420 para-Substituted Poly(styrene peroxide)s: Synthesis, Characterization, Thermal Reactivities, and Chain Dynamics Studies in Solution Priyadarsi De, D. N. Sathyanarayana* Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560012, India Fax: +91-080-3600683/3601552; E-mail: dns@ipc.iisc.ernet.in Keywords: copolymerization; kinetics; NMR; polystyrene; transitions; Introduction In 1977, Cais and Bovey reported a study of the chain flex- ibility and molecular dynamics of poly(styrene peroxide) (PSP). [1] Polyperoxides had previously received attention only with regard to their intermediacy in the inhibition by oxygen of vinyl polymerization. [2, 3] Recently, studies on polymeric peroxides have been successful in providing a thermochemical basis for the unusual exothermic thermal degradation of these polymers. [4, 5] It has resulted in detect- ing a unique phenomenon of autopyrolysis in PSP, which has made it a candidate for specialized fuels of the future. [6] The property of autopyrolysis exhibited by these polymers is due to their highly exothermic heats of degra- dation. Apart from this their technological importance as polymeric thermal [7] and photo-initiators [8] for vinyl mono- mers to synthesize homopolymers and block copolymers, and their applications as curators in coating and molding are well known. [9] An evaluation of the heats of degradation of different polymeric peroxides is difficult for lack of data. The number of polyperoxides reported so far is only about two dozen, [10] and except for very few, they have hardly been characterized. In view of their potential as highly exothermically degrading materials it is desirable to study polyperoxides. By a comparison of the available heat of degradation of PSP [4] and poly(methyl methacrylate per- oxide) (PMMAP), [5] (the former being higher) it was of interest to synthesize new polyperoxides from aromatic monomers. Hence para-substituted styrenes were chosen as monomers for the preparation of polyperoxides. Studies on the dynamics of polymer chains have attracted considerable interest because chain dynamics play an important role in determining the macroscopic properties of the polymeric systems. Among the various techniques employed for the study of chain dynamics, nuclear magnetic resonance has proved to be a powerful Full Paper: The synthesis and spectroscopic characteriza- tion of three polymeric peroxides of styrene monomers with substituents in the para position are discussed. NMR spectroscopy revealed the alternating copolymer structure with labile peroxy bonds (1O1O1) in their main chain. The thermal reactivity of the polymers was studied by dif- ferential scanning calorimetry and thermogravimetry. The measured heat of degradation of these polymers is nearly the same as that of poly(styrene peroxide). The mechan- ism of the primary exothermic degradation has been sub- stantiated by thermochemical calculations. The chain dynamics studies of these polyperoxides in terms of 13 C spin-lattice relaxation time (T 1 ) have been carried out to understand their main chain flexibility. The temperature dependence of correlation time has been utilized for the determination of the activation energy for the overall seg- mental motion and internal group rotation. Their flexibil- ity in terms of glass transition temperature (T g ) have been examined. The flexibility trend observed in solution paral- lels that in the bulk. Macromol. Chem. Phys. 2002, 203, No. 2 i WILEY-VCH Verlag GmbH, 69469 Weinheim 2002 1022-1352/2002/0201–0420$17.50+.50/0 Macromol. Chem. Phys. 2002, 203, 420–426