Low dielectric thermoset. I. Synthesis and properties of novel 2,6‐dimethyl phenol‐dicyclopentadiene epoxy

A 2,6‐dimethyl phenol‐dicyclopentadiene novolac was synthesized from dicyclopentadiene and 2,6‐dimethyl phenol, and the resultant 2,6‐dimethyl phenol‐dicyclopentadiene novolac was epoxidized to 2,6‐dimethyl phenol‐dicyclopentadiene epoxy. The structures of novolac and epoxy were confirmed by Fourier transform infrared spectroscopy (FTIR), elemental analysis, mass spectroscopy (MS), nuclear magnetic resonance spectroscopy (NMR), and epoxy equivalent weight titration. The synthesized 2,6‐dimethyl phenol‐dicyclopentadiene epoxy was then cured with 4,4‐diaminodiphenyl methane (DDM), phenol novolac (PN), 4,4‐diaminodiphenyl sulfone (DDS), and 4,4‐diaminodiphenyl ether (DDE). Thermal properties of cured epoxy resins were studied by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), dielectric analysis (DEA), and thermal gravimetric analysis (TGA). These data were compared with those of the commercial bisphenol A epoxy system. Compared with the bisphenol A epoxy system, the cured 2,6‐dimethyl phenol‐ dicyclopentadiene epoxy resins exhibited lower dielectric constants (～3.0 at 1 MHz and 2.8 at 1 GHz), dissipation factors (～0.007 at 1 MHz and 0.004 at 1 GHz), glass transition temperatures (140–188°C), thermal stability (5% degradation temperature at 382–404°C), thermal expansion coefficients [50–60 ppm/°C before glass‐transition temperature (T_g)], and moisture absorption (0.9–1.1%), but higher modulus (～2 Gpa at 60°C). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2607–2613, 2003     

Flame retardancy and dielectric properties of dicyclopentadiene‐based benzoxazine cured with a phosphorus‐containing phenolic resin

A dicyclopentadiene‐based benzoxazine (DCPDBZ) was prepared and separately copolymerized with melamine–phenol formaldehyde novolac or phosphorus‐containing phenolic resin (phosphorus‐containing diphenol) at various molar ratios. Their curing behaviors were characterized by differential scanning calorimetry. The electrical properties of the cured resins were studied with a dielectric analyzer. The glass‐transition temperatures were measured by dynamic mechanical analysis. The thermal stability and flame retardancy were determined by thermogravimetric analysis and a UL‐94 vertical test. These data were compared with those of bisphenol A benzoxazine and 4,4′‐biphenol benzoxazine systems. The effects of the diphenol structure and cured composition on the dielectric properties, moisture resistance, glass‐transition temperature, thermal stability, and flame retardancy are discussed. The DCPDBZ copolymerized with phosphorus‐containing novolac exhibited better dielectric properties, moisture resistance, and flame retardancy than those of the melamine‐modified system. The flame retardancy of the cured benzoxazine/phosphorus‐containing phenolic resins increased with increasing phosphorus content. The results indicate that the bisphenol A and 4,4′‐biphenol systems with a phosphorus content of about 0.6% and the dicyclopentadiene system with a phosphorus content of about 0.8% could achieve a flame‐retardancy rating of UL‐94 V‐0. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and properties of fluorinated biphenyl‐type epoxy resin

