Segmented polyurethanes based on poly(l-lactide), poly(ethylene glycol) and poly(trimethylene carbonate): Physico-chemical properties and morphology

Abstract

Binary and ternary segmented polyurethanes (SPU) based on low molar mass (2kDa) homopolymers – poly(ethylene glycol), poly(l-lactide) and poly(trimethylene carbonate) (PEG, PLLA and PTMC, respectively) – and 2,4-toluene diisocyanate were synthesized using 1,4-butanediol and dibutyltin dilaureate as the chain extender and catalyst, respectively. Rigorous control of the OH/NCO stoichiometry and temperature allowed the synthesis of sixteen uncrosslinked polyurethanes with modulated compositions and properties. The molecular characterizations of the SPUs were performed using 1H NMR and GPC, and the thermal, dynamic mechanical and morphological features were investigated using DSC, DMTA and AFM, respectively. The blocks were randomly distributed in the polymer chains, which resulted in suppression of the crystallization of the blocks in most of the SPUs. The binary and ternary SPUs are heterogeneous, presenting morphologies of dispersed phase in a matrix, whose compositions depend on the global composition. The hydrophilicity of the SPUs were evaluated using water swelling experiments, and the hydrophilic/hydrophobic balance of the SPUs can be controlled by altering the composition to achieve a completely water soluble SPU (in PEG-rich SPUs), a higher water uptake capability, resulting in a hydrogel (intermediate composition), or a non-swellable polymer (PLLA-PTMC binary SPUs). The dependence of water uptake on temperature was observed mainly in PEG-rich SPUs. The intrinsic properties of each block, such as the hydrophilicity of PEG, stiffness of PLLA and elasticity of PTMC, are combined and modulated in the SPUs. PTMC confers unique properties to ternary SPUs owing to its partial miscibility with both PEG and PLLA.