shows promise as a monomer for polyester fibers. Studies for polymerization of a,a-dimethyl-p-propiolactone are under way at several companies (Shell, Eastman, Kodak, ICI, Montecatini [424, 432, 510, 794, 795]). 

The lipase-catalysed ROP of the four-membered P-BL was first reported by Nobes and co-workers [74], Poly(3-hydroxybutyrate), with a weight average MW ranging from 256 to 1,045 Da were prepared after several weeks of polymerisation using approximately equal weights of P-BL and lipase. An enantioselective polymerisation of four-membered lactones was demonstrated. Racemic MPL was stereoselectively polymerised by PsCL to generate an optically active (S)-enriched polyester with... 

Jedlinski, Z. (1996) Polyesters (synthesis from lactones), in Polymeric Materials Encyclopedia, Vol. 8 (ed. ).C. Salomon), CRC Press, Boca Raton, FL, p. 5897. 

---