Cristina Maria Santos Gaudêncio Baptista

L-lactic acid was the starting material for obtaining bioahesives. Reaction with 1,4-butanediol provided a telechelic lactic acid prepolymer with hydroxyl end groups further functionalized with 2-isocyanatoethyl methacrylate. Films were produced upon UV irradiation, 2 min, after addition of Irgacure 2959. This was a solvent and catalyst free process. Thermal characterization of films confirmed stability at physiological temperature, enabling photocuring. Adhesion properties were assessed with good results. In vitro degradation tests showed moderate hydrolytic instability dependent on thickness. SEM images revealed a uniform and compact structure. Thrombosis tests confirmed the materials’ thrombogenicity while biocompatibility experiments showed fibroblast viability and antimicrobial behavior. GRAPHICAL ABSTRACT

A study on lactic acid polycondensation under melt conditions was carried out and a preliminary assessment revealed tin powder as a very good catalyst for poly(lactic acid) (PLA) synthesis by melt polycondensation while confirming previous information on SnCl₂ good performance. However, these catalysts also promoted side reactions leading to racemization and yellowing of the final polymer. The use of p‐toluenesulphonic acid (p‐TSA) or triphenylphosphine (PPh₃) as co‐catalysts proved to be very effective hindering colour formation and allowing synthesizing PLA samples with enhanced properties. The addition of these compounds to neat tin powder increased the PLA optical purity, whereas their addition to SnCl₂ speeded up the polymerization. A significant increase in molecular weight, from 32,500 to 52,000 g mol⁻¹, was recorded, with the new catalytic system SnCl₂/PPh₃ showing catalytic activity comparable with the one reported in the literature for SnCl₂/p‐TSA. Several characterization techniques were used for assessing polymer samples: the molecular weights were determined by SEC, thermal behavior measured by DSC, and racemization extent calculated from specific rotation measurements. UV/vis spectroscopy was confirmed as a powerful technique for evaluating yellowing of final polymers. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013