In this study, we examined the thermal characteristics of chlorobutyl rubber (CIIR) before and after press heat treatment. Differential scanning calorimetry (DSC) measurements revealed the appearance of a melting peak in the temperature range of 0 °C to 50 °C, indicating the formation of a microcrystalline structure as a result of heat treatment. The melting enthalpy of CIIR increased with longer heat treatment. In contrast, butyl rubber (IIR) did not exhibit any melting peak in the DSC test even after undergoing the same press heat treatment. Thus, it is suggested that the formation of the microcrystalline structure in CIIR is due to the existence of chlorinated isoprene molecules. X-ray diffraction (XRD) experiments also confirmed the exist of a microcrystalline structure. Upon gamma ray radiation, IIR showed approximately 100% degradation without any gel formation, whereas CIIR exhibited dominant cross-linking reactions and 80% gel formation at 30 kGy radiation. And the microcrystalline structure formed during heat treatment contributed to the increase in cross-linking density during gamma radiation, which is thought to be due to the changes of amorphous structure during the formation of microcrystals.

The T₂ distribution obtained by Gaussian expansion of the transverse relaxation measured by pulsed NMR (or time domain NMR) represents the non-uniformity of the crosslinked structure and stress state. However, since calculation of Gaussian expansion is not easy, there are few examples of rubber research using Gaussian expansion. In this study, to simplify the calculation of the Gaussian expansion, we examined the formulation of the T₂ distribution of Weibulltype free induction decay (FID). When the Weibull coefficient (W) is 1, i.e., Lorentzian relaxation, an approximate solution is obtained as the product of a power function and a decaying exponential function, and this has been analytically proven. For 1<W<2, a highly accurate approximation was obtained by generalizing the approximation solution for W=1 and correcting it with a growing exponential function.