Epoxy resin/poly(ϵ‐caprolactone) blends cured with 2,2‐bis[4‐(4‐aminophenoxy)phenyl]propane. II. Studies by Fourier transform infrared and carbon‐13 cross‐polarization/magic‐angle spinning nuclear magnetic resonance spectroscopy

Abstract

Crystalline thermosetting blends composed of 2,2′‐bis[4‐(4‐aminophenoxy)phenyl]propane‐crosslinked epoxy resin (ER) and poly(ϵ‐caprolactone) (PCL) were investigated by means of Fourier transform infrared (FTIR) spectroscopy and high‐resolution solid‐state NMR spectroscopy. FTIR investigations indicated that there were specific intermolecular interactions between ER and PCL and that the intermolecular hydrogen‐bonding interactions were weaker than the self‐association in pure epoxy. The intermolecular hydrogen bonding was considered to be the driving force for the miscibility of the thermosetting blends. For the examination of the miscibility of the thermosetting blends at the molecular level, high‐resolution solid‐state 13C cross‐polarity/magic‐angle spinning (CP‐MAS) NMR spectroscopy was employed. The line width of 13C CP‐MAS spectra decreased with increasing PCL contents, and the chemical shift of the carbonyl carbon resonance of PCL shifted to a low field with an increasing epoxy content in the blends. The proton spin–lattice relaxation experiments in the laboratory frame showed that all the blends possessed identical, composition‐dependent relaxation times (i.e., the proton spin–lattice relaxation times in the laboratory frame), suggesting that the thermosetting blends were homogeneous on the scale of 20–30 nm in terms of the spin‐diffusion mechanism, and this was in a good agreement with the results of differential scanning calorimetry and dynamic mechanical analysis. For the examination of the miscibility of the blends at the molecular level, the behavior of the proton lattice relaxation in the rotating frame was investigated. The homogeneity of the thermosetting blends at the molecular level was quite dependent on the blend composition. The PCL‐lean ER/PCL blends (e.g., 70/30) displayed a single homogeneous amorphous phase, and the molecular chains were intimately mixed on the segmental scale. The PCL‐rich blends displayed biexponential decay in experiments concerning the proton spin–lattice relaxation times in the rotating frame, which was ascribed to amorphous and crystalline phases. In the amorphous region, the molecular chains of epoxy and PCL were intimately mixed at the molecular level. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1099–1111, 2003

A perspective approach on the amine reactivity and the hydrogen bonds effect on epoxy-amine systems

“…86,87 Results showed that PCL is partially miscible in epoxy amine mixture due to the H bond formation between ester oxygen atoms and hydroxyl or amine moieties of epoxy-amine system. However, depending on the mixture nature, phase separation can start at a certain content of PCL, while a fully homogeneous PCL/epoxy blends can be obtained with a reasonable amount of PCL, as showed Zheng et al 88 Some other examples of modifiers exist as poly(vinyl acetate), 89 poly(etherimide), 90 more complex structures, such as poly(phthalazinone ether nitrile ketone), 91 and even poly(styrene), 92 which cannot form H bonds but can interact with π-bonds with aromatic epoxy and amine reactants, allowing initial miscibility.…”

Ionic Liquid-Cured Epoxy/PCL Blends with Improved Toughness and Adhesive Properties

“…Initiation Mechanism Reference [59] Polymers 2022, 14, x FOR PEER REVIEW 2 of 16 have been used as epoxy modifiers and reported in the literature, including polyetherimide (PEI) [25], polymethylmethacrylate [26], polyethylene oxide [27], polycarbonate [28], and poly(ε-caprolactone) (PCL) [17,19,[29][30][31][32][33][34][35][36][37][38].…”

“…The use of different curing agents and PES with different molecular weights resulted in varying morphologies. Many other thermoplastic polymers have been used as epoxy modifiers and reported in the literature, including polyetherimide Polymers 2022, 14, 2679 2 of 14 (PEI) [25], polymethylmethacrylate [26], polyethylene oxide [27], polycarbonate [28], and poly(ε-caprolactone) (PCL) [17,19,[29][30][31][32][33][34][35][36][37][38].…”

“…This difference is due to the fact that amines can interact via hydrogen bonding with the PCL's ester groups [23,30], which favours miscibility. Zheng et al [38] reported miscible epoxy/PCL blends on the nanoscale, with homogeneity at the molecular level depending on the composition. However, depending on the curing conditions, thermoplastic concentration, and molecular weight [36], phase-separated morphologies have also been reported with PCL, such as in 4,4 -diaminodiphenylsulfone (DDS)-cured PCL/epoxy blends.…”

Phase behavior, crystallization, and morphology in thermosetting blends of a biodegradable poly(ethylene glycol)‐type epoxy resin and poly(ϵ‐caprolactone)

“…During the past decade, thermosetting polymer blends have attracted considerable interest. A number of thermosetting blends, in which one component is a crystallizable linear homopolymer and another is highly crosslinked, have been proved to be miscible or partially miscible by Guo and coworkers1–15 and by other researchers 16–22. It has been shown that miscibility, that is, the ability to form a homogeneous single phase in the melt and/or in the amorphous state, can exist between the components for crosslinked blends with hydrogen‐bonding interactions.…”