3.2　Molecular Architecture

Molecular architecture deals with the shape of a polymer molecule. Examples of polymers with different molecular architecture are shown in Figure 3.3. A short-chain branch has an oligomeric nature whereas a long-chain branch is of polymeric length. A network polymer consists of many interconnected chain segments and many different molecular paths existing between any two atoms.

Figure 3.3　Schematic representation of structure of polymers with different molecular architecture

The molecular architecture is important for many properties. Short-chain branching tends to reduce crystallinity. Long-chain branches have profound effects on rheological properties. Typical of ladder polymers is a high strength and a high thermal stability. Hyperbranched polymers consist of molecules with an approximately spherical shape， and it has been shown that their melt viscosity is significantly lower than that of their linear analogue with the same molar mass. Crosslinked polymers are thermosets， i.e. they do not melt. They also show little creep under constant mechanical loading.