Effect of diisocyanates and chain extenders on the physicochemical properties and morphology of multicomponent segmented polyurethanes based on poly(l-lactide), poly(ethylene glycol) and poly(trimethylene carbonate)

Multicomponent segmented polyurethanes (SPUs) based on poly(ethylene glycol), poly(l-lactide) and poly(trimethylene carbonate) as macrodiols, 2,4-toluene diisocyanate (2,4-TDI) or 1,6-hexane diisocyanate (HDI) as diisocyanate, and 1,4-butanediol (BDO) or 2,2-bis(hydroxymethyl)propionic acid (DMPA) as chain extenders were synthesized. The molecular, thermal, dynamic mechanical and morphological features of this set of uncrosslinked polyurethanes are characterized using H-1 NMR, gel permeation chromatography, differential scanning calorimetry, dynamic mechanical thermal analysis (DMTA) and atomic force microscopy techniques. The lower reaction rate of HDI in comparison with 2,4-TDI allows for better control of the SPU compositions, so that the intrinsic properties of each block can be better combined and modulated. HDI-based SPUs are semi-crystalline, while those based on 2,4-TDI are amorphous, affecting the mechanical properties of these polyurethanes. All SPUs are heterogeneous, presenting morphologies of a disperse phase in a matrix which varies with the macrodiol ratios as well as with the nature of the diisocyanate and chain extender (a finer dispersion of the disperse phase is observed for SPUs of HDI and BDO). DMTA results indicate that the phases are complex mixtures of the different blocks with at least one rich in PLLA. The PEG content is shown to be the most important factor influencing the water sorption capability, while the incorporation of hindering carboxylic acid groups by the use of DMPA allows the water uptake of SPUs to be controlled by the solution pH. All SPUs show a significant loss of molar mass in hydrolytic degradation experiments and, in general, the PLLA-rich SPUs are more susceptible to degradation. (c) 2015 Society of Chemical Industry