Synthesis and viscoelastic properties of α,ω-diquaternary ammonium polybutadiene ionomers

Telechelic ionomeric elastomers with quaternary ammonium groups (Me₂RN⁺) attached terminally to polybutadiene (M¯_n ˜ 2.7 × 10³; M¯_w/M¯_n = 1.27; containing 62% 1,4-linkages) have been synthesised by an anionic technique using a functionalised initiator and terminator, followed by quaternisation of the resulting a,?-bis(dimethylamino)polybutadiene. By using differing alkyl halides for quaternisation and by ion exchange chromatography, a series of dialkylated telechelic cationomers has been produced containing alkyl groups, R = Me, Et, n-Pr, n-Bu or n-C₅H₁₁ with counter anions X = I^-, Br^-, PF₆^- or SO₄^2-. The glass transition temperatures, T_g, of these cationomers are c.6°C higher than for the precursor, non-quaternised polymer but are essentially unchanged with variations in groups R or anions X. Dynamic mechanical thermal analyses of the cationomers have been carried out and a secondary transition, T_i, associated with relaxation of ionic cross-linking interactions, observed. Values of T_i decrease as the size of R increases from C₁ to C₅, and as the anion X is changed from Br^- to I^- to PF₆^- or SO₄^2- to PF₆^MIN. Activation energies can be derived from the frequency dependence of T_i values or from the temperature dependence of shift parameters, obtained from the master curves of the dependence on frequency of the shear storage (G') and loss (G?) moduli; these activation energies are dependent on the nature of the counter anion, being greatest for the polymer containing the dinegative SO₄^2-, but are essentially unchanged by the variations in alkyl group, R, implemented in this study. Other results of the dynamic mechanical analyses on the cationomeric elastomers are discussed in relation to their ionic cross-linking.