Slow calorimetry and heat of fusion of poly(4-methyl pentene-1)

Abstract

The heat of fusion of nascent poly(4-methyl pentene-1)(P4MP) has been measured with a slow temperature-ramp. Two melting ranges have been observed. A broad endotherm is found mostly below the equilibrium melting temperature,Tm,o. The total heat of fusion ΔHtotal is the sum of ΔHdsc, the melting enthalpy found by rapid heating and a second endotherm, ΔHnetwork, a contribution associated with the heat of disordering of a physical network. Similar reported analysis have been presented before on polyethylene and isotactic polypropylene. The ΔHtotal for P4MP is found to be 100±10 J g−1, in the upper range of the expected values of ΔHo, the heat of fusion of perfect crystals. The value of ΔHtotal constitutes a lower limit of ΔHo in cases like that of P4MP where other methods lead to ambiguous results. The comparison ofTm andTd, the melting and dissolution temperatures, and other results support the hypothesis that the equilibrium phase at the melting of P4MP is partially rigid while it is a liquid (or a mixture of a glass and a liquid) at the dissolution.