Kinetics of radical polymerization of styrene at high concentration of diisopropyl dicarbonate

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Styrene was polymerized at 20° at high concentration of diisopropyl dicarbonate (DIPDC). When [DIPDC] = 0.55 mol] −1, transfer to DIPDC predominates at almost all stages of conversion. The average chain length (≤ 90) of the polymers is less than 300, the value at which polymer molecules entangle in undiluted polymer solution. Thus, the termination rate can be treated by considering only the free volume theory. The value of γv ∗ (γ = overlap factor and v ∗ = critical free volume to permit a segment to jump) is found to be 0.39, in good agreement with the value 0.37 estimated previously from data obtained under conditions such that the termination rate depends on both entanglement and free volume. These values may be reasonable, because they yield the magnitude of 10 −5 cm 2 sec −1 as the diffusion constant of monomer at low conversion. In spite of the absence of entanglement, the polymerization changes abruptly at about 70% conversion. Thus, the previous definition should be modified so that the onset of the gel effect is the point at which the termination rate changes abruptly as a result of the decrease of the free volume when the entanglement is absent, or at a critical chain length of polymers when entangling occurs.