To get a clear idea of the phase state of matter it is necessary to understand the concept of phase. The term ‘phase’ can be defined structurally and thermodynamically. It is part of a system separated from other parts by interfaces and differing from them in thermodynamic properties. A phase must possess sufficient spatial extension for the concepts of pressure, temperature and other thermodynamic properties to be valid. Structurally, phases differ in the order of mutual arrangement of their molecules. Depending on this order, there are three phase states, namely: crystalline, liquid and gaseous.
Polymer substances possess high molecular mass and hence their boiling points must be very high. They decompose when heated, and their decomposition temperatures are always far below their boiling points. Due to this, polymeric substances cannot be converted to the gaseous state and exist only in the condensed state—liquid or solid. A study of the phase states and ordering of polymers reveals a number of specific features related to the large size of their molecules.
It is pertinent to discuss the possibility of formation of an ordered state in a polymer system. In any ordering process, the existence of short-range and long-range orders are defined by the distance over which the order extends, vis-a-vis, the dimensions of the monomers. A polymer is associated with two types of structural elements: monomers and chains. Hence, while discussing short-range or long-range order, it is informative to assign which of these elements is ordered. In practice, the existence of long-range order may comprise the arrangement of both structural elements. It is clear that long-range order of monomers in one dimension can generate a linear chain of polymers.