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Introduction Isotactic poly(4-methyl-pentene-1) (P4MP1) exhibits a disordered 7 2 helical conformation in the ordinal crystallite, form I, and these helices form a tetragonal lattice with four chains per unit cell [ 1 ]. The

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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,T m,o. The total heat of fusion ΔH total is the sum of ΔH dsc, the melting enthalpy found by rapid heating and a second endotherm, ΔH network, 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 ΔH total for P4MP is found to be 100±10 J g−1, in the upper range of the expected values of ΔH o, the heat of fusion of perfect crystals. The value of ΔH total constitutes a lower limit of ΔH o in cases like that of P4MP where other methods lead to ambiguous results. The comparison ofT m andT d, 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.

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