Sodium naphthalene, as initiator

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. 

For the synthesis of the (PI)3PS(PI)3 super-H copolymers,161 a difunctional PS chain, derived from the polymerization of isoprene in THF using sodium naphthalene as initiator, was reacted with a large excess of SiCL, giving a PS chain with three Si—Cl active bonds at each end. After elimination of excess SiCL and the addition of excess PILi living arms, the (PI)3PS(PI)3 super-H shaped copolymer was isolated (Scheme 74). Using the same synthetic strategy, (PS—PI)3PS(PI—PS)3 block copolymers were also synthesized.162... 

The apparent propagation rate constant for polymerization of styrene in THF at 25°C using sodium naphthalene as initiator is 550 L mol s . If the initial concentration of styrene is 156 g/L and that of sodium naphthalene is 0.03 g/L, calculate the initial rate of polymerization and, for complete conversion of the styrene, the number average molecular weight of the polystyrene formed. Comment upon the expected value of the polydispersity index (M /M ) and the stereoregularity of the polystyrene produced. 

In place of phenyl lithium, if we use sodium naphthalene as the initiator, then the chains may grow in both the direction and... 

Preparation of Cellulose-Polystyrene Graft Copolymers. The polystyr-yl mono- and di-carbanions were prepared in THF at -78 °C by using n-butyl lithium and sodium naphthalene as the initiators, respectively. The carban-ions were reacted with dry carbon dioxide. The products were precipitated in methanol, filtered, washed with water and methanol, and dried. Size exclusion chromatography (SEC) established that the molecular weight of the polystyryl monocarboxylate was 6,200 and that of the polystyryl di-carboxylate 10,2000. The mono- and di-carboxylates were reacted with mesylated cellulose acetate in dimethylformamide at 75 °C for 20 h to give the cellulose-polystyrene graft copolymer (GP 1) and crosslinked cellulose-polystyrene graft copolymer (GP 2), respectively. 

Compounds such as sodium naphthalene can initiate polymerization by mechanisms involving addition. This is known to occur for ethylene oxide [95], viz. 

Alkali metal naphthalene complexes have also been used to initiate epoxide polymerizations. Solov yanov and Kazanski [25] studied the polymerization of EO in tetrahydrofuran using sodium, potassium or cesium naphthalene as initiator. A living polymer was produced there is no chain rupture or transfer. The rate of polymerization depends on the concentration of active centres in a complex manner. The kinetic order varies from 0.23 for Na" (or 0.33 for K and Cs" ) up to full first order as initiator concentration decreases. The polymerization is first order in monomer, but deviations are observed at high concentrations. 

Another variant for the synthesis of hydroxy telechelic polybutadiene is based on the anionic living polymerisation of butadiene, using sodium naphthalene as catalyst [16]. Sodium naphthalene generates, by reaction with butadiene, a radical anion (9.8). If two of these radicals are coupled together, they generate a dianion (9.9), which is an ideal bifunctional initiator for the synthesis of perfectly bifunctional polybutadiene by anionic polymerisation. 

Preparation of AB and ABA Type Block Copolymers of Ethylene Oxide and Isoprene. The block copolymers were synthesized by Szwarc s anionic polymerization technique (11) with cumyl potassium and sodium naphthalene as the initiators for EO-Is diblock copolymers and EO-Is-EO triblock copolymers, respectively, and the ethylene oxide and isoprene contents varied from 0 to 100%. The detailed procedure is being published (12). 

The alkyl-lithium initiated, living anionic polymerization of elastomers was described in 1928 by Ziegler. To polymerize styrene-isoprene block copolymers Szwarc et al., [1956] used sodium naphthalene as an anion-radical di-initiator, while Shell used an organolithium initiator. The polymerization mechanism was described by By water [1965]. 

The polystyryl monocarbanion 4 was prepared in THF at -78 C using sec-butyl lithium as the initiator while the polystyryl dicarbanion (Scheme 2) was prepared using sodium naphthalene as the initiator. The initiator was added first followed by the styrene. A bright, reddish orange-colored solution was obtained confirming the presence of the polystyryl carbanions. 

Living" polystyrene of desired molecular weight (6000 and 9000) was prepared using sodium naphthalene as the initiator and reacted with the oxidized cellulose (Scheme 2). The polystyryl carbanion attacks the electrophilic carbonyl carbon and in principle one could get mono-substituted. 

The kinetics of polymerization of EO have also been investigated in pure ethereal solvents. In THE ( =7.6, 25 °C) in the presence of sodium, potassium, and cesium naphthalene as initiators, a living polymerization takes place, ° the rate of propagation increasing with the size of the counterion. The kinetics are however complicated by strong association of alkoxide end groups manifesting itself by the low fractional kinetic order of the reactants, that is, 0.25 for Na alkoxide and 0.33 for K and Cs salts. ° Dissociation constants are very low (see Table 1). 

While the free anion kp remains the same with different counterions, the ion pair kp decreases significantly with the size of the metal cation. The equilibrium constant Keq is also a strong function of the metal type with two orders of magnitude decrease from Li to Cs. It is noted that Keq have small values and the equilibria are in favor of ion pair formation. Most ions are thus in pairs. Take the system initiated by 10 mol sodium naphthalene as an example. Only about 1% of the ions, 1.2 x 10" mol 1", are free ions. However, it is this small percentage of free ions that consume the majority of monomer, kp [P" ]/fep [P j 10. The rate of polymerization is... 

