Thin-Film Behavior of Poly(methyl methacrylates). 5. Characteristics of the Poly(methyl methacrylate) Monolayer Stereocomplexation Process

Characteristics of the stereocomplexation process in mixed monolayers of isotactic and syndiotactic poly(methyl methacrylate) (i- and s-PMMA), as introduced in the preceding paper in this series, are addressed. The surprising shift of the stereocomplexation transition to lower surface pressures upon raising the temperature appears to be caused by dominating effects of the segmental mobility. The observation that, in many cases, an incomplete conversion is attained can be attributed to the combination of a limited mutual accessibility of the components in the monolayer, caused by chain segregation effects in the pseudo-two-dimensional system formed and immobilization effects that may become operative upon compression. Especially when using higher molecular weight samples, the effect of this limited extent of mixing appears to be a strongly limiting factor. The kinetics of the monolayer process suggest the existence of a lamellar growth regime only at low surface pressures and high temperatures, similar to mechanisms suggested for solution and melt mixtures. In general, the length of the complexed sections formed during the monolayer stereocomplexation process appears to be (much) shorter than that of the helical structures formed in monolayer crystallized i-PMMA. Attempts to spread preformed stereocomplexes from a solution in a complexing solvent were not successful.