Chemical modification of 1,4-polydienes by di(alkyl or aryl)phosphates

Abstract

Synthesis of 1,4-polydienes bearing di(alkyl or aryl)phosphate groups in side position of the polydiene chains was considered by using a chemical modification procedure. The synthesis was carried out according to a two-step process. Firstly, functionalized intermediate polydienes were prepared by partial epoxidation of 1,4-polyisoprene or 1,4-polybutadiene units. Secondly, the introduction of the di(alkyl or aryl)phosphate groups was realized by using the reactivity of the acidic function P–OH of di(alkyl or aryl)phosphate reagents toward oxirane rings. A preliminary study on model molecules of epoxidized 1,4-polydienes (4,5-epoxy-4-methyloctane for epoxidized 1,4-polyisoprene, 4,5-epoxyoctane for epoxidized 1,4-polybutadiene) allowed the characterization of polymers derived from the various types of polydienes: epoxidized synthetic 1,4-polybutadiene, and epoxidized synthetic 1,4-polyisoprene or epoxidized liquid natural rubber (ELNR), as well as that of the side reactions. In all cases, the oxirane rings are opened and two categories of 1:1 phosphate adducts are obtained: five-membered cycle adducts (2-(alkoxy or aryloxy)-2-oxo-1,3,2-dioxaphospholane structures) and 1:1 β-hydroxyphosphate adducts, in proportions depending on the di(alkyl or aryl)phosphate that is the alkyl (or aryl) group nature (methyl, ethyl, butyl, phenyl), and the model structure. The whole phosphate adduct yields are generally limited to about 80%, due to the side reactions. The addition of di(alkyl or aryl)phosphates on the epoxidized units of epoxidized liquid 1,4-polydienes proceeds in a way nearly similar to that observed on the model molecules. The partial modification of oxirane rings by the phosphate compounds lets unreacted epoxides so available for a latter reaction, for instance for a crosslinking process.