Acceleration and Inhibition Effect of Tertiary Amines on Thermal Degradation of Poly(Vinyl Chloride)

Abstract

Poly(vinyl chloride) (PVC) is occasionally discolored yellow or red by the formation of polyene chains in the polymer backbone. It has been noted that the formation of such polyene structures is caused by dehydrochlorination of the PVC, accelerated by tertiary amines. Thus, in the present study, we investigated the influence of amines on the formation of polyene structures in PVC, using resonance Raman spectroscopy. The amount of polyene produced by thermal treatment with amine vapor exposure was determined based on the resonance Raman intensity ratio of the polyene band to the PVC band. The results showed that the discoloration of PVC, indicating the formation of polyene structures, was most prominently caused by 1,4‐diazabicyclo[2.2.2.]octane (DABCO), bis(2‐dimethylaminoethyl)ether (BDMEE), or N,N,N′,N′‐tetramethyl‐1,6‐diaminohexane (TMDAH), because of their high basicity and nucleophilicity. In addition, the formation of polyene structures was inhibited by the co‐presence of amine and protic solvent (water, ethanol, and 2‐propanol) or additives containing hydroxyl groups (glycerin, poly[vinyl alcohol]), suggesting that amine nucleophilicity toward PVC is reduced by the protonation of amine to lone pairs of tertiary amines. J. VINYL ADDIT. TECHNOL., 26:253–258, 2020. © 2019 Society of Plastics Engineers