STUDY OF MOLECULAR-MOTION OF BLOCK COPOLYMERS IN SOLUTION BY HIGH-RESOLUTION PROTON MAGNETIC-RESONANCE

In experiments reported, samples studied include block copolymers of polystyrene-poly(ethylene oxide), polybutadiene-poly(ethylene oxide) and poly-(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide). NMR measurements were carried out varying molecular weight, temperature, and solvent composition. For AB copolymers of polystyrene and poly(ethylene oxide), two peaks caused by the phenyl protons of low-molecular-weight (M//n equals 3,300) copolymer were clearly resolved in D//2O at 100 degree C, but the phenyl proton peaks of high-molecular-weight (M//n equals 13,500 and 36,000) copolymers were too broad to observe in the same solvent, even at 100 degree C. It is concluded that polystyrene blocks are more mobile in low-molecular-weight copolymer in water than in high-molecular-weight copolymer in the same solvent because the molecular weight of the polystyrene block of the low-molecular-weight copolymer is itself small.