Study On Reaction Kinetics Of Cationic Thermopolymerization Of Epoxy Resin

Epoxy resin cationic polymerization system has been widely used in adhesive field because of its rapid reaction,no oxygen resistance and no by-products.The chain propagation process consists of two mechanisms.The activated chain end(ACE)mechanism is dominated in the early stage of polymerization with fast reaction rate.While the activated monomers(AM)mechanism dominated in the later stage of polymerization with slow reaction rate.In this paper,the cycloaliphatic epoxy resin ERL-4221 as the matrix,4-hydroxyphenyl dialkyl sulfonium salt as cationic curing agent,three different types of siloxanes:vinyltrimethoxysliane(VTS),3-glycidoxypropyltrimethoxysilane(GPTS)and 3-methacryloxypropyltrimethoxysilane(MPTS)as coupling agents were used to prepare epoxy resin materials,and characterized by FTIR,DSC,TMA,DMA and TGA.(1)The influence of cationic curing agent content on cationic polymerization of epoxy resin was studied: With the increase of curing agent content,the activation energy corresponding to ACE chain propagation mechanism decreased from 87.81 k J/mol to 83.76 k J/mol,while the activation energy corresponding to AM propagation mechanism decreased from 91.82 k J/mol to 90.38 k J/mol first and then increased to95.06 k J/mol.(2)For EP-0.5CI,EP-1.0CI,EP-1.5CI and EP-2.0CI system,the adhesive strength for the large chip at room temperature is 151.79 g,166.73 g,201.33 g and 143.98 g,respectively.The value increases first and then decreases with the increase of curing agent content.At 160℃,the adhesive strength increased with the increase of curing agent content,which were 108.98 g,117.58 g,136.41 g and 147.51 g,respectively.(3)The effects of different siloxane type and their content on cationic polymerization of epoxy resin were studied: in the early stage of polymerization,with the increase of siloxane content,the activation energy corresponding to the ACE propagation mechanism of EP-VTS system decreased from 84.81 k J/mol to 71.27 k J/mol,and then increased to91.35 k J/mol.And that of EP-MPTS system decreased from 84.81 k J/mol to 60.43 k J/mol and then increased to 98.57 k J/mol.However,that of EP-GPTS system decreased from 84.81 k J/mol to 60.05 k J/mol.At the later stage of polymerization,the activation energies corresponding to AM propagation mechanism increased from 90.38 k J/mol to 102.50 k J/mol,110.15 k J/mol and 99.01 k J/mol for EP-VTS,EP-GPTS and EP-MPTS systems,respectively.(4)The three organosiloxanes have effectively improved the bonding ability of the epoxy resin adhesives,among which the bonding strength of EP-VTS system and EP-MPTS system has been significantly improved.For the pure epoxy resin system,EP-10 VTS system,EP-10 GPTS system and EP-10 MPTS system,the adhesive strength of small chip at room temperature is 30.2g,92.1g,64.1g and 91.7g,respectively.