Modeling of Complex Polymers and Processes

Abstract

Creating new macromolecular architectures with increasing complexity can constitute a challenge for synthetic chemists but can additionally be justified if it would result in new material properties. For example, joining monomeric units into linear polymer chains, results in a dramatic change of properties of products with respect to properties of substrates. Whereas, a monomer in bulk can usually be only liquid-like or solid (e.g., glassy), the polymer can additionally exhibit a rubbery state with properties, which make these materials extraordinary for a large number of applications. This new state is due to the very slow relaxation of polymer chains in comparison with a fast motion of the monomers, especially, when the chains become so long that they can entangle in a bulk melt. The dynamic mechanical characteristics indicate a single relaxation in the monomer system (Fig. 1a) in contrast to the two characteristic relaxations in the polymer (Fig. 1b). The rubbery state of the polymer extends in the time scale between the segmental (monomer) and the chain relaxation times and is controlled by a number of parameters related to the polymer structure. The most important among these parameters is the chain length determining the ratio of the two relaxation rates. In the rubbery state, the material is much softer than in the solid state. If expressed by the real part of the modulus, the typical glassy state elasticity is of the order of 109 Pa and higher, whereas the rubber like elasticity in bulk polymers is of the order of 105-106 Pa.