Global ETD Search

1	Molecular Weight Limit Identified for the Synthesis of Externally Initiated Poly(3-hexylthiophenes) and Further Macrocyclic Constructions Wong, Michael 19 March 2013 (has links) Externally initiated o-tolyl initiated poly(3-hexylthiophene) (P3HT) was synthesized according to Grignard metathesis polymerization at varying chain length to compare number average molecular weights (Mn) obtained by gel permeation chromatography (GPC) and 1H NMR end group analysis. The extent of overestimation by GPC (1.3) was determined to be lower than previously reported for low Mn polymers. However, an apparent GPC quantification limit was observed as NMR Mn correlated well to predicted results. Static light scattering studies on high Mn polymers provided evidence that the true molecular weight was more similar to GPC-derived Mn. Despite nearly 100% external initiation efficiency, at a certain Mn limit new uninitiated chains may be synthesized. It is suggested that the synthesis of externally initiated P3HT should be limited to Mn below 40 kDa to ensure fully externally initiated chains. A proposal for the synthesis of externally initiated macrocyclic P3HT will also be discussed. poly(3-hexylthiophene) external initiation gel permeation chromatography end group analysis size exclusion chromatography conjugated polymers molecular weight limit Grignard metathesis polymerization 0495
2	Molecular Weight Limit Identified for the Synthesis of Externally Initiated Poly(3-hexylthiophenes) and Further Macrocyclic Constructions Wong, Michael 19 March 2013 (has links) Externally initiated o-tolyl initiated poly(3-hexylthiophene) (P3HT) was synthesized according to Grignard metathesis polymerization at varying chain length to compare number average molecular weights (Mn) obtained by gel permeation chromatography (GPC) and 1H NMR end group analysis. The extent of overestimation by GPC (1.3) was determined to be lower than previously reported for low Mn polymers. However, an apparent GPC quantification limit was observed as NMR Mn correlated well to predicted results. Static light scattering studies on high Mn polymers provided evidence that the true molecular weight was more similar to GPC-derived Mn. Despite nearly 100% external initiation efficiency, at a certain Mn limit new uninitiated chains may be synthesized. It is suggested that the synthesis of externally initiated P3HT should be limited to Mn below 40 kDa to ensure fully externally initiated chains. A proposal for the synthesis of externally initiated macrocyclic P3HT will also be discussed. poly(3-hexylthiophene) external initiation gel permeation chromatography end group analysis size exclusion chromatography conjugated polymers molecular weight limit Grignard metathesis polymerization 0495
3	Characterization and Control of an Electrospinning Process Liu, Kaiyi 18 June 2013 (has links) No description available. Materials Science Nanotechnology Polymers electrospinning polymer liquid jet illumination high speed video stereo pictures bending frequency handedness coil mergence Brewster's angle polarized glint glint trace birefringence multiple jet Taylor cone external initiation jet motion

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