the first law methodd is an application of the first law of thermodynamics to the crystallisation and melting of a polymer sample on heating in a calorimeter. it involves two separate measurements. the first one determines the overall enthalpy changes on heating a partially crystalline polymer from t to above the melting point, t2 the second is a virtual experiment of measuring the enthalpy change on cooling the liquid from t2 to t1 without crystallisation occurring, see fig 1. for a closed system, the difference between these two steps is the enthalpy of fusion of the sample at t1
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