Friedel-Crafts Polymers Containing Thiophen

The reaction between p-di(chloromethyl) benzene (DCMB) and thiophen, catalysed by stannic chloride, has been studied with a view to elucidating the kinetics and mechanism of the reaction. In this way it was hoped to gain a clearer insight into the structure of the resultant polymer and so to account for its reported thermal stability. By studying the rate of production of involatile material it was established that the self-polymerisation of thiophen would have little or no effect on the DCMB-thiophen reaction. Analyses of these involatile materials were carried out using I.R., U-V and n. m. r. spectroscopy and molecular weight determinations. The rate of selfcondensation of DCMB was also found to be negligable, by studying the rate of evolution of HCl from DCMB-SnCl4 mixtures. Products of the DCMB-thiophen reaction, with molecular weights up to 850, have been separated using both gas liquid chromatography (GLC) and gel permeation chromatography (GPC), and identified using mass, I.R. and n. m. r. spectroscopy. A total of eight reaction products were separated and identified. However the techniques available did not permit separation and identification of products of molecular weight greater than 850 or an estimation of the extent of isomerism among the reaction products. A kinetic analysis of the reaction was carried out using both GLC and GPC for the separation and analysis of products. Using GLC the dependence of the rate of the first two reactions on the first power of the concentration of each of the reactants was established. This allowed a mechanism for the overall reaction to be proposed and rate constants and activation. energies for the first two steps in the polymerisation to be calculated. From the GPC results reaction curves for all the identified products were constructed. The extremely complex nature of the reaction and the resultant products prevented a complete kinetic analysis of the later stages of the reaction being made. It was possible, however, to arrive at semi-quantitative conclusions about the relative reactivity of the reaction products and hence construct a useful picture of the structure of the resultant polymer. Polymers were also prepared by reaction of DCMB with thiophen, 2-methyl thiophen, 3-meihyl thiophen, 2.5-dimethyl thiophen and 2-chlorothiophen and an assessment was made of their relative stabilities using both thermal gravimetric analysis and thermal volatilisation analysis. I.R. spectroscopy indicated that all the polymers had the same basic structure and so it was possible to correlate the observed degradative features with the differences in the thiophen monomers. These studies have allowed the following conclusions to be drawn concerning the reaction of DCMB with thiophen and the structure of the resultant polymer. The overall reaction may be represented by a series of competing, consecutive reactions of the type, As the reaction proceeds it rapidly becomes highly complex with a proliferation of isomers at each molecular level being brought about by the onset of branching through the disubstituted thiophen nuclei of the products The ultimate polymer has been shown to be a highly cross-linked, insoluble material which exhibits good thermal stability in vacuum, inert atmospheres and air