Step-Change Polymerization

Consider the following mechanism for step-change polymerization of monomer M (Px) to P2, P3. Pr,. The mechanism corresponds to a complex series-parallel scheme series with respect to the growing polymer, and parallel with respect to M. Each step is a second-order elementary reaction, and the rate constant k (defined for each step)1 is the same for all steps. 

These rate laws are coupled through the concentrations. When combined with the material-balance equations in the context of a particular reactor, they lead to uncoupled equations for calculating the product distribution. For a constant-density system in a CSTR operated at steady-state, they lead to algebraic equations, and in a BR or a PFR at steady-state, to simultaneous nonlinear ordinary differential equations. We demonstrate here the results for the CSTR case. 

the product distribution (distribution of polymer species P,) leaving the CSTR can be calculated, if cUo, k, and r are known. 

For a BR or a PFR in steady-state operation, corresponding differential equations can be established to obtain the product distribution (problem 7-15). 

7-1 The rate of production of urea, (NH CO, from ammonium cyanate increases by a factor of 4 when the concentration of ammonium cyanate is doubled. Show whether this is accounted for by the following mechanism  

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An illustration of a series-parallel network is provided by the step-change polymerization kinetics model of Section 7.3.2. The following example continues the application of this model to steady-state operation of a CSTR. 

For step-change polymerization at steady-state in a CSTR represented by the kinetics model in Section 7.3.2, derive equations giving the weight fraction of r-mer, wr, on a monomer-free basis, as a function of r, the number of monomer units in polymer Pr at the reactor outlet. This is a measure of the distribution of polymers in the product leaving the reactor. 

This problem continues Example 18-7 for use of the step-change polymerization kinetics model of Chapter 7 in a CSTR at steady-state. 

Starting from equations 7.3-3 to -6 applied to a constant-volume BR, for polymerization represented by the step-change mechanism in Section 7.3.2, show that the product distribution can be calculated by sequentially solving the differential equations ... 

Figure 24. Simulated response of third reactor of a continuous vinyl acetate polymerization to a step change in setpoint at high emulsifier feed concentration (0.06 mol/L H>0) and manipulation of initiator flow rate to the third reactor at 50°C ((---------------------] optimum PID) (-----) Z transform)...

Numerical integration is performed as indicated in the previous section on Equations 8, 15, 20, 21, and 22 at constant temperature over time intervals selected by the user. Up to 10 step changes in temperature can be made in the course of a batch polymerization. Provision is made for up to five initiators (primarily for suspension polymerization) in addition thermally initiated polymerization can be calculated with or without initiators. 

Figure 12. Degree of polymerization with time in response to step change in monomer ratio in a controlled semi-batch reactor. Key -----, WADP -------, NADP.

Fluorinated PU Two-step Bulk polymerization Fluorine content Platelet adhesion and activation Static, in vitro Human PRP Increasing content of fluorine = increasing contact angle, decreasing platelet adhesion and shape change [74]... 

Ghosh, R Gupta, S.K. Saraf, D.N. (1998) An experimental study on bulk and solution polymerization of methyl methacrylate with responses to step changes in temperature. Chemical Engineering Journal, 70, 25-35. 

Ghosh, P., Gupta, K.S., Saraf, D.N., 1998. An Experimental Study on Bulk and Solution Polymerization of Methyl Methacrylate with Responses to Step Changes in Temperature. Chemical Engineering Journal 70 25-35. 

More specific topics, such as block copolymer synthesis by changing the polymerization mechanism [18], by step-growth polymerization [19], via macroinitiators [20], living free-radical polymerization [21, 22] or ionic polymerization [23] were reviewed later on, as well as the synthesis of selected block copolymer types, for example hydrophilic-hydrophilic copolymers [24], copolymers based on PEO [10,16]. 

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