Synthesis of Ethylene/Isoprene Copolymers Containing Cyclopentane/Cyclohexane Units as Unique Elastomers by Half-Titanocene Catalysts

• Published in: Macromolecules 2023-02, Vol.56 (3), p.899-914
• Main Authors: Guo, Lijuan, Makino, Ryoji, Shimoyama, Daisuke, Kadota, Joji, Hirano, Hiroshi, Nomura, Kotohiro
• Format: Article
• Language: English
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/acs.macromol.2c02399

Ethylene (E) copolymers with isoprene (IP) possessing higher glass-transition temperatures (T g values, −7.1 to 29.2 °C) than those prepared by the reported catalysts (T g below −18 °C) have been prepared in the copolymerization by using half-titanocene catalysts containing phenoxide ligand, Cp′TiCl2(O-2,6- i Pr2-4-R-C6H2) [Cp′ = C5Me5 (Cp*), R = H (1), SiEt3 (2)]. Their microstructural analysis by NMR spectra revealed that the copolymers contained cyclopentane (major) and cyclohexane units, formed by cyclization after IP and subsequent ethylene insertions, in addition to 1,4- and 3,4-IP inserted units observed as major units in those prepared by reported catalysts. The 1,2,4-Me3C5H2 analogue (R = H) showed better IP incorporation, but the resulting E/IP copolymers possessed rather low T g values compared to those prepared by 1,2 due to less cyclopentane unit in the microstructure. The T g value in the E/IP copolymer increased upon the increase of the IP content, and the degree was dependent upon the catalyst employed. Due to their unique microstructure, the resulting E/IP copolymers prepared by 1,2–MAO catalyst systems exhibit promising tensile and elastic properties. The tensile strength initially decreased with an increase in the IP content along with an increase of the elongation at break (up to 600%, IP 3.3–15.6 mol %) and then increased gradually with further increase in the IP contents (IP 18.1–21.5 mol %); the elongation at break then decreased with preserving the tensile strength along with the observation of the yield stress.