22.2 Properties of Polymers

  • Degree of polymerisation (\(D\)): It is the number of monomer units present in the polymeric chain to form the polymer. \[D= \frac{M_p}{M_o}\]

    where

    \(M_p\) = average molecular weight of polymer
    \(M_o\) = molecular weight of monomer

    Significance of degree of polymerisation:

    • Polymers with low degree of polymerisation (10–100) are called oligopolymers or oligomers.

    • Polymers with high degree of polymerisation (10\(^4\)–10\(^6\)) are called macromolecules or high polymers.

  • Melt flow index (MFI) / Melt flow rate (MFR): It is the amount of grams of polymer that can flow in 10 minutes through a capillary of a given diameter when subjected to a certain load at a certain temperature. The conditions vary from polymer to polymer. MFI usually decides the grade of polymer formed and hence impacts where the polymer can be used. MFI is reported in g/10 min.

  • Glass transition temperature (\(T_g\)): A polymer is a soft, and leathery material below its \(T_g\); and it will be a hard and brittle one above its \(T_g\).