Vinylpyridines anionic polymerization

Application of amphiphilic block copolymers for nanoparticle formation has been developed by several research groups. R. Schrock et al. prepared nanoparticles in segregated block copolymers in the sohd state [39] A. Eisenberg et al. used ionomer block copolymers and prepared semiconductor particles (PdS, CdS) [40] M. Moller et al. studied gold colloidals in thin films of block copolymers [41]. M. Antonietti et al. studied noble metal nanoparticle stabilized in block copolymer micelles for the purpose of catalysis [36]. Initial studies were focused on the use of poly(styrene)-folock-poly(4-vinylpyridine) (PS-b-P4VP) copolymers prepared by anionic polymerization and its application for noble metal colloid formation and stabilization in solvents such as toluene, THF or cyclohexane (Fig. 6.4) [42]. 

Alkyl derivatives of the alkaline-earth metals have also been used to initiate anionic polymerization. Organomagnesium compounds are considerably less active than organolithiums, as a result of the much less polarized metal-carbon bond. They can only initiate polymerization of monomers more reactive than styrene and 1,3-dienes, such as 2- and 4-vinylpyridines, and acrylic and methacrylic esters. Organostrontium and organobarium compounds, possessing more polar metal-carbon bonds, are able to polymerize styrene and 1,3-dienes as well as the more reactive monomers. 

Penultimate effects have been observed for many comonomer pairs. Among these are the radical copolymerizations of styrene-fumaronitrile, styrene-diethyl fumarate, ethyl methacrylate-styrene, methyl methacrylate l-vinylpyridine, methyl acrylate-1,3-butadiene, methyl methacrylate-methyl acrylate, styrene-dimethyl itaconate, hexafluoroisobutylene-vinyl acetate, 2,4-dicyano-l-butene-isoprene, and other comonomer pairs [Barb, 1953 Brown and Fujimori, 1987 Buback et al., 2001 Burke et al., 1994a,b, 1995 Cowie et al., 1990 Davis et al., 1990 Fordyce and Ham, 1951 Fukuda et al., 2002 Guyot and Guillot, 1967 Hecht and Ojha, 1969 Hill et al., 1982, 1985 Ma et al., 2001 Motoc et al., 1978 Natansohn et al., 1978 Prementine and Tirrell, 1987 Rounsefell and Pittman, 1979 Van Der Meer et al., 1979 Wu et al., 1990 Yee et al., 2001 Zetterlund et al., 2002]. Although ionic copolymerizations have not been as extensively studied, penultimate effects have been found in some cases. Thus in the anionic polymerization of styrene t-vinylpyri-dine, 4-vinylpyridine adds faster to chains ending in 4-vinylpyridine if the penultimate unit is styrene [Lee et al., 1963]. 

Preparation of a Multiblock Copolymer of 4-Vinylpyridine and Styrene by Anionic Polymerization... 

Eor comparison, polystyrene and poly(4-vinylpyridine) are prepared by anionic polymerization with sodium naphthalene as initiator. Poly(4-vinylpyridine) precipitates from THE the mixture is poured into 200 ml of diethyl ether and the polymer filtered off.The polymer is then reprecipitated from pyridine solution into a ten-fold amount of diethyl ether and dried in vacuum. 

One of the most interesting processes in electrically initiated polymerization was an initiation with the solvated electron proposed by Laurin and Parravano (22), who studied electro-anionic polymerization of 4-vinylpyridine in liquid ammonia solution of alkali metal salts in the temperature range — 33 to — 78° C. Rapid and efficient polymerization occurred and conversions of monomer to polymers formed exclusively at the cathode in the form of an orange-red, porous, solid deposit, suggesting the formation of a pile of living polymers. 

The solvation of ion pairs may also arise from intramolecular interaction. For example, the high reactivity of living poly(2-vinylpyridine) is probably caused by the intramolecular solvation of the Na+ ion by the adjacent pyridine rings (16, 23, 32). Interesting example of such a solvation has been discovered by Smets and van Beylen (30), who studied anionic polymerization of p- and o-methoxystyrene. The ion pair of the latter living polymer, but not of the former, showed exceptional reactivity, and the model reveals that only the o-methoxy group can participate in the intramolecular solvation. 

Catalysts of the Ziegler type have been used widely in the anionic polymerization of 1-olefins, diolefins, and a few polar monomers which can proceed by an anionic mechanism. Polar monomers normally deactivate the system and cannot be copolymerized with olefins. However, it has been found that the living chains from an anionic polymerization can be converted to free radicals in the presence of peroxides to form block polymers with vinyl and acrylic monomers. Vinylpyridines, acrylic esters, acrylonitrile, and styrene are converted to block polymers in good yield. Binary and ternary mixtures of 4-vinylpyridine, acrylonitrile, and styrene, are particularly effective. Peroxides are effective at temperatures well below those normally required for free radical polymerizations. A tentative mechanism for the reaction is given. 

