Analysing the Temperature Effect on the Competitiveness of the Amine Addition versus the Amidation Reaction in the Epoxidized Oil/Amine System by MCR-ALS of FTIR Data
The evaluation of the temperature effect on the competitiveness between the amine addition and the amidation reaction in a model cure acid-catalysed reaction between the epoxidized methyl oleate (EMO), obtained from high oleic sunflower oil, and aniline is reported. The study was carried out analysing the kinetic profiles of the chemical species involved in the system, which were obtained applying multivariate curve resolution-alternating least squares (MCR-ALS) to the Fourier transform infrared spectra data obtained from the reaction monitoring at two different temperatures (60 C and 30 C). At both experimental temperatures, two mechanisms were postulated: non-autocatalytic and autocatalytic. The different behaviour was discussed considering not only the influence of the temperature on the amidation reaction kinetic, but also the presence of the homopolymerization of the EMO reagent. 1. Introduction The development of environmentally compatible polymers is one of the current challenges in polymer chemistry. In this sense, epoxy resins from vegetable oils are extremely promising as environmentally friendly polymers for industrial applications because they share many of the characteristics of conventional petro-chemical based epoxy resins [1]. It is generally admitted that, when epoxide monomers are cured with amines, the addition of the amine is the strongly predominating reaction proceeding in two steps. According to the type of the epoxide-amine system and to the experimental conditions, etherification reaction (3) can be done [2]. With an excess of epoxide, at high temperature and in the presence of Lewis bases, inorganic bases, or Lewis acids catalysts, homopolymerization of epoxides (4) also takes place [2]. These two parallel reactions promote the presence of ether groups. If the epoxide monomers (or prepolymers) contain an ester functional group, as occurs in the epoxidized oils, it is possible to consider that an amide is also formed (5) as a consequence of the reaction between the amine and the ester group. The existence of the homopolymerization and etherification reactions is related to such characteristics of the experimental conditions, as the temperature, the concentration of the reagents, and the presence of catalysts. However, the amidation reaction is only related to the ester-containing monomer used. As a consequence of the dependence of the morphology and the properties of the final product on the curing process, there has been worldwide research interest in elucidating the reaction mechanism and in quantifying the kinetics of epoxy
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