STYRENE/STYRENE-DERIVATIVE COPOLYMERIZATION BY PH2Zn-METALLOCENE-MAO SYSTEMS: HOMO- AND COPOLYMERIZATION OF á-METHYLSTYRENE WITH STYRENE

The copolymerization of styrene with α-methylstyrene has been tested using combined metallocene-MAO initiator systems with and without diphenylzinc.The metallocenes used were biscyclopentadienyltitanium dichloride, Cp 2 TiCl 2 , bis(n-butylcyclopentadienyl)titanium dichloride, (n-BuCp) 2 TiCl 2 , and the halfsandwich metallocene indenyltitanium trichloride, IndTiCl 3 .The results indicate that both binary metallocene-MAO, and ternary Ph 2 Zn-metallocene-MAO systems are capable of polymerizing α-methylstyrene to poly(α-methylstyrene) as well of its copolymerization with styrene.These initiator systems also show that despite the I+ inductive effect of the methyl group, which enhances electron density at the vinyl double bond of styrene, the steric consequence of vinyl substitution hinders monomer coordination to active species, causing a decrease in conversion of either α-MeS to homopolymer or S/α-MeS to the corresponding copolymer.The nature and structure of the metallocene included in the initiator system are determinant of the initiator system's efficiency.For the metallocenes used the efficiency follows the order IndTiCl 3 > Cp 2 TiCl 2 > (n-BuCp) 2 TiCl 2 , with the half-sandwich metallocene IndTiCl 3 showing greater efficiency than the true metallocenes.