Computer Simulation Of SEBS Chain Structrue And Mechanism Of SEBS Thermal Reaction

The computer simulation is employed to investigate the micro-structure of SEBS which is a kind of three-block copolymer in this thesis. Molecular Mechanics method (MM) and Molecular Dynamics method (MD) are used in our simulation. The key idea of this research is to disclose the influence of side ethyl with different content on SEBS molecular chain micro-structure; Non-isothermal analysis kinetics method with several scan speed rate is introduced in this paper and linear heating-up data of DSC is used to study the mechanism model of SEBS containing different cross-linking agent; The two-dimensional correlation spectrum method is also introduced. Through the two-dimensional correlation infrared spectrum, the thermal oxidative mechanism of YH-503 SEBS and the mechanism of YH-501 SEBS grafted by MAH are studied in details.The results in research are as follows:1. From the computer simulation results it can be found that, with the mole content of side -CH2CH3 of EB block in SEBS chains increasing, the micro-phase separation between soft-block (EB) and hard-block (PS) is increased, simultaneously, the mean square end to end distance of whole SEBS chainsincreases and therefore the size of SEBS chains enlarges. On the contrary, the Free Volume of SEBS amorphous decreases with the mole content of side -CH2CH3 increasing. We also find that, once the side -CH2CH3 is introduced in EB block, the SEBS bulk grows stable; The more content of side -CH2CH3, the more stabilization. Through the analysis of RDF of EB block, it can be proved that the degree of disorder of long-range increases and the degree of order of shorten-range has no variation with the mole content of side -CH2CH3 increasing. All results, which we obtain in simulation, are the most valuable information in designing thermoplastic elastomer of super-high performance, like SEBS.2. From the results of thermal analysis kinetics, it can be proved that, the reactions, which are initiated by two different cross-linking agents, both have three steps. Simultaneously, the activity energy of cross-linking agent A generating radicals is less than that of cross-linking agent B and there are about 80kJ/mol difference between two quantity. This is therefore proved that the control step of reaction which is initiated by cross-linking agent A is cross-linking reaction of SEBS and that of reaction which is initiated by cross-linking agent B is decompose of cross-linking agent B. We find that not only the initiation speed of cross-linking agent A is more fast, but also the cross-linking reaction have more inclination to take place than B in the identical temperature.3. Through two-dimensional correlation infrared spectrum analysis, we find that the reaction sequence of functional groups of EB block in thermal oxidation is like this: CHEB^CH2EB-?CH3EB and the reaction sequence of PS block is: CHPS—>CH2PS.We also discover that the oxidation of EB block is before that of PS block. A great many CH2 groups convert to C=O and C-0 groups in the course of oxidation of SEBS and partial CH3 convert to OO groups. But the generatingof C-0 has nothing with CH3 groups. There are three kinds of C=O structure produces in oxidation. The course of producing C-0 and C-O-C structure is more complex and there may be various paths and means.4. Through two-dimensional correlation infrared spectrum analysis, it finds that the main position of SEBS grafted by MAH is CH2 groups of fundamental chain. The number of PS block's CH2 groups, which involves in reaction, is more than that of EB block. The grated reaction has nothing with CH2 groups that have asymmetric stretching vibration. On the contrary, it has much relationship with CH2 groups that have symmetric stretching vibration. Before MAH grafting on SEBS fundamental chain, MAH monomers firstly convert to -CH-- radicals and then participate in the reaction. Unexpectedly, MAH monomers grafting on PS block is easier than grafting on EB block. The reason, we think, is that MAH monomers maybe have inclination to aggregate in PS phase, so the form of diffusion determines the area of grafted reaction.