Potassium naphthalene, initiation

This method has been extended by Rempp and co-workers [39,40] as a general core-first method to prepare star-branched polymers, as shown in Scheme 4. The plurifimctional metalorganic initiator (A) was prepared by potassium naphthalene-initiated polymerization of DVB in tetrahydrofuran (THF) at -40°C with [DVB]/[K ] ratios of 0.5-3. Microgel formation was reported outside of this stoichiometric range or when m-DVB was used instead of either / -DVB or the commercial mixture. Within the prescribed stoichiometric ratios, star polymers (B) with arm functionalities varying from 8 to 42 were reported. As expected for this type of process, the polydispersities were described as being quite broad and were attributed primarily to a random distribution of core sizes and functionalities. 

Anionic polymerization of 1,4-DVB by n-BuLi leading to the microgels was also reported by Eschwey et al. [236,237]. In their experiments, n-BuLi was used at very high concentrations of 17 and 200 mol % of the monomer. Contrary to the results of Hiller and Funke [231], they observed a transition from microgel to macrogel with decreasing n-BuLi concentration. Similar results were also reported by Lutz and Rempp [238]. They used potassium naphthalene as the initiator of the 1,4-DVB polymerization and THF as the solvent. Soluble polymers could only be obtained above 33 mol % initiator, whereas below this value macrogels were obtained as by-products. 

For the synthesis of the PEO stars, potassium naphthalene was used to generate the multifunctional initiator. The molar ratio [DVB] [K+] was less than 3 in all cases. The functionalities of the stars, as determined by LS measurements, were also rather large, ranging from 5 to 219. 

It was foimd that PS-h-PCHD block copolymers can be prepared in hydrocarbon solvents using s-BuIi as the initiator without the presence of any additive [34]. Efficient crossover reactions were obtained from either PSLi (Scheme 12 route A) or PCHDLi (Scheme 12 route B). Using potassium/naphthalene as a difunctional initiator PS-fo-PCHD-fc-PS and PCHD-fo-PS-fo-PCHD were prepared. However, the molecular weight distributions were rather broad, and side reactions were observed when copolymers with high CHD contents were required. To avoid this problem several additives were tested in order to improve the copolymerization characteristics. The best results were obtained with dimethoxyethane, DME, or... 

An interesting variation of this approach was recently reported by Yagci and coworkers [60], who showed that the stable TEMPO radical could undergo a one-electron redox reaction with potassium naphthalene. While the TEM PO alcoho-late thus formed does not initiate the polymerization of styrene, the polymerization of EO was readily accompHshed. PEO obtained in this way possessed TEMPO terminal units, and was subsequently used as an initiator for NMRP of styrene to produce block copolymers (Scheme 11.11). 

PEO-PIP-PEO symmetric triblock copolymers were also synthesized using sodium or potassium naphthalene as a difunctional initiator. In these samples, isoprene (IP) was polymerized first followed by the addition of ethylene oxide (EO) (Scheme 2). The final copolymers synthesized were well defined and exhibited compositional and molecular homogeneity. Due to the fact that Na or K naphthalenide is soluble in only polar solvents (e.g., THE), the microstructure of PIP was mostly 3,4-microstructure. 

Since this was also the time when the non-terminating ( living ) nature of certain carbanionic polymerizations was discovered, it is not surprising that this knowledge was applied to the siloxane systems. Thus potassium naphthalene was found in our laboratory to be an effective initiator for polymerization of the cyclic tetrasiloxane, and, at the same time, block copolymers of styrene or isoprene and the siloxane were successfully synthesized. 

Other initiators based on alkali metals such as sec-butyllithium (s c-BuLi) as well as sodium and potassium naphthalene were also surveyed.Sodium and potassium naphthalene, when used as electron-transfer reagents for the initiation of styrene polymerization, react with neopentyl carbonate as a nucleophile. The investigation of oligomers obtained in the initial stages of the polymerization by means of GPC using a UV-detector revealed naphthalene to be incorporated into the growing chain. 

