Molecular Dynamic Simulation Of Single Chain Dynamics Behavior For Polyimides

The researches of molecular motion on a series of high performance polymerscontaining both the phenyl group and flexible kinks in their main chains are very importantand recently a great deal of effort has been devoted to these kinds of studies. In this work, weemployed the Molecular Dynamics Simulations (MD) methods to study the molecular motionof two polyimides (PIs) with different structure (M-PI, O-PI), and obtained some interestingand important results.On the Accelrys workstation, the Materials Studio software is used to simulate themolecular dynamics motion for a single chain. Two single-chain models of two kinds of PI, i.e.M-PI and O-PI, were built and simulated respectively at two different temperatures, 300 Kand 600 K. One temperature of 300 K is below the glass transition temperature of eachpolymer and the other is above. From Dynamics Analysis, it was found that there are the interactions between chainsegments from calculating the radial distribution function. The models of the cooperativephenylene ring rotation and the cooperative large segment torsion were built. It is shown thatthe former is mainly an in-phase cooperative rotation, while the latter is mainly a put-of-phasetorsion. The formula of the mean square displacement of the phenylene ring rotational(MSDOR) and large segment torsional angle (MSDOT) were set up and used to obtain therotational and torsional self-diffusion constants (RDC and TDC) by calculating the slopes ofMSDOR and MSDOT versus time, respectively. In M-PI chain, ether-ether ring rotation is themost mobile, the ether-nitrogen ring rotation is more mobile and the nitrogen -methylene ringrotation is the least mobile. In O-PI, nitrogen -methylene ring rotation is the most mobile,the ether-ether ring rotation is more mobile and the ether-nitrogen ring is the least mobile. Thetorsional motions of the large segments in M-PI are more active than those in O-PI. Due to thedifferent structure of the two PIs, the mobilities of them are different. The results of RDC andTDC indicate that the molecular motion of M-PI is more active than that of O-PI.