Reactivity relative ratio

Epichlorohydrin Elastomers without AGE. Polymerization on a commercial scale is done as either a solution or slurry process at 40—130°C in an aromatic, ahphatic, or ether solvent. Typical solvents are toluene, benzene, heptane, and diethyl ether. Trialkylaluniinum-water and triaLkylaluminum—water—acetylacetone catalysts are employed. A cationic, coordination mechanism is proposed for chain propagation. The product is isolated by steam coagulation. Polymerization is done as a continuous process in which the solvent, catalyst, and monomer are fed to a back-mixed reactor. Pinal product composition of ECH—EO is determined by careful control of the unreacted, or background, monomer in the reactor. In the manufacture of copolymers, the relative reactivity ratios must be considered. The reactivity ratio of EO to ECH has been estimated to be approximately 7 (35—37). 

There is some increase in selectivity with functionally substituted carbenes, but it is still not high enough to prevent formation of mixtures. Phenylchlorocarbene gives a relative reactivity ratio of 2.1 1 0.09 in insertion reactions with i-propylbenzene, ethylbenzene, and toluene.212 For cycloalkanes, tertiary positions are about 15 times more reactive than secondary positions toward phenylchlorocarbene.213 Carbethoxycarbene inserts at tertiary C—H bonds about three times as fast as at primary C—H bonds in simple alkanes.214 Owing to low selectivity, intermolecular insertion reactions are seldom useful in syntheses. Intramolecular insertion reactions are of considerably more value. Intramolecular insertion reactions usually occur at the C—H bond that is closest to the carbene and good yields can frequently be achieved. Intramolecular insertion reactions can provide routes to highly strained structures that would be difficult to obtain in other ways. 

The relative reactivity ratios rx and r2 are the ratios of rate constant for a given radical adding to its own monomer to the rate constant for its adding to the other monomer. For example when r, >1, radical prefers to add to Mi while if rx < 1, i.e. M prefers to add to M2. Now, we can write... 

What is meant by relative reactivity ratios in copolymerization process How the copolymerization depends on the relative reactivity ratios Discuss. 

The best test for functionality would be in a copolymerization study. A polystyrene with a methacrylate terminal functional group was prepared. A review of relative reactivity ratios indicated that vinyl chloride reacts very rapidly with methacrylates. Therefore, a copolymerization of the polystyrene terminated with a methacrylate functional group in vinyl chloride would be a good test case, and one should observe the disappearance of the MACROMER if the reaction is followed by using GPC analysis. 

It was demonstrated that MACROMER will copolymerize with conventional monomers in a predictable manner as determined by the relative reactivity ratios. The copolymer equation ... 

When the product of monomer relative reactivity ratios is approximately one r x r2 = 1), the last inserted monomeric unit in the chain does not influence the next monomer incorporation and Bernoullian statistics govern the formation of a random copolymer. When this product tends to zero (r xr2 = 0), there is some influence from the last inserted monomeric unit (when first-order Markovian statistics operate), or from the penultimate inserted monomeric units (when second-order Markovian statistics operate), and an alternating copolymer formation is favoured in this case. Finally, when the product of the reactivity ratios is greater than one (r x r2 > 1), there is a tendency for the comonomers to form long segments and block copolymer formation predominates (or even homopolymer formation can take place) [448],... 

Table 3.4 Relative reactivity ratios ( = 22/ 21) of ethylene and higher a-olefins (M2) with respect to propylene (Mi)...

Table 3.5 Monomer relative reactivity ratios, r (ethylene) and r2 (propylene), for ethylene/propylene copolymerisations with various Ziegler-Natta catalysts 1...

Typical values of comonomer relative reactivity ratios in ethylene/propylene copolymerisations run with various heterogeneous and homogeneous Ziegler-Natta catalysts are listed in Table 3.5 [30, 72, 454]. 

While ethylene is vastly more reactive than cyclopentene in copolymerisation with the (IndCH2)2ZrCl2 [AI(Mc)0]x. catalyst (relative reactivity ratio of ethylene r = 80 300), norbornene is quite readily incorporated, with... 