Typical examples of initiators for cycHc carbonates-as shown for DTC-are alkali metal organic compounds such as sec-butyUithium (seoBuLi), sodium- and potassium naphthalene, and Hthium-, sodium- and potassium alkoxides or polymeric living vinyl or diene polymers with alkah metal counterions, as weU as polymeric alcoholates. The use of these macroinitiators enables the identification of side reactions, as will be shown exemplarily for polystyrene lithium (PS li ) [25]. Besides the initiation reaction of PS"Li, which represents a site transformation of... 

The aromatic cyclic carbonates based on bisphenol-A or substituted o,o -methy-lenebisphenols were polymerized in tetrahydrofuran (THE) and in toluene with potassium-based initiators, for example potassium naphthalene at 60 C and 25 C, respectively [29]. In a rapid reaction the polymer was obtained in equilibrium with cycHc oligomers. However, with Hthium-based initiators the chain propagation does not occur under these mild conditions, due to the low nucleophUidty of the active species, which arises from the covalent character of the Hthium phenolate hnkage. 

The cyclic dimer was completely converted within 10 min at 300 °C, whereas in the case of the trimer a small part remained unpolymerized even after 30 min at 300 °C. The tetramer exhibits an even lower reactivity. Such lower reactivity is due to a slower initiation of the larger ring monomers. At this point, it should be noted that a mixture of cyclic monomers polymerizes much more rapidly than pure cyclic trimers or tetramers. Solid-state thermal polymerization produces a high-molecular-weight polymer (M > 10 ). Cyclic carbonates derived from o,o -bisphe-nols 43-49 and of cyclic carbonates derived from p,p -bisphenols, such as biphenol-A (50), were polymerized and copolymerized in solution using potassium naphthalene, potassium tert-butoxide or phenyl trimethylsilylether in combination with tris (dimethylamino)sulfonium trimethylsilyldifluoride as initiator [7]. From a practical viewpoint, these polycarbonates, which have high heat-deformation temperatures, may be used for moldings [85]. 

The primary starting material for the synthesis of perylene tetracarboxylic acid pigments is the dianhydride 71. It is prepared by fusing 1,8-naphthalene dicar-boxylic acid imide (naphthalic acid imide 69) with caustic alkali, for instance in sodium hydroxide/potassium hydroxide/sodium acetate at 190 to 220°C, followed by air oxidation of the molten reaction mixture or of the aqueous hydrolysate. The reaction initially affords the bisimide (peryldiimide) 70, which is subsequently hydrolyzed with concentrated sulfuric acid at 220°C to form the dianhydride ... 

Reduction of poly(butyl)naphthalenes with sodium-potassium alloy in ether causes their isomerization (Goldberg et al. 1976). The reduction of l,3,6,8-tetra(tcrt-butyl)naphthalene produces an anion-radical, which disproportionates yielding the initial tetrabutylnaphthalene and corresponding dianion (Scheme 6.32). 

Anionic graft-polymerization of paraformaldehyde onto starch and dextrin has been effected in methyl sulfoxide solution, polymerization being initiated by the carbohydrate potassium alcoholate formed from the reaction of the carbohydrate with naphthalene potassium, a metallation procedure not previously described for carbohydrates.220... 

The initiation step is normally fast in polar solvents and an initiator-free living polymer of low molecular weight can be produced for study of the propagation reaction. The propagation step may proceed at both ends of the polymer chain (initiation by alkali metals, sodium naphthalene, or sodium biphenyl) or at a single chain end (initiation by lithium alkyls or cumyl salts of the alkali metals). The concentration of active centres is either twice the number of polymer chains present or equal to their number respectively. In either case the rates are normalized to the concentration of bound alkali metal present, described variously as concentration of active centres, living ends or sometimes polystyryllithium, potassium, etc. Much of the elucidation of reaction mechanism has occurred with styrene as monomer which will now be used to illustrate the principles involved. The solvents commonly used are dioxane (D = 2.25), oxepane (D = 5.06), tetrahydropyran D = 5.61), 2-methyl-tetrahydrofuran (D = 6.24), tetrahydrofuran (D = 7.39) or dimethoxy-ethane D = 7.20) where D denotes the dielectric constant at 25°C. 

