Branched, Ladder, and Network Polymers

Branched, ladder, and network polymers deviate from the linear macromolecules discussed up-to now. In order to remain fusible and plastic, the molecule must contain sufficient segments that are flexible and linear. Even without branches, linear molecules may have insufficient flexibility to melt. The linearpoly(p-phenylene), for example, is a rigid macromolecule (class 3 of Sect. 1.1.3), because rotation about its bonds does not change the molecular shape. One must thus watch in such molecules that sufficient flexibility exists for plastics applications. 

Short and long branch polymers example polyethylene 

Regularly branched polymers examples brushes and dendrimers 

The regularly-branched polymers separate at fixed points and present special shapes that can be used to modify surfaces. The three-dimensional dendrimers [6] form a sphere with an interesting space-fiUing character which depends on the chemical structure of the chains and branch points. 

The ladder, sheet, and some of the space network polymers shown are listed under letters B, C, and D in Fig. 1.21. They are often rigid, and are thus class 3 macromolecules (see Sect. 1.1.3). The flexible molecules of interest, however, are difficult to make with a specific stmcture so that they can be named (for a ladder polymer, see the isomers of polybutadiene in Fig. 1.20). Even epoxies and rubbers are usually so poorly characterized, that precise naming is impossible. 

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