Wimol Klaichim, Pairote Klinpituksa, and Wae-asae Waehamad

pp. 57 - 62

Abstract

A novel polymeric herbicide based on phenoxyacetic acid derivatives was prepared by the reaction of epoxidised liquid natural rubber (ELNR) with 2,4-dichlorophenoxyacetic acid (2,4-D) or 2-methyl-4-chlorophenoxyacetic acid (MCPA). The liquid natural rubber (LNR) was firstly obtained from the degradation of natural rubber latex with tert-butyl hydroperoxide and cobalt acetylacetonate at 65°C for 72 hrs. The epoxidised liquid natural rubber was prepared from the reaction of LNR with formic acid and hydrogen peroxide at 50°C for 6 hrs. The reaction of epoxidised liquid natural rubber with 2,4-D or MCPA using triethylamine as a catalyst in toluene was performed at 70, 80, and 90°C for 6, 9, 12, 18, and 24 hrs. The polymeric herbicides obtained were characterized and the grafting percentage of 2,4-D or MCPA onto liquid natural rubber were also determined by FT-IR and ¹H-NMR spectroscopy. It was found that the grafting percentage increased with
increasing amount of reactants, temperature, and reaction time. The release of 2,4-D and MCPA from polymeric herbicides was investigated in pH 6, 7, and 8 buffers at room temperature. The results show that the slowest release of 2,4-D and MCPA was found to be constant at pH 7 for 14 and 10 days, respectively.