Preferential salvation. effect on polymer dimensions†

In this paper we discuss the light scattering theory of preferential solvation. We also present a more recent theory predicting a preferential solvation dependence on polymer molecular weight. These theories have been confirmed by the experimental results of the present work. It was established that the polymer coil dimensions depend on the local solvent composition and not on the analytical one. The local solvent composition can be calculated, in certain cases, from the value of the preferential solvation coefficient. © 1976, Taylor & Francis Group, LLC. All rights reserved

Characteristic numbers of polymers in dilute solution : a universal description of the cross-over effects

The viscosimetric behaviour of eleven polymer-solvent systems is analysed in order to determine the characteristic numbers in the beginning and in the end of the cross-over region. In the beginning we have a cross-over between Gaussian and excluded volume behaviour and in the end a cross-over between partial excluded-volume and complete excluded-volume behaviour (in the second cross-over the chain exhibits an excluded volume statistics on a macroscopic scale and starts the linearity between log [η ] and log M). We show that in the beginning and in the end of the cross-over region the characteristic molecular weight or the characteristic number of monomers is different for different polymers and the second is related to the stiffness of the chain. In the contrary, the characteristic number of statistical segments in the beginning and in the end of the cross-over region are about the same for all the polymers, and this result confirms the validity of a universal description of polymer solutions.Le comportement viscosimétrique de onze systèmes polymère-solvant a été analysé afin de déterminer les nombres caractéristiques au début et à la fin d'une zone de raccordement. Au début de cette zone les polymères passent d'un comportement gaussien à un comportement de volume exclu (masse moléculaire Mc) et à la fin de cette même zone les polymères passent d'un comportement partiellement obéissant au volume exclu à un comportement obéissant pleinement au volume exclu (masse moléculaire M'c). A ce deuxième point on peut dire que nous avons une statistique de volume exclu à longue échelle et nous avons le début de la linéarité entre log [η] et log M. Nous avons montré qu'au début et à la fin de la zone de raccordement le poids moléculaire ou le nombre des motifs monomères sont différents pour les différents polymères et il existe une relation linéaire entre les motifs monomères et la rigidité de la chaîne pour le deuxième point de raccordement. Par contre, le nombre des segments statistiques au début et à la fin de la zone de raccordement est presque le même pour tous les polymères et cela confirme la validité d'une description universelle de solutions des polymères

The Relationship between the Unperturbed Dimensions of Polymers in Mixed Solvents and the Thermodynamic Properties of the Solvent Mixture

The unperturbed dimensions of polystyrene and poly(2-vinylpyridine) have been measured in solvent-precipitant mixtures of various compositions using the Stockmayer–Fixman representation. It is possible to obtain a linear relationship between Kθ and ΔGE (the excess free enthalpy of mixing of the solvents) if, instead of using the bulk composition of the mixture, one introduces its “local” composition. This composition is calculated from the values of the preferential adsorption coefficient measured by light scattering. © 1973, American Chemical Society. All rights reserved

COPOLYMÈRES SÉQUENCES ET GREFFES : STRUCTURE ET PROPRIÉTÉSL'INCOMPATIBILITÉ DES POLYMÈRES : SON INFLUENCE SUR LA STRUCTURE DES COPOLYMÈRES

Lorsqu'on essaye de mettre en solution deux polymères de nature différente dans un même solvant, on observe dans la majorité des cas une séparation de phase. Celle-ci s'explique, du moins qualitativement, par des considérations thermodynamiques simples et ne souffre d'exceptions que dans le cas des polymères fortement polaires ou susceptibles de former des liaisons hydrogène. Lorsqu'on a affaire à un copolymère séquence, on peut s'attendre à une séparation de phase à l'échelle moléculaire et à une structure ségrégée de la molécule. On donne quelques résultats expérimentaux qui justifient cette hypothèse et l'on montre qu'il est possible, par élévation de la température, de passer d'une forme ségrégée à une chaîne statistique.If one tries to mix solutions of two different polymers in the same solvent, usually phase separation is observed. This phenomenon can be explained qualitatively from considerations based on the theory of regular solutions and of cohesive energy density. The only exceptions are encontoured for polar polymers or polymers able to form hydrogen bonds. This shows that intramolecular phase separation or more precisely segregation should occur for block copolymers. Some results are shown which support this hypothesis and a case of transition from segregated form to Gaussian coil is discussed

Influence de la solvatation preferentielle sur les dimensions des polymeres en solution dans des melanges de solvants

