Synthesis of thermally cleavable multisegmented polystyrene by an atom transfer nitroxide radical polymerization (ATNRP) mechanism

Abstract

Based on the common features of well-defined nitroxide radical coupling (NRC) reaction, atom transfer radical polymerization (ATRP) and nitroxide mediated radical polymerization (NMRP) mechanisms, an atom transfer nitroxide radical polymerization (ATNRP) mechanism was presented by integrating these three mechanisms into one polymerization system simultaneously, and further used to construct multisegmented polystyrene (PS_m) embedded with multiple alkoxyamine linkages. The initiator 1-oxyl-2,2,6,6-tetramethylpiperidinyl-4-yl 2-bromo-2-methylpropanoate (Br-TEMPO) containing one bromoisobutyryl group and one stable nitroxide radical was firstly designed and synthesized. Then, the ATNRP mechanism was systematically investigated by optimizing factors such as polymerization temperature, solvent, catalyst, time and operation technology. The results showed that the NRC reaction, ATRP and NMRP mechanisms can synergistically proceed in ATNRP due to the thermally reversible dissociation–combination behavior of the formed alkoxyamine linkages, and the polymerization temperature and solvent were the key factors. Finally, the thermal behaviour of the formed PS_m was monitored by TGA and DSC analyses. The result showed that the alkoxyamine linkages can undergo a thermal cleavage at an elevated temperature of 110 °C and the PS_m can be cleaved in the presence of excess stable nitroxide radicals. The PS_m embedded with multiple alkoxyamine linkages and the cleaved PS possessing one nitroxide radical have the same thermal stability, however the T_g of PS_m gradually approached that of the cleaved PS when several heating–cooling (40–150 °C) cycles were performed. Due to the versatile functions of the as-prepared PS_m and cleaved PS, this ATNRP mechanism will hopefully find more potential applications in polymer chemistry.