Oligomers interfacial synthesis

A knowledge of the chemistry of bisphenol-A oligomer carbonate synthesis is useful in the interpretation of GPC data. Bisphenol-A carbonate oligomers can be prepared by reaction of bisphenol-A with phosgene in the presence of an acid acceptor. The reaction can be conducted interfacially (6), in homogeneous pyridine solution (7), or by merely passing phosgene into an alkaline solution of bisphenol-A (8). The chemical reactions that occur in each of these systems are complicated and consist of multiple and competitive reactions. 

The interfacial synthesis of bisphenol-A carbonate oligomers is conducted by passing phosgene into an agitated, two-phase mixture of a water-insoluble organic solvent and an alkaline solution of bisphenol-A. Reactions 1-4 shown on p. 260 illustrate some of the reactions believed to occur in the interfacial system. 

Due to the low reaction temperature and the use of chain terminator, the molecular weight distribution in interfacial synthesis is kinetically controlled and may be far from thermodynamic equilibrium. In two parametric studies Mills [179] and Munjal [180] have tried to model the full molecular weight distribution of polycarbonate. Varying the ratio of mass transfer/kinetic rates, they show how mass transfer limitations can lead to a higher polydispersity or a higher oligomer content. 

Amine-terminated siloxane oligomers have also been utilized in the synthesis of various siloxane-amide and siloxane-imide copolymers, High molecular weight siloxane-amide copolymers have been synthesized by the solution or interfacial co-polymerization of siloxane oligomers with sebacoyl chloride or terephthaloyl chloride respectively 1S5,165). In some reactions diamine chain extenders have also been utilized. Thermal and dynamic mechanical characterization of these copolymers have shown the formation of multiphase systems160). Compression molded films displayed very good elastomeric properties. 

Synthesis of piperazine-terminated oligomers as prepolymers for interfacial membrane formation was also examined.46 48 Excess piperazine was reacted with di- and triacyl chlorides in an inert solvent such as 1,2-dichloroethane. The resulting amine-terminated polyamide oligomers had low solubility in the solvent system and precipitated. This served to limit the degree of polymerization of the oligomer. Even so, a portion of the product was insoluble in water and was filtered out during preparation of the aqueous oligomeric amine solution for the interfacial reaction step. 

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