Flow-accelerated polycondensation reaction to prepare rigid rodlike poly(p-phenylene-cis-benzobisoxazole)

Under the conditions specified in this work, the polycondensation reaction to prepare rigid rodlike poly(p-phenylene-cis-benzobisoxazole) (PBO) is diffusion-controlled. This work aims to study the flow-driven polycondensation reaction of PBO. The effect of mixing efficiency through changing the stirring speed on the polycondensation reaction of PBO was first investigated in a paddle impeller reactor (PIR). In the initial stage of polymerization, the increase of stirring speed is obviously conducive to accelerating the polycondensation reaction. However, the promoting effect of stirring speed on the polycondensation reaction is greatly reduced in the middle and late stages of polymerization. The effect of the flow pattern with different proportions of shear flow, elongational flow and rotational flow on the polycondensation reaction of PBO was further investigated by comparing three reactors including Couette-Taylor reactor (CTR) with a complete shear flow, PIR with strong shear and elongational flows, and double helical ribbon reactor (DHR) with strong shear and rotational flows. Result shows that the improvement of proportions of rotational flow and elongational flow is beneficial to accelerate the polycondensation reaction of PBO in the middle and late stages of polymerization, especially for the rotational flow.