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Oxydation du polystyryl(lithium) avec l'oxygene moleculaire a l'etat solide (avec et sans tetramethylethylenediamine) dans le benzene et dans le melange benzene/THF

The functionalization reaction of poly(styryl)lithiums (Mn = 1.3–9.9 × 103) with ethylene oxide in benzene proceeds quantitatively ( > 99%) to produce the corresponding hydroxyethylated polymer as determined by vapor phase osmometry, size exclusion chromatography, end-group titration, thin layer chromatography, and 1H- and 13C-NMR spectroscopy. 13C-NMR spectral analysis of the functionalized polystyrene with Mn = 1.3 × 103 was consistent with addition of only one ethylene oxide unit to poly(styryl)lithium, i.e., no evidence for ethylene oxide oligomerization was observed.

Heats of interaction of Lewis bases with hexameric and tetrameric alkyllithiums in hydrocarbon solution at 25° have been determined by high dilution solution calorimetry at low base to lithium atom ratios. The Lewis bases utilized include tetrahydrothiophene, tetrahydrofuran, triethylphosphine, triethylamine, and diethyl ether. The organolithiums investigated were n -butyllithium, ethyllithium, isopropyllithium, trimethylsilylmethyllithium, and t -butyllithium. The basicity order based on initial enthalpies of interaction is independent of the alkyllithium compound. Larger enthalpies of interaction were observed for the tetrameric versus hexameric alkyllithiums with the exception of tetrameric t -butyllithium which does not interact significantly with these bases. The sensitivities of the enthalpies to the steric requirements of the base were probed by comparison of the enthalpies for tetrahydrofuran, 2-methyltetrahydrofuran, and 2,5-dimethyltetrahydrofuran. Base coordination to hexameric n -butyllithium is more sensitive to the steric requirements of the tetrahydrofuran bases than is coordination to tetrameric trimethylsilylmethyllithium or isopropyllithium. These results are interpreted in terms of coordination of tetrahydrofuran bases to the intact hexameric aggregate for n -butyllithium; however, it is concluded that the corresponding interaction with hexameric trimethylsilylmethyllithium leads directly to base-solvated tetramers.

The carbonation reactions of polymeric organolithium compounds with high purity, gaseous carbon dioxide have been investigated in benzene and benzene/tetrahydrofuran (75/25) solutions. The polymers investigated were poly(styryl)lithium, poly(isoprenyl)lithium, and poly(styrene-b-isoprenyl)lithium. In Benzene solution the products are a mixture of the carboxylic acid and the ketone (dimer). No tertiary alcohol product (trimer) was observed. In benzene/tetrahydrofuran solution, the quantitative carboxylation of chain ends was observed.

The use of the rearrangement of hex-5-enyl radical intermediates as a mechanistic probe has been examined in the reductive demercurations of hex-5-enyl-l-mercuric bromide (1). Methylcyclopentane and 1-hexene are the major products from reductions of 1 by sodium borohydride, lithium aluminum hydride, and tri-n-butyltin hydride. The formation of methylcyclopentane and the absence of cyclohexane are consistent with a noncage, free-radical chain mechanism for these reductions. The sodium amalgam reduction of 1 produces only 1-hexene. Hex-5-en-l-ol and a peroxide are formed from sodium borohydride reductions of 1 in the presence of molecular oxygen. Isotope effects for transfer of hydrogen to the intermediate hex-5-enyl radicals have been determined from the 1-hexene/methylcyclopentane product ratio, since rearrangement of the 5-hexenyl radical competes with hydrogen abstraction. The magnitude of these isotope effects (1.8 +- 0.2) is the same for reductive demercurations of 1 by sodium borohydride, lithium aluminum hydride, and tri-n-butyltin hydride; these results provide evidence for a common hydrogen-transfer agent, such as hex-5-enyl-1-mercuric hydride, for all of these metal-hydride reductions. The validity of the competing rearrangement method of determining hydrogen isotope effects has been demonstrated by determining the isotope effect for the tri-n-butyltin hydride reduction of 6-bromo-1-hexene (2.8 +- 0.2) at 40/sup 0/C.

