Analisis Of The Microstructure, Stress-Induced Crystallization And The Network Model Of Ethylene-propylene Copolymer

In the21st century, the modern industrial products and daily supplies getdiversification gradually, and the requirements on the properties materials arealso different. Therefore the study of the relationship between materialstructures and properties becomes important correspondingly. The successfulestablished relationships between structure and properties, can not only decidethe application fields and the condition of materials from the structureconsiderations, but also favor the structural design for the new applicationareas and circumstances.In this paper，the composition and structure of EPDM were analyzed byFT-IR,¹H-NMR,¹³C-NMR. The¹³C-NMR experiment was found to get thecomposition and sequence distribution more precise and detailed undercomparison. The compositions of a series of ethylene-propylene copolymerswere quantitatively determined by13C-NMR at300K in the solvent ofo-dichlorobenzene. The monomer composition and sequence distributionwere analyzed. The glass transition temperature T_g, half temperature of decomposition and crystallinity were found to be closely related to thesequence structures of methylene. The T_g, half temperature of composition,and the crystallinity appeared an abrupt change when the methylene lengtharrived7⁸because of the movement of the ethylene segments. Also, the T_gofcopolymers were simulated according to the monomer compositions.The composition and sequence structure of EPDMs supplied by JilinPetrochemical Industrial Corporation were analyzed according to the13C-NMR analysis. The stress-induced crystallization was occurred in EPDM3080when the segment chains of methylene were long enough. Themechanical properties of stress-induced crystallization of EPDM3080wereincreased rapidly when the extension ratio reached about4.5. With theobservation by the synchrotron two-dimensional wide angle X-ray diffraction,it confirmed that the increasing stress just begin at the extension ratio of4.5,which can be attributed to the stress-induced crystallization. Based on therubberlike network model with crosslinking, entanglement and stress-inducedcrystallization, the constitutive equation can be obtained according to rubberstatistical distribution function and the deformation free energies. In themeantime, according to the experimental resulting crystallinities from thetwo-dimensional wide angle X-ray diffraction, the modified constitutiveequation was proposed and the theoretical results were compared with thestress-strain experimental data. It showed that the deduced stress-inducedcrystallization constitutive equation of EPDM rubber was in good agreement with the experimental results, which offered a theoretical base for theprediction of the stress-induced crystallization rubber materials.