Vinyl polymers multiple-site

The wall-PRISM theory has been extended to multiple site models [95], A simple example of a multiple-site model is a vinyl polymer (e.g., polypropylene) where there are three types of united-atom sites corresponding to CH2, CH, and CH3 groups. Ignoring end effects as before the PRISM equations take the form... 

In both the above types of polymerization through multiple bonds, namely vinyl and diene polymerization, a carbon-carbon double bond is the active site. However, multiple bonds involving elements besides carbon may also be utilized in the preparation of polymers, which then contain hetero-atoms in the main chain. The most common unsaturated monomers used for the preparation of polymers of this kind are carbonyl compounds. Formaldehyde has been the most widely studied in this respect and its polymers are of commercial importance. The product of polymerization of formaldehyde may be regarded as a polyether ... 

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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