Copolymerization, radical

TABLE 6-1 Predicted and Experimental Compositions in Radical Terpolymerization  

The discussions thus far have been quite general without any specification as to whether copolymerization occurs by radical or ionic propagation. Consider now some of the specific characteristics of radical copolymerization. 

As already discussed for homopolymerization, radical copolymerizations can be carried out in bulk, in solution, and in dispersion. The composition of the copolymer obtained in suspension or emulsion may be different from that obtained by polymerization in bulk or solution if one of the monomers is more soluble in water than the other. In such a case the composition of the monomer mixture in the organic phase, or in the micelles where the copolymerization takes place, is not the same as the original composition. 

There are no essential differences in experimental technique required for ionic copolymerizations, as compared with ionic homopolymerizations. However, the type of initiator and the solvent have a potential influence on the course of ionic copolymerizations as well as on the composition of the copolymers so that the optimum conditions for each monomer pair must be individually determined. 

Finally, it should be mentioned that there exist two other routes for the synthesis of copolymers. First the partial chemical conversion of homopolymers (see Sect. 5.1), for example, the partial hydrolysis of poly(vinyl acetate). Secondly, by homopolymerization of correspondingly built monomers. An example for these macromolecular compounds, sometimes called pseudo-copolymers, is the alternating copolymer of formaldehyde and ethylene oxide synthesized by ringopening polymerization of 1,3-dioxolane. 

It should be pointed out that in both cases the copolymers cannot be obtained via normal copolymerization of the corresponding monomers. 

Copolymerization of Styrene with Methyl Methaaylate (Dependence on Type of Initiation) 

VFc has been copolymerized with common monomers such as styrene [19], methyl methacrylate [19], N-vinylpyrollidone [20], and acrylo nitrile [19]. The electron richness of VFc has been demonstrated in its copolymerization with maleic anhydride, in which an alternating composition of the copolymer was observed over a wide range of feed ratios [16, 19]. The Q and e values of VFc were determined. The value of e = -2.1 again emphasizes the electron rich nature of the vinyl group of VFc [21]. Therefore it looked rather hopeless to apply anionic initiators for the polymerization of VFc. 

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Styrene-butadiene rubber is prepared from the free-radical copolymerization of one part by weight of styrene and three parts by weight of 1,3-butadiene. The butadiene is incorporated by both 1,4-addition (80%) and 1,2-addition (20%). The configuration around the double bond of the 1,4-adduct is about 80% trans. The product is a random copolymer with these general features ... 

In some instances, the resist polymer can be prepared in a single step by direct polymerization of the protected monomer(s) (37,88), entirely avoiding the intermediate PHOST. HOST-containing resist polymers have also been prepared by free-radical copolymerization of a latent HOST and a stable, acid-labile monomer, eg, the copolymerization of acetoxystyrene with tert-huty acrylate, followed by selective removal of the acetoxy group (89) (Fig. 30). 

Fig. 30. Synthesis of an acid-labile copolymer by radical copolymerization using a latent HOST, followed by selective deprotection (89).

In all manufacturing processes, grafting is achieved by the free-radical copolymerization of styrene and acrylonitrile monomers in the presence of an elastomer. Ungrafted styrene—acrylonitrile copolymer is formed during graft polymerization and/or added afterward. 

Table 5. Free-Radical Copolymerization Reactivity Ratios,...

Free-radical copolymerizations have been performed ia bulb (comonomers without solvent), solution (comonomers with solvent), suspension (comonomer droplets suspended ia water), and emulsion (comonomer emulsified ia water). On the other hand, most ionic and coordination copolymerizations have been carried out either ia bulb or solution, because water acts as a poison for many ionic and coordination catalysts. Similarly, few condensation copolymerizations iavolve emulsion or suspension processes. The foUowiag reactions exemplify the various copolymerization mechanisms. 

Free-Radical Gopolymerization. Examples of the types of copolymers formed by free-radical copolymerizations are shown ia equations 18—20, where S = styrene [100-42-5] B = butadiene [106-99-0] and AIBN = azobisisobutyronitrile [78-67-1] (see Initiators) (27—29). 

