Kinetics of Heterogeneous Polycondensations

What is known as interfacial polycondensation is the best known heterogeneous polycondensation. In interfacial polycondensation two monomers react at the phase boundary between two immiscible solvents. The polycondensate that is produced mostly precipitates in the form of a 

To date, interfacial polycondensation has almost exclusively utilized the Schotten-Baumann reaction. In this reaction, a diacyl chloride in, for example, chloroform reacts with a diol or diamine in, for example, water according to 

Since the greater basicity of the diamine causes the acyl chloride to react more quickly with the amine than with water, only relatively small amounts of acyl chloride are hydrolyzed to acid. A noncondensing base, e.g., pyridine, is often added to bind the HCl produced in the reaction. 

In interfacial polycondensation, the hydrated diamine diffuses through the continuously thickening film and reacts with the diacyl chloride on the organic solvent side. The reaction is obviously diffusion controlled since the diffusion rate is an order of magnitude smaller than the reaction rate. The growth rate of the film dLjdt decreases as the thickness of the film increases, i.e., dLjdt = k cJL). The proportionality constant k includes the diffusion coefficient of the diamine in the film. 

Water droplets accumulate with time on the organic solvent side, and these increase in size with time. The transported water hydrolyzes COCl groups  

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