Poly , atactic experimental

In one example, the Tics of the non-crystalline methyl, methine and methylene carbons of iPP, 70% crystalline, were compared at room temperature with those of model atactic poly(propylene), hydrogenated poly(2-methyl-l,3-pentadiene) [163]. It was found that, within the experimental error, the Tic values of each of the carbons were the same in both polymers. The conclusion can then be reached that the fast segmental motion, at or near the Larmor frequency of... 

The unperturbed dimensions and their temperature coefficients are evaluated for poly n-pentene-1), poly(n-butene-l), and PS with the RIS model. The calculated values of the unperturbed dimensions for atactic and isotactic chains are in good agreement with the experimental data. The measured temperature coefficients, however, are described satisfactorily by the model for atactic polypentene and polybutene only. 

Unsymmetrical Alkyl-Substituted Polysilylenes A detailed comparison of theoretical predictions and experimental results for the atactic polysil-ylenes is more diflScult for several reasons (1) the observed transitions are much broader, (2) the effects of random substitutional disorder are not included in the theory, and (3) the magnitudes of the consequences of stereochemical disorder are expected to vary for different atactic polymers. Nevertheless, for all the asymmetrically substituted polysilylenes studied, except poly(n-dodecylmethylsilylene), the predictions discussed earlier... 

This can be seen from the data in Table 10.1, where isotactic, syndiotactic, and atactic poly(methyl methacrylate) (PMMA) have different a values. If the size of a polymer chain can be affected by its configuration, the microstructure must be well characterized before an accurate assessment of experimental data can be made. This can be achieved using nuclear magnetic resonance (NMR) and infrared techniques. 

Representative poly( 1-pentene) tacticity data is provided in Table 4.4 representative polypropylene tacticity data is provided in Table 4.2. Poly(pentene) was produced using neat 1-pentene poly(propylene) was produced using neat propylene or a 50/50 (v/v) mixture with toluene. These scandocenes and yttrocenes provide atactic polymers. The tacticity values range from [r] = 28.62% to [r] = 52.12% for poly( 1-pentene) samples, and from [r] = 48.77% to [r] = 61.13% for poly(propylene) samples. Within experimental error, polymerization temperature and monomer dilution appear to exert a minimal effect on polymer tacticity. 

As an example of the analysis, we show in Fig. 2 the results for the gelation of poly(vinyl alcohol) in water [8]. Poly(vinyl alcohol) (PVA) is known to be a typical crystalline polymer, but it also gels in aqueous solution under large supercooling. There are several experimental evidences that the cross links are formed by partial crystallization of the polymer segments in which syndiotactic sequence dominates, while subchains connecting the junctions consist mainly of atactic non-crystalline sequences on PVA chains. The micro-crystals at the junctions are supposed to be stabilized by hydrogen bonds... 

Comparison between theoretical calculations and experimental results are in good agreement for polystyrene and substituted polystyrenes on the basis of atactic chains. Unfortunatdy, the experimental information available at present cm the dipole moment of poly(vinyl chloride) shows large variations between woricets l Nevertheless, there are good indications based on didectric and other data that ndiotactic placements are favoured in poly(vinyl chloride). Mark ihscusses the influence of side chain size in poly(vinyl chloride) and poIy(/K hIorostyrene). 

From Table 2, it can be seen that atactic polypropylene (PP) and atactic poly(1-butene) (PB) exhibit C values of 6.0 and 5.6, respectively. As expected from the above cited RIS results, these values are considerably smaller than the Ctj, value for PE of ca. 8. The decrease in C is slightly greater for ethyl versus methyl substituents. Additional comparisons of RIS predictions and experimental results for PP and PB will be presented below. 

Fig. 5. Experimental spectrum of atactic poly(propylene) recorded at T = 260 K, below the calorimetric glass transition temperature. The various resonances are considerably broadened and partly structured...

Fig. 13. Experimental solid state spectrum of atactic poly(propylene) (top) and solution spectrum of configurational splitting in the methylene region (bottom). The broadening in the solid state spectrum is appreciably larger than the configurational splitting. Reprinted with minor changes from [63]...

In this formula, pconfig is the experimental configurational statistics of the sample to be simulated it is fully determined by the synthetic conditions and is not subject to change. For ideally atactic poly (propylene), the configurational statistics is easily calculated, pco yig( i> 2> 3) = ( ) = 0.125, Xi 6 m, r. I x ) is the conditional conforma-... 

Experimental spectrum of the methylene region of glassy atactic poly(propylene) (b) recorded atT 240 K on a BRUKER MSL-300 with a DAS probehead. The two angles for evolution and detection, respectively, were =81.7° and = S m = 54.7°. The rotation frequency was 3000 Hz, and 128 fi-increments were recorded. The theoretical values (o) are superimposed on the experimental contour plot. The absolute positions were adjusted like in the ID spectrum. A qualitative agreement of theory and experiment is seen... 

D ) corresponds to that calculated for Prc O.7. The higher value (1.22 D ) observed for the atactic sample is, however, at variance with the results presented in Figure 5(b). Observed dipole moments for poly(isobutyl vinyl ether) vary little with the tacticity in the moderately isotactic to atactic region. Experimental values of < >/x=0.95 to 1.35 are reasonably approximated by the curve in the moderately isotactic range. 

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