Relationship between structure and aromatic solvent permeability of crosslinked polyurethanes based on hyperbranched polyesters

Abstract

This work investigates the relationship between structure and aromatic solvent permeability of polyurethanes based on trimethylolpropane (TMP) as a classical crosslinker and self-made hyperbranched polyesters (HBPEs) as newly developed crosslinking agents. For this purpose three groups of samples were synthesized using toluene diisocyanate, poly(tetramethylene glycol) and different pseudo-generation numbers of crosslinkers in the variable hard segment content. The results obtained from characterization tests indicate that replacing TMP by HBPE leads to an increase of crosslink density resulting in significant reduction of sorption capacity and conversely leads to an increase of the diffusion coefficient due to the lower glass transition temperature (Tg) of soft segments. In this way, the toluene permeability of hyperbranched polyurethane (HBPU) is considerably lower than that of classical polyurethane. The HBPUs with sufficient amount of hard segment have the lowest solvent uptake and diffusion coefficient leading to optimal barrier performance. By increasing the generation number of HBPE, the crosslink density of HBPU increases, but the crystallinity as well as Tg of soft segments decrease. These two contradictory changing trends of the structural characteristics cause a slight decrease in sorption coefficient of membranes and an increase of diffusivity. Therefore the barrier performance of HBPUs is weakened with increasing generation number of crosslinkers. © 2015 Society of Chemical Industry