DETERMINATION OF THE REFRACTIVE INDEX INCREMENT OF NATURAL AND SYNTHETIC POLY(CIS-1,4-ISOPRENE) SOLUTIONS AND ITS EFFECT ON STRUCTURAL PARAMETERS

Abstract

& 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.

SEC‐MALS study of dynamic structuring of natural rubber: Comparative study of two Hevea brasiliensis genotypes

“…The integration limits used for calculation were from 27–27.5 to 40–41 min according the sample. The differential refractive index increment (d n /d c ) value at 633 nm was 0.130 mL/g 42…”

Comparative study of the microstructure of solid rubber from Ficus carica and Hevea brasiliensis

“…The obtained data were analyzed with the Astra Software (Wyatt). An RI increment value ( dn/dc ) of 0.130 ml/g 18 was used for all natural rubber samples.…”

Influence of nonrubber components on properties of unvulcanized natural rubber

“…In order to determine the gel content, the total rubber peak from the concentration detector observed in SEC separation was integrated using 0.13 mL/g as the value of dn/dc . The amount of gel retained during filtration (Gel >1μ ) was estimated from the difference between the initial concentration of the solution and concentration after injecting the solution into SEC‐MALS system, as follows: where C 1 is the initial concentration of the analyzed sample solution that passes through the 1‐μm filter and C 2 is the concentration of the microaggregates that pass through the 1‐μm filter.…”

“…In order to determine the gel content, the total rubber peak from the concentration detector observed in SEC separation was integrated using 0.13 mL/g as the value of dn/dc. 29 The amount of gel retained during filtration (Gel >1μ ) was estimated from the difference between the initial concentration of the solution and concentration after injecting the solution into SEC-MALS system, as follows:…”