Long-chain branching and tree-like polymers exhibit quite different flow
behaviors compared to linear polymers. They can be a good additive in the
bulk linear polymers to improve the rheological performance of polymers upon
processing.- Block copolymers.The multi-component systems are intramolecular, with each
component occupying a certain length of chain sequences, as shown in Fig.2.8a.
They can be diblock, triblock or even multi-block copolymers. Upon the change
of composition, the microphase separation in block copolymers can fabricate
various geometries of regularly packed microdomain patterns with nano-scale
resolution, as will be introduced in Sect.9.3. - Star polymers.Derived from the same center, the star arms may belong to the
same species, as shown in Fig.2.8b, or to the different species. The arms with
different components can form the nano-scale microdomain patterns as well. - Polymer brushes.One end of each polymer chain is anchored on the same solid
surfaces of a rod or a flat-plate. When the graft density becomes high, polymer
chains will stretch out due to the overcrowding on the surfaces, as shown in
Fig.2.9. Polymer brushes can change the surface properties and thus give solid
surfaces a responsive function. - Cross-linking networks.The degree of cross-linking is characterized by the
density of cross-linking points in the network, as shown in Fig.2.10a.Examplesof
low-density cross-linking are the vulcanized rubber and chewing gum, which
release the entropy elasticity of polymer chains, and only swell when in solvents.
Examples of high-density cross-linking are the phenol-formaldehyde resin, the
Fig. 2.7 Illustration of (a) comb-like polymers and (b) hyper-branched polymers
Fig. 2.8 Illustration of (a) diblock copolymers and (b) star polymers
28 2 Structure–Property Relationships