“…It is also interesting to observe that the slopes of the two plots are very similar at the beginning of the reaction but become very different after approximately an 1 h. This effect could be due to the initial solvating effect of propylene oxide. Propylene oxide can interact with the lithium cation as a Lewis base, in the same fashion as THF can, therefore influencing the propagation rate constant ( k p ) or the equilibrium constant for the dimer−ion pair dissociation ( K diss ) and consequently increasing the overall rate of reaction. 1 1 Rate of addition for the functionalization reaction of poly(styryl)lithium with propylene oxide in the presence and in the absence of THF.…”
The room-temperature functionalization reaction between
poly(styryl)lithium and propylene
oxide in benzene was studied. The functionalized polymer was
characterized by 1H NMR, 13C NMR,
and
APT-13C NMR. 13C-methyl-labeled propylene
oxide-functionalized polystyrene was also synthesized and
characterized. Hydroxylated polystyrene was obtained in only 93%
yield, but with high regioselectivity
(97% of addition of the anionic chain-end to the least substituted
carbon of the propylene oxide ring) and
no oligomerization. The lower than quantitative yield was ascribed
to the proton-transfer reaction of
poly(styryl)lithium from the methyl group of propylene oxide,
which formed unfunctionalized polystyrene.
“…It is also interesting to observe that the slopes of the two plots are very similar at the beginning of the reaction but become very different after approximately an 1 h. This effect could be due to the initial solvating effect of propylene oxide. Propylene oxide can interact with the lithium cation as a Lewis base, in the same fashion as THF can, therefore influencing the propagation rate constant ( k p ) or the equilibrium constant for the dimer−ion pair dissociation ( K diss ) and consequently increasing the overall rate of reaction. 1 1 Rate of addition for the functionalization reaction of poly(styryl)lithium with propylene oxide in the presence and in the absence of THF.…”
The room-temperature functionalization reaction between
poly(styryl)lithium and propylene
oxide in benzene was studied. The functionalized polymer was
characterized by 1H NMR, 13C NMR,
and
APT-13C NMR. 13C-methyl-labeled propylene
oxide-functionalized polystyrene was also synthesized and
characterized. Hydroxylated polystyrene was obtained in only 93%
yield, but with high regioselectivity
(97% of addition of the anionic chain-end to the least substituted
carbon of the propylene oxide ring) and
no oligomerization. The lower than quantitative yield was ascribed
to the proton-transfer reaction of
poly(styryl)lithium from the methyl group of propylene oxide,
which formed unfunctionalized polystyrene.
“…6 These telechelic APs self-assemble into starlike flowers in dilute regime and develop a fully connected network of flowers above some threshold concentration. 14 In order to improve our understanding of hydrophobic segment influence on rheological behavior, we have developed a method to prepare asymmetric functional (PEOs) by taking advantage of living anionic polymerization of ethylene oxide (EO) [15][16][17][18][19][20][21] initiated by alkoxides. The hydroxy telechelic oneended PEO is then modified by esterification.…”
Section: Introductionmentioning
confidence: 99%
“…In order to improve our understanding of hydrophobic segment influence on rheological behavior, we have developed a method to prepare asymmetric functional (PEOs) by taking advantage of living anionic polymerization of ethylene oxide (EO) – initiated by alkoxides. The hydroxy telechelic one-ended PEO is then modified by esterification.…”
A method was developed to prepare asymmetric end-capped poly(ethylene oxide)s (PEOs), containing an alkyl group on one chain end and a perfluoroalkyl group on the other one (C18H37−PEO−C2H4−C8F17 and C18H37−PEO−C10H20−C8F17). These new telechelic associative polymers (APs) were synthesized by anionic polymerization of ethylene oxide initiated by an alkoxide (C18H37−O−K+) followed by esterification. The rheological behavior of asymmetric and analogous symmetric APs in aqueous solutions has been investigated as a function of polymer concentration (C), hydrophobic end-cap and surfactant used to homogenize the system: sodium dodecyl sulfate (SDS) or lithium perfluorooctyl sulfonate (LiFOS). A steep increase of the static viscosity η, attributed to the formation of a multiconnected network, is observed for C ≈ 1 wt %. Semidilute solutions present a Maxwellian rheological behavior with only one relaxation time τ associated with the least hydrophobic end group. The viscoelastic response is modified by the interactions between hydrophobic end groups and surfactant inside mixed aggregates.
“…However, there are various, fragmentary reports that lithiumbased initiators may, under certain conditions, effect the polymeri zation of ethylene oxide (11,14,15). Since anionic polymerizations of non-polar monomers involving lithium offer considerable advantages in terms of control of the major variables affecting polymer properties (13), it is important to determine if conditions can be found to use well-characterized, polymeric organolithium compounds to polymer ize ethylene oxide.…”
The anionic polymerization of ethylene oxide has been investigated using poly(styryl)lithium, α-lithium poly(methyl methacrylate), cumylpotassium, and sodium tributyl magnesate as initiators. No ethylene oxide polymerization was detected in tetrahydrofuran using initiators with the lithium counterion. In a mixture of benzene and dimethylsulfoxide (2/1), ethylene oxide polymerization was observed using the ethylene oxide adduct of poly(styryl)lithium. Size exclusion chroma tography and viscosity measurements indicate that the hydrodynamic volume of the triblock polymer, poly-(styrene-b-ethylene oxide-b-styrene) is very similar to that of the corresponding diblock polymer, poly(stryene -b-ethylene oxide) with half the molecular weight.Ethylene oxide is an inherently reactive monomer from a thermodynamic point of view. Because of the ring strain in the three-membered ring the enthalpy of polymerization of ethylene oxide is comparable to that of cyclopropane, -27 kcal/mole(l). A variety of simple and com plex catalysts and initiators can be used to effect the polymeri zation of ethylene oxide and homologous compounds (_2-4)· Therefore, it is somewhat surprising that lithium hydroxide and lithium alkox ide s have been reported to be ineffective initiators for the polym erization of ethylene oxide and propylene oxide(_5-9). This apparent lack of reactivity of these lithium salts stands in sharp contrast with kinetic studies of the reactions of ethylene oxide with alkali metal derivatives of fluoradenyl(10) and polystyryl(11) carbanions where the lithium derivatives are the most reactive species by sev eral powers of ten. This lack of polymerization activity has been used to advantage for the hydroxyethylation of simple(12) and poly meric (2,9,13) organolithium compounds in high yields (Equation 1).PLi 2) Η^7 ΐθηβ °X ide> PCH 2CH 2 0H(1)
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
