Depolymerization behavior

For testing depolymerization behavior, about 0.2 to 0.3g of the polymeric substance is carefully and gently heated to a maximum of 500°C in a small distillation flask. The distillate, is collected in a receiver and its boiling point and refractive index are determined. 

Of further interest is the thermal depolymerization behavior of these polymers in the crystalline state. This behavior has been investigated by observing the continuous changes of the X-ray diffraction pattern and of the TG-DSC diagram during the heat treatment of poly-DSP10,65). Changes of X-ray diffraction patterns on thermal treatment of as-polymerized poly-DSP crystals and photopolymerization of DSP crystals are shown in Fig. 16. 

The thermal depolymerization behavior in the crystalline state has been observed of most of polymers prepared by four-center photopolymerization, e.g. poly-p-PDA Me31. The X-ray diffraction patterns (d) and (e) in Fig. 16 will be discussed in Sect. Vl.a. 

Though the theoretical calculation on the basis of model 11, it was found that the boron species are mainly existed 6303(011)4- and B(OH)4- while the concentration of 6405(011)42- is very low when the total concentration of boron is low in weak solution. This result demonstrated that the polymerization or depolymerization behaviors of borate are complex. 

Stable as a pure crystaUine solid, but polymerized spontaneously when the mixture of the dehydration reaction of 1-PI-l was concentrated without the elimination of PTSA. In order to understand this apparently peculiar behavior, the ethyl ester of acid 1-PI-l was synthesized and showed the same spontaneous polymerization behavior as BFl. The stabihty of pure BF-ATl was assumed to be related to the probable intermolecular interaction of its COOH with the imidazole nitrogen in the solid state otherwise prevented by the presence of PTSA, which was assumed to protonate the heterocychc nitrogen atoms. Poly-BF-ATl showed a thermoinduced depolymerization behavior similar to that shown by poly-BFl. The depolymerization process at 55 °C was very slow and became significantly more rapid at 80 °C at 140 °C it was even faster since it was almost complete after 1 h heating. At 120 °C the unzipping process showed an intermediate velocity and reached an apparent equihbrium after 4 h heating (Fig. 6). Thus, poly-BF-ATl displayed a thermoreversible polymerization behavior similar to that shown by poly-BFl, but characterized by a faster kinetics. 

Moreover, poly-2-MOEG-3-BFl and poly-2-MOEG-9-BFl showed characteristic NMR features, absorption/emission spectra, and thermoinduced depolymerization behavior very similar to those shown by poly-BFl obtained by spontaneous polymerization. 

Subsequent studies performed with poly-BFl obtained by anionic polymerization with PhLi as the initiator (poly-BFl-AP) (tenonstrated that the polymerization method could affect the depolymerization behavior of the resulting polymer [23]. 

The application of our methodology to poly-BFl-AP revealed a thermoinduced depolymerization behavior similar to that shown by poly-BFl obtained by spontaneous polymerization, with the difference that the reaction appeared to reach an apparent equilibrium after 24 h heating (Fig. 20), whereas an almost complete depolymerization was observed for poly-BFl-SP after 3-6 h heating in nitrobenzene at 150 °C. 

The subsequent structure manipulation of benzofulvene structure in BFl and BF3k gave further information about the role of substituents in affecting the ther-moinduced depolymerization behavior. 

These techniques help in providing the following information specific heat, enthalpy changes, heat of transformation, crystallinity, melting behavior, evaporation, sublimation, glass transition, thermal decomposition, depolymerization, thermal stability, content analysis, chemical reactions/polymerization linear expansion, coefficient, and Young s modulus, etc. 

A typical fit of the theoretical depolymerization kinetics to the experimentally determined rate behavior for dilution-induced depolymerization is illustrated in Fig. 2... 

Interestingly, it should not be assumed that a polymer will be useless above its ceiling temperature. A dead polymer that has been removed from the reaction media will be stable and will not depolymerize unless an active end is produced by bond cleavage of an end group or at some point along the polymer chain. When such an active site is produced by thermal, chemical, photolytic, or other means, depolymerization will follow until the monomer concentration becomes equal to [M]c for the particular temperature. The thermal behavior of many polymers, however, is much more complex. Degradative reactions other than depolymerization will often occur at temperatures below the ceiling temperature. 

Laszlo A. Heredy There is NMR spectroscopic evidence for the presence of both a- and /3-CHa groups in coal, based on depolymerization work with phenol-BF.3 reagent. For example, isopropyl groups were shown to be present in a high volatile bituminous coal. Is there a distinct difference in the behavior of these two types of CHs groups with respect to the reagent used in wet analytical methyl group determination ... 

Although reinforcements can improve the structural behavior of the composite at elevated temperature, the polymer, irrespective of its composition, begins to disassociate chemically in the presence of oxygen. Phthalic resins having the weaker ester bonds depolymerize readily at temperatures over... 

In Figure 6 Equation 37 combined with Equation 38 was used to evaluate the copolymerization behavior. It is now assumed that the sequence with two monomer units Mi cannot depolymerize, but that longer sequences are subject to the polymerization-depolymerization equilibrium. 

Conversely, if the polymer could be made by some other route (for example, by macromolecular substitution), it might be stable at moderate temperatures where the rate of depolymerization is very slow, but would depolymerize to the cyclic trimer or tetramer when heated to higher temperatures. In fact, this behavior is found for uncross-linked polymers such as [NP(OPh)2] , that appear to be kinetically stabilized at moderate temperatures, but are sufficiently destabilized thermodynamically by the bulky aryloxy side groups that they depolymerize when heated above 150-200 °C. 

Abstract Tubulin is a fascinating molecule that forms the cytoskeleton of the cells and plays an important role in cell division and trafficking of molecules. It polymerizes and depolymerizes in order to fulfill this biological function. This function can be modulated by small molecules that interfere with the polymerization or the depolymerization. In this article, the structural basis of this behavior is reviewed with special attention to the contribution of NMR spectroscopy. Complex structures of small molecules that bind to tubulin and microtubules will be discussed. Many of them have been determined using NMR spectroscopy, which proves to be an important method in tubulin research. 

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