Polymer backbone of poly

Aromatic hydrogens on the polymer backbone of poly(diiq>hene)s can be activated electrochemically to the overoxidized state and substituted by nucleophiles Cr, Bi or CH30"(5). However, poly(3-alkyldiiophene)s in the neutral state are electron rich due to the extended K-system and die electralkyl side chain, and thus the 4-hydrogen of the thienyl ring should be more susceptible to electrophilic substitution. 

The question then arises of whether these BNC materials are mixtures of BN and graphite or whether they are ternary compounds in which a carbon has been inserted into the BN lattice structure. A number of other workers have proposed the formation of ternary BNC materials by CVD reactions. Given that wo have previously shownl that the carbon polymer backbone of poly(vinylpentaborane) becomes incorporated into the B4C ceramic produced upon polymer thermolysis, it is reasonable that the BNC materials formed from pyrolyses of poly(vinylborazine) or the poly(vuiylborazine)/polystyrene copolymers, discussed below, may also be ternary materials. We are presently investigating the properties of these materials. 

COE and a COE-based cross-linker, that is, tris(cyclooct-4-en-l-yloxy)methylsilane (TCOMS). This development was guided by the idea that the polymer backbone of poly (COE)-derived materials consists of sec-allylic carbons and, therefore, presents a viable alternative to NBE-based systems. However, compared to NBE-based monomers, COEs are characterized by a significantly reduced ring strain, which makes the use of a more active initiator than the commonly used first-generation Grubbs initiator inevitable. These changes in monomer, cross-linker, and initiator required a comprehensive redesign of monolith synthesis. As a direct consequence of... 

Certain commercially important crosslinking reactions are carried out with unsaturated polymers. For example, as will be described later in this chapter, polyesters can be made using bifunctional acids which contain a double bond. The resulting polymers have such double bonds at regular intervals along the backbone. These sites of unsaturation are then crosslinked by reaction with styrene monomer in a free-radical chain (addition) process to give a material consisting of polymer backbones and poly(styrene) copolymer crosslinks. 

Furthermore, our results on the characterization of the physico-mechanical properties of tyrosine-derived poly(iminocarbonates) provide preliminary evidence for the soundness of the underlying experimental rationale The incorporation of tyrosine into the backbone of poly(iminocarbonates) did indeed result in the formation of mechanically strong yet apparently tissue-compatible polymers. 

Repeated scanning results in a continuous increase in the size of the wave at 0.6 V vs. Ag+/Ag, which is believed to be the oxidation wave of the polythiophene backbone of poly(I). The amount of polymer produced per unit of charge in the deposition has not been measured, but is qualitatively similar to polythiophene itself. A film of poly(I) on the Pt electrode can be seen with the naked eye. After deposition of poly(I), the polymer-modified electrode is transferred, after thorough rinsing, to clean electrolyte for further characterization. 

Since 1985, a major effort has been devoted to incorporating heterocyclic units within the backbone of poly(arylene etherjs (PAE). Heterocyclic units within PAE generally improve certain properties such as strength, modulus and the glass transition temperature. Nucleophilic and electrophilic aromatic substitution have been successfully used to prepare a variety of PAE containing heteorcyclic units. Many different heterocyclic families have been incorporated within PAE The synthetic approaches and the chemistry, mechanical and physical properties of PAE containing different families of heterocyclic units are discussed. Emphasis is placed on the effect variations in chemical structure (composition) have upon polymer properties. 

Stabilization of the mesophase was observed as the degree of polymerization was increased. The Tg values of the poly(norbornene)-polymers were about 30 °C higher than those of the poly(butadiene) polymers. Both polymers showed similar isotropization temperatures, but they differed substantially in their liquid crystalline behaviors. Poly-(IX-n)s with a poly(norbornene) backbone exhibited textures typical of nematic mesophases, whereas the poly-(butadiene)-based polymers poly-(X-n) displayed textures representative of smectic A mesophases. The more flexible backbone of poly(butadiene) allowed a higher order of alignment of the mesogenic units, resulting in the more ordered liquid crystalline smectic A phase. 

As the name implies, polysilane polymers consist of chains made up exclusively of sihcon atoms. (In the ht-erature these polymers are named either as polysUanes or poly(silylenes) thus (Et2Si) can be called polydiethylsilane or poly(diethylsilylene).) Unlike the heteroatomic polysiloxanes, with alternating silicon and oxygen atoms in the polymer backbone, the poly silanes are homoatomic and therefore structurally closer to aUcene polymers. However, because the atoms in the main chain are all silicon, the polysilanes show quite special properties. ... 

Similarly to small molecules, polymers can be classified based on their chemical nature, i.e. based on the functional groups present in their molecule. However, different from small molecules, one important element in polymer classification is the chemical structure of the polymeric backbone. The attached side atoms or groups of atoms to the polymer backbone play a different role compared to that of the presence of various atom types or groups of atoms in the backbone. For example, it is a significant difference between poly(oxy-1,4-phenylene-oxy-ethylene) that contains phenyl groups and oxygen atoms in the polymer backbone and poly(phenyl vinyl ether) that is a vinyl type polymer with a carbon chain as backbone, although both polymers are ethers. The two polymers are synthesized differently and have quite different properties. Their structures are shown below ... 

However, there is another parameter which seems to prepare the ground for resonance effects to occur. The bulky groups linked to the terminal C 1 atom of the free radical (XVI) formed by scission of a carbon-carbon bond in the polymer chain backbone of poly(a-methylstyrene), can have more room and hence, can lessen steric interaction among themselves as well as with the other groups and atoms in the polymer chain when... 

Discussion of the effect of the polymer backbone in Sec. 3.4 of this chapter already provided examples of highly isotactic po-ly(f )-endo,exo-5,6-di [n-[4 -(4"-methox-yphenyl)phenoxy]alkyl]carbonyl bicy-clo[2.2.1]hept-2-ene s [190] and syndiotactic poly n-[4 -(4"-methoxyphenyl)phen-oxyjalkoxy methacrylate s [42, 44] which crystallize and form more ordered meso-phases than those of the corresponding atactic polymers (Fig. 15). Although more flexible backbones are more able to achieve the conformation necessary to order, the side chains are evidently already attached to the polymer backbone of these tactic polymers with the proper configuration to order, which obviates the need to distort their conformation for such purposes. 

The combination of PBD as an electron transporting compound with PVK finds frequent application. The direct attachment of PBD to the backbone of poly(p-phenylene vinylene) (PPV) enhances the electroluminescent efficiency. This is attributed to a more facile electron injection and an enhancement of the electron transporting properties of the polymer. ... 

A polymer composite with a low glass transition temperature has been described as based on layered photoconductive polymers, namely, poly(p-phenylene terephthalate carbazole)s. " These polymers consist of a rigid backbone of poly(pentylene terephthalate) with pendant oxyalkyl carbazole groups. When the host polymers are mixed with various dopants, the layers are preserved and their layer distance increases, indicating that all the guest molecules are confined to the nanoscale interlayer space. 

Pak Pak, S. J., Lyle, G. D., Mercier, R., McGrath, J. E. Synthesis and characterizatiOTi of novel toughened thermosets derived from pendent amines oti the backbone of poly (aiylene ether sul-phones)s. Polymer 34 (1993) 885-895. 

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