Crystallization Kinetics, Crystallization and Melting Lines of Deuterated and Hydrogenous Isotactic Polybutene‑1

The kinetics of crystallization, lamellar long period, and melting temperatures (T_m) of hydrogenous isotactic polybutene-1 (hPB-1) and its fully deuterated counterpart (deuterated isotactic polybutene-1, dPB-1) with similar molecular weight at different isothermal crystallization temperatures (T_c) were investigated by means of fast scanning chip calorimetry and synchrotron microfocus small-angle X-ray scattering techniques. The Hoffman–Weeks plot where T_m was plotted as a function of T_c was used to determine the equilibrium melting point by extrapolating the data to T_m = T_c. Moreover, following the Gibbs–Thomoson equation and Strobl’s multistage crystallization model, the melting line and crystallization line where T_m or T_c is plotted as a function of inversed lamellar long period (1/d_ac) were constructed to determine the equilibrium melting temperature and equilibrium crystallization temperature by extrapolating the corresponding lines to infinite lamellar long period. The hPB-1 displays faster crystallization rates across the entire temperature range, suggesting a higher supercooling driving its crystallization than in dPB-1. However, hPB-1 possesses a lower equilibrium melting point/temperature but a higher equilibrium crystallization temperature than dPB-1. This peculiar isotope effect on the crystallization behavior of isotactic polybutene-1 provides a unique example supporting the crystallization mechanism proposed by Strobl where the supercooling with respect to the equilibrium crystallization temperature determines the crystallization kinetics.