Synthesis of exo-Olefin Terminated Polyisobutylene by Sulfide/Base Quenching of Living Polyisobutylene

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Polymers and High Performance Materials


exo-Olefin (methyl vinylidene)-terminated polyisobutylene (PIE) was synthesized in one pot by quenching TiCl(4)-catalyzed living PIB with a dialkyl (or) diaryl sulfide at 60 to 40 degrees C, followed by addition of a base (e.g., triethylamine), followed by warming of the reaction mixture to 20 to 10 C and final termination with methanol. The initiator was 2-chloro-2,4,4-trimethylpentane (TMPCl); the solvent system was 60/40 hexane/methyl chloride, and 2,6-lutidine was used as a nucleophilic additive during polymerization. (1)H NMR spectroscopy was used characterize end-group composition of the product PIBs. Increasing yield of exo-olefin end groups was observed in the approximate order of increasing bulkiness of the substituent on the sulfide, i.e., tert-butyl (100%) > isopropyl (98%) > phenyl (70%) > n-alkyl (39-55%). With diisopropyl sulfide (DIPS), optimized yield of exo-olefin (98%) required stoichiometric excess of DIPS relative to chain ends (CE), e.g., [DIPS]/[CE] = 4, addition of a base, and warming of the reaction prior to addition of methanol. With di-tert-butyl sulfide (DtBS), optimized yield was obtained with lesser stoichiometric excess, e.g., [DtBS]/[CE] = 1.5, with or without addition of a base, and with or without warming of the reaction prior to methanol termination. DtBS yielded 100% exo-olefin end groups under concentrated conditions, e.g., [CE] = 0.1 M, and 98% exo-olefin when the reaction was up-scaled to produce 0.8 kg of PIB. The method was successfully adapted to the synthesis of telechelic (difunctional) exo-olefin terminated PIE with quantitative functionality (100%).

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