Structures of Oxyethylene/Oxybutylene Diblock Copolymers in Their Solid and Liquid States

A series of ethylene oxide/1,2-butylene oxide diblock copolymers (E m B n ) was synthesized. Across the series, the oxyethylene E-block length was approximately constant (m = 26-32 units) and the oxybutylene B-block length varied (B n , n = 3-30 units). All copolymers had narrow chain length distributions (M w /M n < 1.08). The melts were investigated by small-angle X-ray scattering (SAXS), and the semicrystalline solids were investigated by SAXS, wide-angle X-ray scattering (WAXS), and low-frequency Raman spectroscopy. The melting behavior of the solids was investigated by differential scanning calorimetry (DSC). The SAXS patterns found for the liquid copolymers were consistent with disordered systems, with the melts of the longer copolymers close enough to the order-disorder transition to show substantial contributions from composition fluctuations in a system of unstretched chains. In the solid state, copolymers with n ≤ 20 formed lamellae in which the whole chain was in extended conformation, i.e. the E blocks crystallized in their usual helical conformation, and extended B blocks formed a liquid-crystalline array. For a copolymer with a longer B block (n = 30), the E blocks crystallized in once-folded conformation, while the B blocks remained extended.