A comparative study of new linear and hyperbranched polyurethanes built up from a synthesized isocyanate-terminated polyester/urethane

Abstract

In the present study, the effects of architecture and structural building blocks of the polyurethane chains on their properties were studied. New linear and hyperbranched polyurethanes (LPU and HPU) were prepared via A2 + B2 and A2 + B3 methodologies, respectively. Polyethylene glycol (PEG-1000) and castor oil (CO) were used as bi- and trifunctional monomers (B2 and B3), respectively. However, A2 monomers were synthesized by the reaction between ethylene glycol (EG) with terephthaloyl chloride (TPC) and reacting the product with excess toluene diisocyanate (TDI) to produce isocyanate-terminated PU (NCO-PU). NCO-PU was reacted with PEG to synthesize LPU; however, its reaction with CO synthesized HPU. NCO-PU, LPU and HPU were characterized by FTIR, H-NMR, GPC, TEM, TGA, DSC and XRD. The prepared PUs were applied as coatings and their physical, chemical and mechanical properties were investigated. The results showed that the degree of branching of HPU was 79%. No phase separation was observed in NCO-PU as indicated by its DSC curve. However, two phases are detected in HPU and LPU that represent to the hard and soft segments. NCO-PU displayed the highest crystallinity index (CrI = 89.26%). However, the high degree of branching in HPU led to lower CrI than LPU. The lack of entanglements in HPU led to its slightly lower solution viscosity than LPU. TEM images showed spherical PU nano-particles. The surface of HPU coating showed the highest gloss which is due to its low degree of crystallinity. HPU and LPU exhibited excellent chemical resistivity.