双向拉伸聚乙烯的微观结构及热学表征

The chain structures of the two samples of biaxially oriented polyethylene, M1, M2 were characterized respectively by infrared spectrum, nuclear magnetic resonance spectroscope and gel permeation chromatograph to determine their comonomers, branching degree, relative molecular weight and its distribution. The melting and crystallization behaviors of two products were studied by differential scanning calorimeter. The distribution of methylene sequence length (MSL) in different copolymers was determined by continuous self-nucleation annealing (SSA) thermal fractionation method. The results show that the short chain branching is dominant in M1 sample, and the long chain branching is dominant in M2 sample. The total branching degree of M1 sample is slightly higher than that of M2 sample, which is consistent with the results of the IR test. The distribution of MSL increases monotonously with the increase of MSL. The MSL of M2 is concentrated in 198, whose peak area accounts for 52.4% of the total peak area. The MSL distribution of M1 sample has two peaks, one peak of MSL is at 61, whose peak area accounts for 8.3% of the total peak area, and the content of MSL is the highest at 273, whose peak area accounts for 35.1% of the total peak area, which corresponds to the double melting temperature measured by differential scanning calorimeter(DSC).