Polystyrene viscosity number

The crystallization of the acetone-insoluble polystyrene is completed by boiling for 2 h in freshly distilled butanone it is then allowed to stand overnight at room temperature and finally filtered and dried in vacuum at 60 °C. Yield of crystalline isotactic polystyrene 95-100% of the acetone insoluble portion.The crystalline melting range and the density see Sect. 2.3.4.1) are determined, as is also the limiting viscosity number in toluene at 20 °C. 

Fig. 23. Polymerization of monomers in masticating polystyrene and polymethyl methacrylate. Curves 1-6 1 ml methacrylic acid, styrene, methyl methacrylate, ethyl acrylate, acrylonitrile, and vinyl acetate, respectively, in 3 g polystyrene. Curves 7-12 2 ml methacrylic acid, methyl methacrylate, acrylonitrile, ethyl acrylate, styrene, and vinyl acetate, respectively, in 3g polymethyl methacrylate. The limiting viscosity numbers for points along Curves 2 and 3...

A universal calibration curve was established by plotting the product of the limiting viscosity numbers and molecular weight, Mw[iy], vs. the elution volume, EV, for a variety of characterized polymers. The major usefulness of the universal calibration curve was to validate individual molecular-weight values and to provide extended molecular-weight calibration at the ends of the calibration curve where fractions of narrow dispersion of the polymer being analyzed are not available. The calibration curve was monitored daily with polystyrene fractions certified by Pressure Chemicals. The relationship between the polyethylene fractions and polystyrene fractions was determined using the universal calibration curve. 

Haranov et al. (1986, 1987) have proposed a way of measuring the limiting viscosity number at a finite polymer concentration [q]c and shown that, as the polymer concentration in a good solvent (polystyrene in bronioform, 25 C) increases, [ ]c gradually diminishes to the value of [ /) in the theta solvent (polystyrene in decaline, 25 C). 

Figure 5.13 Log-log plots of limiting viscosity number [T ] for atactic polystyrene solutions against the weight-average molecular weight Q), Benzene at 25 and 30°C , cyclohexane at 34.5°C (0 temperature). From ref. 38, reprinted by permission of John Wiley Sons Inc.

Schulz GV, Baumann H. Thermodynamic behavior, expansion coefficient, and viscosity number of polystyrene in tetrahydrofuran. Makromol Chem 1968 114 122-138. 

The molar masses of a series of homodisperse polystyrene samples were measured by osmosis. The limiting viscosity number [17] was found for each sample in toluene at 30°C using an Ubbelohde viscometer and the results are given below. 

It should be noted that polystyrene with a number average molecular weight of 50000 has a Tg only about 2°C less than would be expected of a polystyrene of infinitely high molecular weight. Hence increasing the molecular weight beyond this point in order to raise the Tg would not be very effective and at the same time it would lead to large increases in melt viscosity. 

A better combination of fiber and polymer is achieved by an impregnation of [44] the reinforcing fabrics with polymer matrixes compatible with the polymer. Polymer solutions [40,45] or dispersions [46] of ]ow viscosity are used for this purpose. For a number of interesting polymers, the lack of solvents limits the use of the method of impregnation [44]. When cellulose fibers are impregnated with a bytyl benzyl phthalate plasticized polyvinylchloride (PVC) dispersion, excellent partitions can be achieved in polystyrene (PS). This significantly lowers the viscosity of the compound and the plasticator and results in cosolvent action for both PS and PVC [46]. 

The most widely used molecular weight characterization method has been GPC, which separates compounds based on hydrodynamic volume. State-of-the-art GPC instruments are equipped with a concentration detector (e.g., differential refractometer, UV, and/or IR) in combination with viscosity or light scattering. A viscosity detector provides in-line solution viscosity data at each elution volume, which in combination with a concentration measurement can be converted to specific viscosity. Since the polymer concentration at each elution volume is quite dilute, the specific viscosity is considered a reasonable approximation for the dilute solution s intrinsic viscosity. The plot of log[r]]M versus elution volume (where [) ] is the intrinsic viscosity) provides a universal calibration curve from which absolute molecular weights of a variety of polymers can be obtained. Unfortunately, many reported analyses for phenolic oligomers and resins are simply based on polystyrene standards and only provide relative molecular weights instead of absolute numbers. 

Heat transfer can, of course, be increased by increasing the agitator speed. An increase in speed by 10 will increase the relative heat transfer by 10. The relative power input, however, will increase by 10In viscous systems, therefore, one rapidly reaches the speed of maximum net heat removal beyond which the power input into the batch increases faster than the rate of heat removal out of the batch. In polymerization systems, the practical optimum will be significantly below this speed. The relative decrease in heat transfer coefficient for anchor and turbine agitated systems is shown in Fig. 9 as a function of conversion in polystyrene this was calculated from the previous viscosity relationships. Note that the relative heat transfer coefficient falls off less rapidly with the anchor than with the turbine. The relative heat transfer coefficient falls off very little for the anchor at low Reynolds numbers however, this means a relatively small decrease in ah already low heat transfer coefficient in the laminar region. In the regions where a turbine is effective,... 

Studies of polystyrene standards in THF solvent are not uncommon. however, bothersome discrepancies still exist in the literature and in practice. For example, the published Mar 1<-Houw i nk parameters are in wide disagreement il. The purpose of this work is to examine a large number of PS standards from multiple suppliers, covering a wide range of molecular weights. T -,e intrinsic viscosities and GPC retention volumes have been measured and used independently to correlate and crosscheck the molecular weights provided by the suppliers. 

In several cases the melt viscosity of a series of lightly-branched polymers has been determined as a function of MW, and compared with that of linear polymers, and it has been found or may be deduced from the published data that there is a cross-over molecular weight, below which the branched polymer is less viscous, but above which it more viscous, than the linear polymer of equal MW. This behaviour is observed with some comb-shaped polystyrenes (35) and poly(vinyl acetate)s (59, 89), star polybutadienes (57, 58, 123), and randomly-branched polyethylenes (56,61). Jackson has found (141) that if the ratio ZJZC of the number of chain atoms at the cross-over point, Zx, to the number at the kink in the log 0 — logM curve, Zc, [as given in Ref. (52)], is plotted against nb, the number of branches, a reasonable straight line is obtained, as in Fig. 5.1. 

Tager and co-workers (51) have invoked bundle structures to explain correlations between the viscosities of concentrated polymer solutions and the thermodynamic interactions between polymer and solvent. They note, for example, that solutions of polystyrene in decalin (a poor solvent) have higher viscosities than in ethyl benzene (a good solvent) at the same concentration, and quote a number of other examples. Such results are attributed to the ability of good solvents to break up the bundle structure the bundles presumably persist in poor solvents and give rise to a higher viscosity. It seems possible that such behavior could also be explained, at least in part, by the effects of solvent on free volume (see Section 5). Berry and Fox have found, for example, that concentrated solution data on polyvinyl acetate in solvents erf quite different thermodynamic interaction could be reduced satisfactorily by free volume considerations alone (16). Differences due to solvent which remain after correction for free volume... 

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