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& The refractive index increment (dn=dc) of a solution is a constant that indicates the variation of the refractive index with the solute concentration. It is used in the multi-angle light scattering technique to determine the concentration and the weight-average molar mass of polymers. It depends on many parameters, including the structure of the polymer, the solvent, the wavelength of the light and the temperature of the solution. To obtain accurate results, it is necessary to determine the dn=dc at the same condition as for the multi-angle light scattering measurement. In this work, the dn=dc at 633 nm of standard synthetic monodispere poly(cis-1,4-isoprene) (PI) and natural rubber (NR) solutions in THF were determined at 25 and 40 C using an Optilab DSP refractometer. The mean value of the dn=dc obtained for NR and PI was 0.13 mL=g. No significant difference between different types of samples and temperatures (25 C and 40 C) were observed. The nanoaggregates in NR solution that were not retained after filtration through 1 lm filter had no effect on the dn=dc. The intercept value of the conformation plot increased in line with the dn=dc, but the Flory exponent remained unchanged.

The objective of our work was to characterize natural rubber (NR) samples with different macromolecular structures by measuring Mooney viscosities (VR) at variable rotor speeds _2 rpm, called variable speed Mooney viscosity (MVS). Model samples of technically specified rubbers of constant Mooney viscosity (TSR5CV) were prepared with chosen specific clones. The structures of the samples were characterized by size-exclusion chromatography coupled with an online multi-angle light-scattering detector (SEC-MALS). Rheological properties of the samples were also characterized by a dynamic moving die rheometer. Measuring monoclonal model samples by MVS showed three types of VR flow curves. The VR at high rotor speed (2 rpm) was correlated with number-average molar mass (Mn), whereas VR at low rotor speed (0.05 rpm) was correlated with weight-average molar mass (Mw). Measuring MVS revealed the rheological behaviors of samples and enabled discrimination between samples with different macromolecular structures and should thus help in predicting processability. (Résumé d'auteur