Chinese Journal of Applied Chemistry ›› 2019, Vol. 36 ›› Issue (11): 1237-1247.DOI: 10.11944/j.issn.1000-0518.2019.11.190115

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Chain Structure and Properties of Four Commercial Low Density Polyethylene Resins

LI Peiab,ZHANG Jiaqia,LIU Weia,CHEN Quana,TANG Yujingc,JI Xianglinga,XUE Yanhua*(),SUN Guangpingb()   

  1. a State Key Laboratory of Polymer Physics and Chemistry,Changchun Institute of Applied Chemistry,Chinese Academy of Sciences,Changchun 130022,China
    b College of Materials Science and Engineering,Jilin University,Changchun 130022,China
    c Beijing Research Institute of Chemical Industry,SINOPEC,Beijing 100013,China
  • Received:2019-04-17 Accepted:2019-06-26 Published:2019-11-01 Online:2019-11-05
  • Contact: XUE Yanhu
  • Supported by:
    Supported by the National Natural Science Foundation(No.20734006, No.50921062, No.21704100)

Abstract:

Four commercial low density polyethylene(LDPE) resins with different melt flow rates were selected and their chain microstructures and the rheological properties were studied by high-temperature gel permeation chromatography(HT-GPC), 13carbon nuclear magnetic resonance spectroscopy(13C NMR), differential scanning calorimetry(DSC) and rheometer. The above resins are divided into two groups, D-1 and Q-1, D-3 and Y-1. Two resins in the same group have similar relative molecular mass. The results of 13C NMR spectroscopy show that the four LDPE resins not only contain short chain branches(SCB), but also have long chain branches(LCB), and the content of SCB is much higher than that of LCB, while the butyl branch in SCB is the highest one. The thermal fractionation(successive self-nucleation/annealing, SSA) results show that every resin contains different crystallizable methylene sequence lengths, i.e., the distribution of SCB in the intramolecular chain exhibits heterogeneity. The effects of molecular mass and its distribution, methylene sequence length and its distribution, branching content and crystallinity on melting behavior, rheological behavior and mechanical properties of the films were investigated. It is found that the low relative molecular mass end in Q-1 and LCB content in Y-1 influence their melt flow rate, the average methylene sequence length determines the melt temperature peaks, and the crystallinity influences the mechanical property of films. Based on the above results, the relationship between structure and property is established.

Key words: low density polyethylene (LDPE), chain structure, rheological property, mechanical property