Chemorheology Study On The Modification Of Polyolefin Elastomer Melt Via Free Radicals Course

All structures on different scales inside polymer materials experience various complicated physical and chemical alterations during the reacting processing, which is ready to form a heavily nonlinear problem in substance. Besides the chemical reaction, the effect of applied flow field is more important, which makes chemorheology, one important hotspot of the present researches about reacting processing of polymer, to be the core issue to resolve. So it is very essential for us to reveal how the chemical raction of polymer proceeds under the flow; however the mechanism and the kinetics of polymer reaction in the flow field are unclear so far. In this thesis, the reaction behavior of polyolefin elastomer (POE) via the free radical mechanism is focused, and the purpose is to investigate the role that the flow field plays in the reaction mechanism, the reaction rate and the topological structure of the products of the macromolecular reactions. This doesn't only has the engineering background but also the theoretical significance. Firstly, some new reaction mechanisms of POE initiated by peroxides (POE/DCP) in static state were discovered and the rheokinetic analysis was carried out which was different from what the researchers had already acquired; Secondly, the mechanism under simple shear flow was proposed and the effect of polymer chains'movements on the chemical reaction was revealed; Finally, the feasibility of preliminary tailoring of LCB through complex flow field was evaluated in the torque rheometer with the compensation of temperature. And a new long chains branched (LCB) index (DLCB) was defined from nonlinear oscillatory shear was founded, which could be a map to quantify LCB level by Fourier Transform Rheology (FTR); The main content and the results are as followed:1. Peroxide-initiated reaction of POE was studied at elevated temperatures using an on-line electron paramagnetic resonance (EPR) spectrometer. It is clear that the reaction process experienced the free radical mechanisms. Notable changes in signal hyperfine structures, the intensities and the lifetimes of the radicals were recognized. A kind of 7-line EPR signal corresponding to the ternary carbon radical was discovered for the first time. Whether the primary carbon radical appears and the lifetime are both dependent on the co-monomer content of POE. A rheokinetic analysis was made by correlating the EPR data and the rheogical responses recorded by the rotational rheometer. The kinetic coefficients of coupling and disproportionating reactions are not fixed, but the functions of the reacting time or the system viscosity, which indicates the reaction is diffusion controlled. The scaling between termination coefficient and viscosity is lower than what de Gennes predicted on the base of theory, which should be induced by the low diffusion coefficient for such system with plenty of reactive sites.2. The mechanism of reaction of POE initiated by peroxides under the simple shear, including transient shear flow and oscillatory shear flow, was paid attention to, which's the important instruction for the actual reacting processing. There's an intensity threshold of shear flow, above which degrading behavior throughβ-scission of the ternary carbon macroradicals could be observed besides the coupling reaction. Degradation depentent on the distance between the two parts created byβ-scission is controlled by diffusion and the shear flow field imposed upon the reaction system. Moreover, degradation starts on the products of long chain branching (LCB) and the probability of degradation on linear chains increases with the intensity of shear flow. Taking into consideration that the key factor favoring tertiary carbons as sites for scission was the distance between branches, the chain scission is possible when there were two tertiary carbons in a chain separated by only one carbon atom, which has been confirmed by 13C-NMR spectroscopy. The concentration of such structures affect the intensity threshold of shear flow for degradation.3. The feasibility of preliminary tailoring of LCB through complex flow field was evaluated in the torque rheometer, for the reaction of melt POE with peroxides at elevated temperatures. With the compensation of temperature, the strength of complex shear flow could be the only factor affecting the reaction kinetics and mechanism. According to the fact that degradation starts on LCB firstly, the length and the concentration of long chain branching can be controlled by the intensity of flow field. What's more, a certain amount of LCB degraded to be linear chains again due to the scission approaching the branching point in intense mixing condition. Although the rotational speed can not represent the complex flow field exactly, all the characterizations can give the significant instruction to tailor the polymer architecture more or less. In addition, there's only one adjustable window of the topological structure and content of LCB here through altering the processing flow field. High temperature can not promote the degradation. 4. One new LCB index (DLCB) was defined from nonlinear oscillatory shear followed by Fourier Transform Rheology (FTR) on the base of cDCR-CS model, through which a map to quantify LCB level could be founded. This index is independent on the molecular weight and the distribution of polymer chains, and is more convenient compared with the one defined from the characters of polymer melt rheology and diluted solution.5. The characteristics of vGP plot of various long chains branching, including symmetric star, asymmetric star, H-shaped, comb and Caylay tree polymers, have been evaluated by BOB model, which could predict the linear viscoelasticity of polymer very successfully so far. The characteristic transitions of various LCB in vGP polt were compared with the ones acquired from the experimental data in publishments and good agreement has been obtained. The protocol for characterization of the topological structure of LCB was raised according to the vGP map of topology. However, it is difficult to distinguish the asymmetric star and comb polymers only by the linear viscoelasticity.