Synthesis, Structure, and Properties of Poly(isoprene)s of Different Constitutions and Configurations from Catalysts Based on Complexes of Nd, Co, and Fe

• DOI: 10.1021/acs.macromol.3c00615
• Publication Date: 2023-06-05T18:48:26Z
• Authors: Miriam Scoti; Fabio De Stefano; Giorgia Zanchin; Giuseppe Leone; Claudio De Rosa; Giovanni Ricci
• Keywords: polyisoprene; iron; polymerization; cobalt; 01 natural sciences; catalysts; neodymium; 0104 chemical sciences

Poly(isoprene)s of different molecular structures have been synthesized with various catalysts based on complexes of Nd-, Co-, and Fe-bearing pyridylimine, phosphine, and bipyridine ligands. Poly(isoprene)s with essentially cis-1,4 structure, 3,4 syndiotactic structure, and regular alternating cis-1,4-alt-3,4 structure have been obtained. Moreover, polymers with an unusual prevalent alternating cis-1,4-alt-3,4 structure but containing cis-1,4 units sequences of different lengths (3 or 5 units) within the chain have also been obtained. The structure and mechanical properties of all of the synthesized poly(isoprene)s, some of them completely new, have been investigated. Poly(isoprene)s with a cis-1,4 structure and with a perfectly alternating cis-1,4-alt-3,4 structure or prevalent alternating cis-1,4-alt-3,4 structure are amorphous, exhibiting mechanical behavior with a viscous flow at relatively high deformation. The sample of poly(isoprene) with almost a regular 3,4 syndiotactic structure (about 79% of 3,4 units) crystallizes in the stable orthorhombic form of 3,4-syndiotactic poly(isoprene). This crystalline sample shows better mechanical properties of deformability and flexibility than the other amorphous poly(isoprene)s without a viscous flow with plastic deformation and breaking at relatively high strain around 300-400% and remarkable elastic properties. The plastic deformation and the elastic behavior are associated with a reversible transformation during tensile deformation of the crystalline orthorhombic form into a disordered mesomorphic form, which recrystallizes into the orthorhombic form upon relaxation during elastic recovery. The glass transition temperature of the different poly(isoprene)s decreases linearly with the increasing cis-1,4 content, from 16 °C of the poly(isoprene) with the prevalent 3,4 structure and 21% of cis-1,4 units to -64 °C of the poly(isoprene) with 98% of cis-1,4 units.