The effect of process control on the microstructure of styrene/butadiene copolymers in reaction extrustion

By means of a closely intermeshing twin-screw extruder as the reactor the mixture of styrene (S) and butadiene (B) as the monomer and THF as the polar catalyst, a copolymer (S/B) was synthesized by bulk polymerization with the organic lithium initiator. The PB chain of copolymers was cleaved by reaction with hydrogen peroxide in the presence of osmium tetraoxide, then the small molecules were removed out of the system by purification. The copolymers and the segments after oxidization were characterized by GPC cooperating with a multi-angle laser light scattering instrument (MALLS). It was found that the molecular weight distributions of the S/B copolymers were broadened, on the other hand, the molecular weights of the segments after oxidization decreased by addition of THF. The content of 1, 2-PB was derived from H-1-NMR. It was confirmed that the content of I, 2-PB increased obviously as THF was stepped up, but to a great extent the trend of increasing was slow down. Cooperated with the survey of TEM photographs, it was confirmed that the phase of polybutadiene was minished by THF, and its distribution was more uniform. So it could be concluded that the basic mechanism of anionic polymerization during reactive extrusion was consistent with that in anionic solution polymerization, the difference only resulted from process factors during the reactive extrusion.