A novel fluorinated biphenyl‐type epoxy resin (FBE) was synthesized by epoxidation of a fluorinated biphenyl‐type phenolic resin, which was prepared by the condensation of 3‐trifluoromethylphenol and 4,4′‐bismethoxymethylbiphenyl catalyzed in the presence of strong Lewis acid. Resin blends mixed by FBE with phenolic resin as curing agent showed low melt viscosity (1.3–2.5 Pa s) at 120–122°C. Experimental results indicated that the cured fluorinated epoxy resins possess good thermal stability with 5% weight loss under 409–415°C, high glass‐transition temperature of 139–151°C (determined by dynamic mechanical analysis), and outstanding mechanical properties with flexural strength of 117–121 MPa as well as tensile strength of 71–72 MPa. The thermally cured fluorinated biphenyl‐type epoxy resin also showed good electrical insulation properties with volume resistivity of 0.5–0.8 × 10¹⁷ Ω cm and surface resistivity of 0.8–4.6 × 10¹⁶ Ω. The measured dielectric constants at 1 MHz were in the range of 3.8–4.1 and the measured dielectric dissipation factors (tan δ) were in the range of 3.6–3.8 × 10^?3. It was found that the fluorinated epoxy resins have improved dielectric properties, lower moisture adsorption, as well as better flame‐retardant properties compared with the corresponding commercial biphenyl‐type epoxy resins. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and characterization of organosoluble polyfluorinated polyimides derived from 3,3′,5,5′‐tetrafluoro‐4,4′‐diaminodiphenylmethane and various aromatic dianhydrides

A polyfluorinated aromatic diamine, 3,3′, 5,5′‐tetrafluoro‐4,4′‐diaminodiphenylmethane (TFDAM), was synthesized and characterized. A series of polyimides, PI‐1–PI‐4, were prepared by reacting the diamine with four aromatic dianhydrides via a one‐step high‐temperature polycondensation procedure. The obtained polyimide resin had moderate inherent viscosity (0.56–0.68 dL/g) and excellent solubility in common organic solvents. The polyimide films exhibited good thermal stability, with an initial thermal decomposition temperature of 555°C–621°C, a 10% weight loss temperature of 560°C–636°C, and a glass‐transition temperature of 280°C–326°C. Flexible and tough polyimide films showed good tensile properties, with tensile strength of 121–138 MPa, elongation at break of 9%–12%, and tensile modulus of 2.2–2.9 GPa. The polyimide films were good dielectric materials, and surface and volume resistance were on the order of a magnitude of 10¹⁴ and 10¹⁵ Ω cm, respectively. The dielectric constant of the films was below 3.0 at 1 MHz. The polyfluorinated films showed good transparency in the visible‐light region, with a cutoff wavelength as low as 302 nm and transmittance higher than 70% at 450 nm. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1442–1449, 2007     

Structural effects of pendant groups on thermal and electrical properties of polyimides

Two series of aromatic polyimides containing various‐sized alkyl side groups were synthesized by thermal imidization of the poly(amic acid)s prepared from the polyaddition of benzophenonetetracarboxylic dianhydride and hexafluoro‐isopropylidene bis(phthalic anhydride) with 4,4′‐methylenedianiline, 4,4′‐methylene‐bis(2,6‐dimethylaniline), 4,4′‐methylene‐bis(2,6‐diethylaniline), and 4,4′‐methylene‐bis(2,6‐diisopropylaniline). The extent to which alkyl substitutes affect the thermal properties of polyimides was examined by differential scanning calorimetry, thermomechanical analyzer, and thermogravimetric analysis techniques. The analytical results demonstrated that the incorporation of alkyl moieties causes a moderate increase in the coefficient of thermal expansion and a slight decrease in thermal stability. Notably, all polymers had a decomposition temperature exceeding 500°C. The glass transition temperature increases markedly when hydrogen atoms at ortho positions on aniline rings are replaced with methyl groups, but decreases with growing alkyl side group size. The dielectric measurements show that the polymer possessing a large alkyl side group would have the lower dielectric value. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4672–4678, 2006     

Synthesis and characterization of polyimide–silica nanocomposites using novel fluorine‐modified silica nanoparticles

