Many controlled polymerization processes proceed via intermittent activation (i.e., by a series of activation/deactivation cycles), and this interrupted growth process may affect not only polydispersities but also (co)polymer microstructure. The computer modeling indicates that, in systems with intermittent and selective activation, rates of consumption of comonomers may be different from conventional systems, and this can result in different copolymer composition, microstructure, and different apparent reactivity ratios. The effect of several parameters such as concentration of the involved reagents, rate constants of homopropagation, cross-propagation, activation, and deactivation on the copolymer composition was studied. Deviations from the conventional systems are predicted for systems such as controlled/living radical polymerization, atom transfer radical polymerization, group transfer radical polymerization, "living" carbocationic polymerization, and other systems with intermittent activation. Use of chiral activators/deactivators may convert stereoselective polymerization to stereoelective polymerization even in the presence of nonselective initiators. The topology of polymers formed by self-condensing vinyl polymerization (branch distribution) may also depend on the dynamics of exchange reactions.