Abstract : Synthetic biodegradable polymers have attracted increasing interest over the last ten years. Polyesters occupy a leading position due to their additional bioassimilable character. : They can be of natural or synthetic origin. At any rate, they can be prepared by ring-opening polymerization (ROP) from lactons1.
The use of these lactones is sometimes restricted because of their weak reactivity. This problem can be avoided by the use of very reactive catalytic systems based on strong metal reactivity which are not always compatible with an application in biology (pharmacology, environment)2. An approach to offset this problem consists in 'chemically 'speeding up these monomers to improve the process of polymerization. L-lacOCA is an analogue of L-lactide which has a function O-Carboxyanhydride (OCA). This monomer is much more reactive than the identical cyclical dilactone: it polymerizes in a controlled way and in a living manner in softer conditions3.
This work begins with a theoretical study of ROP of L-lacOCA and L-lactide catalyzed by 4-diméthylaminopyridine (DMAP) in the presence of alcohol. The mechanism of polymerization revealed consists in a basic activation of the initiator by the DMAP. For this catalyst, it has been shown for the first time an unusual bifunctional mode of action, where a weak energy hydrogen bonding was involved4.
The second part of the manuscript describes the development of ROP of L-lacOCA with an ecofriendly catalytic system: the enzymatic catalysis. Up to now, enzymes accomplished ROP of the lactide hardly. With lipases Novozyme 435 and PS, it was possible to obtain easelier polylactide of high molecular weight from the activated analogue of lactide. In the case of Novozyme 435, the polymerization was controlled and has a living character.
In a last part, we tried to extend the principle of activation of the OCA moiety to other monomers. We studied ROP of β-OCAs, 6-rings O-carboxyanhydrides which could give access to natural polymers as polyhydroxybutyrate. Three monomers of this type, PivOCA, MepOCA and ButOCA were synthetized. The study of their reactivity put forward a problem of selectivity between the two carbonyls of the OCA moiety during the nucleophilic attack. Because of secondary reactions, experiments of ROP have shown that it was difficult to achieve properly the synthesis of these polyesters.
1. Biopolymers, Wiley VCH, 2003, Vol. 3a-3b-4.
2. O. Dechy-Cabaret, B. Martin-Vaca, D. Bourissou, Chem. Rev., 2004 (104) 6147.
3. O. Thillaye du Boullay, E. Marchal, B. Martin-Vaca, F. P. Cossio and D. Bourissou., J. Am. Chem. Soc., 2006 (128) 16442.
4. C. Bonduelle, B. Martin-Vaca, F.P. Cossio, D. Bourissou, Chem. Eur. J., 2008 , 14, 5304.