Polymerisation radical lifetimes

The lamps may be operated on AC or DC, but for polymerisation studies and radical lifetime measurements DC must be used. For a low-pressure lamp the intensity falls to nearly zero 120 times per second for a 60 cycles AC source " the high-pressure lamp also tends to be unstable with AC . Circuits (Fig. 35) are shown for medium-pressure and high-pressure lamps operating procedures are given quite clearly in these last two references. The low-pressure lamp reaches stable operating conditions quite quickly, but the other two types require some time to do so (10-15 min). The high-pressure lamp also has a very short lifetime. 

Equation (4) clearly shows that the number average degree of polymerisation Xn is inversely proportional to the reaction rate Rp, meaning that, in radical chain polymerisation high reaction rates are linked to low molecular masses and vice versa. One way to avoid this dilemma is to use emulsion polymerisation where the lifetime of a radical (i.e., the "kinetic" chain length) is independent of... 

This reaction has been shown to be very rapid77. Sulphuric and acetic acids sup press the polymerisation. Evidently their anions are ineffective as initiators, and the enhanced proton concentration provided by them must reduce the chain lifetime. The slight retarding effect of oxygen could be due to electron scavenging. However, the authors suggest that there may be a small free radical component of the chain reaction, which is inhibited in the presence of oxygen. 

In the photoinitiated polymerisation of Jl-vinylpyrrolidinone and N-vinylcaprolactam in dioxane and ethanol, the rate was higher in the latter solvent and monomerlO. This was attributed to the influence of the two additional methylene groups in the caprolactam ring which increases monomer reactivity. Other interesting effects have included the radiation dose on the photopolymerisation of diallyl oxydiethylene dicarbonate O. Here long lived radicals were produced which continue to react in the dark. The rate appears to fit a relaxation model that considers double bonds as traps with increasing lifetimes that are able to transfer to radical sites. 

The photoinduced polymerisation of methacrylic acid by sodium peroxide has been determined to have an activation energy of 17.7 kJ/molel03. From this the macroradical lifetimes were determined to be 3.9 secs. In the intermittent photoinitiation of methyl methacrylate-styrene the dependence of the rate of propagation on monomer feed composition was understood in terms of a penultimate model and not a terminal model as previously assumed 4 with some evidence for cross-termination. An eosin-periodate combination has been found to induce the photopolymerisation of acrylonitrile where the dye was found to act as both the sensitiser and reducing agent. Hydroxyl radicals are assumed to initiate polymerisation while the N-bromosuccinimide induced photopolymerisation of N,N -methylenebisacrylamide is faster in 2-propanol solution O . 

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