Living polymerization of butadiene at both chain ends via a bimetallic nickel initiator. Preparation of hydroxytelechelic poly(butadiene) and symmetric poly(isocyanide-b-butadiene-b-isocyanide) elastomeric triblock copolymers

Article abstract of DOI:10.1021/ja00085a016

A bifunctional nickel initiator, bis(μ-trifluoroacetato)(η³:η ³-2,2′-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 initiators, [1,4-phenylenebis((η³-1-allyl)nickeltrifluoroacetate)] _n),II, and[1,4-cyclohexanediylbis((η³-1-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 P1 with 0.5 equiv of 2,3-bis((trifluoroacetoxy)methyl)-1,3-butadiene in the unit cell with constants of a = 9.5600(8) A?, b = 9.6554(9) A?, c = 11.7615(10) A?; α = 73.711(7)?, β = 73.537(7)?, γ = 71.938(7)?; V=967.50(15) A?³; 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_?|>3.0σ/(|F_?|)). 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, ¹³C 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.