Polymerisation velocity

The outlet from the mixing chamber of the gradient generator may be led into a device such as that of Caton and Goldstein (1971), ( 8.3.4.1), or by way of a manifold into the tubes individually. Mirault and Scherrer, on the assumption that the polymerisation velocity is proportional to the acrylamide concentration on the one hand, and that of TEMED and persulfate on the other, arranged that both the latter components were added at a concentration inversely proportional to that of the acrylamide (e.g. for 10 ml of 2% acrylamide 50 pi each of 10% TEMED and 10% persulfate were added, but for 10 ml of 6% acrylamide 16.7 p only of each). The gels were prepared at room temperature but the acrylamide... 

The resulting polymerisation velocity will of course depend on the reaction constants Ki,... 

Biesenberg, J. S. etal., J. Polym. Eng. Sci., 1976,16, 101-116 Polymerisation of methyl methacrylate initiated by oxygen or peroxides proceeds with a steady increase in velocity during a variable induction period, at the end of which a violent 90°C exotherm occurs. This was attributed to an increase in chain branching, and not to a decrease in heat transfer arising from the increasing viscosity [ 1 ]. The parameters were determined in a batch reactor for thermal runaway polymerisation of methyl methacrylate, initiated by azoisobutyronitrile, dibenzoyl peroxide or di-ferf-butyl peroxide [2],... 

One surface chain (polymerisation index N), anchored on the solid by one extremity, experiences a friction force due to all the other flowing chains from the melt (polymerisation index P) which are entangled with it. The N chain elongates under the action of this friction force. Two delicate questions have to be answered in order to estimate the friction force exerted by the melt on one surface chain first, one needs to evaluate the relative velocity of one melt... 

Therefore, the kinetic parameters of fast polymerisation processes kp and k,) and the linear velocity of reagent flow V determine the geometric size (R, L) and optimal configuration of a reaction zone. New opportunities and methods of process control have been revealed, allowing the control of the monomer conversion rate and MW characteristics of the forming polymer products, in particular, due to the forced change (limitation) of the reaction zone geometry (R, L). The principal conclusion is the necessity to reduce the reactor dimensions to the scale of a reaction zone. 

As an energy transfer from a monomer radical to a macro-radical is all that occurs, the heat of activation of this type of reaction is much lower, namely of the order of 3 to 6 kcal/mol, leading to a reaction velocity which is from 10 to 10 times greater than that of the start reaction at the same temperature. The situation therefore is often that chain growth cannot occur, because no monomer radicals have yet been formed, so that the velocity of the whole polymerisation is governed by the velocity of the start reaction. As soon as a monomer radical has been formed however, the chain growth as a rule will start immediately. 

On cooling, T decreases, and consequently the velocity v of the molecules diminishes, ultimately leading to a cessation of the Brownian motion. On polymerisation however the mass m increases, leading to the same result. 

Plasma-polymerised thiophene for passivating the surface defects on GaAs has been employed [70]. The paper showed the passivation of GaAs surface was made possible by sulfur present in an overlayer, provided by the thin film of plasma-polymerised thiophene. The deposition of polythiophene lowered the barrier height, reduced the surface recombination velocity and increased diffusion length. 

In contrast to CSTRs, PFRs are tubular in structure. The monomer emulsion enters one end of the PFR, where it begins to polymerise. Conversion increases as a function of the distance travelled by the emulsion as it passes through the PFR. The final latex then exits the other end of the tubular PFR. Ideally, each fluid element that passes through a PFR travels the same distance, at the same velocity, for the same amount of time. As a consequence, the particles produced in a PFR can be more uniform in size and composition. In practice, tubular reactors are not very flexible in terms of processing and production capabilities, and are not used extensively in industry for emulsion polymerisation. 

---