We have studied the dependence of the intrinsic viscosity number of polymers on the composition of binary solvents. The systems studied are: polystyrene in CCl4/CH3OH, C6H6/CH3OH and C6H6/heptane and poly-2-vinylpyridine in CHCl3/CH3CH2OH. We have also studied, for the same systems, preferential solvation of the polymers, using light scattering. We have observed that, near the θ point, short polystyrene chains exhibit a higher expansion than long chains. This was explained in terms of the dependence of preferential solvation on molecular weight. For the system poly-2-vinylpyridine/CH3CH2OH/CHCl3, we have established the viscosity increment dependence on solvent composition. The curve describing this increment differs markedly from the theoretical curve based on GE values (excess free energy) of the solvent mixture. However, taking into consideration the process of preferential solvation, the experimental curve can be corrected and becomes very similar in shape to the theoretical curve but there still remains a quantitative difference between the two curves. © 1973

Segregation and conformational transitions in triblock copolymers in dilute solution: 3. Viscometric investigations in solvent mixtures

Viscometric measurements were carried out on a triblock copolymer PMMA/PS/PMMA at two temperatures in two binary solvent mixtures, in order to establish to what extent segregation between the two kinds of blocks is maintained as the composition of the solvent mixture i.e. its preferential affinity to one of the blocks, changes. From the variation of the limiting viscosity number of the polymer versus composition of the solvent mixture, taking into account the corresponding plots for the two homopolymers, it was established: that at relatively low temperature the molecular dimensions of the block copolymer are very close to those calculated neglecting the heterocontact interactions, i.e. assuming segregation, and that at higher temperatures the dimensions observed for the block copolymer are higher than the values calculated by assuming segregation, thus showing that the heterocontacts exert some influence, inducing the chain to expand. A comparison with a PS/PMMA random copolymer of the same composition showed, however, that in the same solvent mixtures the number of heterocontacts was far lower in the case of the block copolymer than in the case of the random copolymer, even at elevated temperatures. © 1975

Shear viscosity measurements in the binary mixture butyl cellosolve-water near its upper and lower critical consolute points

To further probe the hypothesis of universality of critical phenomena, the shear viscosity has been measured for a two-component critical liquid system, butyl cellosolve-water, in the region of both the entropy-driven lower (LCST) and the enthalpy-driven upper (UCST) critical solution temperature. The values of the critical exponents ϕn for the shear viscosity were obtained by analysing the results from the viewpoint of multiplicative renormalization of transport coefficients. We have obtained ϕn = 0.038 ± 0.001 (30.14 wt. %) and 0.036 ± 0.007 (24.78 wt. %) for the UCST mixture, and ϕ n, = 0.038 ± 0.001 (30.14 wt. %) and 0.037 ± 0.003 (24.78 wt. %) for the LCST mixture. These exponent values agree well with mode-mode coupling and renormalization-group predictions and satisfy the universality hypothesis.Afin de tester l'universalité des concepts régissant les phénomènes critiques, la viscosité de cisaillement de mélanges binaires n-butylglycol (1)-eau a été étudiée au voisinage des deux températures critiques LCST et UCST respectivement d'origine entropique et enthalpique. Les valeurs des exposants critiques ϕn de la viscosité de cisaillement sont obtenues par une analyse des résultats utilisant une renormalisation des coefficients de transport. Soient, pour le mélange UCST, ϕ = 0,039 ± 0,001 (30,14 % en poids de n-butylglycol) et 0,036 ± 0,007 (24,78 %) tandis que pour le mélange LCST, ϕ = 0,038 ± 0,001 (30,14 %) et 0,037 ± 0,003 (24,78 %). Ces exposants sont en bon accord avec le concept de couplage mode-mode et les prévisions du groupe de renormalisation

Etude des dimensions moleculaires des polymeres dissous dans des melanges binaires de solvants polaires et non polaires-I. Polyvinyl-2 pyridine

We have studied the molecular dimensions of poly-2-vinylpyridine in solution in binary solvent mixtures consisting of a non polar and a polar component, viz. benzene-ethanol and benzene-chloroform. We have also studied the preferential solvation of the same polymer in the above mixtures using light scattering. We have observed a conformational transition of P2VP taking place in a composition region for each solvent mixture. This transition shows as a discontinuity in the unperturbed dimensions, in the long range interactions parameter and in the parameter of preferential solvation of the polymer. We think that this transition is related to the existence of two ordered structures of the polymer chain, one stable before and the other after the transition region. © 1974