Thermal Degradation Kinetics of Para-Substituted Poly (styrene Peroxide)s in Solution Priyadarsi De, 1 Sujay Chattopadhyay, 2 Giridhar Madras, 2 D. N. Sathyanarayana 2 1 Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore-560012, India 2 Department of Chemical Engineering, Indian Institute of Science, Bangalore-560012, India Received 4 June 2001; accepted 8 January 2002 Published online 15 August 2002 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/app.11032 ABSTRACT: The thermal degradation of three polymeric peroxides of styrene monomers with substituents in the para position was studied at various temperatures (65, 75, 85, and 95°C). A continuous distribution model was used to evalu- ate the rate coefficients for the random-chain and chain-end scission degradation from the evolution of molecular weight distributions with time. The activation energy determined from the temperature dependence of the rate coefficients was in the range 18 –22 kcal mol -1 . This result suggests that the thermal degradation of polyperoxide is controlled by the dissociation of the O—O bonds in the polymer backbone. The thermal stability for poly(p-methylstyrene peroxide) lies in between that of poly(p-tert-butylstyrene peroxide) (high- est) and poly(p-bromostyrene peroxide) (lowest). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 957–961, 2002 Key words: polyperoxide; thermal degradation; molecular weight distributions; activation energy INTRODUCTION Research on vinyl polyperoxides, which are a narrow but important class of polymers, is witnessing a re- naissance because of the unique physicochemical be- havior of these chemicals. 1 The polyperoxides, which are alternating copolymers of the vinyl monomers and oxygen, find importance as polymeric thermal-, photo-, and base-catalyzed initiators for vinyl mono- mers to synthesize homopolymers, block, and comblike copolymers. 2 Most polymers degrade endo- thermally, whereas vinyl polyperoxides are an unique class of polymers that pyrolyze exothermally. 3 Fur- ther, their unique properties, such as auto-pyrolyz- ability and auto-combustibility, make them potential candidates for specialized fuels. 3 The investigation of the decomposition kinetics of the initiator is essential to understand the kinetics of vinyl polymerization initiated by vinyl polyperoxides. Though the decomposition of common initiators, such as benzoyl peroxide, 2,2'-azobis(isobutyronitrile) (AIBN), etc., have been well studied, 4 no studies have been made on the chemical reactivity of polyperox- ides. This is the first systematic study of the thermal degradation in solution of three polymeric peroxides that can be used as initiators for vinyl polymerization. The polyperoxides are poly(p-methylstyrene perox- ide) (PPMSP), poly(p-bromostyrene peroxide) (PP- BrSP) and poly(p-tert-butylstyrene peroxide) (PPT- BSP), and each has have the following general struc- ture: where R is CH 3 , Br, and C(CH 3 ) 3 for PPMSP, PPBrSP, and PPTBSP, respectively. The synthesis and charac- terization of these polymers have been recently re- ported. 5 EXPERIMENTAL The monomers were freed from inhibitor by distilla- tion at reduced pressure. Other chemicals, such as azobisisobutyronitrile (AIBN), chloroform etc., were purified by distillation and filtration. All polyperoxides were prepared by oxidative polymerization as reported elsewhere 5 and character- ized by proton and carbon-13 nuclear magnetic reso- nance spectroscopy ( 1 H and 13 C NMR, respectively) recorded on a Bruker AC-F 200 MHz spectrometer in CDCl 3 and CH 2 Cl 2 (D 2 O external lock), respectively. Thermal decomposition of polyperoxides was stud- ied in toluene at 65, 75, 85, and 95°C. First, 100 mL of the polymer solution (2.5 g L -1 ) was placed in a 250-mL two-necked round-bottomed flask that was fitted with a reflux condenser to avoid loss of any volatile products. The flask was kept in an oil bath, and the solution was continuously stirred while the Correspondence to: G. Madras (giridhar@chemeng.iisc. ernet.in). Journal of Applied Polymer Science, Vol. 86, 957–961 (2002) © 2002 Wiley Periodicals, Inc.