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

From the results of this study it can be concluded that higher stearic acid concentration as a part of curing activator and high level of curative (i.e. sulfur and accelerator) causes higher crosslink density, tensile strength, modulus and hardness, and lower NBR to nylon-PET cord adhesion. Accelerator type also affects NBR/nylon-PET cord adhesion and using NOBS the highest coating adhesion is achieved. Using semi-efficient vulcanizing (i.e. accelerator/sulfur ratio around 1) is the most suitable way for achieving high NBR/nylon cord adhesion. And finally, independent from accelerator type, sulfur amount and efficiency of vulcanizing system, coating adhesion is a semi-linear function of crosslink density of nitrile rubber.

Poly[2,2‐bis(methylol)propionic acid] hyperbranched polymers containing cores with higher functionality are less affected by the negative substitution effect, and consequently their structures have a lower proportion of linear units.