Pregledni rad
Calorimetric investigation of high conversion homopolymerization, graft polymerization and copolymerization reactions
Franjo RANOGAJEC
; Institut Ruđer Bošković, Zagreb
Sažetak
The calorimetry was used to follow the course of polymerization, graft polymerization and copolymerization reactions. Comparison with widely used point-by-point methods has been performed. Great advantages of calorimetry are direct and continuous measurement of the reaction rate independently from the physical state of reaction system and using only one sample for the whole conversion range. The accuracy and sensitivity achieved are better than those achieved by other methods. The gel-effect which is not pronounced in the spontaneous polymerization of styrene and could not be easily detected with other methods has been readily detected by calorimetry. Calorimetric investigation of grafting kinetics of styrene and methylmethacrylate on air-preirradiated polyethylene have shown that in low density polyethylene peroxides have the dominating role in the grafting reaction, while in high density polyethylene peroxy radicals have a significant role. The change of the viscosity of reaction medium in the course of grafting reaction as well as the structure of polymer influence the kinetics of reaction. The decay of active species in time can be followed by calorimetry.
The great advantage of calorimetry was demonstrated in investigation
of the copolymerization of electron donor and electron acceptor monomers. It was observed that the alternating copolymerization of a-methylstyrene with maleimides, regardless of ratio of comonomers in the feed, and the homopolymerization of maleimides are not simultaneous but are consecutive reactions. Homopolymerization starts only after the completion of alternating copolymerization when a-methylstyrene is exhausted. The end of copolymerization and start of homopolymerization was strictly detected by calorimetry. The conversion of alternating copolymer was close to theoretically expected. a-Methylstyrene as a strong electron donor forms stable charge transfer complexes with electron acceptors like maleimides. The competitive character of copolymerization and homopolymerization is a consequence of the participation of charge transfer complex in the copolymerization reaction.
Ključne riječi
alternating copolymerization; calorimetry; charge transfer complex; gel-effect; graft polymerization; high conversion polymerization
Hrčak ID:
36723
URI
Datum izdavanja:
29.4.2009.
Posjeta: 1.350 *