Eigenschaften von gelösten und gequollenen Polymethylmethacrylaten in Abhängigkeit von der Struktur

Abstract

ZUSAMMENFASSUNG :Die Bildung von Stereokomplexen, die man beim Mischen von stereoregularen Polymethylmethacrylaten (PMMA) in verschiedenen Losungsmitteln beobachtet, wurde dielektrisch und viskosimetrisch untersucht. Rontgenweitwinkelaufnahmen losungsmittelfreier stereoregularer Polymergemische lassen erkennen, daB die Stereokomplexe aus kristallinen Bereichen bestehen. Aus Viskositatsmessungen an Losungen verschiedener Taktizitiit und dem Vergleich von Quellungseigenschaften an vernetztem PMMA kann gefolgert werden, daB die Assoziation isotaktischer und syndiotaktischer Sequenzen, die als Ursache der Stereokomplexbildung anzusehen ist, auch in Losungen und Gelen von ataktischeni PMMA auftritt. Dem Temperaturverlauf der reduzierten spezifischen Viskositiit, der komplexen Dielektrizitlitskonstante und der Quellung kann man entnehmen, daB die Assoziation uber mikrokristalline Bereiche zur Ausbildung physikalischer Vernetzungsstellen fuhrt, die in einem mehr oder weniger breiten Temperaturbereich aufschmelzen. Die Eigenschaften von verdunnten Losungen, die aus Mischungen von isotaktischem und syndiotaktischem PMMA und Toluol hergestellt werden, konnen mit einer vornehmlich intermolekularen Assoziation gedeutet werden. Die beobachteten Anomalien bei sehr verdunnten Losungen aus ataktischem PMMA lassen sich mit einer intramolekular auftretenden Assoziation erklaren. Die Eigenschaften der assoziierenden Losungen sind abhangig von ihrer thermischen Vorbehandlung und Vorgeschichte. SUMMARY:The stereocomplex formation, which is observed after mixing of stereoregular samples of polymethylmethacrylate (PMMA) in various solvents was studied by dielectric and viscosimetric measurements. By means of X-ray wide angle diffraction measurements of mixtures of stereoregular polymers freed from solvent it was found that the stereocomplex consists of crystalline regions. From viscosity measurements of solutions of various tacticity in comparison with swelling properties of crosslinked PMMA it is concluded that the association of isotactic and syndiotactic sequences, which is considered to be the reason for stereocomplex formation, also exists in solutions and gels of atactic PMMA. From the temperature dependence of the reduced specific viscosity, the complex dielectric constant, and the swelling we deduce that * Vortrag anlaBlich derTagung der GDCh-Fachgruppe ,,Makromolekulare Chemie"

Mechanical Properties and Orientation of Atactic Poly(methyl methacrylate): Sub-Tg Annealing and Stereocomplex Formation

“…[20 -24] As for atactic PMMA, Spevacek et al and Borchard et al proved the formation of the stereocomplex in solution based on NMR results and viscometric experiments, respectively. [15,25,26] In a previous paper, [27] we showed that the stereocomplex formed in films cast from the strongly complexing solvent acetone (A-aPMMA) but not Communication: The mechanical properties and orientation behavior of atactic poly(methyl methacrylate) films cast from acetone (A-aPMMA films) and chloroform (CaPMMA films), with subsequent sub-T g annealing, have been studied. The formation of a stereocomplex in sub-T gannealed A-aPMMA films and C-aPMMA films was demonstrated by means of differential scanning calorimetry.…”

Surface Characterization of Atactic Poly(methyl methacrylate) Aggregates Using Atomic Force Microscopy

“…Spevacek et al and Borchard et al have proved that stereocomplex was able to form in atactic PMMA solutions. [3][4][5] Studying with DSC and FT-IR, 6,7 we also found that a stereocomplex formed in atactic PMMA film from strong complexing acetone, while not in that from noncomplexing chloroform. Stereocomplex in the film derived from the solution from which the film was cast.…”

“…1,2 As for atactic poly(methyl methacrylate), Spevacek et al and Borchard et al proved that stereocomplex was able to form in its solution. [3][4][5] And a stereocomplex was also found in atatic PMMA film from strong complexing solvent acetone. 6,7 In this note, the effects of solvent and substrate on the patterning of a-PMMA aggregates were studied using by atomic force microscopy (AFM).…”

Photoelasticity and structure of PMMA networks

“…The measured value Aa + is an average value of Aa, the optical anisotropy of the free segments according to the definition of Kuhn and Griin [1], and Aa,,, the optical anisotropy of the associations. To exclude the influence of the stereo-associations the polar solvent chloroform CHC13 with a tendency to hydrogen bonding can be used [22,23]. But the optical anisotropy determined for PMMA-CHC13-gels is never the true value of a statistical segment.…”