INTERFACIAL ASPECTS OF STRENGTH DEVELOPMENT IN POLY(METHYL METHACRYLATE)-BASED LATEX SYSTEMS

Film formation from poly(methyl methacrylate) (PMMA) latex and PMMA co polymer latexes incorporating N-(iso-butoxymethyl)acrylamide (IBMA) or methacrylic acid (MAA) has been investigated in terms of the developm ent of tensile strength as a function of annealing time and temperatur e. Tensile strength is developed through a combination of macromolecul ar interdiffusion and interfacial crosslinking. The relative rates of interdiffusion vs. crosslinking reactions were studied as a function o f temperature and the chemical nature and concentration of the IBMA an d MAA functional groups. For low concentrations of these two functiona l monomers it appears that polymer chain interdiffusion between adjace nt latex particles during the film formation process dominates the kin etics of strength development. However, at higher IBMA and MAA concent rations, the higher glass transition temperature at the latex particle surface and intraparticle crosslinking hinders interdiffusion, as ref lected by differences in the power law exponent values obtained from t he log-log dependence of tensile strength on annealing time. The power law exponents were higher in the case of PMMA than for both IBMA- and MAA-containing copolymers. There was a greater influence of annealing temperature on the tensile behavior for the MAA copolymer system as c ompared to the IBMA copolymer. In the interfacially crosslinked latex polymer system, there is competition between the interdiffusion and cr osslinking mechanisms in determining the final mechanical strength of films during the annealing process. (C) 1995 John Wiley & Sons, Inc.