Monomer feed ratios

Fig. 1. Copolymer composition as a function of monomer feed ratio for various reactivity ratio combiaations, designated I—V and explained ia the text...

Copolymerization occurred when the olefin had a basicity lower than that of the aldehyde (with respect to the initiator used), but sufficiently high occasionally to displace a molecule of initiator and give rise to an active species this situation produced copolymers with varying proportions of ether units in the chain, depending on the monomers feed ratio and on the olefin used. Isopropenylbenzene gave the best results with alternate copolymerization over a fairly wide range of feed ratios rt = 0.03 0.03, r2 = 0.4 0.1 (2-furaldehyde = Mj) indene produced copolymers with lower 2-furaldehyde contents. 

The existence of an azeotropic composition has some practical significance. By conducting a polymerization with the monomer feed ratio equal to the azeotropic composition, a high conversion batch copolymer can be prepared that has no compositional heterogeneity caused by drift in copolymer composition with conversion. Thus, the complex incremental addition protocols that arc otherwise required to achieve this end, are unnecessary. Composition equations and conditions for azeotropic compositions in ternary and quaternary eopolymerizations have also been defined.211,21... 

One final point should be made. The observation of significant solvent effects on kp in homopolymerization and on reactivity ratios in copolymerization (Section 8.3.1) calls into question the methods for reactivity ratio measurement which rely on evaluation of the polymer composition for various monomer feed ratios (Section 7.3.2). If solvent effects arc significant, it would seem to follow that reactivity ratios in bulk copolymerization should be a function of the feed composition.138 Moreover, since the reaction medium alters with conversion, the reactivity ratios may also vary with conversion. Thus the two most common sources of data used in reactivity ratio determination (i.e. low conversion composition measurements and composition conversion measurements) are potentially flawed. A corollary of this statement also provides one explanation for any failure of reactivity ratios to predict copolymer composition at high conversion. The effect of solvents on radical copolymerization remains an area in need of further research. 

Values of 0 required to fit the rate of copolymerization by the chemical control model were typically in the range 5-50 though values <1 are also known. In the case of S-MMA copolymerization, the model requires 0 to be in the range 5-14 depending on the monomer feed ratio. This "chemical control" model generally fell from favor wfith the recognition that chain diffusion should be the rate determining step in termination. 

The solvent in a bulk copolymerization comprises the monomers. The nature of the solvent will necessarily change with conversion from monomers to a mixture of monomers and polymers, and, in most cases, the ratio of monomers in the feed will also vary with conversion. For S-AN copolymerization, since the reactivity ratios are different in toluene and in acetonitrile, we should anticipate that the reactivity ratios are different in bulk copolymerizations when the monomer mix is either mostly AN or mostly S. This calls into question the usual method of measuring reactivity ratios by examining the copolymer composition for various monomer feed compositions at very low monomer conversion. We can note that reactivity ratios can be estimated for a single monomer feed composition by analyzing the monomer sequence distribution. Analysis of the dependence of reactivity ratios determined in this manner of monomer feed ratio should therefore provide evidence for solvent effects. These considerations should not be ignored in solution polymerization either. 

Thus a log-log plot of the apparent copolymer composition ratio against the monomer feed ratio should yield a straight line with slope two. In fact, a slope near two was observed for several comonomer pairs with different polarities. 

Styrene-SQ., Copolymers. I would now like to discuss two systems which illustrate the power of C-13 nmr in structural studies. The first is the styrene-SO system. As already indicated, this is of the type in which the chain composition varies with monomer feed ratio and also with temperature at a constant feed ratio (and probably with pressure as well.) The deviation of the system from simple, first-order Markov statistics, —i.e. the Lewis-Mayo copolymerization equation—, was first noted by Barb in 1952 ( ) who proposed that the mechanism involved conplex formation between the monomers. This proposal was reiterated about a decade later by Matsuda and his coworkers. Such charge transfer com-... 

The copolymerization between two different monomers can be described using only four reactions, two homo-polymerizations and two cross-polymerization additions. Through appropriate arrangements, equations that allow copolymer composition to be determined from the monomer feed ratio are developed. 

The high electron richness of vinylferrocene as a monomer is illustrated in its copolymerization with maleic anhydride, where 1 1 alternation copolymers are formed over a wide range of monomer feed ratios and ri -2 = 0.003. Subsequently, a large number of detailed copolymerization studies have been undertaken using metal-containing vinyl monomers. 

