Neat systems

Chemorheological models for neat (unfilled) curing systems can be grouped into the following categories  

Malkin and Kulichikin (1991) initially reviewed the rheokinetics of cured polymers and highlighted the first empirical chemorheological models. They showed that for a simple homogeneous reaction with no diffusion limitations or gel effects for reacting epoxy-resin systems the chemoviscosity could be described by 

For reacting polyurethane systems with gel effects Malkin and Kulichikin (1991) also showed that the chemoviscosity could be described by 

---

TPD and EELS experiments have shown coadsorbed NO/NH3 to form a surface stabilized complex on Pt(lll). This assertion was based in part on the very large vibrational shifts observed for the neat (NO or NH3) systems compared to the mixed system, and in part on the simultaneous desorption of NO and NH3 from the mixed system at values of Tg higher than typical of desorption from the neat systems at comparable initial coverage Kinetit y, desorption from this system has been characterized as reaction limited,... 

Figure 13.8 Fracture energy of epoxy networks cured with DDS (diamino dipheny sulfone) versus the initial DGEBA (diglycidyl ether of bisphenol A) ( ) neat systems ( ) with 10% CTBN (27% AN). Rubber = CTBN carboxy-terminated butadiene acrylonitrile random copolymer. (Pearson and Yee, 1989 with kind permission from Kluwer Academic Publisher.)... 

Figure 13.10 Toughness (K C) and toughening mechanisms of epoxy networks modified with 10 phr CSR versus molar mass between crosslinks, Me (O) neat systems ( ) with 10 phr CSR. (Adapted from Lu, 1995.)...

Figure 55. 2H NMR spectra for type B glasses at 777), ss 0.85. Results for the neat systems lolucncw/,. polybinadiene-7,. and decaline-7,s are shown together with those for the binary mixtures 45% chlorobenzene-<7 in decaline and 55% decalincw/, s in chlorobenzene. Solid-echo delays...

Nitrosyl Halide Systems. Although some difficulty has been encountered in maintaining the purity of F—N=0 and Cl—N=0 in our apparatus prior to irradiation studies, we have obtained interesting data both with neat systems and the mixed systems as well. Again, with three or four different atoms in the molecules under study, we find many ambiguities in assigning mass spectrometric m/q values to specific ions thus we can say little concerning the identity of products from these irradiations. 

Fig. 13. TXT cure diagram temperature of cure vs. the times to phase separation (doud point), gelation and vitrification for a neat and two rubber-modified systems. of the neat system is also included. The systems studied were DER331/TMAB O, gelation , vitrificaticm modified with IS parts rubber per hundred parts epoxy 1) pr eacted carboxyl-terminated butadiene-acrylonitrile (CTBN) copolymer containing 17% acrylonitrile (K-293, Spencer Kellog Co.) A, phase separation , gelation , vitrification, and 2) polytetramethylene oxide terminated with anmiatic amine (ODA2000, Polaroid Corp.) A. phase separation O, gelation O, vitrification. (DER331/TMAB/ K-293 data from Ref. )...

Isothermal TBA scans of rubber-modified systems show no evidence of phase separation, and they only differ from the neat systems in terms of the transition times. In the subsequent temperature scans, however, the presence of the rubber-rich... 

The rate of autoxidation increases with the degree of unsaturation. In neat systems without adding initiators, linoleate having two double bonds was 40 times more reactive than oleate, which has only one double bond, hnolenate having three double bonds was 2.4 times more reactive than linoleate, and arachidonate having four double bonds was 2 times more reactive than linolenate (2, 3). 

Figure 5 shows this plot for 3 different binary mixtures, as well as for a neat system (the epoxy resin PPGE). A good superposition for the a-relaxation frequency is obtained, as it is expected, since the steepness index of Za(T) m (fragility according to Angell definition ) is almost constant under pressure... 

Poncet et al. (1999) monitored frequency-dependent dielectric measurements to examine the phase-separation process in poly(2,6-dimethyl-1,4-phenylene ether) (PPE) in a DGEBA-MCDEA resin. Dielectric measurements measured the build up in Tg both in the PPE-rich continuous phase and in the epoxy-rich occluded phases for 30-60-wt.% PPE mixtures. In the 30% PPE mixmre, the rate of reaction of the thermoset phase is equivalent to that of the neat system due to two opposing effects, namely a slower reaction rate due to dilution and a low level of conversion at vitrification due to the presence of high-Tg PPE. In the 60-wt.% mixture the dilution effect of the PPE has a large effect of decreasing the reaction rate. The continuous thermoplastic-rich phase vitrifies first, followed by the thermoset occluded phase. The final morphology (size of occluded particles and composition of continuous phase) is affected by kinetics, diffusion and viscosity during phase separation. 

