epoxy resin and the unsaturated polyester resin (commonly reinforced by the glass
fibers), which exhibit a good thermal resistance, and do not even swell in solvents.
8. Interpenetrated networks.We can first make the cross-linked polymer swell in
the monomer solvent, and then initiate polymerization of the solvent molecules to
form another cross-linking network, as shown in Fig.2.10b.Bythisway,the
interpenetrated network (IPN) allows two thermodynamically incompatible
polymers to be mixed on the molecular level, and thus integrates their favorable
properties. The case for the solvent monomers to perform only polymerization
without further cross-linking, is called the semi-interpenetrated network.
The complexity of macromolecular architectures is limited only by our imagi-
nation and our chemical synthesis skills. As in the building blocks, the physical
behaviors of linear polymers are of essential importance in determining the physical
behaviors of high-level complex structures of macromolecules.
2.6 Sequence Irregularities
Crystallization is a compact-packing process of polymer chains, which is very
sensitive to any mismatch in the geometries of chain sequences. The
crystallizability of polymers is thus restricted by the high content of sequence
irregularities. Therefore, the sequence regularity is a very important chemical factor
to characterize polymer microstructures. There are commonly three kinds of
irregularities in chain sequences, i.e., chemical irregularities, geometrical
irregularities and spatial irregularities.
Fig. 2.9 Illustration of
molecular structures of
polymer brushes
Fig. 2.10 Illustration of (a)
cross-linking network and (b)
interpenetrated network (IPN)
2.6 Sequence Irregularities 29