Microporous Thermosetting Film Constructed from Hyperbranched Polyarylate Precursors Containing Rigid Tetrahedral Core: Synthesis, Characterization, and Properties

Porous organic thermosetting film with pore size smaller than 20 Å was constructed through the self-cross-linking reaction from hyperbranched polyarylate precursors with rigid tetrahedral skeleton. Using hydroquinone diacetate as the A 2 monomer and tetrakis(4-carboxyphenyl)silane as the B 4 monomer, the hyperbranched polyarylate precursors were successfully synthesized with high yields, during which the gelation process was efficiently suppressed by heterogeneous polycondensation method by means of the elaborate selection of reaction medium. The control of monomer ratio in the polymerization system led to two types of precursors, i.e., mainly carboxyl-terminated hyperbranched polyarylate (CTHP) and mainly acetoxy-terminated hyperbranched polyarylate (ATHP). They had degree of branching values of 0.53−0.69, molecular weights of 10100−34000 g/mol, inherent viscosities of 0.12−0.18 dL/g, and good solubility in the common solvents. The precursor film, obtained by spin coating from the mixture solution of CTHP and ATHP with equivalent amount of reactive carboxylic group and acetoxy groups, was readily thermally cured via a transesterification reaction to form a cross-linked network, which exhibited excellent thermal stability, good chemical resistance, low birefringence, and low dielectric constant, as well as microporosity, with an average pore size of 11.2 Å and surface area of 158 m 2 /g.