Living cationic polymerization of ethyl 2-(vinyloxy)ethoxyacetate: A vinyl ether with an ether and an ester function in the pendant

Ethyl 2-(vinyloxy)ethoxyacetate ( 4 ; CH₂?CH? OCH₂CH₂OCH₂? COOC₂H₅), a vinyl ether having both carboxylic acid ester and oxyethylene unit in its pendant, afforded well-defined living polymers when polymerized by the hydrogen iodide/iodine (HI/I₂) initiating system in toluene at ?40°C. The polymers possessed a narrow molecular weight distribution (M _w/M _n ≤ 1.15), and their molecular weight (M _n) increased proportionally to monomer conversion or the molar ratio of the monomer to hydrogen iodide. The polymer molecular weight also increased upon addition of a fresh feed of the monomer to a completely polymerized reaction mixture. Polymers of high molecular weights (M _n > 5 × 10⁵) and broad molecular weight distributions were obtained by BF₃OEt₂ in toluene at ?40°C. Polymerization rate of 4 with HI/I₂ is ca. 100 times greater than that of the corresponding alkyl vinyl ether, and thus 4 was found to be one of the most reactive vinyl ethers thus far studied. Alkaline hydrolysis of the pendant ester groups of the polymers gave a vinyl ether-based polymeric carboxylic acid 6 with a narrow molecular weight distribution.     

Sampling modulation technique in radio-frequency helium glow discharge emission source by use of pulsed laser ablation

An emission excitation source comprising a high-frequency diode-pumped Q-switched Nd:YAG laser and a radio-frequency powered glow discharge lamp is proposed. In this system sample atoms ablated by the laser irradiation are introduced into the lamp chamber and subsequently excited by the helium glow discharge plasma. The pulsed operation of the laser can produce a cyclic variation in the emission intensities of the sample atoms whereas the plasma gas species emit the radiation continuously. The salient feature of the proposed technique is the selective detection of the laser modulation signal from the rest of the continuous background emissions, which can be achieved with the phase sensitive detection of the lock-in amplifier. The arrangement may be used to estimate the emission intensity of the laser ablated atom, free from the interference of other species present in the plasma. The experiments were conducted with a 13.56 MHz radio-frequency (rf) generator operated at 80 W power to produce plasma and the laser at a wavelength of 1064 nm (pulse duration:34 ns, repetition rate:7 kHz and average pulse energy of about 0.36 mJ) was employed for sample ablation. The measurements resulted in almost complete removal of nitrogen molecular bands (N₂⁺ 391.44 nm). Considerable reduction (about 75%) in the emission intensity of a carbon atomic line (C I 193.03 nm) was also observed.     

Polymerization of phenylacetylenes. VI. Chain-transfer reaction in the polymerizations of phenylacetylene and styrene by WCl6

Chain-transfer reactions to alkylbenzenes were investigated in the polymerizations of phenylacetylene and styrene by WCl₆ in benzene at 30°C. In the polymerization of phenylacetylene, alkylbenzenes did not work as chain-transfer agents, and further ethyl iodide was not a terminating agent. These findings suggest that the polymerization of phenylacetylene by WCl₆ differs from the conventional cationic or anionic mechanisms. On the other hand, the ability of alkylbenzenes as chain-transfer agents in the polymerization of styrene by WCl₆ increased in the following order: toluene < p-xylene < m-xylene < o-xylene. This order is similar to that in the polymerization by SnCl₄. These results indicate that the polymerization of styrene by WCl₆ proceeds by a conventional cationic mechanism.     

Effects of organometallic cocatalysts on the polymerization of disubstituted acetylenes by TaCl5 and NbCl5

The effects of organometallic cocatalysts on the polymerization of disubstituted acetylenes were investigated. Diphenylacetylene did not polymerize with TaCl₅ alone, while it produced a polymer quantitatively in the presence of appropriate cocatalysts (Me₄Sn, Et₃SiH, etc.). The poly(diphenylacetylene) formed was an insoluble yellow solid. 1-Phenyl-1-alkynes (1-Phenyl-1-butyne and -1-octyne) polymerized with TaCl₅ and NbCl₅ alone to yield polymers whose weight-average molecular weights (M _w's) were ca. 5 × 10⁵. Use of cocatalysts (nBu₄Sn etc.) to the polymerization of these monomers accelerated the reaction, and increased the polymer molecular weights up to ca. 1.5 × 10⁶. The poly(1-phenyl-1-alkynes) were soluble white solids. Internal octynes (2-, 3-, and 4-octynes) gave mixtures of a polymer and cyclotrimers with TaCl₅ alone. In contrast, cyclotrimers formed virtually selectively by addition of cocatalysts. Thus, various effects of organometallic cocatalysts were observed depending on the kind of monomer.     

