Light scattering has proved itself an efficient technique to determine particle diameters in heterogeneous dilute dispersions in the micrometer range. Extrusion of polymer blends is expected to give rise to very small particles, typically in the range from hundreds of nanometers to tens of micrometers. A light scattering device developed in OUT laboratory has been used to study the morphology of polymer blends obtained in a twin-screw extruder. The main advantage of this technique is the immediate response obtained without any surface or interface modification that can occur during the sample preparation by using more conventional techniques like electron microscopy. To show the possible applications of this light scattering device, preliminary tests have been carried out. First, we present a comparison between experimental measurements and theoretical results for dilute systems. Second, we have investigated the effect of shear flow on the droplet deformation. Finally, we have studied the variations of the light scattering pattern for a reactive blend.

Date de reception: 28 janvier 1975) R~S U M E :On a 6tudiC par diffraction des rayons X aux petits angles de Bragg la solubilisation d'une serie de polystyrenes de masse molCculaire variable dans la phase lamellaire d'un copolymkre biskquence polystyrkne, polyisopr5ne.On a d'abord montre que la solubilisation correspond B un &at d'Cquilibre veritable du systeme et non pas B un Ctat mktastable dii B I'insertion accidentelle de I'homopolymbe dans I'Cdifice.On a corrobore ensuite les conclusions 6noncCes prCcCdemment : l'homopolymere se solubilise tant que sa masse molCculaire ne depasse pas une masse comparable A celle des sequences parentes; il se localise 2 l'interieur des microdomaines de segregation qui contiennent les sequences de m&me nature; il s'y distribue enfin de manikre assez uniforme.On a observe, enfin, un phenomenede fractionnement, lie sans doute B la polydispersitC non negligeable des Cchantillons. SUMMARY:This is a low-angle X-ray diffraction study of the solubilization of a series of polystyrenes with varying molecular weight in the lamellar structure of a two-block polystyrene/polyisoprene copolymer.It has first been shown that the solubilization corresponds to a true equilibrium state, and not to a metastable one due to the accidental insertion of the homopolymer into the system. Previous conclusions in the field have then been confirmed. Homopolymer is solubilized only when its molecular weight does not exceed a value comparable to that of the *) De I'lkole Polytechnique de Lodz (Pologne), en stage post-doctoral au C.R.M. au

ABSTRACT:The free-radical polymerization of methyl methacrylate (MMA) at high temperature (120 to 180°C) has been studied in the presence of di-tertiobutyle peroxide as an initiator and 1-butanethiol as a chain transfer agent. No solvent was used, and the polymerization was run to high monomer conversion. Based on the experimental data collected with a dilatometric reactor, the features of the reaction have been pointed out. Working at high temperature with a chain transfer agent proved efficient to reduce the intensity of the gel effect and control the molecular weight obtained. At a temperature up to 170°C, however, the burn-out of the initiator limits the final conversion, and the increase of the polymerization rate during the gel effect has been more difficult to detect and quantify. An empirical expression of the termination rate constant has been adopted to describe the autoacceleration and predict the conversion versus time curves and the average molecular weight of the polymer obtained. The mathematical model includes two adjustable parameters that have been determined as a function of the temperature and the initial concentration of the chain transfer agent. The agreement between the predicted and experimental data on conversion and molecular weight was good, while the polydispersity index was often underestimated.

International audienceA model for the packing stage in injection molding of thermoplastics is proposed. It allows one to calculate the time evolution of pressure and temperature fields and mass variations in simple geometries. The model holds for amorphous as well as for crystalline polymers if the kinet-ics of crystallization are known for temperatures far from the melting point. It applies after filling stage; initial temperature and pressure conditions are available from filling-simulating software. The principles rest on finite difference schemes computing simultaneously temperature and velocity of compressible non-Newtonian fluid in a filled cavity. The pressure field is determined from an equation of state at any time, owing to a mass balance in each gridmesh. The meaningful results of the simulation are local shrinkage and a good approximation of final weights of finished products. The algorithm is essentially checked for the influence of physical, thermal, and processing parameters on the cavity pressure for the injection of a polystyrene (Gedex 1541) into a rectangular mold cavity

Kinetic studies of the bulk polymerization of methyl methacrylate at high temperature have been carried out first without any additives and then in the presence of 1-Butanethiol as a chain transfer agent. A pressurised dilatometric reactor operating at high temperature is used to determine the time-conversion curves at temperatures between 150 and 180°C. A two-stage polymerization is observed. The high polymerization rate obtained initially is attributed to traces of an initiating impurity, while the second, slower polymerization stage could be considered as the actual thermal polymerization. The chain transfer agent or an impurity it may contain also initiates the reaction. Therefore, the rates of both the initial polymerization and of the second stage are increased when the thiol is added.Experimental data on the degree of conversion versus time and on the final average molecular weight are used to determine the chain transfer constants to the monomer and to the mercaptan as well as the initiation rate constants. These constants are used to model the thermal polymerization of MMA at high temperatures where these initiation reactions can no longer be neglected, especially when an industrial polymerization process has to be optimized and controlled.