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The method for producing polyvinyl alcohol (PVA) by the solution polymerization of vinyl acetate first and then alcoholysis strategy is industrial. Where solvent plays a vital role in control over stereoregularity, molecular weight and its distribution, crystallinity and so on. In this report, when methyl acetate was used as a solvent in the polymerization of vinyl acetate instead of methanol, prepared PVA was characterized by Fourier-transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results showed that PVA obtained in methyl acetate has a higher content of syndiotactic structure, crystallinity melting temperature and enhanced thermal stability compared with PVA obtained in methanol due to the formation of [PI] - [PI] complex between methyl acetate and vinyl acetate and the enhanced steric hindrance effect during polymerization. Additionally, methyl acetate has a smaller chain transfer constant (1.31 * [10.sup.-4]), which benefits to decrease the branching degree and molecular weight distribution index of PVA. This research provides more ideas for the choice of solvents in the industrial production of polyvinyl alcohol. KEYWORDS branching degree, molecular weight distribution, polyvinyl alcohol, tacticity, vinyl acetate, 1 | INTRODUCTION Polyvinyl alcohol (PVA) is a biodegradable synthetic polymer with excellent characteristics including transparency, gas barrier property, water-solubility, mechanical properties, which has been widely used in various fields [...]

Aiming at the problems of more blind monitoring areas and unable to show the distribution of gas flow field in single point monitoring mode of gas in mining face, based on edge computing technology, a method of constructing gas concentration field in mining face, visual display of gas flow field and monitoring and early warning of abnormal gas emission is proposed. The platform revolutionized the traditional methane monitoring model, replaced single-point monitoring with area monitoring, replaced methane substations with edge computing gateways, and realized global monitoring of methane in coal mining faces, built methane data fields underground, displayed methane cloud diagrams, and captured methane emission abnormally. The specific ideas are as follows: the distribution characteristics of “step rise” and “gradual rise” of methane in mining face are obtained by field measured data. Based on this, a full coverage monitoring scheme of methane is designed, and the full coverage monitoring layout system of methane is completed by using a new MEMS methane sensor; the monitoring data are transmitted to the edge computing gateway by wireless or wired means; edge computing gateway is located in mining roadway, embedded data processing model, single point methane concentration abnormal jump recognition model and periodic abnormal fluctuation discrimination model. The data processing model to build methane digital field, methane dynamic cloud diagrams, the jump model of single point methane concentration anomaly are used to judge the fluctuation of single point methane concentration anomaly, the discrimination by region mode to complete the mining face methane abnormal fluctuation behavior capture. Finally, the macroscopic display of methane concentration field cloud diagram and microscopic capture of abnormal fluctuation of methane concentration are realized.