Poly atactic polymer

Figure 7.10 shows the 60-MHz spectra of poly (methyl methacrylate) prepared with different catalysts so that predominately isotactic, syndiotactic, and atactic products are formed. The three spectra in Fig. 7.10 are identified in terms of this predominant character. It is apparent that the spectra are quite different, especially in the range of 5 values between about 1 and 2 ppm. Since the atactic polymer has the least regular structure, we concentrate on the other two to make the assignment of the spectral features to the various protons. 

This category includes such polymers as atactic polystyrene (25-291 or poly(vinylchloride) (30.31 and references therein). A closely related problem is the gelation of non-block copolymers (5), which share with atactic polymers the feature that chemically and conformationally homogeneous sequences may be relatively short, so that when two or more chains interact, large crystalline domains are prevented from forming. 

The ORD and CD curves of optically active polymers containing chromo-phoric groups show that the chromophores can be asymmetrically perturbed by the chirality of the substituents and of the main chain conformation. This is the case with poly( ec-butyl vinyl ketone) (377), which presents a Cotton effect at 292 nm, its intensity being greater in the prevalently isotactic polymer than in the atactic polymer. 

Figure 1 shows the exposure characteristics of atactic and isotactic poly(a,a-dimethylbenzyl methacrylate) resists with CH3ONa development together with those of the poly (methyl methacrylate) resist with MIBK/IPA development. Poly(a,a-dimethylbenzyl methacrylate) s showed high sensitivity and very good contrast between exposed and unexposed areas. The atactic polymer with alkaline development was improved in the sensitivity and 7-value by a factor of more than three over poly(methyl methacrylate) with MIBK/IPA development. 

When the atactic poly(a,a-dimethylbenzyl methacrylate) was heated at 170°C for 30 min under vacuum, it decomposed into volatile and nonvolatile components. The former was found to be a-methylstyrene and the latter was to be very similar to polyfmethacrylic acid) as determined by H NMR spectroscopy. Figure 3 shows the infrared spectra of atactic and isotactic poly(a,a-dimethylbenzyl methacrylate)s heated at 174°C under vacuum for various times. In the spectra of the atactic polymer, the absorption of the ester carbonyl at 1729 cm-1 decreased and that of the acid carbonyl at 1700 cm-1 increased as the heating time increased. After heating for a period of 30 min... 

The carbonyl stretching band in the infrared spectrum of isotactic poly (a,a-dimethylbenzy 1 methacrylate) prebaked at 142°C for 1 hr indicated the formation of a small amount of acid group during the prebake, while the atactic polymer showed no change in the spectrum at this temperature. This may be the reason why the isotactic polymer showed a lower 7-value than the atactic polymer (Table III). 

The optical rotatory dispersion of poly-(+)-l-methyl-benzyl-methacry ate has been measured between 320 and 230 raft. The optical activity for polymer and model has values of the same sign and of the same order of magnitude, but the isotactic polymer seems to have a larger [M] than the syndiotactic and the atactic polymers [K. J. Liu, J. S. Lignowski, R. Ullman ACS Polymer Preprints, 6, 904 (1965)]. Optically active N-methyl-N-methylbenzyl-acrylamide and N-(n-propyl)-N-methylbenzyl-acrylamide have been polymerized by Kaiser and Schulz and the optical rotation dispersion between 589 raft and 365 raft has been... 

Ribbed helices (costal helices) are important in organic chemistry because linear polymers contain side chains as well as backbones. We may, then, discern not only the catenal helix of the backbone, but the intercostal helix formed by all of the ribs and the infracostal helicesof the individual side chains. The intercostal helix may be iterative (as in an isotactic head-to-tail vinyl polymer or homogeneous poly-a-amino acid) or non-iterative (as in a random copolymer, an atactic polymer or typical protein). The intracostal helices can best be analyzed as short-chain crooked lines, as in Section III. Important as costal helicity is, it is secondary to catenal helicity and we therefore limit our attention to the primary helicity, that of long chains. Indeed, we limit our attention to catenal helices having chain motifs of two atoms and two bonds as found in head-to-tail vinyl homopolymers ... 

