The degree of polymerization DP refers to the number of monomer units in a polymer chain. In the case of polystyrene, the monomer unit is styrene. The physical properties of a polymer, such as its melting point and glass transition temperature, are significantly influenced by the degree of polymerization.1. Melting Point:Polystyrene is an amorphous polymer, which means it does not have a well-defined crystalline structure. As a result, it does not have a sharp melting point like crystalline polymers. However, the degree of polymerization can still affect the softening and flow behavior of polystyrene. As the DP increases, the molecular weight of the polymer chains also increases. This leads to stronger intermolecular forces such as van der Waals forces between the polymer chains, which require more energy to overcome. Consequently, the temperature at which the polymer softens and flows will increase with increasing DP. However, this effect is not as pronounced as in crystalline polymers, and the melting behavior of polystyrene will still be broad and gradual.2. Glass Transition Temperature Tg :The glass transition temperature is the temperature at which a polymer transitions from a glassy, brittle state to a rubbery, more flexible state. The Tg of polystyrene is influenced by the degree of polymerization. As the DP increases, the molecular weight of the polymer chains also increases, which leads to a higher entanglement of the polymer chains. This increased entanglement results in a higher resistance to chain mobility and, therefore, a higher Tg.In summary, as the degree of polymerization of polystyrene increases, both the softening/melting behavior and the glass transition temperature will generally increase. This is due to the increased molecular weight and intermolecular forces between the polymer chains, as well as the increased entanglement of the chains, which restricts their mobility.