Deconvolution of the segmental and chain modes in amorphous polymers: Do the short-chain modes affect the bulk relaxation?

A new method for calculating the retardation spectra for linear viscoelastic materials is presented. The method uses the analytical expressions among the viscoelastic functions through the numerical evaluation of the Inverse Laplace Transform (ILT) with the Gaver–Wynn–Rho (GWR) algorithm. It is applied to study three polymers' relaxation mechanisms: a star Polystyrene and two Polycyanurate networks with two different crosslink densities. The shear spectrum is de-convoluted to separate the segmental and the chain modes responsible for the softening dispersion. The retardation mechanisms extracted from the shear response are then compared with the volumetric bulk response. The results show that the shear segmental contribution is narrower than the volumetric bulk response and finishes about two decades before the shoulder's appearance in the shear retardation spectrum. Thus, the volumetric bulk response, mainly exerted by the segmental mode, is also affected at long times by the short time chain mechanism, usually claimed to be Sub-Rouse modes. [Display omitted] •A new method for evaluating the spectra of viscoelastic materials is proposed.•The molecular mechanisms contributing to the shear response of polymers are de-convoluted.•The de-convolution allows the quantitative comparison of the volumetric and shear mechanisms.•Sub-Rouse modes affect the long-time tail of the volumetric bulk response.