| 초록 |
Living polymerization is one in which the average molecular weight can easily be controlled. No termination is involved in the usual sense in the polymerization but rather the termination is controlled by a chain-transfer agent and/or a catalyst, thereby leading to the controllability of the average molecular weight. More transfer agent (catalyst) is needed for lower average molecular weight. In general, the chain-transfer agent is more effective than the catalyst. Theoretical analysis of such living polymerization with chain-transfer agents has been made1,6 to examine the nature of the resulting molecular weight distribution. The results are, however, for the polymerization in a batch reactor. Characteristic of the molecular weight distribution resulting from a batch reactor is the existence of a bimodal molecular weight distribution4,5, i.e., a combination of two distinct molecular weight distribution. One is due to living polymer and the other due to dead polymer or end-capped polymer. Although batch reactors are typically used in experiments, continuous reactors are also used in practice such as continuous stirred tank reactors (CSTR). In this paper, it is shown that the use of a CSTR always leads to a monomodal molecualr weight distribution and thus to a monomodal polydispersity index (PDI). It is desirable in any polymerization including the living polymerization with chain-transfer agents that the desired average molecular weight be obtained, that the PDI be minimized, and that the conversion of monomer and thus the yield be maximized. It has been revealed (Benedicto et al. 1995) that such objectives can be realized only for a narrow range of the kinetic parameters for the living polymerization in batch reactors. In this paper, it is shown theoretically that the average molecular weight and the yield can be completely controlled when the living polymerization is carried out in CSTRs.
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