Dilute solution properties of high molecular weight poly(isobutyl methacrylate). III. Effect of centrifuging on various parameters

Abstract

Three high molecular weight samples of poly(isobuty1 methacrylate) designated as 937, SW63/0082, an3 SW62/0298 were obtained from Edgewood Arsenal, Maryland. Sample 937 has been fractionated a n l described1Ia) earlier. Initial investigations have shown that the solution viscosities were shear dependent. The three samples were subjected to centrifugation at constant velocity for various times. The intrinsic viscosity and molecular weight (Rw) dropped slightly for sample 937, but dropped drastically for the other two samples.The number average molecular weight (mn) remained constant for each sample under these conditions. In this presentation we have also shown the necessity for taking measurements a t low angles during light scattering measurements in order to obtain the correct molecular weight (&) for these bigh molecular weight species. ZUSAMMENFASSUNG:Drei Proben von Polyisobutylmethacrylat mit bohem Molekulargewicht, 937 1n *), SW 63/0082 und SW62/0298, Edgewood Arsenal, Maryland, wurden verschiedene Zeiten hindurch bei konstanter Geschwindigkeit zentrifugiert. Erste Untersuchungen zeigten, daI3 die Losungsviskositfiten von der Scherkraft abhangig sind. Die Viskositatszahl und das Molekulargewicht (mw) der Probe 937 fielen leicht ab, ein starker Abfall jedoch wurde bei den beiden anderen Proben festgestellt. Das Durchschnittsmolekulargewicht (Ha) blieb unter diesen Bedingungen bei allen drei Proben konstant. Bei dieser Untersuchung haben wir auch gezeigt, dal3 es notwendig ist, Lichtstreuungsmessungen bei kleinen Winkeln zu machen, um bei diesen hohen Molekulargewichten einen genauen Wert des Molekulargewichts (P,) zu erhalten.

Some Reflexions on the Cooperative Movement in Haiti

“…12 In 1962, the total number of officially recognized agricultural cooperatives was as low as 19, and these were mainly marketing cooperatives, although a substantial number of non-recognized units were known to exist, bringing the total to 178. 13 It would appear that the situation did not change very much during the next one and a half decades. 14 In 1969, it was reported that the Conseil National de la Cooperation had only 25 actually functioning units registered (excepting caisses populaires).…”

“…MarieTherese Valles reports that in 1962 there were 8 cooperatives that owned a coffee washing plant and 23 more that prepared cafe pize 20 and cocoa. 21 In 1978, only 11 were left and "the existence of certain of these [was] so precarious that one does not know whether to include them ... ,, 22 Only ten new coffee cooperatives were registered between 1959 and 1978. 23 On the whole, very few peasants were touched by these efforts.…”