Radical copolymerization is used in the manufacturing of random copolymers of acrylamide with vinyl monomers. Anionic copolymers are obtained by copolymerization of acrylamide with acrylic, methacrylic, maleic, fu-maric, styrenesulfonic, 2-acrylamide-2-methylpro-panesulfonic acids and its salts, etc., as well as by hydrolysis and sulfomethylation of polyacrylamide Cationic copolymers are obtained by copolymerization of acrylamide with jV-dialkylaminoalkyl acrylates and methacrylates, l,2-dimethyl-5-vinylpyridinum sulfate, etc. or by postreactions of polyacrylamide (the Mannich reaction and Hofmann degradation). Nonionic copolymers are obtained by copolymerization of acrylamide with acrylates, methacrylates, styrene derivatives, acrylonitrile, etc. Copolymerization methods are the same as the polymerization of acrylamide. 

Poly(MA-CDA) was synthesized by a free radical copolymerization of maleic anhydride and 7,12-diox-aspiro-[5,6]-dodec-9-ene, followed by hydrolysis in... 

Poly(MA-CDA) was synthesized as described previously by a free radical copolymerization followed by hydrolysis in aqueous solution. By the fractional precipita- n of the copolymerization product (MW = 14,200, MW/Mn = 3.1) different average-molecular weight po-ly(M A-CDA)s with narrow polydispersity were obtained as shown in Table 2. 

It was recently found that j3-PCPY can also be used as a radical initiator to obtain an alternate copolymer of MMA with styrene [35], which was only possible in the presence of Lewis acids [36,37] in the past. The kinetics of the system has been formulated as Rp a[/3-PCPY] a[MMA] (l/a[Styrene] The values of kp /k, and AE were evaluated as 1.43 x 10 L mol -s and 87 kJ/ mol, respectively, for the system. NMR spectroscopy was used to determine the structure composition and stereochemistry of copolymers. Radical copolymerization of AN with styrene [38] by using /3-PCPY as the initiator at 55-65°C also resulted in an alternate copolymer. Rp is a direct function of /3-PCPY and AN, and is inversely related to styrene. 

In contrast to /3-PCPY, ICPY did not initiate copolymerization of MMA with styrene [39] and AN with styrene [40]. However, it accelerated radical polymerization by increasing the rate of initiation in the former case and decreasing the rate of termination in the latter case. The studies on photocopolymerization of MMA with styrene in the presence of ICPY has also been reported [41], /8-PCPY also initiated radical copolymerization of 4-vinylpyridine with methyl methacrylate [42]. However, the ylide retarded the polymerization of N-vinylpyrrolidone, initiated by AIBN at 60°C in benzene [44]. (See also Table 2.)... 

MMA and DMAPMA poly(MMA-co-DMAPMA) 23, obtained by radical copolymerization, can produce a photografting reaction with acrylonitrile (AN) using BP as the initiator [61]. The formation of a graft copolymer, poly[(MMA -c<7-DMAPMA)- -AN] was confirmed by FT-IR spectrophotometry. Based on ESR studies and end group analysis, the mechanism of grafting reaction is proposed as follows ... 

Fig. 1. Comparison of experimental and theoretical values of Mc at free-radical copolymerization of AAm with MBAA as a crosslinking agent CT — total concentration of monomers, C — that of MBAA C = 10 wt% (/), CT = 6.7 g dl-1 (2). From Baselga et al. [18]...

To determine the crosslinking density from the equilibrium elastic modulus, Eq. (3.5) or some of its modifications are used. For example, this analysis has been performed for the PA Am-based hydrogels, both neutral [18] and polyelectrolyte [19,22,42,120,121]. For gels obtained by free-radical copolymerization, the network densities determined experimentally have been correlated with values calculated from the initial concentration of crosslinker. Figure 1 shows that the experimental molecular weight between crosslinks considerably exceeds the expected value in a wide range of monomer and crosslinker concentrations. These results as well as other data [19, 22, 42] point to various imperfections of the PAAm network structure. 

In which the ratio m/n is close to 3. The silane was produced by free radical copolymerization of vinyltriethoxysilane with N-vinylpyrrolidone. Its number-average molecular weight evaluated by vapour-phase osmometry was 3500. Porous silica microballs with a mean pore diameter of 225 A, a specific surface area (Ssp) of 130 m2/g and a pore volume of 0.8 cm3/g were modified by the silane dissolved in dry toluene. After washings and drying, 0.55% by weight of nitrogen and 4.65% of carbon remained on the microballs. Chromatographic tests carried out with a series of proteins have proved the size-exclusion mechanism of their separation. 