Finally, we noticed that in the last stages of the reaction, in contrast to the neat systems for which vitrification limited the conversion to about 0.9 at Tx = 180 °C, the conversion of all the rubber-modified systems easily reached 0.95 or more, a result indicating that the vitrification effect was delayed and suggesting that part of the rubber dissolved in the matrix and decreased its Tg(t). The same conclusion could be drawn from the glass-transition temperatures of the final networks (Tg00), which are displayed in Table III. Such an effect was not observed for the Unilink 4200-DPEDC mixture (without rubber). 

If the ZPL is weak, then variable temperature studies can identify its location from hot electronic and vibronic structure, with the latter illustrated in Fig. 10. The vibronic structure can be used to identify certain symmetry types of transition, for example Ti-T2 (Table 4). One viewpoint has been put forward that the spectral interpretation is confused by phonon dispersion in the vibronic sidebands of transitions. However, this complexity of the vibronic structure can in fact be utilized to provide a fingerprint to identify the location of the electronic origin. Where possible, it is more certain to compare both emission and absorption (or excitation) spectra for a particular transition in order to locate the electronic origin. Otherwise, transitions from different emissive states (with different state irreps) can be employed to confirm the symmetries and locations of terminal levels. Whereas other neat systems such as PrCl3 show additional features not present in the electronic spectra of the diluted crystal (LaCl3 Pr3+) due to interactions between... 

The most studied system is the (Me2SiO) family because of its commercial importance. Although the neat system is ca. 83 % polymeric, dilution of the system to ca. 20% Me2SiO with solvents (e.g., THF, toluene) precludes linears at equilibrium. The equilibrium cyclics are predominantly tetramer and pentamer, with decreasing amounts of the larger oligomeric cyclics. The abundances parallel their probabilities, determined by the same factors that are operative in other cyclic distributions. The distribution of tetramers, pentamers, hexamers, etc., may vary with the substituents (i.e., polarity, bulk), but this has not been studied definitively. 

VanderHart and co-workers [37] used solid-state NMR ( H C) spectroscopy for the first time as a tool to study the morphology, surface chemistry and to a very limited extent the dynamics of exfoliated PCN. This method uses the reduction in the spin-spin relaxation time,, of a nanocomposite when compared with the neat system, as an indicator for the organoclay layer separation. It was shown that the paramagnetic Fe " ions in the crystal lattice of the montmorillonite provide an additional relaxation mechanism of the protons. The additional relaxation depends on average Fe - H distance, which is determined by clay concentration and dispersion of clay in the matrix. 

The relative rates of autoxidation of different unsaturated fatty acids and esters were compared on the basis of oxygen absorption measurements (Table 1.1). In neat systems without added initiator, linoleate was 40 times more reactive than oleate, linolenate was 2.4 times more reactive than linoleate, and arachidonate was 2 times more reactive than linolenate. The oxidizability of polyunsaturated fatty acid (PUFA) esters was also compared on the basis of oxygen uptake measured kinetically by the induction period method described above, in solution in the presence of azo initiators. The oxidizability of 18 2,18 3,20 4, and 22 6 was linearly related to the number of bis-aUyUc positions present in the fatty esters. From this relationship, the oxidizability of each PUFA was increased approximately two fold for each active bis-allylic methylene group. Thus, the oxidizability of 22 6 was 5 times greater than that of 18 2. 

According to the definition, electrostatic interactions must play an important role. From the Debye-Hiickel theory, it can be concluded that in dilute systems these interactions should be long ranged, whereas in concentrated or neat systems, they are screened and therefore short ranged. However, it should be stressed that very often other interactions (e.g., due to the ions polarizability and geometry) are of the same order of magnitude and must not be neglected. 

An important characteristic feature of metal cluster chemistry is the promotion of bond-dissociation and bond-formation reactions that involve attached organic moieties. The Os-W mixed-metal clusters happen to be a neat system to illustrate this characeteristic. A review article on this area has also been written. A large number of Os-W cluster complexes are known, and their chemistry has essentially been uncovered by several research groups, including Shapley, Ghi, and Park. 

We present quantitative comparisons of the dynamic controllability of these two flowsheets in this chapter. Two different control structures are considered for the one-column neat system and one for the two-column excess reactant system. 

DCPD offers superior impact resistance while maintaining physical properties that compare too many HSU, cold molded and engineering thermoplastic systems. Applications within the truck industry employ the neat system, which allows for a homogeneous material that flows well and needs very tittle preparation prior to painting and installation. Surface quality is quite good, as ttie lack of filler and glass give a fiat surface. 

---