The polyacrylonitrile-methyl acrylate (AN/MA mole ratio 100/0-70/30) copolymers and copolymers (AN/MA mole ratio 85/15) containing up to 40 wt % of microencapsulated n-octadecane (NhcroPCMs) are synthesized in water. The MicroPCMs were incorporated at the step of polymerization. The effect of the MA mole ratio and MicroPCMs content on structures and properties of the copolymers were studied by using Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (H-1 NMR), scanning electronic microscope (SEM), differential scanning calorimetry (DSC), thermogravimetry analysis (TG), gel permeation chromatography (GPC), and X-ray diffraction (XRD). The feeding ratio agreed well with the composition of the AN/MA copolymers. The copolymers are synthesized in the presence of MicroPCMs. The melting point moves to lower temperature (206 degrees C), while the decomposition temperature moves to higher temperature (309 degrees C) with increasing of the MA mole ratio and microcapsules content. The number-average molecular weight of the copolymer is similar to 30,000. The crystallinity of the copolymer decreases with increasing of the MA mole ratio and microcapsules content. (c) 2006 Wiley Periodicals, Inc.