With the purpose of increasing the range of available block copolymers, comonomers other than methacrylates and acrylates can also be involved in sequential polymerization, provided that they are susceptible to anionic polymerization. Dienes, styrene derivatives, vinylpyridines , oxiranes and cyclosiloxanes are examples of such comonomers. The order of the sequential addition is, however, of critical importance for the synthesis to be successful. Indeed, the pX a of the conjugated acid of the living chain-end of the first block must be at least equal to or even larger than that of the second monomer. Translated to a nucleophilicity scale, this pK effect results in the following order of reactivity dienes styrenes > vinylpyridines > methacrylates and acrylates > oxiranes > siloxanes. 

The macromonomers were prepared by anionic polymerization of 2-vinylpyridine followed by reaction with ethylene oxide and methacrylic acid chloride [111] as shown in Scheme 1. MALDI-TOF mass spectroscopy was utilized in order to determine the absolute molar mass and the degree of end-functionalization as given in Table 4. The sample code MM-PVPXY comprises the polymerizable unit (MM=methacrylate), the side chain (PVP=polyvinylpyridine) and the side chain degree of polymerization XY. 

Electropolymerization Based on 4-Vinylpyrldlne and Related Ligands. The third technique for preparing electrode/film interfaces is in many ways the most interesting both in terms of the chemistry involved and the results so far obtained. The strategy is to induce polymerization directly at the electrode surface by oxidation or reduction and our emphasis has been on the reduction of coordinated 4-vinylpyridine and related compounds. It is known that 4-vinylpyridine is susceptible to anionic polymerization (38). 

Optically active poly(3-methyl-4-vinylpyridine) ([a]-4589 +14.2°) (39) has been prepared by anionic polymerization of the corresponding monomer using the (—)-DDB—DPEDA—Li complex in toluene at —78... 

Hogen-Esch et al.172 synthesized a,a -dilithium poly(2-vinylpyridine) by anionic polymerization of 2-vinylpyridine with 1,4-dilithio-l, 1,4,4-tetraphenyl-butane, in THF at —78 °C under inert atmosphere. The cyclization reaction was performed in high dilution by adding 1,4-bis(bromomethyl)benzene (Scheme 83). The main indication for the formation of the cyclic polymers was the significant difference in the Tg value between the cyclic and the linear precursor. 

Predict the order of reactivity (and justify your prediction) of the given monomers, (a) Styrene, 2-vinylpyridine, 3-vinylpyridine, and 4-vinyl pyridine in anionic polymerization, (b) Styrene, p-methoxystyrene, p-chlorostyrene, and p-methylstyrene in cationic polymerization. 

It has been demonstrated by Bhadani and Parravano that pyridine anion radicals, formed by electrochemical reduction, are able to initiate the polymerization of 4-vinylpyridine, if the monomer is added to the yellow or blue pre-electrolyzed pyridine solution54. The yellow color is attributed to the Py and the blue one to the 4,4 -Bipy anion radicals. 4-Vinylpyridine, if present during the electrolysis undergoes direct cathodic reduction giving rise to anionic polymerization. 

Anionic polymerization of 4-vinylpyridine by Ba[CMe2Ph]2 occurs in THF, giving a non-stereospecific polymer 2-vinylpyridine is also polymerized by Ba[CMe2Ph]2 or difunctional initiator Ba[Ph2CCH2CH2CPh2], giving >50% isotactic linkages. ... 

Use SpartanView to compare electrostatic potential maps of styrene + hydride anion, 2-vinylpyridine + hydride anion, and 3-vinylfuran + hydride anion. Are either of the two heterocycles as effective as styrene at delocalizing the developing negative charge during anionic polymerization Next, compare electrostatic potential maps of neutral styrene, 2-vinylpyridinc, and 3-vinylfuran. Why don t the heterocyclic alkenes lend themselves to cationic polymerization ... 

Polar Vinyl Monomers The anionic polymerization of polar vinyl monomers is often complicated by side reactions of the monomer with both anionic initiators and growing carbanionic chain ends, as well as chain termination and chain transfer reactions. However, synthesis of polymers with well-defined structures can be effected under carefully controlled conditions. The anionic polymerizations of alkyl methacrylates and 2-vinylpyridine exhibit the characteristics of living polymerizations under carefully controlled reaction conditions and low polymerization temperatures to minimize or eliminate chain termination and transfer reactions [118, 119]. Proper choice of initiator for anionic polymerization of polar vinyl monomers is of critical importance to obtain polymers with predictable, well-defined structures. As an example of an initiator that is too reactive, the reaction of methyl methacrylate (MMA)... 

