Control of particle morphology and film structures of carboxylated poly (n butylacrylate)/poly (methyl methacrylate) composite latex particles

Particles with a soft (s) core of poly (n-butyl acrylate)/poly (methyl methacrylate) (PBA/PMMA) copolymer and a hard (h) shell of PMMA were synthesized via a two-stage polymerization process. Two synthesis parameters were investigated: (i) the phase ratio of the core and the shell; and (ii) the compatibility of the two phases. The s/h phase ratio was varied from 100:0 to 0:100. The compatibility between the two phases was changed by (i) using acrylic acid (AA); (ii) by using pure PBA as core material; and (iii) by cross-linking the shell. Particle morphology was characterized by atomic force microscopy (AFM) on freeze-dried and on tempered single particles. The degree of coverage was found to depend on the shell content and the phase compatibility. The results are in good agreement with findings from transmission electron microscopy and solid state NMR given in Acta Polymerica [50 (1999) 347]. The experimental results are compared to predictions from simulation work on the particle morphology based on thermodynamic and kinetic considerations. The second part of the paper focuses on the phase distribution and the film morphology of films formed by the structured particles. Phase distribution at the surfaces, degree of film formation and the phase distribution in the bulk are characterized by AFM, cross-correlated and compared to the findings regarding particle structure in the first part of the paper. This approach is to our knowledge unique regarding its completeness and new in its methodology. The microscopic results concerning the bulk, the single particle and the surface properties are correlated to macroscopic properties like the minimum film forming temperature, pendulum hardness and gloss.