Pyridine anionic polymerization

As previously described, all microspheres discussed in this chapter were synthesized from AB type diblock copolymers. Precursor block copolymers, poly(styrene-b-4-vinyl pyridine) (P[S-b-4VP]) diblock copolymers, were synthesized using the additional anionic polymerization technique [13]. The basic properties of the block copolymers were determined elsewhere [24,25] and are listed... 

As these block copolymers were synthesized using the anionic polymerization technique, their molecular weight distributions were narrow. The microspheres with narrower size distribution are better for well-ordered self-organization. Actually, all block copolymers synthesized for these works formed poly(4-vinyl pyridine) (P4VP) spheres in the PS matrices with narrow size distributions. 

The poly(styrene-b-isoprene) (P(S-b-IP)) and poly(-styrene-b-2-vinyl pyridine) (P(S-b-2VP)) block copolymers with narrow molecular weight distributions for blending with the microspheres were also synthesized using the additional anionic polymerization technique. The number-average molecular weights (Mns) and PS contents are also shown in Table 1. 

Twenty weakly acidic drugs, including niclosamide, were determined by a nonaqueous catalytic thermometric titration method. Catalysis of the anionic polymerization of acetonitrile was used for endpoint indication. The solvent used was a mixture of acetonitrile and dimethylformamide or pyridine, and the titrant was sodium methoxide, potassium hydroxide, tertiary butanol, or tertiary butanol-sodium nitrite. Recoveries, limits of detection and relative standard deviations were tabulated [31]. 

The stereoselective polymerization of various acrylates and methacrylates has been studied using initiators such as atkyllithium [Bywater, 1989 Pasquon et al., 1989 Quirk, 1995, 2002]. Table 8-12 illustrates the effects of counterion, solvent, and temperature on the stereochemistry of the anionic polymerization of methyl methacrylate (MMA). In polar solvents (pyridine and THF versus toluene), the counterion is removed from the vicinity of the propagating center and does not exert an influence on entry of the next monomer unit. The tendency is toward syndiotactic placement via chain end control. The extent of syndiotacticity... 

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. 

The anionic polymerization of 2-vinyl pyridine initiated by benzyl-2 pyridy lmethylmagnesiurn (benzyl picolyl magnesium) in hydrocarbon solvents, leads to highly isotactic polymers. 

Grodzinsky studied extensively the polymerization of nitroethylene using pyridine derivatives as catalyst and reported that this monomer polymerizes readily by anionic mechanism but not in the radical one (26). It is, at present, known to be one of the typical monomers of anionic polymerization. 

PL, unlike other lactones, undergoes polymerization with weakly nucleophilic initiators such as metal carboxylates, tertiary amines, phosphines, and a variety of other initiators [81-83]. This is primarily due to the high ring-strain in the four-membered ring. Pyridine and other tertiary amines initiate the anionic polymerization via a betaine that rapidly transforms into a pyridinium salt of acrylic acid. In order to minimize the chain transfer reactions, the polymerization is performed at a temperature between 0 and 10 °C (Scheme 9). 

Formaldehyde polymerizes by both anionic and cationic mechanisms. Strong acids are needed to initiate cationic polymerization and anionic polymerization is initiated by relatively weak bases (e.g., pyridine). Boron trifluoride (BF3) or other Lewis acids are used to promote polymerization where trioxane is the raw material. 

ABC copolymers polystyrene-polyisoprene-poly(vinyl-2-pyridine)(S.I.V2P) with number-molecular average weight of 23000,102000, and 23000 were prepared by stepwise anionic polymerization. Films obtained by solvent casting from methylcyclohexane and benzene were observed by electron microscopy after staining the polyisoprene block with osmium tetroxide or the poly(vinyl-2-pyridine)... 

