The Study On The Building For The Segment Structure Model And Thermal Stability Of PVC

Polyvinyl chloride（PVC）, which has been widely used in many fields for their advantages of good electrical insulation, wear resistance, easy processing and low cost. However, some irregular structures were introduced inevitability during the polymerization of vinyl chloride or in the later processing of the resin, leading the poor thermal stability and the limitation of its employment. Therefore, in order to improve the quality of the resin and giving support for PVC modification, the relationship between segment structures and performance of resin were build, which has the vital significance for the source controlling and quality enhancement of PVC.This paper focus on build conjugated polyene sequence structure model, internal allyl chloride structure model and epoxy structure model in the PVC chain by using thermal treatment and chemical treatment methods. And in order to lay a foundation for functional modification of PVC resin, the relationship between segment structures and thermal stability of resin were explored. The molecular weight、conjugated polyene sequences, functional types and internal allyl chloride contents of PVC resin were characterized with Gel permeation chromatography（GPC）, UV-Vis spectrometry（UV-Vis）, Fourier-transform infrared spectrometer（FT-IR）, X-ray photoelectron spectroscopy（XPS） and Nuclear magnetic resonance（NMR）. The thermal stability of PVC resin were tested by Thermal gravity analysis（TG）. And the conclusions were obtained as follows:1. In order to build the conjugated polyene sequence structure model, a method was used by treating the PVC resin at 120 ℃ under nitrogen atmosphere, and the segment structures and thermal property were analyzed by combing UV-Vis,FT-IR,1H-NMR and TG. The result showed the initial coloration of the resin were influenced by conjugated polyene sequence, and the initial thermal stability had no obvious variation.2. In order to build internal allyl chloride structure model, a method was used by treating the PVC resin in alkali solution. 1H-NMR result showed that the content of internal allyl chloride structures increased as a function of time, and the attack of OH- is random on the PVC molecular chain. The content can reach 15.2/1000 VC when the sample pretreated for 12 h under the condition of ice water bath. Contrast that conjugated polyene sequence structure model and combining with FT-IR, UV-Vis, 1H-NMR and TG technologies to analyze the segment structures and thermal stability of the resin. The result showed that the thermal stability was greatly influenced by the internal allyl chloride structure, but the whole degradation process of PVC was not affected;3. In order to build epoxy structural model, two different epoxidation reagent were used. The result showed that the long chain conjugated polyene sequence structure in the molecular chain was prioritize attacked by the epoxidation reagent, leading the decrease of long chain conjugated polyene and increase the content of short chain conjugated polyene at a certain degree. TG result showed that the initial thermal stability of resin was improved by the epoxidation reaction and making the color of resin gradually became shallow. The resin exhibited superior thermal stability when pretreatment for two hours by using HCOOH and H₂O₂, and the increase of T_5% is nearly 32℃ higher.