Poly synthesis using pure monomer

Synthetic polymers applied in everyday life rarely possess well-defined stereochemistries of their backbones. This sharply contrasts with the polymers made by Nature where perfect control is the norm. An exception is poly-L-lactide this polyester is frequently used in a variety of biomedical applications. By simply playing with the stereochemistry of the backbone, properties ranging from a semi-ciystalline, high melting polymer (poly-L-lactide) to an amorphous high Tg polymer (poly-mes o-lactide) can be achieved. The synthetic synthesis of such chiral polymers typically starts from optically pure monomers obtained form the chiral pool. The fermentation product L-lactic acid, for example, is the starting material for the synthesis of poly(L-lactide). 

Block Copolymers. Several methods have already been used for the synthesis of block copolymers. The most conventional method, that is, the addition of a second monomer to a living polymer, does not produce the same spectacular results as in anionic polymerization. Chain transfer to polymer limits the utility of this method. A recent example was afforded by Penczek et al. (136). The addition of the 1,3-dioxolane to the living bifunctional poly(l,3-dioxepane) leads to the formation of a block copolymer, but before the second monomer polymerizes completely, the transacetalization process (transfer to polymer) leads to the conversion of the internal homoblock to a more or less (depending on time) statistical copolymer. Thus, competition of homopropagation and transacetalization is not in favor of formation of the block copolymers with pure homoblocks, at least when the second block, being built on the already existing homoblock, is formed more slowly than the parent homoblock that is reshuffled by transacetalization. 

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