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Polyimides in High-Performance Electronics Packaging and Optoelectronic Applications
Published in Malay K. Ghosh, K. L. Mittal, Polyimides Fundamentals and Applications, 2018
Another BTDA-based group of polyimide is the Thermid IP series (6001, 6010, 6015, and 6030; National Starch; Fig. 19) [189, 190]. These acetylene-terminated, thermosetting polyimides are applied from polyisoimide solutions. Isoimides do not evolve water during the conversion to polyimides and exhibit higher solubility compared to the respective imides in solvents typically used for spin coating. Since the precursors are of low molecular weight, good planarization can be achieved. However, isoimide solutions are sensitive to moisture, which reacts with the isoimides to form amic acids. Even relatively small amounts of water change the processing characteristics of the isoimide solution, although the ultimate product after cure of amic acid and isoimide is the corresponding polyimide. Thermid’s excellent adhesion to substrates, to itself, and to other polyimides has been utilized in a number of applications, among them one of IBM’s recent MCMs [173]. Many other BTDA-based polyimides exist such as the Probimide 300 series (OCG), and Durimide 100 and 120 (Rogers). Of particular interest are the intrinsically photosensitive polyimides [191–193] that utilize the inherent photosensitivity of the benzophenone structure in BTDA (Fig. 20). An important ingredient in these polyimides is the presence of an α C–H bond (allylic C–H) from which a hydrogen radical can be abstracted by the photogenerated C–O biradical. This process, which can also be activated at high temperatures, leads to cross-linking [190]. Polyimides of this kind are available under the tradename Probimide 400 Series and are being evaluated for a number of MCM packaging applications. The same cross-linking mechanism is also employed in Amoco’s Ultradel 9000 [193].
17O
Published in Guillaume Madelin, X-Nuclei Magnetic Resonance Imaging, 2022
Blanc et al. [74] also showed that natural abundance 17O NMR of solids could be obtained in minutes with DNP. In this study, electron spin polarization could be transferred either directly to 17O spins or indirectly via 1H spins in inorganic oxides and hydroxides using an oxygen-free solution containing a biradical polarization agent (bTbK). These results open up a method for rapidly acquiring high SNR 17O solid-state NMR spectra to probe sites on or near the surface of the samples, without the need for isotope labeling.
Recent Advances and Future Perspectives in Heterophase Polymerization
Published in Hugo Hernandez, Klaus Tauer, Heterophase Polymerization, 2021
On the other side of the spectrum, it is also possible to release the control on the radical polymerization process leading to ultrahigh-molecular-weight (UHMW) polymers. Laurino et al. [83] found a particular type of photoinitiator (Fig. 4.8) capable of producing biradical polymer chains, resulting in a snowballing radical generation, leading to the formation of polymer chains with UHMW, beyond 107 Da.
4,5,9,10-Tetrahydrocycloocta[1,2-c; 5,8-c′]dithiophene from bis(2-chloropropen-3-yl)sulfide: spectral and theoretical monitoring of the formation
Published in Journal of Sulfur Chemistry, 2021
Vladimir I. Smirnov, Lidiya M. Sinegovskaya, Vladimir A. Shagun, Valentina S. Nikonova, Nikolai A. Korchevin, Igor B. Rozentsveig
The interaction of biradicals (A–A) can proceed via two routes that differ in binding sites to afford adducts B and/or B′ (Scheme 2). The activation barrier of adduct B formation (TS1, Figure 3(b)) does not exceed 4.8 kcal/mol, and enthalpy of the exothermic reaction is 29.5 kcal/mol (Figure 3(b)). The subsequent transformation of biradical B into a cyclic dimer depends on the topology of the interacting radical sites and can lead to either a symmetric structure 1 stabilized in a chair form or an asymmetric structure 1′ (Figure 2). According to thermodynamic and kinetic parameters, the first route is more preferable. The barrier of rearrangement B → 1 is 6.2 kcal/mol, which is by 2.1 kcal/mol lower than that of the alternative route B → 1′. The enthalpy value for the first route is 71.2 kcal/mol that is by 2.5 kcal/mol higher than that for the rearrangement B → 1′ (Figure 3).
The gas-phase pyrolysis of cyclopropylamine. Quantum chemical characterisation of the intermediates involved
Published in Molecular Physics, 2021
Yeljair Monascal, María Paula Badenes
Our attempts to study in detail the conformational preferences of singlet biradical ĊH2CH2ĊHNH2 with the uB3LYP and others spin-unrestricted functionals were unsuccessful. Consequently, the corresponding structures were optimised with the complete active space self-consistent field (CASSCF) method [39], which is more suitable for the treatment of open-shell biradical species [40]. Then, the dynamic correlation effects in the total energies were included with a CAS second-order perturbation theory (CAS-MP2) single-point [41]. The initial active space for the wave functions in our calculations was selected taking into account the electronic occupation of the natural orbitals. As depicted in Figure 4, this consists of two electrons into two molecular orbitals.
On approximate projection models
Published in Molecular Physics, 2019
Lee M. Thompson, Hrant P. Hratchian
To resolve errors associated with spin contamination, multi-reference wave functions are formally required. However, due to the exponential scaling [18] and complexity of such approaches, a number of alternative methodological approaches have been developed. One popular model used in the study of biradical systems and transition metal clusters is the Approximate Projection (AP) family of approaches developed independently by Noodleman [19–22] and Yamaguchi [23–28]. AP has been widely used to compute exchange coupling between spin sites in bimetallic and biradical systems [29–32], determine accurate singlet–triplet energy gaps [33–35], and also compute improved structures and vibrational modes [17, 36–38]. These studies have found AP is able to model complex systems with a level of success that exceeds what one might expect given its relative simplicity and affordable cost in many cases. Despite the success of AP described above, the model is observed to perform poorly in a number of other cases. In general, the AP method will fail where there is core polarisation and the system is no longer well described by a two electron in two orbital picture [39]. The purpose of this investigation is to further develop an understanding of the circumstances and underlying reasons when and why the AP model is successful. Furthermore, this work seeks to identify where a more rigorous method is required and to identify ways by which current AP models might be improved.