Experimental polystyrene samples

In figure 1 we present the experimental and calculated mK values of the copolymer poly(styrene-co-p-bromostyrene). From this study (3) we were able to show unequivocally that the tacticity of this polystyrene sample is pr — 0.55, where pr is the probability of racemic dyad replication. 

Since the creep rate of polystyrene samples during irradiation is relatively constant, this value minus the creep rate just before irradiation can be used as a measure of the increase in creep rate owing to the irradiation. This increase in creep rate, or incremental creep rate, can then be related to the other experimental variables. 

Like S-FFF, Th-FFF is one of the oldest FFF techniques [29,193]. Thompson described a basic experimental arrangement and a successful fractionation of polystyrene (PS) standards with narrow distribution of molar masses [29,193] followed by studies on some fundamental theoretical and experimental aspects of Th-FFF [34,194]. The theory of the retention of macromolecules in Th-FFF was advanced later [ 195]. The dependence of retention on the molar mass of polystyrene samples was proven experimentally [109,194], since D is a linear function of M of the form D=AxM b. It was possible to find a linear dependence of X values on M 0 5 [194]. Analogous experimental results, confirming theoretical relationships for retention in Th-FFF, were also reported for other polymers [196,197]. In a critical review of polymer analysis by Th-FFF, Martin and Rey-naud [197] specified the requirements for successful separation. 

Since for each experimental point a new specimen is required, the data in Fig. 17 were obtained with a commercial polystyrene sample, available in larger quantities than the anionic and deuterated polymers used for the SANS experiments. The curves in Fig. 17 suggest the following expression for the tensile stress ... 

Experimental evidence of this hypothesis is given in Fig. 18. Two monodisperse polystyrene samples (N = 50 and P = 5) are blended with different concentrations and the complex shear modulus is measured in a wide range of fi quendes allowing us to scan the relaxation of the two components. The reduced imaginaiy part of the complex viscosity ( n" = G /o)) shows, at intermediate concentrations, two maxima connected to the relaxation time of each component (x=l/tOmax)- The most striking point is the large decrease of the relaxation time of the longest N-chains (increase of (Omax ) ... 

NMR Measurements. In all cases, ten percent solutions of thepoly-styrene samples dissolved in a 9 1 1,2,4-trichlorobenzenetnitro-benzene-ds mixture were used for the NMR studies. 75 MHz 13C-NMR 1H-decoupled spectra of the epimerized polystyrene samples were recorded at 150-160° using a Bruker WH-300 NMR Spectrometer. A 70° pulse width, an acquisition time of 0.82 seconds with a 16K data size, and a pulse delay of 0.1 second were employed. The number of transients collected varied from 3000 to 10,000 and the data were processed with a line broadening of 0.8-1.0 Hz. A Tx study done on the aromatic C-l and aliphatic carbon resonances of polystyrene at 200°C, using a Varian XL-400 NMR Spectrometer, revealed that within experimental error the individual components of these resonance patterns had the same relaxation time(35). This indicates that the conditions described above are appropriate for obtaining resonance patterns that could be analyzed quantitatively. 

For instance, by the described method one can determine the MWD of polymers which are produced under kinetic conditions for which a Poisson distribution is expected. That is the case in anionic polymerization when only contact on pairs are present and when the dissociation is suppressed by addition of counter ions. Moreover, the reaction time must be equal for all growing molecules. These conditions are realized for the polystyrene samples shown in Figure 9 (10, II, 12). The curves are calculated for the corresponding Poisson distributions, and the points are the experimental values. For a Poisson distribution, the nonuniformity is given by the equation... 

Equation (9.19) accurately describes the observed characteristics associated with the transformation of the G t) line shape with changing molecular weight. To illustrate the capability of the theory in describing these characteristics, the relaxation modulus curves calculated from Eq. (9.19) at Mw/Me = 10, 20 and 40, all with the polydispersity of Mm/M = 1.05, are shown in Fig. 9.4 for comparison with the experimental results, as shown in Fig. 4.6. In Chapter 10, in terms of the theory, quantitative analyses of the relaxation modulus curves of a series of nearly monodisperse polystyrene samples will be described in detail. 

Fig. 15.1 Comparison of the s (AT)/sq values (with Sq = 1,500) of polystyrene samples A(o), B(0) and C(D obtained by analyzing the J(t) line shapes A by matching the calculated and experimental steady-state compliance values) with the diffusion enhancement factors /r(AT) of OTP ( isothermal desorption A NMR) as a function of AT = T — Tg. The solid line is calculated from the modified VTF equation (Elq. (14.13)) which best fits the s (AT)/sq results of the three polystyrene samples collectively. The dashed line represents the curve calculated from the modified VTF equation best fitting the fj, AT) data of OTP.

Fig. 17.7 Comparison of the equilibrium-simulated G(t) curve (o) for the twenty-bead Praenkel chain with Hp = 400kT and the predicted experimental curve (solid line) for an ideally monodisperse polystyrene sample with the molecular weight equivalent to N = 20 also shown are the points (+) representing the relaxation times of the 19 Rouse normal modes.

