Polyisobutylene, spectrum

Figure 10 shows a spectrum of butyl rubber gum stock obtained on the solid at 80°C using normal pulsed FT techniques. Clearly it could be identified as a component in fabricated materials by direct nmr spectral analysis. Figure 11 shows spectra obtained from various portions of typical rubber products. These samples were cut from the rubber product, placed in an nmr tube without solvent, and spectra obtained at an elevated temperature. The data show how polyisoprene, a polyisoprene/polybutadiene blend and a polyisobutylene/polyisoprene/polybutadiene rubber blend are quickly identified in the materials. Figure 11a shows processing oil was present, and which was confirmed by solvent extraction. 

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

Figure 11.14 -NMR spectrum of (a) commercial butyl rubber and (b) polyisobutylene, observed at 500 MHz [84]...

Andrews, R. D., and A. V. Tobolsky Elastoviscous properties of polyisobutylene. IV. Relaxation time spectrum and calculation of bulk viscosity. J. Polymer Sci. 7, 221 (1951). 

Figure 7.2 SANS spectrum of mixtures of polyisobutylene (PIB), polyethylene (PE) and polyethylene -polypropylene bi-block copolymer (PE-PP) at different temperatures. The compositions of the polymer blends are fixed at 40 vol.% of PIB, 40 vol.% of PE and 20 vol.% PE-PP. (From Ref. [12], reprinted with permission of the American Chemical Society.)...

Tobolsky and his coworkers made extensive efforts to characterize the stress relaxation characteristics of elastomers, notably polyisobutylene. The stress would decay over time to zero at a rate dependent on temperature and molecular weight (Fig. 2). They expressed the relaxation through a series of exponentials or a spectrum of relaxation times. Consider the shear stress decay a t) following an shear imposed strain yo- This may be used to define a shear relaxation modulus G i) through... 

Tobolsky and his coworkers found that the H t) relaxation spectrum function for polyisobutylene may be represented by the combination of a wedge and box, i.e., as... 

Concerning the observation of ESR spectra, an important technical point must be added Since spectra of the free radicals in polymeric chains are sensitive to power saturation, the spectra must be observed at very low microwave power. A most remarkable example in the authors experience was the case of polyisobutylene where a power of less than 0.39 pW had to be applied in order to obtain a good spectrum. Usually, a power of less than 50 pW is used for observing carbon radicals like alkyl or allylic radicals. The saturation behavior is less pronounced when the spectrum of peroxy radicals is observed. This character of peroxy radicals is helpful for enhancing signals of peroxy radicals when the spectra of peroxy and carbon radicals are superposed (Sect. 6). Of course, the saturation of the spectrum is closely related to the spin-lattice relaxation and constitutes an essential problem of polymer physics. However, this point will be excluded in the present article and only a few studies on the power saturation in the case of polymer radicals will be listed in the reference section... 

Fig. 5. TSC spectrum of polyisobutylene after polarization at the temperature indicated by the arrow.

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