Abstract
Thermoplastic polyimide (TPI) was synthesized via a traditional one-step method using 2,3,3′,4′-biphenyltetracarboxylic dianhydride (3,4′-BPDA), 4,4′-oxydianiline (4,4′-ODA), and 2,2′-bis(trifluoromethyl)benzidine (TFMB) as the monomers. A series of semi-interpenetrating polymer networks (semi-IPNs) were produced by dissolving TPI in bisphenol A dicyanate (BADCy), followed by curing at elevated temperatures. The curing reactions of BADCy were accelerated by TPI in the blends, reflected by lower curing temperatures and shorter gelation time determined by differential scanning calorimetry (DSC) and rheological measurements. As evidenced by scanning electron microscopy (SEM) images, phase separation occurred and continuous TPI phases were formed in semi-IPNs with a TPI content of 15% and 20%. The properties of semi-IPNs were systematically investigated according to their glass transition temperatures (Tg), thermo-oxidative stability, and dielectric and mechanical properties. The results revealed that these semi-IPNs possessed improved mechanical and dielectric properties compared with pure polycyanurate. Notably, the impact strength of semi-IPNs was 47%–320% greater than that of polycyanurate. Meanwhile, semi-IPNs maintained comparable or even slightly higher thermal resistance in comparison with polycyanurate. The favorable processability and material properties make TPI/BADCy blends promising matrix resins for high-performance composites and adhesives.
Highlights
Cyanate ester (CE) resins have been widely utilized as matrix resins in electronic and aerospace industries thanks to several distinct advantages over conventional epoxy resins, including low dielectric constant and loss factor, high glass transition temperature (Tg ), reduced moisture absorption and outgassing, good processability, compatibility with various substrates and reinforcements, and favorable mechanical properties [1,2,3,4]
CE resins can copolymerize with epoxy resins, affording thermosets with enhanced fracture toughness [12,13]
After cooling to room temperature, the polyimide solution was poured into methanol (2 L), collected by filtration, Soxhlet extracted with methanol for 24 h, and dried in vacuum at 150 ◦ C for 48 h to afford an off-white fibrous solid (53.4 g, yield: 96.1%)
Summary
Cyanate ester (CE) resins have been widely utilized as matrix resins in electronic and aerospace industries thanks to several distinct advantages over conventional epoxy resins, including low dielectric constant and loss factor, high glass transition temperature (Tg ), reduced moisture absorption and outgassing, good processability, compatibility with various substrates and reinforcements, and favorable mechanical properties [1,2,3,4]. Polycyanurates, the cured products of CE resins, possess higher fracture toughness in comparison with other traditional thermosets (epoxy, bismaleimide, etc.). A diversity of thermosetting resins (such as epoxides, bismaleimides (BMI), and imide oligomers) has been investigated for the modification of CE resins [7,8,9,10,11]. Meier et al prepared sequential interpenetrating polymer networks (IPNs) from novolac-type CE and phenylethynyl-terminated imide oligomer (PETI) with the aid of DABPA. Polyimide/polysiloxane block copolymers were explored as CE modifiers by Liang and coworkers. Thermoplastic polyimide (TPI) simultaneously possessing a high Tg (360 °C) and and excellent solubility (>20% in BADCy) was prepared using 2,3,30 ,40 -biphenyltetracarboxylic excellent solubility (>20% in BADCy) was prepared using 2,3,3′,4′-biphenyltetracarboxylic dianhydride (3,40 -BPDA), 4,40 -oxydianiline (4,40 -ODA), and 2,20 -bis(trifluoromethyl)benzidine (TFMB). Structures of bisphenol A dicyanate (BADCy) and thermoplastic polyimide (TPI)
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