Several wide-porous affinity and size-exclusion chromatographic supports were prepared by Ivanov, Zubov et al. by means of acylation of aminopropyl-glass supports by copolymers of N-vinyl pyrrolidone (N-VP,1) and acryloyl chloride (AC,2), M = 7700 and 35000 respectively [50, 51]. The copolymers prepared by free radical copolymerization contain their units almost in equimolar proportion, with high tendency to alternation expected from the copolymerization parameters (rj = 0.035, r2 = 0.15 [52]). Residual carbonyl chloride groups of the chemisorbed copolymer could be transformed to 2-hydroxyethylamides which were solely... 

Kuchanov, S. Modern Aspects of Quantitative Theory of Free-Radical Copolymerization. Vol. 103, pp. 1-102. 

Several radical copolymerizations of vinyl 2-furoate with well-known monomers (50 50) were also studied. Complete inhibition was obtained with vinyl acetate, very strong retardation with styrene, vinyl chloride and acrylonitrile methyl methacrylate homopolymerized without appreciable decrease in rate. It is evident that the degree of retardation that vinyl 2-furoate imposes upon the other monomer depends on the stability of the latter s free radical. With styrene and vinyl chloride the small amounts of fairly low molecular-weight products contained units from vinyl 2-furoate which had entered the chain both through the vinyl bond and through the ring (infrared band at 1640 cm-1). 

As early as 1940 it has been established9 that diketene does not polymerize by a radical mechanism. It has, however, been shown later10 that it undergoes reactions of radical copolymerization with many vinyl monomers11. In this reaction the double bond is involved and the lactone ring is preserved in the copolymer. 

It has been shown by Schulz and Kern2 J that the radical polymerization of acrolein can take the course of the 1,2-mechanism as well as that of the 1,4- or 3,4-mechanism leading to formylethylene, oxy-2-propenylene, or oxy-2-propenylidene units, respectively. This behaviour of acrolein and its derivatives seems to be also retained to a certain extent, in the radical copolymerization of 4 with AN causing a decrease fo the content of aldehyde groups in the copolymers. 

The rates of addition to the unsubstituted terminus of monosubstituted and 1,1-disubstiluted olefins (this includes most polymerizable monomers) are thought to be determined largely by polar Factors.2 16 Polymer chemists were amongst the first to realize that polar factors were an important influence in determining the rate of addition. Such factors can account for the well-known tendency for monomer alternation in many radical copolymerizations and provide the basis for the Q-e, the Patterns of Reactivity, and many other schemes for estimating monomer reactivity ratios (Section 7.3.4). 

Studies on radical copolymerization and related model systems have demonstrated that many factors can influence the rate and course of propagation in copolymerization. These include ... 

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 effects of solvent on radical copolymerization are mentioned in a number of reviews.69 72 97,98 For copolymerizations involving monomers that arc ionizablc or form hydrogen bonds (AM, MAM, HEA, HEMA, MAA, etc.) solvent effects on reactivity ratios can be dramatic. Some data for MAA-MMA copolymerization are shown in Table 8.4.w... 

Matyjaszewski and coworkers 190,191 have explored living radical copolymerization (ATRP and RAFT) in the presence of Lewis acids. 

One of the major advantages of radical polymerization over most other forms of polymerization, (anionic, cationic, coordination) is that statistical copolymers can be prepared from a very wide range of monomer types that can contain various unprotected functionalities. Radical copolymerization and the factors that influence copolymer structure have been discussed in Chapter 7. Copolymerization of macromonomers by NMP, ATRP and RAFT is discussed in Section 9.10.1. 

An issue in living radical copolymerization is that the conditions for dormant chain activation can vary substantially according to the particular propagating radical. The problem may be mitigated by two factors. 

Atom transfer radical copolymerization can be described by a scheme similar to that shown in Scheme 9.48 except that bimolecular activation steps must be added ( Section 9.4). Copolymerization by ATRP through 2001 has been reviewed by Kelly and Matyjaszewski.554 A summary of ATRP copolymerizalions appears in Table 9.21. 

The grafting through approach involves copolymerization of macromonomers. NMP, ATRP and RAFT have each been used in this context. The polymerizations are subject to the same constraints as conventional radical polymerizations that involve macromonomers (Section 7.6.5). However, living radical copolymerization offers greater product uniformity and the possibility of blocks, gradients and other architectures. 

The book commences with a general introduction outlining the basic concepts. This is followed by a chapter on radical reactions that is intended to lay the theoretical ground-work for the succeeding chapters on initiation, propagation, and termination. Because of its importance, radical copolymerization is treated in a separate chapter. We then consider some of the implications of these chapters by... 

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