Synthetic routes to polymers

DI-TOI mass spectral analysis is becoming increasingly important as a method for the determination of molecular weights of synthetic polymers, since in comparison to traditional methods (such as GPC), the results can be obtained in a few minutes. In the simplest terms, the macromolecule is dispersed in a UV-absorbing matrix, and becomes volatilized when subjected to a pulse of laser energy the volatile particles are then ionized and subsequently 

NMR is not, of course, the only analytical technique used to establish the composition and microstructure of polymeric materials. Others include 66 ultraviolet-visible spectroscopy (UV-Vis), Raman spectroscopy, and infrared (IR) spectroscopy. IR and Raman spectroscopy are particularly useful, when by virtue of cross-linking (see. e.g. Chapter 9), or the presence of rigid aromatic units (see Chapter 4). the material neither melts nor dissolves in any solvent suitable for NMR. The development of microscopy based on these spectroscopic methods now makes such analysis relatively simple (see below). Space precludes a detailed account of these and many other techniques familiar to the organic chemist. Instead we focus for the remainder of the chapter on some of the techniques used to characterize the physical properties of polymeric materials. 

---

Reduction is an important method for polymer modification resulting in a variety of useful elastomers and thermoplastics with unique structures and properties. Reduction also offers a convenient synthetic route to polymers with special monomer sequences, which are inaccessible, difficult or too expensive to prepare by conventional polymerization... 

Scheme 4.19 Two synthetic routes to polymer 89. Poly[hexa(3-octylthiophene)] analog 90 was prepared by method B.

Marks and co-workers. Scheme 15.12 outlines the synthetic routes to polymers 79a and 79b basically established by Kenny et al. [95] and later modified by Marks et al. [96]. The routes involve the preparation of dichloro(phthalocyaninato)metals and their hydrolysis yielding the respective dihydroxy(phthalocyaninato)-metals. Dehydration of dihydroxy(phthalocyaninato)-metals thus obtained at 440° C in vacuo gives polymers 79a and 79b, [M(Pc)0] . Polymer 79a is obtained as dark-purple crystals and soluble in cone. H2SO4 and HSO3CH3 without decomposition, while polymer 79a decomposes in cone. H2SO4. 

Scheme 40 presents a synthetic route to polymer-supported Weinreb amides starting from commercially available BAL-linker [216]. Whilst most approaches to Weinreb linkers start with the conversion of alcohol functionalities (and following Mitsunobu approach), the BAL linker 260 has to be reacted via reductive amination into the desired methoxyamines 261. Afterwards resin 261 is treated with carboxylic acids 262 in the presence of coupling reagents to give amides 263 containing the target structure. 

Economic Aspects. Oxetanes are expensive monomers and are not readily available in commercial quantities. Commercial production of PBCMO has been discontinued its end uses were not able to support its comparatively high selling price. Energetic polymers prepared from appropriately substituted oxetanes have opened a new market for their use to prepare soHd rocket propeUants and explosives. Should this specialty market result in the large-scale production of these oxetanes even at current (1996) high prices and/or in a cheap synthetic route to oxetanes, this economic picture could change. 

It would be preferable to incorporate both fluorescent and electron transport properties in the same material so as to dispense entirely with the need for electron-transport layers in LEDs. Raising the affinity of the polymer facilitates the use of metal electrodes other than calcium, thus avoiding the need to encapsulate the cathode. It has been shown computationally [76] that the presence of a cyano substituent on the aromatic ring or on the vinylene portion of PPV lowers both the HOMO and LUMO of the material. The barrier for electron injection in the material is lowered considerably as a result. However, the Wessling route is incompatible with strongly electron-withdrawing substituents, and an alternative synthetic route to this class of materials must be employed. The Knoevenagel condensation... 

Figure 21. Atom transfer radical polymerization (ATRP) synthetic route to tetrafunctional initiators of a star polymer with adamantyl (adamantane core). Taken from Ref. [91] with permission.

West (p. 6), Miller (p. 43), Zeigler (10), and Sawan (p. 112) outline the synthesis of a wide variety of soluble, processable polydiorganosilanes, a class of polymers which not long ago was thought to be intractable. Matyjaszewski (p. 78) has found significant improvements in the synthetic method for polydiorganosilane synthesis as well as new synthetic routes to unusual substituted polydiorganosilanes. Seyferth (p. 21, 143) reports synthetic routes to a number of new polycarbosilanes and polysilazanes which may be used as precursors to ceramic materials. 

