By studying the molecular weights of various solutions of cis‐1,4‐polyisoprene the authors arrived at the formula \documentclass{article}\pagestyle{empty}\begin{document}$$\left[ \eta \right] = \sqrt {2/c} \sqrt {\eta _{sp} - {\rm l}n\eta } _{rel} $$\end{document} which allowed the calculation of the intrinsic viscosity of the polymer solutions by a single viscosity determination. The formula was verified for different systems of polymer–solvent and the values are in accord with those obtained by extrapolation. An operating concentration of about 0.2% is recommended.

SynopsisThe properties of poly-N-vinylcaprolactam organic and aqueous solutions were studied.Aqueous solutions present a very accentuated diminishing of [ q ] from 10 to 30°C. Above 30°C. the polymer precipitates from ita aqueous solutions. The precipitation temperature does not depend on the concentration but on the molecular weight of the polymer. Some acid and basic agents have a marked inhence on [q] and the precipitation temperature of the aqueous solutions.Toluene solutions present an increasing [?] from 10 to 40°C.There are no studies about the behavior of poly-N-vinylcaprolactam solutions. It is only known that some poly-N-vinyllactams precipitate with heat from their aqueous solutions.The temperature at which the precipitation phenomenon appears is dependent on the number of C atoms of the lactamic ring: for po1y-Nvinylcaprolactam this temperature is about 35°C. and for poly-N-vinylpiperidone it is 64-65OC.lIn the case of poly-N-vinylpyrrolidone such a precipitation does not take place in the usual temperttture range (O--lOO°C.). It was admitted that this abnormal phenomenon is due to the colloidal nature of aqueous solutions of poly-N-vinyllactams,2 and it was supposed that the increasing temperature diminishes the polymer ~olvation.~ The object of the present work was the study of the behavior of po1y-Nvinylcaprolactam solutions from the viewpoint of their viscosity and of the factors that influence the temperature at which the polymer precipitates from its aqueous solutions.

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SynopsisThe crosslinking of polyethylenes by free radicals, produced by complete decomposition of crosslinking a g e n t s tert-butyl peroxide and tertbutyl perbenzoate, w a s carried out in a Brabender Plastograph, which gave continuous viscosity-time curves and s o permitted the crosslinking to be measured a t the same time. T h e soluble fraction and Brabender viscosity were determined simultaneously; the latter represents an exact measure of the variation in degree of crosslinking under the given conditions. A great number of reactions with different quantities of peroxides were carried out. A quantitative equation relating degree of crosslinking and Brabender viscosity w a s established. With the u s e of equations valid in radiation crosslinking some equations relating degree of crosslinking to molecular weight and other characteristics were established. T h e s e lead to the analytical fractionation of polyethylene a n d the establishment of polydispersity curves. Crosslinking by macroradicals obtained by the mechanicochemical degradation of polyethylene of molecular weight 3,000,000 w a s followed in the same way.La reticulation du polythhylkne a suscit; c e s derniers temps un intdrgt particulier du point de w e pratique e t thgorique (1). P a r diffikence a v e c le caoutchouc dont la vulcanisation au soufre e s t f a i t e sur la b a s e d e s doubles liaisons existentes, d a n s le c a s de la macromoldcule du polydthylkne le nombre d e c e s doubles liaisons &ant extrgmement re'duit (0,6-1,s doubles liaisons pour 1000 atomes de carbone) la r6ticulation n e c e s s i t e l'intervention d e certains radicaux libres produits par un agent ext6rieur.Du point de vue pratique la r6ticulation du polydthylkne est possible d e trois manikres diffe'rentes: par lumikre ultraviolette, par radiations ionisantes e t I'aide de peroxydes organiques. L e s deux derniGres mithodes ont trouve c e s derniers temps des applications industrielles.Chacun de c e s proce'de's a son avantage e t son ddsavantage. La me'thode radiochimique, plus perfectionnge thgoriquement a i n s i qu'exp6rirnentalement, pre'sente le ddsavantage d e ndcessiter d e s conditions complexe s de travail e t en ge'ne'ral l e processus a un caractkre superficiel. La + P r e s e n t a d r e s s -Cornbinatul Petrochimic P i t e s t i -Arges t P r e s e n t a d r e s s -Polytechnical Institute -C a l e a Victoriei 149 Bu care s t