DGEBA-piperidine

Pearson and Lee (1991) examined the effects of particle-size and particle-distribution effects on rubber-toughened epoxy resins. They examined a variety of CTBN liquid rubbers and a methacrylated butadiene styrene core-shell particle in a DGEBA-piperidine system. They found that the toughening mechanism for small particles was internal cavitation of the... 

DGEBA-Piperidine. The DGEBA-piperidine system has an Mc value of about 560 g/mol. Therefore, this system is likely to form dilatation bands. Indeed, when the DN-4PB and PEELS experiments were conducted, the dilatation bands were found around the crack tip (Figure 8, bottom). The density inside the dilatation bands was about 1.08 g/cm3, which is about 7% lower than that of the surrounding matrix. This dilatation band feature resembles those of the BCB-MI-M and CET resins. 

The DGEBA-piperidine investigated here is a commonly studied epoxy... 

Figure 8. TEM images of the crack tip (arrow) of the DN-APB damage zone of BCB—MI—M (top), CET (middle), and DGEBA—piperidine (bottom). The crack propagates from right to left in all three images.

Figure 11 Mechanical properties of a thermoplastic-modified epoxy (DGEBA/ piperidine). Note that the toughness increases with thermoplastic content while the yield strength remains unchanged.

EFFECT OF RUBBER CONTENT AND CURE CYCLE ON Kjc OF DGEBA/PIPERIDINE... 

We then compare the measured linewidth to that implied by the "lifetime broadening" of at an rf field of 66 kHz and static field of 15 MHz for the piperidine cured DGEBA epoxy at 33°C. 

Resing and Moniz 60) cured DGEBA with three different curing agents, piperidine, hexahydrophthalic anhydride (HHPA) and nadic methyl anhydride (NMA). Spectra were collected with C-13 NMR using cross polarization and high power decoupling. 

Fig. 12. C- 13 spectrum of the piperidine (PIP) cured DGEBA epoxy polymer at room temperature. The assignments have been discussed and the structure indicates a possible polymerization mechanism 2 ...

The DGEBA based epoxies were reacted with various curing agents. These spectra were than compared to the solution spectra of unreacted epoxy. It was shown that the peaks due to the epoxide carbons were not present in the polymerized DGEBA. In their previous study, Sojka and Moniz 481 showed that DGEBA partially cured with piperidine, exhibited a peak near the methylene peak that increased in intensity and complexity with the curing reaction. This peak was assigned to the carboxyl-methine ether carbon and the methylene carbon near the reaction site. These studies addressed the questions ... 

Fig. 17. The C-13 spectra over a 200 K temperature range for DGEBA epoxy cured with piperidine. The chemical structure on the left shows one half of the (symmetrical) monomer (top half) and a possible curing structure with piperidine (bottom half). In the spectra the methyl resonance broadens and then disappears at low temperature the remaining peak at about 25 x 10 6 is assigned to the piperidine. The low-temperature splittings of peaks c and d.collapse at higher temperature, indicating reorientation of the phenyl group with respect to the backbone 641...

Garroway, Ritchie, and Moniz 70 continued the characterization of epoxy polymers with respect to molecular motion using variable temperature, solid state C-13 NMR. DGEBA was the epoxy of interest. The DGEBA was cured with piperidine, m-phenylene diamine, hexahydrophthalic anhydride and nadic methyl anhydride. The piperidine cured DGEBA had the best resolved polymer spectra. This system... 

In a fundamental study of the factors affecting the growth of the rubber domains in a CTBN-toughened DGEBA epoxy resin cured by piperidine (Manzione and GilUiam, 1981) the kinetics of phase separation were linked to the diffusivity, Uab, of the rabber (A) dissolved in the epoxy resin (B). The relevant dependence on the molar volume of the rubber (proportional to the radius of the rubber molecules when dissolved in the epoxy resin) at the viscosity for the temperature T of reaction is given by the Stokes-Einstein equation ... 

Materials. The thermosetting resins investigated include (1) 1,2-dihy-drobenzocyclobutene and maleimide (BCB-MI) resin, (2) a modified version of the BCB—MI resin (BCB-MI-M), (3) cross-linkable epoxy thermoplastic (CET, which is chemically similar to TACTIX 695 epoxy resin from Dow Chemical Co.), and (4) DGEBA epoxy (D.E.R. 332, Dow Chemical Co.) cured with piperidine. The chemical structures of the resins are shown in Chart I. 

Acronyms Tg - glass transition temperature. DGEBA = diglycidyl ether of bisphenoSA, MPD = m-phenylene diamine, DCD dicyandiamide, DACH = diaminocycbhexane. DDS = diaminodiphenyl sulfone, PIP = piperidine, IPD = ist orone diamine, AEP = aminoetiiyl piperazine, BA = n-butyl acrylate, B = butadiene, S styrene, MMA methyl methacrylate, AN acrylonitrile, GMA glycidyl methacrylate, DVB divinyl benzene, EA = ethyl acrylate. 

Chen and Jan [133] showed that bimodal distributions could be obtained by using two different rubbers as modifiers of a DGEBA-based epoxy resin cured with piperidine. The rubbers were two acrylonitrile-butadiene copolymers (CTBNs), with different AN content, i.e. 18 and 26%. The miscibility with the epoxy resin (and the corresponding cloud-point conversion) increased with the AN content. Therefore, when 10 wt% of CTBN (26% AN) was used as modifier, a high concentration (Cp == 13.4 pm ) of small particles (D = 0.2 pm) was obtained. When the same amount of CTBN (18% AN) was used as modifier. 

Levita et al. [53] incorporated 10 wt% of a rubber composed of core-shell particles (D = 0.2 pm) and an amine-terminated butadiene acrylonitrile copolymer (ATBN) in different proportions in a DGEBA-based epoxy resin cured with piperidine at 120°C for 12h. The core-shell particles were always immiscible in the epoxy resin while the ATBN phase separated during poly-... 

DGEBA/CTBN resin studies were made with DGEBA cured with 5 parts per hundred piperidine reinforced with 5, 10 and 15 parts per hundred CTBN rubber cured at 120 C for 16 h. It was found from this study that there is epoxy present in the separated rubbery particles, and that rubber is dissolved in the epoxy matrix. 

Figure 6.8 Variable-temperature MAS/CP/DD NMR spectra of an epoxy resin diglycidyl ether of bisphenol A (DGEBA) cured with piperidine. After [48].

Epoxy resins have been studied extensively with high-resolution solid-state C-NMR spectroscopy. The epoxy spectra are shown in Fig. 9.21 of four phases of DGEBA the resin cured with 5% piperidine, an amorphous resin, a polycrystalline resin, and the starting resin in the liquid state [71]. 

Fig. 9.21. spectra of the epoxy resin DGEBA in four different phases (a) polymerized with 5% (by mass) piperidine, 247 K (b) amorphous resin, 230 K (c) polycrystalline resin, 230 K and (d) in CCI4, with the solvent peak deleted. (Reproduced with permission from Ref. [71], 1981 American Chemical Society.)... 

For example, the strain-to-failure of the network formed by curing DGEBA with nadic methyl anhydride (NMA) and the catalyst benzyldimethylamine (BDMA) decreases from 12 % to 6 % after 56 days at 23 °C [5]. Physical aging has also been observed in amine cured epoxy resin systems and in an uncross-linked 28,000 g/mol linear epoxy resin tested under wet conditions [6]. In contrast, DGEBA homo-polymerized with piperidine (subsequently... 

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