Polylactide copolymers polymerization

Alternatively, block polymers may be prepared by the sequential polymerization of two monomers using a bifunctional initiator, as exemplified by the preparation of diblock peptide-polylactide copolymers. tert-Butoxycarbonylaminopropanol is first engaged in the zinc-promoted ROP of lactide and, after deprotection of the terminal amine chain-end, the polyamide block is obtained by ROP of the N-carboxyanhydride (NCA) derived from y-benzyl glutamate (Scheme 10.15) [63], Such diblock peptide-polylactide copolymers also have interesting self-assembling properties [63]. 

Arimura H, Ohya Y, Ouchi T (2005) Formation of core-shell type biodegradable polymeric micelles from amphiphilic poly(aspartic acid)-Wock-polylactide diblock copolymer. Biomacromolecules 6 720-725... 

One of the potential applications of these ABC triblock copolymers was explored by Hillmyer and coworkers in 2005 [118]. They have prepared nanoporous membranes of polystyrene with controlled pore wall functionality from the selective degradation of ordered ABC triblock copolymers. By using a combination of controlled ring-opening and free-radical polymerizations, a triblock copolymer polylactide-/j-poly(A,/V-dimethylacrylamide)-ib-polystyrene (PLA-h-PDMA-h-PS) has been prepared. Following the self-assembly in bulk, cylinders of PLA are dispersed into a matrix of PS and the central PDMA block localized at the PS-PLA interface. After a selective etching of the PLA cylinders, a nanoporous PS monolith is formed with pore walls coated with hydrophilic PDMA. 

Over the past several decades, polylactide - i.e. poly(lactic acid) (PLA) - and its copolymers have attracted significant attention in environmental, biomedical, and pharmaceutical applications as well as alternatives to petro-based polymers [1-18], Plant-derived carbohydrates such as glucose, which is derived from corn, are most frequently used as raw materials of PLA. Among their applications as alternatives to petro-based polymers, packaging applications are the primary ones. Poly(lactic acid)s can be synthesized either by direct polycondensation of lactic acid (lUPAC name 2-hydroxypropanoic acid) or by ring-opening polymerization (ROP) of lactide (LA) (lUPAC name 3,6-dimethyl-l,4-dioxane-2,5-dione). Lactic acid is optically active and has two enantiomeric forms, that is, L- and D- (S- and R-). Lactide is a cyclic dimer of lactic acid that has three possible stereoisomers (i) L-lactide (LLA), which is composed of two L-lactic acids, (ii) D-lactide (DLA), which is composed of two D-lactic acids, and (iii) meso-lactide (MLA), which is composed of an L-lactic acid and a D-lactic acid. Due to the two enantiomeric forms of lactic acids, their homopolymers are stereoisomeric and their crystallizability, physical properties, and processability depend on their tacticity, optical purity, and molecular weight the latter two are dominant factors. 

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