LIVING POLYMERIZATION OF BUTADIENE AT BOTH CHAIN-ENDS VIA A BIMETALLIC NICKEL INITIATOR - PREPARATION OF HYDROXYTELECHELIC POLY(BUTADIENE) AND SYMMETRICAL POLY(ISOCYANIDE-B-BUTADIENE-B-ISOCYANIDE) ELASTOMERIC TRIBLOCK COPOLYMERS

A bifunctional nickel initiator, bis(mu-trifluoroacetato)(eta3:eta3-2,2'-biallyl)dinickel(II), IV, was synthesized to promote the living polymerization of butadiene to high cis-1,4-content polymer with both chain ends active. Other potential initiator, [1,4-phenylenebis(eta3-1-allyl)nickel trifluoroacetate)]n, II, and [1,4-cyclohexanediylbis((eta3-1-allyl)-nickel trifluoroacetate)]n, III, were found to be completely ineffective due to intermolecular carboxylate bridges which gave the complexes polymeric structures. The intramolecular bridges in IV and its molecularity were confirmed by X-ray crystallography. IV cocrystallizes in space group P1BAR with 0.5 equiv of 2,3-bis((trifluoroacetoxy)methyl)-1,3-butadiene in the unit cell with constants of a = 9.5600(8) angstrom, b = 9.6554(9) angstrom, c = 11.7615(10) angstrom; alpha = 73.711(7)degrees, beta = 73.537(7)degrees, gamma = 71.938(7)degrees; V= 967.50(15) angstrom3; and Z = 2. Refinement of the model, which contained a disordered C6H8 unit, led to convergence with R(F) = 5.8%, R(wF) = 6.9%, and GOF = 2.21 for 276 variables refined against those 2852 data with \F(o)\>3.0sigma/(\F(o)\)). The living polybutadiene samples were successfully used to prepare triblock copolymers of the structure poly(1-phenylethyl isocyanide-b-butadiene-b-1-phenylethyl isocyanide), which have been characterized using gel permeation chromatography, differential scanning calorimetry, C-13 NMR, elemental analysis, and transmission electron microscopy. The bifunctional living polybutadiene was also successfully end-capped with p-(trifluoromethyl)benzaldehyde to afford a telechelic polymer with hydroxy functionalities at both chain ends.