POLYISOBUTYLENE Subject

Figure 10.14 Synchronous, two-dimensional Raman spectrum for polyisobutylene subjected to a 1.5% strain at 82 Hz and at room temperature.

When the butyl rubber was compounded with up to 30 percent of polyisobutylene, which, lacking the unsaturated isoprene units, did not enter into the cross-linking reaction, the tensile strengths were, of course, considerably reduced. They were found nevertheless to be accurately represented by the same equation, (53), provided merely that Sa is taken as the fraction of the composite specimen consisting of network chains subject to orientation. Thus, in this case... 

Despite the proximity of flow curves, as well as values r) and 0 for these polymers (values r 0 and 0 are usually subject to dimensionless representation, normalization ofo0 and t), the time during which the maximum possible strain is attained In max = 2.8 for polyethylene and exceeds that of polyisobutylene at the same o0 by factor of 6. In this case the dependency In e(t) in the region of measurement for polyisobutylene is characterized by increasing strain velocity x = d(ln e)/dt in contrast to which x(t) decreases strictly in low-density polyethylene within a significant section of s and becomes approximately constant at high values of t. 

H. Hopff and N. Balint developed a copolymerization process for tetrachloroethylene with ethylene. Radiation-induced chlorination of polyisobutylene is the subject of the chapter of C. Schneider and P. Lopour. M. Litt, V. T. Stannett, and E. Vanzo show that the polymerization of vinyl caproate follows the kinetics of styrene. 

Figure 10.13 Dynamic in-phase (single prime) and out-of-phase (double prime) signals for the birefringence, An, and the Raman anisotropy for the C-C bond, T, for a room temperature polyisobutylene melt subjected to a strain of 1.5%. The phase is relative to the applied strain.

The simplest way to correct viscosity data to constant friction coefficient is to first fit the temperature dependence of viscosity of each individual sample to the WLF equation [Eq. (8.134)], which determines 5//q. At a given reference temperature, sufficiently long chains have the same 5//o and progressively lower values of 5//o are obtained for shorter chains, since they have more free volume at a given temperature. The viscosity data at the reference temperature can then be corrected to the friction coefficient of the long chains at the reference temperature using Eq. (8.133). Viscosity data subjected to such a correction are shown in Fig. 8.17 for polybutadiene, polyisobutylene and polystyrene, roughly... 

A few plastics which tend to be naturally brittle require an improvement in both their drop (impact) strength and their top loading (compression) strength. In the case of polystyrene, rubber is widely used as an impact modifier. Rigid PVC, particularly when used as a container, may suffer weakness when subjected to, say, a 3 4 foot drop test. Up to 15% of methyl methacrylate butadiene styrene (MBS) copolymer is usually added to improve impact strength. Chlorinated polyethylene has more recently been introduced as a PVC impact modifier. Vinyl acetate is frequently used as a modifier for PVC film. Polythene, LDPE-HOPE can have resistance to stress (environmental stress cracking), improved by the use either of rubber or polyisobutylene. These modifications have not as yet had any pharmaceutical applications. 

The optimum solids level of cements to be applied by various methods is, of course, subject to broad variation depending on the solvent selected (i.e., the viscosity which results), filler content, etc. In general, butyl rubber and polyisobutylene cements for application by spraying contain 5-10% solids, for dipping 10-30%, for spreading 25-55 %, and for application by finger or spatula, 50-70%. 

John D. Ferry is known as the leading figure in the history of polymer science on the subject of viscoelasticity. He graduated from Stanford University at the age of 19, as noted above. For his doctoral work with George Parks he studied the properties of polyisobutylene as a function of temperature. He found the glass transition temperature and characterized the viscoelastic properties (Fig. 5.6). 

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