PS systems

If the crossover points Q (x) are determined from Fig. 45, taking the x-values at half-step height, Q (x) = 1/1 (x) = (0.7 + 0.2)x is obtained in the case of the PS system. This has to be compared with static value Qs (x) = 1.6x, derived from the same polymer solvent system by elastic neutron scattering [103], As long as no corresponding data from other polymer solvent systems are available, the final decision as to whether static and dynamic scaling lengths coincide or not, is still open. 

The Si02-g-PS systems were prepared by adding the methacy-terminated PS to the silica dispersion in DMF. The mass ratio PS Si02 used in each case is recorded in Table III. The dispersion was then heated at 120°C, under nitrogen, for varying periods up to 45 hr. 

Figure 4. Critical flocculation solvent composition toluene + n-hexane (v = volume fraction of toluene), versus log (particle volume fraction, (J>) for various SiC -g-PS systems at 24 1°C V, S12/PS13c 0, S12/PS13a ...

When Fernandez et al. studied partially polymerized Series P PB/PS systems, SANS results yielded peaks in the scattering patterns, see Figure 14 [ ]. Early attempts at understanding these peaks were troublesome due to the multiple causes for such peaks. Later, similar peaks were observed in another set of samples, which were partially swollen, then fully reacted (series S) by An et al. [41], but, in this case, shoulders instead of distinct maximum were observed (Figure 15). In both cases, such maximum or shoulders appeared at mid-range compositions, then were replaced by smoothly decreasing curves on further polymerization of monomer II. 

At higher shear rates, Watanabe and Kotaka (1983) observed thixotropy, i.e. stress decay increasing as a function of shear rate, in PS-PB diblocks in dibutyl phthalate (DBP), which is a selective solvent for PS.The fact that the flow crossed over from plastic to viscous non-Newtonian on increasing the shear rate indicated the breakdown of the micellar lattice structure, rather than of the individual micelles. This was confirmed by parallel measurements on a cross-linked PB-PS system, where stress decay and recovery were also observed. Thus the... 

Fig. 8.8 Free volume theory prediction of mutual binary diffusion coefficient for the toluene-PS system based on parameters (19). [Reproduced by permission from J. L. Duda, J. S. Vrentas, S. T. Ju and H. T. Liu, Prediction of Diffusion Coefficients, A.I.Ch.E J., 28, 279 (1982).]...

Figure 12.33 gives velocity profiles for the PP/PS system, which were obtained with the aid of Eqs. 12.3-21 and 12.3-22, using volumetric flow rates and pressure gradients determined experimentally in a rectangular channel. Figure 12.34 gives plots of viscosity versus shear stress for the PP and PS employed. It is seen that the polymer melts obey a Power Law model for y > 10s 1. 

In this paper we briefly review all positronium (Ps) decay rate measurements (including those of the excited states and the Ps negative ion) that have been completed to date. The results are compared with theoretical values. The Ps system represents the most rigorous confrontation with theoretical decay rate calculations for any QED system. 

Miscibility doors can be observed when the homopolymer A is miscible with the homopolymer consisting of segments of type 2. Usually, only very near to the miscibility-immiscibility boundary can a temperature dependence of the phase behavior be seen, i.e. an LCST occurs. Figure 5 shows examples for miscibility doors. Further systems are listed in Table 1. Miscibility doors were also observed for blends of styrene copolymers and polyfvinyl methyl ether) (PVME) (Fig. 6, Table 2). In contrast to PPO/PS systems blends of PVME and PS... 

Figure 3. PMMA/PS system with PMMA (Mn = 8400 W = 5.01 wt %) the dispersed phase and PS the continuous phase. 1000X.

For the PMMA/PS system summarized in Table I, three distinct types of fracture morphologies and phase relationships are observed, these being ... 

Figure 14. Regions of three types of phase relationships for the low-molecular-weight PMMA/PS system for various values of number-average molecular weight (STJ of PMMA and weight percent (W) of PMMA...

