Synthesis of block copolymers based on the alternating anionic copolymerization of styrene and 1,3-cyclohexadiene

A series of poly(1,3-cyclohexadiene-alt-styrene)-containing block copolymers that exhibited predictable molecular weights and narrow molecular weight distributions were synthesized with various 1,3-cyclohexadiene contents (13-57 mol %). In situ FTIR spectroscopy in combination with the Mayo-Lewis graphical method was employed to determine the reactivity ratios for the anionic copolymerization of styrene and 1,3-cyclohexadiene. The reactivity ratios for 1,3-cyclohexadiene and styrene were 0.022 and 0.024, respectively, which indicated the formation of an alternating copolymer. The alternating copolymers served as suitable precursors for chemical modification and were either quantitatively aromatized or hydrogenated in a controlled fashion. The thermal stabilities of the modified copolymers were determined, and as expected, the hydrogenated copolymers exhibited improved thermal stability compared to that of poly(1,3-cyclohexadiene-alt-styrene)-containing block copolymers. However, the aromatized copolymers unexpectedly exhibited reduced thermal stability in both nitrogen and oxygen environments due to the introduction of labile benzylic hydrogens in the repeating unit.