Tetrahydrothiophenium monomer

Abstract In situ spectroscopy is an important tool to characterize polymers synthesized via a precursor route. Highly conjugated polymers such as po y(p-phenylene vinylene) (PPV) and PPV derivatives are commonly prepared from a precursor polymer because the final polymers are very insoluble and intractable. Preparation in the precursor form enables the polymer materials to be cast as films. The PPV polymers are obtained from the precursor forms using a thermal elimination reaction. The exact conditions of the reaction are important as they influence the properties of the resultant polymer. The details of this thermal elimination reaction have been analyzed using thermal gravimetric analysis (TGA) coupled with infrared analysis of the evolved gas products. In situ infrared spectroscopy of the precursor films during thermal conversion to the polymers has provided further details about the elimination reaction. We have characterized PPV synthesized from a tetrahydrothiophenium monomer (sulfonium precursor route) and via the xanthate precursor route. PPV derivatives under study include poly(2,5-dimethoxy-p-phenylene vinylene) and poly(phenoxy phenylene vinylene). 

The solid state thermal elimination reaction is a very important step in the formation of the final PPV or PPV derivative. In situ infrared spectroscopy therefore plays a critical role in the ability to monitor the reaction that converts the precursor polymer to the final product. We have characterized the mechanism of this conversion reaction in the formation of PPV synthesized by both the sulfonium precursor route (SPR) and the xanthate precursor route (XPR). The polymerization reaction of PPV from the tetrahydrothiophenium monomer is shown in Figure 1. After polymerization of the precursor polymer, the material is thermally converted to the final PPV product. This SPR method involves the thermal elimination of the tetrahydrothiophenium (THT) group and HCl as shown. 

Figure 1. Synthesis of poly(p-phenylene vinylene)(PPV) from the tetrahydrothiophenium monomer via the sulfonium precursor route...

A. Kikkawa, T. Takata, and T. Endo, Cationic polymerization of vinyl monomers with latent initiators. 3. l-(Para-methoxybenzyl)tetrahydrothiophenium hexafluoroantimonate as a new potent cationic initiator. Makromol. Chem. Macromol. Chem. Phys. 1991,192(3), 655-662. 

We have previously reported the synthesis of PPV and the analysis of the thermal elimination reaction in the polymer prepared from the tetrahydrothiophenium (THT) monomer via the sulfonium precursor route. The reaction is shown in Figure 1. PPV prepared via the xanthate precursor route has been recently described.The reaction is shown in Figure 2. 

Sample Preparation. The preparation of PPV precursor is briefly shown in Figure 1. The synthesis of p-xylylene-bis(tetrahydrothiophenium chloride) monomer IV was according to the method of Lenz et al (7 7) 10 g dichloro-p-xylene (V, Tokyo... 

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