Styrene undergoes copolymerisation with ethylene and various a-olefins in the presence of heterogeneous Ziegler-Natta catalysts. Its reactivity in the copolymerisation is quite low, which is illustrated by the values of the relative reactivity ratios, r and r2, presented in Table 4.5 [118]. One may note, however, a considerably high relative reactivity of styrene in copolymerisation with vinyl-cyclohexane. The copolymerisation of styrene with small amounts of a-olefin, such as 1-octene or 1-decene, yields copolymers of reduced crystallinity and thus reduced brittleness compared with the homopolymer of styrene. 

Table 4.5 Relative reactivity ratios for copolymerisation of styrene (ri) and a-olefins (r2) with heterogeneous Ziegler-Natta catalysts...

According to literature data vinyl esters of saturated aliphatic carboxylic acid copolymerize randomly with each other (I), the monomers being incorporated into the copolymer in about the same ratio at which they are present in the monomer mixture. This means that for practical purposes the relative reactivity ratios ri and r > can be taken to be equal and unity. 

Table 5-12) [221]. The relative reactivity ratio of the tertiary hydrogen atoms,...

The classical Mayo-Lewis scheme relating comonomer feeds to relative reactivity ratios (5i) is often applied to copolymerization of cyclosiloxanes. This scheme presumes that no depropagation of the copolymer occurs, that the copolymerization rate constants depend only on the ultimate comonomer units, and that instantaneous comonomer feed ratios and copolymer compositions are used in the analysis of data. When these assumptions hold, the Mayo-Lewis method is very useful for the analysis of copolymerization data. 

If two of the three monomers belong to the group described above and one is weakly conjugated, i.e. of the group of vinyl chloride, vinyl esters, olefins and the like, the product probabilities are approximately 0.006. It is evident that knowledge of the product probabilities permits to predict relative reactivity ratios for a wide variety of monomers. 

For the non-catalyzed urethane reactions It was established (23) that the relative reactivities (ratios of rate constants) of substituted aromatic Isocyanates correlated with the structural parameter a of the substituent R (measuring the electron withdrawing ability of the substituent R) according to the Hammett equation ... 

A combination of variables controls the outcome of the copolymerization of two or more unsaturated monomers by CCT free-radical polymerization.382 Of course, all of the features that control the outcome of a normal free-radical polymerization come into effect.40 426 429 These include the molar ratio of monomers, their relative reactivity ratios and their normal chain-transfer constants, the polymerization temperature, and the conversion. In the presence of a CCT catalyst, the important variables also include their relative CCT chain-transfer constants and the concentration of the Co chain-transfer agent. The combination of all of these features controls the molecular weight of the polymer and the nature of the vinyl end group. In addition, they can also control the degree of branching of the product. 

In order to determine the reactivity of pentachlorophenyl acrylate, 8, in radical initiated copolymerizations, its relative reactivity ratios were obtained with vinyl acetate (M2), ri=1.44 and r2=0.04 using 31 copolymerization experiments, and with ethyl acrylate (M2), ri=0.21 and r2=0.88 using 20 experiments.The composition conversion data was computer-fitted to the integrated form of the copolymer equation using the nonlinear least-squares method of Tidwell and Mortimer,which had been adapted to a computerized format earlier. 

The synthesis of polystyrene-g-polytetrahydrofurane [188] was achieved by ATR copolymerization of methacrylic PTHF macromonomer, MA-PTHF, with styrene (Scheme 105). The PTHF macromonomer was synthesized by cationic ring opening polymerization of THF with acrylate ions, formed by the reaction of methacryloyl chloride and AgC104. The polydispersity indices of the graft copolymers determined by SEC ranged between 1.3-1.4. Kinetic studies revealed that the relative reactivity ratio of the macromonomer to St was independent of the molecular weight of PTHF. 

Copolymer compositions were determined by proton NMR. The relative proportions of the comonomers were estimated by comparing the areas of the MMA 0-methylene peak and the pendant methylene peak of the itaconates. Compositions determined by NMR compare very well with those calculated from relative reactivity ratios given in the literature. 

The relative reactivities of monomers to a given radical can be obtained from analysis of the relative reactivity ratios. This can be seen by considering the inverse of the monomer reactivity ratio ... 

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