Adhesion behaviour of polyamic acid cured epoxy

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.

Ultra-low pressure PES ultrafiltration membrane with high-flux and enhanced anti-oil-fouling properties prepared via in-situ polycondensation of polyamic acid

Polyamic acid (PAA) is a flexible polymer and has abundant valuable hydrophilic groups. Herein, we developed an ultra-low pressure ultrafiltration (UF) membrane by integrating PAA into the polyethersulfone (PES) matrix via the "in-situ polycondensation" method. PAA was well compatible with PES and distributed uniformly in the membrane. The introduction of PAA improved membrane hydrophilicity. Meanwhile, the membrane pore structures were also refined. The membrane exhibited an excellent permeability under ultra-low pressure due to its improvement of hydrophilicity and pore structures. Under 0.3 bar, compare with the water flux of PES membrane, PES/PAA membrane improved nearly 2 times (571.05 L/(m²·h)), with a high BSA rejection (≥90%). Even under a lower pressure, 0.1 bar, >300 L/(m²·h) still can be achieved. Interestingly, the membrane we developed could maintain a high performance after drying, and then is very suitable for dry preservation. PES/PAA membrane showed a high oil removal (≥92%) and could remove oil from water effectively. Besides, the membrane exhibited excellent anti-oil-fouling properties. The flux recovery rate of PES/PAA (70.0%) far exceeds that of PES (37.9%) after three filtration and cleaning cycles. The membrane we developed is very valuable in oily wastewater treatment.

Spatial Distribution of the Network Structure in Epoxy Resin via the MAXS-CT Method

We have succeeded in visualizing the spatial heterogeneity of the reaction ratio in epoxy resins by combining medium-angle X-ray scattering (MAXS) and computed tomography (CT). The reaction ratio is proportional to the degree of cross-linking between epoxy and amine in epoxy resins. The reaction ratio and its spatial inhomogeneity affect the toughness of epoxy resins. However, there has been no non-destructive method to measure the spatial inhomogeneity of the reaction ratio, although we can measure only the spatially averaged reaction ratio by Fourier-transform infrared spectroscopy (FT-IR). We found that the scattering peak reflected the cross-linking structures in the q region of MAXS and that the peak intensity is proportional to the reaction ratio. By reconstructing CT images from this peak intensity, we visualized the spatial heterogeneity of the reaction ratio. The application of this method may not be limited to epoxy resins but may extend to studying the heterogeneity of cross-linked structures in other materials.

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.