The enthalpies of interaction of N,N,N′,N′-tetramethylethylenediamine (TMEDA) with poly-(isoprenyl)lithium and poly(styryl)lithium were measured as a function of R ([base]/[Li]) by using high-dilution solution calorimetry at 25°C. Both polymeric organolithiums exhibit initial exothermic enthalpies of interaction with TMEDA (R ≃ 0.1) of ca. −13 kcal/mole. The concentration dependencies show a break (decrease) in the plot of ΔH vs. R at ca. R = 0.5 for poly(isoprenyl)lithium and at ca. R = 1.0 for poly(styryl)lithium.

The results reported herein established the complexity of the alkyllithium-initiated anionic homopolymerization, styrene copolymerization and styrene block copolymerization of 1,3,5-hexatriene in comparison to the controlled, predictable behavior observed with dienes. As a result of 1,6- and 1,2-enchainment, conjugated diene units are formed along the polymer backbone which can react with the living carbanionic centers to produce branched polymers as indicated in Equation (1). The general effect of solvent on microstructure, as indicated by infrared spectral analyses, is analogous to that of dienes in that 1,2-addition is increased in polar versus hydrocarbon solvents. The observation of branching reactions suggests that conjugated trienes may be useful as branching agents for copolymerizations or linking reactions analogous to the behavior of divinylbenzenes.

This review describes recent results for preparing graft copolymers with controlled structures. In general, the macromonomer approach appears to be the most promising method for preparation of graft polymers with well defined structures. Not only can macromonomers be prepared using radical, cationic, or anionic polymerization procedures, but the resultant macromonomers can be polymerized using these same methods. Obviously, the macromonomer functionality must be high and well defined. In addition, the average chain length and chain length distribution should be well characterized. In principle, the macromonomer approach can provide comb-type graft copolymers with a random distribution of well characterized graft branches. However, the actual copolymerization of the macromonomers with a variety of comonomers requires careful examination under a variety of reaction conditions before that expectation can be realized. These macromonomers provide an excellent opportunity to examine the effects of chain length on the problem of heterogeneity (i.e., phase-separation) which is expected and found in many grafting systems. “Grafting-from” reactions also should provide graft polymers whose structures are more amenable to prediction and analysis. Like the macromonomer method, it should be possible to eliminate the presence of unwanted homopolymer using this method. However, much more research is required before the generality and value of this method can be evaluated. In conclusion, this era appears to be an exciting time for graft polymerization research. The potential exists for the preparation of model graft polymers with precise structural definition using the methods described herein. This development will, at last, provide graft polymers which can be used to define the relationships between the structure, morphology, and properties of these materials.

Heats of interaction of tetrahydrofuran, tetrahydrothiophene, triethylamine, and triethylphosphine with solutions of n-butyllithium in hexane have been determined by high dilution solution calorimetry. The relative heats of interaction of these bases are in the order tetrahydrofuran > triethylphosphine ≈ triethylamine > tetrahydrothiophene. These results are interpreted in terms of an acid—base interaction which is dominated by electrostatic effects. The alkyllithium aggregate is characterized as a relatively hard Lewis acid species.

Alkyllithium-initiated, anionic polymerization of vinyl monomers is a very useful synthetic method since the major variables affecting polymer properties can generally be controlled, i.e., molecular weight, molecular weight distribution, copolymer composition, diene microstructure, molecular architecture, and chain-end functionality.1–3 This control is a direct consequencce of the fact that in the absence of reactive impurities these polymerizations are termination and chain transfer free; therefore, the products of these polymerizations are polymer chains with carbanionic chain ends (“living polymers”).4 An illustrative mechanistic description is shown in Scheme I for the sec-butyllithium-initiated polymerization of styrene.

A new dissociative mechanism involving enolate anion intermediates is proposed for the process currently categorized as nucleophile-catalyzed “group transfer polymerization” (GTP). A rapid, reversible complexation of small concentrations of enolate anions with silyl ketene acetals (reversible termination) is proposed to explain the living nature of these polymerizations and the role of the silyl ketene acetals in “GTP”. It is proposed that these polymerizations do not involve “group transfer” in the chain-propagating step. These mechanistic conclusions are based on studies of the tetrabutylammonium 9-methyl-fluorenide- and methyllithium-initiated polymerizations of methyl methacrylate at ambient temperatures in the presence and absence of silyl ketene acetal.

