H. Kricheldorf, Gert Schwarz
Apr 1, 1984
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0
Influential Citations
25
Citations
Journal
Polymer
Abstract
Abstract The condensation of 4-hydroxybenzoic acid by means of various carboxylic acid anhydrides, acid chlorides and diphenylcarbonate has been investigated. All condensations were conducted in ‘one-pot procedures’. The average degrees of polymerization ( DP ) were determined by means of 1H nuclear magnetic resonance (n.m.r.) spectroscopic end-group analyses. The bulk condensation of 4-hydroxybenzoic acid by means of acetic anhydride at temperatures between 320° and 350°C was found to be the simplest and least expensive procedure. Yields between 97 and 99% and DP up to 300 were obtained in this way. Bulk condensations of purified acetoxybenzoic acid or condensations of 4-hydroxybenzoic acid with acetic anhydride in an inert solvent gave similar yields and DP . Also, the bulk condensations of 3,5-dimethyl-4-hydroxybenzoic acid, 3-methoxy-4-hydroxybenzoic acid, 3-chloro-4-hydroxybenzoic acid, 3,5-dichloro-4-hydroxybenzoic acid and 3,5-dibromo-4-hydroxybenzoic acid by means of acetic anhydride gave yields above 90%. However, the DP 's varied greatly with the nature of the substituents. ‘One-pot procedures’ using a variety of phosphorus derivatives as condensing reagents did not yield pure polyesters. The differential scanning calorimetry (d.s.c.) curves of the substituted poly(4-hydroxybenzoate)s do not show any endotherm, although X-ray diffraction measurements indicate a high degree of crystallinity. The thermogravimetric analyses demonstrate that the thermal stability depends largely on the synthetic procedure.