We successfully synthesized monomer casting polyamide 6 (MCPA6)/poly(methyl methacrylate) (PMMA) blends in two steps: (1) radical polymerization of methyl methacrylate in epsilon-caprolactam and (2) anionic ring-opening polymerization of this epsilon-caprolactam solution. The influence of PMMA on the crystallization behavior of MCPA6 was studied with differential scanning calorimetry and X-ray diffraction, which showed that PMMA could act as a heterogeneous nucleation agent and favored the formation of the gamma-crystalline form. The rheological properties were also studied and indicated that PMMA reduced the interaction between MCPA6 chains by lowering the density of hydrogen bonding. This study used a novel and convenient method to prepare microporous MCPA6/PMMA particles that involved removing the continuous phase. Their surface area and thermal stability were characterized by the Brunauer-Emmett-Teller method and thermogravimetric analysis, respectively. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 101-107, 2009