Die Bestimmung der Molekulargewichtsverteilung von nichtkristallisierenden Polymeren mit dem Elektronenmikroskop, 4. Weiterentwicklung der Präparationsmethode durch Gefriertrocknung

Abstract

Molecular weight distribution curves determined by electron microscopy exhibit a deviation when approaching a molecular weight of 10'. Picturing of single molecules therefore was improved by the introduction of shadowing by electron beam. Techniques of preparation (by freeze-drying) and shadowing are described in detail. The scanning size of the electron beam shadowing is in between 15 and 20 A and is given by the structure of the supporting film. By double shadowing from different sides it is demonstrated, that there is no "decoration effect" in electron beam shadowing. The lower limit of an exact determination of the dimensions is a molecular weight of ca. lo5. It is shown with latex particles that there is a change of shape with time of the particles after sedimentation on the support which is dependent on the kind of polymer and of the conditions. Their volume though remains constant within the limits of error.

Enthalpy recovery in low molecular weight PMMA

“…In this respect a possible role of the entanglement was invoked. It is also worth noting that it has been recently evidenced the influence of the chain entanglements on the structural relaxation features of polycarbonate [36], polystyrene and poly(ether sulfone) [37] and poly(vinyl chloride) [38] with the use of special drying methods [39][40][41] which provide highly disentangled polymeric systems. In particular after annealing the samples in the glass, the enthalpy recovery measured by DSC thermograms showed a quite different behavior for the disentangled systems with respect to the entangled ones.…”

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. , …”

Glass Transition of Disentangled and Entangled Polymer Melts: Single-Chain-Nanoparticles Approach

“…Their corresponding properties can be compared to that of an entangled melt of bulk polymers. 16 − 18 SCNPs can be prepared using a variety of techniques such as precipitation, 19 − 22 freeze-drying, 16 , 23 , 24 crystallization, 17 , 18 spin-casting, 25 and electrospraying. 26 − 28 All these preparation methods have the use of very dilute polymer solutions in common.…”

“…Heating SCNPs of high molecular weight above T g leads to the formation of a metastable disentangled melt of polymers. Their corresponding properties can be compared to that of an entangled melt of bulk polymers. − SCNPs can be prepared using a variety of techniques such as precipitation, − freeze-drying, ,, crystallization, , spin-casting, and electrospraying. − All these preparation methods have the use of very dilute polymer solutions in common. In electrospraying, electric fields are applied to facilitate the production of extremely small droplets out of polymer solutions, almost exclusively containing only one polymer chain each.…”