| Abstract
| - 1H NMR and dynamic light scattering (DLS) measurementshave been employed toinvestigate the dispersion copolymerization of n-butylmethacrylate (BMA) with poly(ethylene oxide) (PEO)macromonomer in a deuterated methanol−water medium. During thefirst quarter of the polymerizationBMA and the macromonomer react at nearly the same polymerization rate.Subsequently, the BMApolymerization rate increases markedly, due to partitioning of the BMAinto the particle phase. Whenthis occurs, one observes broadening of the 1H NMRabsorption lines of the unreacted BMA. The PEOpeak intensity was monitored relative to that of an internal standard.As conversion proceeds, the sharppeak represents a superposition of signal due to unreacted macromonomerand to chains attached to theparticle which maintain their high mobility. 1Hsignals from immobilized EO segments appear as aweak broad background which grows in intensity as the reactionproceeds. At the end of the reaction,27% of the intensity in the sharp PEO resonance is lost, implying thatthis fraction of the chain segmentshave become immobilized due to surface adsorption or entrapment withinthe particle interior. Fromthese data, the amount of PEO bound to the surface as a function of theextent of reaction can be calculated.This in turn suggests that there is a sharp increase, toward theend of the reaction, in the fraction of EOchain segments which have high mobility and appear in the NMR with anarrow line shape. Calculatedpacking densities are consistent with a transition to a brushlikeconformation of the PEO chains.
|
