Synthesis And Properties Of Photo-cross-linkable Functional Fluoroelastomers

Fluoroelastomers are a type of synthetic polymeric elastomer where the carbon atoms of main chains or side chains are bonded to fluorine atoms.Due to the excellent performance in physical and chemical properties,fluoroelastomers play an essential role in key industries,including the aerospace,transportation,and electronic circuits.Very few common curing groups can be found in traditional fluoroelastomers.Traditional fluoroeasomters have almost no conventional curing groups,and the curing of traditional fluoroelastomers requires complex,time-consuming,and energy-intensive processes.This dissertation addresses the question of how to achieve efficient curing of fluoroelastomers.By using the functionalization of fluoroelastomers,the author synthesized a series of UV-curable fluoroelastomer materials that can be rapidly cured with simple operation processes.This dissertation also discusses the application of these UV-curable fluoroelastomer materials in the release and protection industry.Firstly,based on the methods of low-temperature degradation,group conversion,and high-efficiency condensation,a route that featured mild reaction conditions and simple operation processes was designed.By using the low-temperature degradation method,the carboxyl-terminated fluorinated prepolymer(VF-COOH)was prepared,and the key reaction conditions such as the temperature,pressure,ratio of oxidant to alkali,and feeding mode were determined.By using the FT-IR and NMR characterization methods,the degradation mechanism of fluoroelastomers was studied,and the evidence that proved the presence of carboxyl groups was provided.Then,by using VF-COOH as raw materials,acrylate terminated fluorinated prepolymers VF-HEMA and VF-(GMA-IEM)were prepared by means of Steglich esterification and ring-opening condensation.The two prepolymers can be crosslinked within 60 s under UV light.After UV curing,the performance of fluoroelastomers was greatly improved in terms of heat resistance,hydrophobicity,mechanical properties,and solvent resistance.VF-HEMA was also introduced to produce fluorinated acrylic pressure-sensitive adhesives(PSAs)by using the in situ polymerization method,in order to improve the adhesion of the PSAs to inert materials.A hybrid fluoropolymer((VF-POSS)-IEM)was obtained through the copolymerization of the hydroxy terminated prepolymer(VF-OH),hexamethylene diisocyanate(HDI),SO1440 POSS(POSS-OH),and isocyanoethyl methacrylate(IEM).The structure of the hybrid fluoropolymer((VF-POSS)-IEM)was characterized by using infrared spectrometry,nuclear magnetic resonance spectroscopy,and gel permeation chromatography.The synthesized functional silsesquioxane(POSS-IEM)and the hybrid prepolymer were then used to prepare a UV-curable fluorinated hybrid material((VF-POSS)-POSS).The surface properties of the UV-curable fluorinated hybrid material were investigated by using atomic force microscopy(AFM),scanning electron microscopy(SEM),and X-ray photoelectron spectroscopy(XPS).According to the results,the contact angle of the hybrid material can be up to 130 o,and the hybrid material shows strong adhesion to base materials.Additionally,this dissertation explores the application of POSS hybrid coatings in circuit board protection.The findings indicated that POSS hybrid coatings had distinct advantages in the industrial application,including high anti-vulcanization performance,high resistance to acid and solvent,high resistance to high and low temperature,and low water absorption.In order to eliminate the adverse effect of small molecule photoinitiators and improve the cohesive strength of the hybrid material,a hybrid fluorinated prepolymer(FGO-HFM)with FGO and benzophenone structures in its molecular chain was synthesized.When FGO-HFM is exposed to UV light,the crosslinking reaction spontaneously occurs on this hybrid fluorinated prepolymer.The results of differential scanning calorimetry(DSC)and transmission electron microscopy(TEM)revealed that SEM was well compatible with FGO.After UV curing,the Tg of FGO-HFM increased from-15 oC to-9oC.The thermogravimetric analysis(TGA)result indicated that the T10% of FGO-HFM increased by more than 100 oC after UV curing.The DSC and TGA techniques were employed to study the effectiveness of the photocuring reaction.Additionally,the application of FGO-HFM in fluorinated releasing films was studied in detail.According to the findings,when the FGO in the FGO-HFM was less than 0.15 wt%,the light transmittance of PET films coated by the hybrid materials exceeded 90%.The optimum amount of FGO was 0.1wt%～0.2wt%.If the amount of FGO was in this range,UV-curable fluorinated releasing films exhibited high performance,such as a stable release force(150 g/25mm),high residual adhesion(> 90%),excellent aging resistance,and convenient storage,which makes the films suitable for the cold coating and transfer coating of silicone products.Based on the current situation and test results of the release and protection industry,pilot testing was performed on two types of fluorinated materials with practical value.A new solution was proposed to offer PSAs with high initial viscosity and low peeling strength,and release coatings with medium release.This dissertation studies the properties,performance,and application of the two materials,providing theoretical and empirical references for the large-scale production of industrial coatings.