Aromatic radical anions, such as lithium naphthalene or sodium naphthalene, are efficient difunctional initiators (eqs. 6,7) (3,20,64). However, the necessity of using polar solvents for their formation and use limits their utility for diene polymerization, since the unique abiUty of lithium to provide high 1,4-polydiene microstmcture is lost in polar media (1,33,34,57,63,64). Consequentiy, a significant research challenge has been to discover a hydrocarbon-soluble dilithium initiator which would initiate the polymerization of styrene and diene monomers to form monomodal a, CO-dianionic polymers at rates which are faster or comparable to the rates of polymerization, ie, to form narrow molecular weight distribution polymers (61,65,66). 

Polymerization of ethylene oxide might be initiated by electron transfer process if metallic Na or Li is used as an initiator. On the other hand, initiation by sodium naphthalene involves not electron transfer but addition to naphthalene- ion. 

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. 

Szwarc and coworker have studied the interesting and useful polymerizations initiated by aromatic radical-anions such as sodium naphthalene [Szwarc, 1968, 1974, 1983]. Initiation proceeds by the prior formation of the active initiator, the naphthalene radical-anion (XVIII)... 

The radical-anion proceeds to propagate in the same manner as discussed above for initiation by sodium naphthalene. (Polymerizations in liquid ammonia are very different from those in organic solvents in that free ions probably constitute the major portion of propagating species.)... 

Difunctional initiators such as sodium naphthalene are useful for producing ABA, BABAB, CAB AC, and other symmetric block copolymers more efficiently by using fewer cycles of monomer additions. Difunctional initiators can also be prepared by reacting a diene such as /n-diisoprope ny I benzene or l,3-bis(l-phenylethenyl)benzene with 2 equiv of butyl-lithium. Monomer B is polymerized by a difunctional initiator followed by monomer A. A polymerizes at both ends of the B block to form an ABA triblock. BABAB or CABAC block copolymers are syntehsized by the addition of monomer B or C to the ABA living polymer. The use of a difunctional initiator is the only way to synthesize a MMA-styrene-MMA triblock polymer since MMA carbanion does not initiate styrene polymerization (except by using a coupling reaction—Sec. 5-4c). 

Isocyanates are polymerized through the carbon-nitrogen double bond to 1-nylons by anionic initiators such as metal alkyls, sodium naphthalene, and sodium cyanide [Bur and Fetters,... 

The anionic polymerization of epoxides such as ethylene and propylene oxides can be initiated by metal hydroxides, alkoxides, oxides, and amides as well as metal alkyls and aryls, including radical-anion species such as sodium naphthalene [Boileau, 1989 Dreyfuss and Drefyfuss, 1976 Inoue and Aida, 1984 Ishii and Sakai, 1969]. Thus the polymerization of ethylene oxide by M+A involves initiation... 

A variation of the sequential anionic polymerization is the use of dianions as initiator, like sodium naphthalene. One starts with the polymerization of monomer A. Then monomer B is fed to the reaction mixture which adds immediately to the living anions at each end of block A and thus leads to a triblock copolymer with an A-middle block and two B-outer blocks. This triblock copolymer is still alive and repetition of the above procedure results in a multiblock copolymer (see Example 3-49). 

Monomeric styrene is destabilized as in Example 3-1 and pre-dried with calcium chlo-ride.The monomer is now allowed to stand over calcium hydride for 24 h and then distilled under reduced pressure of nitrogen into a previously flamed-out Schlenk tube. Pure 4-vinylpyridine is distilled twice over KOH pellets in vacuum.lt is then vacuum distilled under nitrogen through a column packed with Raschig rings into a previously flamed out Schlenk tube (bp 62 °C/12 torr).The closed Schlenk tubes containing the monomers are stored in a refrigerator until required.The preparation of the initiator solution (sodium naphthalene) is described in Example 3-19. 

McCormick (11) and Worsfold and Bywater (72) initiated the polymerization of a-methylstyrene by using sodium naphthalene, brought the system to equilibrium at the desired temperature, and then killed the living polymers. They showed that at 0° C the concentration of the monomer attains its equilibrium value in less than 16 hours, and they observed no further polymerization over periods lasting for as long as 124 hours. Furthermore, they showed that the monomer equilibrium concentration was independent of the concentration of living ends, i.e. of the amount of catalyst applied. 

Aromatic radical anions, such as lithium naphthalene or sodium naphthalene, arc efficient difunctionai initiators, However, the necessity of using polar solvents for their formation and use limits their utility for diene polymerization. 

On the other hand, Ishizu et al. [58] reported the synthesis of cyclic polystyrene using interfacial condensation reaction of a/o-dibromopolyslyrcnc prepared from living polystyrene initiated with sodium naphthalene and terminated with 1,4-dibromobutane and then tetramethylenediamine as depicted in Fig. 11. The reaction was carried out in organic solvent/water to yield in more than 90%. The effect of solvent on the yield of cycUc polymer was observed, and the yield of cyclic product obtained in DMSO was higher than that in toluene. Since DMSO dissolves in both water and toluene, the reaction proceeded faster than that in toluene. 

Electron transfer initiators such as free alkali metals (e.g., Na, Li) or complexes of alkali metals and unsaturated or aromatic compounds (e.g., sodium naphthalene). These bring about initiation as shown in the following scheme ... 

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