Reduced-viscosity measurements

Fig. 13. Reduced viscosity w. polymer concentration and dynamic elastic modulus vs. polymer concentration relationships. Left reduced viscosity measured at a shear rate of 3.4 sec. ...

Infrared spectra (IR) were taken on a Nicolet 7199 FT-IR. Thermal analyses were obtained on a DuPont 1090 thermal analyzer. Thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) were performed at lO C/min. heating rates under N2. Reduced viscosity measurements (4) were made at 40-C in OC Ubbelohde viscometers. Values reported are the average of at least two measurements, which were within 0.2% of each other. Reduced viscosity is defined as follows ... 

Polymerization of these bisdichloromaleimides was carried by nucleophilic displacement of chlorine with 9,9-bis(p-aminophenyl)fluorene. The resulting polymers were characterized by IR spectroscopy and reduced viscosity measurements. Anaerobic char yields of these polymers at 800°C ranged from 55-60%. In presence of air, a complete loss of weight was observed between 600-650 C. Thermal cross-linking of these polymers was also investigated. 

Dilute Polymer Solutions. The measurement of dilute solution viscosities of polymers is widely used for polymer characterization. Very low concentrations reduce intermolecular interactions and allow measurement of polymer—solvent interactions. These measurements ate usually made in capillary viscometers, some of which have provisions for direct dilution of the polymer solution. The key viscosity parameter for polymer characterization is the limiting viscosity number or intrinsic viscosity, [Tj]. It is calculated by extrapolation of the viscosity number (reduced viscosity) or the logarithmic viscosity number (inherent viscosity) to zero concentration. 

The viscosities were measured with an Ubbelohde Cannon 75-L, 655 viscometer. Formic acid was chosen as the solvent for the viscosity measurement because the polymer (VII) showed very low or no solubility in other common solvents. In a salt free solution, a plot of the reduced viscosity against the concentration of the polymer showed polyelectrolytic behavior, that is, the reduced viscosity ri sp/c increased with dilution (Figure 4). This plot passed through a maximum at 0.25 g/dL indicating that the expansion of the polyions reached an upper limit, and the effects observed on further dilution merely reflected the decreasing interference between the expanded polyions. 

Experimental considerations For the measurement typically several concentrations are prepared and the specific viscosity t]sp or reduced viscosity f)red — r jr 0 are extrapolated to zero concentration. In the literature three different approaches are used to obtain the intrinsic viscosity and, with known [f)]-M relation, the molar mass. 

Fig. 56. Dependence of Mwof the microgels on the polymer yield in the anionic polymerization of EDMA in toluene by n-BuLi [254] (see Figure 53 caption for the reaction conditions). Reduced viscosity vs concentration of microgels a) Composition (mol %) N,N -methyl-enebisacrylamide (55%), methacrylamide (33%), methacrylic acid (2%), methacrylamido acetaldehyd-dimethylacetal (10%),measured at 20 °C in water, b) Composition (mol %) 1,4-DVB (35%), propenic acid amide-2-methyl-N-(4-methyl-2-butyl-l,3-dioxolane prepared by emulsion copolymerization and measured in dimethylformamide.

Polvcondensation of DHTN with dibromomethane under phase transfer conditions. The polycondensation of DHTN [13.13g, 0.080 mole] with 32mL dibromomethane was carried out in the presence of tetrabutyl ammonium bromide [2.48g or 0.008 mole] and 160mL 60 wt% aqueous KOH solution with vigorous stirring at room temperature for 24h. The polymer was precipitated in methanol and purified by reprecipitation from THF solution into distilled water to afford 13.51 g (94.8%) of the desired polyether which exhibits a reduced viscosity of 0.27 dL/g [measured at 30°C in DMF at a concentration of 0.5g/dL]. The polymer had an IR spectrum with a prominent C-O-C peak at 1210 cm". The NMR spectrum of the polyether [CDC13] showed peaks atff 1.7-2.5 (C-CH2-CH2-C), 4.6-5.3 (0-CH2-0), and 7.3-8.0 (aromatic). 

The phase angle changes with frequency and this is shown in Figure 4.7. As the frequency increases the sample becomes more elastic. Thus the phase difference between the stress and the strain reduces. There is an important feature that we can obtain from the dynamic response of a viscoelastic model and that is the dynamic viscosity. In oscillatory flow there is an analogue to the viscosity measured in continuous shear flow. We can illustrate this by considering the relationship between the stress and the strain. This defines the complex modulus ... 

Table III. Measured Relative Molecular Weight, Passed Through GPC and Reduced Viscosities. Estimated Intrinsic Viscosities of Polymers Columns in Benzene ...

Viscosity measurements on a series of CPSs having the same polymerization degree but different carboxyl contents have provided clear evidence for self-association in solutions. Figure 30 shows the reduced viscosities in butanone and THF (2 mg/ml) at 30.0 °C as a function of carboxyl content. When the carboxyl content is below 3.4 mol%, the reduced viscosity decreases as carboxyl groups are introduced into the CPS. This behavior reflects the constriction of polymer... 

Gamma radiation can be used with macroscopic amounts of polymer. This is particularly welcome when polymers are not compatible with the GPC technique. Larger samples can be characterized by viscosity changes, usually measured in dilute solutions. All that is needed is a suitable solvent. If the Mark-Houwink parameters are known, it is possible to calculate viscosity-average molecular weight, Mv, from dilute solution viscosities. However, even the raw viscosity-concentration data in terms of the reduced viscosity may be enough to indicate the sensitivity of a given polymer in qualitative terms. The reduced viscosity at concentrations c is isp/c where t]sp — (solution viscosity — solvent viscosity)/solvent viscosity. 

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