Narrow Molecular Mass Distribution Research Articles

Viscoelastic Characteristics of Polymers of Narrow Molecular-Mass Distribution in Various Physical States According to Data on Small-Amplitude Oscillating Shear

Abstract This work is concerned with the results of dynamic investigations of 1,2-polybutadienes of narrow molecular-mass distribution over a wide temperature-frequency range covering various physical states of the material, from the fluid to the glassy state. The limits of applicability of the use of the temperature-frequency reduction are given. The experimental results have been obtained under the following test conditions: at variable frequency and constant temperature; at variable temperature and constant frequency.

Fracture of uncured linear flexible-chain polymers of narrow molecular mass distribution in triaxial stress (behaviour of elastomers as adhesives)

Possibly the simplest method of studying polymers under conditions of triaxial stress is the investigation of the behaviour of thin films of adhesive between two rigid surfaces. The adhesives used were uncured linear flexible chain polymers-polybutadienes. These polymers were of narrow molecular mass distribution ( MMD). The use of high molecular polymers of narrow MMD allows the evaluation of the behaviour of elastomers as adhesive joints to be simplified. It has been shown recently that, depending on the rate of deformation, the behaviour of polymers of this kind may be similar to that of viscoelastic liquids or systems in the high-elastic state, which behave as quasi-cured systems, The transition from the fluid to the high-elastic state is a pure relaxation process. It would be expected that the behaviour of the adhesive would vary substantially, depending on its physical state. The fracture behaviour of the adhesive and the rupture of its contact with the solid surface must be dependent on this factor. Cohesive, cohesive-adhesive and adhesive fractures may be observed in such cases. Cohesive fracture is typical for regimes of polymer deformation upon transition from the fluid to the high-elastic state. The further the transition of the polymer to the high-elastic state, the more sharply pronounced is the adhesive fracture of the polymer in triaxial stress. The present work is concerned with the investigation of the temperature-time dependence of the parameters characterizing the fracture of the adhesive and its contact with the solid surface. The results of experiments carried out under conditions of triaxial stress are compared with the data obtained for the same polybutadienes by experiments involving simple shear and uniaxial extension.

Fluid polymeric systems and their filling. 1. High-molecular linear polymers of narrow molecular mass distribution

Fluid polymeric systems and their filling. 1. High-molecular linear polymers of narrow molecular mass distribution

Dynamic viscoelastic behaviour of low-molecular-mass polystyrene melts

Measurements have been made of the viscoelastic properties of a range of low-molecular-mass polystyrenes each having a narrow molecular mass distribution. Several experimental techniques using alternating shear have been employed covering the frequency range 10 -2 Hz to 450 MHz and at temperatures from the glass transition temperature to T g + 80 K. The equilibrium (limiting low-frequency) compliance, J e , and the limiting high-frequency compliance, », have each been determined as a function of temperature. Jw is found to be independent of molecular mass at any given value of T— T g . The sample of molecular mass 580 shows a behaviour closely similar to that of non-polymeric supercooled liquids. Samples of molecular mass above 1100 show distinct polymeric behaviour as an additional lowfrequency contribution to the complex shear modulus which can be accounted for by summation over a limited number of Rouse modes of the unentangled polymer molecule. This, combined with the ‘liquid-like’ behaviour of short elements of the polymer chain, gives calculated curves which are in good agreement with experimental results. An alternative analysis describes the complete behaviour by a single equation for the complex compliance of the form J*(jw) = J∞+1/1wn+Jr/(1+jwTr)B, where J r is the retardational compliance. It is not possible to distinguish between these two approaches on the basis of the present data. At temperatures above T g + 40 K measured values of J e are in agreement with calculations based upon the Rouse equations, which can therefore be used as a basis for predicting the observed behaviour both as regards the equilibrium properties and over the relaxation region.

Phase equilibria of polystyrene solutions

AbstractThe cloud‐point curves for polystyrene (PS) solutions in ethylbenzene, decalin, and cyclohexane have been studied. Investigations of the spinodal for these systems were carried out using the light scattering method proposed by Chu and Scholte. The existence of the upper critical solution temperature polystyrene–for the system ethylbenzene has been demonstrated. For the sample of PS with a narrow molecular mass distribution the cloud‐point curves are binodal. The tops of binodals and spinodals coincide.From the temperature and angle dependences of light scattering the radius of gyration were calculated using the theory of Debye and of Vrij and Esker.