SPECIAL FEATURES OF NETWORK FORMATION BY CHAIN CROSS-LINKING COPOLYMERIZATION

Special features of free-radical crosslinking copolymerizations and the structure of the resulting products have been reviewed. Characteristic is the effect of spatial correlations on the apparent reactivity of pendant double bonds. These correlations make the apparent reactivity in the course of copolymerization to increase (cyclization) and decrease (steric hindrances). At intermediate and higher concentrations of the crosslinker, compact structures are formed which are internally crosslinked. Only pendant double bonds in the peripheral layer are able to take part in polymerization reactions whereas the internal ones cannot react. The state of theoretical simulations of this structure growth is discussed with a special emphasis on the development of the kinetic (coagulation) network formation theories so that the above mentioned features may be taken into account. Also, the important role of the presence of a diluent during polymerization is discussed. It can result in a change of network chain conformations necessary for networks exhibiting volume phase transitions. Alternatively, it can induce liquid-gel phase separations resulting in inhomogeneous networks having a variety of morphologies.