Combined theoretical and experimental study of the linear rheology of modeland commercial polymers

Polymer Rheology;Tube Model;Hierarchical;Polyolefin;H Polymer;Linear Viscoelastic;Chemical Engineering;Engineering;Chemical Engineering

Chen, XueZiff, Robert M. ;

University of Michigan

关键词: Polymer Rheology;    Tube Model;    Hierarchical;    Polyolefin;    H Polymer;    Linear Viscoelastic;    Chemical Engineering;    Engineering;    Chemical Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/86296/xuec_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Polymer rheology is a very sensitive indicator of polymer long chain branching, and therefore can be used as a tool to determine polymer structures. This dissertation is thus focused on the study of the relationship between polymer linear viscoelastic properties and polymer structures using both rheological experiments as well as theoretical modeling methods applied to both model polymers and commercial polymers. In this work, the two advanced tube models, namely the ;;hierarchical model” and the ;;BOB” model, were firstly introduced and compared before being applied to predict the rheological properties of model polymer melts and commercial polymer melts. For the model polymer melts, symmetric and asymmetric ;;H” model polybutadienes of high quality were synthesized by a collaborator using a novel synthesis strategy, and characterized by another collaborator using temperature gradient interaction chromatography (TGIC) as well as by the rheological measurements carried out in our lab. The ;;hierarchical model” was employed to predict their rheological behaviors as well as to identify the impurities in the materials using the ;;analytical rheology” concept. After validating the tube model theory successfully on the model polymer melts, we developed and validated a method to obtain tube model parameters for commercial polyethylene copolymers and tried to access the validity of the modeling predictions for commercial polyolefins. We are the first team to work on the asymmetric ;;H” shaped polymers. The most interesting findings in this work include: (1) The methods of TGIC, rheology measurement and theory modeling need to be combined to determine reliable long-chain branching information for branched polymers, and to identity the impurities in the materials. (2) The polydispersity of a branched polymer is not only due to molecular weight variations but also due to different molecular structures. (3) Even long-chain branching levels as low as 0.335 long chain branches per million carbon atoms can be detected by polymer rheology, which is not detectable by any other experimental method. (4) The ;;hierarchical model” can predict the rheology for both model polymers, such as linear-，star-, and H-shaped polymers, and commercial polyolefins, and thus it is a useful tool to predict polymer linear rheology.