Curve // Monomer Feed Ratio B/I Temp. °C sec-BuLi mole/1. x 103 Propagation Rate ki (sec-1) Initial Constant x 101 After Inversion... 

The NMR analysis (21) of the chemical composition for copolymers from various monomer feed ratios at fairly low conversion are shown in Table IV. The results were then used to estimate the reactivity ratios for the diene monomers under the conditions employed. Various published methods of calculating monomer reactivity ratios have been examined. These include the once popular but now somewhat out of favor Fineman-Ross method... 

The reactivity ratios may be evaluated by performing a series of low-conversion copolymerizations at different, monomer-feed ratios, isolating the copolymer, and determining its composition. A number of mathematical analyses have been proposed in order to provide, from the experimental data, correct values for the two unknown reactivity ratios. There is some difference of opinion as to the best method for obtaining values having quantifiable errors.84,64" However, several of... 

In 1979, Maciejewski et al. also explored Method 3 for the preparation of main-chain poly(vinylidene chloride-/ -CD rotaxane) 35 [74, 75]. Radiation polymerization and AIBN-initiated solution polymerization of the complex of vinyli-dene chloride with 21 gave products with min = 0.34 and 0.49, respectively. However, the polyrotaxane via Method 1 had a much lower min (0.087) with much lower CD/monomer feed ratio than for those via the polymerization of the complex (1 1 ratio). Therefore, the reported min values are not comparable, so the difference between the two methods in terms of threading efficiencies cannot be distinguished. Although the authors did not see any threading via Method 2 for the same polyrotaxanes, Ogino and coworkers prepared a true CD-based polyrotaxane of Type 5 using metal complexes as stoppers [76]. It was also found that... 

The copolymer produced during the polymerization precipitated as a white powder, soluble in DMF, chloroform, and liquid S02. Elementary analysis proved the exact alternating composition irrespective of monomer feed ratio. On heating, they decomposed at 220°-230°C without melting. 

Binary copolymerization of the CPT-AN system was carried out at 40°C using AIBN as initiator. From the Finemann-Ross plot of the copolymer composition and monomer feed ratios, the monomer reactivity ratios were determined. (CPT) = 0, r2 (AN) = 1.97. The increase of the relative reactivity of CPT by forming a complex with SC is calculated as follows. 

When butadiene and styrene are mixed in the presence of an organolithium initiator, the resulting copolymerization process and product will be governed by the reaction conditions. The rate of copolymerization, the relative composition of the copolymer, and the distribution of monomer units (i.e., block, random, etc.) will be determined by such factors as solvent, temperature, and monomer feed ratio. 

Coincidental with Ivin and Spensley, O Driscoll and Gasparro (12) studied the free radical copolymerization of styrene-methyl methacrylate but at 250°C. The latter workers varied monomer feed ratio over a wide... 

Note In all cases the initial monomer feed ratio of monomers 1, 2, and 3 was 20 40 40, respectively. Additional perfluoro monomers are described by the author [1] in a subsequent investigation. 

Monomers feed ratio (min) (J) yield/kJ (%) time (s) (j) yield/kJ(%) factor... 

Suppose we wish to prepare a nylon with an M of 16,000 using adipic acid (H02C(CH2)4C02H) and hexamethylene diamine (H2N(CH2)gNH2), which represents an A-A, B-B type of polycondensation. The common, or trade name of the product, poly(hexamethylene adipamide), H0[0C(CH2)4 CONH(CH2)gNH] H, is nylon 6,6, or nylon 66. The first 6 refers to the number of carbon atoms between amide nitrogens for the amine component, and the second 6 refers to the number of carbon atoms separating nitrogens for the acid component. What monomer feed ratio would be required to achieve this M ... 

It is noted that for both methods, the instantaneous copolymer composition, F, is approximated by the composition of the final copolymer, and the actual drift in the monomer feed ratio, /, is neglected because of the low conversions for the experiments. Therefore, the reactivity ratios obtained from both methods might be inaccurate for high conversion. 

To minimize the effect of the drift in the monomer feed ratio, Kelen and Ttidos proposed a new method. In their work, the following equation was introduced, based on Eq. (5) ... 

To overcome the errors brought in by the approximation for instantaneous copolymer composition and the drift in monomer feed ratio, the integration equation for Eq. (5) was used to determine the monomer reactivity ratios, which was given as ° ... 

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