Dielectric behavior and microwave heating mechanism of poly(4-acetoxystyrene) synthesized through microwave-polymerization

Abstract

Poly(p-hydroxystyrene) (PHS) serves as a key raw material for synthesizing deep ultraviolet(KrF) photoresist film-forming resins. To address the issues of lengthy preparation times and suboptimal performance associated with conventional heating methods, this study proposes a novel microwave-assisted polymerization process for synthesizing poly(4-acetoxystyrene), the precursor of PHS, thereby achieving efficient synthesis of poly(4-acetoxystyrene). 4-Acetoxystyrene was used as the monomer, benzoyl peroxide (BPO) as the initiator, and toluene as the solvent. To verify the feasibility of microwave polymerization, the dielectric properties of the monomer, solvent, initiator, and their mixed solution were characterized by the resonant cavity perturbation method at 2450 MHz, and the thermal stability of the reaction system was evaluated by thermogravimetric analysis (TG). Polymerization experiments were conducted using a laboratory-built microwave reactor to monitor the temperature profile during reaction. The results showed that all components and the mixed solution exhibited excellent microwave dielectric loss characteristics. Finally, the samples were systematically characterized by ¹H nuclear magnetic resonance spectroscopy (¹H NMR), Fourier transform infrared spectroscopy (FT-IR), and gel permeation chromatography (GPC). The results confirmed the successful synthesis of poly(4-acetoxystyrene) with a weight-average molecular weight (M_w) of 23,641 g/mol, a polydispersity index (PDI) of 1.86, and a monomer conversion of 98.86%. Furthermore, the mechanism of microwave action in the polymerization process was proposed. This study provides important guidance for the industrial preparation of poly(4-acetoxystyrene) and offers new insights into the efficient synthesis of functional polymer resins.