Polyvinyl formal, preparation

Plastic films can be formed from a number of polymers two of the most common are collodion (nitrocellulose) and polyvinyl formal (Formvar). A number of other plastic materials can be used for thin films, some with specific advantages (101). Plastic films are usually prepared either by spreading a drop of solution of the plastic (in an appropriate solvent) onto a clean water surface, or by stripping off a film that has been coated onto a clean, flat surface (such as a glass slide) onto the surface of clean water. 

Plastic, carbon and metal films (Section 4.7) are used as specimen supports on TEM grids. There are two plastic support materials in use collodion, 0.5% solution of nitrocellulose in amyl acetate and formvar, 0.25% polyvinyl formal in ethylene dichloride. These polymers are available as powders, solutions or prepared films on TEM grids. Formvar films, especially holey ones, are used as substrates for the formation of holey carbon films. Today, collodion is not used too often, as it is not as stable in the electron beam as formvar or carbon films. 

Several vinyl monomers are used to prepare thermoplastics that are useful in certain adhesive applications. The most important vinyl resins for adhesives are polyvinyl acetate, polyvinyl acetals (butyral and formal), and polyvinyl alkyl ethers. PVC and copolymers of both vinyl chloride... 

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