Mechanical spectroscopy of magnetite filled polyurethane shape memory polymers

Magnetite-polyurethane (PU) shape memory polymer (SMP) composites containing 10-40vol.% magnetite have been prepared and their mechanical properties in a temperature range from 255 K to 355 K at vibrating frequencies of 0.1 Hz, 1.0 Hz and 10 Hz were investigated. The damping peak at glass transition around 318 K is decreased by the addition of magnetite while it becomes simultaneously broader. Also activation energies for the main relaxation at glass temperature of the composites are varying between 265 kJ/mol and 382 kJ/mol with magnetite content. The storage modulus shows a major drop around 318 K corresponding to the glass transition. Storage modulus of the filled composites increases from 1911 MPa for pure PU shape memory polymer up to 11000 MPa for PU shape memory polymer with 40 vol. % magnetite. Calorimetric investigations show that glass transition temperature is slightly lowered by magnetite content, while the amount of crystallites is increased. Additionally, thermogravimetric analyses show that magnetite increases slightly thermal stability of the first decomposition step of the investigated shape memory polymer. (C) 2007 Elsevier B.V. All rights reserved.