Interpenetrating polymer networks (IPNs) are mixtures of two cross-linked polymers formed as a result of chemical reactions of in situ synthesis of components from single-phase initial mixtures. As a rule, due to the incompatibility of the components, a physical process of phase separation takes place with the formation of heterogeneous systems with insignificant interphase adhesion, which can have a negative effect on the physicochemical properties. To increase the compatibility of the components and to stabilize the systems, compatibilizers are introduced into the reaction mixtures. In this work the kinetics of the in situ formation of the components of polyurethane/poly(methyl methacrylate) interpenetrating polymer networks and the phase separation induced by chemical reactions in the presence of methyl methacrylate polymerization oligoazoinitiators in the reaction mixture have been studied. Oligoazoinitiators contained fragments of a polyurethane chain also. The process of phase separation that accompanies chemical reactions takes place in two stages. The nucleation mechanism is preferred at the first stage; the spinodal mechanism is preferred at the second one. It has been shown that the introduction of oligoazoinitiators of various chemical natures can control the process of IPNs formation due to the formation of block copolymers during synthesis, which are compatibilizers of the mixture. They slow down the phase separation process and favor the formation of a finer IPNs structure. The formation of the different phase-separated morphology of the obtained IPNs is confirmed by the results of optical microscopy: the dimensions of phase-separated structures in the IPNs with oligoazoinitiators are smaller then in the IPNs without them.
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