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Poly(lactic acid)-based polymers are highly suitable for temporary biomedical applications, such as tissue support or drug delivery systems. Copolymers of different molecular weight based on poly(lactic acid) and poly(ethylene glycol) were prepared by polycondensation, catalysed by hydrochloric acid. A chain-extension reaction with l-lysine ethyl ester diisocyanate was employed afterwards to obtain polyester urethanes with enhanced properties. The GPC results showed that the molecular weights of the products reached about 50,000 g·mol−1 and the hydrolytic progress was rapid in the first 2 weeks; the drop in Mn equalled approximately 70%. Additionally, elemental analysis of the buffer medium proved that hydrolytic degradation was more rapid in the first stage. Tensile-strength testing revealed that ductility increased alongside reduced molecular weight of poly(ethylene glycol), also suggesting that polymer branching occurred due to side reactions of isocyanate. Based on the envisaged biomedical applications for these polymers, cytotoxicity tests were carried out and the cytotoxic effect was only moderate in the case of 100% polymer extract prepared according to ISO standard 10993-12. In their research, the authors focused on preparing metal-free, catalysed synthesis of polyester urethanes, which could prove useful to numerous biomedical applications.

The work presented here investigates the synthesis of poly(lactic acid)-poly(ethylene oxide) diisocyanate chain-linked copolymer, and its application in the nano-encapsulation of bioactive compounds. Study was conducted on the effect of the type of chain-linking agent, along with molecular weight, thermal properties and hydrophilic/hydrophobic behavior, through the methods of gel permeation chromatography, Fourier transform infrared spectroscopy-attenuated total reflectance, differential scanning calorimetry, light scattering, water uptake experimentation, and water contact angle measurements. Nanoparticle formation was performed via a single solvent evaporation process, and the particles obtained were characterized by dynamic light scattering and scanning electron microscopy. Results show the significantly enhanced molecular weight of the final product after the chain-linking reaction (up to 300,000 g/ mol), as well as the non-linear nature of the sample due to broad polydispersity, ranging from 4-13. The final products exhibited glass transition temperatures of between 30 and 44°C, while their crystalline quality was either significantly suppressed or a completely amorphous attribute was observed. Nanoparticles in the range of 300 nm that contained metazachlor were successfully prepared, and their releasing behavior exhibited first order release kinetics. A slower rate of release was observed in samples containing 4,4′-methylenebis(phenyl isocyanate) as a chain-linker.

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