Investigation of polymer texture by electron microscopy

Electron microscopy represents the only direct method that permits to see with our own eyes the interior of a sample with a resolution of a few nanometers. To characterize the texture of hypercrosslinked polystyrenes both transmission and scanning electron microscopy have been appfied. In the former case, ultrathin sections with a thickness of about 600 A were cut firom a sample fixed in epoxy resin, and then directly examined in transmission mode. Alternatively, two-step replicas have been prepared firom the cleavage face. To prepare the repfica the surface was first coated with a collodion film appfied from amyl acetate solution, and then with a carbon—platinum film. Finally, the collodion support was dissolved and the free carbon—platinum repfica examined under a transmission microscope. 

In the case of scanning electron microscopy, a fresh cleavage face was coated with gold and examined. 

According to simple calculations, the diameter of a dry densely packed polystyrene species with a molecular weight of 300000 Da and density of 1.05 g/cm corresponds to 98 A. Intensive crosslinking of such species in solution introduces 0.5 cm /g of voids in the dried material, and, therefore, the diameter of the dry porous cods should increase to 113 A. As a rule, the dimensions of spherical species observed on the cleavage exceed this 

our conclusion on the restricted overlapping of individual polystyrene coils in the hypercrossHnked network and in the initial polymer solution was further corroborated by a direct experiment, namely by the preparation of a hypercrossHnked material deHberately constructed from individual polystyrene macromolecules. The initial Hnear polystyrene was first crosslinked intramolecularly in a very ddute solution and then the individual intramolecularly crossHnked cods, nanosponges, were additionally crosslinked intermolecularly in a concentrated solution, thus giving a bulk hypercrossHnked material. Both the nanosponges and the final polymeric material were subjected to electron microscopic investigation. 

Soluble intramolecularly hypercrossHnked polystyrene (nanosponges) represent a fundamentady new macromolecular object that wdl be described in detail in Chapter 8. For the above two-step modeling experiments, nanosponges were prepared from the industrial Hnear polystyrene having a molecular weight of 300 000 Da and a wide molecular weight 

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