Copolymerization reaction media

Tetiafluoioethylene—peifluoiopiopyl vinyl ethei copolymeis [26655-00-5] aie made in aqueous (1,2) oi nonaqueous media (3). In aqueous copolymerizations water-soluble initiators and a perfluorinated emulsifying agent are used. Molecular weight and molecular weight distribution are controlled by a chain-transfer agent. Sometimes a second phase is added to the reaction medium to improve the distribution of the vinyl ether in the poljmier (11) a buffer is also added. 

The refined grade s fastest growing use is as a commercial extraction solvent and reaction medium. Other uses are as a solvent for radical-free copolymerization of maleic anhydride and an alkyl vinyl ether, and as a solvent for the polymerization of butadiene and isoprene usiag lithium alkyls as catalyst. Other laboratory appHcations include use as a solvent for Grignard reagents, and also for phase-transfer catalysts. 

The different physical properties, the reactivity of comonomers, and the reaction medium affect copolymerization. The majority of the real processes of copolymerization of acrylamide are complicated. Therefore, copolymerization may not be characterized by the classic equations. The following are the main complicating factors in the copolymerization of acrylamide. 

The investigations have shown, however, that graft copolymerization carried out according to this method is accompanied with a simultaneous reaction of monomer homopolymerization which, naturally, reduces the effectiveness of the method. This is explained by the presence of hydroxyl radicals in the reaction medium, which are formed as formulated in the above scheme. 

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. 

The rate of copolymerization in a binary system depends not only on the rates of the four propagation steps but also on the rates of initiation and termination reactions. To simplify matters the rate of initiation may be made independent of the monomer composition by choosing an initiator which releases primary radicals that combine efficiently with either monomer. The spontaneous decomposition rate of the initiator should be substantially independent of the reaction medium, as otherwise the rate of initiation may vary with the monomer composition. 2-Azo-bis-isobutyronitrile meets these requirements satisfactorily. The rate Ri of initiation of chain radicals of both types Ml and M2 is then fixed and equal to 2//Cd[7], or twice the rate of decomposition of the initiator I if the efficiency / is equal to unity (see Chap. IV). The relative proportion of the two types of chain radicals created at the initiation step is of no real importance, for they wall be converted one into the other by the two cross-propagation reactions of the set (1). Melville, Noble, and Watson presented the first complete theory of copolymerization suitable for handling the problem of the rate. The theory was reduced to a more concise form by Walling, whose procedure is followed here. 

Short chain branches are frequently introduced into polymers by copolymerization. The chemical structure of the comonomer controls the type and length of the short chain branch. The polymerization catalyst, reaction conditions, and comonomer content in the reaction medium determine the probability of finding a branch at any particular location along a chain. Comonomers, and hence the short chain branches derived from them, can be introduced at random or as blocks. 

Radical polymerization is the most useful method for a large-scale preparation of various kinds of vinyl polymers. More than 70 % of vinyl polymers (i. e. more than 50 % of all plastics) are produced by the radical polymerization process industrially, because this method has a large number of advantages arising from the characteristics of intermediate free-radicals for vinyl polymer synthesis beyond ionic and coordination polymerizations, e.g., high polymerization and copolymerization reactivities of many varieties of vinyl monomers, especially of the monomers with polar and unprotected functional groups, a simple procedure for polymerizations, excellent reproducibility of the polymerization reaction due to tolerance to impurities, facile prediction of the polymerization reactions from the accumulated data of the elementary reaction mechanisms and of the monomer structure-reactivity relationships, utilization of water as a reaction medium, and so on. 

Monomer reactivity ratios are generally but not always independent of the reaction medium in radical copolymerization. There is a real problem here in that the accuracy of r values is often insufficient to allow one to reasonably conclude whether r or rx varies with changes in reaction media. The more recent determinations of r values by high-resolution NMR are much more reliable than previous data for this purpose. It has been observed that the... 

Deviations are also observed in some copolymerizations where the copolymer formed is poorly soluble in the reaction medium [Pichot and Pham, 1979 Pichot et al., 1979 Suggate, 1978, 1979]. Under these conditions, altered copolymer compositions are observed if one of the monomers is preferentially adsorbed by the copolymer. Thus for methyl methacrylate (M1 )-/V-vinylcarbazole (M2) copolymerization, r — 1.80, r2 = 0.06 in benzene but r — 0.57, > 2 0.75 in methanol [Ledwith et al., 1979]. The propagating copolymer chains are completely soluble in benzene but are microheterogeneous in methanol. /V-vinylcarba-zole (NVC) is preferentially adsorbed by the copolymer compared to methyl methacrylate. The comonomer composition in the domain of the propagating radical sites (trapped in the precipitating copolymer) is richer in NVC than the comonomer feed composition in the bulk solution. NVC enters the copolymer to a greater extent than expected on the basis of feed composition. Similar results occur in template copolymerization (Sec. 3-10d-2), where two monomers undergo copolymerization in the presence of a polymer. Thus, acrylic acid-2-hydroxyethylmethacrylate copolymerization in the presence of poly(V-vinylpyrrolidone) results in increased incorporation of acrylic acid [Rainaldi et al., 2000]. 

Another characteristic feature of ionic copolymerizations is the sensitivity of the monomer reactivity ratios to changes in the initiator, reaction medium, or temperature. This is quite different from the general behavior observed in radical copolymerization. Monomer reactivity ratios in radical copolymerization are far less dependent on reaction conditions. 

The simplest procedure for grafting copolymerization, in terms of number of components in the reaction medium, is a bulk polymerization of the monomer in mixture with the molten polyamide. This has been claimed in an earlier patent (2), related to improvements in dyeability and hydrophylic properties of the resulting yam, obtained by melt spinning of the product of reaction with monomers such as 2,5-dichloro styrene, lauryl methacrylate, N-vinyl pyrrolidone, and N-vinyl carbazole. 

