Hyperbranched Cyclic and Multicyclic Polymers by a2+b4 Polycondensations

At first, theoretical aspects of a(2)+b(4) polycondensations (meaning polycondensations of difunctional and tetrafunctional monomers) are discussed and compared with what is known about a(2)+b(3) polycondensations. The following review of experimental results is subdivided into three sections. First, syntheses of hyper-branched polyethers and polyesters by polycondensations based on equimolar feed ratios will be reported. Second, kinetically controlled (i.e., irreversible) syntheses of multicyclic polymers using equifunctional feed ratios (i.e., a(2)/b(4) ratios of 2:1) will be described. In the third section, syntheses of multicyclic polyrners via thermodynamically controlled (reversible) a(2)+b(4) polycondensations will be discussed. Characteristic for these polycondensations are again equifunctional feed ratios and metal alkoxides as a(2) or b(4) monomers, which catalyze rapid equilibration reactions. Finally, potential applications of the new polymers will shortly be mentioned. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1971-1987, 2009