Study On The Polarization Methods And Properties Of SIS Thermoplastic Elastomers

SIS thermoplastic elastomer is often used as a hot-melt pressure-sensitive adhesive matrix due to its good fluidity and high bonding strength.However,SIS is a non-polar polymer and has poor compatibility and adhesion with polar substances.Therefore,the scope of application of SIS hot melt pressure sensitive adhesive is limited.In order to broaden its application,it is necessary to modify the polarity of SIS thermoplastic elastomer.Commonly used polarization methods include the introduction of polar monomers in the polymerization process and post-functional polar modification.The former can choose a narrow range of polar monomers and is not easy to implement.The introduction of the polar group epoxy group can significantly improves the polarity of the polymer,and the strong polar group(hydroxyl group,sulfonic acid group,etc.)or side chain can also be further introduced through ring opening and grafting reaction.Previous studies mainly focused on the impact of specific groups or segments on polymer buproperties,but the research on the impact of diblock SI content and degree of polarity on polymer properties was not systematic.Based on the above considerations,in this paper,using 3-chloroperbenzoic acid(m-CPBA)in-situ epoxy method,using cyclohexane and tetrahydrofuran as mixed solvents,three kinds of SIS with different diblock content(SI)were epoxidized and a series of epoxidized SIS(ESIS)with different epoxidation degrees were prepared,and their structure was characterized.After calculation,the epoxidation efficiency reached more than 90%.On this basis,through the method of ZrCl₄ catalyzed ring-opening,the above-mentioned ESIS was respectively subjected to nucleophilic ring-opening reaction to prepare hydroxylated SIS(HOSIS),and its structure was characterized by means of nuclear magnetic resonance spectrometer.After calculation,the ring-opening efficiency is about 80%,and the degree of hydroxylation is about 55%.Finally,using differential scanning calorimeter(DSC),contact angle measuring instrument,plate vulcanizing machine,material tensile testing machine and other experimental instruments,the effects of SI content and degree of polarity on the thermal properties,surface energy,mechanical properties,T peel strength and other properties of polarized SIS thermoplastic elastomers were systematically studied.The main findings are as follows:(1)The introduction of epoxy groups increases the rigidity of the polymer,hinders the movement of molecular segments,increases the glass transition temperature(T_g),and in the meantime significantly decreases the water contact angle and increases the polarity.After the ring is opened,the polarity is further enhanced,the T_g increases significantly,and the polymer changes from an elastomer material to a brittle material.When the degree of polarization is similar,the contact angle and surface energy do not change significantly.(2)With the degree of epoxidation increasing,the elastic modulus rises,but the SI content is 53 mol%,and the elastic modulus does not change significantly.As the degree of hydroxylation increases,the modulus of elasticity increases,and brittle fracture occurs.Among the polarized products,the peel strength of ESIS-815-20 is the largest,reaching 0.875N/mm.The introduction of epoxy groups not only improves the cohesive strength but also enhances the adhesion to the PET substrate.Meanwhile,the free ends existing in the SI will also improve the adhesion of the elastomer to the substrate.(3)Among the series of polarized products,ESIS-815-20(SI=53mol%,EO=20%)has excellent comprehensive performance.Appropriate SI content and epoxy polarization degree are beneficial to its comprehensive performance and have important guiding significance in the application of SIS hot-melt pressure-sensitive adhesives.