Synthesis and characterization of epoxy film cured with reactive polyimide

Thermal and Mechanical Characterization of Epoxy/Polyimide Blends via Postcuring Process

In this study, the effects of polyimide (PI) content and postcuring on thermal and mechanical properties in PI and epoxy (EP) blending systems were investigated. EP/PI (EPI) blending reduced the crosslinking density and improved the flexural and impact strength due to ductility. On the other hand, in the postcuring of EPI, the thermal resistance improved due to the increased crosslinking density and the flexural strength increased by up to 57.89% due to the enhanced stiffness, but the impact strength decreased by up to 59.54%. EPI blending induced the improvement in the mechanical properties of EP, and the postcuring process of EPI was shown to be an effective method to improve heat resistance. It was confirmed that EPI blending induces improvement in the mechanical properties of EP, and the postcuring process of EPI is an effective method for improving heat resistance.

Interpenetration Networked Polyimide-Epoxy Copolymer under Kinetic and Thermodynamic Control for Anticorrosion Coating

Epoxy (EP) was copolymerized with polyamic acid (PAA, precursor of polyimide (PI)) with termanil monomers of (1) 4,4'-Oxydianiline (ODA) and (2) pyromellitic dianhydride (PMDA) individually to form (PI-O-EP) and (PI-P-EP) copolymers. The FTIR spectrum of PI-O-EP copolymerization intermediates shows that some amide-EP linkages were formed at low temperature and were broken at higher temperature; in additoin, the released amide was available for subsequent imidization to form PI. The curing and imidization of the amide groups on PAA were determined by reaction temperature (kinetic vs. thermodynamic control). In PI-P-EP, the released amide group was very short-lived (fast imidization) and was not observed on FTIR spectra. Formation and breakage of the amide-EP linkages is the key step for EP homopolymerization and formation of the interpenetration network. PI contributed in improving thermal durability and mechanical strength without compromising EP's adhesion strength. Microphase separations were minimal at PI content less than 10 wt%. The copolymerization reaction in this study followed the "kinetic vs. thermodynamic control" principle. The copolymer has high potential for application in the field of higher-temperature anticorrosion.

Polymerization of Meldrum's Acid and Diisocyanate: An Effective Approach for Preparation of Reactive Polyamides and Polyurethanes

Meldrum's acid (MA) is utilized as a monomer to polymerize with diisocyanates to result in polyamides, containing MA moieties at polymer chains. This reaction is also employed to prepare isocyanate-terminated polyamide segments which are utilized as a precursor for preparation of MA-containing polyurethanes. Based on the thermolysis reaction of MA groups, followed by ketene dimerization reaction, the reactive polyamides and polyurethanes show self-cross-linkable features. The cross-linked polyurethanes exhibit good film formability, thermal stability, and mechanical properties. A new MA-based polymerization method and a novel synthesis route for preparation of reactive polyamides and polyurethanes are demonstrated.

High-Tg, Low-Dielectric Epoxy Thermosets Derived from Methacrylate-Containing Polyimides

Three methacrylate-containing polyimides (Px⁻MMA; x = 1⁻3) were prepared from the esterification of hydroxyl-containing polyimides (Px⁻OH; x = 1⁻3) with methacrylic anhydride. Px⁻MMA exhibits active ester linkages (Ph⁻O⁻C(=O)⁻) that can react with epoxy in the presence of 4-dimethylaminopyridine (DMAP), so Px⁻MMA acted as a curing agent for a dicyclopentadiene-phenol epoxy (HP7200) to prepare epoxy thermosets (Px⁻MMA/HP7200; x = 1⁻3) thermosets. For property comparisons, P1⁻OH/HP7200 thermosets were also prepared. The reaction between active ester and epoxy results in an ester linkage, which is less polar than secondary alcohol resulting from the reaction between phenolic OH and epoxy, so P1⁻MMA/HP7200 are more hydrophobic and exhibit better dielectric properties than P1⁻OH/HP7200. The double bond of methacrylate can cure at higher temperatures, leading to epoxy thermosets with a high-Tg and moderate-to-low dielectric properties.

