Preparation of Carboxyl-Terminated Liquid Natural Rubber Using Hydrogen Peroxide

Abstract

Functionalization of an existing polymer at the end-chain is of interest as it can be further
modified to a block or graft copolymer. In this study, liquid epoxidized natural rubber (LENR) was
firstly prepared by oxidative degradation of epoxidized natural rubber (ENR) latex using periodic
acid at 30oC. It was found that the resulting rubber possesses carbonyl moieties as evidenced by
FTIR spectroscopy at 1719 cm-1. The carbonyl content was determined by the UV absorption of the
reaction of LENR with 2,4-dinitrophenylhydrazine at 355 nm. An increased amount of carbonyl
function was obtained at a longer reaction time of degradation and increased amount of periodic acid.
1H-NMR analysis confirmed the presence of the same amount of the epoxide unit on LENR
comparing with the starting ENR. The LENR was then further treated with H2O2 at 70oC. FT-IR
spectrum showed an increase of the absorption signals at 3442 and 1715 cm-1 corresponding to the
hydroxyl group and the carbonyl function of carboxylic acid, respectively. This may come from the
oxidation of the aldehyde function into carboxylic acid. The acid content of the carboxyl-terminated
liquid natural rubber (CLNR) was analyzed by the titration method using tetramethylammonium
hydroxide in a toluene solution. It was found that the amount of carboxylic acid was increased when
the amount of the oxidizing agent was increased, as well as the amount of epoxide unit of starting
LENR and the reaction time.

Keywords: degradation, epoxidation, carboxyl-terminated rubber