Triblock and random polyampholytes based on DMAEM-MMA-MAA were examined for their phase separation behaviour [52]. Triblock polyampholytes have a much broader phase separation region than the random ones. The specific structure of PMAA-fc-PlM4VPCl with the excess of cationic or anionic blocks at the lEP is close to the structure of non-stoichiometric IPC. It is suggested that its nucleus consists of intraionic IPC surrounded by cationic blocks protecting it from precipitation [53]. ABC triblock copolymers of polystyrene-b/ock-poly(2-(or 4)vinylpyridine)-fc/ock-poly(methacrylic acid) were synthesized by living anionic polymerization [53 a]. Interpolymer complexation of the polyvinylpyri-dine and poly(methacrylic acid) blocks in the micellar solution was studied in relation to pH in solution by potentiometric, conductimetric and turbidimetric titration and in bulk by FTIR spectroscopy. 

In the context of the anionic polymerization of CA derivatives, as considered in Section 10.3.2.2.1, it is notable that the polymerization of cyanoacrylates is also photoinitiated by substituted pyridine pentacarbonyl complexes of tungsten or chromium, i.e. M(CO)5L with M = Cr or W, and L = 2- or 4-vinylpyridine [60]. Photo-released pyridine adds to CA, and the resulting zwitterion initiates the anionic chain polymerization (see Scheme 10.16). 

Anionic polymerization is known to give model block copolymers with controlled molecular weights, narrow molecular weight distributions and versatile architecture. Anionic polymerization has been used for the synthesis of DHBCs in several eases although this type of polymerization teehnique is relatively intolerant to the presence of polar functionalities on the monomers utilized. A recent example has been described by Hadjichristidis and coworkers [6]. They have presented the synthesis of a series of poly (2-vinylpyridine-b-... 

In contrast, the anionic polymerization of 4-vinylpyridine suffers from an extremely rapid propagation and poor polymer solubility in THF. An improved procedure has recently been proposed to prevent polymer precipitation by using a mixed solvent of pyridine and THF (9/1, v/v) [66]. Even at 0 °C, the polymerization proceeded homogeneously, yielding well-defined poly(4-vinylpyridine)s. 

The living anionic polymerization of 4-(2-pyridiyl)styrene was reported by Lee et al. [67]. The resulting living polymer was very similar in behavior and reactivity to living poly(2-vinylpyridine), but not to living PS. 

The addition reaction of the functional DPE derivative to a Hving anionic polymer is not, in itself, a termination reaction. After the reaction, the chain-end anion is changed to a DPE-derived anion, which can initiate an anionic polymerization of additional monomers, such as styrene, 2-vinylpyridine, or methyl methacrylate, to extend the chain or to form a new block (Scheme 5.17). Thus, this reaction offers the potential of providing a quite novel chain-functionalization procedure, with which the functional groups can be introduced at essentially any position in a polymer chain [174]. Accordingly, functionalization using functional DPE derivatives is a versatile procedure, not only for the preparation of chain-end-functionaUzed polymers but also for in-chain-functionalized polymers that are difficult to synthesize by any other method [172-174]. 

In contrast, the order of monomer addition is critical among monomers with different reactivities. As described in Section 5.1, a more-reactive chain-end anion is produced by a less-reactive monomer, and vice versa. Accordingly, less-reactive monomers should first be polymerized, followed by the polymerization of more-reactive monomers. In the block copolymer of styrene and MMA, for instance, it is necessary first to polymerize styrene, after which MM A is polymerized to prepare the second block, as the chain-end enolate anion produced by MMA cannot initiate the polymerization of styrene. Similarly, and for the same reason, the synthesis of P(2)-b-PMMA is possible only by the addition of 2-vinylpyridine first, and then MMA. For the successful design and synthesis of block copolymers, the pJ values of the conjugated acids of chain-end anions, as well as the e- and a-values of monomers (as mentioned above) are valuable guides. The details of almost all block copolymers synthesized to date, using living anionic polymerization, have been summarized by Quirk and Hsieh [190]. With the monomer addition order in mind, ABC triblock terpolymers composed of PS (A), PB (B), and PMMA (C), as well as PS (A), poly(2-vinylpyridine) (P(2VP)) (B), and P BMA (C), could be successfully... 

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