Synthesis and Properties of Hydroxy-ContainingOrtho-Linked Poly(Ether-Imide)s

A series of hydroxy-containing poly(ether-imide)s having ortho-linked, main chain aromatic units were prepared via the solution polycondensation of bis(ether anhydride)s such as 1,2-bis(3,4-dicarboxyphenoxy)benzene dianhydride and 1,2-bis(3,4-dicarboxyphenoxy)-4- tert-butylbenzene dianhydride with bis( o-aminophenol)s such as 3,3′-dihydroxybenzidine, 3,3′-diamino-4,4′-dihydroxybiphenyl and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane. All the poly(ether-imide)s were amorphous, as evidenced by x-ray diffraction analysis, soluble in various polar solvents such as N,N-dimethylacetamide, and most of them afforded transparent and flexible films by solution casting. These hydroxy-containing poly(ether-imide)s had glass transition temperatures in the range from 241 to 277 °C and underwent thermal conversion to poly(ether-benzoxazole)s upon heating between 420 and 550°C under nitrogen. The thermally converted benzoxazole polymers did not show significant weight loss up to 500 °C in nitrogen.

Comparison of hybrid polyimide films with silica and organosilica obtained via sol–gel process

A series of polyimide/silica (PI–S) and polyimide/organosilica (PI–OS) hybrid films were prepared via a sol–gel process from mixtures of poly(amic acid) (PAA) and tetraethoxysilane or a silane coupling agent in solution. The PAA was synthesized from bis-(3-phthalyl anhydride) ether and 1,4-bis (4-aminophenoxy) benzene. The hybrid films were produced via an imidization reaction to form silica particles or a silica network in a polymer matrix through a programmed heating process. The derived films were characterized and compared by Fourier transform infrared spectroscopy, field emission scanning electron microscopy, thermogravimetric analysis, tensile testing, contact angle measurements, moisture absorption measurements, and dielectric property analysis. Both the PI–S and PI–OS hybrid matrixes showed strong regularity with the increasing silica content and greatly improved thermal stability and mechanical properties. Among them, the PI–OS hybrid films possessed superior interphase interactions and were found to have better physicochemical properties.

Synthesis, Characterization and Clay-Reinforcement of Epoxy Cured with Benzoxazine

Epoxy resin (EP) was cured with in situ polymerized monofunctional benzoxazine monomer, Pa, in the absence and presence of organically modified montmorillonite (OMMT). DSC showed that the onset and maximum of the exotherm due to copolymerization of EP and Pa, at 223 'C and at 262 'C, respectively, without OMMT, decreased as large as 60 'C in the presence of OMMT The XRD patterns and transparency of the films suggested nanoscale dispersion of the clay layers into the EP/Pa copolymer. Dynamic mechanical analyses indicated that the Tgs of the hybrid materials were higher than that of the pristine resin and the Tg shifted to higher temperature when the OMMT surfaces contain reactive functionalities. Isothermal and dynamic TGA showed that the dispersion of the clay nanolayers into the EP/Pa network gave better thermal properties.

Synthesis and characterization of high refractive epoxy prepolymers with different molecular structures

Three kinds of epoxy prepolymers with high refractive index, diglycidyl ether of thiodibenzenethiol (DGETDBT), diglycidyl ether of thiobis-phenol (DGETP), and diglycidyl ether of oxydiphenol, were synthesized via a two-step method, and the relationship between the chemical structure and refractive index of epoxy prepolymer was discussed. Their chemical structures were characterized using Fourier transform infrared (FTIR) spectrometer and proton nuclear magnetic resonance spectrometer. The curing behavior of all the epoxy prepolymers cured with methylhexahydrophthalic anhydride (MHHPA) was studied using differential scanning calorimetry and was compared with that of diglycidyl ether of bisphenol A (DGEBA). Thermal and optical properties of these cured epoxy resins were investigated using thermogravimetric analyses, ultaviolet–visible scanning spectrophotometer, and Abbe refractometer, respectively. The results showed that three kinds of epoxy prepolymers had the similar thermal property and curing behavior. The sulfur atoms in DGETDBT and DGETP had contributed to an obvious increase in their refractive indexes, while the methyl group in DGEBA cut down its refractive index. The DGETDBT has the biggest refractive index (1.665), followed by the DGETP with 1.612. But the high cost and the lower thermal decomposition temperature of cured DGETDBT/MHHPA resin will limit its application. The refractive index of cured DGETP/MHHPA resin, with preferable thermal stability and acceptable price, is 1.595, which is higher than that of DGEBA/MHHPA resin (1.568). Therefore, DGETP resin can be expected to be a kind of the more effective encapsulant to light-emitting diode.