Synthesis And Analysis Of The Hydrogen Capped Polydimethylsiloxane

Organic-silicon compounds are consisted of main chains that arranged alternately by oxygen atoms and silicon atoms containing organic group. This structure entitiled organic-silicon compounds certain special properties, such as hot oxygen stability, low surface tension, permeability, excellent dielectric property, physiological inert, wet resistance and so on. Therefore, organic-silicon compounds are widely used and play an important role in various fields.Polydimethylsiloxane (PDMS) is the most popular organic-silicon polymer in use. In fact, the products of PDMS are still mixtures without any separation and purification in practical application. It is common sense that there must be some relationships between the properties of products and its structure.Thus,it is very important to study the synthesis conditions of organic-silicon compounds, and have a qualitative and quantitative analysis. 'In this paper, we select hydrogen-terminated polydimethylsiloxane as the object, study the effect that synthesis conditions on the products, and analyze hydrogen-terminated polydimethylsiloxane qualitatively and quantitatively. The main work and results are as follows:(1) Hydrogen-terminated polydimethylsiloxane was prepared by ring-opening polymerization, using octamethyl cyclotetrasiloxane and 1,1,3,3-tetramethyl-disiloxane as raw material and acidic clay as catalyst meanwhile. We focus on the factors that influence the process of polymerization such as temperature, time for reaction, the type of the catalyst, the amount of the catalyst and the proportion between the two reactants. It was found that incorporating acidic clay as catalyst made a higher quality of the product with shorter time to reach the equilibrium and also improved safety and environmental protection. The optimal process conditions of the polymerization is as follows:when nD4/nHMM=5(D4:0.1mol; HMM:0.02mol),weight percentage concentration of acidic clay is 3%, the reaction time is 8h, the reaction time is 60℃, the conversion rate of the octamethyl cyclotetrasiloxane is up to 94%.(2) After analyzing hydrogen-terminated polydimethylsiloxane through the spectrum, chromatography, mass spectrometry respectively, it is found that there are four types of homologs in the sample, including 2 types of catenarian polydimethylsiloxane oligomer and 2 types of ringed polydimethylsiloxane oligomer were identified, the 4 series of homologues contained 100 components from molecular weight 134 to 3908, and quantitative of low molecular weight components. (3) Using the spectrum,chromatography and mass spectrometry to analyze the composition of the polysiloxane, the result sound that, each method has advantages, but none of them can get the complete composition information of polysiloxane. Because of wider range distribution of molecular weight, the polysiloxane can't be tested by ordinary GC-MS, however, time of flight mass spectrometer (TOF) plays an important role on the analysis of organic-silicon compounds for its larger scanning area, for its powerless in testing low molecular weight components, we using the analysis results of gas chromatography mass spectrometry together, so that we can get the the exact qualitative analysis results. This method can be applied to other organic silicon polymer.The originality in this thesis:For polydimethylsiloxane, use GC-MS and ESI-Q-TOF for qualitative analysis of its entire composition.