Copolymerization Of Diphenylphosphostyrene And Isoprene By Half-sandwich Scandium Complexes

The triphenylphosphine group possesses many useful potentials,such as tunable oxidation states,high alkylation efficiency,electron donating property,thermal and base stability,high ionic conductivity,and ionic aggregation.The synthesis of polymers containing triphenylphosphine groups can developing polymer materials with gene delivery,biomedical applications,3D printing,ionic liquids,catalysis,etc.In this thesis,the copolymerization of diphenylphosphine styrene（St PPh₂）and isoprene（IP）by half-sandwich scandium complexs has been carried out.The effect of and the position of diphenylphosphino group and catalyst steric hindrance on copolymerization activity and copolymers structure was found.A new series of phosphine-functionalized isoprene-styrene copolymers with different compositions and sequence structures has been prepared.1.The position of diphenylphosphino group and catalyst steric hindrance directly affected the polymerization of St PPh₂.The scandium complex bearing relatively small cyclopentadienyl ligand（C₅H₅）Sc（CH₂C₆H₄NMe₂-o）₂（1）did not show activity for the homopolymerization of p-St PPh₂and m-St PPh₂,however,showed high activity for the homopolymerization of o-St PPh₂.The analogous scandium complex with larger cyclopentadienyl ligand（C₅Me₄Si Me₃）Sc（CH₂C₆H₄NMe₂-o）₂（2）with large steric hindrance showed high activity for the homopolymerization of p-St PPh₂,however,did not show activity for the homopolymerization of o-St PPh₂and m-St PPh₂.The coordination insertion of St PPh₂was determined by the position of diphenylphosphino group and catalyst steric hindrance.The reasonable combination of the two can avoid catalyst deactivation and realize the polymerization of St PPh₂.2.The copolymerization of o-St PPh₂with IP by scandium complex 1 afforded o-St PPh₂-IP copolymers with controllable composition in nearly 100%yield.The analysis of kinetics of copolymerization and structures of o-St PPh₂-IP copolymers showed that o-St PPh₂was randomly copolymerized with IP at the initial stage of copolymerization,after all the o-St PPh₂was consumed,and the remaining IP was also polymerized.The obtained o-St PPh₂-IP copolymers contained o-St PPh₂-IP random sequences and long cis-1,4-poly IP block（the selectivity of cis-1,4-IP was 94%）.The o-St PPh₂-IP copolymers with different compositions possessed two glass transition temperatures（T_g）.The T_goriginating from o-St PPh₂-IP random sequences increased from 98 ^oC to 182 ^oC with the increase of o-St PPh₂content in the copolymers,the T_goriginating from cis-1,4-poly IP block maintained about-60^oC.The copolymerization of p-St PPh₂or m-St PPh₂with IP by scandium complex 1 did not give any polymer.3.The copolymerization of p-St PPh₂with IP by scandium complex 2 afforded p-St PPh₂-IP copolymers with controllable composition in nearly 100%yield.The analysis of kinetics of copolymerization and structures of p-St PPh₂-IP copolymers showed that the incorporation of p-St PPh₂into the polymer chains started after IP was almost completely consumed,yielding the p-St PPh₂-IP diblock copolymers containing a syndiotactic-rich poly（p-St PPh₂）block and a poly（IP）block containing 1,4-and 3,4-structures.The p-St PPh₂-IP copolymers with different compositions possessed two T_gs（5℃–12℃ and95℃–101℃）originating from the poly（IP）and poly（p-St PPh₂）block.4.Although scandium complex 2 showed very low activity for the homopolymerization of o-St PPh₂,the copolymerization of o-St PPh₂with IP occurred smoothly,affording the o-St PPh₂-IP copolymers with o-St PPh₂content of 11-51 mol%in nearly 100%yield.The analysis of kinetics of copolymerization and structures of p-St PPh₂-IP copolymers showed that the o-St PPh₂-IP alternating copolymer was exclusively formed in the coexistence of the two monomers,because the successive insertion of o-St PPh₂was difficult due to steric hindrance caused by the phosphine/styrene chelation to the catalyst metal center.When an excess amount of IP was used in the copolymerization of o-St PPh₂and IP,the formation of a poly（IP）block was achieved after o-St PPh₂was consumed for the alternating copolymerization,thus affording block copolymers containing an o-St PPh₂-IP alternating block and a poly（IP）block.Moreover,the incorporation of IP in the alternating copolymerization with o-St PPh₂took place in a regio-,stereospecific cis-1,4-fashion（95%）,suggesting that the coordination（chelation）of o-St PPh₂to the catalyst could influence the regio-and stereoselectivity of IP polymerization.The o-St PPh₂-IP alternating copolymer possessed a T_gof 96℃;The poly IP block possessed a T_g of about 2℃.