Polymers molecular weight analysis

R382 J. U. Izunobi and C. L. Higginbotham, Polymer Molecular Weight Analysis by H Nuclear Magnetic Resonance Spectroscopy , J. Chem. Educ., [online computer file], 2011, 88, 1098. 

Figure 1 Is a flow sheet showing some significant aspects of the Iterative analysis. The first step In the program Is to Input data for about 50 physical, chemical and kinetic properties of the reactants. Each loop of this analysis Is conducted at a specified solution temperature T K. Some of the variables computed In each loop are the monomer conversion, polymer concentration, monomer and polymer volume fractions, effective polymer molecular weight, cumulative number average molecular weight, cumulative weight average molecular weight, solution viscosity, polymerization rate, ratio of polymerization rates between the current and previous steps, the total pressure and the partial pressures of the monomer, the solvent, and the nitrogen.

If the preceding analysis of hydrodynamic effects of the polymer molecule is valid, K should be a constant independent both of the polymer molecular weight and of the solvent. It may, however, vary somewhat with the temperature inasmuch as the unperturbed molecular extension rl/M may change with temperature, for it will be recalled that rl is modified by hindrances to free rotation the effects of which will, in general, be temperature-dependent. Equations (26), (27), and (10) will be shown to suffice for the general treatment of intrinsic viscosities. 

OS 61] ]R 20] ]P 44] The polymer molecular-weight distribution of a static mixer-based processing, which was determined both by UV and refractive index analysis. 

Gel permeation chromatograms were generated from a Waters Associates, Inc. GPC equipped with a refractive index detector. The following operating conditions were employed mobile phase, THF flow rate 1 ml/min., columns ICP, 10, 500, 100 A . Sample concentrations were prepared at 0.2% (w/w) a 100 microliter aliquot was used for molecular weight analysis. Standard polystyrene samples (Polymer Laboratories, Inc.) were used to create a calibration curve. 

The detailed treatment of the molecular weight analysis of polymers is left to other texts. We should be aware that there are two types of molecular weights, number average and weight average. 

A more sensitive viscometer than the drop-time glass capillary method is also needed in size exclusion chromatography (SEC) such as the gel permeation chromatographic (GPC) analysis of polymer molecular weight distribution (MWD). In an SEC system, a concentration detector is commonly used for providing the weight concentration profile of the polymer elution curve. 

The number average molecular weight analysis of the polymers obtained, gives values about twice those calculated from the amount of Bz2 Mg reacted (Table 1). 

Frechel and coworkers reported the hydrosilylation polymerization of the AB2 and AB3 carbosiloxy monomers 13, 14 and 15184-187. After polymerization in bulk, soluble polymers were obtained in 55-69% yields. Molecular weight analysis revealed the... 

Hydrosilylation is not the only reaction available for the preparation of hyperbranched poly(carbosiloxanes). In a recent report, Weber and Londergan described the preparation of hyperbranched poly(carbosiloxanes) by ruthenium-catalyzed addition of ortho C—H bonds across terminal double bonds (Scheme 26)190. Depending on reaction conditions, soluble or insoluble polymers could be obtained. NMR endgroup molecular weight analysis of the soluble polymer gave a value of 12,200. The structure of the polymer was established with XH, 13C and 29Si NMR analysis. 

Jaacks and Franzmann30 studied the polymerization of this monomer by triphenyl-phosphine solely with the aim of demonstrating the existence of macroz wit ter ions. To facilitate end group analysis, a high ratio of initiator to monomer was used to give relatively low polymer molecular weight. The UV spectrum of the polymer obtained was identical to that of the model compound D. 

The values of Kic and Gic, determined at various temperatures for all the SAPA samples, are given in Tables 4 and 5, respectively. Data analysis will be carried out in three successive stages. First, some general features will be extracted. Then, emphasis will be put on the sensitivity of Kk and G to polymer molecular weight. And finally, the influence on toughness of the details of polymer chemical stmcture will be discussed. 

If the values of A, 6, and Dj are available, the molecular weight of a polymer can be directly determined from its retention time using Eq. (3). If Dj is not available, one may use a calibration curve [log DlDj) versus log M] constructed with a series of narrow polystyrene standards of known molecular weights. For the molecular-weight analysis of an unknown, the DlDj value of the sample is first calculated from its measured retention time, and then the molecular weight is determined from the calibration curve. 

The study by Czerwinski and coworkers,79 described earlier, included an analysis of the molecular weight of soluble poly(3-pentylthiophene) by GPC. An estimate of the polymer molecular weight was made using polystyrene standards, and the average... 

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