Molecular weight measurements poly

Molecular Weight. Measurement of intrinsic viscosity in water is the most commonly used method to determine the molecular weight of poly(ethylene oxide) resins. However, there are several problems associated with these measurements (86,87). The dissolved polymer is susceptible to oxidative and shear degradation, which is accelerated by filtration or dialysis. If the solution is purified by centrifiigation, precipitation of the highest molecular weight polymers can occur and the presence of residual catalyst by-products, which remain as dispersed, insoluble soHds, further compHcates purification. 

Table XXIX.—Molecular Weights of Poly-(Methyl Methacrylate) Fractions from Sedimentation and Diffusion Measurements ...

Microspheres were monitored by scanning electron microscopy (SEM JEOL 35C), and their diameters were determined from the corresponding SEM microphotographs. Typically, ca. 500 particles in randomly sampled areas of microsphere specimens were analyzed. Molecular weight of poly(L-Lc) was determined by GPC. A system consisting of a LKB 2150 pump, Ultrastyragel 1,000, 500, 100, 100 columns, and Wyatt Optilab 903 interferometric refractometer was used for the measurements. GPC traces were analyzed by using calibration with narrow polydispersity < 1.15)... 

Du Pont Lucite 130 Poly (methyl methacrylate). This material was injection-molded in the same way as the polystyrene. No molecular weight measurements were made. 

The number-average molecular weights of poly(4-methyl-1 -pentene) s were measured in toluene at 37° C with a Hewlett-Packard membrane osmometer (model 503). 

The bulk polymerization rate of trideuterovinyl acetate was found to be 1.78 times that of vinyl acetate. In emulsion polymerization the same result was found. The molecular weight of poly(trideuterovinyl acetate) was 2.59 times that of poly(vinyl acetate). The overall isotope effect on chain transfer to monomer was calculated to be 3.04. Chain transfer was shown to be 94% on the vinyl hydrogens and 6% on the acetyl hydrogens. The measurement of polymerization rates in emulsion polymerization showed that the chain transfer on acetyl hydrogens is kineti-cally insignificant. 

Fig. 6. Reduced osmotic pressure vs. reduced concentration, plotted on a log-log scale, measured through osmometry by Noda el al. (1981). Symbols denote various molecular weights of poly(a-methylstyrene) in toluene at 25 C. The solid line has a slope of 1.32.

Perhaps the most striking evidence for the existence of helices in solution has been obtained from electron microscopy of poly-y-benzyl-L-glutamate and poly-L-glutamic acid (Hall and Doty, 1958). Micrographs of these polymers sprayed onto mica from solutions in which their helical properties are established, ethylene dichloride and water at pH 4.5, respectively, clearly show rods with diameters roughly those of a-helices and lengths of the same order as those expected for a-helices from molecular weight measurements in solution. The random coils of these polymers reveal no structure whatsoever upon similar visualization. 

Suwa T, Takehisa M, Machi S (1973) Melting and Crystallization Behavior of Poly(tetrafluoroethylene). New Method for Molecular Weight Measurement of Poly(tetrafluoroethylene) Using a Differential Scanning Calorimeter. J Appl Polymer Sci 17 3253-3257,... 

Graft copolymers of PMMA with poly(3-hydroxybutyrate) (PHB) segments as long side chains were prepared by the macromonomer method. PHB macromonomers were prepared from the esterification of oligomers with HEMA at their carboxylic acid end. Esterification products displayed low poly-dispersity indices ( 1.2) and a functionality over 83%, with a molecular weight measured by NMR of 2020 g mol". Using... 

Figure 4-16. Weight-average radii of gyration of poly(methyl methacrylates) in acetone (O), butylchloride ( ), and in the solid state (A), as a function of the weight-average molecular weights. Measurements at 20and 35.4°C (butylchloride). (After R. G. Kirste and W. Wunderlich.)...

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