P. Mandal, S. Ponnupandian, S. Choudhury, N. Singha This investigation reports the thiol-ene modification of high vinyl content styrenebutadiene-styrene (SBS) block copolymer (BCP) in toluene at 70 °C using different thiolating agents. 1H NMR analysis confirmed the participation of vinyl double bond in thiol-ene modification reaction of SBS. Surface morphology of the block copolymers evaluated by AFM analysis showed higher roughness after thiol-ene reaction. The thiol- modified SBS block copolymer showed better adhesion strength and oil resistance properties than the pristine SBS. Block copolymers (BCP) are an important class of materials, because they can self assemble leading to nanostructured materials. BCPs are used in shape memory materials, emulsifiers, and as thermoplastic elastomers (TPE). TPEs exhibit excellent physio-mechanical properties, elasticity, processability, recyclability, and resistance to heat, chemicals, and ultraviolet radiation. Among the different types of thermoplastic elastomers, the triblock copolymer styrene-butadiene-styrene (SBS) is widely used. The SBS comprising of glassy polystyrene (PS) as outer blocks and elastomeric polybutadiene (PB) as inner block are well known to demonstrate their phase separation leading to nanostructured morphology depending on the composition of the constituent blocks. They are extensively used in different important applications, such as adhesives, paints, coatings, shoe soles, tire treads, and in sealants owing to their superior balance between properties and processability. Incorporation of fillers like nano-silica further enhances its mechanical, thermal properties and the fi-nal performance. However, these BCPs suffer from several drawbacks. SBS is nonpolar in nature, hence its compatibility and bonding ability towards polar material is poor. The oil and fuel resistance properties of SBS are also inferior. Incorporation of polar group via chemical modification can improve the oil and fuel resistance properties of SBS as well as can increase its compatibility towards polar polymers or substrates. Polar modification can also enhance the adhesive strength towards the polar substrate. Polar modification is carried out via grafting as well as via addition reaction. In recent years, thiol-ene addition chemistry has been a versatile synthetic route for the functionalization of different type of polymers like homopolymers [23 – 26], copolymers [27, 28], polypeptides [29], rubbers [30 – 32] and thermoplastic elastomers [33, 34]. Thiol-ene reaction can also be used to prepare complex dendritic structures, glycopolymers, nanostructured networks and end group modified polymers. Thiol-ene reaction takes place via the radical addition of thiols towards carbon-carbon double bond in anti-Markovnikov pathway due to the prevalent emergence of more stable radical intermediate. Thiol-ene addition reactions are associated with several possible side reactions like formation of cyclic group, undesired coupling reactions leading to gel formation. Incorporation of thiol units via thiol-ene reaction in the copolymer matrix increases the interaction between polymer units thereby changes its morphologies and enhances the properties like oil resistance, adhesive properties, thermal properties and hydrophilicity. To the best of our knowledge there is no report on the thiol-ene modification of high vinyl SBS and the study of the properties of thiolmodified SBS. This investigation reports controlled thiol- ene modification onto an elastomeric block copolymer having well known phase segregation behaviour. We have chosen high vinyl content SBS block copolymers and modified using different thiols. The idea behind such investigation is to obtain the thiol-modified SBS block polymer having improved properties, like adhesion and oil resistance properties. The thiol-modified block copolymers were characterized by 1H NMR and FT-IR analyses. Hydrophobicity of the surface was evaluated by water contact angle (WCA) measurement using Goniometer. Surface morphology was characterized by AFM and SEM analyses. The oil-resistance as well as adhesive properties of the thiol-modified SBS were also evaluated and were compared with those of pristine SBS. Conclusions SBS block copolymer having high vinyl content was successfully modified via thiol-ene reaction using different thiolating agents as evidenced by 1H NMR and FT-IR spectroscopy. The surface properties of modified SBS were studied by Goniometer and AFM analyses. The surface properties of thiol modified SBS (BZSSBS) have been changed in terms of contact angle and surface roughness. After incorporation of thiol moiety, the benzyl mercaptan modified SBS (BZS-SBS) exhibited significantly improved oil resistance property and better adhesion strength in the metal-rubber bonding compared to the pristine SBS. Preparation of the thiol-modified elastomers can be turned by varying the extent of thiolation as well as by using different types of thiolating agents. The phase segregation behavior of the modified SBS was changed due to thiolation of the vinyl butadiene block parent block copolymer. These materials can have potential applications in specialty adhesives having better oil and fuel resistance. Source:TPE Magazine