From soft hyperbranched polymers to hard crosslinkers: UV curable macromers that contained oxetane on and around hyperbranched frameworks

On the basis of aliphatic nucleophilic substitution polycondensation reactions, a series of hyperbranched macromers that contained cationic polymerizable groups, e.g., oxetane, internally and peripherally, was prepared using 3,3-dibromomethyl-1-oxetane and 3,5-dihydroxybenzoic acid as A2 and CB2 monomers, respectively. The structures of these macromers were confirmed via proton nuclear magnetic resonance, Fourier transform infrared spectroscopy (FT-IR), and gel permeation chromatography analyses. The effect of the hyperbranched macromers on the ultraviolet (UV) curing of commercial resin was investigated via photo-differential scanning calorimetry and rheological experiments. The addition of hyperbranched macromers substantially improves the performance of the coating, such as its mechanical properties, pencil hardness, adhesive force, and thermogravimetric stability. It is superior to the addition of small molecule monomers, linear macromers, and hyperbranched macromers with oxetane only at the periphery under the same conditions. The best overall performance of the coating is achieved when the molar ratio of A2 to CB2 is 1.4. Results show that because hyperbranched internal units can also participate in crosslinking during the curing process, such macromers may be good candidates for high-performance UV curing coatings.