RATE OF IMIDIZATION OF POLYMERIZABLE REACTION MIXTURES - PMR-15

Imidization of PMR-15 was investigated using Fourier transform infrare d spectroscopy (FTIR) as a function of time and temperature. Imidizati on was performed at 65 less than or equal to T less than or equal to 3 00 degrees C for 3 less than or equal to t less than or equal to 150 m in. FTLR spectroscopy showed that imidization (measured by the changes in the imide carbonyl absorption at 1778 sm(-1)) increased with tempe rature and time. Imidization was found to be nearly completed in 2.5 h at 300 degrees C. Imidization of PMR-15 occurred in three stages: (i) the initial imidization region characterized by gradual reaction foll owed by (ii) a very rapid reaction region that spans about 0.5 h and ( iii) a final imidization region characterized by a gradual reaction an d spans about 2 h. An Avrami-type kinetic analysis was used to obtain the reaction order of 1.5 and 1.7 and the rate constant for imidizatio n of 1.3 x 10(-3) and 1.5 x 10(-3) min(-3/2) at 135 and 165 degrees C, respectively. Comparison with other kinetic models shows agreement at low conversions (p less than or equal to 15%). At high conversions of p > 20%, a second-order kinetic model seems to fit the data reasonabl y well in agreement with the observed 3/2 order. (C) 1997 John Wiley & Sons, Inc.