Facile photo-flow synthesis of branched poly(butyl acrylate)s
We present the synthesis of branched poly(butyl acrylate)s using photo-induced free radical polymerization of (n/t)-butyl acrylate in the presence of tri(propylene glycol) diacrylate (TPGDA) as a crosslinker and varying amounts of dodecanethiol (DDT) as a chain transfer agent to prevent macroscopic gelation. Thereby, the monomer–thiol ratio strongly influences the molecular weight of the obtained materials from 5000 g mol−1 up to 100 000 g mol−1. Reactions were performed in a scalable photo-flow reactor to allow homogenous irradiation and prevention of local “hot spots”, to increase monomer conversion, and to improve control over reaction conditions (i.e. temperature and viscosity). The reactions were monitored by NMR spectroscopy and size exclusion chromatography (SEC) to determine the conversion and molecular weight, respectively. The robustness of this system is demonstrated by using different photo initiators, thiols and tube diameters. Due to their inherently low viscosity, branched poly(n-butyl acrylate)s could be synthesized in the bulk up to full conversion within 20 min and, hence, under solvent free conditions, which is very untypical of flow radical polymerization.