Vinyl resins formulation considerations

A current version of the low molecular weight concept is the use of bismaleimides made from aromatic diamines and/or mixtures thereof and maleic anhydride in admixture with other vinyl monomers. Several commercial formulations of this type are now available as the neat resins or as FRP prepregs. There is considerable current research in this area because of the favorable processibility. However, to date, FRP products of this type are outperformed by the PMR-type polyimides by about 50 C at elevated temperatures. 

Solvents used for paint removal are able to dissolve or considerably swell physically drying binders (e.g., vinyl chloride copolymers, cellulose nitrate, polyacrylates) and chemically cross-linked coatings (e.g., oil-based paints, dried alkyd resins, cross-linked polyester-melamine resins, cross-linked epoxy and isocyanate coatings) [14.237]. A combination of dichloromethane with low-boiling ketones or esters is particularly suitable. Small amounts of high-boiling solvents with a low volatility (e.g., tetrahydronaphthalene, solvent naphtha, methyl benzyl alcohol, or benzyl alcohol) are added to these mixtures to retard evaporation and increase the solvency. Modern paint removers do not contain chlorinated hydrocarbons, they are formulated on the basis of high boilers (e.g., dimethylformamide, dimethyl sulfoxide, propylene carbonate, and yV-methylpyrrolidone) in combination with alcohols and aromatics, or consist of aqueous, frequently alkaline or acidic systems. 

We can easily see that the structures of beta-pinene and dipen-tene resins are quite different. The polymer chain of a beta-resin is more extended and flexible than that of a dipentene resin. Thus, from a consideration of the structures of the polymer repeating units, dipentene resins should exhibit a lower viscosity than beta-pinene resins at equal degree of polymerization. Actually, the viscosity of dipentene resins also has a greater dependence on temperature it is reduced to a greater extent than a comparable beta-resin. Dipentene resins are also more compatible with ethylene-vinyl acetate copol3nners. The cloud point, obtained in a compatibility test using a 10 20 20 blend of resin wax ethylene-vinyl acetate, is about 90°C and can be compared with about 175°C for a beta-resin. Thus, these resins are preferred over beta-pinene resins for hot melt adhesives. Since formulations employing dipentene resins reach a compatible cloud-free liquid state at a lower temperature, less oxidation is likely to occur. Dipentene resins have also been found to be more color stable than beta-pinene resins, which probably reflects the presence of fewer olefinic sites where oxidation can occur. Dipentene resins also tend to be thermally stable because of their multiple strand structure. 

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