In this study, organocatalytic systems containing both basic and acidic sites, which can activate simultaneously the chain end and the monomer, were investigated in the ring-opening polymerization of L-lactide. To this end, equivalent amounts of (N,N-dimethylamino)pyridine (DMAP) and of its protonated form (DMAP 3 HX) were used as a dual catalytic system for L-lactide polymerization initiated by different alcohols. It is shown that the corresponding DMAP/DMAP 3 HX systems are significantly more active than DMAP alone, and yield well-controlled poly(L-lactide). Depending on the reaction conditions, the transesterification reaction can be prevented.
Polypeptide nanoparticles were obtained by the miniemulsion polymerization of S-(o-nitrobenzyl)-L-cysteine (NBC) N-carboxyanhydride (NCA). Through process optimization, reaction conditions were identified that allowed the polymerization of the water sensitive NCA to yield nanoparticles of about 220 nm size. Subsequent UV-irradiation of the nanoparticle emulsions caused the in situ removal of the nitrobenzyl group and particle cross-linking through disulfide bond formation accompanied by the shrinkage of the particles.
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