Die bestimmung der molekulargewichtsverteilung von nichtkristallisierenden polymeren mit dem elektronenmikroskop. I. Präparationsmethoden und kontrollen

Abstract

ZUSAMMENFASSUNG:Bei der elektronenmikroskopischen Abbildung von Einzelmolekulen treten eine Reihe von praparativen, Schwierigkeiten auf, welche dazu gefuhrt haben, daS man trotz zahlreicher Arbeiten diese Methode bisher noch nicht zu einem Standardverfahren entwickeln konnte. Ein Haupthindernis stellt das Auftreten von Artefakten dar, die den nichtkristallinen Polymermolekiilen tauschend ahnlich sehen.Zur Erkennung und Vermeidung dieser ,,ScheinmolekCle" ist es notwendig, quantitative Praparations-und Kontrollmethoden zu entwickeln. Es eignen sich zwei Verfahren : einmal die sogenannte Tropfenmethode und zum anderen die Gefriertrocknuugsmethode. Mit Hilfe dieser Verfahren gelingt es, das Artefaktproblem zn losen und die Homogenitat der Praparate zu testen. SUMMARY:The imaging of single polymer molecules by electron microscopy faces a lot of difficulties with regard to preparation, thus preventing this method from developing to a standard technique, in spite of numerous attempts. A main obstacle is the appearance of artefacts which look strikingly similar to polymer molecules.It is necessary to develop preparation methods enabling quantitative analysis in order

Influence of Entanglements on the Glass Transition and Structural Relaxation Behaviors of Macromolecules. 1. Polycarbonate

“…Isolated single- or pauci-chain polymer particles can be obtained using several different methods, all relying on isolation of the molecules from dilute solutions. Once the polymer is dissolved, the rapid addition of a bad solvent can lead to precipitation of isolated single-chain polymer particles. − Alternatively, the solution can be rapidly frozen and the solvent removed subsequently by sublimation, leaving isolated single-chain particles. − A variety of spray methods have also been used to generate isolated polymer particles. These rely on the evaporation of the solvent from droplets of dilute solutions containing single polymer molecules. − Recently, Kumaki developed a new method to obtain single-chain particles of polymers; they were obtained by spreading dilute polymer solution in benzene on a water surface. , …”

“…[1][2][3][4] Alternatively, the solution can be rapidly frozen and the solvent removed subsequently by sublimation, leaving isolated single-chain particles. [5][6][7] A variety of spray methods have also been used to generate isolated polymer particles. These rely on the evaporation of the solvent from droplets of dilute solutions containing single polymer molecules.…”

Single- and Few-Chain Polystyrene Particles by Electrospray

“…Since the polymer is relatively monodisperse, different particle sizes must originate from different numbers of polymer chains in the particle. The number of polymer chains in a particle can be calculated assuming that the particle density is the same as the bulk density (ρ), as established in the literature for particles produced with different techniques. ,, On the basis of these assumptions, the number of molecules in a particle can be estimated from where m u is the atomic mass unit (1.66 × 10 -27 kg). Because of possible deviation of the large particles from semispherical, eq 2 gives only an upper limit for the number of chains in the large particles.…”

“…Isolated single-chain polymer particles were obtained using several different methods, all relying on isolation of the molecules from dilute solutions. Once the polymer is dissolved, the rapid addition of a bad solvent can lead to precipitation of isolated single-chain polymer particles. − Alternatively, the solution can be rapidly frozen and the solvent removed subsequently by sublimation, leaving isolated single-chain particles. − In both cases the particles have to be below their glass transition temperature ( T g ) to avoid complications from agglomeration of the resulting particles. A variety of spray methods have also been used to generate isolated particles.…”

“…An alternative spraying technique, electrospray (ES) employs an electrical field to facilitate the production of very fine droplets. Spraying methods have been applied to a variety of different polymers, including polystyrene, , polyethylene, poly(methyl methacrylate), several other polyacrylates, polyisobutene, and natural rubber …”