Structure and Dynamics in Large Polymer Systems

University Of Akron, Akron OH

Investigators

Abstract

Stereochemical composition exerts strong and sometimes surprising effects on the dynamic and static properties of polymers, as illustrated by the dependence of the miscibility of a polypropylene melt on the stereochemical composition of the chains. This subtle effect has been captured and explained by the PI in prior simulations performed with support from NSF. The PI and Co-PI will now address the influence of stereochemical composition in two other important areas: The nanoscale objects spontaneously formed by dendronized polymers with a backbone that raises tacticity as an issue, and the detailed analysis of melt dynamics when the molecular weight and monomer unit are held constant, and stereochemical composition is the only variable. The proposed simulations of dendronized polymers, using a new bridging method developed by the PI, will identify procedures that control the stabilities of nanoscale objects, search for new objects not yet realized (but potentially realizable) in the laboratory, and determine the approach that should be taken if bends are required at specific positions in nanoscale rods. In the dynamic study, the Co-PI will examine polypropylene melts by various nmr techniques that provide the translational diffusion coefficient and also characterize the local mobility. This information will be used by the PI for a critical test of the fundamental basis for the dynamic Monte Carlo method in the study of polymer dynamics. This critical test avoids using the molecular weight as a variable, and instead focuses on the changes in mobility with alterations in the stereochemical composition of polypropylene chains. This part of the project will benefit from collaboration with Prof. Theodorou (National Technical University, Athens), who will provide mobility data from classical Molecular Dynamics simulations of the same systems that are studied by dynamic Monte Carlo methods by the PI and nmr by the Co-PI. The intellectual merit of this research is the development of new methods for understanding and predicting the structures of sophisticated dendronized polymers that promise to be important in newly emerging nanotechnologies, and providing a critical assessment for a popular simulation technique, dynamic Monte Carlo, that is somewhat controversial because it purports to provide dynamic information without explicitly taking account of the momenta of the components of the system. The project has several broader impacts. It contributes to fundamental knowledge by a critical assessment of the basis for the dynamic Monte Carlo method and by creating a new approach to the development and control of nanoscale objects based on polymers. The insights gained from the project are used by the PI and Co-PI in their formal and informal instruction of young scientists (undergraduates, graduate students, postdocs, visiting scientists) in the classroom and in their research groups. The PI also uses this knowledge in continuing education of professionals in industry, through his direction of the ACS short course on Molecular Modeling of Polymers. His students and postdocs assist in this short course, thereby gaining valuable insights from the industrial participants, and assisting in the education of the participants by sharing their learning experience in the use of simulations to understand and predict the properties of polymers. The PI will endeavor to expand on his successful record of assisting in the placement of underrepresented groups in the professorial ranks by employing outstanding young scientists from such groups in the project.