Anionic polymer synthesis

In the following sections, synthesis of the anionic polymers, copolymer molecular weight, limiting viscosity number, electrolyte effects, solution shear thinning, screen factor, polymer radius of gyration, and solution aging will be discussed and data on the copolymers presented. 

Polymer Synthesis and Characterization. This topic has been extensively discussed in preceeding papers.(2,23,24) However, we will briefly outline the preparative route. The block copolymers were synthesized via the sequential addition method. "Living" anionic polymerization of butadiene, followed by isoprene and more butadiene, was conducted using sec-butyl lithium as the initiator in hydrocarbon solvents under high vacuum. Under these conditions, the mode of addition of butadiene is predominantly 1,4, with between 5-8 mole percent of 1,2 structure.(18) Exhaustive hydrogenation of polymers were carried out in the presence of p-toluenesulfonylhydrazide (19,25) in refluxing xylene. The relative block composition of the polymers were determined via NMR. 

The controlled radical polymerization techniques opened up a new era in polymer synthesis, and further growth and developments are certain. However, the control of the molecular characteristics and the variety of macro-molecular architectures reported by these methods cannot be compared with those obtained by other living polymerization techniques such as anionic polymerization. 

These days anionic polymers have attracted attention for the synthesis of monodisperse polymers and the specialised types of copolymers. 

Compared to today s elegant methods based on anionic polymerization, the early work involved relatively crude free radical polymerization, but the idea itself (and the concomitant nomenclature) represented a real advance in polymer synthesis. 

Guerrero-Sanchez C, Abeln C, Schubert US (2005) Automated parallel anionic polymerizations enhancing the possibilities of a widely used technique in polymer synthesis. J Polym Sci Part A Polym Chem 43 4151-4160... 

The phenomenal growth in commercial production of polymers by anionic polymerization can be attributed to the unprecedented control the process provides over the polymer properties. This control is most extensive in organolithium initiated polymerizations and includes polymer composition, microstructure, molecular weight, molecular weight distribution, choice of functional end groups and even monomer sequence distribution in copolymers. Furthermore, a judicious choice of process conditions affords termination and transfer free polymerization which leads to very efficient methods of block polymer synthesis. 

Oxidation of Anionic Polymers In the Solid State The ability of the macroradical and of the macroions to diffuse In the mixture, and to interreact Is responsible for the secondary products formation coupling reaction and alcoholate synthesis. To prevent the diffusion phenomenon, we have carried out the deactivation In the solid state. The living polymers have been prepared In benzene, with or without a solvating agent (THF or TMEDA) and the solution has been freeze dried before the oxygen introduction. The experimental results are collected in Table VII. 

A large variety of organometallic compounds, e.g., metal alkoxides and metal carboxylates, has been studied as initiators or catalysts in order to achieve effective polymer synthesis [35]. Many reactions catalyzed by metal complexes are highly specific and, by careful selection of metal and ligands, reactions can be generated to form a desired polymer structure [36, 37]. The covalent metal alkoxides with freep or d orbitals react as coordination initiators and not as anionic or cationic inititors [38]. Fig. 1 summarizes some of the most frequently used initiators and catalysts. 

Application of pulse radiolysis to polymers and polymerization was motivated at first by the success of radiation-induced polymerization as a novel technique for polymer synthesis. It turned out that a variety of monomers could be polymerized by means of radiolysis, but only a little was known about the reaction mechanisms. Early studies were, therefore, devoted to searching for initiators of radiation-induced polymerization such as radicals, anions and cations derived from monomers or solvents. Transient absorption spectra of those reactive intermediates were assigned with the aid of matrix isolation technique. Thus the initiation mechanisms were successfully elucidated by this method. Propagating species also were searched for enthusiastically in some polymerization systems, but the results were rather negative, because of the low steady state concentration of the species of interest. 

Ring-opening polymerization is an important field of research in the chemistry of polymer synthesis. Usually, it proceeds by ionic mechanisms, i.e. cationic, anionic and coordinate anionic mechanisms. Research on ring-opening polymerization proceeding via free-radical propagating species in which the so-called molecular design of monomer plays an important role has recently been reported. 

Semiconductor nanoclusters (quantum dots) possess chemical and physical properties that differ substantially from those of the analogous bulk solids [36-38]. Quantum dots have been synthesized using hosts such as zeolites [39], porous glass [40], micelles [41], membranes [42], and anionic polymers [43]. The synthesis and characterization of CdS quantum dots in dendrimer hosts have been studied [44-48]. Here, two PAMAM dendrimers are used one is G3.5 with surface carboxyl group and the other is G4 with surface amino group. Mixing solutions of Cd2+ and S2 in pure methanol result in a yellow precipitate of... 

Schwab FC, Murray JG (1985) Anionic dispersion polymerization of styrene. In Culbertson BM, McGrath JE (eds) Advances in polymer synthesis. Plenum, New York... 

Two related procedures have been developed to effect this transformation. Both Involve the Initial synthesis of mono- or dlfunctlonal living anionic polymers of styrene, butadiene, or block copolymers of both. They are then reacted via Grlgnard Intermediates (7 ) with either excess bromine or with excess m-xylylyl dlbromlde (8-10) to yield polymers with reactive halide terminal groups (benzyllc or allyllc depending upon the polymer and terminating agent). The reactions for polystyrene are shown In equations 2 and 3. 

Anionic Methods. Of the various methods used for nonpolar block polymer synthesis, the anionic approach is by far the most useful and most precise in producing a given segmented chain design [A-B-A, (A-B)j, A-B-C, etc.]. The linear A-B-A block polymer may be synthesized by two basic routes, sequential polymerization of all three blocks or sequential polymerization of two blocks, followed by coupling. The "sequential" method is illustrated in Reaction la for the preparation of S-B-S the "coupling" process is depicted in Reaction lb. 

A historical perspective on the development of hydrophobe-modified, water-soluble polymers is presented. The various synthetic procedures used to obtain different associative thickeners are discussed in terms of the complexities in ionogenic monomer polymerizations. This discussion serves two purposes. The first is to present the peculiarities in anionic and cationic polymer synthesis in contiguity with previous work on water-soluble polymers that related only to their use. The second purpose is to draw parallels between the discontinuities in the classical chain-growth polymerization of nonionic with ionogenic monomers and those that should be expected to occur with hydrophobe-modified monomers, but for which there are insufficient data in associative thickener technology to define properly. 

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