Cyclization And Properties Of Styrene-Based Thermoplastic Elastomers

The cyclization reaction can introduce cyclic structures into the polymer chain,which is of great significance for improving the properties of polymer materials and developing new polymer materials.In this paper,the cationic cyclization behaviors of SBS with low,medium and high vinyl contents and S-SB-S were studied using trifluoromethanesulfonic acid as the catalyst,and the structure and properties of cyclized molecules were characterized by NMR,GPC,TG and SAXS,and the effects of cyclization on physical and mechanical properties and dynamic mechanical properties of elastomeric materials were investigated.The main research contents and results are as follows:The cyclization reaction of three SBS copolymers with vinyl content of8.1%,38.3%and 78.4%,respectively,was carried out,and the results showed that the cyclization was mainly intramolecular cyclization.The cyclization reaction rate of the three SBS copolymers was L-SBS（low vinyl contents）（29）M-SBS（medium vinyl contents）（29）H-SBS（high vinyl contents）,indicating that the cyclization activity of the double bond in the chain was higher than that of the side group double bond.CF₃SO₃H can efficiently catalyze the cyclization reaction,and the cyclization rate of L-SBS can reach91.5%at a concentration of 19 mmol·L^-1for 10 min.The hydrodynamic volume of the molecular chain of the cyclized products decreased and the PDI broadened with the increase of the cyclization degree.The _gof L-SBS was-80.7°C,-64.3°C,-41.1°C,-1.29°C for the cyclization degrees of 9.42%,25.2%,40.6%,and 57.6%,respectively,which showed a linear increase with the increase of cyclization degree.The cyclization reduced the degree of phase separation of the two phases,and the L-SBS cyclization degrees of 9.42%,25.2%,and 40.6%,the lamellar spacing gradually decreased from the original30.0 nm to 29.4 nm,29.1 nm and 28.3 nm,respectively,and the lamellar structure disappeared when the cyclization degree was 57.6%,but the phase-separated structure still existed.The tensile strength and elongation at break of the cyclization products were reduced.When the cyclization degree of M-SBS was 19.7%,the tensile strength decreased from 31.5 MPa to 25.7MPa,a decrease of 18.4%,and the elongation at break decreased from 1400%to 1340%,a decrease of 4.3%;when the cyclization degree of H-SBS increased from 5.4%to 56.7%,the tensile strength decreased sharply,from21.6 MPa to 4.40 MPa,a decrease of 80%,and the elongation at break decreased from 1210%to 1140%,a decrease of 5.8%.The samples before and after cyclization have good damping characteristics.The effective damping temperature range of L-SBS increases from（-120℃～-75℃）to（-40℃～0℃）when the cyclization degree of L-SBS is 40.6%;the damping temperature range of M-SBS increases from（-85℃～-35℃）to（-60℃～0℃）when the cyclization degree of M-SBS is 19.7%;As the cyclization degree of H-SBS increased from 5.4%to 56.7%,its damping temperature range gradually approached to room temperature,changing from（-20℃～30℃）to（0℃～60℃）.The cyclization reaction was performed on SSBS and it was found that only intramolecular cyclization occurred.The reaction was essentially complete cyclization at a CF₃SO₃H concentration of 19 mmol·L^-1for 15 min.After cyclization,the hydrodynamic volume decreased and the PDI broadened;after complete cyclization,T_gwas 110°C,which increased roughly 150°C;at50.0%cyclization,T_gcould increase above room temperature;cyclization reduced the degree of phase separation of the two phases,and the phase separation structure completely disappeared at 64.8%cyclization.The cyclization degree below 29.2%showed an increasing trend of tensile strength,from 29.5 MPa to 32.3 MPa,an increase of 9.5%;elongation at break decreased from 630%to 540%,a decrease of 14.3%.When the cyclization degree was higher than 41.8%,brittle fracture occurred,and the elongation at break were around 20%,and the tensile strength increased sharply,from 11.7MPa to 22.5 MPa when the cyclization degree increased from 41.8%to 64.8%.Cyclized plastics exhibit good shape memory behavior.