| Anionically polymerized "living" polybutadiene (BR) was grafted onto chlorinated poly(isobutylene-co-isoprene) (CIIR) to form a series of elastomeric graft copolymers (CIIR-g-BR) of comb-type, long-chain branching structure (LCB) with systematically varying length and number of branches.;A comprehensive program of analytical characterization of the structure and morphology of these materials using SEC/DRI-DV, NMR, FT-IR, DSC, TGA, TEM and other techniques, was designed to determine all relevant structural variables and parameters, as well as to exclude the presence of the potential compositional interferences (gel, residual solvent, unattached branch parent polymer, etc.) for intended correlations between branching structure and rheological properties. The principal branching characteristics of comb-like long-chain branched structures were derived from the stoichiometry of the grafting reaction, confirmed by compositional analysis using a combination of NMR/FT-IR/SEC and supplemented by SEC characterization of the parent linear polymers constituting the backbone (CIIR) and the branch of the graft (BR), respectively.;Linear viscoelastic properties of these materials were determined by a Rheometrics Mechanical Spectrometer (RMS-800) using small amplitude, dynamic (sinusoidal oscillatory) shear. These measurements were supplemented by Rubber Process Analyzer (RPA 2000;Non-linear viscoelastic properties in shear were investigated in a series of isothermal strain and frequency sweeps using large strain (up to 800%) oscillations (RPA 2000), and by stress following a large-amplitude (;An insight into the morphology of the grafts by means of the TEM and DSC has been compared to the results of the thermo-mechanical analysis (DTMA) in tension, using the Rheometrics Solids Analyzer (RSA-II).;Phenomenological correlation between long-chain branching and rheological parameters was attempted and observed effects of branch length and branching frequency on rheological properties are discussed. Long-chain branching has a profound effect on the behaviour of graft copolymers in the plateau and terminal zones of the viscoelastic spectrum. Systematic changes in the frequency dependence of the dynamic moduli and time dependence of the stress relaxation modulus can be related to the length and the number of branches. On the other hand, modifications in the transition and plateau zones due to grafting are influenced primarily by chemical composition of the graft copolymers. A new method to characterize LCB in elastomers by means of a normalized Cole-Cole plot has been proposed. |
