The Mountain View Tribune-Progress

Weekly newspaper from Mountain View, Oklahoma that includes local, state, and national news along with advertising

Ring-Opening Polymerization of L-Lactide Catalyzed by an Organocatalytic System Combining Acidic and Basic Sites

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 center dot HX) were used as a dual catalytic system for L-lactide polymerization initiated by different alcohols. It is shown that the corresponding DMAP/DMAP center dot 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

Controlled bulk polymerization of L-lactide and lactones by dual activation with organo-catalytic systems

The acid-base catalytic system based on N,N-dimethyl-4-aminopyridine (DMAP) and a protic acid that has already been revealed to be efficient for the ring-opening polymerization (ROP) of L-lactide in solution at room temperature was tested for the same polymerization in bulk at 100 degrees C. As observed in solution, the presence of the DMAP center dot HX (X Cl, CH3SO3, CF3 SO3) salt enhanced yields. Linear and star-like polylactides with 3 and 4 branches were prepared. Polylactides were thus easily prepared reaching high molar masses (up to 75 000 g mol(-1) for linear PLLA and 140 000 g mol(-1) for star-like PLLA) with good control in less than 1 h. In all cases, the appearance of transesterification reactions was shown to occur only at very high yield. The ROP of lactones (epsilon-caprolactone and delta-valerolactone) was also investigated with the same catalytic systems in bulk conditions. In contrast to lactide polymerization, only the DMAP/DMAP center dot HOTf allowed lactone polymerization with a slower rate. However, the control over the molar masses remained very good. Block copolymers were also synthesized

Influence of the block copolypeptide surfactant structure on the size of polypeptide nanoparticles obtained by mini emulsion polymerisation

Polypetide nanoparticles obtained by miniemulsion polymerisation of amino acid N-carboxyanhydrides (NCA) are a novel class of tuneable bio-derived functional nano materials for potential applications in nutraceutics, agriculture, and medicine. This work discloses a facile route to stable hydrophobic polypeptide nanoparticles comprising a poly(l-phenylalanine) and poly(l-leucine) core, respectively, using two amphiphilic glycosylated block copolypeptide surfactants with hydrophobic poly(l-phenylalanine) or poly(l-leucine) blocks. All surfactant/core combinations produce stable nanoparticle dispersions with average particle sizes between 160 and 220 nm. However, analyses using light scattering techniques, SEM imaging and Asymmetric Field Flow Fractionation, reveal a particle size dependence on the surfactant/core combination in that particles are reproducibly 20-30% larger if the surfactant block is identical to the amino acid polymerised in the core. It is hypothesised that this is caused by complex hydrophobic and secondary structure interactions between the surfactant and particle core. These fundamental insights will inform the future design of polypeptide nanoparticle libraries utilizing many different amino acids for example in nanomedicine