Crystallinity degrees exert influence on the stability of high molecular weight poly(ethy1ene oxide)s, POEs, in solid state. It was found that the degradation of these POEs is connected with an increase of crystallinity degrees. Samples being prepared under the terms of the strontium carbonate initiated bulk polymerization, without stabilizer, degradated during 18 days just after the polymerization has been brought to an end, while at the same time the crystallinity degrees rose by 7-20% up to an end value of about 70%. On the contrary the phenothiazine stabilized sample preserved its starting crystallinity degree during the whole time of investigation without suffering a significant degradation. The POE prepared by the calcium amide initiated solution-precipitation polymerization at room temperature exhibited a higher starting crystallinity degree of about 70% and, as a consequence, it was stable during the whole time of investigation. Because the bulk polymerization must be carried out at least at 90 "C, the POE formed crystallizes from the melt and a greater part of amorphous zones results than in the case of the solution-precipitation polymerization, rendering the polymer less stable. The parameters established for the unit cell in the monoclinic system remained unchanged during the whole time of investigation in spite of changes in crystallinity degrees and molecular weights.
We present an overview of the synthesis, physical characterization and catalytic properties of polymer-supported reagents and consider the major advantages and drawbacks in the use of polymeric supports for synthesis and catalysis. The most important development in recent years appears to be the characterization of polymeric supports by thermal analysis, advanced spectroscopic and scattering methods, and electron microscopy. As a result, the mechanism of catalytic activity is better understood; the challenge remains to prepare supported catalysts with good mechanical properties, and high chemical stability at elevated temperatures, and to prevent the loss of often pricey catalysts such as rhodium during numerous catalytic cycles.
Ring-opening reactions of maleic anhydride (l)/isobutene (2) copolymer (aw = 2.76 * lo' g/mol), carried out by the use of: NaOH solution (hydrolysis); NH,; NH(CH,),; N(CHd3; NH(C,HS), and H,N(CH,CH,NH),CH,CH,NH, (TETA), resp., yielded water-soluble products, with the exception of the TETA-modified copolymer. The degrees of conversion a were found to be in the range between 87 to 100%, with the exception of the N(CH,),-reacted copolymer where a = 41,6%. As a result of the conversion reactions, the weight-average molecular weights M, dropped significantly, by 30% in the case of hydrolysis, and by 40% in the cases of ammoniation or amination, despite the mild conditions which were employed. Based on nitrogen contents found analytically, as well as on 13C NMR spectra, it was concluded that under the given conditions the reactions using ammonia or amines do not proceed beyond the half-amidation step.13C NMR investigations on products of both the ammoniation and amination reactions indicate a directing influence produced by the CH, groups of the isobutene unit. As a result, only those carbonyl groups remote from the pendant substitutents are prone to an attack which causes amidation.0 1990, Hitthig 8t Wepf Verlag, Basel CCC 0025-1 16X/90/$03.00
With thermogravimetric analysis, IR and ESR measurements it could be shown that the low stability of high molecular poly(ethy1ene oxide) is due to a statistical degradation following a radical mechanism which leads to the formation ofaldehyde groups at the end positions of the fragments. Mass spectroscopical investigations of degraded (aged) as well as of freshly prepared poly(ethy1eneoxide) revealed a consistent and easily comprehensible picture. Always 3 series of peaks could he found and the difference between two successive peaks amounts to 44 mass units in each series, corresponding to the oxyethylene unit. The mass spectra of degraded poly(ethy1ene oxide) were found to be always more rich in fragmentations than those of non degraded ones. The mechanism of poly(ethy1ene oxide) degradation caused by the action of electrons could be explained with the help of the obtained mass spectra. The degradation of high molecular poly(ethy1ene oxide), which even takes place at room temperature in the dark and in the absence of air, could he restricted considerably by adding a suitable stabilizer to the polymerization mixture. Einleitung
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