Poly anionic polymerization

Polymerization ofiVIasked Disilenes. A novel approach, namely, the anionic polymerization of masked disilenes, has been used to synthesize a number of poly(dialkylsilanes) as well as the first dialkylamino substituted polysilanes (eq. 13) (111,112). The route is capable of providing monodisperse polymers with relatively high molecular weight M = lO" — 10 ), and holds promise of being a good method for the synthesis of alternating and block copolymers. 

Commercially, the poly(styrene-Aelastomer-Astyrene) materials are made by anionic polymerization (7,45—47). An alkyllithium initiator (RLi) first reacts with styrene [100-42-5] monomer ... 

Commercial narrow standards [such as poly(ethylene glycol) (pEG), polystyrene sulfonate, pAA, poly w-vinyl pyrrolidinone, dextrans] are available from American Polymer Standards Corporation, Polymer Laboratories, Polymer Standards Service USA, Toyo Soda, and others. While these standards are often not as narrow as pSty or pMMA that has been anionically polymerized, they are acceptable for narrow standard calibrations. 

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. 

When undiluted 2-vinylfuran was added to metallic sodium (mirror or particles) an orange colour developed and some resinous material was deposited on the metal surface. On prolonged contact much of the monomer was converted into a partly-insoluble reddish resin with spectra unrelated to those of standard poly(2-vinyl-furan). Reaction of diluted monomer with sodium gave a milder interaction, but no evidence of living anionic polymerization. 

Anionic polymerization of ethylene oxide by living carbanions of polystyrene was first carried out by Szwarc295. A limited number of methods have been reported in the preparation of A-B and A-B-A copolymers in which B was polystyrene and A was poly(oxyethylene)296-298. The actual procedure was to allow ethylene oxide to polymerize in a vacuum system at 70 °C with the polystyrene anion initiated with cumyl potassium in THF299. The yields of pure block copolymers are usually limited to about 80% because homopolymers are formed300. ... 

Anionic polymerization of lactams was shown to proceed according to what is called the activated monomer mechanism. With bischloroformates of hydroxy-terminated poly(tetramethyleneglycol) and poly(styrene glycol) as precursors for a polymeric initiator containing N-acyl lactam ends, block copolymers with n-pyrrol-idone and e-caprolactam were obtained by bulk polymerizations in vacuum at 30 and 80 °C, respectively361. ... 

The difficulties encountered in the early studies of anionic polymerization of methyl methacrylate arose from the unfortunate choice of experimental conditions the use of hydrocarbon solvents and of lithium alkyl initiators. The latter are strong bases. Even at —60 °C they not only initiate the conventional vinyl poly-addition, but attack also the ester group of the monomer yielding a vinyl ketone1, a very reactive monomer, and alkoxide 23). Such a process is described by the scheme. 

Some tailor-made homopolymers can serve as starting points for chemical modifications to yield new species. Poly(hydroxyethyl methacrylate) and poly(glyceryl methacrylate) 16), already mentioned, are obtained upon hydrolysis of the OH-protecting groups that allow the anionic polymerization to proceed. Another example is the acid hydrolysis of poly(t-butyl methacrylate), a reaction which proceeds easily to completion, yielding poly(methacrylic acid) of known degree of polymerization and narrow molecular weight distribution 44 45). 

Analogous principles should apply to ionically propagated polymerizations. The terminus of the growing chain, whether cation or anion, can be expected to exhibit preferential addition to one or the other carbon of the vinyl group. Poly isobutylene, normally prepared by cationic polymerization, possesses the head-to-tail structure, as already mentioned. Polystyrenes prepared by cationic or anionic polymerization are not noticeably different from free-radical-poly-merized products of the same molecular weights, which fact indicates a similar chain structure irrespective of the method of synthesis. In the polymerization of 1,3-dienes, however, the structure and arrangement of the units depends markedly on the chain-propagating mechanism (see Sec. 2b). 

Polystyrene standards used were narrow molecular weight distribution sample produced by anionic polymerization and available from Pressure Chemical Co. Also sample NBS7C from the National Bureau of Standards was used. The sample of poly n-butyl methacrylate was obtained from Aldrich Chemical. It was produced by free radici polymerization with an Mw of 320,(XK) and an Mn of 73,500 (Cat. No. 18,153-6). 

