Copolymer composition vs. monomer feed

Copolymer composition vs. monomer feed data were then obtained for 1-hexene (M ) and 5-methyl-1,4-hexadiene copolymerizations (Table VI). The data show that the copolymer compositions measured by 300 MHz %-NMR spectroscopy are essentially identical to the monomer feed. The calculated reactivity ratios were 1.1 + 0.2 for each of the two monomers. 

COPOLYMER COMPOSITION vs MONOMER FEED COMPOSITION FOR 1-HEXENE/5-CH3-l,4-HEXADIENE COPOLYMERIZATIONS... 

The kinetic copolymerization models, which are more complex than the terminal one, involve as a rule no less than four kinetic parameters. So one has no hope to estimate their values reliably enough from a single experimental plot of the copolymer composition vs monomer feed composition. However, when in certain systems some of the elementary propagation reactions are forbidden due to the specificity of the corresponding monomers and radicals, the less number of the kinetic parameters is required. For example, when the copolymerization of two monomers, one of which cannot homopolymerize, is known to follow the penultimate model, the copolymer composition is found to be dependent only on two such parameters. It was proposed [26, 271] to use this feature to estimate the reactivity ratios in analogous systems by means of the procedures similar to ones outlined in this section. 

Figure 7.1 Plot of the instantaneous copolymer composition vs monomer feed composition (/a) for the situation where (a) rAB rHA=1.0 (-- ), (b) rAA=rsA=0.5...

Another area in which both proton and carbon-13 nmr have proved very powerful is the determination of the structure of copolymers. This has a long history (ref. 6, Chap. X 15,16)9 beginning with the observations of butadiene-styrene copolymers in 1959, Again, the information content of the spectra has increased remarkably since these early reports. Although compositional sequence lengths and probabilities can be calculated from the copolymer equation using the traditional data of polymer composition vs. monomer feed composition, nmr allows direct measurement of the sequences and gives in addition much structural detail not available from overall composition alone. 

Typically, copolymer composition can be manually adjusted by slowly feeding the more reactive monomer in throughout the reaction but this may not be helpful when trying to overcome monomer transport limitations. Therefore, Reimers and Schork [ 102] performed identical copolymerization experiments in miniemulsions, where monomer transport is less significant, in order to determine what effect this would have on the evolution of the copolymer composition. Data on the MMA/VS (and other) copolymerizations indicate that the Schuller equation (and not the Samer adaptation) fits the copolymer composition data. This points to the effect of extremely low monomer water solubility on copolymer composition in macroemulsion polymerization, and the relative insensitivity of miniemulsion polymerization to this effect. 

The parameters rA and rs are known as monomer reactivity ratios representing the ratio of rate constants for a radical to add to its own type polymer vs. rate constants for a radical to add to the other type polymer. When kAA = 0 and ksB = 0, it can be seen that rA = 0, re = 0, and each radical reacts exclusively with the other monomer. Rel. (2.3.20) is then reduced to d[P ]/d[P ] = 1, and the monomers alternate regularly along the chain of the copolymer, regardless of the composition of the monomer feed (an excess of one monomer may remain unreacted). This is an ideal case, but copolymers such as that made from (a) styrene and (b) diethyl fumarate (rA = 0.3, re = 0.07) can be close to the ideal case. The styrene/diethyl fumarate polymerization has the tendency to lead to an azeotropic copolymer with 57 mole percent styrene, regardless the feed composition. When the initial composition of the monomers is different from 57 mole percent, the alt-copolymer is formed until one of the materials is finished and the remaining monomer forms a homopolymer. 

The composition of the surface-attached copolymer is determined by the composition of the monomer feed and the reactivity of the propagating species from the comonomers (homopropagation vs. crosspropagation). The chemical composition represented by the mi/mj molar ratio of monomers 1 and 2 at low degrees of polymerization is described by the well-known copolymerization equation ... 

Crud Chemicals is producing a copolymer of uniform composition in a semibatch reactor, as illustrated in Fig. 12.4a. For their system, = 10, f2 = 0.5, and fm = 0.5. They adjust the rate of addition of the more reactive monomer according to the heat evolution in the reactor. Normally, the system works quite well. One day, however, the feed valve sticks full open at 50% conversion, suddenly dumping the remaining monomer into the reactor. Nevertheless, they let the reaction go to completion. Plot Pj and vs. conversion (of all monomer) for this screwed-up reaction. 

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