Analysis Method Development Of Polyether Modified Silicones And Their Collision-Induced Dissociation And Helical Conformation Study

Polyethermethylsiloxanes(PEMSs)are silicone based polymers formed by attaching one or more poly(ethylene oxide)(PEO)/poly(propylene oxide)(PPO)chains to a siloxane chain.The chemical composition,end group structure,monomer distribution and oligomer conformation of PEMSs affect its physicochemical properties.Fourier transform infrared spectroscopy(FT-IR),gel permeation chromatography(GPC)and nuclear magnetic resonance(NMR)are the must used methods to characterize PEMSs.However,only the average information,including average molecular weight,the numbers of EO/PO,end-group structure,and silicon groups can be determined by these methods without the respective oligomer information.The exact molecular weight,distribution status and conformation of each oligomer are not detected.Reversed-phase ultra high performance liquid chromatography-electrospray ionization-collision induced dissociation-TOF mass spectrometry(RP-UHPLC-ESI-CID-TOFMS),which can get the above informations used to characterize polymers.Little research has been conducted on the use of UHPLC-MS to analyze PEMSs oligomers with more than 4 silicone groups because of their low polarity and poor solubility in water,methanol and acetonitrile.As the siloxane chain is lengthened,the polarity of the PEMSs is reduced and it is hard to eluted form the column(C18);the collision-induced dissociation(CID)mechanism and conformation of its polyether chains are not clear.To solve these three problems,the UHPLC method of PEMSs was established which broke through the bottleneck that UHPLC could not analyze PEMSs with multiple siloxane groups;the fragment was studied,the CID mechanism of PEMSs with inert end groups was elucidated;the conformation of the PEO-alkali cation was studied and conformation of PEO complex was predicted.The study in this paper is helpful to the control of PEMSs production process and the precise control of product quality.The main works of this paper are as follows:1.RP-UHPLC-ESI-TOFMS method setup of PEMSs A high chromatographic resolution method of PEMSs and polyether oligomers was developed using the water-acetonitrile-isopropanol tertiary gradient solvents.PEMSs oligomers containing one EO pendant chain and 3-13 silicone groups were analyzed.More than 102 PEMSs oligomers and 21 polyether oligomers were separated within 45 min and identified by accurate molecular masses.As a good solvent of PEMSs,isopropanol improved the solubility and elution effect of PEMSs from the column.PEMSs oligomers with low polarity,poor solubility and similar properties were separated by both precipitation-redissolution and adsorption mode;oligomers of polyether and PEMSs containing different EO groups were seperated by adsorption and exclusion mode.This efficient separation method for PEMSs would broaden the characterization of silicone surfactants.2.CID mechnisum study of PEMSsCID fragments of PEMSs containing different end groups(CH3O-,HO-and CH3COO-)were studied and the CID mechemism of PEMSs containing intert end group was illumniated.Characteristic fragments from[PEMSs+NH4]+by charge-induced fragmentation were used to identify different end groups(CH3O-,HO-and CH3COO-).The CID mechanism of PEMSs containing an inert end groups(CH3O-and CH3COO-)can be understood as the independent fragmentation of the silicone and polyether chains.However,the active end group HO-can affect the fragmentation of silicone chain in PEMSs;the closer the HO-group is to the silicone chain,the greater the impact on the fragmentation of silicone chain.The study provides theoretical guidance for CID analysis of PEMSs.3.UHPLC-ESI-CID-TOFMS,pre-HPLC,NMR and FT-IR to analyze PEMSs formualitonFor complex PEMSs formulations,it is difficult to identify the compositions of the formulations and the structure of PEMSs only by one analytical method.In this study,UHPLC-ESI-CID-TOFMS,pre-HPLC,NMR and FT-IR were used to analyze PEMSs products commonly used in industry.UHPLC-ESI-CID-TOFMS was used to separate and analyze an effective wetting agent of UV ink containing 3 kinds of PEMSs with cyclic silicone chain,11 kinds of PEMSs with line silicone chain and 3 kinds of polyethers.FT-IR,NMR and CID were used to identify the end group CH3COO-;NMR and pre-HPLC were used to identify the structure of PEMSs with cyclic silicone chain;UHPLC-ESI-TOFMS and NMR were used to identify the polyethers with different alkyl chains.The thorough analysis of the product will help the understand of its special characters.4.PEO helical conformation and its alkali cation selectivity studyThe relative peak abundance of PEO(iso-C10H21(OC2H4)n OH(n average=7)oligomers to five alkali cations(Li+,Na+,K+,Rb+and Cs+)was studied by positive electrospray ionization mass spectrometry(ESI-MS).The ion selectivity of PEO oligomers to alkali cations was corresponding to the peak abundance in the competitive mode of ESI-MS spectrometry.PEO formed the first helix when EO units number reached to six and the helix played an important role in ion selectivity of PEO.For larger PEO oligomers with helix,the ion selectivity of PEO decreased in order of K+>Rb+>Cs+>Na+>Li+depending on the host-guest matching degree of cations and the helix.The highest selectivity of PEO to K+was due to the best shape matching of the helical cavity with K+.For smaller PEO oligomers without helix,the ion selectivity of PEO decrased in order of Li+>Na+>K+?Rb+? Cs+due to the reduction of the charge density of the ions.The PEO helix with 6 EO units was predicted.