Polycondensation of Hydroxyacids and Esters

Many lipases, such as porcine pancreatic lipase (PPL), Candida cylindracea lipase (CCL), Chromobacterium viscosum lipase (CVL), Candida antarctica lipase (CAL), Candida antarctica lipase B (CALB, Novozyme-435), polyethylene glycol (PEG)-modified Pseudomonas fluorescens lipase (PEL), Pseudomonas cepacia lipase (PsCL), 

Candida rugosa lipase (CRL), Aspergillus niger lipase (ANL), Pseudomonas sp. lipase (PSL) and Mucor miehei lipase (MML), have been used for the construction of polyesters from the hydroxyacids and their esters (Table 12.1) in accordance with the following scheme [7]  

Ricinoleic acid was polymerised via dehydration with an immobilised poly(e-caprolactone) (PCL) catalyst to give a polymer with MW up to 8,500 Da [14]. Immobilised CALB was efficient as a catalyst for the dehydration polycondensation of cis-9,10 epoxy-18-hydroxyoctadecanoic acid (from the outer birch bark) in toluene, in the presence of molecular sieves at 75 C, to give a polyester with the highest MW of 2.0 X lO Da after 68 h [15]. 

As reported by Kanca and co-workers, the enantioselective transesterification polycondensation of racemic AB-type monomers containing a secondary hydroxy group and a methyl ester moiety led to chiral polyesters by iterative tandem catalysis. The concurrent actions of an enantioselective acylation catalyst (such as CALB) and a racemisation catalyst (Ru(Shvo)) resulted in the high conversion of the racemic monomers to enantioenriched polymers. AB-type monomers used were typically methyl 6-hydroxyheptanoate, methyl 8-hydroxynonanoate and methyl 13-hydroxytetradecanoate. The polycondensation at 70 C in toluene gave a polyester of high yield with a M of around several thousand and an enantiomeric excess higher than 74% [18]. 

---