Table II. Dispersed Particle Size (S)° in Microns as a Function of Weight Percent PMMA (W) and Number-Aver age Molecular Weight PMMA (Mn) for the PMMA/PS System...

In the previous section we have described the three types of phase behavior observed in the low-molecular-weight PMMA/PS system and reviewed the four types observed in the low-molecular-weight PS/PMMA system. These various phase relationships have been studied in terms of their dependence on the molecular weight (Mn) and weight percent (W) of the initial polymer present. Further, we have presented quantitative data concerning the sizes of the dispersed particles, again correlated to variations in Mn and W. In this section we will discuss the results in terms of the poly (methyl methacrylate )/polystyrene/styrene and poly-styrene/poly( methyl methacrylate)/methyl methacrylate ternary phase diagrams, whichever is appropriate. 

The molecular weight of PS 148H is Mw = 238 000, whereas PS 168N has a notably higher value of Mw = 354000. As shown in Figs. 10 and 11, both PS systems exhibit a severe decrease in fatigue crack growth resistance when tested under the influence of the oil The whole curve is shifted toward lower A K values, which implies a decrease in the threshold value A An, and there is an increase in the slope of the curve. 

The comparison of both PS systems clearly shows an improved ESCR under fatigue loading of the PS with an increasing molecular weight, both with and without oil. This is reflected in a lower slope of the FCP curve and its displacement to higher AK values such as AKC and AfQh for PS 168N. 

Analysis of the fracture surfaces in Fig. 18c reveals the different size of the rubber particles in the two PS systems. Tested in air, in both cases the crack... 

Miscible blends of poly(vinyl methyl ether) and polystyrene exhibit phase separation at temperatures above 100 C as a result of a lower critical solution temperature and have a well defined phase diagram ( ). This system has become a model blend for studying thermodynamics of mixing, and phase separation kinetics and resultant morphologies obtained by nucleation and growth and spinodal decomposition mechanisms. As a result of its accessible lower critical solution temperature, the PVME/PS system was selected to examine the effects of phase separation and morphology on the damping behavior of the blends and IPNs. 

For the PS system, the value of Ojlf)rii obtained from Eq. (24) is unrealistically high (above the value of Z/ which has to be an upper limit for c j,n(). This implies that, in addition to a localized craze zone at the interface, other dissipative mechanisms, e.g. crazes nucleated from rubber particles well away from the interface, are active. 

As found previously for the PPO/PS system ( 2 ). the agreement between this prediction and experiment is fairly good when the trimethyl comonomer level in the copolymer is low. As the trimethyl comonomer level increases, however, the observed Tg variation with PEC in the blend falls increasingly below the line predicted by the Fox equation. The reason for this behavior is unclear. The concave upward Tg behavior shown for these blends is relatively normal for miscible systems, and there is no evidence of strong interactions, such as hydrogen bonding, between the components which can lead to convex upward Tg vs. composition curves (26). 

The difficulty of directly measuring the heats of mixing for two polymers is well known ( 35 ). but indirect routes which measure the heat of dilution (36,37) suggest that B for the PPO/PS system is -4 to -5 cal/cc at 35 °C. Gas sorption experiments (38) are also consistent with B values in this range. 

The transient surface pressure (tt) of adsorbed (3-lg, PS and mixed (3-lg/PS systems was determined. Figure 25.1 shows 7r-time curves for the systems with KO, KLVF, and X. The increase in the surface pressure with time observed for (3-lg should be associated with protein adsorption at the air-water interface (Graham and Phillips, 1979 Damodaran and Song, 1988). The value of surface pressure after long adsorption time of 5000 sec, r(775000) for 0.1 wt% protein concentration was 14 mN/m, a value close to that... 

These are, without doubt, the most widely used solid supports. PS systems used for the synthesis of peptides and small molecules consist of 1% cross-linked hydrophobic resins obtained by suspension polymerization from styrene and divi-nylbenzene. For other uses, PS with 2% cross-linking, which is mechanically more stable than those with less cross-linking, is also employed. This 2% PS was used... 

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