Synthesis, Characterization and Curing Studies of Polyisobutylene Based Macromonomers

The syntheses of new polyisobutylene (PIB) macromonomers with methacrylate (MA), acrylate (A), vinyl ether (VE) and epoxy (EP) end-functionality have been accomplished using simple nucleophilic substitution reactions of bromoallyl end-functional polyisobutylene. Use of a phase transfer catalyst such as tetra-n-butylammonium bromide significantly increased the rate of substitution reactions. The macromonomers were characterized by 1H, COSY and 13C NMR spectroscopic, GPC and MALDI-TOF MS analyses. The end-functionality was calculated to be ∼2 in all the cases. The GPC-RI traces indicated that the nucleophilic substitution reactions were carried out without side reactions affecting the polymer chain.;Epoxy telechelic PIBs (EP-PIB-EP), potentially useful to obtain flexible epoxies, were synthesized by reacting bromoallyl end-functional PIB with glycidol in the presence of NaH. The epoxy end capped macromonomers were mixed with bisphenol A diglycidylether (DGEBA) and triethylenetetramine as curing agent, and cured at elevated temperature. Field Emission Scanning Electron Microscopy (FESEM) indicated nanophase segregation of rubbery domains at EP-PIB-EP ≤ 15 wt%, and the fracture toughness increased by 100% relative to the unmodified epoxy network, while the tensile and flexural strengths remained adequate. However, at EP-PIB-EP ≥ 20 wt% macrophase separation resulted in a drastic reduction in toughness along with other mechanical properties. The use of oligo(tetramethyleneoxide) modified epoxy telechelic PIB (EP-oTHF-PIB-oTHF-EP) as soft segment significantly improved the miscibility and cured materials with excellent fracture toughness were obtained even at 40 wt% rubber content. Thermal stability of the amine cured epoxy resin was not affected by the incorporation of PIB. These flexible networks possess superior fracture toughness compared to polyethylene glycol/DGEBA networks commercialized by Dow Chemical Company.;Polyisobutylene-based UV cured networks potentially useful as sealants were synthesized by photopolymerization of well-defined polyisobutylene methacrylate (PIBMA), acrylate (PIB-A) and vinyl ether (PIB-VE) di- and trifunctional macromonomers. The kinetics of photocrosslinking were measured using an optical pyrometer apparatus. The initial rates of photopolymerization were manipulated and optimized with respect to different experimental parameters. PIB-MA/A macromonomers displayed enhanced reactivity in radical photopolymerization in the presence of a bis(acylphosphine) oxide photoinitator. PIB-VE macromonomers exhibited a high initial rates of photopolymerization with (4-n-octyloxyphenyl)phenyliodonium hexafluroantimonate as the photoinitiator. The rate as well as the ultimate monomer conversion were increased by increasing the irradiation light intensity. The inherent induction period associated with oxygen inhibition in the photopolymerization of PIB-MA was significantly reduced by the choice of photoinitiator. A detailed investigation of the concentration of MA/A/VE end groups revealed the presence of a prominent saturation effect in the photopolymerization of PIB-A, which was absent with PIB-MA and PIB-VE. An investigation of the photopolymerized networks by attenuated total reflectance—Fourier transform infrared spectroscopy (ATR-FTIR) indicated nearly complete end group double bond conversion. A similar conclusion was reached from solvent extraction studies. Dynamic mechanical analysis (DMA) of the UV cured networks obtained using trimethylolpropane triacrylate (TMPTA), 1,6-hexanediol diacrylate (HDODA) and 1,4-butanediol divinyl ether as reactive diluents indicated a low temperature transition at ∼ -60 °C and a high temperature transition at ∼ -45 °C.