Synthesis and characterization of interpenetrating polymer networks with hyperbranched polymers through thermal-UV dual curing

The aim of this study was to investigate the possibility of using acrylated hyperbranched polyesters (HBP) as UV curable component in dual curing automotive applications. Dual curing is one of possible ways to obtain fast curing, scratch resistant coatings for use in OEM and car refinish applications. Dual curing systems, upon hardening, can give interpenetrating networks (IPNs). All the IPNs were obtained by UV-thermal dual cure process and they consisted of an UV curable acrylic component and a classic 2-pack urethane component. The acrylic component was acrylated hyperbranched polyester (HBP(A)) and 2-ethyl hexyl acrylate (EHA). The classic 2-pack urethane component consisted of a hydroxyl functional acrylate copolymer (HA) and Desmodur® N3390. The weight ratio of HBP(A) and EHA in the IPNs was varied from 100/0 to 25/75, while the urethane component remained the same in all the IPN samples. The IPNs were characterized by dynamic-mechanical analysis (DMA), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The mechanical properties of the IPNs were also investigated. A single glass transition temperature, Tg, indicated that a homogeneous material with no separation domain was obtained. DMA showed that with increasing HBP(A) in the IPNs, the crosslink density increased, while the flexibility decreased. The data obtained by DMA and DSC showed a decrease of the Tg values with increasing amount of HBP(A). There were slight differences in the thermal stability of the IPNs.