| Autor: |
Cayuela, Julien, Bounor-Legaré, Véronique, Cassagnau, Philippe, Michel, Alain |
| Zdroj: |
Macromolecules; February 2006, Vol. 39 Issue: 4 p1338-1346, 9p |
| Abstrakt: |
Ring-opening polymerization of ε-caprolactone initiated by titanium n-propoxide Ti(O-n-Pr)4 was compared to the one initiated by titanium phenoxide or Ti(OPh)4. Polymerization was confirmed to proceed via a coordination−insertion mechanism for both initiators after end groups analysis by 1H and 13C NMR (nuclear magnetic resonance) spectroscopy. Bulk polymerization at 100 °C and with a M0/I0 (monomer/initiator ratio) equal to 300 was studied and compared with both initiators. The polymerization with Ti(OPh)4 exhibits a slower kinetic of reaction and the polymer synthesized an higher number-average molecular weight and higher polydispersity than with Ti(OPr)4. These results are consistent with evolution of the average number of active aryloxide groups per initiator (%@mt;sys@%%@ob@%%@ital@%N%@rsf@%%@sb@%aag%@sbx@%%@obx@%%@mx@%) during polymerization for this initiator. Indeed, %@mt;sys@%%@ob@%%@ital@%N%@rsf@%%@sb@%aag%@sbx@%%@obx@%%@mx@% determined by 1H NMR increases gradually during the polymerization to 2 for around 70% conversion and then decreases at the end of the polymerization and even over the time required for total conversion. This decrease of %@mt;sys@%%@ob@%%@ital@%N%@rsf@%%@sb@%aag%@sbx@%%@obx@%%@mx@% at the end of the conversion may be explained by important transesterification reactions with phenoxyl end groups of the polymer, which lead to the formation of larger poly(ε-caprolactone) chains. That is consistent with the increase in the number-average molecular weight of the polymer beyond the end of the conversion. The rheological study also confirms this result. |
| Databáze: |
Supplemental Index |
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