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. 

Preliminary Experiments. Initial work centered on the study of the reaction of potassium with tetrahydrofuran and with naphthalene in tetrahydrofuran. 

The rates of reduction of tetrahydrofuran (Curve A), naphthalene in tetrahydrofuran (Curve B), and a mixture of naphthalene and Illinois No. 6 coal in tetrahydrofuran (Curve C) are shown in Figure 1. These preliminary experiments established that potassium reacted only very slowly with tetrahydrofuran under the experimental conditions used for the formation of the coal polyanion. Naphthalene was rapidly converted to a mixture of anion radicals and dianions under the same conditions. The initial reaction between the electron transfer reagent and the Illinois No. 6 coal was quite rapid. However, the reaction slowed to nearly constant rate after about 12 hr. During the last 4 days of reaction the coal molecules acquired about 0.1 negative charge per 100 carbon atoms per hour. 

The results presented in Figure 1, Curve C, reveal that Illinois No. 6 coal undergoes an initial, very rapid reduction reaction. There is no initial, rapid reaction when the insoluble alkylation products are treated with potassium and naphthalene in tetrahydrofuran in a second alkylation reaction. The observations suggest that accessible acidic hydrogen atoms and other very readily reduced functional groups, e.g., quinoid... 

The dihalocyclopropane route is the method of choice for the synthesis of benzocyclopropenes and linearly fused cyclopropanaphthalenes, but is unsuccessful for angular cyclopropa[u]naph-thalene. Treatment of l,l-dichloro-la,2,3,7b-tetrahydro-l/f-cyclopropa[a]naphthalene(5) with potassium /ert-butoxide gave a mixture of 1-chloromethylnaphthalene, 1-terr-butoxymethyl-naphthalene and 2-terf-butoxy-l-chloromethylene-l,2,3,4-tetrahydronaphthalene, but none of the expected cyclopropa[n]naphthalene. The failure of the reaction has been attributed to difficulties in the aromatization. Isomerization of the initially produced cyclopropenyl double bond into the cyclohexane ring would require disruption of the aromatic character of the adjacent benzene nngT t-r>> 62 Similarly, attempted aromatization of l-chloro-l,2,3,7b-tetra-hydro-l//-cyclopropa[a]naphthalene (6) with 2,3-dichloro-5,6-dicyanobenzoquinone or via N-bromosuccinimide bromination followed by reaction with base afforded 4,5-benzotropone instead of cyclopropa[fl]naphthalenc. ... 

A more complex substrate is hexaketone (139), which has three possible initial aldolization modes (Scheme 5 a, b and c). Treatment of this material with sodium bicarbonate or silica gel provides naphthalene derivative (140), the result of mode b aldolization. On the other hand, use of aqueous KOH gives resorcinol derivatives (141) and (142), resulting from aldolization modes a and c. Further aldolization of (142) to (143) is achieved by treatment with potassium carbonate. 

The nanosecond pulse radiolysis technique has been described (8, 14). Carbon tetrachloride was purified as follows Matheson Research grade CC14 was dried over anhydrous potassium carbonate for several days, and subsequently distilled, discarding initial and final fractions. However, untreated research grade CCLj gave identical results to that treated as above. Zone refined naphthalene, anthracene, biphenyl, and N,N,N, N -tetramethyl-paraphenylenediamine (TMPD) were used pyrene, 1 2 benzanthracene were recrystallized from absolute alcohol, and aniline was purified as described in an earlier paper (6). Normal hexane, cyclohexane, 3-methylpentane, benzene, and toluene were Matheson research grade methanol and ethyl alcohol were analytical grade. 

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). 

---