Polystyrene constants 99

An assortment of values of the Hamaker constant A is collected in Table VI-4. These are a mixture of theoretical and experimental values there is reasonable agreement between theory and experiment in the cases of silica, mica, and polystyrene. 

Use values of the constants for polystyrene from Table 4.4 to calculate the shift factors needed to connect those segments in Fig. 4.17 measured at 96.3 and 108.7°C, with the isotherm measured at Tg = 100.0°C. Are the values reasonable ... 

Combination and disproportionation are competitive processes and do not occur to the same extent for all polymers. For example, at 60°C termination is virtually 100% by combination for polyacrylonitrile and 100% by disproportionation for poly (vinyl acetate). For polystyrene and poly (methyl methacrylate), both reactions contribute to termination, although each in different proportions. Each of the rate constants for termination individually follows the Arrhenius equation, so the relative amounts of termination by the two modes is given by... 

Under 0 conditions occurring near room temperature, [r ] = 0.83 dl g for a polystyrene sample of molecular weight 10. f Use this information to evaluate tg and for polystyrene under these conditions. For polystyrene in ethylcyclohexane, 0 = 70°C and the corresponding calculation shows that (tQ /M) = 0.071 nm. Based on these two calculated results, criticize or defend the following proposition The discrepancy in calculated (rQ /M) values must arise from the uncertainty in T>, since this ratio should be a constant for polystyrene, independent of the nature of the solvent. 

Fox and Floryf used experimental molecular weights, intrinsic viscosities, and rms end-to-end distances from light scattering to evaluate the constant in Eq. (9.55). For polystyrene in the solvents and at the temperatures noted, the following results were assembled ... 

For polystyrene in butanone at 67 C the following values of KC2/R0 X 10 were measuredf at the indicated concentrations and angles. Construct a Zimm plot from the data below using k = 100 cm g" for the graphing constant. Evaluate M, B, and from the results. In this experiment... 

Creep. The creep characteristic of plastic foams must be considered when they are used in stmctural appHcations. Creep is the change in dimensions of a material when it is maintained under a constant stress. Data on the deformation of polystyrene foam under various static loads have been compiled (158). There are two types of creep in this material short-term and long-term. Short-term creep exists in foams at all stress levels however, a threshold stress level exists below which there is no detectable long-term creep. The minimum load required to cause long-term creep in molded polystyrene foam varies with density ranging from 50 kPa (7.3 psi) for foam density 16 kg/m (1 lb /ft ) to 455 kPa (66 psi) at foam density 160 kg/m (10... 

The spreading rate of a polymer droplet on a surface has been measured (363,364). The diffusion constant was at least an order of magnitude smaller than that of the bulk. The monomer—surface friction coefficient for polystyrene has been measured on a number of surfaces and excellent... 

TABLE 16-7 Equilibrium Constants for Polystyrene DVB Cation and Anion Exchangers... 

Figure 4 The reflectivity multiplied by kjQ as a function of for a bilayer of normal polystyrene on perdautarated polystyrene before and after heating at 105.5° C for 2 minutes. The data is plotted in this manner since for sharp interfaces RkjQ is a constant at large k -...

Poly(methyl methacrylate) is a good electrical insulator for low-frequency work, but is inferior to such polymers as polyethylene and polystyrene, particularly at high frequencies. The influence of temperature and frequency on the dielectric constant is shown in Figure 15.9. 

In common with other thermoplastic melts polystyrene exhibits pseudoplastic behaviour. At shearing stresses below 60/M,J, MPa (where = average molecular weight), the ratio of shear stress to shear rate is almost constant and the melt is substantially Newtonian. Above this shear stress non-Newtonian... 

The latter equation contains constants with well-known values and can therefore be used to predict the fracture stress of most polymers. For example, the bond dissociation energy Do, is about 80 kcal/mol for a C-C bond. For polystyrene, the modulus E 2 GPa, A. 4, p = 1.2 g/cm, = 18,000, and we obtain the fracture stress, o A1 MPa, which compares well with reported values. Polycarbonate, with similar modulus but a lower M. = 2,400 is expected to have a fracture stress of about 100 MPa. In general, letting E 1 GPa, p = 1.0 g/cm, and Do — 335 kJ/mol, the tensile strength is well approximated by... 

Capacitance is related to the area of the plates (yi), the distance between the plates (d), and the dielectric constant (e) of the material between the plates (Figure 2, equation I). The dielectric constant or permittivity of a material is the increased capacitance observed compared to the condition if a vacuum was present between the plates. Common dielectric materials are polystyrene (e = 2.5), mylar (e = 3), mica (e = 6), aluminum oxide (e = 7), tantalum oxide (e = 25), and titania (e = 100). In the Leyden jar the dielectric is silica. 

FIGURE 6.11 The energy released or absorbed as heat by a reaction at constant pressure can be measured in this simple calorimeter. The outer polystyrene cup acts as an extra layer of insulation to ensure that no heat enters or leaves the inner cup. The quantity of energy released or absorbed as heat is proportional to the change in temperature of the calorimeter. 

The correct explanation of the peculiar behaviour of the butadiene-styrene system was provided by O Driscoll and Kuntz 144). As stated previously, under conditions of these experiments butadiene is indeed more reactive than styrene, whether towards lithium polystyrene or polybutadiene, contrary to a naive expectation. This was verified by Ells and Morton 1451 and by Worsfold 146,147) who determined the respective cross-propagation rate constants. It is germane to stress here that the coordination of the monomers with Li4, assumed to be the cause for this gradation of reactivities, takes place in the transition state of the addition and should be distinguished from the formation of an intermediate complex. The formation of a complex ... 

The kinetics of lithium polystyrene polymerization obeys a first order law at constant concentration of TMTCT. The first order constant increases linearly with the concentration of this complexing agent149) and becomes constant for [TMTCT] [lithium polystyrene] as shown in Fig. 23. 

Under these conditions the maximum propagation constant, kpc = 750 M-1 sec-1, gives the absolute rate constant of the monomer addition to the complexed unassociated lithium polystyrene, a value obviously larger than that of the unassociated but also uncomplexed polymer. 

Once all the remaining sites have reacted a polystyrene fitted with grafts of known length at approximately constant intervals is obtained. As the backbone arises by polycondensation, fractionation is necessary when samples of low polydispersity are needed. Whether the grafts are distributed regularly or randomly hardly affects the behavior of the graft copolymer 91). 

---