Changes in minimum film-formation temperature (MFFT) during storage of latexes prepared from 91:9 wt % vinylidene chloride (VDC)-methyl methacrylate (MMA) monomer mixture by seeded batch and seeded semicontinuous emulsion polymerization were investigated, with attention centered on polymer-crystallization behavior during storage in the dispersed state. MFFT of latex prepared by the seeded batch process rose to 47 degreesC, whereas that of latex prepared by seeded semicontinuous process remained below 14 degreesC with storage at 20 degreesC for 12 weeks. Infrared absorption of latexes in the dispersed state and wide-angle X-ray diffraction of powder polymers obtained by lyophilization of fresh and stored latexes both indicated a much greater increase in polymer crystallinity during storage with latex prepared by the seeded batch process than with that prepared by the seeded semicontinuous process. Analysis of the copolymer composition drift calculated from reactivity ratios and H-1 NMR analysis indicated a wider sequence distribution and longer VDC sequences in polymer prepared by the seeded batch process than in polymer prepared by the seeded semicontinuous process. This explained the higher rate of crystallization during storage with latex prepared by the seeded batch process than with that prepared by the seeded semicontinuous process. Rising crystallinity during storage in the dispersed state is believed to have caused the MFFT rise.