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Sorption and addition of bromine from aqueous solutions on cis‐1,4‐polyisoprene
Author(s) -
Lewin Menachem,
Penhasi Adel
Publication year - 1993
Publication title -
polymers for advanced technologies
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.61
H-Index - 90
eISSN - 1099-1581
pISSN - 1042-7147
DOI - 10.1002/pat.1993.220040801
Subject(s) - bromine , sorption , enthalpy , partition coefficient , aqueous solution , molecule , natural rubber , materials science , chemistry , organic chemistry , thermodynamics , adsorption , physics
The sorption of bromine from bromine water on cis‐1,4‐polyisoprene film and the initial stages of bromination are studied at concentrations of 0.002–0.1 mol/l and temperatures of 15–35°C. The diffusion coefficient of bromine into natural rubber (NR) is 1.3–2.0 × 10 −6 cm 2 /sec for the total sorption and 5–13 × 10 −7 cm 2 /sec for the irreversible sorption. The partition coefficient of bromine between water and rubber increased from 17.3 at 15°C to 37.1 l/kg at 35°C. The chemical potential, enthalpy and change in entropy of partition are, at 25°C, respectively: −1.9 kcal/mol, 6.6 kcal/mol and 28.4 cal/mol. K. The irreversible sorption is due to a charge‐transfer complex between bromine molecules and double bonds of the rubber. The complex is the first stage of the addition reaction, which becomes noticeable at concentrations above 0.012 mol/l. With increasing bromine concentration the concentration of the complex decreases and the added bromine increases. The charge transfer complex appears to change the conformation of the cis‐NR chains so that the bromine addition occurs in the trans‐conformation, as shown by FT–IR spectra. The bromination is accompanied by a marked crystallization effect as illustrated by thermal analysis and WAXS measurements.