A Kinetic Study of the Polymerization of Pure meta-Divinylbenzene and Pure para-Divinylbenzene

摘要

The kinetics of the polymerization of pure meta-divinylbenzene (DVB) and pure para-divinylbenzene at 70 deg C have been studied in the presence of toluene and 2-ethylhexanoic acid. The apparent rate constant ratios (k_p/k_t)~(1/2) for these systems have been calculated. meta-Divinylbenzene polymerizes at a higher rate than the paraisomer in both toluene and 2-EHA, and the polymerization rates of meta-DVB and para-DVB before the gel point were both higher in the presence of 2-EHA than in toluene. The monomer conversion at the visual gel point is higher for para-DVB than for meta-DVB. The gel point has also been determined indirectly by size exclusion chromatography, and these results are consistent with the gel times observed visually. The conversion of pendant vinyl groups during the polymerization has been determined by bromination. It is found that the homopolymers of poly(para-DVB) have a substantially higher content of pendant vinyl groups than poly(meta-DVB) both during and at the end of the polymerization. The molecular weight distribution (MWD) prior to gelation has been determined by size exclusion chromatography (SEC). Weight average ((M-bar)_w) and number average ((M-bar)_n) molecular weight prior to gelation and of the sol fractions after gelation have also been measured by SEC. There are larger fractions of high molecular weight polymers prior to gelation, when the polymerization was run in the presence of toluene, than in 2-EHA, mainly due to the differences in solvating power of the two diluents.