Building poly

First, there are two types of sugars used to build poly(nucleic acids), /S-ribose, which has the structure shown in the center of Figure 9-40, and /3-2-deoxyribose, shown at the top of this figure. They differ only in the presence of an -OH group in /1-ribose that is absent in /3-2-deoxyribose. This apparently minor difference has a profound effect on the conformation of the nucleic acids from which they are made and their ability to form certain structures, as we will discuss shortly. 

As mentioned above, the classical polyoxoanion forming metals are molybdenum and tungsten in the oxidation state VI. It is assiuned that for these metal cations the combination of ion-radius and -charge and the availability of empty d-orbitals for the formation of metal-oxygen-rx-bonds is especially favorable. However, other metals can act as polyoxoanion-builders as well. Vanadimn-, niobiiun- and tantalum-V, technetium-, rhenium-, ruthenium- and osmium-Vl, chromium-, molybdenum-, timgsten-, technetium- and rhenium-V and tita-niiun-, vanadium-, chromium-, molybdenum- and tungsten-IV can build poly-oxometallate-clusters. 

Heat-SensitiZingProcess. Another process used to make latex mbber articles of thicker section involves sensitizing the compound so that it coagulates when heated to a given temperature, then using heated molds to build the article to the desired thickness. Ammonia-preserved latex is used in this process, and polyether, polythioether, or poly(vinyl methyl ether) (PVME) can be used as heat-sensitizing agents. 

Poly(vinyl chloride). Poly(vinyl chloride) (PVC) [9002-86-2] is a thermoplastic for building products. It is prepared by either the bulk or the suspension polymerization process. In each process residual monomer is removed because it is carcinogenic. Oxygen must be avoided throughout the process (see Vinyl polymers). 

Polymethacrylates. Poly(methyl methacrylate) [9011-14-7] is a thermoplastic. Itis the acryUc resin most used in building products, frequendy as a blend or copolymer with other materials to improve its properties. The monomer is polymerized either by bulk or suspension processes. Eor glazing material, its greatest use, only the bulk process is used. Sheets are prepared either by casting between glass plates or by extmsion of pellets through a sHt die. This second method is less expensive and more commonly used. Peroxide or azo initiators are used for the polymerization (see Methacrylic polymers). 

Poly(L-malic acid) denotes a family of polyesters derived from L-malic acid as the building unit. By chemical synthesis, three kinds of poly(L-malic acid) have been obtained, depending on the molecular position of the ester bond the a-type(I) [1], the j8-type(II) [2], and the a,j8-mixed-type(III) [3). 

A large part of organic and macromolecular chemistry starts with the chemical functionalization of benzene, and benzene units serve us building blocks for important polymers. Naturally, benzene-based aromatic materials also represent an important subclass of jt-conjugaled architectures. Despite some synthetic difficulties related to the generation of structurally well-defined oligo- and poly(phenyl-... 

The versatility of poly(phenylcne) chemistry can also be seen in that it constitutes a platform for the design of other conjugated polymers with aromatic building blocks. Thus, one can proceed from 1,4- to 1,3-, and 1,2-phenylene compounds, and the benzene block can also be replaced by other aromatic cores such as naphthalene or anthracene, helerocyclcs such as thiophene or pyridine as well as by their substituted or bridged derivatives. Conceptually, poly(pheny ene)s can also be regarded as the parent structure of a series of related polymers which arc obtained not by linking the phenylene units directly, but by incorporation of other conjugated, e.g. olefinic or acetylenic, moieties. 

The small molecules used as the basic building blocks for these large molecules are known as monomers. For example the commercially important material poly(vinyl chloride) is made from the monomer vinyl chloride. The repeat unit in the polymer usually corresponds to the monomer from which the polymer was made. There are exceptions to this, though. Poly(vinyl alcohol) is formally considered to be made up of vinyl alcohol (CH2CHOH) repeat units but there is, in fact, no such monomer as vinyl alcohol. The appropriate molecular unit exists in the alternative tautomeric form, ethanal CH3CHO. To make this polymer, it is necessary first to prepare poly(vinyl ethanoate) from the monomer vinyl ethanoate, and then to hydrolyse the product to yield the polymeric alcohol. 

Bmin P, Veensda GJ, Nijenhuis AJ, and Pennings AJ. Design and synthesis of biodegradable poly(ester-urethane) elastomer networks composed of non toxic building blocks. Makromol Chem Rapid Common, 1988, 9, 589. 

Although of limited success, this Ni-catalysed coupling strategy builds on a previous report of the successful, direct synthesis of poly(4,4 -diphenylphenyl-phosphine oxide) (70c) from bis(p-chlorophenyl)-phenylphosphine oxide (71) (Scheme 21) [66]. The white soluble material (70c) (Aj ax 280 nm) was found to have a single phosphorus environment by NMR spectroscopy, a comparatively high molecular weight (Mn= 15,300) together with a low molecular... 

Ferrocene has been extensively used as a building block to prepare organo-metallic polymers and heteroatom-bridged poly(metallocenes)(G )-(G ")(Fig 4). 

Although the initially reported tissue compatibility tests for subcutaneous implants of poly(BPA-iminocarbonate) were encouraging (41,42), it is doubtful whether this polymer will pass more stringent biocompatibility tests. In correspondence with the properties of most synthetic phenols, BPA is a known irritant and most recent results indicate that BPA is cytotoxic toward chick embryo fibroblasts in vitro (43). Thus, initial results indicate that poly(BPA-iminocarbonate) is a polymer with highly promising material properties, whose ultimate applicability as a biomaterial is questionable due to the possible toxicity of its monomeric building blocks. 

It was therefore particularly inteipesting to investiage whether it would be possible to replace BPA by various derivatives of L-tyrosine as monomeric building blocks for the synthesis of poly-(iminocarbonates). In order to be practically useful in drug delivery applications, the replacement of BPA by derivatives of tyrosine must give rise to mechanically strong yet fully biocompatible polymers. 

Based on these monomeric building blocks a series of four structurally related poly(iminocarbonates) were synthesized carrying either no pendant chains at all [poly(Dat-Tym) ], a N-benzyloxycarbonyl group as pendant chain [poly(Z-Tyr-Tym)], a hexyl ester group as pendant chain (poly(Dat-Tyr-Hex) ], or both types of pendant chains simultaneously (poly(CTTH)] (Fig. 7). 

In 1996, Wegner et al. published the synthesis of poly(oligophenylenevinyle-ne)s (96), consisting of biphenylene-, terphenylene- and quinquephenylene moieties as aromatic building blocks, via Suzuki-type aryl-aryl cross coupling of AA/BB-type monomers [121]. By judicious choice of the arylene moieties, the optical properties of the resulting polymers can be tailored within a wide range. 

FIG. 9 Schematic illustration of adsorption of poly(styrenesulfonate) on an oppositely charged surface. For an amphiphile surface in pure water or in simple electrolyte solutions, dissociation of charged groups leads to buildup of a classical double layer, (a) In the initial stage of adsorption, the polymer forms stoichiometric ion pairs and the layer becomes electroneutral, (b) At higher polyion concentrations, a process of restructuring of the adsorbed polymer builds a new double layer by additional binding of the polymer. 

Some research groups also tried to build up bi- and multilayers of latex particles by using self-assembly techniques [92-94,97]. Either the alternate adsorption technique outlined in Figure 14 was used, in which cationic and anionic particles are successively adsorbed, or a slightly modified version of successive adsorption of anionic particles and a cationic poly-... 

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