Abstract
Crystallization and morphology of polyethylene glycol with molecular weight M~n~ = 2000 (PEG2000) capped with cholesterol at one end (CSโPEG2000) and at both ends (CSโPEG2000โCS) were investigated. It is found that the bulky cholesteryl end group can retard crystallization rate and decrease crystallinity of PEG, especially for CSโPEG2000โCS. Isothermal crystallization kinetics shows that the Avrami exponent of CSโPEG2000 decreases as crystallization temperature (T~c~). The Avrami exponent of CSโPEG2000โCS increases slightly with T~c~, but it is lower than that of CSโPEG2000. Compared to the perfect spherulite morphology of PEG2000, CSโPEG2000 exhibits irregular and leafโlike spherulite morphology, while only needleโlike crystals are observed in CSโPEG2000โCS. The linear growth rate of CSโPEG2000 shows a stronger dependence on T~c~ than PEG2000. The cholesterol end group alters not only the free energy of the folding surface, but also the temperature range of crystallization regime. The small angle Xโray scattering (SAXS) results show that lamellar structures are formed in all these three samples. By comparing the long periods obtained from SAXS with the theoretically calculated values, we find that the PEG chains are extended in PEG2000 and CSโPEG2000, but they are onceโfolded in CSโPEG2000โCS. ยฉ 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2464โ2471, 2007