Block crystallization effect on the conformation of triblock oligomers α-n-alkyl-ω-n-alkoxyoligo(oxyethylene)s in the solid state

Abstract

The IR spectra of triblock oligomers α-n-alkyl-ω-n-alkoxyoligo(oxyethylene)s, C6EmC6 (m=6–8), C8EmC8 (m=6–8) and C10EmC10 (m=1–8), were measured in the solid state at liquid nitrogen temperature, and the crystallinity and conformational behavior with changing block chain length was studied. The results of the spectral analysis showed that the solid of the CnEmCn compounds with n≳m is crystalline and the molecular form is definitive, while the alkyl block in the compounds with n≲m is partially crystalline or noncrystalline and contains conformational defects such as end-gauche and kink. The crystallinity and conformational properties of the CnEmCn compounds are elucidated in terms of rate of crystallization of the constituent blocks. If the oxyethylene block crystallizes faster than the alkyl block, the alkyl chain deforms with formation of conformational defects to fit in the void formed by the helical oxyethylene chain. If the crystallization of the alkyl block takes place faster, on the other hand, the oxyethylene chain assumes an all-trans planar conformation with a cross-sectional area similar to that for the alkyl chain.