Solid-state studies of the crystalline/amorphous character in linear poly (ethylenimine hydrochloride) (PEI·HCl) polymers and their copper Complexes

Abstract

Linear poly(ethylenimine hydrochloride) (PEI·HCl) polymers with different molecular weights (22, 87, and 217 kDa) and their copper complexes (Cu-PEI) were studied with particular attention to the crystalline/amorphous character of the polymeric chains in lyophilized and crystallized samples by using 1D and 2D solid-state nuclear magnetic resonance, X-ray photoelectron spectroscopy, and X-ray diffraction techniques. Different 13C{1H} cross-polarization and magic angle spinning experiments using delayed contact time, 1H dipolar filter and 1H spin-lock filter were crucial to determine the different mobility domains in the crystallized and lyophilized samples of PEI·HCl and Cu-PEI. 13C direct polarization experiments allowed the quantification of the crystalline/amorphous segments in each sample. The lyophilization process produced an increase in the amorphous fraction, even when some ordered domains were present, whereas the coordination of copper/sulfate ions produced a significant decrease in the mobility of polymer chains, leading to homogeneous and ordered materials even when Cu was desorbed.