<p>1,1-diphenylethylene (DPE) was used as the molecular weights regulator of the copolymerization system of butyl acrylate/methyl methacrylate/acrylic acid (BA/MMA/AA) and participated the free radical copolymerization. The copolymers were characterized by gel permeation chromatography (GPC) and hydrogen spectroscopy of nuclear magnetic resonance (¹H NMR) to investigate the influences of reaction temperature, the contents of initiator, chain transfer agent and copolymer monomer DPE on polymerization process, molecular weights, molecular weight distributions and structure of copolymers. Experimental results showed during copolymerization of BA/MMA/AA and DPE, the initiator and chain transfer agent had little influences on molecular weights and distributions of copolymers, and the copolymers compositions were relatively stable. Investigation of the influence of reaction temperature on polymerization process and copolymers confirmed the copolymers prepared at 200&#xa0;°C were characterized by low molecular weights and narrow molecular weight distributions, while the polymerization rate was controllable. After introduction of copolymerization monomer DPE, the polymerization showed the characteristics of active polymerization, molecular weights of copolymers (1.4 × 10⁴–6.4 × 10³&#xa0;g/mol) and distributions (2.5–1.2) were significantly decreased with increasing content of DPE. The above findings indicated the addition of DPE can indeed act as molecular weight regulator, the acrylic resins with low molecular weights and narrow molecular weight distributions were successfully prepared by regulating the content of DPE.</p>