Influence de la nature du solvant et de la température sur les dimensions non perturbées des copolymères statistiques PS–PMM

Abstract

The STOCKMAYER‐FIXMAN method has been applied to determine the unperturbed dimensions of a polymer chain from viscosity measurements on several fractions in a good solvent. Homopolymers yield values of the unperturbed dimensions which are independent of the nature of solvent and which hardly depend upon temperature. Using the same method for [η] measurements in different solvents, the values obtained for random copolymers PS–PMMA are quite different from the “ideal” values calculated on the basis of additivity rules from the unperturbed dimensions of corresponding homopolymers. The discrepancy was shown to depend on the χAB parameter, which also governs the critical concentration for phase separation for a solution of the corresponding homo polymers. Since χAB is solvent and temperature dependent, the observed variation in the unperturbed dimensions from one solvent to another can be qualitatively explained. Linear relation was found between χAB and KΘ leading to KΘ “ideal” for χAB = 0. Moreover, the temperature dependence of unperturbed dimensions for a random copolymer, in a given solvent, is much stronger than for an homopolymer. As temperature increases χAB decreases and the unperturbed dimensions approach the “ideal” values. These results show the influence of heterocontact interactions on chain conformation. They clearly demonstrate their importance at theta conditions by influencing the dimensions of the chain.

On the existence of two theta points for polymers in binary mixtures

“…In preceding articles (1,2), we have shown the difficulties encountered in the extrapolation t o ternary systems of thermodynamic behavior established for a polymer in a single solvent.…”

Dilute solution properties of alternating copolymers from acrylonitrile and α‐methylstyrene

“…We note that the unperturbed dimensions mol-'), are shown in Table 3. [2,3]. The values of the dielectric constant, E , for the solvents are shown in Table 3, and the results suggest that, generally, the larger the dielectric constant is, the lower is KO.…”

“…The observed values of A for this copolymers are smaller than the "ideal" values. Dondos and Benoit [3] found that for the statistical copolymer (styrene-methylmethacrylate) the experimental values are higher than the "ideal" values and they explain this phenomenon by the incompatibility of the monomer units. We consider that not only the incompatibility of the monomer units is responsible for this difference, but also…”

“…The viscosity data were extrapolated to zero shear rates and to zero concentration to obtain values for intrinsic viscosity [q],,. 3…”

Μορφολογια Πολυμερων Σε Αραια Και Λιαν Αραια Διαλυματα. Μελετη Των Κρισιμων Συγκεντρωσεων Γραμμικων Και Αστεροειδων Πολυμερων

“…=81000) είναι πολύ μικρή (Σχήμα Α4.4, καμπύλη Β).Μελέτη του στατιστικού συμπολυμερούς στυρένιο/μεθακρυλικός μεθυλεστέρας έχει δείξει ότι οι απωθητικές δυνάμεις μεταξύ PS και ΡΜΜΑ είναι πολύ ισχυρότερες στο π-ξυλόλιο απ' ότι στο THF48 . Με άλλα λόγια, θα πρέπει να παρατηρούμε δομικές αλλαγές του ενός πολυμερούς από την παρουσία του πολυμερούς "διαλύτης" και οι παράμετρος b^ß πρέπει να εκφράζει αλληλοαπωθήσεις μεταξύ των πολυμερών οφειλόμενες ελάχιστα στην χημική τους φύση αλλά κυρίως δε στην διαφορά στην πυκνότητα των μονομερών τους στοιχείων.…”