Polyimide–silica nanocomposites were synthesized with 4,4′‐oxydianiline, 4,4′‐(4,4′‐isopropylidenediphenoxy)bis(phthalic anhydride), and fluorine‐modified silica nanoparticles. Fluorinated precursors such as 4″,4?‐(hexafluoroisopropylidene)bis(4‐phenoxyaniline) (6FBPA) and 4,4′‐(hexafluoroisopropylindene)diphenol (BISAF) were employed to modify the surface of the silica nanoparticles. The microstructures and thermal, mechanical, and dielectric properties of the polyimide–silica nanocomposites were investigated. An improvement in the thermal stability and storage modulus of the polyimide nanocomposites due to the addition of the modified silica nanoparticles was observed. The microstructures of the polyimide–silica nanocomposites containing 6FBPA‐modified silica exhibited more uniformity than those of the nanocomposites containing BISAF‐modified silica. The dielectric constants of the polyimide were considerably reduced by the incorporation of pristine silica or 6FBPA‐modified silica but not BISAF‐modified silica. The addition of a modifier with higher fluorine contents did not ensure a lower dielectric constant. The uniformity of the silica distribution, manipulated by the reactivity of the modifier, played an important role in the reduction of the dielectric constant. Using 6FBPA‐modified silica nanoparticles demonstrated an effective way of synthesizing low‐dielectric‐constant polyimide–silica nanocomposites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 882–890, 2007     

Polyimide foams with ultralow dielectric constants

To explore ultralow dielectric constant polyimide, the crosslinked polyimide foams (PIFs) were prepared from 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA), 4,4′‐oxydianiline (ODA), and 2,4,6‐triaminopyrimidine (TAP) via a poly(ester–amine salt) (PEAS) process. FTIR measurements indicated that TAP did not yield a negative effect on imidization of PEAS precursors. SEM measurement revealed the homogeneous cell structure. Through using TAP as a crosslinking monomer, the mechanical properties of PIFs could be improved in comparison with uncrosslinked BTDA/ODA based PIF. The crosslinked PIFs still exhibited excellent thermal stability with 5% weight loss temperatures higher than 520°C. In the field with frequency higher than 100 Hz, the dielectric constants of the obtained PIFs ranged from 1.77 to 2.4, and the dielectric losses were smaller than 3 × 10^?2 at 25–150°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1734–1740, 2006     

Synthesis and properties of bismaleimide resin containing dicyclopentadiene or dipentene. VI

New aromatic bismaleimides (BMIs), bis(4‐maleimidophenoxy‐3,5‐dimethylphenyl)dicyclopentadiene (DCPDBMI) and bis(4‐maleimido‐phenoxy‐3,5‐dimethylphenyl)dipentene (DPBMI), containing a large dicyclopentadiene (DCPD) or dipentene (DP) and aryl ether linkage, were synthesized from diamine bis(4‐aminophenoxy‐3,5‐dimethylphenyl)dicyclopentadiene (DCPDA) or bis(4‐aminophenoxy‐3,5‐dimethylphenyl)dipentene(DPA) and maleic anhydride by the usual two‐step procedure that included ring‐opening addition to give bismaleamic acid, followed by cyclodehydration to bismaleimide. The monomers were characterized by Fourier transform infrared spectroscopy, proton NMR, elemental analyses, and mass spectra. Their thermal polymerization was investigated by DSC. The presence of a large cycloaliphatic moiety in the backbone of the bismaleimide increased the curing temperature and reduced the reactivity of the maleimide bond. Thermal and electrical properties of cured bismaleimide resins were studied using a dielectric analyzer, dynamic mechanical analyzer, and thermal gravimetric analyzer. These data were compared with that of commercial 4,4‐bismaleimidodiphenylmethane (DDMBMI). The cured DCPDBMI or DPBMI exhibits a lower dielectric constant, dissipation factor and moisture absorption than those of DDMBMI. Copyright © 2006 Society of Chemical Industry     

Studies of dielectric characteristics and surface energies of spin‐coated polyimide films

