Naphthalene sodium anionic polymerization

Problem 8.10 The kinetics of sodium naphthalene initiated anionic polymerization of styrene was studied in a less polar solvent dioxane at 35°C. Using an apparatus which permitted quick mixing of the reaction components in absence of air and moisture, aliquot samples were withdrawn periodically and deactivated quickly with ethyl bromide. From the residual monomer and the average degree of polymerization of the polymer formed the following data were obtained... 

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. 

Only a few publications have appeared in which for the synthesis of reactive microgels other monomers were used than 1,4-DVB or EDMA. Hiller and Funke studied the anionic polymerization of 1,4-diisopropenylbenzene (1,4-DIPB) by n-BuLi in 1,2-dimethoxyethane and by sodium naphthalene in THF [231]. 

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 propagation rate constant and the polymerization rate for anionic polymerization are dramatically affected by the nature of both the solvent and the counterion. Thus the data in Table 5-10 show the pronounced effect of solvent in the polymerization of styrene by sodium naphthalene (3 x 1CT3 M) at 25°C. The apparent propagation rate constant is increased by 2 and 3 orders of magnitude in tetrahydrofuran and 1,2-dimethoxyethane, respectively, compared to the rate constants in benzene and dioxane. The polymerization is much faster in the more polar solvents. That the dielectric constant is not a quantitative measure of solvating power is shown by the higher rate in 1,2-dimethoxyethane (DME) compared to tetrahydrofuran (THF). The faster rate in DME may be due to a specific solvation effect arising from the presence of two ether functions in the same molecule. 

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... 

Another way to initiate anionic polymerization is by electron transfer. The reaction of sodium with naphthalene gives sodium naphthalene (sodium dihydro-naphthylide) in which the sodium has not replaced a hydrogen atom, but has transferred an electron to the electronic levels of the naphthalene this electron can be transferred to styrene or a-methylstyrene, forming a radical anion ... 

Anionic Polymerization of a-Methyi tyrene with Sodium Naphthalene in Solution ( Living Polymerization")... 

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). 

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. 

Anionic polymerization Initiated by electron transfer (e.g., sodium-naphthalene and styrene In THF) usually produces two-ended living polymers. Such species belong to a class of compounds called bolaform electrolytes (27) In which two Ions or Ion pairs are linked together by a chain of atoms. Depending on chain length, counterion end solvent, Intramolecular Ionic Interactions can occur which in turn may affect the dissociation of the ion pairs Into free ions or the llgand-lon pair complex formation constants. 

Polymer Preparation. Poly-para-methylstyrene (P-p-MS) was prepared by anionic polymerization in benzene at 50"C initiated by n-butyllithium (9) or in THF at 25°C initiated by sodium naphthalene (10). Polymerizations in benzene allowed preparation of more monodisperse materials than those prepared in THF since the propagation rate is slower relative to the initiation rate in the nonpolar solvent (11). Two different molecular weight materials were chlorinated (P-p-MS 1 and P-p-MS2). 

Richardson and Sacher (41) showed that the anionic polymerization of butadiene with ethyllithium in THF produces mainly 1.2 structure in the polybutadiene. Roha (2) reviewed the typical anionic polymerization of butadiene to polymers containing 1.2 structure by catalysts such as alkyl sodium and alkyl potassium. Sodium naphthalene with THF produces 88% 1,2 polybutadiene (42). 

A recent paper by Wenger (35a) deserves some comments. This careful worker proved again that mono-dispersed polystyrene can be produced through an anionic polymerization. Most unfortunately, however, he confused some issues and their clarification is therefore necessary. Wenger found, in agreement with Waack (Ph. D. Thesis, Syracuse, June 1959), that polymerization of styrene initiated by sodium naphthalene at —78° C produces polystyrene having a broad molecular distribution. In our opinion this results from an incomplete solution of sodium naphthalene in tetra-hydrofuran at —78° C, whereas Wenger assumes that this indicates the unfavorable position of the equilibrium... 

Figure 10.6. Rate of anionic polymerization of styrene initiated by sodium naphthalene in 3-methyl tetrahydrofuran at 20°C. Left linear variation of rate with (C°)l/2 right inverse linear variation of rate with concentration of Na+ in presence of added sodium tetraphenyl borate. (Data from Schnitt and Schulz [79].)...

The third major breakthrough was by Szwarc and coworkers who reported in 1956 (30. 31) that certain anionic polymerization systems gave "living polymers" to which a second monomer could be added without termination, so that block polymers could be formed. Interest of research groups in this system was dissipated somewhat by the finding that the sodium naphthalene diinitiator used by Szwarc resulted in undesirable 1,2- or 3,4-addition structures in diene polymers. 

Block Copolymers. The manufacture of block copolymers became possible in 1956 by M. Szwarc s discovery (24) of "living" polymers prepared in homogeneous anionic polymerization. Diblock, triblock, and multiblock copolymers are produced ionically in the presence of sodium naphthalene, butyllithium, or Ziegler-type catalysts. 

Ionic polymerization can, in general, be initiated by acidic or basic compounds. For cationic polymerization, complexes of BF3, AICI3, TiCU, and SnCU with water, or alcohols, or tertiary oxonium salts are particularly active initiators, the positive ions in them causing chain initiation. One can also initiate cationic polymerization with HCl, H2SO4, and KHSO4. Important initiators for anionic polymerization are alkali metals and their organic compounds, such as phenyl-lithium, butyllithium, phenyl sodium, sodium naphthalene, and triphenyl methyl potassium. 

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]. 

Isomerization and disproportionation of the monomer are also often observed with other systems. 1,4-Dihydro naphthalene is first isomerized to 1,2-dihydronaphthalene under the influence of sodium naphthalene and then anionically polymerized. The presence of M0O3 on carriers causes propylene to disproportionate to ethylene and butene-2 and then the ethylene polymerizes. 

Difunctional initiators such as sodium naphthalene can be employed to prepare triblock ABA block copolymers. Difunctional initiators produce "living pol3mieric dianions which are capable of adding a second monomer at each end. On the addition of a second monomer the ABA structure results. For example, consider the preparation of poly(butadiene-b-styrene-b-butadiene) by anionic polymerization initiated by sodium naphthalene. 

---