Molecular dynamics simulation study on the bulk modulus above and below the glass transition temperature

Bulk moduli of amorphous polymers such as polyethylene, polypropylene, and polyisobutylene were investigated in the wide temperature range near the glass transition temperatures by means of molecular dynamics simulations. The large changes in the bulk moduli from 1 similar to 2 GPa to 3 similar to 4 GPa with lowering temperature below the glass transition temperatures were calculated in the case of polyethylene and polyisobutylene. These calculations agreed well with experimental results that these polymer materials having an amorphous phase lose their rubber elasticity at temperatures below their glass transition temperatures. With some exceptions, the calculated values of bulk moduli in the wide temperature range were almost the same as the experimentally observed ones.