Preparation Of Modified Thermoplastic Elastomer SIS And The Effect On The Performance Of Hot-Melt Pressure Sensitive Adhesive

Polystyrene-polyisoprene-polystyrene（SIS）is a widely used block-type thermoplastic elastomer,also known as thermoplastic rubber,which is the third generation of rubber after natural rubber and synthetic rubber.It is widely used in the fields of adhesives,architectural coatings,inks,decorative waterproofing membranes,plastics and asphalt modification because of its high elasticity,easy processing,low modulus,low viscosity,easy blending,and reusable residual materials.However,SIS is a non-polar polymer and has poor compatibility and adhesion with polar materials,so the use of SIS products is somewhat limited.In this thesis,we firstly carried out the exploration work on the preparation process of SIS to determine the optimal polymerization reaction conditions,followed by the hydrophilic modification of the prepared SIS and finally the preparation of hydrophilic SIS-based hot melt pressure sensitive adhesive.1.SIS preparation:SIS was prepared by anionic polymerization mechanism,cyclohexane as solvent,n-butyl lithium as initiator and styrene and isoprene as raw materials through a three-step addition method.The effects of polymerization temperature and time on polymerization yield were studied experimentally and the molecular weight of SIS was determined by gel permeation chromatography（GPC）.The results showed that the best yield of the prepared SIS polymerization was obtained when the reaction temperature of the first block was 65°C and the reaction time was 30 min,the reaction temperature of the second block was 80-85°C and the reaction time was 30 min,and the reaction temperature of the third block was 80-85°C and the reaction time was 25-30 min,and the GPC showed a value of 111685 for Mn.Secondly,two types of SIS products were prepared with reference to the two products D1111 and D1162 of Craton USA.2.SIS hydrophilic modification.In this paper,three methods are used for modification,（1）polymerization modification:toluene as solvent,n-butyllithium as initiator,2-vinylpyridine（2-VP）as functional monomer,styrene and isoprene as basic monomer using stepwise addition method to prepare four-block polymerization of polystyrene-polyisoprene-poly（vinyl pyridine）（SISV）,two-block polymerization of polystyrene-polyisoprene-pyridine（SIV）three-block polymers and polyisoprene-poly（vinyl pyridine）（IV）two-block polymers.The results of water contact angle and water expansion test showed that SISV,SIV and IV were better hydrophilic than SIS.（2）Physical doping modification:polyvinylpyridine（PVP）was prepared by initiating 2-VP polymerization with n-butyllithium as initiator.The films were doped into SIS at different doping ratios,and the tests showed that the hydrophilicity of each doping ratio was better than that of the native SIS and the hydrophilicity of the films prepared at 60 wt%doping ratio was the best.（3）Sulfonation modification:The sulfonated SIS with different sulfonation degrees were synthesized in N₂ atmosphere using acetyl sulfate as the sulfonating agent.Water contact angle and water expansion tests showed that the hydrophilicity of sulfonated SIS with each doping ratio was better than that of SIS and reached the best at 60 wt%.3.Preparation of hot-melt pressure-sensitive adhesive.The tackifying resin,antioxidant,filler and modified SIS are added step by step by mechanical stirring at a certain temperature,and then poured into the mold after cooling to a certain temperature to get hot melt pressure sensitive adhesive.The results show that the mechanical properties of SIS-based hot melt pressure-sensitive adhesive modified with physical doping of PVP are not affected by the doping ratio,except for a slight decrease in 10%and 20%of the doping ratio,and the mechanical properties of the rest of the doping ratio are not affected.The mechanical properties of the chemically polymerized SIS-based hot-melt pressure-sensitive adhesive,SIV-based hot-melt pressure-sensitive adhesive and pure SIS-based hot-melt pressure-sensitive adhesive are basically unchanged,while the decrease of SISV and IV-based hot-melt pressure-sensitive adhesive is maintained at about 5%;the hydrophilicity test results show that the hydrophilicity test of SISV,SIV and IV-based hot-melt pressure-sensitive adhesive is also better than that of pure SIS-based hot-melt pressure-sensitive adhesive.A comparison between the physically doped and chemically polymerized modified adhesives revealed that the hydrophilicity of the chemically polymerized SIS-based hot melt adhesive was better than the doping modification and more stable at the same PVP content.