Kyoko Shimizu, Kristoffer Malmos, Allan Hjarbæk Holm, Steen Uttrup Pedersen, Kim Daasbjerg, and Mogens Hinge
In this work, various lengths and densities of poly(methyl methacrylate) (PMMA) brushes were synthesized on stainless steel (SS) surfaces via surface initiated atom transfer radical polymerization. Subsequently, the joints between the bulk PMMA and the PMMA brushed stainless steel were obtained by injection molding, and for these the degree of adhesion was assessed by tensile testing. Several conditions are required to facilitate the mixing between the brushes and the bulk polymer and to reduce the residual stress at the interface: preheating of the SS samples before the injection molding; a long packing time; and a mold temperature above the glass transition temperature (Tg) of PMMA during the injection molding. This treatment leads to a cohesive failure in the bulk PMMA. It was observed that the stress concentrated at the rim, due to contraction of bulk PMMA during cooling, results in a weak adhesion at the rim of the joint. A combination of high density and long brush length of PMMA film provides better adhesion. The large number of PMMA brush chains apparently promotes good penetration into the bulk PMMA chains and ultimately results in high adhesion strength.