The effect of thermal history on the melting behavior of nylon 1212 has been studied by differential scanning calorimetry (DSC).Two or three melting peaks were observed on DSC curves at different thermal history.The mechanism of melting peaks of nylon 1212 was analyzed according to the theory of polymer crystallization.Lower temperature melting peaks (PⅠ) in DSC curves were mainly attributed to melting of minicrystal or lamellar crystal which developed from nylon 1212 annealed for 120 min at different temperatures.The peak temperature of these peaks is low

and their area is small.The main melting peak (PⅢ) is the melting of perfect crystals which are formed in a recrystallization process of the polymer after PⅠ and PⅡ.The value of main peak temperature is much higher and the area is much larger.The melting peak (PⅡ) might be developed from melting of crystals which formed during quenched process of nylon 1212. The position of melting peak changed slightly with different heating rate

which indicates that these crystals have similar form.Increasing crystallization time is favorable for perfect crystals formation.The sample annealed at two different temperatures exhibits two additional melting peaks.Temperatures of these additional melting peaks are higher than annealing temperatures.Moreover

the position and area of additional peak reduced with the annealing temperature decreasing.The equilibrium melting temperature of nylon 1212 was determined as 202.8℃ by Hoffman’s method according to results of isothermal crystallization.