Viscoelastic behavior of polybutadienes with high 1,4-microstructure and narrow molecular weight distribution

Polybutadienes (PBs) of narrow molecular weight distributions with high 1,4 -microstructure were synthesized by sec-butyllithium-initiated, living poly merization. The shoulder-like anomalous behavior of the storage modulus G'( omega) in the terminal zone for PBs was studied using size exclusion chroma tography (SEC) and rheometric mechanical spectrometry (RMS). It was found t hat a high-molecular-weight fraction in the PBs was the main reason for the occurrence of the shoulders. The linear viscoelastic spectra were successf ully obtained by the Pade-Laplace method from experimental dynamic data, us ing either the dynamic storage, G'(omega), or loss, G "(omega), modulus. Bo th the dynamic moduli and stress relaxation in the linear regime were then calculated with reasonable precision. The feasibility of time-temperature-m olecular weight superposition for PBs using this method was demonstrated. T he dependencies of relaxation spectra on temperature and molecular weight w ere obtained by a fitting procedure. Thus, with a known reference state, th e relaxation spectrum for a given molecular weight PB at a given temperatur e can be predicted. The predicted dynamic moduli are in good agreement with experimental data. (C) 1999 John Wiley & Sons, Inc.