Polymer Chemical Shift Anisotropic Tensors And Chain Conformations Studied By Machine Learning Assisted Solid State NMR

Polyvinyl acetate(PVAc)is a typically amorphous polymer which was synthesized by vinyl acetate based on radical polymerization.Benefited from its characteristics of low toxicity and chain flexibility above glass transition temperature,polyvinyl acetate was widely used as matrix of chewing gum and protective coating layer of fruits surface in food industry,and it is also used as matrix to control the rate of drug releasing in the area of drug production.In addition,the main amount of polyvinyl acetate is consumed to produce derivative polyvinyl alcohol(PVA)and polyvinyl butyral(PVB).At the same time,polyvinyl acetate has the ability of forming polycrystal with poly iodine.In the presence of polyiodine,the amorphous chain of polyvinyl acetate transformed into ordered polycrystal which is an interesting phenomenon catching the focus of research.So it is meaningful to obtain the chain conformation distribution of polyvinyl acetate in demonstrating the complexation mechanism between the polyvinyl acetate and polyiodine.Schimdt Rohr had demonstrated its effectiveness in study the conformation distribution of model polymer chain,such as polyethylene(PE),polyethylene terephthalate(PET),polyformaldehyde(POM)and polyethylene oxide(PEO),based on DOuble Quantum Spectroscopy(DOQSY)simulation and 13C-13C labeling technique.This study based on above method trying to make an attempt to extend this approach in characterizing polyvinyl acetate conformation.This study contains four main components:firstly,both of the 13C-13C labeled and without vinyl acetate copolymerized to form about 4%13C-13C labeled polyvinyl acetate in the main chain.The purpose is to increase the DOQSY NMR signal intensity,because the 13C-13C dipole-dipole interaction and chemical shift anisotropy interaction are the main interaction used to analyses the polymer chain conformation distribution in DOQSY simulation;Secondly,combining the 1D NMR(cross polarization experiment in static and MAS),2D NMR SUPER(the separation of undistorted powder patterns by effortless recoupling),ROCSA(recoupling of chemical shift anisotropy),PISEMA(polarization inversion spin exchange at the magic angle)and 13C-13C labeled PVAc PISEMA simulation technique to make a precisely well-defined analysis of main chain 13C chemical shift anisotropy values of PVAc;thirdly,machine learning assisted 2D PISEMA NMR analysis used to obtain the 13C chemical shift anisotropy values demonstrating by four model materials(PE,POM,Histidine,Acetylvaline).Fourthly,according to DOQSY NMR signal equation establish DOQSY simulation method,simulating DOQSY of three stable conformations of 13CH-13CH2 configuration segment,and add these three spectra with different weighting factors together to compared with the experimental DOQSY,these three weighting factors stands for the conformation distribution in polyvinyl acetate sample.