Star-shaped polymers by living cationic polymerization. VII. Amphiphilic graft polymers of vinyl ethers with hydroxyl groups: Synthesis and host–guest interaction

Amphiphilic graft polymers of vinyl ethers (VEs) ( 6 ) where each branch consists of a hydrophilic polyalcohol and a hydrophobic poly(alkyl vinyl ether) segment were prepared on the basis of living cationic polymerization, and their properties and functions were compared with the corresponding amphiphilic star-shaped polymers. In toluene at ?15°C, the HI/ZnI₂-initiated living block polymer 2 of an ester-containing VE (CH₂? CHOCH₂CH₂OCOCH₃) and isobutyl VE (IBVE) was terminated with the diethyl 2-(vinyloxy)ethylmalonate anion [ 3 ; ^ΦC(COOEt)₂CH₂CH₂OCH ? CH₂] ( 2/3 = 1/2 mole ratio) to give a macromonomer ( 4 ), H[CH₂CH(OCH₂CH₂OCOCH₃)] _m-[CH₂CH(OiBu)]_n? C(COOEt)₂CH₂CH₂OCH ? CH₂ (m = 5, n = 15; M?_n = 2600, M?_w/M?_n = 1.13, 1.10 vinyl groups/chain). Subsequently, 4 was homopolymerized with HI/ZnI₂ in toluene at ?15°C. In 3 h, 85% of 4 was consumed and a graft polymer ( 5 ) was obtained [M?_w = 15000, DP_n (for 4 ) = 6]. The apparent M?_w (10,900) of 5 by size-exclusion chromatography (SEC) is smaller than that by light scattering as well as that (18,300) by SEC of the corresponding linear polymer with the almost same molecular weight, indicating the formation of a multi-branched structure. Hydrolysis of the pendant esters in 5 gave the amphiphilic graft polymer 6 where each branch consists of a hydrophilic polyalcohol and a hydrophobic poly(IBVE) segment. The graft polymer 6 was found to interact specifically with small organic molecules (guests) with polar functional groups, and 6 differed in solubility and host-guest interaction from the corresponding star-shaped polymer. © 1993 John Wiley & Sons, Inc.     

Studies on the construction of glycosidic linkage in guanofosfocins. Glycosylation of 8-oxoinosine and 8-oxoguanosine derivatives with mannopyranosyl bromide

In model studies directed to the total synthesis of guanofosfocins, a unique glycosydic bond formation between the 8-oxoinosine derivatives and mannopyranosyl donor is described. The reaction employing previously reported conditions resulted in the formation of two regioisomers, the 8-O- and N7-mannosylated inosine derivatives. However, the use of tetrabutylammonium iodide as a catalyst was found to improve the chemoselectivity towards O-glycosylation to afford the desired 8-O-mannosylated products in satisfactory yields. The established procedure was successfully applied for the synthesis of 8-(mannopyranosyloxy)guanosine derivative.     

Equilibrium concentration of trioxane in cationic polymerization

In the cationic polymerization of trioxane and tetraoxane near room temperature, the equilibrium trioxane concentration is not negligible during polymerization. In this work, tetraoxane was polymerized with BF₃ ? O(C₂H₅)₂ in various solvents and the equilibrium concentration of trioxane produced during the polymerization of tetraoxane and equilibrated with the growing polyoxymethylene chain was determined. The equilibrium trioxane concentrations were 0.05, 0.13, and 0.19 mole/l. in benzene, ethylene dichloride, and nitrobenzene at 30°C, respectively, and 0.20 mole/l. in thhylene dichloride at 50°C. The values in ethylene dichloride showed that the approximate values of ΔH_p and ΔS were ?4.2 kcal/mole and ?9.7 cal/mole-deg., respectively.     

