Chapter 21
Polycondensation of Carboxylic Acids and Carbinols in Heterogeneous Media Downloaded by UNIV OF CALIFORNIA SAN DIEGO on January 12, 2017 | http://pubs.acs.org Publication Date: May 5, 1996 | doi: 10.1021/bk-1996-0624.ch021
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Lei Jong and John C. Saam Michigan Molecular Institute, Midland, MI 48640-2696
Glycols and dicarboxylic acids condense in acidic water-in-oil (w/o) emulsion, microemulsion or solid-in-liquid (s/l) dispersion to form moderate molecular weight polyesters at temperatures substantially below those normally employed in direct polyesterifications. Removal of by -producedwater is unnecessary and effective catalysts are the strongly acidic oil-soluble surfactants or cation exchange resins. The formation of linear oligomeric polyesters having temperature sensitive reactive end groups demonstrate the absence of side reactions such as alcoholysis, acidolysis and transesterification. Controlling factors are elucidated with kinetic data based on a system intended to simulate alkyd resins. Industrial polyesterifications are typically melt processes where a viscous polymerizing mass of carboxylic acids and glycols is held at temperatures as high as 250°C to drive the polymerization and remove the by-produced water. Among the consequences are troublesome side reactions that can include etherification of hydroxyl groups, ene or Diels-Alder additions, decarboxylation, chain cleavage by ester pyrolysis, acidolysis, alcoholysis and ester redistributions (1 ),(2), (3). This leads to broadened molecular weight distributions^,), sporadic gelation and loss of functionality. Thus, while adequate for many materials, the process is unsuitable for preparing polyesters with ordered or temperature sensitive structures due to the extreme processing conditions. An unexplored alterative is to conduct esterifications in heterogeneous media so that the water produced forms in a hydrophobic phase. Transfer of water to a hydrophilic phase can then reduce the net free energy to favorably shift the equilibrium: Hydrophobic Phase