A two‐step method, that is, polyamic acid formation with subsequent curing, was used to synthesize six kinds of polyimides. Dielectric constants and surface energies were investigated to determine the nature of the fluorinated and nonfluorinated polyimides. The dielectric constant decreased from 3.3 (at 100 kHz) for PMDA/ODA to 2.6 (at 100 kHz) for 6FDA/4,4′‐6F when the fluorine content increased from 0 to 30.7 wt %. Simultaneously, the water contact angle increased from 65° for PMDA/ODA to 78° for 6FDA/4,4′‐6F. Experimental results indicated that fluorinated polyimides contained a lower dielectric constant with improved water resistance. The surface energy values obtained from experiments agreed well with Holmes' correlation between surface energy and dielectric constant. The surface energies and dielectric constants were significantly affected by the polymer backbone structures, especially by the fluorination effect. Therefore, by choosing the appropriate monomers, polyimides of low dielectric constants with hydrophobic surfaces could be obtained. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1642–1652, 2001     

Novel adamantane‐containing epoxy resin

A novel adamantane‐containing epoxy resin diglycidyl ether of bisphenol‐adamantane (DGEBAda) was successfully synthesized from 1,3‐bis(4‐hydroxyphenyl)adamantane by a one‐step method. The proposed structure of the epoxy resin was confirmed with Fourier transform infrared, ¹H‐NMR, gel permeation chromatography, and epoxy equivalent weight titration. The synthesized adamantane‐containing epoxy resin was cured with 4,4′‐diaminodiphenyl sulfone (DDS) and dicyandiamide (DICY). The thermal properties of the DDS‐cured epoxy were investigated with differential scanning calorimetry and thermogravimetric analysis (TGA). The dielectric properties of the DICY‐cured epoxy were determined from its dielectric spectrum. The obtained results were compared with those of commercially available diglycidyl ether of bisphenol A (DGEBA), a tetramethyl biphenol (TMBP)/epoxy system, and some other associated epoxy resins. According to the measured values, the glass‐transition temperature of the DGEBAda/DDS system (223°C) was higher than that of the DGEBA/DDS system and close to that of the TMBP/DDS system. TGA results showed that the DGEBAda/DDS system had a higher char yield (25.02%) and integral procedure decomposition temperature (850.7°C); however, the 5 wt % degradation temperature was lower than that of DDS‐cured DGEBA and TMBP. Moreover, DGEBAda/DDS had reduced moisture absorption and lower dielectric properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Design and synthesis of organosoluble and transparent polyimides containing bulky substituents and noncoplanar structures

A new diamine monomer, 3,3′‐diisopropyl‐4,4′‐diaminophenyl‐4″‐phenyltouene, was designed, synthesized, and then polymerized with five commercial dianhydrides to obtain a series of novel polyimides via a one‐step method. The obtained polymers showed excellent solubility in most common solvents, even in low‐boiling solvents, such as chloroform, dichloromethane, and tetrahydrofuran. They exhibited a high thermal stability with the glass‐transition temperature in the range 262–318°C and 10% weight loss temperatures in the range 464–488°C under a nitrogen atmospheres. Meanwhile, these polymer films also displayed a high optical transparency with a cutoff wavelength in the range 305–365 nm; prominent mechanical properties with a tensile strength of 65.6–94.9 MPa, a Young's modulus of 1.6–2.8 GPa, and an elongation at break of 9.3–13.7%; a low dielectric constant in the range of 2.91–3.18 at 1 MHz; and an outstanding hydrophobicity with a contact angle above 90.6°. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43266.     

Polyimide–polydimethylsiloxane copolymers for low‐dielectric‐constant and moisture‐resistance applications

Novel, randomly coupled, soluble, segmented polyimide–polydimethylsiloxane (PI–PDMS) copolymers were prepared from aminoalkyl‐terminated polydimethylsiloxane (At–PDMS), 4,4′‐oxydianiline diamine, pyromellitic dianhydride, and 4,4′‐diphenylmethane diisocyanate (MDI). When At–PDMS was introduced into the polyimide chain, the polyimide copolymers exhibited lower dielectric constants and better moisture resistance and mechanical properties. The reductions in the dielectric constant of the PI–PDMS copolymers could be attributed to the incorporation of polydimethylsiloxane (PDMS) into the polyimide chain and the nanopores in the film generated by carbon dioxide evolvement during the reaction. The lowest dielectric constant was 2.58 with 25 wt % PDMS and 5 wt % MDI. In addition, the water contact angles of the resultant copolymers increased from 51 to 109° when the contents of PDMS increased from 0 to 25 wt %. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and characterization of benzimidazole‐based low CTE block copolyimides

