Copolymerization experiments

Styrene readily copolymerizes with many other monomers spontaneously. The styrene double bond is electronegative on account of the donating effect of the phenyl ring. Monomers that have electron-withdrawiag substituents, eg, acrylonitrile and maleic anhydride, tend to copolymerize most readily with styrene because their electropositive double bonds are attached to the electronegative styrene double bond. Spontaneous copolymerization experiments of many different monomer pair combiaations iadicate that the mechanism of initiation changes with the relative electronegativity difference between the monomer pairs (185). 

Hence by assigning two parameters, a Q and an c, to each of a set of monomers, it should be possible according to this scheme to compute reactivity ratios ri and V2 for any pair. In consideration of the number of monomer pairs which may be selected from n monomers—about n /2—the advantages of such a scheme over copolymerization experiments on each pair are obvious. Price has assigned approximate values to Q and e for 31 monomers, based on copolymerization of 64 pairs. The latitude of uncertainty is unfortunately large assignment of more accurate values is hampered by lack of better experimental data. Approximate agreement between observed and predicted reactivity ratios is indicated, however. 

In agreement with the theoretical analysis, C2- and /(-symmetric metallocenes scarcely insert ( > and (Z)-butene, respectively, whereas C2- and Cs-symmetric metallocenes insert relevant fractions of (Z)- and (//(-butene, respectively. Moreover, in agreement with QM/MM analysis, when copolymerization experiments are run with a 40% (Z)-2-butene-60% ( )-2-butene mixture, the presence of the better coordinating (Z)-butene inhibits the reaction... 

In the literature one can find extensive compilations of reactivity ratios for numerous monomer pairs. For evaluation of the copolymerization experiments and for calculating the reactivity ratios, there is now extensive software available. 

Copolymerization reactions Copolymerization experiments with styrene and MMA employed molar fractions of 20, 40, 60, and 80% comonomers, which were reacted in ethanol 1,2-dichIorethane 60 40 (by volume) mixtures and benzoyl peroxide as catalyst. Polymerizations were carried out at 70°C. The reactions were quenched by the addition of methanol as non-solvent, and the copolymer was isolated by centrifugation. Copolymer analysis employed UV spectroscopy for copolymers with MMA, and methoxyl content determination according to a procedure by Hodges et al. (16) in the case of styrene copolymers. Reactivity ratios were determined in accordance with the method by Kelen-Tiidos (17) and that by Yezrielev-Brokhina-Roskin (YBR) (18). Experimental details and results are presented elsewhere (15). 

No triester of levoglucosan was found92 that polymerized at temperatures much below 0°. At —78°, the triacetate complexed with phosphorus pentafluoride, and, at high concentration, precipitated from solution.91 The tris(monofluoroacetate) failed to polymerize under a variety of conditions.91 The trinitrate polymerized at 0°, but the product was not fully characterized.92 Polymerization of the triacetate proceeded to reasonable conversions with a number of catalysts at 0°, but the viscosity and the stereoregularity of these polymers were low.92 In a simple, copolymerization experiment, it was demonstrated that the low polymerizability of levoglucosan triacetate was due not only to a failure to initiate but also to sluggish propagation.92... 

In the copolymerization experiments of MMA and AN with sodium acetate in a mixture of acetic acid and acetic anhydride, a platinum anode and mercury cathode, the reaction at the cathode proceeds by a free-radical mechanism where anionic ends may be terminated by acetic acid (36). 

The copolymerization experiments indicate that polymerization does not proceed through an anionic but a free-radical mechanism. Free radical has been found to remain after polymerization. The authors explain that the dimerization of semiquinones is inhibited with its steric hindrance, while the formation of monomer radical is not disturbed, which initiates the polymerization. An anionic end may be protonized with di-methylformamide. 

The subject of graft polymerization is usually regarded as beginning with the work of Carlin, and Shakespeare (1) in 1946. However, it is interesting to note that already in 1943 Ushakov (2) reported on the synthesis of vinyl and allyl esters of cellulose which he used for subsequent copolymerization experiments with maleic esters. It seems safe... 

A specific way of grafting onto cellulose with respect to the attachment points of the side chains is being given through the introduction of polymerizable substituents. As mentioned at the beginning of this article, already in 1943 Usakov (2) synthesized vinyl and allyl esters of cellulose and made copolymerization experiments with maleic esters. 

From the results of the copolymerization experiments with I and 2 with styrene it can be concluded that the azo monomer behaves ideally (i.e. incorporation of the azo monomer in the polymer is equal to its proportion in the monomer mixture) when the C = C double bond is electronically identical with that in the comonomer. 

The results of several copolymerization experiments with 7 are given in Table 3.8, from which it is clear that the assumption of similarity between 7 and benzyl methacrylate is reasonable. From Fig. 3.4. it is predicted that both MMA and MAN should copolymerize with 7 almost ideally , whereas styrene will deviate considerably from ideality . These predictions are verified by the results in Table 3.8. If the azo monomer is incorporated into the polymer in the same proportion as it is present in the initial monomer mixture, then it is possible to convert the, relatively valuable, azo monomer essentially 100% into polymer without changing the composition of the copolymer with conversion an important consideration for the technical utilisation of such products as the starting materials for graft copolymers. If the poly-... 

Fig. 12.6 Symyx secondary screen, which is used to rank primary screening discoveries and to optimize the most promising catalyst leads. In this example, high-temperature ethylene-1-octene copolymerization experiments were performed on a focused 96-member amine-ether library.

