H-1 NMR study of dispersion copolymerization of n-butyl methacrylate with poly(ethylene oxide) macromonomer in deuterated methanol-water

H-1 NMR and dynamic light scattering (DLS) measurements have been employed to investigate the dispersion copolymerization of n-butyl methacrylate (BMA) with poly(ethylene oxide) (PEO) macromonomer in a deuterated methanol-water medium. During the first quarter of the polymerization BMA and the macromonomer react at nearly the same polymerization rate. Subsequently, the BMA polymerization rate increases markedly, due to partitioning of the BMA into the particle phase. When this occurs, one observes broadening of the H-1 NMR absorption lines of the unreacted BMA. The PEO peak intensity was monitored relative to that of an internal standard. As conversion proceeds, the sharp peak represents a superposition of signal due to unreacted macromonomer and to chains attached to the particle which maintain their high mobility. H-1 signals from immobilized EO segments appear as a weak broad background which grows in intensity as the reaction proceeds. At the end of the reaction, 27% of the intensity in the sharp PEO resonance is lost, implying that this fraction of the chain segments have become immobilized due to surface adsorption or entrapment within the particle interior. From these data, the amount of PEO bound to the surface as a function of the extent of reaction can be calculated. This in turn suggests that there is a sharp increase, toward the end of the reaction, in the fraction of EO chain segments which have high mobility and appear in the NMR with a narrow line shape. Calculated packing densities are consistent with a transition to a brushlike conformation of the PEO chains.