Additive Effect of Triphenylphosphine on the Living Polymerization of 1,3‐Butadiene with a Cobalt Dichloride‐Methylaluminoxane Catalytic System

Abstract

AbstractThe additive effect of triphenylphosphine (Ph3P) was investigated in 1,3‐butadiene polymerization with cobalt dichloride (CoCl2) activated by methylaluminoxane (MAO); the catalytic system resulted in slowly‐initiated living polymerization with a high cis‐1,4 content (about 99%) at 0 °C. The polymerization behavior, such as the relationship of polymer yield and number‐average molecular weight ($\overline M _{\rm n}$) with polymerization time, was dependent on the amount of Ph3P added. In the presence of a small amount of Ph3P (Ph3P/Co = 0.025), the kinetic behavior qualitatively resembled that observed in the absence of Ph3P, which indicated that the catalytic system conducted slowly‐initiated living polymerization. An increase in the amount of Ph3P (Ph3P/Co > 0.025), however, caused chain transfer reaction. The 1H NMR analysis of the produced polymers showed that Ph3P changed the microtacticity from 99% of cis‐1,4 to 88% of 1,2‐unit, depending on the amount of Ph3P added. At the maximum amount of Ph3P (Ph3P/Co = 0.025) necessary for maintaining the livingness of the propagating species, 14% of the 1,2‐inserted unit was incorporated at the expense of the cis‐1,4‐inserted unit. The addition of Ph3P (Ph3P/Co = 0.025) during the polymerization did not affect the livingness and gave a regio‐block copolymer of 1,3‐butadiene.Number‐average molecular weight as a function of polymerization time.magnified imageNumber‐average molecular weight as a function of polymerization time.