The tensile strength of polystyrene decreases with decreasing molecular weight and with increasing temperature, showing S mark curves with the change of molecular weight and temperature.
As amorphous polymers such as polystyrene maintain their strength with the entangled bonds of molecular chains, the following theoretical equations representing the relation between the molecular weight M and the tensile strength Ts have been introduced from by the three dimensional network structure model based on the entangled bonds of molecular chains of linear polymers.
Ts=K(1-2meM-4mem0/meM-m02-2mem0), M≤m0
Ts=K(1-2m0me/M2+m0me), M≥m0
K is a constant related not only to the rate of effective molecular chains determined by the directional distribution, chain length distribution and non-uniformity of the density of molecular chains, but also to the strength and breaking mechanism of molecular chains, m0 is the molecular weight at the condition that the three dimensional perfect network structure is formed, and me is the molecular weight of unit molecular chain between two connecting positions.
The experimental data of polystyrene indicate a sufficient agreement with the theoretical curve.
