Acrylonitrile copolymerization reactivity ratios

In studies of the polymerization kinetics of triaUyl citrate [6299-73-6] the cyclization constant was found to be intermediate between that of diaUyl succinate and DAP (86). Copolymerization reactivity ratios with vinyl monomers have been reported (87). At 60°C with benzoyl peroxide as initiator, triaUyl citrate retards polymerization of styrene, acrylonitrile, vinyl choloride, and vinyl acetate. Properties of polyfunctional aUyl esters are given in Table 7 some of these esters have sharp odors and cause skin irritation. 

In relation to the emulsion polymerization of SBR the greatest difference with nitrile rubber is in the disparity of the copolymerization reactivity ratios. At 50 C Tb is reported to be 0-35 0 08 and Ta = 0 0 0 04 (where B stands for butadiene and A for acrylonitrile). At 5 C the ratios are rB = 0-28 and rA = 0 02. In these cases the product of the reactivity ratios is much less than 1 and one of the monomers polymerizes much faster than the other. This aspect was discussed in Section 6.2. 

An emulsion model that assumes the locus of reaction to be inside the particles and considers the partition of AN between the aqueous and oil phases has been developed (50). The model predicts copolymerization results very well when bulk reactivity ratios of 0.32 and 0.12 for styrene and acrylonitrile, respectively, ate used. 

An example of a commercial semibatch polymerization process is the early Union Carbide process for Dynel, one of the first flame-retardant modacryhc fibers (23,24). Dynel, a staple fiber that was wet spun from acetone, was introduced in 1951. The polymer is made up of 40% acrylonitrile and 60% vinyl chloride. The reactivity ratios for this monomer pair are 3.7 and 0.074 for acrylonitrile and vinyl chloride in solution at 60°C. Thus acrylonitrile is much more reactive than vinyl chloride in this copolymerization. In addition, vinyl chloride is a strong chain-transfer agent. To make the Dynel composition of 60% vinyl chloride, the monomer composition must be maintained at 82% vinyl chloride. Since acrylonitrile is consumed much more rapidly than vinyl chloride, if no control is exercised over the monomer composition, the acrylonitrile content of the monomer decreases to approximately 1% after only 25% conversion. The low acrylonitrile content of the monomer required for this process introduces yet another problem. That is, with an acrylonitrile weight fraction of only 0.18 in the unreacted monomer mixture, the low concentration of acrylonitrile becomes a rate-limiting reaction step. Therefore, the overall rate of chain growth is low and under normal conditions, with chain transfer and radical recombination, the molecular weight of the polymer is very low. 

Acrylonitrile copolymerizes readily with many electron-donor monomers oilier than styrene. Hundreds of acrylonitnle copolymers have been reported, and a comprehensive listing of reactivity ratios for acrylonitrile copolymerizations is readily available. 

Copolymers. Vinyl acetate copolymenzes easily with a few monomers, e g, ethylene, vinyl chloride, and vinyl neodecanoate, which have reactivity ratios close to its own. Block copolymers of vinyl acetate with methyl methacrylate, acrylic acid, acrylonitrile, and vinyl pyrrolidinone have been prepared by copolymerization in viscous conditions, with solvents that are poor solvents for the vinyl acetate macroradical,... 

Previous kinetic study of emulsion copolymerization of styrene (S) and acrylonitrile (AN) leads us to determine (4) the reactivity ratios as ... 

Example 13.6 The following data were obtained using low-conversion batch experiments on the bulk (solvent-free), free-radical copolymerization of styrene (X) and acrylonitrile (Y). Determine the copolymer reactivity ratios for this polymerization. 

However, the ratio 22/ 21 is the reactivity ratio f2 for copolymerization of acrylonitrile with methacrylonitrile, so that... 

Table 64 Values of reactivity ratios calculated according to Eqs. (6.10) and (6.11) used in Ref. [276] to treat the data on products of copolymerization of acrylonitrile with methacrylic acid in solution of dimethyl sulfoxide (I) and its equimolar aqueous mixture (III The conversion in all cases does not exceed 7%...

Table 6.8 Parameters (2.4) of the penultimate model (2.3) describing copolymerization of styrene M, with acrylonitrile M2 in toluene solution at T = 60 °C. The values of reactivity ratios were obtained [283] from the data on copolymer composition (I) and triad distribution (II)...

Acrylonitrile copolymerizes readily with many electron-donor monomers other than styrene. Hundreds of acrylonitrile copolymers have been reported, and a comprehensive listing of reactivity ratios for acrylonitrile copolymerizations is readily available (34,102). Copolymerization mitigates the undesirable properties of acrylonitrile liomopolymer, such as poor thermal stability and poor processability. At the same time, desirable attributes such as rigidity, chemical resistance, and excellent barrier properties are incorporated into melt-processable resins. 

Rank the following monomers in order of their increased tendency to alternate in copolymerization with butadiene and explain your reasoning vinyl acetate, styrene, acrylonitrile, and methyl methacrylate, Hint Use Q-e values if reactivity ratios are not readily available.)... 

An examination of reported reactivity ratios (Table 6) shows that the behaviour rj > 1, r2 1 or vice versa is a common feature of anionic copolymerization. Only in copolymerizations involving the monomers 1,1-diphenylethylene and stilbene, which cannot homopolymerize, do we find <1, r2 <1 [212—215], and hence the alternating tendency so characteristic of many free radical initiated copolymerizations. Normally one monomer is much more reactive to either type of active centre in the order acrylonitrile > methylmethacrylate > styrene > butadiene > isoprene. This is the order of electron affinities of the monomers as measured polarographically in polar solvents [216, 217]. In other words, the reactivity correlates well with the overall thermodynamic stability of the product. Variations of reactivity ratio occur with different solvents and counter-ions but the gross order is predictable. 

