| dc.description.abstract | PMSP was synthesized by thermal oxidative polymerization of AMS at relatively lower temperatures with high yield. Thermal oxidative polymerization of AMS has been studied at different temperatures and pressures, and the kinetics of the process analyzed. A distinctive feature of the polymerization is its exhibition of ‘autoacceleration’ during the process. The decomposition of the formed polyperoxide (PMSP) to alkoxy radicals, which is further catalyzed by its own decomposition product, namely acetophenone, appears to be the main cause of autoacceleration. This behavior can be used to our advantage for using them as low-temperature initiators and curatives. Besides, polyperoxides are cheap materials containing 20-50% oxygen, which could be obtained readily from air.
The present investigation provides an elegant, hitherto new, method of oxidative polymerization at low temperatures. This could be christened as “oxygen transfer polymerization.” The unique multifaceted role of CoTPP Py complex as an initiator and oxygen supplier in the oxidative polymerization of vinyl monomers has been established. Since CoTPP Py mimics the role of hemoglobin or hemocyanin for transporting molecular O2 from the air to the polymerization site, we believe that such polymerization reactions could serve as a model for biological oxygenation processes.
The FTIR, NMR, 13C NMR of PAPSP and its analysis of the degradation products by GC-MS and NMR very well support a strictly alternating structure of PAPSP as given below. Being crystalline and powdery, besides having higher thermal and photo stability, PAPSP is perhaps the most eligible candidate for exploring its novel application potentials. Unlike other polyperoxides, which are generally stored in cold, PAPSP can be safely stored at room temperature. Besides, PAPSP is much less hazardous than simple organic peroxides. Since the helical structure is the most important secondary structure in biological macromolecules, any knowledge on the helical structure of synthetic polymers would be of considerable interest.
Whereas it is not possible to synthesize a copolymer of styrene and ?-phenyl styrene due to the steric effect and radical stability, their copolyperoxides can be prepared as it overcomes all the above drawbacks. Accordingly, we envisage that copolyperoxides involving monomers such as styrene & ?-methyl styrene, and maleic anhydride and stilbene could also be prepared. We have shown here that the conventional vinyl copolymerization models are also applicable to the oxidative copolymerization reactions.
In the case of the oxidative copolymerization of styrene and APS, although the composition and sequence distributions are explained from the Mayo-Lewis terminal model, it could not adequately explain the copolymerization rates. It was shown that the copolymerization rates are well explained from the penultimate model. The copolyperoxides of styrene and ?-phenyl styrene are white semi-crystalline powder. From the DSC thermograms, it appears that these copolyperoxides are fairly stable and hence they could be stored under normal storage conditions.
Thermal degradation in bulk, and photodegradation of polyperoxides in solution, produce the same products, but they give different orders in the rate of thermal and photodegradation, suggesting that the rate-controlling processes are different in these two modes of degradation. While thermal degradation basically depends upon the dissociation of the O-O bond, the photodegradation in solution is controlled by the stability of the bialkoxy radicals. The presence of crystalline domains, and the influence of its own degradation products on the thermal and photo degradation respectively, seems to be significant in imparting unusual thermal and photo stability to PAPSP. Polyperoxides are perhaps the unusual and rare class of polymers where such a behavior is observed, i.e., in spite of products of thermal and photo degradation being the same, their mechanisms are still very different. | |
