Polymethyl Methacrylate And Single Molecule Force Spectroscopy For Determination Of Polymer Molecular Weight

Poly(methyl methacrylate)(PMMA)is a linear polymer with a C-C chain as the main chain and ester carbonyl as the side chain.It was first synthesized by German chemist O.R?hm in 1902.PMMA has become the “superstar” in the field of medical due to its excellent hydrophilicity and biocompatibility.However,the molecular mechanism underlying its interaction with water molecules is still unclear.In this thesis,we have investigated the molecular mechanism between water molecules and PMMA by single-molecule force spectroscopy(SMFS).It is well known that relative molecular mass is an important parameter of polymer.However,there are certain limitations in each of the current methods for measuring the molecular weight of certain polyelectrolytes(such as polyelectrolytes).In this work,we have utilized single-molecule force spectroscopy(SMFS)to investigate the chain length of PMMA and poly(sodium-styrene sulfonate)(PSSNa)with narrow molecular weight distribution.The chain lengths of PMMA in decane,PSSNa in high vacuum and water environment have been obtained,and the experimental procedure were simulated by Monte Carlo.In this thesis,an SMFS-based method for the determination of molecular weight(chain length)of polymer is proposed.Finally,the effect of substrate hydrophobicity on the adsorption capacity of PMMA was analyzed.Based on the above research,this thesis draws the following main conclusions:(1)PMMA exhibits its single chain elasticity in decane,DMSO/water mixed solvent and n-propanol,which is consistent with the intrinsic elasticity of C-C backbone polymers.However,PMMA exhibits different single-chain elasticity in water environment.Through further experimental and theoretical model verification,it can be known that PMMA will form a water bridge structure in the water.(2)In this thesis,we selected PMMA and PSSNa as the target polymer,and SMFS experiments were performed on the two polymer separately.The experiments were simulated by the Monte Carlo algorithm.This work shows that for a rigid polyelectrolyte,when its conformation is stretched(such as the dissolution of PSSNa in the water environment),SMFS can be used to roughly estimate the average length of the polymer chain.(3)The effect of substrate hydrophobicity on the adsorption capacity of PMMA was investigated.Deionized water was selected as the experimental environment for SMFS,and glass slides were selected as the substrate.The glass slides were subjected to two different modifications: substrate hydroxylation and amination treatment.The statistics of the adsorption force of PMMA on the two substrates show that the desorption force of PMMA on the aminated glass sheet is higher than that on the hydroxylated glass sheet.The adsorption force of PMMA on the substrate increases with the hydrophobicity of the substrate.