Chemical Degradation of Epoxidized Natural Rubber Using Periodic Acid: Preparation of Epoxidized Liquid Natural Rubber P. Phinyocheep, 1,2 C. W. Phetphaisit, 1,2 D. Derouet, 3 I. Campistron, 3 J. C. Brosse 3 1 Department of Chemistry, Faculty of Science, Mahidol University, Rama VI Road, Phayathai, Bangkok 10400, Thailand 2 Institute of Science and Technology for Research and Development, Mahidol University, Salaya Campus, Puthamonthon, Nakorn Pathom 73170, Thailand 3 Laboratoire de Chimie Organique Macromoleculaire-Chimie des Polyme `res, UMR CNRS 6011, Universite ´ de Maine, Avenue Olivier Messiaen, 72085 Le Mans Cedex 9, France Received 16 October 2003; accepted 14 April 2004 DOI 10.1002/app.20812 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Oxidative degradation of epoxidized natural rubber (ENR) was effectively performed in latex phase by using periodic acid at 30°C. The ENR was prepared from the epoxidation of natural rubber in latex phase using performic acid generated in situ by the reaction of hydrogen peroxide and formic acid. The prepared ENR latex was subsequently treated with periodic acid. It was found that the higher the amount of the periodic acid employed the faster the molec- ular weight of the ENR decreased. Different epoxidation levels of the ENR had no significant effect on the degrada- tion reaction. Based on 1 H NMR analysis, the epoxide con- tent in the epoxidized liquid natural rubber (ELNR) ob- tained was about the same as that observed in the ENR before degradation. FT-IR analysis showed an increase in carbonyl signal after prolonged reaction time or when higher amounts of periodic acid were employed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 6 –15, 2005 Key words: degradation; epoxidation; modification; rubber; telechelics INTRODUCTION Chemical modifications or functionalizations of poly- meric materials are of wide interest to research scien- tists as they often produce new materials that cannot be prepared or are costly to prepare by means of conventional polymerization reactions. These meth- ods are also used to improve the properties of some commercial polymers or to introduce specific reactive intermediates on the polymer chains for further mod- ification. Epoxide function is considered to be one of the most important intermediate in organic synthesis. The introduction of epoxides on the backbone of nat- ural rubber (NR) will render NR essentially resistant to oil. 1 The epoxide function is also susceptible to various chemical reactions involving hydrogen-donor molecules, such as amines, alcohols, and carboxylic acids. The NR is a high-molecular-weight natural polymer. Therefore, degradation of NR into low-mo- lecular-weight rubber and functionalization with spe- cific functional groups, such as epoxide, would widen the applications of NR. It is possible to lower the molecular weight of the NR before the process of introducing functional groups to NR is conducted. Oxidative degradation of NR promoted by phenylhy- drazine/oxygen system has been reported. 2 The method was employed by Phinyocheep and Duang- thong 3 to prepare liquid natural rubber (LNR) before conducting an epoxidation reaction by using perfomic acid generated in situ from the reaction of formic acid and hydrogen peroxide. However, the obtained LNR has a brown color, which may be due to the contam- ination of the reagents used or to the nonrubber con- stituents in the NR. Oxidative degradation of depro- teinized NR by using potassium persulfate provided the LNR with a light color. 4,5 However, the epoxida- tion of deproteinized LNR in latex phase using in situ performic acid carried in our laboratory was accom- panied by side reactions, such as epoxide ring opening reaction, leading to 1,2-diol unit and formyl addition adducts. Lead tetraacetate, Pb(OAc) 4 and periodic acid (H 5 IO 6 ) are chemicals of interest used for degradation of the polyisoprenic chain. Typically, both reagents cause cleavage of vic-glycols to yield carbonyl com- pounds. Studied by Burfield and Gan, 6 Pb(OAc) 4 was found to cause degradation of hydrolyzed epoxidized synthetic rubber (EIR) faster than that of EIR. Syn- thetic polyisoprene sample (IR), which presumably contains no 1,2-diols, was also slowly degraded by Correspondence to: P. Phinyocheep (scppo@mahidol.ac.th). Journal of Applied Polymer Science, Vol. 95, 6 –15 (2005) © 2004 Wiley Periodicals, Inc.