Polystyrene comparisons

Table VIII. Recovery of Waxes from Polystyrene Comparison of SFE vs. Soxhlet Extraction...

We will focus on one experimental study here. Monovoukas and Cast studied polystyrene particles witli a = 61 nm in potassium chloride solutions [86]. They obtained a very good agreement between tlieir observations and tire predicted Yukawa phase diagram (see figure C2.6.9). In order to make tire comparison tliey rescaled the particle charges according to Alexander et al [43] (see also [82]). At high electrolyte concentrations, tire particle interactions tend to hard-sphere behaviour (see section C2.6.4) and tire phase transition shifts to volume fractions around 0.5 [88]. 

Whilst it is inevitable that polypropylene will be compared more frequently with polyethylene than with any other polymer its use as an injection moulding material also necessitates comparison with polystyrene and related products, cellulose acetate and cellulose acetate-butyrate, each of which has a similar rigidity. When comparisons are made it is also necessary to distinguish between conventional homopolymers and the block copolymers. A somewhat crude comparison between these different polymers is attempted in Table 11.7 but further details should be sought out from the appropriate chapters dealing with the other materials. 

Figure 6.3 shows a comparison of elution patterns of standard polystyrene between a linear-type column and a standard-type column. Because of the high linearity of its calibration curve, the linear series has improved the efficiency of oligomer domain separation. 

FIGURE 6.17 Comparison of calibration curves using various standard samples. Column Shodex GPC KD-802.S, 8 mm i.d. X 300 mm. Eluent DMF. Sample O, Polystyrene. A, PEG. 

FIGURE 11.4 Comparison of chromatograms obtained on conventional (A) and solvent-efficient Styragel columns (B). In each case the column bank was a bank of Styragel HR 0.5, HR I, HR 2, and HR 3 columns at 3S°C with THF as the solvent. The sample is a mixture of polystyrene standards. With proper care and optimized instrumentation, good resolution can be obtained with solvent-efficient Styragel columns. (Courtesy of Waters Corp.)... 

The ISO method prescribes polystyrene standards with tetrahydrofuran as the eluent, but this equation can also be used with other narrow distribution standards, provided the same elution solvent and the same standards are used for a comparison. Further, the ISO method requires the result to be greater than 6 for one decade of the molar mass. Because calibration curves are usually not linear, this decade should lie nearly symmetrically around the peak maxima of the samples in question. The required value of 6 is easy to fulfill, as results of 10 or more are usual with modern columns. If so-named linear or mixed... 

FIGURE 22.4 Comparison of OTHdC experiments on polystyrenes in THF ( ) and in diethyl malonate (x). Column diameter 2.68 fim. (Reprinted from ]. Chromatogr. Lib. Sen, 56, 106, Copyright 1995, with permission from Elsevier Science.)... 

Table 5 Comparison of Properties of Lactide Polymers with Polystyrene and Poly(vinyl chloride) ...

Thermogravimetric data indicate that the structure of a polymer affects stability in a neutral environment (HI). A polymer such as Teflon, with carbon-carbon bonds which are (by comparison) easily broken, and with strong carbon-fluorine bonds, is quite stable thermally. However, polyethylene, also with carbon-carbon bonds but containing carbon-hydrogen bonds which are broken relatively easily in comparison with the carbon-fluorine bond, is less stable than Teflon. In turn, polyethylene is more stable than polypropylene. This difference in stability is probably caused by tertiary carbon-hydrogen bonds in polypropylene. Polypropylene is more stable than polyisobutylene or polystyrene, which decompose principally by unzipping mechanism. 

El Fray, M., Puskas, J.E., Tomkins, M., and Altstadt, V. Evaluation of the Eatigue Properties of a Novel Polyisobutylene-Polystyrene Thermoplastic Elastomer in Comparison with other Rubbery Biomaterials. Paper 76, ACS Rubber Division, 166th Technical Meeting, October 5-8, Columbus, OH, 2004. Puskas, J.E. and Chen, Y. Novel Thermoplastic Elastomers for Biomedical Applications. Paper 40, ACS Rubber Division, 163nd Technical Meeting, April 28-30, San Erancisco, CA, 2003. 

A general method has been developed for the estimation of model parameters from experimental observations when the model relating the parameters and input variables to the output responses is a Monte Carlo simulation. The method provides point estimates as well as joint probability regions of the parameters. In comparison to methods based on analytical models, this approach can prove to be more flexible and gives the investigator a more quantitative insight into the effects of parameter values on the model. The parameter estimation technique has been applied to three examples in polymer science, all of which concern sequence distributions in polymer chains. The first is the estimation of binary reactivity ratios for the terminal or Mayo-Lewis copolymerization model from both composition and sequence distribution data. Next a procedure for discriminating between the penultimate and the terminal copolymerization models on the basis of sequence distribution data is described. Finally, the estimation of a parameter required to model the epimerization of isotactic polystyrene is discussed. 

Table XXVIII.—Comparison of Light Scattering with Osmotic Molecular Weights for Polystyrene Fractions (Brice, Halwer, and Speiser )...

Fig. 113.—Comparison of observed entropies of dilution (points and solid lines with results calculated for ASi according to Eq. (28) (broken line). Data for polydimethyl-siloxane, M =3850, in benzene, A (Newing ), obtained from measured activities and calorimetric heats of dilution. Entropies for polystyrene (Bawn et in methyl ethyl ketone,, and in toluene, O, were calculated from the temperature coefficient of the activity. The smoothed results for benzene solutions of rubber, represented by the solid curve without points, were obtained similarly.

Figure 7. Comparison of polystyrene calibration curves for HDC and porous Fractosil systems (eluant ionic strength, 7.29/wM AM A (O) HDC ( 2) Fractosil)...

Figure 5. GPC and absolute Mw comparison (polystyrene standards) ( see Figure...

In Ref. [107] the procedure above has been employed for the measurement of the molar mass distribution of a broad molecular weight polystyrene, obtained by radical polymerization with ethylacetate as solvent. The scaling parameters for this polystyrene in this marginal solvent have been determined to be a 2.8 x 10-4 cm2/s and b 0.52 [107]. The upper curve in Figure 17 shows the resulting molar mass distribution in comparison with the one obtained by SEC. 

A comparison of the crystal structures, NMR and IR spectra of various Yb(ll) and calcium complexes demonstrated that they were strikingly similar, a reflection of the nearly identical radii of Ybz+ and Ca2+.25 Nevertheless, the dibenzylytterbium(ll) analog of 127 produces polystyrene of high syndiotacticity (r= 94.9%, rr= 90.0%), whereas 127 itself yields only atactic or slightly syndiotactic polymer. A difference in Yb-L and Ca-L bond strengths, despite their similar lengths, has been proposed as the source of the difference.315... 

---