Effect of the temperature modulation period on the total and reversing heat flow signals in a polystyrene sample. Experimental parameters sample mass 9.5 mg. / = 2 K/min, p = 25, 50, 100 s and x = b.4 K... 

The molecular weight distributions of the oligomers were determined by means of gel permeation chromatography. These were done by Dr. Julian F. Johnson who was then at the Chevron Research Company. A Waters Analytical G.P.C. Model 300 was used. A combination of one 100,000 R, one 15,000 A, one 100 R, and one 45 R column was used. The columns were calibrated with normal alkanes and monodisperse polystyrenes. Samples were dissolved in toluene to obtain 60 mg/100 ml concentration they were eluted with toluene at a flow rate of 1 ml per minute at room temperature. The results were machine-computed to obtain relative molecular weights. From these, absolute values of the molecular weights were obtained by means of scaling factors calculated from experimental viscosity or vapor pressure osmometry data. The calibration curve is shown... 

In order to estimate the experimental error in the VPO method, Kamide et al. repeatedly determined Mn values of atactic polystyrene samples and cellulose diacetate samples with their apparatus [18]. They obtained an value for a polystyrene sample of 7.22 x 10" within an accuracy of 0.54 x 10" at the 95% significance level for polystyrene, and that for a cellulose diacetate sample, with total degree of substitution 2.46, of 3.7 x 10" 0.36 x 10" at the same significance level as polystyrene. The VPO method is reproducible to 7-9% or better, which is of the same order of magnitude as that observed in membrane osmometry (MO) or GPC. Of course, the relative experimental error will differ greatly depending on the nature of the solvent (especially the vapour pressure and the heat of condensation), and the temperature. 

The fractionation of each resultant broadly distributed hyperbranched polystyrene sample by precipitation led to a set of perfect narrowly distributed hyperbranched polystyrene chains with uniform subchains but different overall molar masses. We have, for the first time, experimentally elucidated their formation kinetics and established scaUng laws between their size and overall mass. Armed with such prepared hyperbranched chains, we will be able to further study correlations between their microscopic structures and macroscopic properties. In this section, we wiU focus on the formation kinetics section, and the fractal properties of these perfect hyperbranched polystyrenes will be discussed in the next chapter. 

The influence of polymer architecture on intermolecular interactions in dilute solutions was investigated by membrane osmometry in toluene (good solvent for polystyrene), cyclohexane (theta or 0 solvent), and methylcyclohexane (poor solvent Striolo et al., 2001). The osmotic second virial coefficient (B22) measured for arborescent polystyrene in toluene was lower than for homologous linear polymers, as expected due to their smaller Rg. In a 0 solvent (cyclohexane), branching lowered the 0 temperature from 34.5 °C (linear homolog) to 32.2 °C (GO polymer). The 0 temperature for the GO polystyrene sample in methylcyclohexane was likewise lowered to 36 °C, as compared to values estimated between 60 and 70 °C for linear polystyrene samples. The experimental osmotic pressure data were successfully fitted with a molecular-thermodynamic equation suitable for colloids, indicating that the behavior of arborescent polystyrene molecules in dilute solution corresponds to a perturbed (weakly interacting or interpenetrable) hard sphere. 

McIntyre et al. (74) report to have found an experimental relation between the ratio q>d(pth critical and threshold concentrations and the 6-value of their polystyrene samples. Fig. 52 gives some q>d th (b) curves, calculated on the basis of Eq. (1) for different types of fetribution. It is dear that the unique rdation mentioned by McIntyre etal. implies that their samples must have had distributions of similar shape. After calibration, one might in such a case use q>dq>m for estimating 6. 

The purpose of the present communication is to provide experimental support for the idea that Tp (TTg) are all issued from a unique relaxation kinetics which is primary responsible for the Tg effect The suggestion that Tp is a precursor of Tg is not new 2.4 the idea that T// behaves like a classical kinetic transition, i.e., like a sort of Tg is not new eitfaer. > Frenkel in the USSR suggests that the 7 transition merges with the Tg transition on a log frequency vs. 1/7 plot at a temperature which corresponds to 7//. These observations all concur separately with our own attempt to reconcile into a unique relaxation mechanism the 7 Tg, and Tn "transitions." Atactic polystyrene is chosen here for the experimental data because the physical properties relevant to our discussion are well-documented in the literature for this particular polymer, representative of the class of amorphous polymers. Furthermore, TSC (Thermally Stimulated Current) and DSC results on rheomolded polystyrene samples can be systematically compared since the influence of the rheomolding parameters (frequency of vibration during molding, amplitude of vibration, and post treatment armealing effects) are simultaneously studied and analyzed by both techniques. " ... 

For a sample of polystyrene in benzene, experimental values of Kcj/R are entered in the body of Table 10.2. The values are placed at the intersection of rows and columns labeled c and 9, respectively. In the following example... 

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