Heterogeneous Copolymerization. When copolymer is prepared in a homogeneous solution, kineiic expressions can be used to predict copolymer composition Bulk and dispersion polymerization are somewhat different since the reaction medium is heterogeneous and polymeri/aiion occurs simultaneously in separate loci. In bulk polymerization, for example, the monomer swollen polymer particles support polymerization within the particle core us well as on the particle surface, lit aqueous dispersion or emulsion polymeri/aiion the monomer is actually dispersed in two or three distinct phases a continuous aqueous phase, a monomer droplet phase, and a phase consisting of polymer particles swollen at Ihe surface with monomer. This affect the ultimate polymer composition because llie monomers are partitioned such that the monomer mixture in the aqueous phase is richer in the more water-soluble monomers than the two organic phases. 

At present, we can say that copolymerization initiated by various salts proceeds by an anionic mechanism, after dissociation of the initiators in the reaction medium. The primary step is the addition of the initiator anion to the epoxide. In the initiation by Lewis bases, i.e. by tertiary amines, initiation involves formation of a primary active centre of an anionic character. This active centre is probably generated by interaction of the tertiary amine with the anhydride and an allyl alcohol. The allyl alcohol can be formed by a base-catalyzed isomerization of the epoxide. In the presence of a proton donor, the formation of active centres is possible through interaction of tertiary amine, anhydride and proton donor without epoxide isomerization. Another way of initiation consists in a direct reaction of epoxide with tertiary amine yielding an anionic primary active centre. We believe that in both kinds of initiation in the strict absence of proton donors, the growing chain end has the character of a living polymer. The presence of proton donors, however, gives rise to transfer reactions. 

Thus the use amphiphilic macromonomers is another method to achieve the particle formation and their subsequent stabilization. Macromonomers can be pre-reacted to form graft copolymers, which are be introduced into the reaction medium afterwards. Macromonomers can also be copolymerized with classical monomers in situ to form graft copolymers. This is a simple and flexible method for producing monodisperse micron-sized polymer particles. Macromonomers can produce ion-free acrylic lattices with superior stability and film forming properties compared to conventional charge stabilized lattices. These non-con-... 

Reaction medium. When lignosulfonate was subjected to graft copolymerization with vinyl monomers, the extent of copolymerization due to the effect of medium varied from one monomer to another. In a LS-styrene system (16), it was found that methanol was a better medium than water under certain given conditions while in a LS-acrylonitrile system (17),the contrary was true, i.e., water better than methanol. This contradiction was thought due to the fact that styrene has electropositive (i.e., electronreleasing) substituent while acrylonitrile has electronegative (i.e., electron-attracting) substituent. In the present study,... 

Table II. Homogeneous Graft Copolymerization of Styrene onto Cellulose Using a SO2-DEA-DMSO Solution as a Reaction Medium...

Thermoplasticization of Wood by Graft Copolymerization in De-crystallized State. We have reported that wood can effectively be decrystallized without a weight-loss by treating with a non-aqueous cellulose solvent, the SO2-DEA-DMSO solution (11). Thus, use of the non-aqueous cellulose solvent as a reaction medium for the graft-copolymerization of monomers to wood was expected to result in products with branch polymers more uniformly distributed. The results obtained by the homogeneous grafting of cellulose (10) were expected to support this idea. 

Figure 9. Plots of the deformation vs. temperature for W-O, untreated wood, and SW—1, -3, —5, and -6, the wood-polysulfone composites prepared by the graft copolymerization using a SO3-DEA-DMSO solution as a reaction medium. The weight increases are SW-1, 7.9% SW-3, 11.4% SW-5, 14.9% and SW-6,...

During the initial polymerization of trioxane with (C4H9)2OBF3 in melt or solution, no solid polymer is formed, and the reaction medium remains clear. Using a high resolution NMR spectroscope, C. S. H. Chen and A. Di Edwardo observed the appearance of soluble linear polyoxy-methylene chains. In the cationic copolymerization of trioxane with 1,3-dioxolane, V. Jaacks found also that a soluble copolymer forms first and turns later into a crystalline copolymer of different composition. Crystallization and polymerization proceed simultaneously in the solid phase. 

Arylcarbonyl Compounds as Initiators for Unsaturated Polyester/ Styrene Copolymerization Systems. Gel Time Determination and Reaction Curves. Ten blanks (gel time of 20 grams Vestopal A without initiator) gave a mean deviation from the average of 3.3% and a maximum deviation of 7.2%. Five measurements with l-phenyl-2-propanone as initiator gave a mean deviation from the average of 3.3% and a maximum deviation of 7.7%. An experimental error of 10% was therefore assumed and proved correct by spot checks. The exceptions (not used in the discussions) are most probably caused by the insolubility of the initiators in the reaction medium. 

Tn the cationic polymerization and copolymerization of trioxane in the - melt or in solution, an induction period usually exists, during which no solid polymer is formed and the reaction medium remains clear. Nevertheless, reactions are known to occur during this period. By using BF3 or an ether ate as catalyst, in homopolymerization, Kern and Jaacks (I) reported the formation of formaldehyde via depolymerization of polyoxymethylene cations. 

Figure 4 shows that the formation of the methacrylic network is also somewhat influenced by the amount of OcSn, though a 100% conversion is always reached after about two hours. This observation may be related to the viscosity of the reaction medium its increase accelerates the radical copolymerization. The already mentioned OcSn-AIBN interaction has a similar effect, by inducing a faster decomposition of AIBN into radicals (Tabka, M. T. Widmaier, J. M. Meyer, G. C., to be published). 

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