Study on the Microwave Absorption Characteristics and Temperature Rising Behavior of Poly(4-hydroxystyrene) Precursors in Microwave Field

To address the challenges of high energy consumption and long polymerization times in the traditional synthesis of poly(4-hydroxystyrene) (PHS) resins, this study proposes a novel PHS synthesis method. The method utilizes microwave-assisted heating to synthesize PHS precursors [poly(4-acetoxystyrene) and poly(p-tert-butoxystyrene)]. To assess its feasibility, the dielectric properties of four different PHS precursor reaction systems and their respective monomers were characterized using resonant cavity perturbation techniques over a temperature range of 25-130 °C. The microwave heating characteristics of these systems (or their raw materials) were examined under microwave irradiation at 400 W. Additionally, complementary Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were performed from 30 °C to 300 °C. The results indicate that the dielectric constants of all four types of systems exceed 4, and the lowest dielectric loss tangent is 0.05. Both (2,2-azobisisobutyronitrile) AIBN initiator systems are capable of increasing their temperature from room temperature to 70 °C within 2 minutes in the microwave field. Similarly, both (2,2,6,6-tetramethylpiperidine-1-oxyl radical) TEMPO and (benzoyl peroxide) BPO systems can elevate their temperature from room temperature to 125 °C in just 4 minutes. These findings provide significant guidance for the development of microwave polymerization-based methods for preparing PHS.