A series of block and random copolyimide films were synthesized from various molar ratios of two diamines, rigid 2‐(4‐aminophenyl)‐5‐aminobenzimidazole (APBI) and flexible 4,4′‐oxydianiline (ODA) by polycondensation with dianhydride 3,3′,4,4′‐biphenyltetracarboxylic dianhydride. The contents of APBI ranged from 10 to 60 mol % in copolyimides. The copolyimide films obtained by thermal imidization of poly(amic acid) solutions, were characterized by TMA, DMA, TGA, DSC, wide‐angle X‐ray diffraction, FTIR, tensile testing, water uptake (WU), and dielectric constant measurements. Rigid heterocyclic diamine APBI with interchain hydrogen bonding capability, led to low coefficient of thermal expansion (CTE), high T_g, high thermal stability and better mechanical properties. Increasing the APBI mol % caused a gradual decrease in the CTE and increase in T_g, thermal stability and tensile strength properties of the copolyimides films. Moreover, significantly enhanced thermal and mechanical properties of the block copolyimides were also found as compared to random copolyimides. The block copolyimide with APBI content of 60 mol %, achieved excellent properties, that is, a low CTE (4.7 ppm/K), a high T_g at 377°C, 5% weight loss at 562°C and a tensile strength at 198 MPa. This can be interpreted because of comparatively higher degree of molecular orientation in block copolyimides. These copolyimides also exhibited better dielectric constant and WU. This combination of properties makes them attractive candidates for base film materials in future microelectronics. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthesis and properties of aromatic polyimide,poly(benzoxazole imide), and poly(benzoxazole amide imide)

Two series of heterocyclic aromatic polymers were synthesized from 4,4′‐(4,4′‐isopropylidenediphenoxy)bis(phthaltic anhydride) and 2,2′‐bis(3,4‐dicarboxyphenyl)hexafluoropropane dianhydride by two‐step method. The inherent viscosities were in the range of 24–45 cm³/g. The effects of the rigid benzoxazole group in the backbone of copolymer on the thermal, mechanical, and physical properties were investigated. These polymers exhibit good thermal stability. The temperatures of 5% weight loss (T₅) of these polymers are in the range of 403–530°C in air and 425–539°C in nitrogen. The chard yields of these polymers are in the range of 15–24% in air and 54–61% in nitrogen. These polymers also have high glass‐transition temperatures and a low coefficient of thermal expansion and good mechanical properties. The poly(benzoxazol imide) has a higher tensile strength and modulus than those of neat polyimide. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Comparison of the effects of linking diglycidyl ether‐terminated PDMS and BPA onto polyurethane with respect to the tensile and thermal properties

Flexible poly(dimethylsiloxane) (PDMS) or rigid bisphenol A (BPA) with diglycidyl ether end groups was linked to polyurethane (PU), which was composed of 4,4′‐methylenebis(phenyl isocyanate) as a hard segment and poly(tetramethylene ether)glycol as a soft segment. A control PDMS (CPDMS) series was prepared with an additional deprotonation step by NaH. The spectroscopic, thermal, tensile, shape memory, and low‐temperature flexibility properties were compared with those of plain PU to investigate the effects of linking the flexible PDMS or the rigid BPA on PU. The soft segment melting peaks were not affected by the PDMS content for the PDMS series but disappeared as the BPA content increased in the BPA series. The soft segment crystallization of PU was completely disrupted as the linked BPA content increased in the differential scanning calorimetry results and disappeared in the dynamic mechanical analysis results. The glass transition temperature (T_g) of the BPA series increased with increasing BPA content, whereas that of the PDMS series remained the same. The tensile strength of the PDMS series sharply increased with increasing PDMS content. The shape retention of the BPA series at ?25 °C sharply decreased as the BPA content increased. Finally, the BPA series linked with rigid aromatic BPA demonstrated excellent low‐temperature flexibilities compared with the PDMS series and plain PU. Compared with PUs linked with PDMS, PUs linked with rigid BPA demonstrated a significant change in the cross‐link density, thermal properties, shape retention, and low‐temperature flexibility. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43284.     