Reactivity of itaconic add in copolymerization is dependent upon pH and degrees of ionization of the add. Acid reactivity has been studied most carefully in acrylonitrile copolymerization 33, 37). Under acidic conditions an increase in itaconic concentration greatly decreases the polymerization rate, while at pH s of 7—9.8 moderate increases of itaconate do not reduce the rates so strongly. Monomer reactivity ratios and Q and e values have been calculated for the various states of ionization of the acid as reported in Table 5. As the pH rises, drops from 1.57 to 0.1 suggesting, as stated earlier, that the dianion undergoes little homopolymerization. The change in is less than 2-fold which indicates appreciable copolymerization of the dianion. The much greater decrease... 

Another aspect of free radical polymerizations under pressure which has been recently studied is the effect of pressure on comonomer reactivity ratios (5). In two copolymerization systems—styrene-acrylonitrile and methyl methacrylate-acrylonitrile—it was found that the product of the reactivity ratios, rif2, approaches unity as the pressure is increased. The monomer-polymer composition curves for these two copolymerizations at 1 and 1000 atm. are illustrated in Figures 1 and 2. The effect of pressure on the individual reactivity ratios and on the fit2 product is given in Table II. 

Errors in variables methods are particularly suited for parameter estimation of copolymerization models not only because they provide a better estimation in general but also, because it is relatively easy to incorporate error structures due to the different techniques used in measuring copolymer properties (i.e. spectroscopy, chromatography, calorimetry etc.). The error structure for a variety of characterization techniques has already been identified and used in conjunction with EVM for the estimation of the reactivity ratios for styrene acrylonitrile copolymers (12). 

Recently, the Research Group on NMR, SPSJ, assessed reliability of copolymer analysis by NMR using three samples of radically prepared copolymers of MMA and acrylonitrile with different compositions. 1H and 13C NMR spectra of the copolymers were collected from 46 NMR spectrometers (90 500 MHz) and the composition and sequence distribution were determined.232 Table 14 summarizes the monomer reactivity ratios determined by 13C NMR analysis. The large difference between rxx and r2X indicates the presence of a penultimate effect in this radical copolymerization, as previously reported.233 The values of riy, especially rxx, depended on the comonomer feed ratio, suggesting higher order of neighbouring unit effect on the reactivity of chain-end radicals. 

The acrylate- and methacrylate-derivatized r 5-(benzene)tricarbonylchromium monomers 20 65,66,68,72 21,69>72 and 2273 (Scheme 1.2) were synthesized from benzyl alcohol or 2-phenylethanol when reacted with Cr(CO)6. The alcohols were esterified with either acrylyl or methacrylyl chloride in ether/pyridine and purified by multiple recrystallizations from CS2. Homopolymerizations proceeded in classic fashion with no special electronic effects from the rr-complexed Cr(CO)3 moiety.65,73 Acrylate 20 was copolymerized with styrene and methyl methacrylate and the reactivity ratios were obtained.65 Acrylate 21 and methacrylate, 22, copolymerized readily with styrene, methyl acrylate, acrylonitrile, and 2-phenylethyl acrylate to give bimodal molecular-weight distributions using AIBN initiation.69 Copolymerization of 20 with ferrocenylmethyl acrylate, 2, generates copolymers with varying mole ratios of two transition metals, Cr and Fe (see structure 34).65... 

Novel iron carbonyl monomer, r)4-(2,4-hexadien-l-yl acrylate)tricarbonyl-iron, 23, was prepared and both homopolymerized and copolymerized with acrylonitrile, vinyl acetate, styrene, and methyl methacrylate using AIBN initiation in benzene.70,71 72 The reactivity ratios obtained demonstrated that 23 was a more active acrylate than ferrocenylmethyl acrylate, 2. The thermal decomposition of the soluble homopolymer in air at 200°C led to the formation of Fe203 particles within a cross-linked matrix. This monomer raised the glass transition temperatures of the copolymers.70 The T)4-(diene)tricarbonyliron functions of 23 in styrene copolymers were converted in high yields to TT-allyltetracarbonyliron cations in the presence of HBF4 and CO.71 Exposure to nucleophiles gave 1,4-addition products of the diene group.71... 

Monomer 13 homopolymerization was very sluggish, but it copolymerized in good yields with acrylonitrile, methyl methacrylate, and /V-vinyl-2-pyrrolidonc (Scheme 1.6).59,61 However, styrene copolymerizations required several subsequent reinitiations to get good yields of copolymers. The reactivity ratios obtained in 13/styrene copolymerizations were fj = 0.16 and r2 = 1.55 (when Mj = 13),61 giving values of Q = 1.66 and e = —1.98 for monomer 13 in direct accord with the Qe values found for monomers 1, 8, 10, 11, and 12, as discussed earlier.61... 

The reactivity ratios for the free-radical copolymerization of styrene (rj = 0.4) and acrylonitrile (r2 = 0.04) result in uneven incorporation of each monomer into the copolymer as seen in Figure 3. Thus, most SAN and ABS polymers are made at the crossover point (A in Figure 3) to avoid composition drift. 

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