Fractionnement par extraction du polythi?ne par V. DESREUX et M. C. SPIEGELS (Libge) HCsi 5iL.-Les auteurs dtcri\.cn t la technique d'cxlraction atloptk pour Ic fraclioiinement d u polythenc aprhs a\oir euposi. Ics clifficultPs expCrimcntalcs cl'une d8termination des courhes dc palydispersitC d e CP polyiiiPrc (1'apri.s les mtthoclrs classiques rle 1)rPcipitaticirr.Lty Iri~is ~'~hantillons Pludies ont des poids molkculaircs viscosimEtriques triks yoisins ( 2O.oOo) inais dtwx d'cutre eux, signalt5s coninie ayant rles propri6tCs i n k c a n i q~~s diffkrentea, se caractbrisent par des courbcs dc solubilit6 et de distril,ution des poids molkculaires trEs divergentes. On yrut supposer, de I'allure des courhcs de distribution, que ces &hantilloris ne sont pas chimiquement homogbnes.Enfin. Irs iiitcractions mol6culaires stninblent etre t.rEs faiblcs. * *Ce travail a PtB effectue dans le cadre des recherches du Centre des Hauts Polymhres subsidiB par 1'1. R. S. I . A. Nous tenons 3 remercier ces deux organismes pour leur appui financier.
The activation ofDNase I by Mg, Mn, Co, Ni, Fe, Cd, Zn, Ba, Sr, Ca, and Cu ions has been studied by several methods, at different pH and salt concentrations. Mg, Mn, and Co are the best activators for initial stages of degradation. A synergistic effect is shown only by the pair Mg-Ca. Optimal pH of action is always situated at 6.5. DNase II is activated to about the same degree by alkaline earths and Mn ions. Cd and Cu are strong inhibitors. Optimal pH is always 4.6. By titration of liberated secondary phosphate groups, two stages in the hydrolysis of DNA by DNase I are evidenced: a rapid phase activated most by Mg and a slow phase activated by Ca. Some possible mechanisms of action of both enzymes are outlined and the general influence of metal ions is discussed.Two main categories of deoxyribonucleases specifically hydrolyze the phosphoester bonds in deoxyribonucleic acid (DNA): the first one (DNase I), extracted and crystallized from pancreas by Kunitz (1950), requires divalent cations (in particular Mg); the second one, DNase II, extracted from thymus or spleen and purified by chromatography (Koerner and Sinsheimer, 1957; Shimomura and Laskowski, 1957;Fredericq and Oth, 1958), is already active in the absence of metallic cations but is activated by several divalent cations.Wiberg (1958) showed that Mg and Mn are the most powerful activators of DNase I. He also reported a very interesting synergistic effect of Ca ions when added to Mg ions, although they had themselves very little activity. His method of determination was, however, restricted to the earlier stages of hydrolysis and under conditions in which DNA was partially denatured. The synergistic effect of Ca and Mg was confirmed by Feinstein (1960) using a viscometric assay and by one of us (Fredericq, 1959), using a titration of secondary phosphate; differences in the activation of hydrolysis of DNA and oligonucleotides were also observed.In the present paper we describe a study of the activation of DNase I by a variety of divalent cations and its extension to subsequent stages of DNA 93
Nous utilisons la méthode de transmission pour calibrer la diffusion lumineuse. Nous vérifions en utilisant des solutions d'indices de réfraction différents que la correction de réfraction est pratiquement n2 pour l'intensité diffusée, l'intensité incidente à travers la cellule devant être corrigée empiriquement pour une réfraction due à la légère divergence du faisceau primaire. A partir de ce calibrage, nous obtenons pour le rapport de Rayleigh du benzène à 20°C. et pour λ 4358 A. R = (48,4 ± 1,5)10−6 cm.−1. Pour les mesures de dissymétrie dans la cellule commerciale semioctogonale “Pyrocell,” nous montrons la présence de réflexions totales pour les solutions d'indice de réfraction ≥ 1,41, réflexions qui peuvent être éliminées aisément en plaçant un verre absorbant dansle fond de la cellule. D'autre part, nous calculons la correction à apporter à la dissymétrie du fait des réflexions de Fresnel quand le faisceau lumineux émerge normalement à la paroi de la cellule.
The microtacticity of polymethacrylates prepared by radical initiated polymerization of monomers with side groups of increasing bulkiness is determined by high resolution nuclear magnetic resonance of the corresponding poly(methy1 methacrylates).The syndiotacticity decreases systematically from poty(methy1 methacrylate) to poly-(triethylrnethyl methacrylate) in the series of the saturated polymers.The aromatic polymethacrylates have a lower syndiotacticity than the corresponding saturated polymers and poly(trity1 methacrylate) is the extreme case.The microtacticity of the polymers is undoubtedly determined by the bulkiness and the polarisability of the ester group as well as by specific interaction between the aromatic rings. ZUSAMMENFASSUNG:Die Mikrotaktizitiit von radikalisch polymerisierten Polymethacrylaten, die in der Seitenkette des Monomeren immer grol3ere Gruppen haben, wird durch die hochaufgelosten Kernresonanzspektren der entsprechenden Polymethylmethacrylate bestimmt.Die Syndiotaktizitiit vermindert sich schrittweise von Polymethylmethacrylat bis zu Polytriathylmethylmethacrylat in der Reihe der gesattigten Polymeren. Die aromatischen Polymethacrylate haben eine geringere Syndiotaktizitat als die entsprechenden gesattigten Polymeren. Polytritylmethacrylat stellt den Extremfall dar.Die Mikrotaktizitiit der Polymeren folgt sowohl aus der GroDe und der Polarisierbarkeit der Estergruppe als auch aus der Wirkung, die die aromatischen Ringe aufeinander ausuben.
The thermal degradation of poly(vinyl acetate) under high vacuum between 230 and 300°C. was investigated by gas chromatographic analysis of the volatile products, rate measurements by the loss‐of‐weight method, and infrared determinations of the residue at different stages of the reaction. Acetic acid was proved to be the main component of the volatile products (90 to 95%). Kinetic measurements of numerous samples obtained in different polymerization conditions showed that the rates of degradation were identical for all the samples and, in particular, independent of the molecular weight. This is contrary to data previously published. Infrared absorption shows a progressive deacetylation of PVAc; very little absorption appears in the region of conjugated double bonds. A crosslinking reaction probably occurs in the very early stages of the degradation and, on the basis of C–H analysis, one has to admit that a chain‐breaking process coexists with the deacetylation reaction.
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