Inclusion of covalent triazine framework into fluorinated polyimides to obtain composites with low dielectric constant

Polyimides possess good mechanical properties, favorable dielectric properties, and chemical inertness, which enabled them to find applications in microelectronic industries. The dielectric constant of the polyimides varies between 2.5 and 4, which is rather high for such applications. Hence, synthesizing polyimides with still lower dielectric constant has become one of the critical research confronts. As the properties of a terpolyimides (TPI) could be altered as per the requirement, it was synthesized by combining the dianhydrides 3,3′,4,4′-biphenyldianhydride, 3,3′,4,4′-oxydiphthalicdianhydride, and 4,4′-(hexafluoroisopropylidene) with a diamine 4,4′-(hexafluoroisopropylidene)dianiline or 2,2-bis[4-(4-amino phenoxy)phenyl]hexafluoropropane. As porous covalent triazine framework (CTF-1) is capable of capturing much air within its pores and interfacial voids, it was combined with the TPI matrix in different loadings to obtain CTF-1/TPI composite films with low dielectric constant. The composites exhibited high thermal stability, as their thermal decomposition occurred above 520°C. The tensile properties and the dielectric constant of the composites declined with the raise in CTF-1 loading up to 4%. The decrease in dielectric constant is essentially due to the incorporation of air voids (dielectric constant of air ~1) in the TPI matrix due to the inclusion of porous CTF-1.     

Functionalized KIT‐6/Terpolyimide composites with ultra‐low dielectric constant

Polyimides with low dielectric constants are important raw materials for the fabrication of flexible printed circuit boards and other microelectronic applications. As creation of voids in polyimide matrix could decrease dielectric constant, in this study mesoporous KIT‐6, synthesized hydrothermally, was functionalized with 3‐aminopropyltriethoxysilane (APTS) and mixed with 4,4′‐oxydianiline (ODA) in the synthesis of terpoly(amic acid) using 3,3′,4,4′‐biphenyldianhydride (BPDA), 3,3′,4,4′‐oxydiphthalic dianhydride (ODPA) and 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA) and subsequently stage‐cured to obtain APTS‐KIT‐6/Terpolyimide composites (APTS‐KIT‐6/TPI). The asymmetric and symmetric vibrations of imide O?C? N? C?O groups of APTS‐KIT‐6/TPI composites showed their peaks at 1772 and 1713 cm^?1. The dielectric constant decreased with the increase in KIT‐6 loading from 2 to 4%, but increased at higher loadings, and at 4% loading it was 1.42. Its tensile strength (103 MPa), tensile modulus (2.5 GPa), and percentage elongation (8.2) and high thermal stability (>540°C) were also adequate for application in microelectronics such as flexible printed circuits. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40508.     

Structure and characterization for conterminously linked polymer of short‐chain epoxy resin with triallyl isocyanurate and bismaleimide

The short‐chain epoxy resin (SCER) was prepared direct from epichlorohydrin/bisphenol A (ECH/BPA). The resulted SCER and 4,4′‐diaminodiphenyl sulfone (DDS) with various weight percent of triallyl isocyanurate/4,4′‐bismaleimidophenylmethane (TAIC/BMI) were subsequently thermally coreacted to the corresponding high performance materials for high frequency application. They were characterized using potentiometry, Fourier transform infrared (FTIR), differential scanning calorimetry (DSC), thermogravimetric analyses (TGA), dielectric analyzer, and scanning electron microscope (SEM). Dynamic mechanical analysis (DMA) of polymers showed only a T_g indicating a low entropy, amorphous state and formed a conterminously linked polymer. The morphology of polymers revealed no phase separation. The formation of polymer was in good agreement with the proposed molecular structure, and has enhanced good thermal, mechanical, and electric properties. Furthermore, with lower nitrogen content was achieved UL‐94 V‐0 rating. No fume and toxic gas emission were observed during burning test for this system. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2470–2480, 2006     

