Study on Modification of Polystyrene Pressure-sensitive Adhesive

Styrene block copolymers (SBCs) are widely used in a variety of pressure sensitive adhesive articles (including adhesives and labels), of which the most commonly used is a three-stage structure with an elastomer in the middle and a thermoplastic block at both ends. Such copolymers are prepared by anionic polymerization and are available in both non-hydrogenated and hydrogenated copolymer forms. According to DuPont, hydrogenated styrene block copolymers have better heat resistance and light resistance.

The branching caused by the thermal polymerization of latex styrene-butadiene rubber (SBR) makes these rubbers very suitable for use as adhesives. U.S. Ameripol Synpol recently used styrene-butadiene latex polymers as modifiers to modify styrenic block polymers. The styrene block copolymer has been modified to form a thermoplastic polymer SIS and SBS with styrene ends and polyisoprene or polybutadiene as the middle segment respectively. It has two different glasses. The transition temperature has the properties of an elastomer at room temperature and shows thermoplasticity when processed at high temperatures. The alternating block copolymers of this structure, after coupling with difunctional or polyfunctional resins, form a linear microstructure, a radial structure or a star structure, resulting in a wide variety of products. Such products can be further differentiated into more different specifications of the final product after further blending treatment.

Ameripol Synpol's modification studies show that there are three main parameters that affect the performance of adhesives made from block copolymers, which are block components, molecular structures, and molecular weights. As the styrene content increases, the polymer hardness, glass transition temperature, and shear tack strength also increase, but the melt viscosity decreases. The shear adhesive failure temperature (SAFT) is affected by both the total molecular weight and the polystyrene block molecular weight. When the temperature rises to approximately 93°C (ie, the glass transition temperature of the polystyrene endblocks), the SBS material Loss of bond strength.

The researchers believe that SBR can act as a viscosity modifier or "helper" when it is required that hot melt blends remain on porous substrates without being absorbed. For example, the addition of SBR latex to SBS used in roofing deck tab adhesives prevents the tabs from being blown up when high winds are encountered.