Whereas the two-tank arrangement permits monomer feed profiles which vary smoothly in one direction, the three-tank scheme leads to inflections and concentration reversals as illustrated in Figure 4. Such reversals are useful in preparing hard-soft-hard, hydrophilic-hydrophobic-hydrophilic polymer variations and the like. In addition, three tank power feed has been useful as a means of calculating monomer inventory in copolymerization experiments (4). 

In most copolymerization experiments the molar macromonomer concentration [M] is low with respect to the molar concentration [A],... 

Based on the spectra obtained from copolymerizations (Figures 2-6), the presence of 1,3-dioxolane could not be ascertained. This again might be attributed to low concentrations which could not be detected by NMR. Parallel copolymerization experiments were carried out, vapor-phase aliquots were analyzed during the polymerization by mass spectrometry, and the formation of 1,3-dioxolane was detected. 

Despite certain intrinsic statistical disadvantages the linear least-square procedures can sometimes provide satisfactory rlf r2 estimates when the copolymerization experiment is properly designed. Instead of conducting all the measurements over the random range of the initial monomer feed composition, one should carry them out only at the two following values ... 

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 last four methods cited [8-11] are statistically inexact, in that they cannot give good estimates of the reactivity ratio values, but they can provide good estimates of r and r2 if the copolymerization experiments are suitably designed. 

The extensive reactivity ratio data in the literature exhibit a wide scatter for many monomer pairs. This is partly due to errors in copolymer analysis and computational methods that result in larger uncertainties in n and Z2 than was realized when the results were reported. Another factor reflects the frequent reliance on an inadequate number of data points because copolymerization experiments lend to be tedious and time consuming. 

Table 1 is a compilation of relatively large scale copolymerization experiments carried out to collect material sufficient for characterization and jdiysical property studies. Results of experiments conducted to elucidate the effects of reaction variables on reactivity ratios i.e., small scale runs ( 20 ml), are listed separately later. 

Yamashita et al. [146] point out some features of the basicity of cyclic ethers. The basicity is affected by chemical structure, ring size, and substituents. The ring size affects basicity in the order 4 > 5 > 6 > 3. In 5-membered rings the basicity order is ether > lactone > formal. Methyl substitution increases the basicity and chloromethyl substitution decreases basicity. The relative basicities of the monomers are broadly in agreement with their reactivity in copolymerization experiments [58, 122]. 

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. 

Consequently, the PEMA azlrldlnlum Ion and the TBA azlrldlnlum Ion must have similar reactivities towards the TBA monomer. This Is a strong evidence that the main reason for the much slower polymerization of PEMA compared with TBA must be the lower reactivity of the PEMA monomer rather than a lower reactivity of the PEMA azlrldlnlum Ion. The validity of this statement Is now further Investigated by copolymerization experiments. 

H5P, an a-methylstyrene derivative, seems to have a low ceiling temperature and consequently did not homopolymerize but underwent copolymerization with styrene, methyl methacrylate, and n-butyl acrylate. Based on the homopolymerization attempts, it appears that 2H5P is present as isolated monomer units in these copolymers. The co-polymerization parameters of 2H5V and 2H5P with styrene, methyl methacrylate, and n-butyl acrylate have also been determined. The results are shown in Figure 3 The copolymerization experiments were done to 5 conversions. 

If the complexed radical is inactive (k n = kx 2 = k22 = k21 = 0), Eq. (7.8) reduces to the ordinary Mayo-Lewis equation and no solvent effect on the reactivity ratio will be observed. Busfield et al.108) studied the solvent effect on the free radical copolymerization of vinyl acetate and methyl methacrylate. The methyl methacrylate content is unaffected by benzene and ethyl acetate. This result seems to be consistent with our assumption that the complexed radical is inactive in propagation. However, the solvent effect might not be observed in the case in which the reactivity of the complexed radical is proportional to that of the uncomplexed radical, because also in this case Eq. (7.8) reduces to the Mayo-Lewis form. It is difficult, therefore, to expect from the copolymerization experiment some evidence to support the concept of the complex formation. 

Methacrylic anhydride was prepared from methacroyl chloride and either sodium methacrylate (14) or methacrylic acid (15). The relative intensity of resonance observed at 6=11.6 ppm in the nmr spectrum of this monomer and the intensity of carbonyl absorption observed at 1700 cm-1, relative to that observed at 1724 and 1782 cm-1 Indicated that the monomer had less than 3 mole percent methacrylic acid. For the most part, monomer used for copolymerization experiments, b.p. 50° (1 mm), was prepared from sodium methacrylate. It contained less than one mole percent methacrylic acid ... 

The view of chain growth at the transition metal center finds strong support from the results of copolymerization experiments... 

The copolymerization behavior of VC A has been the subject of several investigations including some in industry (12-20). Comonomers of different types have been used for copolymerization experiments however, with the exception of N-vinylpyrrolidone (14) and isobutyl vinyl ether (20), VCA was incorporated into the copolymer only slightly. 

All copolymerization experiments were carried out in DMF (1.5 ml) at 65°C using azobis(isobutyronitrile) (AIBN) as initiator. The concentration of AIBN was kept constant (0.01 mole/kg monomer mixture), and the total weight of both monomers was always 3 g. The products were precipitated in a water/methanol mixture, and they were characterized by elemental analysis and IR spectrometry. 

Copolymerization of Vinylene Carbonate with Some Halo-Substituted Olefins. Copolymerization experiments were conducted using trans-dichloro-ethylene, vinylidene chloride, and CTFE since these monomers have a structural relation to the inhibiting impurities discussed above. With frans-dichloro-ethylene, no polymerization occurred, and only oligomers of VCA with a molecular weight of 300 were formed. Like dichlorovinylene carbonate, trans-dichloroethylene acts as an inhibitor, probably through degradative chain transfer by abstraction of a chlorine atom. 

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