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SYNOPSISA multistage melt polycondensation of bisphenol-A and diphenyl carbonate has been studied experimentally using LiOH -H 2 0 catalyst. The reaction process consists of batch and semibatch periods with different temperature and pressure conditions. It was observed that a small amount of diphenyl carbonate lost from the reaction mixture by vaporization had little effect on the molecular weight in the batch reaction period but the efficiency of subsequent low-pressure semibatch polycondensation was affected by the change in the mol ratio of the phenyl carbonate group to the hydroxyl end group. A molecular species model developed for the multistage process was used to analyze the kinetics of the polycondensation process. The composition of the reaction mixture was analyzed by HPLC and compared with model simulations. In particular, the effect of evaporative loss of diphenyl carbonate on the progress of reaction is discussed in detail.

Multiproton transfer in which more than one proton is transferred, either synchronously or asynchronously, is an important phenomenon in chemistry and biology. The hydrogen bonds with a very low barrier, leading to proton delocalization in the H-bond, are called "short strong" or "low-barrier" hydrogen bonds (SSHB or LBHB). It has recently been proposed that they may provide an unusually large amount of stabilization to high-energy enzyme-bound intermediates and/or transition states. In order to study the role of such hydrogen bonds in the multiproton transfer, we have performed high-level ab initio quantum mechanical calculations for the potential energy surface of the formamidine-formic acid complex. The double-proton transfer occurs asynchronously with a strongly hydrogen bonded intermediate, and the barrier height is 3.95 kcal mol -1 , which is about 5-12 kcal mol -1 lower than those of the concerted reactions in formamidine dimer and in formic acid dimer. The SSHB changes not only the barrier height but also the mechanism of the doubleproton transfer. The strength of SSHB depends on environments. We have calculated the solvent effect at the HF and the B3LYP levels using the self-consistent isodensity polarized continuum model (SCIPCM). The strength of SSHB is reduced rapidly with increasing dielectric constants. It is about 29 kcal mol -1 at ) 10. The barrier height is also reduced with increasing dielectric constants, which indicates that the proton transfer becomes faster in a polar medium. These results suggest that the SSHB contribute to the proton transfer greatly, and the energetics is changed very much with environment.

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