Yield of high polymer

If more isobutene was added rapidly after the slow addition was complete, there was no polymerisation. If isobutene was added rapidly at first, a 100% yield of high polymer was obtained. 

The yields of high polymer from this synthesis depend on the exact conditions and the nature of the substituent groups, but are typically low, from a few percent up to 60-70% in the most favorable cases. The by-products are mainly cyclosilanes, (RR Si) where n = 4 6. The molecular weight distributions of the polymers obtained by this procedure are usually bimodal, as shown in Figure 5 Various attempts have been made to improve the sodium condensation, including sonication and the addition of crown ethers and other additives, with some success. ... 

The opening of the caprolactam ring for nylon 6 involves an equilibrium reaction which is easily catalysed by water. In the case of nylon 12 from dodecanelactam, higher temperatures, i.e. above 260°C, are necessary for opening the ring structures but since in this case the condensation is not an equilibrium reaction the process will yield almost 100% of high polymer. ... 

Considerable low molecular weight, oligomeric material is usually produced along with high polymer, so that the yield of true polymer is often less than 50%. In a typical workup, a small amount... 

This may suggest that either propagation is very slow due to the low reactivity of the derived species or that the equilibrium constant K=kp/kcyclic tetramer is more stable than the polymer chain. This is apparently in agreement with the high yield (up to 40%) of cyclic tetramer the yield of the polymer in the classical... 

Lipase-catalyzed polymerization of divinyl adipate or divinyl sebacate with a, co-glycols with different chain length has been reported [40]. Lipases CA, MM, PC, and PF showed high catalytic activity toward the polymerization. A combination of divinyl adipate, 1,4-butanediol, and lipase PC afforded the polymer with number-average molecular weight (Mn) of 2.1 x 104. The yield of the polymer from divinyl sebacate was higher than that from divinyl adipate, whereas the opposite tendency was observed in the polymer molecular weight. 

High Pressure. Irradiation under high pressure increases the crosslinking yield of some polymers (64-66). This has mechanistic implications which need to be further explored. 

Studies by Heinze etal. on donor-substituted thiophenes or pyrroles [33] such as methylthio (= methylsulfonyl) or methoxy-substituted derivatives provide further clear evidence for this reaction pathway. They found, for instance, that 3-methylthiothiophene or 3-methoxythio-phene (2) undergo a fast coupling reaction. However, deposition processes or insoluble film formation could not be detected in usual experiments with these compounds, even at high concentrations. Similarly, the corresponding 3,3 -disubstituted bithiophenes (2a) do not polymerize, but the anodic oxidation of 4,4 -disubstituted bithiophenes (2c) produces excellent yields of conducting polymers. 

All of the ruthenium polymers show emission when excited at (absorption). A large Stokes shift and a small quantiun yield characterize the emission behavior the luminescence quantum yield of the polymers is 1%. Thermo-gravimetric analyses in air indicate high thermal stabihty of the polymers, with thermal decomposition starting at approximately 290 °C. The polymers have no glass transition temperature. 

This suggestion was supported by experiments. First, the polymerization catalyzed by the hexamethylphosphoramide complex, which has a monomeric structure, gave a high yield of isotactic polymer even... 

In the field of high polymers the relationships between optical activity and conformations have been mostly investigated in the case of natural and synthetic polyaminoacids. Thus very interesting results have been obtained, as the optical activity can be determined very easily and yields interesting informations even when operating on not fractionated polymers 125). 

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