Kinetic resolution polymerization

Following route A (Fig. 1), Yan Xiao et al. reported the chemoenzymatic synthesis of poly(8-caprolactone) (PCL) and chiral poly(4-methyl-8-caprolactone) (PMCL) microparticles [5]. The telechelic polymer diol precursors were obtained by enzymatic polymerization of the corresponding monomers in the presence of hexanediol. Enzymatic kinetic resolution polymerization directly yielded the (R)-and (S )-enriched chiral polymers. After acrylation using acryloylchloride, the chiral and nonchiral particles were obtained by crosslinking in an oil-in-water emulsion photopolymerization. Preliminary degradation experiments showed that the stereoselectivity of CALB is retained in the degradation of the chiral microparticles (Fig. 2). 

Dynamic Kinetic Resolution Polymerization of AA-BB Monomers and AB Monomers... 

Recently, Spassky has demonstrated that the chiral Schiff base complex 4 is highly selective for the kinetic resolution polymerization of rac-lactide [34]. At 50% conversion, the residual monomer is approximately 80% ee (Rr s=20) (Scheme 3). In addition, the polylactides exhibit narrow molecular weight distributions, consistent with the absence of significant transesterification. 

Chiral polyesters by dynamic kinetic resolution polymerization. Angew. Chem. Int. Ed., 45 (13), 2130-2132. 

A more elegant approach towards lipase-catalyzed synthesis of chiral polymers is to take advantage of the intrinsic ability of lipases to discriminate between ena-tiomers. Chiral polymers can be formed when one of the two enantiomers of a chiral monomer preferentially reacts during the polymerization reaction. This is referred to as a kinetic resolution polymerization (KRP) and allows the optically active polymer to be directly procured from a racemic mixture, albeit in a maximum of 50% yield. 

A straightforward extension of DKR to polymer chemistry is the use of diols and diesters (AA-BB monomers) or ester-alcohols (AB monomers) as substrates (Scheme 11.13, routes a and b). Such reactions have been referred to as dynamic kinetic resolution polymerizations (DKRP) and inevitably lead to the formation of oligomers/polymers because of the bifunctional nature of the reagents. The extension of DKR to polymer chemistry is not trivial since side reactions that are relatively unimportant in DKR (dehydrogenation, hydrolysis) have a major impact on the rate of polymerization and attainable chain lengths since the stoichiometry of the reactants is an important issue. As a result, the reaction conditions and catalyst combinations used in a typical DKR process will not a priori lead to chiral... 

S) -isopropylmorpholine-2,5 -dione immobilized porcine pancreas lipase iterative tandem catalysis indium tin oxide kinetic resolution polymerization large... 

Fig. 16 Dynamic kinetic resolution polymerization of a 1,4 diol and dimethyl adipate, and structures of Noyori (i) and Shvo (2) type racemization catalyst [140]...

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