title: Binuclear initiators for the telechelic synthesis of elastomeric polyolefins.
abstract: Novel binuclear complexes, 4,4'-bis{[N-(2,6-diisopropylphenyl)-2-(2,6-diisopropylphenylimino)propanamidato-κ(2)-N,O-(trimethylphosphine)nickel(II)]methyl}-1,1'-biphenyl (2a) and 4,4'-bis{[N-(2,6-diisopropylphenyl)-2-(2,6-diisopropylphenylimino)-4-methylpentamidato-κ(2)-N,O-(trimethylphosphine)nickel(II)]methyl}-1,1'-biphenyl (2b), were synthesized by linking two nickel centers through a bis(benzyl) fragment. When activated with nickel bis(1,5-cyclooctadiene) (Ni(COD)(2)), 2a and 2b are capable of polymerizing ethylene in a quasi-living fashion, producing polymers with approximately twice the molecular weights relative to those obtained by using a structurally related mononuclear system. In addition, 2b/Ni(COD)(2) was utilized to synthesize a series of pseudo-triblock polyethylene (PE) macroinitiating copolymers, bearing atom-transfer radical polymerization (ATRP) initiators. Pseudo-pentablock copolymers were also prepared by taking advantage of a pressure-pulsing technique, wherein the ethylene pressure was increased from 100 to 500 psi in order to produce semicrystalline ethylene-rich end-blocks. Copolymers with elastomeric properties were synthesized by grafting n-butyl acrylate from the PE macroinitiators via ATRP. Examination using monotonic and step-cyclic stress-strain tests demonstrates that the materials exhibit large strains at break (1600-2000%) and excellent elastic recoveries at large strains (∼80%). That materials with such desirable properties could not be attained using a mononuclear initiator demonstrates the clear advantage of growing the polymer via a telechelic mechanism.
authors.affiliation: Department of Chemistry & Biochemistry, Mitsubishi Chemical Center for Advanced Materials, University of California, Santa Barbara, California 93106, USA.
authors.forename: Robert C
authors.initials: RC
authors.lastname: Coffin
authors.forename: Yanika
authors.initials: Y
authors.lastname: Schneider
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Kramer
authors.forename: Guillermo C
authors.initials: GC
authors.lastname: Bazan
mesh_terms: D018360:Crystallography, X-Ray; D008958:Models, Molecular; D015394:Molecular Structure; D009532:Nickel / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D011090:Polyenes / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D009942:Organometallic Compounds; D011090:Polyenes; D009532:Nickel; C035051:PL 732