| The flexible design of polybenzoxazine molecules gives it a diversity of synthetic routes and application prospects;Organosilicon dendrimers can have different properties and use by bonding different functional groups at the dendrites,and endow them with the flexibility of molecular polysiloxane;The chemical versatility of phosphorus-based synergistic flame retardants,diverse flame retardant mechanisms and high efficiency at low loadings make them increasingly the first choice for the preparation and modification of flame retardant materials.Based on these characteristics,scholars have designed a large number of flame retardants based on the structure of polybenzoxazine,which has further enriched the structure and performance of flame retardants,and has been applied in many research fields.However,in the current research content,there are few studies that combine benzoxazine with organosilicon dendrimers and further explore its properties.In order to explore more uses of silicone dendrimers in the field of materials and meet the new requirements for common adhesives in a fire-resistant environment,develop new polybenzoxazine materials and research silicone benzoxazine-type flame retardant adhesives are of paramount significance.This thesis aims to:(1)synthesize silicone dendrimers with a dendritic structure of benzoxazine,and study their curing kinetics and adhesion properties;(2)Introduce flame-retardant molecules containing P and N elements into the organosilicon dendrimer to construct a phosphorus-based synergistic flame retardant,and fully study the performance of this flame-retardant adhesive;(3)High synthesis The heat-resistant main-chain benzoxazine,compare the results and factors of the main-chain siloxane with different molecular weights on the heat resistance of the material when constructing the new polybenzoxazine structure;(4)The benzoxazine-type compound of silicon dendrimer is introduced into epoxy resin for modification,and the performance of the modified resin is studied.To this end,we have carried out the following four aspects of research:1.Study on the synthesis and performance of benzoxazine-based adhesives based on organosilicon dendrimersIn order to design a multifunctional benzoxazine-based adhesive,it is planned to synthesize a new benzoxazine monomer G1.0-t-BOZ from paraformaldehyde,catechol,and a silicone dendrimer with a dendritic structure of amino groups.The adhesive is obtained after thermal ring opening and curing.For this reason,we first synthesized the amino-terminated organosilicon dendrimer G1.0 through Michael addition and amidation reaction.Using it as an ammonia source,we synthesized the benzoxazine monomer through Mannich reaction with catechol and paraformaldehyde,and optimized its synthesis conditions.The target product was successfully synthesized by FTIR,NMR,and MALDI-TOF characterization;the curing behavior of G1.0-t-BOZ containing benzoxazine structure was studied by non-isothermal DSC method,and the curing reaction activation energy was Ea=111.68KJ/mol,the reaction order n=0.77,the curing process is an approximate first-order reaction;we tested the G1.0-t-BOZ on polymer materials polyimide(PI)and high-density polyethylene(HDPE).The bonding strengths were 4.35MPa and 0.54MPa,respectively,and the bonding sections showed cohesive failure and coexistence of cohesive failure and interface failure.The reasons for the difference between the bonding strength and the bonding section are analyzed:during the bonding process of PI and G1.0-t-BOZ,the imide ring and the hydroxyl group generated by the ring opening of the adhesive form a hydrogen bond,resulting in a strong bond.In the HDPE bonding process,there is no new hydrogen bond formed between the adhesive and the board,and the bonding effect is weak.This work provides a method for the synthesis of new benzoxazine-based adhesives.2.Study on the synthesis and performance of flame-retardant silicone adhesive In order to construct an organosilicone adhesive with excellent flame retardant properties,we have prepared a series of flame retardant adhesives.First,the flame retardant molecule DFD was synthesized through the aldehyde amine condensation reaction and addition reaction.The target product was successfully synthesized through FTIR and NMR characterization;after that,DFD was added to G1.0-t-BOZ,and a set of flame-retardant modified adhesives G1,G1-DFD-2,G1-DFD-4,G1-DFD-6 and G1-DFD-8 were prepared according to a certain proportion of