Star Polymers - Dynamic Rheological and NMR studies
Abstract
Polybutadiene star polymers, of nominal functionality 3, 4 8 and 12, all with arm lengths of approxiamately 30 000g mol-1, have been synthesized. Dynamic mechanical studies have been carried out using parallel-plate rheometry at various temperatures, and the data frequency-temperature shifted to produce master-curves. Fits to the Ball-McLeish constraint release theory indicate an effective entanglement molecular weight somewhat higher than the literature value for a linear polymer. This has been interpreted by considering a dilution of constraints effect caused by the Rouse diffusion of the ends, leading to a predicted modified entanglement molecular weight similar to that found experimentally. An extension of the theoretical fits to include the high-frequency Rouse-mode spectrum shows a divergence between theory and experiment which is indicative of the onset of the glass transition. ^2H NMR carried out on segmentally deuterated polybatadiene stars probes the its dynamics on a molecular level, thus providing a more stringent test for the modified theoretical model.
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 1997
- Bibcode:
- 1997APS..MAR.C3008A