Low-melting Phthalonitrile Oligomers: Preparation, Polymerization and Polymer Properties

Abstract

A series of low-melting phthalonitrile oligomers were prepared in which variable-length multiple aromatic ether linkages interconnect the terminal phthalonitrile units. These materials were designed to address the need for a processable resin system with good high-temperature properties. The melt-processable oligomers are obtained using a modified-Ullman ether reaction between a bisphenol and a dihalobenzene to form a hydroxyl-terminated oligomeric intermediate that is endcapped by reaction with 4-nitrophthalonitrile. Viscosity measurements show that the phthalonitrile oligomers are polymerized at a moderate temperature (200°C) using the typical aromatic diamine curing additives, bis[4-(4-aminophenoxy)phenyl]sulfone and 1,3-bis(3-aminophenoxy)benzene. The oligomeric phthalonitrile/diamine mixtures exhibit a low complex melt viscosity (0.01-0.1 Pa s) at 200°C. Differential scanning calorimetric analysis is used to follow the polymerization as the oligomeric phthalonitrile/diamine mixtures are heated to elevated temperatures. Thermal and dynamic mechanical properties of thermally-cured oligomeric phthalonitrile polymers are systematically evaluated and compared with those of two other high temperature thermosetting phthalonitrile polymers, 4,4~-bis(3,4-dicyanophenoxy)biphenyl and 1,3- bis(3,4-dicyanophenoxy)benzene. After thermal treatment at 425°C for 8 h, the oligomeric phthalonitrile polymers exhibit char yields of 70% when heated to 1000°C in flowing nitrogen and decomposition temperatures in excess of 500°C when heated in either flowing nitrogen or air. Rheometric measurements indicate that the fully cured oligomeric phthalonitrile polymers do not soften or exhibit a glass transition temperature upon heating to 450°C. Overall, studies on the phthalonitrile oligomers and the corresponding polymers reveal an attractive combination of processability, thermal and thermo-oxidative stability and good dynamic mechanical properties for these materials

Preparation and thermal properties of novel phthalonitrile oligomer containing biphenyl ethernitrile/bisphthalonitrile blends

“…The typical procedure of the synthesis of 2PEN-BPh was as follows 19 : A 500 mL three-necked round-bottom flask equipped with a mechanical stirrer and refluxing, 4,4 0 -biphenol and 2,6-dichlorobenzonitrile with a molar ratio of 2 : 1 19 were taken and then anhydrous potassium carbonate, toluene, and NMP were added. The reaction mixture was refluxed at 160 C for 3h.…”

“…16 Bisphthalonitrile (BPh) was the first phthalonitrile-based high-temperature resin reported 9,17 and had been the most extensively studied phthalonitrile monomer. 18 Although bisphthalonitrile resins processed many advantages, other disadvantages such as great rigidity, 8 low viscosity, 8,19 and a small processing window ($ 20-30 C) 8 had kept these resins from being fully utilized for broad applications; meanwhile, these disadvantages also caused high cost and processing difficulties. 8,19,20 In our laboratory, the previous investigations had demonstrated that incorporating flexible linkages into phthalonitrile terminals could enhance processability without sacrificing high temperature resistance, 21 thermal stability, and mechanical properties 4 ; reactive side-groups incorporated could accelerate the curing rate as well.…”

“…18 Although bisphthalonitrile resins processed many advantages, other disadvantages such as great rigidity, 8 low viscosity, 8,19 and a small processing window ($ 20-30 C) 8 had kept these resins from being fully utilized for broad applications; meanwhile, these disadvantages also caused high cost and processing difficulties. 8,19,20 In our laboratory, the previous investigations had demonstrated that incorporating flexible linkages into phthalonitrile terminals could enhance processability without sacrificing high temperature resistance, 21 thermal stability, and mechanical properties 4 ; reactive side-groups incorporated could accelerate the curing rate as well. 8,21 Based on this idea, a kind of novel n ¼ 2 phthalonitrile oligomer containing biphenyl ethernitrile (2PEN-BPh) was firstly synthesized in this article; 2PEN-BPh had the flexibility which was introduced by the meta-catenated aromatic ether spacer.…”

Effect of bisphenol-A on the structures and properties of phthalonitrile-based resin containing benzoxazine

“…As the only candidate to satisfy the flame standards of United States Navy (MIL-STD-2031), phthalonitrile resins have attracted increased attentions both in laboratory and industry areas, recently. However, high curing temperature (!250°C), high postcuring temperature (!375°C) and narrow processing window ("30°C) have also greatly limited their wide applications [5,6]. To solve these problems, phthalonitrile-based monomers with additional polymerisable groups such as amino, carboxyl, propargyl, oxazine, allyl, etc.…”

Synthesis and Characterization of 4-(2-hydroxyphenoxy) phthalic nitrile

“…Among the wide range of high-temperature resistant resin matrix composites, nitrile resin matrix composites, which possess excellent mechanical property, high-temperature resistance, abrasion resistance, flame resistance and high char yield, are widely applied in the preparation of new-style equipment [1][2]. Therefore, many researchers [3][4][5][6][7][8][9][10][11] have focused on their research of phthalic nitrile. Besides, a lot of researches [12][13][14][15] showed that phenol hydroxyl could improve the self-catalyzed property of phthalic nitrile monomer.…”