Rossi has synthetized block copolymers polyisoprene-poly(vinyl-2-pyridine) and polyisoprene-poly(vinyl-4-pyridine) of various composition and molecular weight by anionic polymerization under high vacuum205, 208. The polymerization in THF dilute solutions with Cumylpotassium as initiator yielded a 1,2 + 3,4-microstructure of the polyisoprene block. The polymerization in toluene solutions with sec-butyl-lithium as initiator yielded a 1,4-c/s-microstructure of the polyisoprene block. 

Using anionic polymerization in THF solution and with diphenylmethylsodium as initiator, Grosius et al.2ls have synthetized block copolymers poly(vinyl-2-pyridine)-poly(vinyl4-pyridine). They have studied by low-angle X-ray scattering the structure of a copolymer V 2 P V 4 P with molecular weight of the blocks 15000 and 8000 respectively. In octanol, they have found a lamellar and a cylindrical structure as a function of solvent concentration. In THF, dioxan, and benzene they have only found a cylindrical structure. 

The preparation of poly(2-vinyl-pyridine), by radical or anionic polymerization of the corresponding monomer, has been described long time ago. Atactic or isotactic, partially crystallizable polymers may be obtained 30). Poly(4-vinyl-pyridine) may be prepared in a similar way 31). 

Catalysts of the Ziegler-Natta type are applied widely to the anionic polymerization of olefins and dienes. Polar monomers deactivate the system and cannot be copolymerized with olefins. J. L. Jezl and coworkers discovered that the living chains from an anionic polymerization can be converted to free radicals by the reaction with organic peroxides and thus permit the formation of block copolymers with polar vinyl monomers. In this novel technique of combined anionic-free radical polymerization, they are able to produce block copolymers of most olefins, such as alkylene, propylene, styrene, or butadiene with polar vinyl monomers, such as acrylonitrile or vinyl pyridine. 

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. 

TABLE 1. Polymer properties from four 50 minute anionic polymerization reactions using n-hexyl isocyante in THE with sodium A-phenyl benzyl amine as initiator and then quenching for 10 minntes using methacryloyl chloride dissolved in pyridine. 

Alkali metal salts with nucleophilic anions are notably good initiators for chloral anionic polymerization (Fig. 26). The most studied initiator is lithium ferf-butoxide. When 0.2 mole % of lithium ferf-butoxide (based on chloral) was added to neat chloral monomer at 60°C the alkoxide (CH3)3C0CH(CCl3)0 Li was formed instantaneously, but no further addition of chloral occurred. This reaction was observed by an NMR study of the system and confirmed by the chemical reactions of the product alkoxide, which acted as the initiator. Tertiary amines such as pyridine and NR3 where R is an alkyl group have been found to be good initiators for chloral polymerization. They are slower initiators than lithium... 

The branching sites can be introduced onto the backbone either by postpolymerization reactions or by copolymerization of the main backbone monomer ) with a suitable comonomer, with the desired functional group (unprotected or in a protected form if this functional group interferes with the polymerization reaction). Branches of comb-shaped polymers are commonly prepared by anionic polymerization, and backbones with electrophilic functionalities such as anhydrides, esters, pyridine, or benzylic halide groups are employed.88 The actual average number of branches in the final copolymer can be found by the determination of the overall molecular weight of the copolymer and the known molecular weights of the backbone and the branches. 

Alkyl cyanoacrylates are used extensively as instant adhesives and are grouped with vinylidene cyanide, methylene malonates, and a-cyanosorbates at the top of the anionic reactivity scale. As well as readily polymerizing in the presence of conventional anionic initiations such as Bu"Li, they also react readily with tertiary amines and phosphines. Pepper and Johnstonhave examined the catalytic action of triethylphosphine and pyridine at —78 °C in tetrahydrofuran. The former initiator appears to add rapidly and irreversibly to monomer to yield a conventional living anionic polymerization. With pyridine, however,... 

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. 

In order to confirm these results, PPV-based copolymers with more controlled stmctures have been also synthesized by anionic polymerization with polystyrene (PS) (copolymer 7) and poly(4-vinyl pyridine) (P4VP) (copolymer 8) coils (as shown in Figure 6)... 

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