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

Poly(isoprene)s of different molecular structures havebeen synthesizedwith various catalysts based on complexes of Nd-, Co-, and Fe-bearingpyridylimine, phosphine, and bipyridine ligands. Poly(isoprene)s withessentially 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 unusualprevalent alternating cis-1,4-alt-3,4 structure but containing cis-1,4 units sequencesof different lengths (3 or 5 units) within the chain have also beenobtained. The structure and mechanical properties of all of the synthesizedpoly(isoprene)s, some of them completely new, have been investigated.Poly(isoprene)s with a cis-1,4 structure and witha perfectly alternating cis-1,4-alt-3,4 structureor prevalent alternating cis-1,4-alt-3,4 structure are amorphous, exhibiting mechanical behavior witha viscous flow at relatively high deformation. The sample of poly(isoprene)with almost a regular 3,4 syndiotactic structure (about 79% of 3,4units) crystallizes in the stable orthorhombic form of 3,4-syndiotacticpoly(isoprene). This crystalline sample shows better mechanical propertiesof deformability and flexibility than the other amorphous poly(isoprene)swithout a viscous flow with plastic deformation and breaking at relativelyhigh strain around 300-400% and remarkable elastic properties.The plastic deformation and the elastic behavior are associated witha reversible transformation during tensile deformation of the crystallineorthorhombic form into a disordered mesomorphic form, which recrystallizesinto the orthorhombic form upon relaxation during elastic recovery.The glass transition temperature of the different poly(isoprene)sdecreases linearly with the increasing cis-1,4 content,from 16 degrees C of the poly(isoprene) with the prevalent 3,4 structureand 21% of cis-1,4 units to -64 degrees C ofthe poly(isoprene) with 98% of cis-1,4 units.