There has been growing interest and research on new synthetic methods for the preparation of well-defined polymers with in-chain and chain-end functional groups.1–14 These functional groups in polymers can participate in: (a) reversible ionic association; (b) chain extension, branching or cross-linking reactions with polyfunctional reagents; (c) coupling and linking with reactive groups on other oligomer or polymer chains; and (d) initiation of polymerization of other monomers. In order to exploit this unique potential of functionalized polymers, it is important to consider the scope and limitations of current functionalization methodology using anionic polymerization.

A block copolymer is defined as a polymer comprising molecules in which there is a linear arrangement of blocks, a block being defined as a portion of a polymer molecule in which the monomeric units have at least one constitutional or configurational feature absent from the adjacent portions.1, 2 In a block copolymer, the distinguishing feature is constitutional, i.e. each of the blocks comprises units derived from a characteristic species of monomer. This definition excludes branched structures in which the branches are composed of blocks, i.e. star or radical block copolymers. This review will consider the synthesis, characterization and morphology of both linear and star block copolymers with well-defined structures.

One of the goals of synthetic polymer chemistry is to prepare polymers with control over the major variables affecting polymer properties. These variables include molecular weight, molecular weight distribution, copolymer composition and microstructure, tacticity and diene microstructure, chain end functionality, branching and morphology. Anionic polymerization methods have approached this goal of synthesizing polymers with well-defined structures in monomer/initiator/solvent systems which proceed in the absence of chain termination and chain transfer reactions.[1–4] For example, under certain carefully controlled conditions, the anionic polymerizations of styrene, diene, methacrylate, epoxide, and lactone monomers proceed without significant contributions from chain termination and chain transfer reactions to produce polymers which retain their reactive anionic chain-end functionality when all of the monomer has been consumed. In these system, the major variables affecting polymer properties can indeed be controlled. The scope and limitations of these anionic polymerization methods are described in several recent books and reviews.[1–5]

One of the goals of synthetic polymer chemistry is to prepare polymers with control over the major variables affecting polymer properties. These variables include molecular weight, molecular weight distribution, copolymer composition, configurational microstructure, branching, and chain-end functionality. Anionic polymerization methods have approached this goal of synthesizing polymers with well-defined structures in monomer/initiator/solvent systems which proceed in the absence of chain termination and chain transfer reactions. For example, under certain carefully controlled conditions, the anionic polymerization of styrene, diene, methacrylate, epoxide, and lactone monomers proceeds without significant contributions from chain termination and chain transfer reactions to produce polymers which retain their reactive anionic chain-end functionality when all of the monomer has been consumed. In these systems, the major variables affecting polymer properties can indeed be controlled. The scope and limitations of these anionic polymerization methods are described in several recent books and reviews.1–3

The preparation, properties and phase-selective crosslinking reactions of poly(p-methylstyrene-b-butadiene-b-p-methylstyrene), PMS-BD-PMS, have been examined. The PMS-BD-PMS triblock copolymer was synthesized anionically by sequential monomer addition. The ability to selectively crosslink the poly(p-methylstyrene) end-block segments was examined by curing with various polymers containing hydroperoxide end groups. Both polystyrene hydroperoxide, PSO2H, and poly(p-methylstyrene) hydroperoxide, PMSO2H, were found to significantly increase tensile stress at break and the percent elongation-at-break of the PMS-BD-PMS triblock copolymer. In addition, the modified triblock copolymer was insoluble in toluene, heptane and methyl ethyl ketone. When unfunctionalized styrene homopolymer was added the effects were quite different. These results have been compared to the unselective, non-phase-selective peroxide, dicumyl peroxide, which dramatically decreases the elastomeric properties of the triblock copolymer after curing. In addition, the specificity of this effect has been investigated by carrying out equivalent experiments with an analogous poly(styrene-b-butadiene-b-styrene), PS-BD-PS, triblock copolymer. No enhancement of tensile properties was observed on the treatment. of the PS-BD-PS triblock copolymer with PS02H, followed by curing. The phase-selective curing of PMS-BD-PMS resulted in a product with better tensile properties at 70oC than that observed for the corresponding uncured PMS-BD-PMS and PS-BD-PS triblock copolymers.

The relative stabilities of several methoxycarbenium ions have been determined directly via a stepwise equilibration method.

This article was written to provide an introduction to the basic concepts of polymer stereochemistry and their applications.