Polymerization of 4‐Methyl‐1,3‐pentadiene with Catalysts Based on Cyclopentadienyl Titanium Chlorides: Effect of anti/syn Isomerism of the Allylic Group on the Chemoselectivity and the Role of Backbiting Coordination in 1,3‐Diene Polymerization

Abstract

Summary: Homopolymerization of 4‐methyl‐1,3‐pentadiene (MP) and copolymerization of 4‐methyl‐1,3‐pentadiene with alkenes (ethylene, 1‐pentene, 4‐methyl‐1‐pentene) were performed to investigate the effect of the so‐called backbiting coordination on the chemoselectivity of 1,3‐diene polymerization. Three homogeneous catalyst systems were used: CpTiCl3‐MAO, Cp2TiCl2‐MAO and Cp2TiCl‐MAO. Backbiting coordination is possible with the first catalyst, but not with the other two. The three catalysts gave similar results, which indicates that backbiting has no effect on the polymerization chemoselectivity, contrary to what has been reported in recent literature. An interpretation is presented for the formation of 1,4 units in MP/alkene copolymers. This interpretation is based on the fact that allyl groups have predominantly a syn configuration in MP homopolymerization, whereas allyl groups of anti configuration are formed in MP/alkene copolymerization. The role of backbiting in diene polymerization is discussed.The effect of anti/syn isomerism on the chemoselectivity in the different polymerizations.imageThe effect of anti/syn isomerism on the chemoselectivity in the different polymerizations.

Copolymerization of Ethylene with 4-Methyl-1,3-pentadiene Promoted by Titanium Complexes Containing a Tetradentate [OSSO]-Type Bis(phenolato) Ligand

“…A deeper insight into the microstructural features of the copolymers was achieved by using 13 C NMR spectroscopy. In contrast to the copolymer obtained in presence of monocyclopentadienyl titanium complexes, 4-MPD is exclusively inserted in 1,2 fashion (or 2,1) and no 1,4 units are detectable by the analysis of the olefinic region. In addition, one can observe from the spectra of the copolymer at different composition and that of isotactic poly(4-MPD) that the signals relative to the olefinic carbon atom bearing the two methyl groups in the side chain and the olefinic methine carbon at 129.0 and 132.1 ppm, respectively, in the homopolymer (DDD sequences in Scheme ) shift in the alternate sequences with ethylene respectively at 130.0 and 131.1 ppm (EDE sequences)(see Figure ).…”

“…In particular, the polymerization of 4-methyl-1,3-pentadiene (4-MPD) to 1,2 syndiotactic polymer is promoted by many homogeneous catalytic systems consisting of titanium or zirconium compounds, soluble in aromatic hydrocarbons activated by methylaluminoxane (MAO) . Notably while many homogeneous catalytic systems promote the copolymerization of ethylene with styrene, the copolymerization of ethylene by using monocyclopentadienyl titanium compounds activated by MAO results in low activity and, more importantly, a decrease of chemoselectivity which causes an increase of the 1,4 units respect to the 1,2 units …”

Allylidene Monomers: Anionically Polymerizable 1,1-Disubstituted 1,3-Diene Derivatives

“…Porri et al synthesized poly­(DMBd)­s by coordination polymerization and determined the composition of microstructures from the peak areas of the 1 H NMR spectrum. The peaks observed at around 5.1, 4.9, and 4.7 ppm were attributed to the 1,4- trans , 1,4- cis , and 3,4-microstructures, respectively . Based on their results, the peaks observed for poly­(AC6) (run 19) can be attributed to the 1,4- trans and 3,4-microstructures.…”

“…The peaks observed at around 5.1, 4.9, and 4.7 ppm were attributed to the 1,4-trans, 1,4-cis, and 3,4microstructures, respectively. 49 Based on their results, the peaks observed for poly(AC6) (run 19) can be attributed to the 1,4-trans and 3,4-microstructures.…”