Synthesis of propylene/1-butene copolymers in liquid pool and gas-phase processes: A comparative analysis

Batch liquid pool and semibatch gas-phase polymerizations were performed with high-activity Ziegler–Natta catalysts to evaluate the effect of 1-butene on the crystallinity, the melt temperature and the average molecular weights of the final 1-butene/propylene copolymers and alloys. According to the obtained results, 1-butene can be significantly incorporated into the polymer chain over the whole range of copolymer compositions in both gas and liquid-phases, leading to the decrease of the melting temperature of the copolymer resins. On the other hand, the properties of the polymer alloys seem to be less sensitive to 1-butene incorporation, indicating the development of a distinct 1-butene phase. The average molecular weights, the polydispersities and the reactivity ratios are quite different in the liquid pool and gas-phase processes, indicating that sorption/ diffusion effects may exert an important role during the copolymerization. The obtained reactivity ratios in the gas-phase are close to 1, while the reactivity ratios of propylene are systematically higher than the reactivity ratios of 1-butene in the liquid pool process. Polymer materials with large molecular weights and good particle morphology can be obtained in all analyzed cases, indicating that development of propylene/1-butene copolymer grades is indeed possible in both liquid pool and gas-phase processes.