Polymer synthesis by direct

UEDA OKADA Ordered Polymer Synthesis by Direct Polycondensaiion 443... 

Feast, W. J. et al J. Chem. Soc., Chem. Comm., 1985, 202-203 The second stage of an improved synthesis of poly(acetylene), which involves disproportionation of a soluble polymer by heating a thin film at 75°C to give 1,2-bis(trifluoromethyl)benzene and poly(acetylene), must not be done in bulk because the reaction then becomes explosive. The earlier synthesis by direct polymerisation of acetylene was considerably more dangerous... 

Postsulfonation of polymers to form PEMs can lead to undesirable side reactions and may be hard to control on a repeatable basis. Synthesis of sulfonated macromolecules for use in PEMs by the direct reaction of sulfonated comonomers has gained attention as a rigorous method of controlling the chemical structure, acid content, and even molecular weight of these materials. While more challenging synthetically than postsulfonation, the control of the chemical nature of the polymer afforded by direct copolymerization of sulfonated monomers and the repeatability of the reactions allows researchers to gain a more systematic understanding of these materials properties. Sulfonated poly(arylene ether)s, sulfonated poly-(imide)s, and sulfonated poly(styrene) derivatives have been the most prevalent of the directly copolymerized materials. 

The use of functional monomers permits ready control of the content and sometimes the distribution of units along the polymer chain this procedure gives more latitude concerning the physical properties of the final product. On the other hand, chemical modification of an existing polymer, when possible, enables the choice of molecular weight and the dispersity of the polymer. It also allows the synthesis of polymers inaccessible by direct route. 

Tan et al. explored the synthesis of monomers that are monofunctional. They have synthesized two hypercrosslinked polymer networks of bishy-dro>ymethyl monomers, e.g., 1,4-benzenedimethanol (BDM), and mono-hydro>ymethyl compounds, e.g., benzyl alcohol (BA) by self-condensation. Precursors of polymers like polystyrene and poly(chloromethylstyrene) ° that are swollen, as well as polyfunctional benzyl chlorides, are synthesized by Friedel-Crafts allq lation in the presence of a Lewis acid. Hydroxymethyl and chloromethyl form a bond with the benzene ring in the presence of an acid catalyst,leading to the design of a new series of hypercrosslinked polymers prepared by directly using the building blocks of hydro)g7methyl aromatics (Figure 3.2). 

Poly(methylphenylphosphazene) can be derivatized through either deprotonation/substitution reactions at the methyl group or electrophilic aromatic substitution of the phenyl group. These reactions have been used to prepare a variety of new polyphosphazenes with all functional groups attached to the polymer backbone by direct P-C bonds. The synthesis and characterization of several of these new... 

The second front originates in the polymer synthesis community. Efforts are mainly directed toward production of monodisperse block copolymers by living polymerizations. These stmctures typically result in microphase separated systems if one block is a high T material and the other is elastomeric in... 

Vaia, R.A., Ishii, H. and Giannelis, E.P. 1993. Synthesis and properties of two dimensional nanostructures by direct intercalation of polymer melts in layered silicates. Chemistry of Material 5 1694-1696. 

We have already referred to the Mo/Ru/S Chevrel phases and related catalysts which have long been under investigation for their oxygen reduction properties. Reeve et al. [19] evaluated the methanol tolerance, along with oxygen reduction activity, of a range of transition metal sulfide electrocatalysts, in a liquid-feed solid-polymer-electrolyte DMFC. The catalysts were prepared in high surface area by direct synthesis onto various surface-functionalized carbon blacks. The intrinsic... 

To avoid problems associated with these polymer reactions, the direct synthesis of lithium borate polymer electrolytes37 was undertaken by dehydrocoupling polymerization using lithium mesitylhydroborate40 (scheme 7). 

Polymer films may also be synthesized by direct chemical routesT 101. These chemical synthesis routes generally involve some form of electrophilic substitution using Grignard reagents or other modified precursors. The purity and electrical properties of the films produced from the chemical route are generally poorer than... 

We chose the tt-bonds of the polybutadiene block as the functional groups to connect different side groups to the polymer block. A direct connection of side groups to the rr-bonds is difficult and leads to unstable products therefore, a two-step synthesis was employed. The first step is a conversion of the Jt-bonds into a more easily accessible species. This can be done by either hydroxylation (hydro-... 

Protein polymers based on Lys-25 were prepared by recombinant DNA (rDNA) technology and bacterial protein expression. The main advantage of this approach is the ability to directly produce high molecular weight polypeptides of exact amino acid sequence with high fidelity as required for this investigation. In contrast to conventional polymer synthesis, protein biosynthesis proceeds with near-absolute control of macromolecular architecture, i.e., size, composition, sequence, topology, and stereochemistry. Biosynthetic polyfa-amino acids) can be considered as model uniform polymers and may possess unique structures and, hence, materials properties, as a consequence of their sequence specificity [11]. Protein biosynthesis affords an opportunity to completely specify the primary structure of the polypeptide repeat and analyze the effect of sequence and structural uniformity on the properties of the protein network. 

The number average diameter of microspheres obtained from polymers synthesized, by emulsification of polymer solutions followed by solvent extraction and/or solvent evaporation methods, can be controlled by choosing the appropriate conditions at which particles are produced. However, by this method particles with 15 p,m and with D D > 1.9 are produced. Spray drying did not provide poly(L-Lc) particles with regular spherical shape. Direct synthesis of poly(L-Lc) microspheres by ring-opening polymerization with stepwise monomer addition can be used as a method of choice for the production of microspheres with diameters controlled to ca. 6 p.m and with diameter polydispersity parameter < 1.20. 

A line of research that has aroused much interest in recent years is the study of head-to-head, tail-to-tail polymers (96-98). Their direct synthesis has little likelihood of being successffil as head-to-tail sequences usually predominate in vinyl polymerization. One possibility for their preparation is through the chemical modification of suitable preformed polymers. In the case of the head-to-head, tail-to-tail polypropylene, different stereoisomeric forms have been isolated, depending on the method of preparation. In the general scheme, the precursor is an unsaturated polymer obtained by polymerization of the disubsti-tuted butadiene (2,3-dimethylbutadiene or 2,4-hexadiene) then, by chemical or catalytic reduction, this polymer is converted into the desired polypropylene, whose stmcture can then be examined by NMR spectra. Head-to-head, tail-to-... 

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