The development of synthetic routes to new polyphosphazene structures began in the mid 1960 s (2-4). The initial exploratory development of this field has now been followed by a rapid expansion of synthesis research, characterization, and applications-oriented work. The information shown in Figure 3 illustrates the sequence of development of synthetic pathways to polyphosphazenes. It seems clear that this field has grown into a major area of polymer chemistry and that polyphosphazenes, as well as other inorganic macromolecules, will be used increasingly in practical applications where their unique properties allow the solution of difficult engineering and biomedical problems. 

Fig. 6. Synthetic routes to conjugated polymers via precursor polymers for (a) polyacetylene, and (b) arylene vinylenes.

A typical synthetic route to the incorporation of pendent carboranyl units into a polymer chain is shown in scheme 3. Poly(o-carboranyl-organo-siloxane)s have been successfully prepared through hydrolysis of dimethyldichlorosilane in the presence of carboranedichloromethylsilane. The polymer has some of the elastomeric characteristics of the parent poly(siloxane) however, the thermal-oxidative cleavage of the o-carboranyl pendent group is reported to occurat lower temperatures than that for the thermooxidative cleavage of Si—O and Si—C bonds.10 Thermal studies have... 

This effect has also been observed in polyphosphazenes containing alkyl- or phenyl-carborane as pendent groups.12 A typical synthetic route to poly(phenyl-carboranyl-di-trifluoroethoxy-phosphazene) having pendent phenyl-carborane groups is shown in scheme 4. A substantial improvement in the thermal stability of the polymer was observed. This is attributed to a retardation of the ring-chain de-polymerization mechanism due to steric hindrance effects of the carborane units, inhibiting helical coil formation. 

In other words, a synthetic route to polypeptides which requires only HCN and water is presented preformed a-amino acids are not necessary. According to Matthews, the pyrolysis of cyanide polymers can give nitrogen-containing heterocycles with purine and pyrimidine structures in other words, the HCN world ... 

The tendency of nitrones to react with radicals has been widely used in new synthetic routes to well-defined polymers with low polydispersity. The recent progress in controlled radical polymerization (CRP), mainly nitroxide-mediated polymerization (NMP) (695), is based on the direct transformation of nitrones to nitroxides and alkoxyamines in the polymerization medium (696, 697). In polymer chemistry, NMP has become popular as a method for preparing living polymers (698) under mild, chemoselective conditions with good control over both, the polydispersity and molecular weight. 

H. Meng, W. Yu, and W. Huang, Facile synthetic route to a novel electroluminescent polymer — poly(p-phenylene vinylene) containing a fully conjugated aromatic oxadiazole side chain, Macromolecules, 32 8841-8847, 1999. 

Interest in these compounds—mainly for use as weakly coordinating anions—has grown rapidly in the last decade. Many synthetic routes to CBnHi2 and its derivatives are shown in Table 17 (Figures 4 and 5). The structures of CBnH12 and its derivatives determined experimentally are summarized in Table 18. The table shows one column for cations where the anions are regarded as discrete entities within the crystal lattice and the other for cations where the anions are viewed as a fragment of a molecule or polymer in the solid state. 

Figure 9.1 Generic synthetic route to dendrigraft polymers...

Chemical reactions on polymers as a synthetic route to new polymers and functionalized polymeric materials... 

Transition-metal nanopartides are of fundamental interest and technological importance because of their applications to catalysis [22,104-107]. Synthetic routes to metal nanopartides include evaporation and condensation, and chemical or electrochemical reduction of metal salts in the presence of stabilizers [104,105,108-110]. The purpose of the stabilizers, which include polymers, ligands, and surfactants, is to control particle size and prevent agglomeration. However, stabilizers also passivate cluster surfaces. For some applications, such as catalysis, it is desirable to prepare small, stable, but not-fully-passivated, particles so that substrates can access the encapsulated clusters. Another promising method for preparing clusters and colloids involves the use of templates, such as reverse micelles [111,112] and porous membranes [106,113,114]. However, even this approach results in at least partial passivation and mass transfer limitations unless the template is removed. Unfortunately, removal of the template may re-... 

Scheme 12 Synthetic route to silole-acetylene polymers...

LRP has attracted enormous attention over the past decade for providing simple and robust synthetic routes to well-defined, low-polydispersify polymers [33-56]. The basic concept of LRP is a reversible activation process... 

---