Activation energy, poly

Polymerization Solvent. Sulfolane can be used alone or in combination with a cosolvent as a polymerization solvent for polyureas, polysulfones, polysUoxanes, polyether polyols, polybenzimidazoles, polyphenylene ethers, poly(l,4-benzamide) (poly(imino-l,4-phenylenecarbonyl)), sUylated poly(amides), poly(arylene ether ketones), polythioamides, and poly(vinylnaphthalene/fumaronitrile) initiated by laser (134—144). Advantages of using sulfolane as a polymerization solvent include increased polymerization rate, ease of polymer purification, better solubilizing characteristics, and improved thermal stabUity. The increased polymerization rate has been attributed not only to an increase in the reaction temperature because of the higher boiling point of sulfolane, but also to a decrease in the activation energy of polymerization as a result of the contribution from the sulfonic group of the solvent. 

Fig. 6. Activation energy for diffusion in poly(vinyl chloride) as a function of penetrant mean diameter (19). To convert to cal, divide by 4.184.

The activation energy of thermolysis of the azo group was measured by DSC [14]. Type II MAIs, which are composed of various prepolymers such as aliphatic polyester, poly(caprolactone), and aliphatic poly (carbonate), showed almost the same activation energy irrespective of difference in prepolymer structure, suggesting that the neighboring group only affects the active site. 

In contrast, aliphatic polyanhydrides such as poly(SA) and poly-(PDP) decreased in molecular weight over time. The decrease in molecular weight shows first-order kinetics, with activation energies... 

Nair et al. studied the kinetics of the polymerization of MMA at 60-95 °C using N,1SP-diethyl-NjW-di(hydroxyethyl)thiuram disulfide (30a) as the thermal in-iferter [142]. The dependence of the iniferter concentration on the polymerization rate was examined. The chain transfer constant of the propagating radical of MMA to 30a was determined to be 0.23-0.46 at 60-95 °C, resulting in the activation energy of 37.6 kj/mol for the chain transfer. Other derivatives 30b-30d were also prepared and used to derive telechelic polymers with the terminal phosphorus, amino, and other functional aromatic groups [143-145]. Thermal polymerization was also investigated with the end-functional poly(St) and poly(MMA) which were prepared using the iniferter 13 [146]. 

Figure 1. Adiabatic potential curves in the main chain scission of a model compound of poly(isobutylene) 2,2-, 4,4-tetramethylpentane (4). AE3l(=0.61eV), aET,(—0.35eV), and AEf (=2.05eV) are the activation energies of the main chain scission in the lowest singlet excited state (S,), the lowest triplet state (T,), and the ground state, respectively.

Occasionally, a negative activation energy is reported. For example, an value of -13.0 kJ mol was obtained for tRNA binding to the E-site of poly(U)pro-grammed ribosomes containing unlabeled tRNA at its P-site. In such circumstances, one must be especially wary, because there are several reasons why an erroneously negative E value is obtained ... 

When cr0 is plotted vs. AE, a linear relationship is obtained (Figure 3). Poly-acenes show a similar linear relationship, which may be parallel to that of the isonitrile complexes investigated and which is displaced toward lower values of o-o- A comparison between the isonitrile complexes and polyacenes demonstrates most clearly the wide ranges of activation energies, AE, and of the constant, o-o, which may be achieved merely in one series of coordination complexes as compared to polyacenes. 

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