The specific refractive index increments of polyisoprenes in various solvents

Abstract

Specific refractive index increments of polyisoprenes with high cis-1,4 content have been determined in six solvents at 20� and λ 546 nm. A linear relationship was found between the refractive index increment dn/dc = n and the refractive index of the solvent nl : N45620 = 1.687 - 1.105n1 The results are compared with the best values reported for natural rubber which are usually employed for polyisoprene in light scattering measurements.

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

“…Arakawa and Kita [15] showed that dn=dc of proteins in water (0.19 mL g À1 ) decreased by increasing the percentage of organic solvent to 0.11-0.14 mL g À1 in aqueous solution containing 80% of organic solvent. All samples had dn=dc values varying from 0.121 to 0.136 mL g À1 , with a mean value of 0.13 mL g À1 , which was closed to the one published by Vavra [10] and Reed and Urwin, [11] at 546 nm, but very different from the one of Angulo-Sanchez [12] extrapolated at 633 nm.…”

“…About 120 mg of the NR or standard PI samples were dissolved in 100 mL THF stabilized with 2,6-di-tert-butyl-4-methylphenol (BHT) Schulz et al [16] NR b 25 0.149 e 0.141 e 0.137 f Vavra [10] SR c 25 -0.128 -Reed and Urwin [11] SR c 20 -0.128 e -Angulo-Sanchez et al [12] NR (100 mg=L). The NR solution was stored for 14 days in the dark, in a hot-water bath at 30 C, and stirred 1 hour daily during the last 7 days.…”

“…From this equation, the dn=dc at 546 nm of a SR solution in THF 38 C. Kim et al was 0.128 mL g À1 , which is in perfect agreement with Vavra. [10] The results published by Reed and Urwin [11] did not enable to determine the value of the dn=dc at 633 nm for a SR solution in THF, but according to Eq. (2), this value should be lower than the one of 546 nm (0.128 mL g À1 ).…”

“…Using Eq. (1), Reed and Urwin [11] showed that the dn=dc at 546 nm of a SR solution in a solvent could be predicted using the equation dn=dc ¼ À1.105 n þ 1.687. From this equation, the dn=dc at 546 nm of a SR solution in THF 38 C. Kim et al was 0.128 mL g À1 , which is in perfect agreement with Vavra.…”

“…THF was the most used solvent to solubilize NR samples because its polarity enables the reduction of the gel phase more than less polar solvents. [8,9] In the literature, the dn=dc values of NR and SR solutions were determined at wavelengths of 436 nm and 546 nm [10][11][12] (Table 1). The values vary from one author to another because the samples and the conditions used were different, especially the solvent.…”