Lifetime of living polymers in cationic polymerization. III. Living polymerization of isobutyl vinyl ether initiated by a cationogen/etalcl2 system in the presence of 1,4-dioxane as an added base

The concentration ([P^*]) and lifetime (half-life) of the propagating species were measured in the living cationic polymerization of isobutyl vinyl either initiated by the 1-(isobutoxy) ethyl acetate [CH₃COOCH (OiBu) CH₃]/ethylaluminum dichloride (EtAlCl₂) system in the presence of excess 1,4-dioxane in n-hexane at 0 to +70°C; the acetate serves as a cationogen that forms an initiating vinyl ether-type carbocation. The measurements were based on the end-capping reaction with sodiomalonic ester [Na^⊕?CH (COOEt)₂], which was shown to react rapidly and quantitatively with the living growing end. From the terminal malonate group of the quenched polymers, [P^*] was determined by ¹H-NMR spectroscopy. In contrast to its constancy during the polymerization, [P^*] progressively decreased with time after the complete consumption of monomer. The postpolymerization decay was first order in [P^*], and the lifetime (half-life) of the living end was determined from the decay rate constant. The lifetime increased on lowering polymerization temperature, decreasing EtAlCl₂ concentration, and increasing dioxane concentration. In particular, the “base-stabilized” living ends, generated by the CH₃COOCH (OiBu) CH₃/EtAlCl₂/dioxane system, turned out extremely stable at 0°C (half-life > 5 days in the absence of monomer).     

Living cationic polymerization of p-methylstyrene by hydrogen iodide/zinc halide initiating systems

Living cationic polymerization of p-methylstyrene has been investigated with use of hydrogen iodide/zinc halide initiating systems (HI/ZnX₂; X = Cl, I) in toluene and methylene chloride solvents. The best results were obtained with HI/ZnCl₂ below 0°C where the zinc salt was employed in excess over hydrogen iodide (HI/ZnCl₂ = 1/5 molar ratio). Under these conditions, the number-average molecular weights $ \left( {\overline {M_n } } \right)$ of the produced polymers increased proportionally to monomer conversion, further increased upon addition of fresh feeds of p-methylstyrene into completely polymerized reaction mixtures, and were in good agreement with the calculated values assuming that one living polymer chain forms per molecule of hydrogen iodide; the molecular weight distributions (MWDs) of the polymers were fairly narrow $ \left( {{{\overline {M_w } } \mathord{\left/ {\vphantom {{\overline {M_w } } {\overline {M_n } }}} \right. \kern-\nulldelimiterspace} {\overline {M_n } }} = 1.1 - 1.3} \right) $ throughout these processes. In contrast, when equimolar mixtures of hydrogen iodide and zinc chloride or iodide were employed, the polymerizations were rather slow even in methylene chloride at +25°C, and the product polymers exhibited bimodal MWDs, the lower-molecular weight fraction of which was mediated by long-lived growing species. Addition of tetra-n-butylammonium iodide as a common ion salt (nBu₄NI/HI = 1/200 molar ratio) led to unimodal MWDs consisting of the long-lived lower polymer fraction alone.     

Synthesis and properties of poly (diphenylacetylenes) having aliphatic para-substituents

1-(p-t-Butylphenyl)-2-phenylacetylene and 1-(p-n-butylphenyl)-2-phenylacetylene were polymerized in catalytic systems based on TaCl₅ to give new polymers in high yields. These monomers were more reactive than diphenylacetylene (DPA) in copolymerization. Unlike poly (DPA), the present polymers were soluble in toluene, CHCl₃, etc. owing to the high configurational entropy induced by the para-substituents. Their relative weight-average molecular weights determined by GPC were in the range of 6 × 10⁵–36 × 10⁵, and films could be obtained by solution casting. These polymers were fairly thermally stable, as seen from their high onset temperatures (320–380°C) of weight loss in TGA in air. The oxygen permeability coefficient of the polymer with t-Bu group was 1100 barrers, the highest among those of all the hydrocarbon polymers. © 1994 John Wiley & Sons, Inc.