S.G. Kulichikhin

Rheokinetics of free-radical polymerization

Abstract The authors elaborate theoretical concepts and obtain mathematical relations describing the increase in viscosity of reactive masses during bulk free-radical polymerization. The results obtained are confirmed experimentally for free-radical polymerization of alkyl methacrylates and styrene.

The effect of deformation on the phase separation in the polycapramide-caprolactam system

Abstract The phase state and phase transitions in melts and solutions of polycapramide (PCA) in caprolactam were studied by means of viscosimetry, optical interferometry, and polarization microscopy. It has been shown that the orientation of macromolecules of PCA in the flow zone results in the expansion of the area of immiscibility in the phase diagram. The isothermal crystallization was traced by the change of the length of the induction period by means of viscosimetry measurements. The dependence of the rate of isothermal crystallization on the rate of shear deformation is quite marked. The decrease of the rate of crystallization at high rates of shear is believed to be associated with the destruction of critical-size nuclei in a high velocity gradient stream.

Kinetics of polysulphone synthesis: nuclear magnetic resonance spectroscopy and rheological investigation

Abstract Time-dependent changes in monomers, dimers, end reactive groups and central links occurring in the synthesis of polysulphone derived from dichlorodiphenylsulphone and the sodium salt of diphenylolpropane in dilute solution in dimethylsulphoxide were investigated by nuclear magnetic resonance spectroscopy. On this basis, a kinetic model of the reaction was designed and elementary reaction constants, which appeared to be dependent on the chain length, were determined. Simultaneously, the time-dependent change in the viscosity of the reaction medium in concentrated solutions was measured and the results obtained were analysed by the rheokinetic method. A correlation was found to exist between the rheokinetic constants and the rate constants in sufficiently high-molecular-weight products determined by nuclear magnetic resonance spectroscopy.

Rheokinetics of radical polymerization

Abstract Kinetic mechanisms and rheological properties of polymerization systems were examined and concrete mathematical ratios describing the increase in the viscosity of reaction masses during radical polymerization, derived. The conclusions drawn were confirmed by experimental results of radical polymerization of methyl methacrylate and styrene available in the literature.

Influence of vitrification on defect formation during curing of epoxies

Defect formation in epoxies due to the chemical shrinkage was observed during isothermal cure over a wide cure temperature range. The observed defects were cohesive cracks and adhesional failures. The influence of the mutual position of the gel and the glass transition points on shrinkage-defect formation was examined. The different types of the cohesive defects can arise in the curing system in both the rubbery and glassy state. The type of defect formed was found to be determined by the relaxational state of the polymer during defect formation. The dependence of the glass transition temperature upon the degree of polymerization is reported for the epoxy/amine polymer system investigated. Experimental parameters of polymer resistance to chemical shrinkage cracking were measured for all investigated cure temperatures.

Rheology and macrokinetics of the hardening of an epoxy oligomer by dicyandiamide

Abstract A rheological method has been used to investigate the macrokinetics of hardening of an epoxy resin based on the diglycidyl ether of bisphenol A with dicyandiamide. The rheokinetic model proposed for the process may be used to substantiate the autocatalytic nature of the hardening reaction, and to find the numerical values of constants forming part of the kinetic equation.

Viscometric investigation of dodecalactam polymerization

Abstract The theoretical concepts developed and mathematical formulae derived in this investigation describe the increase in the viscosity of the reaction mass in ionic bulk polymerization processes, while allowing for the homo- or heterogeneous character of the reaction. Conclusions formed have been verified experimentally, taking as an example the activated anionic polymerization of dodecalactam.

Rheological characteristics of cured melamine-formaldehyde resins☆

Abstract The rheokinetics of the curing of melamine-formaldehyde resins in the melt and in aqueous solutions of various concentrations are studied. It is shown that phase separation of the cured composition and the formation of a microgel structure preceed the gel formation point. The structural inhomogeneity formed during the initial stages of the reaction has a decisive effect on the kinetics of the changes in rheological characteristics of the system during all stages of curing.

Kinetics and rheology of curing of phenylmethylsiloxane oligomers

Abstract Using a complex of rheological methods, the authors have investigated the process of curing of a polyphenlmethsiloxane oligomer. The possibility of solving the back kinetic problem has been shown and a kinetic equation is obtained describing change in the mechanical characteristics of the oligomer during curing.

Viscometric study of some structural features of modified polyethylene terephthalate

Abstract A study has been made of viscosity properties of the dilute solutions and melts of PETP synthesized in the presence of PEO oligomers with epoxy endgroups. It was found that the intrinsic viscosity decreases and there is a simultaneous increase in MW, and that the viscosity of the melt is reduced and the Huggins constant increases, evidencing the appearance of branching in PETP macromolecules (∼1 branch per macromolecule) when 0·41–1·17 mole % of the modifier is introduced into the reaction system.