Effect of surface segregation of ionic end groups on polystyrene latex early-time interdiffusion

Using a direct energy transfer method, ionic end groups on polystyrene were found to increase the early-time apparent interdiffusion coefficients duri ng film formation. The early-time apparent diffusion coefficients of polyst yrene with varying end groups were found to follow the ordering of SO4 > CO OK > H. The higher apparent diffusion coefficients are presumably due to th e surface segregation of the end groups caused by the polar, aqueous enviro nment during latex synthesis. By titration, 60% of the sulfate end groups a nd 30% of the carboxyl end groups were found on the latex particle surfaces . The apparent diffusion coefficients at very early times are separable int o two additive values: that arising from the polymer chains with chain ends on the latex surface, and that caused by polymer with chain ends buried in the latex interior. The present experiments suggest that the location of t he end group is the critical factor determining the initial apparent diffus ion coefficients of the polymers rather than the characteristics of the end groups themselves.