Homogeneous 1-alkene polymerisation catalysts : understanding metallocenes and exploring alternatives

• Main Author: Rodriguez-Delgado, Antonio
• Published: University of East Anglia 2003
• Subjects: 546; Ligand effects
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.268577

The optimisation of I-alkene polymerisation processes by highly active metallocene systems such as racSBIZrMe2 activated by [Ph3C][CN{B(C6Fs)3h] (I) or by [Ph3C][B(C~s)4] (II) was perfonned. Subsequently. a systematic quantitative study of ligand effects on polymerisation activity, molecular weight and polymer microstructure was carried out. Non-bridged and bridged C2y-symmetry zirconocene dimethyls and dichlorides alkylated (or alkyl exchanged) by AlBu'3 (TIBA) and activated by 1 are much less active than Crsymmetric zirconocenes. Propene polymerisations catalysed by those systems afford low molecular weight atactic polypropene. TIBA rapidly alkylates dichloride zirconocenes affording pre-catalysts which, once activated, give a catalytic profile comparable with that obtained with dimethyl zirconocenes. Activities of Crsymmetry raczirconocenes / AlBui3 / I or [Ph3C][H2N{B(C6Fs)3h] (III) in propene polymerisation decrease according to the order SBMbiZrCh (17) > SBIZrCh (16) > EBIZrCh (13) > MBBIZrCh (18) > EBIDMZrCh (19) > EBTHIZrCb (20) > SBSCZrCh (14) > SBBCZrCh (15). These values are not distorted by side effects such as mass transport limitation, so represent real activities, which are the highest reported to date for most of these catalysts under the experimental conditions fixed. The molecular weight of polypropene obtained in propene polymerisation reactions at 1 bar monomer pressure and 20°C ranges from high to low molecular weight (336000 to 4600 g/mol), decreasing according to the precatalyst, in the following order: SBMbiZrCh (17) > SBIZrCh (16) > MBBIZrCh (18) > EBIZrCh (13) > EBTHIZrCh (20) > SBsczrCh (14) > EBIDMZrCh (19) > SBBCZrCh (15). Experiments carried out at 1 bar of monomer pressure and 60°C afford polymers of medium to low molecular weight and the same trend. The order of isotacticity and regiospecificity of the polypropene obtained is: SBMbiZrCh (17) > SBSCZrCh (14) > SBBCZrCh (15) > MBBIZrCh (18) >EBIZrCh (13) > EBDMIZrCh (19) The trityl salt 1 generates more active catalysts than III for the polymerisations perfonned at 20°C, but the situation is reversed at 60 0c. The molecular weight of the polymers obtained by systems activated by III is slightly higher than those obtained using I under both experimental regimes (20 and 60°C / 1 bar). Reactions of L2ZrMe2 (where 4, L= CsMes; 6, L= CSMe4H) with III in presence of AIMe3, fonn [(~)Zr(JlMe) 2AIMe2][H2N{B(C6Fs)3h] (23, L= CsMes; 24, L= CSMe4H) whereas with I, ~ZrMe(Il-Me)B-(C6F5h and L2ZrMe(Il-NC)B-(C6FS)3 were obtained. The protolysis reaction ofY[N(SiMe3)2h with (2-C~sN=CH)(6-Bu)C6H30H (HL3 ) led to a variety of products. Y[N(SiMe3)2h(L3) (29), alongside Y[N(SiMe3)2](L3)2 (30) and Y(L3h (31) were synthesised. M(CH2SiMe3)2(THF)(Ll) (25, M = Sc; 26, M = Y; and L 1 = 2,3,6-Me3C6H3N=CH(6-Bu')C~30H) are highly effective catalysts for the ring-opening polymerisation of E-caprolactone. 26 and 30 also initiate polymerisation of cyc10hexene oxide (CHO).