Reversible addition fragmentation chain transfer (RAFT) and hetero-Diels-Alder chemistry as a convenient conjugation tool for access to complex macromolecular designs

The combination of RAFT chemistry and the hetero-Diels-Alder (HDA) cycloaddition was successfully utilized in the synthesis of poly(styrene) (PS) star polymers with up to 4 arms. This variant of the "coupling onto" method of star polymer synthesis was investigated for two different RAFT end groups (diethoxyphosphoryldithioformate and pyridin-2-yldithioformate) and coupling agents bearing 2, 3, or 4 diene functional groups. When a diethoxyphosphoryldithioformate terminated polymer was reacted with the 2-, 3-, and 4-fold functionalized coupling agents, the yields of 2-arm star, 3-arm star, and 4-arm star polymers were 81%, 77%, and 65%, respectively, and when a pyridin-2-yldithioformate terminated polymer was reacted with the same coupling agents, the yields of 2-arm star, 3-arm star and 4-arm star polymers were 91%, 86% and 82% respectively. The HDA coupling reaction was monitored via UV/vis spectroscopy from the perspective of the RAFT end group as well as by H-1 NMR spectroscopy from the perspective of the diene functionality. The results of these investigations indicated that the phosphoryldiethoxydithioformate terminated polymer achieves 92% conversion within a 24 h time frame and the pyridin-2-yldithioformate terminated polymer achieves 96% conversion in 10 h. The 4-arm star polymers were also subjected to high-temperature environments, and GPC measurements indicated that complete cleavage of all 4 arms from the core was achieved in 24 h at 160 degrees C.