Correlation of molecular dynamic and mechanical properties in the linear and non-linear regime of comb-like homopolymers via FT-rheology and multi-quantum-NMR-spectroscopy

• Applicants: Professor Dr. Kay Saalwächter, Ph.D.; Professor Dr. Manfred Wilhelm
• Subject Area: Preparatory and Physical Chemistry of Polymers ; Experimental and Theoretical Physics of Polymers
• Term: from 2014 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 265358506

This applied project covers the study of molecular dynamics of defined, branched model polymers. The aim is to make a contribution towards a better understanding the basic connection between branched structures and their non-linear rheological properties. Therefore, defined branched, comb-like polymers will be synthesized via living anionic polymerization. On the one hand, partly deuterated (only backbone or only sidechains) comb structures will be prepared for multi-quantum-NMR-spectroscopy and rheology, on the other hand, fully protonated comb structures will be prepared solely for rheological measurements. The formation of comb polymers can be achieved by functionalization of the backbone via hydrosilylation or epoxidation. Afterwards, the living sidechains can be attached to the introduced functional groups by the so called grafting-onto method. The monomers isoprene-d8 and butadiene-d6, which are needed for the deuterated parts of the polymers, can either be self synthesized or can be commercially purchased.The rheological characterization will concentrate on measurements in the non-linear regime with the aid of FT-rheology. These experiments will survey the correlation between structure and nonlinearity, as well detect various relaxation times. Moreover, for the first time, the normal forces during an oscillation shear experiment in the non-linear regime will be examined. Due to the partly deuterated comb structures, multi-quantum-NMR-experiments will allow us to detect the different relaxation processes and the associated relaxation times of the backbone and the sidechains independently of each other. The results can then be compared with relaxation times obtained from rheological measurements. Thus, it will be possible to better understand the mechanical relaxation processes on a molecular level and separate the contribution of backbone and sidechains. Furthermore, varying positions of a deuterated block within the backbone will enable the study of the hierarchy of relaxation modes for a comb structure. With a custom-made rheo-NMR device, nuclear magnet relaxation studies can be simultaneously performed during an oscillatory shear experiment. With this setup, dynamic effects that lie on a time and length scale between NMR-spectroscopy and rheology can be studied.Beyond the proposed project, further cooperations will involve the simulation of relaxation times and thus will help to improve the basic understanding of the processes in the non-linear regime.

• DFG Programme: Research Grants