Meaning
Molecular topology determines the density of temporary connections that restrict the movement of polymer strands. Scientists define entanglement molecular weight as the threshold mass required for a polymer to exhibit rubbery behavior. This value is a fundamental characteristic of the resin chemistry.
Viscosity Correlation
Melt flow resistance increases sharply once the chain length exceeds this critical value. When the actual mass is much higher than the entanglement molecular weight the viscosity follows a power law relationship. This effect governs the pressure required to fill a mould during injection.
Chain Architecture
Linear polymers have a different spacing between knots than branched varieties. Calculating the entanglement molecular weight helps in predicting the melt strength of different resin grades. It also explains why some polymers remain more flexible than others at the same molecular weight.
Mechanical Property
Toughness and crack resistance in the solid state are linked to the number of these physical bridges. A lower entanglement molecular weight generally leads to a more robust material with better environmental stress crack resistance. Moulders must balance this property against the difficulty of processing high viscosity resins.
If the mass falls below this critical threshold the material becomes brittle and loses its ability to form a stable melt. This parameter is used by resin producers to design grades that offer both high strength and ease of flow.
