Effect of hexamethylphosphorictriamide on the “living” radical polymerization initiated by aged Cr2+ BPO
- 1 January 1979
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases
- Vol. 75, 1821-1829
- https://doi.org/10.1039/f19797501821
Abstract
The “living” radical polymerizations with aged Cr2++ benzoyl peroxide (BPO) are carried out in N,N′-dimethylformamide(DMF)+hexamethylphosphorictriamide(HMPA) mixed solvent. The initial rate of polymerization (Rp) in the mixed solvent is about three times that in DMF. The linear plots of conversion against time and the number average degree of polymerization ( text-decoration:overline P n) against conversion plots for the polymerization pass through the origin and for this reason the “living” polymerization can be treated quantitatively. It is found that the rate constants of the propagation step, calculated from the combination of Rp and text-decoration:overline P n using certain assumptions, are very small compared with those for a conventional free radical polymerization. The rate of polymerization at 30°C or below decreases with time during prolonged polymerization. In contrast a steep increase in text-decoration:overline P n is observed in the region of high monomer conversion. The molecular weight distribution curves of polymer obtained at 20°C have a single peak which shifts with conversion. However, these curves become bimodal at high conversion. On the other hand, typical dead-end polymerizations occur at high temperatures (50 and 60°C), i.e., the polymerization stops completely before reaching ≈ 10% conversion. text-decoration:overline P n values of polymer obtained at a high temperature are relatively larger than those obtained at a low temperature and increase with the polymerization time even after the polymerization has stopped. These results are explained in terms of recombinations of growing polymer radicals, i.e., the complexed polymer radicals (P·--- CrIII) which are propagating species in the “living” polymerization dissociate to free radicals and CrIII.Keywords
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