Model Study Of The Chain Behavior And Interaction Of Macromolecules In Solutions

This Ph.D.thesis focuses on the core issues of polymer science,namely,the synergistic regulation of the functional properties of polymer materials by the chemical composition,the topological structure and the interaction between polymer and environmental medium.In this work,we select four typical polymer systems,including non-polar linear polymer(linear polystyrene),non-polar branched polymer(branched polystyrene),polar linear polymer(methylcellulose),and polar branched polymer(starch)to study the model polymer chain behavior and interaction in solutions,including the entropy-dominated polymer’s confined behavior at the stationary phase interface in the environment and the enthalpy-dominated interaction between polymers and molecules in solutions.The main contents are as follows:1)The study of the mechanism for entropy-dominated interaction between the polymer chain and the stationary phase interface in the environment.Firstly,we take non-polar polystyrene as the research model and prepare linear and hyperbranched polystyrene samples,the interaction between nonpolar polystyrene and nanopore wall in solutions under the flow field is studied,and the influence of the confining effect of the nanopore wall on the conformational transformation of polymer is explored.Experimentally,by studying the translocation behavior of mono-and polydisperse linear polystyrenes through 20 nm cylindrical nanopores in toluene,we have quantified the relationship between the macroscopic critical flow rate(Qc)and the concentration(C)in the dilute and semidilute solutions,Qc～Cγ,and the measured |γ|is much smaller than the theoretical value.This finding suggests that the translocation dynamics might be dominated by the fast relaxation dynamics of correlated translocating blobs rather than the slow relaxation of the whole chain/network in the semidilute solutions.On the other hand,the influence of the topological structure of polymer on their translocation through the nanopore behavior is studied.A non-polar comb polystyrene sample library with a linear backbone profile but variable graft density,sidechain length and backbone length is prepared.The effect of molecular structure on the flow-driven translocation through the nanopore behavior of the comb polymer was studied.The increase of lp facilitates the process,which signifies the possibility of enhanced chain orientation.And the increase of Rsidcchain results in a larger critical macroscopic flow rate(Qc)for chains to squeeze into the nanopores.Finally,the feasibility of purifying the graft-onto production by flow-driven translocation through the nanopore technology is proved by one example of the practical purification process of a model sample.Generally,these results answer the core mechanisms for entropydominated interaction between the polymer chains and the stationary phase interface in the environment through the study of typical systems.2)The study of the enthalpy-dominated interaction mechanism between polymer and molecules in solutions.Firstly,we take polar linear methylcellulose as the research model and take 7S globulin as interaction molecules,to study the interaction mechanism between 7S globulin and methylcellulose in solutions.By combining particle sizing,isothermal titration calorimetry and cloud point measurements,it is observed that the addition of 7S globulin induces the formation of 7S globulin/methylcellulose aggregates,mainly driven by the weak hydrophobic force(～0.03 kJ/mol)at room temperature,and facilitates the formation of 7S globulin/methylcellulose fibrils aggregates at elevated temperature(50-70℃),which shows thermo-responsive behavior.Atomic force microscopy and rheology results signify that the 7S globulin probably acts as multi-site centers to bridge fibrils together and eventually formed large spherical aggregates covered with reticular fibrous structures.On the other hand,we take polar hyperbranched starch as a research model and study the synergetic effect of chemical composition,molecule size and topological structure of dialdehyde starch during the modified process.Based on the analysis of the experimental data from quadruple-detection size exclusion chromatography,we have developed a universal theoretical method to quantitatively analyze the chemical composition and the molecule sizes.By taking the polystyrene/polymethyl methacrylate blend as the model system,the theoretical method is proven to show high accuracy(relative deviation within±2%).In particular,the result has demonstrated that the degree of modification is much lower for dialdehyde starch chains with larger molecular sizes.Generally,these results answer the core mechanisms for enthalpydominated interaction between polymer chains and the molecules in the environment through the study of typical systems.