Polymerisation quenching

It is possible to use the square gradient free energy expression to calculate what the fastest growing wavelength should be (de Gennes 1980, Binder 1983). For two polymers of equal degree of polymerisation quenched to a temperature not too far away from the spinodal we find... 

Quartarstruktur quartile stat Quartil, Viertelswert quartz glass Quarzglas quartz microbalance (QMB) Quarz-Mikrowaage (QMW) quartz thermometer Quarzthermometer quasiliving polymerization quasilebende Polymerisation quench polym abschrecken... 

PET suitable for bottle manufacture is produced by a modified process. Here the high-viscosity polymer melt is subjected to a rapid quenching in water to produce clear amoiphous pellets. These are further polymerised in the solid phase at temperatures just below the T . This is useful to reduce aldehyde content, since aldehyde-forming degradation reactions occur less in the lower temperature solid phase polymerisations. Aldehydes can impart a taste to beverages and it is important to keep the aldehyde content to below 2.5 p.p.m. 

Chain polymerisation necessarily involves the three steps of initiation, propagation, and termination, but the reactivity of the free radicals is such that other processes can also occur during polymerisation. The major one is known as chain transfer and occurs when the reactivity of the free radical is transferred to another species which in principle is capable of continuing the chain reaction. This chain transfer reaction thus stops the polymer molecule from growing further without at the same time quenching the radical centre. 

Bent discusses how the sulphur melts to form a fluid liquid, which then becomes quite viscous before being poured into cold water we imagine the breaking of Ss rings, polymerisation of small chains and then quenching of the polymeric chains without re-formation of Ss rings for some time. 

Reactions were followed in an adiabatic calorimeter [4] according to the procedure described [5]. At the end of the polymerisations, the reaction mixture was quenched with ethanolic ammonium hydroxide and evaporated to constant weight in a vacuum oven at 40 °C. 

More recently, Landis et al. studied the polymerisation kinetics of 1-hexene with (EBI)ZrMe( t-Me)B(C5F5)3 64 as catalyst in toluene [EBI = rac-C2H4(Ind)2]. Catalyst initiation was defined as the first insertion of monomer into the Zr-Me bond, 65 (Scheme 8.30). Deuterium quenching with MeOD was used to determine the number of catalytically active sites by NMR. The time dependence of the deuterium label in the polymer was taken as a measure of the rate of catalyst initiation. This method also provides information of the type of bonding of the growing polymer chain to zirconium, as n-or sec-alkyl, allyl etc. Hexene polymerisation is comparatively slow, with high regio- and stereoselectivity there was no accumulation of secondary zirconium alkyls as dormant states [96]. 

By contrast to the polymerisation of hexene with 64, which can be followed conveniently by variable-temperature NMR, the polymerisation of smaller monomers like ethene and propene illustrate the limitations of spectroscopic methods since with most metallocene catalysts they are too fast. The kinetic behavior of (SBI)ZrMe2/AlBu 3/[CPh3][CN B(C6F5)3 2] at 25 °C was therefore investigated by quenched-flow techniques to estimate the rates of initiation, chain propagation and chain termination [SBI = rac-Me2Si(Ind)2] [97]. The results are summarised here for comparison with the results on 1-hexene polymerisation discussed above. 

Electron transfer (ET) reactions play a key role in both natural (photosynthesis, metabolism) and industrial processes (photography, polymerisation, solar cells). The study of intermolecular photoinduced ET reactions in solution is complicated by diffusion. In fact, as soon as the latter is slower than the ET process, it is not anymore possible to measure km, the intrinsic ET rate constant, directly [1], One way to circumvent this problem, it is to work in a reacting solvent [2]. However, in this case, the relationship between the observed quenching rate constant and k T is not clear. Indeed, it has been suggested that several solvent molecules could act as efficient donors [3]. In this situation, the measured rate constant is the sum of the individual ksr-... 

Cyclopentadiene undergoes ionic polymerisation by Friedel-Crafts catalysts32. Its polymerisation by y-rays is markedly suppressed by ammonia or amines but much less by diphenylpicrylhydrazyl or oxygen33. This again points to the ionic rather than the free radical nature of the radiation-induced polymerisation. The quenching effect of ammonia was postulated as due to reactions of the type... 

The use of ethers as cocatalysts for the cationic polymerisation of alkenyl monomers induced by Lewis acids has received little systematic attention and the mechanism through which these compounds operate is not well understood. The complex diethyl-ether-boron fluoride has been extensively used as a very convenient cationic initiator, but mostly for preparative purposes. As in the case of alcohols and water, ethers are known to act as inhibitors or retarders in the cationic polymerisation of olefins, if used obove cocatalytic levels, because they are more nucleophilic than most rr-donor monomers. Imoto and Aoki showed that diethyl ether, tetrahydrofuran, -chloro-diethyl ether and diethyl thioether are inhibitors for the polymerisation of styrene-by the complex BF3 EtjO in benzene at 30 °C, at a concentration lower than that of the catalyst, but high enough (0.5 x 10 M) to quench the active species formation for a time. Their action was temporary in that the quenching reaction consumed them, and therefore induction periods were observed, but the DP s of the polystyrenes were independent of the presence of such compounds, as expected from a classical temporary inhibition. 

Poly-AMMO is synthesized via cationic polymerisation from the monomer 3-azidomethyl-methyl-oxetane (AMMO). The polymerisation reaction is quenched with water to get polymer chains with hydroxyl endgroups which enable to react these pre-polymers later with isocyanate for curing reaction. Poly-AMMO is suggested as - energetic binder component in -< composite propellants and is in the scope of actual research. 

Polymerized Microemulsion Systems. A microemulsion of styrene and divinylbenzene with CTAB + hexanol may readily be made, and subsequently polymerized to form a polymerized microemulsion (5,6,7). This system exhibits two sites of solubilisation for photosystems such as pyrene, one in the surfactant skin layer, and the other in the polymerized styrene-divinylbenzene core. Photochemical reactions induced in the surfactant skin are very similar to those observed in micelles and are not immediately of concern to us at this stage. However, photochemical reactions induced in the rigid polymerized core are of interest, as they essentially confine reactants to a small region of space where movement is restricted as compared to a fluid non-polymerised microemulsion or a micelle. Thus, diffusion is minimised, and it may be possible to investigate reactions which occur over a distance rather than reactions which occur by diffusion. In order to eliminate reactions in the surfactant skin a microemulsion can be constructed which contains cetyl pyridinium chloride in place of CTAB. The pyrene that resides in the surfactant skin layer is immediately quenched by the pyridinium group following excitation. 

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