Dielectric behavior and properties of a cyanate ester containing dicyclopentadiene. I

2,6‐Dimethyl phenol dicyclopentadiene dicyanate ester (DCPDCY) was synthesized through the reaction of 2,6‐dimethyl phenol dicyclopentadiene novolac and cyanogen bromide. The proposed structure was confirmed by Fourier transform infrared, mass spectrometry, NMR spectrometry, and elemental analysis. DCPDCY was then cured by itself or cured with bisphenol A dicyanate ester (BADCY) to form triazine structures. The thermal properties of the cured DCPDCY resins were studied with differential scanning calorimetry, dynamic mechanical analysis (DMA), dielectric analysis, and thermogravimetric analysis; these data were compared with those of BADCY. The cured DCPDCY resins exhibited a lower dielectric constant (2.58 at 1 MHz), a lower dissipation factor (20.2 mU at 1 MHz), less thermal stability (the 5% degradation temperature and char yield were 430°C and 32.1%, respectively), a lower glass‐transition temperature (266°C by thermomechanical analysis and 271°C by DMA), a lower coefficient of thermal expansion (22.5 ppm before the glass‐transition temperature and 124.9 ppm after the glass‐transition temperature), and less moisture absorption (0.88% at 48 h) than BADCY, but they showed higher moduli (6.28 GPa at 150°C and 5.35 GPa at 150°C) than the bisphenol A system. The properties of the cured cocyanate esters (DCPDCY and BADCY) lay between those of cured BADCY and DCPDCY, except for the moduli. The moduli of some cocyanate esters were even higher than those of cured BADCY and DCPDCY. A positive deviation from the Fox equation was observed for cocyanate esters. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2079–2089, 2005     

Synthesis and properties of fluorinated polyimides from 1,1‐bis(4‐amino‐3,5‐dimethylphenyl)‐1‐(3,4,5‐trifluorophenyl)‐2,2,2‐trifluoroethane and various aromatic dianhydrides

A novel aromatic diamine, 1,1‐bis(4‐amino‐3,5‐dimethylphenyl)‐1‐(3,4,5‐trifluorophenyl)‐2,2,2‐trifluoroethane, containing a pendant polyfluorinated phenyl group, a trifluoromethyl group, and methyl groups ortho‐substituted to the amino groups in the structure was synthesized and characterized. The diamine was polymerized with several aromatic dianhydrides, including 3,3′,4,4′‐biphenyltetracarboxylic dianhydride, 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride, 4,4′‐oxydiphthalic anhydride, and 4,4′‐hexafluoroisopropylidene diphthalic anhydride, via a high‐temperature one‐step procedure to afford four polyimides (PIs) with inherent viscosities of 0.47–0.70 dL/g. The PIs exhibited excellent solubilities in a variety of organic solvents. They were soluble not only in polar aprotic solvents but in many common solvents, such as cyclopentanone, tetrahydrofuran, and even toluene at room temperature. The tough and flexible PI films cast from the PI solutions exhibited good thermal stabilities and acceptable tensile properties. The glass‐transition temperatures were in the range 312–365°C, and the 5% weight loss temperatures were all higher than 480°C in nitrogen. The films had tensile strengths in the range 76–99 MPa, tensile moduli of 2.2–2.8 GPa, and elongations at break of 5–8%. In addition, the PI films exhibited excellent transparency in the visible light region with cutoff wavelength as low as 302 nm and transmittance higher than 88% at the wavelength of 450 nm. The PI films showed low dielectric constants ranging from 2.50–2.68 and low moisture absorptions of less than 0.56%. The good combined properties of the PIs mainly resulted from the synergic effects of the different substituents. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009