Effect of polymer cation content on certain film properties.

Mixing of two acrylate-methacrylate copolymers designated A and B and differing only in cation (quaternary ammonium) content in the ratio 2:1 (A:B) provided a means of varying polymer cation content in resulting films. Film permeability to the permeant urea, increased with increase in cation content; a two phase change characterized by a slow increase at a low cation content level followed by about 13 times more rapid increase at high cation content level. The point of transition from the slow to the rapid phase was 53 moles cation per mole polymer chain. On average a fold increase in cation content resulted in a 500 fold increase in permeation rate. Increases in film swelling and pore size also accompanied the increase in cation content, but the change in permeability was more positively correlated with the corresponding change in film pore size. Mutual repulsion by charged groups during film formation is suggested as a factor promoting the formation of large pores in the film at high cation content.