Viscosities, dilute solution poly

We report here the results of our recent studies of poly(alkyl/arylphosphazenes) with particular emphasis on the following areas (1) the overall scope of, and recent improvements in, the condensation polymerization method (2) the characterization of a representative series of these polymers by dilute solution techniques (viscosity, membrane osmometry, light scattering, and size exclusion chromatography), thermal analysis (TGA and DSC), NMR spectroscopy, and X-ray diffraction (3) the preparation and preliminary thermolysis reactions of new, functionalized phosphoranimine monomers and (4) the mechanism of the polymerization reaction. 

Characterization. The series of poly(alkyl/arylphosphazenes) (1-6) was studied by a variety of standard dilute solution techniques including viscosity measurements, membrane os-... 

In concluding this section, we should touch upon phase boundary concentration data for poly(p-benzamide) dimethylacetamide + 4% LiCl [89], poly(p-phenylene terephthalamide) (PPTA Kevlar)-sulfuric acid [90], and (hydroxy-propyl)cellulose-dichloroacetic acid solutions [91]. Although not included in Figs. 7 and 8, they show appreciable downward deviations from the prediction by the scaled particle theory for the wormlike hard spherocylinder. Arpin and Strazielle [30] found a negative concentration dependence of the reduced viscosity for PPTA in dilute Solution of sulfuric acid, as often reported on polyelectrolyte systems. Therefore, the deviation of the Ci data for PPTA in sulfuric acid from the scaled particle theory may be attributed to the electrostatic interaction. For the other two systems too, the low C] values may be due to the protonation of the polymer, because the solvents of these systems are very polar. 

For undiluted poly (propylene) oxide 2025 Baur and STOCKMAYER (13) observed rmaJ (experimental) to be 7.9 x 10 seconds at — 20° C. They found this to be consistent with the RB theory provided that the friction factor is proportional to the viscosity of the undiluted polymer. In going to dilute solution the friction factor changes by a factor of 10s, resulting in an enormous change in the major relaxation time predicted by the RB equation. 

The viscosity behavior of poly[(a-carboxymethyl)ethyl isocyanide] may be studied in neutral organic solvents. The concentration dependence of its reduced specific viscosity in 1,2-dichloroethane is shown in Fig. 11. A linear dependence indicates that the coefficients of higher concentration terms of the usual virial equations are negligibly small—a case which should be found with molecules, such as stiff rods, that give few intermolecular entanglements in dilute solution. 

Physical Measurements. Molecular Weight. Intrinsic viscosities were determined using dilute solution viscometry (Cannon-Ubbelohde viscometers). For the poly (methyl methacrylate) polymer the following empirical expressions were used to obtain molecular weights (4) ... 

C 6 Chinai, S. N. Poly-n-hexyl methacrylate. IV. Dilute solution properties by viscosity and light scattering. J. Polymer Sci. 25, 413 (1957). 

FIG. 16.24 Extensional viscosity data obtained from a spin-line rheometer for very dilute aqueous poly (acryl amide) (1175 grade) solutions, as specified. From Walters and Jones (1988,1989). Courtesy Elsevier Science Publishers. 

Noncovalent self-assembly of complementary pairs of homoditopic building blocks (AA/BB-type), such as bis(crown ether) 125 and diammonium salt 126, has afforded well-defined supramolecular oligomeric/polymeric assemblies <2003JA3522>. In dilute solutions, entropy favored the formation of the cyclic dimer, whereas high equimolar concentration (>0.5 M) of the two components led almost exclusively to linear species aggregation, as revealed by H NMR analysis and viscosity measurements. Closely related linear poly[3]pseudorotaxane supramolecular arrays have also been prepared from cylindrical bis(crown ether) 127 and bisparaquat derivative 128 <2005CC1696>. 

Furthermore, if what we want to determine is the frictional forces between a single polymer molecule and the solvent, then we need to make the measurements in dilute solution, so that there is no contribution from poly-mer/polymer interactions. In fact, just as in osmometry and light scattering, we measure the relative viscosity over a range of dilute solution concentrations and extrapolate to zero concentration. 

Figure 3.14 Curves of intrinsic relative shear viscosity versus dimensionless shear rate for dilute solutions of poly(a-methylstyrene) with molecular weights of (1) 690,000, (2) 1,240,000, (3) 1,460,000, (4) 1,820,000, (5) 7,500,000, and (6) 13,600,000 in toluene (a good solvent), and (7) 13,600,000 in decalin (a theta solvent). (Reprinted with permission from Noda et al.. Journal of Physical Chemistry 72 2890 Copyright 1968, American Chemical Society.)...

Figure 6.17 Normalized intrinsic viscosity [r ]/[)7]o for a dilute solution of poly(y-benzyl-L-glutamate) (PBLG) = 208,000) in m-cresol. The line is a calculation for the rigid-dumbbell model, with the relaxation time t = lj6Dro adjusted to the value 10- sec to obtain a fit. The stress tensor for a suspension of rigid dumbbells is given by Eq. (6-36) with Cstr replaced by k T/Dro-(From Bird et al. 1987 data from Yang 1958, Dynamics of Polymeric Liquids, VoL 2, Copyright 1987. Reprinted by permission of John Wiley Sons, Inc.)...

Figure 6.20 (a) Viscosity of solution of poly(y-benzyl-L-glutamate) (PBLG molecular weight 231,000), in m-cresol as a function of shear rate at 29 C for various mass percentages ranging from dilute ( 0.31%) to semidilute (0.31-2.5%) to concentrated isotropic (5-9.5%). The different symbols and lines refer to data taken on different instruments, (b) Zero-shear viscosity as a function of concentration, (reprinted with permission from Mead and Larson, Macromolecules 23 2524. Copyright 1990 American Chemical Society.)... 

One-shot polyether foams were studied, using a variety of catalysts. The formula contained 100 parts by weight of poly(oxypropylene)triol of 3000 M.W., 38 parts of 80 20-TDI, 2.9 of water, 0.3 of 4-dimethyl-aminopyridine, 0.5 of lV,iV-dimethylbenzylamine, varying amounts of metal catalysts, and 0.1 part of X-520 siloxaneoxyalkylene copolymer. All of the gas was evolved from these systems within 60 sec after mixing. Viscosity measurements were not satisfactory due to fracture of the polymeric phase. Analysis of the reaction mixture at the end of 55 sec reaction time indicated the relative rate of formation of various products, as indicated in Table 22. The importance of selecting the proper catalyst to avoid undesirable side reactions is readily apparent. The results shown in Table 22 indicate that both tin catalysts promote the isocyanate/water reaction more than the isocyanate/hydroxyl reaction in the system studied. This is unusual, since other reports, though often of dilute solution studies, have shown the tin catalysts to promote the isocyanate/ hydroxyl reaction more [145,147,196]. 

Hadjichristidis and coworkers [230] studied the hydrodynamic behavior, in dilute solution, of miktoarm stars of the types A2B and A2B2 where A, B = PS, PI, and PBD in solvents good for both segments or theta for one of the arms and good for the others. Analysis of the results suggests that the experimentally determined values of intrinsic viscosity, [q], viscometric radius, Rv, and Rh for the copolymers are higher than the ones calculated from homopolymer star data. The phenomenon was perceived as an indication of repulsive interactions between A and B chains, which tend to increase the sizes of the individual chains and of the star molecule as a whole [230]. A similar conclusion was reached from SEC experiments on polystyrene-poly-f-butylacrylate miktoarm stars with equal number of branches of the two components [243]. The phenomenon, in this case, was more pronounced as the molecular weight of the branches increased. 

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