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Polystyrene (ethylene butylene) polystyrene (PSEBS) (Weiss and Sen, 1991) is an
aromatic polymer with sulfonation at the phenyl ring. Sulfonated phenyl ring is of great interest
as the solution-cast membranes offer proton conductivities that compete with those
of perfluorosulfonate ionomer membranes such as Nafion (Curtin et al., 2004). Promising data have been reported for its suitability in hydrogen-oxygen (Curtin et al.) and direct methanol fuel cells (Park and Yamazaki, 2005) in earlier reports. The kinetics of
aryl sulfonation is being studied since 1908. Most of the studies showed that the rate
is proportional to the aromatic ring concentration. Akovali and Ozkan (1986) reported
the sulfonation kinetics of polystyrene in sulfuric acid and found that only the para
position of the phenyl ring was sulfonated and also that the rate was of the first order with
respect to the polystyrene repeat unit. Shibuya and Porter, 1992 studied the kinetics of
Poly (Ether Ether Ketone) (PEEK) sulfonation using sulfuric acid (Reynolds et al., 1991). Sulfonation reaction kinetics of Poly (Ether Ketone Ketone) (PEKK) using a mixture
of concentrated and fuming sulfuric acid was studied by Swier et al., 2004. However, no systematic study has been conducted on the kinetics of sulfonation of PSEBS. In
this work, we have studied the reaction kinetics of PSEBS sulfonation by chlorosulfonic
acid in chloroform at highly dilute conditions. With chlorosulfonic acid as the
sulfonating agent, the reaction rate was found to be of the first order with respect to both the
polymer as well as the sulfonating agent.
In this study, sulfonation analyses based on ultraviolet (UV)-visible spectroscopy
were carried out. This method is an efficient one for quantitatively analyzing
compounds possessing double bonds (such as an aromatic structure). The spectroscopy has
been widely applied to kinetic studies (Shibuya and Porter, 1994) since the simple and
fast measurement can give accurate and direct analyses of reaction mixtures. Generally,
the UV-visible spectra of aryl compounds are measured in highly dilute conditions, due
to large absorption coefficient of the compounds. |
