ELECTROCHEMICAL REDUCTIVE BREAKDOWN OF SOLID-PHASE CHLORINATED RUBBER IN APROTIC AND AQUEOUS MEDIA A. A. Pud, G. S. Shapoval, V. K. Skubin, N. V. Kondrashova, Yu. V. Kontsur, and G. M. Tel'biz UDC 541.138.3.64 A study has been made of the electrochemical reductive breakdown (ECRB) of solid-phase chlorinated butyl rubber (CBR). It has been established that CBR does not accept electrons under conditions of fast sweep of electrode potential; however, with prolonged cathodic polarization of the substrate at the polymer~cathode~solution three-phase boundary, it undergoes reduction and subsequent chemical conversion, including intermolecular cross-linking and breakdown of the macromolecules. The rate of ECRB of the CBR depends on the potential and materials of the cathode, and also on the nature of the solvent. In a aprotic medium, the process of CBR breakdown leads to the formation of long polyconjugated structures that color its surface black in the vicinity of the three-phase boundary. In an aqueous medium, no such color is observed, but the products of ECRB are found to contain conjugated double bonds with a shorter conjugation chain than in the case of the aprotic medium~ It has been established that he starting reaction in ECRB of CBR is reduction of the C.--Cl bond and subsequent elimination of Cl-. The features of electrochemical electron transport reactions involving functional groups of polymers in solutions are determined to a considerable degree by the donor-acceptor properties of these groups, their interactions with each other, the conformation of the macromolecules, the rate of diffusion of the macromolecules in the space near the electrode [I], their orientation and mobility in the field of the electric double layer (EDL) of the electrode, and the polarizability of the chemical bonds in the macromolecules. In the case of thin swollen films of electroactive polymers placed directly on the electrode [2], diffusional limitations are evidently removed, but the electrical conductivity of the polymer takes on considerable importance; with high conductivities, such reactions will proceed through the entire thickness of the film [2]. We have established the possibility of electrochemical reactions for solid-phase polymeric dielectrics as well; in this case, however, the reaction zone is evidently limited to a thin layer of the polymer near the surface, this layer extending into the dense part of the EDL at the polymer/electrode/solution three-phase boundary [3]. From our point of view, an important feature of electrochemical processes involving polymers, a feature that is characteristic for all three cases, is the accumulation of a large number of charged or neutral reduced (or oxidized) fragments in the macromoleeules. This may result in instability and breakdown of the macromolecules, both in the solution volume and in the strong field of the dense part of the EDL (108 to 108 V/era). In the case of cathodic polarization of the electrode, the possibility of such breakdown (it may be defined as electrochemical reductive breakdown or ECRB) was established in our earlier work for aprotic media in the example of a number of heterochain and carbochain polymers [3-8]. The results obtained in those studies, together with an analysis of the conditions of synthesis and service of polymers in various electrochemical systems, suggested that ECRB may take place in the formation of polymers and polymeric coatings on a cathode, in using polymeric and polymer-modified electrodes in chemical sources of current, in electrocatalysis, in cases of contract of protective polymeric coatings with a cathodically polarized metal through the three-phase boundary, etc. In this connection, determination of the relationships and mechanism of ECRB of the polymer would make it possible to judge changes in its properties under the influence of cathodic polarization of the electrode. Petroleum Chemistry Branch, Institute of Physical Organic Chemistry and Coal Tar Chemistry, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Teoreticheskaya i ]~ksperimental'naya Khimiya, Vol. 25, No. 6, pp. 710-715, November-December, 1989. Original article submitted June 9, 1987. 0040-5760/89/2506-0653512.50 9 Plenum Publishing Corporation 653