This paper first achieved a triplet "backbone molecular structure-Ca2+ responsivity-synthesis methodology" multiscale study in the field of chemistry through preparing a series of poly(acrylic acid) (PAA) based pH-responsive brush copolymers (i.e., poly(methyl methacrylate (MMA)-co-2-(2-bromoisobutyryloxy)ethyl methacrylate (BIEM)-graft-acrylic acid (AA)) with three backbone composition profiles (random, gradient, and block) and investigating the effect of backbone composition profile on their Ca2+ responsivity. And then, a chemical product engineering perspective was introduced to develop these PAA-based pH-responsive brush copolymers into new chemical products which may be used in water softening. The preceding triplet backbone molecular structure-Ca2+ responsivity synthesis methodology multiscale study was closely related to the completing of chemical product pyramid in chemical product engineering field. The whole study can be seen as a case study of manufacturing a useful product with desired function from individual molecules based on a chemical polymerization method and chemical product engineering perspective. It connects the microscopic and macroscopic world and bridges the gap between chemistry and chemical product engineering.