Polystyrene dilute solutions

In section 2, the different theoretical models for local dynamics are briefly reviewed, and their connection with spectroscopic experiments is recalled. The Fluorescence Anisotropy Decay technique and the synchrotron source are presented in section 3. The fourth section is concerned with two typical examples. Using a series of experiments performed on polystyrene dilute solutions and another one performed on melt poly butadiene, we show how the different theoretical models can be told apart, and we present new information about the processes responsible of backbone rearrangement which has been obtained using the cyclosynchrotron LURE-ACO at Orsay (France). 

It is easy to measure the potential of this system and it has been found that membranes of polystyrene, linseed oil and a tung oil varnish yielded diffusion potentials of 43-53 mV, the dilute solution being always positive to the concentrated. Similar results have been obtained with films of nitrocellulose, cellulose acetate , alkyd resin and polyvinyl chloride . 

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. 

For concentrated solutions of polystyrene in n-butylbenzene, Graessley [40] has shown that the reduced viscosity r red Cnred=(r ( y)- rls)/(rlo rls)) can be represented on a master curve if it is plotted versus the reduced shear rate (3 ((3= y/ ycnt= y-A0). For semi-dilute solutions a perfect master curve is obtained if (3 is plotted versus a slope corrected for reduced viscosity, T corp as shown in Fig. 16. 

Sample Preparation. Calibration standards and test solutes were injected ai dilute solutions in the eluent. Polystyrene standards were 0.03 (w/v). Styrene, ODCB and normal hydrocarbons were 0.15 (w/v), except for dodecane and tridecane (0.65 ). Samples involving more complex matrices were prepared by crushing (if necessary), dissolving a weighed amount in the eluent, and filtering through a 0.45 Millex-SR filter cartridge (Millipore, Bedford, ma). 

Figure 4. UV/Visible absorbance spectra of (a) a dilute solution of lignin/polystyrene extract in toluene and (b) a saturated solution of mesy-lated lignin in toluene.

Stockmayer and Fixman (2) summarised the state of knowledge of the dilute solution properties of branched polymers in 1953. Dexheimer and co-workers (10) have given a comprehesive survey of the literature up to 1968, including the effects of branching (both short and long) on properties. Nagasawa and Fujimoto (11) have reviewed the results of work on rationally synthesised branched polymers (mostly polystyrenes) up to 1973, with particular reference to their viscoelastic properties. 

Fig. 6. Reciprocal diffusivity versus concentration in dilute solutions of linear polystyrenes in CC14> for three polymer molecular weights (indicated) (after Ref.4 >, with permission).

For polystyrene fractions in diethyl phthalate solution (30000average value of 1.6 x 10 18 ( 50%). In dilute solution e/36M is 1.27 x 10 18 for polystyrene (21). No systematic variations with concentration, molecular weight or temperature were apparent, the scatter of the data being mainly attributable to the experimental difficulties of the diffusion measurements. The value of Drj/cRT for an undiluted tagged fraction of polyfn-butyl acrylate) m pure polymer was found to be 2.8 x 10 18. The value of dilute solution data for other acrylate polymers (34). Thus, transport behavior, like the scattering experiments, supports random coil configuration in concentrated systems, with perhaps some small expansion beyond 6-dimensions. 

Orofino,T.A. Dilution-solution properties of polystyrene in 0-solvent media. II. An analysis of environmental effects. J. Chem Phys. 45,4310-4315 (1966). 

Berry,G.C. Thermodynamic and conformational properties of polystyrene. II. Intrinsic viscosity studies in dilute solutions of linear polystyrenes. J. Chem Phys. 46,1338-1352(1967). 

The rather unexpected properties described above seem to be peculiar to PVN, for none of the blends with polystyrene, poIy-4-vinylbiphenyl, and polyacenaphthylene contained significant amounts of amorphous PEO. The modulus curves for these systems are characteristic of blends of incompatible polymers. The photomicrograph in Figure 12 illustrates the different morphologies of PVB and PEO blends. The reason for the apparently different behavior for these polymers as compared with PVN is not yet understood. But there is strong evidence from dilute solution-studies that the conformational properties for these polymers differ markedly. 

For these measurements, temperature has been varied between 55 and 110° C. In this temperature range, the solvent viscosity changes by a factor three 4.7 to 1.5 cps). It is very improbable that a noticeable internal friction factor would change just by the same factor. Moreover, as has already been pointed out at the end of Section 5.2.2, the curves obtained by plotting cot2 c vs reduced shear stress fjN are practically coinciding for dilute solutions of cellulose tricarbanilate fractions with M S 500,000 and for anionic polystyrenes. So one can conclude that the internal friction of the thermodynamically stiff molecules of cellulose tricarbanilate must be rather low. 

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