Unprecedented Adhesive Performance of Propylene-Based Hydroxyl-Functionalized Terpolymers

The synthesis of hydroxyl-functionalized propylene-based terpolymers and their performance as hot melt adhesives were investigated. The products comprise uniformly distributed butyl and 4-hydroxyl-butyl branches along the polypropylene backbone. Despite the low hydroxyl-functionality level of ≤ 0.5 mol %, hydroxyl-functionalized terpolymers show formidable adhesion to aluminum and steel, providing an adhesive strength exceeding 16 MPa, whereas the nonfunctionalized congeners hardly adhere to these metals. As evidenced by rheological measurements, the functional groups form dynamic crosslinks based on hydrogen bonding and electrostatic interactions with aluminum oxide hydroxide residues, remaining in the product after polymerization. At the industrial application temperature of 180 °C, nondeashed and deashed samples of polymers having 0.1 or 0.5 mol % incorporated 5-hexen-1-ol gave, upon cooling to room temperature, comparable adhesive strengths. Deashing and increasing the functionality level lead to a significant improvement of the adhesion strength at a lower application temperature (130 °C), allowing application of the hydroxyl-functionalized propylene-based terpolymers as high-strength hot melt adhesives for combinations of polypropylene and metals.