Polymerization - curves solid State

Kinetic curves relative to polymerization reactions in the solid state commonly show a sigmoidal shape with a slow initiation step followed by a steep increase, even by two orders of magnitude, of the reaction rate. A reaction with this kind of kinetic curve is said to have an autocatalytic behavior. 

Figure 2 GPC curves of polyoxymethylene obtained by various polymerizations (a) bulk polymerization at 70° C initiated by BF3OBu2, Mv — 55,600 (b) suspension polymerization at 70° C initiated by BF3 OBu2, Mw = 64,200 (c) solution polymerization at 32° C initiated by CFjiS03H, Mv = 68,600 (d) y-ray-induced solid-state polymerization at 30° C, Mw = 98,000.

The theory was used to calculate kinetic curves for the polymerization of PTS deducing the ratio cJCp from the known conversion dependence of the lattice parameters. Time conversion curves normalized with respect to the time necessary to reach 50 percent conversion can be calculated for different values of the lattice mismatch using the crystal strain theory. For PTS a satisfactory fit of the experimental data of the thermal and y-ray polymerization can be obtained. However, further studies of the kinetics of the solid-state polymerization of PTS and other monomers provided results which cannot be explained by the theory. 

Figure 9. Differential scanning calorimetry thermograms of polytetraoxanes obtained by y-ray-initiated polymerizations in the solid state. Dotted curves indicate the decomposed endothermic profiles caused by the extended chain crystals and folded chain crystals.

The behavior of PPy I [49] is very similar to that of the short-length oligomers with predominantly localized electronic carriers [25], whereas its continuous cycling results in a further solid-state polymerization of PPy I with the final structure (PPy II), which is less prone to electronic charge localization [47,49]. This example shows that the intercalation-induced phase transition in V2O5 dominates in determining the shape of the differential capacitance curve. 

Solid-state polymerization of diazo compounds 18 and 20 was monitored by IR absorptions at 66 and 35 C, respectively. While an absorption at 3295 cm disappeared smoothly, more than 87<7o of an absorption at 2035 cm remained intact. Here again, the magnetization curves obtained did not obey the Brillouin function with any single S value but with a combination of S values in the range 2-2.5. The alignment of the spins is limited to a short range. 

The time-dependent conversion curves for solid state polymerization display a sigmoidal shape with a steep increase in the polymerization rate with an onset at ca 10% conversion to polymer. The observed autocatalytic effect can be explained with a mechanical... 

Figure 9.34 Thermal solid state polymerization of TS/FBS (PTS is another acronym for TS). (a) Time-conversion curve derived by gravimetrical analysis, (b) Time-permittivity curve derived at 1 kHz for a thin parallel-plate single-crystal capacitor oriented with the polymer chain direction (b-axis) parallel to the electric field, (c) Correlation of conversion and electric permittivity (with time as implicit parameter) obtained by combination of (a) and (b) [73].

While the term strain hardening is widely used to describe the extensional flow behavior of some polymeric liquids, it lacks any basis in polymer physics. It was introduced by G. I. Taylor in 1934 [ 155] to describe the plastic flow of crystalline metals. It has also been used to describe the behavior of glassy and semicrystalline polymers, where it is said to arise from the effect of strain on solid-state structural features. Its use for melts is based solely on the shape of the curve of 7] (t,e) versus time with strain rate as a parameter. At small values of strain (e =t e) the behavior follows the prediction of linear viscoelasticity, as indicated by Eq. 10.93. Dealy... 

Figure 4 shows a comparison of the time dependence curve of the inherent viscosity of the polyimide formed by the microwave-assisted polycondensation of 12PMA with that by a conventional solid-state polycondensation at 250°C. It is obvious that the microwave-assisted polyo)ndensation for curve A proceeded much faster than the solid-state polycondensation for curve B. Thus it is concluded that the internal heating by the microwave irradiation was highly effective compared with a conventional external heating, yielding the polyimide with a high inherent visocisty in a very short polymerization time. 

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