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The thermodynamic properties of n-alkanes have been investigated by using differential scanning calorimetry. The impact of the chain length on the thermodynamic characteristics of the first order phase transitions in n-alkanes has been estimated. The n-alkanes homologous series has been analyzed using the theory of diffused phase transitions. The nuclei sizes of a new phase within the bulk of the initial phase have been estimated.

The thermodynamic properties of long-chain molecular crystals (LMC) have been investigated by using differential scanning calorimetry. The impact of the chain length and of the chain end group type on the thermodynamic characteristics of the first and second order phase transitions in LMC has been studied. A method of the analysis of the peak shape of the first order transitions based on the theory of diffused phase transitions has been developed. The method allows one to estimate the size of the new phase nuclei within the bulk of the former phase. To estimate a true peak shape of the first order phase transition, a method to separate the overlapped heat capacity peaks has been proposed for the first time. This new method takes into consideration the hysteresis effects.

A method is proposed for calculating the dimension distribution of nanocrystalline elements of the lamellar and fibrillar morphologies of a polymer. Calorimetric data were used to calculate the distribution of the longitudinal size of these elements in lamellae and microfibrils of ultrahigh molecular weight polyethylene. The calculation results are consistent with the data obtained by the X-ray method.. Keywords: heat capacity, dimension effect, lamella, microfibril, polyethylene.