Quite often in the ring-opening polymerization, the polymer is only the kinetic product and later is transformed to thermodynamically stable cycles. The cationic polymerization of ethylene oxide leads to a mixture of poly(ethylene oxide) and 1,4-dioxane. In the presence of a cationic initiator poly(ethylene oxide) can be almost quantitatively transformed to this cyclic dimer. On the other hand, anionic polymerization is not accompanied by cyclization due to the lower affinity of the alkoxide anion towards linear ethers only strained (and more electrophilic) monomers can react with the anion. 

Nuclear magnetic resonance has proved to be a valuable tool in determination of configurational sequences in poly(MMA) (14). In Figure 3 is shown the NMR of poly(MMA) synthesized with an anionic polymerization catalyst known to produce predominantly isotactic sequences. In these polymers, the NMR spectrum of the methylene units In the polymer backbone gives an unequivocal determination of tacticity. The methylene signal, occurring about 1.8... 

A radical initiator based on the oxidation adduct of an alkyl-9-BBN (47) has been utilized to produce poly(methylmethacrylate) (48) (Fig. 31) from methylmethacrylate monomer by a living anionic polymerization route that does not require the mediation of a metal catalyst. The relatively broad molecular weight distribution (PDI = (MJM ) 2.5) compared with those in living anionic polymerization cases was attributed to the slow initiation of the polymerization.69 A similar radical polymerization route aided by 47 was utilized in the synthesis of functionalized syndiotactic polystyrene (PS) polymers by the copolymerization of styrene.70 The borane groups in the functionalized syndiotactic polystyrenes were transformed into free-radical initiators for the in situ free-radical graft polymerization to prepare s-PS-g-PMMA graft copolymers. 

Hyperbranched polymers have also been prepared via living anionic polymerization. The reaction of poly(4-methylstyrene)-fo-polystyrene lithium with a small amount of divinylbenzene, afforded a star-block copolymer with 4-methylstyrene units in the periphery [200]. The methyl groups were subsequently metalated with s-butyllithium/tetramethylethylenediamine. The produced anions initiated the polymerization of a-methylstyrene (Scheme 109). From the radius of gyration to hydrodynamic radius ratio (0.96-1.1) it was concluded that the second generation polymers behaved like soft spheres. 

A combination of TEMPO living free radical (LFRP) and anionic polymerization was used for the synthesis of block-graft, block-brush, and graft-block-graft copolymers of styrene and isoprene [201]. The block-graft copolymers were synthesized by preparing a PS-fo-poly(styrene-co-p-chloromethylstyrene) by LFRP [Scheme 110 (1)], and the subsequent re-... 

The precipitated silica (J. Crosfield Sons) was heated in vacuo at 120° for 24h. before use. Two grades of surface areas 186 and 227 m g l (BET,N2), were used during this project. Random copolymers, poly(methyl methacrylates) and polystyrene PS I were prepared by radical polymerization block polymers and the other polystyrenes were made by anionic polymerization with either sodium naphthalene or sodium a methylstyrene tetramer as initiator. The polymer compositions and molecular weights are given in Table I. 

Matyjaszewski et al. [281-285] succeeded in the synthesis of poly(St) with a narrow molecular weight distribution, comparable to the living anionic polymerization, in the atom transfer radical polymerization (ATRP) using Cu complex and alkyl halides (Eq. 74) ... 

The opposite effects of the initiator on the structure of 1,4-DVB polymers in a range of low (1-16 mol %) and a high (17-200 mol %) concentration of 1,4-DVB were explained by a kinetic model of anionic polymerization of 1,4-DVB [239]. Calculations indicated that, at low concentrations of the initiator, the poly-... 

Values for RU differed by up to 100% with 1,4-DVB-microgels [286]. The reliability of methods for determining the RU of 1,4-DVB-microgels was checked [287] with poly(4-vinylstyrene) which was prepared by anionic polymerization of 1,4-DVB (Table 3). From these results, it can be concluded that only quantitative IR-spectroscopy is a reliable method for determining the RU of 1,4-DVB-... 

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