addition,collectively referred to as poly(G-D).The bonding strength of poly(G-D)to PI and HDPE was tested,and it was shown that the adhesive composed of G1-DFD-8 had the highest bonding strength to PI and HDPE,reaching 4.52MPa and 0.67MPa,respectively.Compared with G1.0-t-BOZ,the bonding strength of the two plates is increased by 3.99%and 24.60%;the analysis of the bonding section shows that the two increase the bonding strength by increasing the interface roughness and adhesion;by testing the mechanical properties,moisture resistance,contact angle and crosslinking density of poly(G-D)after curing,G1-DFD-4 exhibits different properties from other modified materials:It has the largest tensile modulus and tensile strength,the lowest water absorption and the largest contact angle,correspond to the properties of maximum mechanical strength,lowest moisture absorption,and strongest hydrophobicity.The thermal and flame retardant properties of cured poly(G-D),G1-DFD-4 has the highest thermochemical stability and the best flame retardant performance.This work provides an idea for the design,synthesis and preparation of flame-retardant adhesives with excellent comprehensive performance in the field of electronics and electrical.3.Synthesis and characterization of main-chain type high heat-resistant benzoxazine Based on the fact that the introduction of bulky rigid groups into the benzoxazine monomer can effectively enhance the heat resistance of the resin,we have synthesized three substances-benzoxazine phenol source FY containing rigid structure,main-chain type high heat-resistant benzoxazine monomer--ADS-BOZ and ASO-BOZ.First,a benzoxazine phenol source FY containing a rigid structure was synthesized.ADS-BOZ is synthesized by the Mannich reaction to make FY react with aminopropyl double caps and 37%aqueous formaldehyde solution;making FY react with amino-terminated silicone oil with a molecular weight of 6000 and 37%aqueous formaldehyde solution to synthesize ASO-BOZ.The above three structures were characterized by FTIR and NMR,indicating that the target product was successfully synthesized;the thermal analysis of the phenol source FY,the two main chain benzoxazines ADS-BOZ and ASO-BOZ was done by TGA.The result showed that the initial pyrolysis temperature of ASO-BOZ synthesized by polysiloxane is higher,but the carbon residue rate is small.The result of the low carbon residue rate is explained:compared with the low molecular weight disiloxane,the polysiloxane with a molecular weight of 6000g/mol shows stronger thermal stability at the initial cracking temperature.After consulting the literature,it is found that with the pyrolysis of polysiloxane and the loss of bisphenol A structure at high temperature,the benzoxazine cross-linking network disappears,resulting in a significant reduction in the carbon residue rate.This work has positive significance for enriching the research on the thermal stability of main-chain type polybenzoxazines synthesized from siloxanes with different rigid groups and molecular weights.4.Preparation and properties of epoxy resin modified by organosilicon dendrimerIn order to enhance the thermal and mechanical properties of epoxy resin,G1.0-t-BOZ containing organosilicon dendrimer is introduced into epoxy resin.G1.0-t-BOZ can be used as second curing agent to participate in the curing process of epoxy resin,forming a denser cross-linked network than a system where a single curing agent participates in the curing;at the same time,it relies on the Si,N and the flame retardancy of the benzoxazine unit to enhances the flame retardancy of the epoxy resin.First,through the observation of the external morphology and the FTIR characterization of the internal structure,the programmed curing temperature conditions of the epoxy resin/isophorone diamine modified system are determined;then the modified epoxy resin/isophorone diamine modified compound is prepared by blending.The thermal properties,dynamic mechanical properties,and surface morphology of the epoxy resin before and after the modification were studied through TGA,DMA,and SEM;the flame retardancy of the epoxy resin before and after the modification was studied through the flame retardant test LOI,UL-94,and MCC.Modification of epoxy resins yields materials with improved thermal,mechanical and flame retardant properties,which provides a new idea for obtaining epoxy resins with excellent comprehensive properties. |
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