Synthesis and application of uracil derivatives as novel thermal stabilizers for rigid poly(vinyl chloride)

Novel uracil thermal stabilizers for rigid poly(vinyl chloride) (PVC), N, N-dimethyl-6-amino-uracil (DAU), N-monomethyl-6-amino-uracil (MAU) and N-monomethyl-6-amino-thiouracil (MATU) were synthesized successfully via a precipitation method, and characterized with 1H NMR spectra. Evaluation of these compounds as thermal stabilizer for rigid PVC was measured by discoloration test, and also using Haake torque rheometer and TGA. The results showed that, these novel uracil derivatives exhibited greater stabilizing efficiency compared with traditional Ca/Zn stabilizers (CZ) and diphenylthiourea (DTU) with the same concentration in PVC mixtures. This is attributed to the ability of these compounds to replace the labile chlorine atoms in PVC chains, and absorb of HCl released by the degradation of PVC, which was proved by the FTIR and 1H NMR spectral analysis. Furthermore, an excellent synergistic effect could be obtained when the model compound MATU combined with zinc stearate (ZnSt2) in different mass ratios, and the initial color and long-term stability of PVC products were remarkably improved.