Polydispersity melt-phase samples

The polydispersity of melt-phase samples is generally lower than that of solid-state samples. Gel permeation chromatography (GPC) analysis of samples prepared from the solid-state showed polydispersity values in the range of 2.57 to 2.84 compared to 2.27 to 2.49 for melt samples [107], The higher polydispersity of solid-state samples can largely be explained by the non-uniformity in the average molecular weight across the pellet radius caused by a SSP reaction rate that is diffusion controlled [11],... 

Presence of small amounts of isotropic material within the mesophase can have important practical implications in processing of polydisperse samples. We have observed, for example, that upon fiber extrusion from the nematic melt, optimum mechanical strength is not developed until extrusion temperatures are below the l/N transition temperature of the shortest components. Similarly, measurement of order parameter shows that presence of a minor isotropic component deters optimum overall alignment until a temperature some 25-30 C below the transition to a "homogeneous nematic phase, as observed by microscopy. ... 

Several experiments performed with l,4-didodecyl-2,5-dipropynylbenzene at 150 °C with trifluoroeresol as cocatalyst furnished didodecyl-PPE 13b in excellent isolated yields (95-98%) with very high molecular weights (P 200-640, GPC vs. polystyrene) and polydispersities ranging from 3-7. All samples of 13b display melting points around 130-160°C and feature homeotropically aligned smectic liquid crystalline phases. ... 

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