Because atactic polymer has no ordered structure and shows only slight intramolecular interactions, the interactions between atactic polymers is the strongest (Fig. 10 a). The isotactic polymers may be stabilized by assuming the helix conformation reported for isotactic poly(methyl methacrylate)401. Nucleic add bases are situated outside the polymer chain so that they can form the complex, although the interaction is not so strong. On the other hand, the syndiotactic polymer may have a rod-like conformation that is supported by the low solubility of the polymer and by NMR spectra321. Tlierefoie, it is well understood that the complex formation ability of the syndiotactic polymers is very low. 

One of the cases of such complementarity may be the atactic polymer which can be considered as a copolymer of isotactic and syndiotactic links. Indeed, the composition and properties of the polycomplex depend on the chain stereoregularity, for example in the case of poly(methyl methacrylate) stereocomplexes16 and polyethylene glycol) with isotactic or atactic PAA complexes33. ... 

Because the transition state of electrophilic addition is rather open or only very weakly bridged, the stereoselectivity is poor, resulting in primarily atactic polymers. Polystyrene and most poly(vinyl ether)s prepared cationically at ambient temperature are atactic with similar proportions of meso and racemic dyads [243,244]. However, meso addition is slightly preferred with vinyl ethers, and varies from 60 to 70% for most monomers, including isobutyl, neopentyl, n-butyl, and ethoxyethyl vinyl ethers [245]. It is higher with benzyl vinyl ether (89%). This tendency to... 

There are a few exceptions to the general rule that atactic polymers do not crystallize. Poly(vinyl alcohol) (1-8) and poly(vinyl fluoride) areexamples. Some monomers with identical 1,1-substituents like ethylene, vinylidene fluoride, and vinylidene chloride crystallize quite readily, and others like polyisobutene do not. The concepts of configurational isomerism do not apply in these cases for reasons given above.]... 

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... 

It seems, therefore, that the study of rj q>, Z) at constant 9 g, variable Z, may offer an opportunity to evaluate the applicability of Bueche s theoretical results. BuECHE, CovEN and Kinzig 58) recognized this fact and studied the variation of Z with 9P2 for the system poly(methyl-methacrylate) diethyl phthalate. Unfortunately, the results are inconclusive, either (p Z) or q l Z) constant will correlate the data. Moreover, in view of the difference in Z estimated for the conventional polymer used by these investigators and that found for the atactic polymer, one must suspect the possibility of some order in the pol5uner chains, even in solution. Thus, this pol5uner may not represent the best material for such a study. 

Syndiotactic polymers, as we have seen above, are stereoregular and so are crystallizable. They, however, do not have the same mechanical properties as isotactic polymers, because the different configurations affect the crystal structures of the polymers. Most highly stereoregular polymers of commercial importance are isotactic, and relatively few syndiotactic polymers are made. Atactic polymers, on the other hand, are usually completely amorphous unless the side group is so small or so polar as to permit some crystallinity. Thus, while atactic poly(vinyl acetate) has never been crystallized, poly(vinyl alcohol), which is derived from it and is also atactic, has been found to crystallize. 

Effects of Structure and Temperature. Both the structure of a polymer and temperature conditions affect the formation and decay of exclmer emission In the polymers discussed above, and these observations can be rationalized by a consideration of the conformational requirements for exclmer formation In these polymers and model compounds. Table 3 reveals that exclmer formation Is favored In Isotactic poly(styrene) compared with the atactic polymer, although these results are In conflict with an earlier qualitative observation and Interpretation (50), or the 80% syndlotactlc polymer In cyclohexane. In Isotactlc poly(styrene) in cyclohexane, the preferred structure Is reported to be a 3/1 helix (61), which corresponds to the ground-state... 

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