Chain transfer reactions of propylene polymerization catalyzed by AlEt3 activated TiCl4/MgCl2 catalyst under very low monomer addition rate

Chain transfer reactions of TiCl4/MgCl2–AlEt3 catalyzed propylene polymerization were investigated under conditions of severely starved monomer supply and suppressed chain transfer to cocatalyst. Slurry polymerization was conducted by injecting gaseous monomer at very low rate to the reactor containing preactivated catalyst. The preactivated solid catalyst has been washed by solvent to remove AlEt3 in the liquid phase, and chain transfer to AlEt3 was nearly completely suppressed. Besides 1-propen-2-yl (vinylidene) end group formed by β-H transfer after primary (1,2-)insertion, 1-propen-3-yl (allyl) end group formed by β-Me transfer after 1,2-insertion and 2-buten-4-yl formed by β-H transfer after secondary (2,1-)insertion were also detected in the polymer by 1H NMR analysis. The monomer dependences of the chain transfer reactions were studied. Because of the unimolecular nature of β-H transfer after a secondary insertion, the content of 2-buten-4-yl end group, which is too low to be detected in PP polymerized under conventional conditions, was markedly increased in the product of monomer-starved polymerization.

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► Propylene was polymerized by TiCl4/MgCl2–AlEt3 at extremely low monomer pressure.
► Chain transfer to AlEt3 was suppressed by removing AlEt3 in the liquid phase.
► 2-Buten-4-yl end group formed by β-H transfer after 2,1-insertion was detected.
► Allyl end group formed by β-Me transfer also increased with decreasing [Pr].