In this research we tried to examine mechanical properties of Polymethacrylimide(PMI)with density The monomers used in this research were Acrylonitrile (AN), Methacrylic acid (MAA) and Acrylamide (AM). Azobisisobutyronitrile (AIBN) was used as the thermal-sensitive initiator. 1-Amylalcohol was used as the foaming agent. The materials were mixed dissolved together and then copolymerized via the mode of bulk casting in the water bath 48-56 °C temperature and atmosphere pressure. Temperature of reaction was measured in 4 temperatures of water bath (48, 52, 54 and 56°C) and temperature changes of samples was recorded. Expandable copolymer boards were foamed by chemical foaming as the boards were put in an oven with the 180 °C temperature for 20-30 min. Time-Temperature curves of samples with four different water bath temperatures were drown. As we can see at 58°C reaction temperature rise up suddenly to about 112°C and it is very difficult to control but at 48°C maximum achievable temperature is about 57°C so our operating temperature is 48°C for studying on mechanical properties. compressive strength against strain for 4 densities measured and ploted. strength increases and flexibility decreases in higher amount of density. The maximum compressive strength before yielding is plotted versus density. As results, strength is increasing continuously when density increases. Occurring reaction in 48 °C water bath is more controllable and produced foam has higher quality. Both compressive strength and module increase in higher densities. When density passes 0.07 gr/cm3 increasing rate of strength grows faster.