Backbone structures, influence

The most common backbone structure found in commercial polymers is the saturated carbon-carbon structure. Polymers with saturated carbon-carbon backbones, such as polyethylene, polypropylene, polystyrene, polyvinyl chloride, and polyacrylates, are produced using chain-growth polymerizations. The saturated carbon-carbon backbone of polyethylene with no side groups is a relatively flexible polymer chain. The glass transition temperature is low at -20°C for high-density polyethylene. Side groups on the carbon-carbon backbone influence thermal transitions, solubility, and other polymer properties. 

Hydrophilic Groups. Water solubility can be achieved through hydrophilic units in the backbone of a polymer, such as O and N atoms that supply lone-pair electrons for hydrogen bonding to water. Solubility in water is also achieved with hydrophilic side groups (e.g., OH, NHi,C02, SOy ). Truly unique in its ability to interact and promote water solubility is the -O-CH2-CH2- group. The interactions of these groups with water and their placement in the polymer structure influence the waler solubility of the polymer and its hydrodynamic volume. 

Since the electronic absorption spectra of polvsilanes and polygermanes also depend strongly on conformation (3), these materials provide a unique opportunity to study the effect of backbone conformation on the NLO properties, particularly since varying alkyl substituents can dramatically influence the backbone structure through intermolecular interactions (e.g., side chain crystallization) while causing... 

The 10 best polymers were reprepared in larger amounts to confirm their properties, and each preparation was repeated twice to check if the random disposition of the acid-derived functional groups on the polyamine backbone was influencing the reducing efficiency. All the polymers were confirmed as active, and the two batches showed comparable activities, confirming the reproducibility of this synthetic method. Several crude indications in terms of SAR were identified, and a structural specificity of reducing efficiency was clearly present, albeit difficult to rationalize. For example, compare the activity of similar composites 11.27 (40% yield) and 11.29 (1.3% yield). Many modifications of the polymeric scaffold (different average MWs, increase of... 

In this chapter we want to discuss the correlation of the mesophase behavior of a cyanobiphenyl-based SCLCP with its backbone structure. As shown before, the backbone structure, the spacer lengths, and the mesogen density per repeat unit have great influence on the LC mesophase evolved. Ligure 8 shows some examples of backbone structures bearing the cyanobiphenyl-moiety that have been reported in literature. The above-mentioned ROMP-derived polymers poly-(II-n) [39],poly-(IV-n) [42,47],poly-(VI-n) [41],andpoly-(VII-n) [53] will be compared with each other and with acrylate-based [56-59], siloxane-based [60] and vinylcyclopropane-based systems [61]. The detected mesophases and their transition temperatures are summarized in Table 6. 

As you might expect, the influence of the nature and density of side groups V5. the backbone structure will strongly depend on the relative composition of each polymer unit, as well as how open the structure is to its environment. Regarding the relative composition of a polymer, even though a polymer may have a polar backbone structure e.g., ether and/or ester linkages), the structure may not be soluble within polar solvents. That is, if long nonpolar side chains are also present in the polymeric... 

Synthetic bipyridine amino acids have been used to construct polypeptides with bipyridine in the backbone. A bipyridine ligand with both an amino and an acid functionality, 4 -aminomethyl-2,2 -bipyridyl-4-carboxylic acid, was incorporated into a hexapeptide and used to coordinate and encapsulate a Ru11 ion. Because the bipyridine group is in the main chain, it can constrain the peptide backbone and influence its secondary structure.171... 

It was, therefore, decided that we would study thermal polymerization of bisdichloromaleimides at 300°C for 30 min. The resulting product was soluble in DMF to a great extent (Table III) with the exception of compound (b). This indicates the absence of thermal polymerization under these conditions. Anaerobic char yields of these thermally treated bisdichloromaleimides depended on their backbone structure a very low value was obtained in compounds (a) and (c) compound (b), which contained phosphorus, was most stable. Condensed phase reactions are influenced by the presence of phosphorus in these polymers. An almost linear relationship is observed between anerobic char yields at 800°C and bridge formula weight of bisdichloromaleimide (Fig. 3). 

The methodology of solid phase peptide synthesis (SPPS) [65, 66] has been credited with the award of 1984 Nobel Prize in chemistry [67] to its inventor, Bruce R. Merrifield of the Rockefeller University. At the heart of the SPPS lies an insoluble polymer support or gel , which renders the synthetic peptide intermediates insoluble, and hence readily separable from excess reagents and by-products. In addition to peptide synthesis, beaded polymer gels are also being studied for a number of other synthetic and catalytic reactions [2]. Ideally, the polymer support should be chemically inert and not interfere with the chemistry under investigation. The provision of chemical inertiKss presents no difficulty, but the backbone structure of the polymer may profoundly influence the course of the reaction on the polymer support. This topic has attracted considerable interest, particularly in relation to the properties of polystyrene (nonpolar, hydrophobic), polydimethylacrylamide (polar, hydrophilic), and copoIy(styrene-dimethylaciylamide) (polar-nonpolar, amphiphilic) (see later). 

Secondary structures are regular elements such as a-helices and p-pleated sheets, which are formed between relatively small parts of the protein sequence. These structural domains are determined by the conformation of the peptide backbone, the influence of side-chains is not taken into account for secondary structures. 

Poly(Aromatics). Poly(p-xylylene) undergoes photooxidation at the methylene group, initially via hydrogen atom abstraction followed by attack on the ring structure. Such instability prevents the long term use of this material in outdoor applications. The backbone structures in PPVs influence the rates of... 

Most quantum chemical modelling studies deal with active site chemistry. That is, the calculations do not really focus on how substrates and products get to and from the active site. Rather, they concentrate on the sequence of events following the arrival of substrate in the active site pocket and seek to uncover the mechanism of conversion of substrate to one or more intermediates and/or product. The obvious reason for such an approach is the assumption that the vast bulk of the protein molecule can be ignored but raises the thorny issue of whether this is a valid assumption. In practical terms, it is not possible (and arguably not desirable) to treat the entire protein quantum mechanically. Moreover, since one of the main roles of the protein is substrate selection and delivery to the active site, and since the computer modeller has explicit control over this feature, one might conclude that there is no need to consider the bulk of the protein molecule. However, the protein backbone may exert a structural influence on the active site—the entatic state [34]—while the groups around the active site produce an electrostatic field different from the in vacuo state which is the default domain of quantum chemistry. In summary, it is obviously critically important to develop a reasonable chemical model of the active site if any conclusions drawn from the calculations are to be believed. 

A comparison of polymers with different polymer backbones is shown in Fig. 5.13 for the non-ionic polymers poly(ethylene oxide) (PEO), poly(acrylamide) (PAAm), and methyl cellulose (ME) in aqueous solution. The heteroatom in the backbone of PEO leads to an expanded coil structure compared to PAAm with the heteroatom in the side chain. Cellulose derivatives have in addition to the heteroatom the ring structure of the anhydroglucose unit in the polymer backbone. The methyl cellulose in this example has a less expanded coil than the synthetic PAAm and PEO. Again, it is hard to distinguish between the influence of the solvation of the polar backbone and the pure steric hindrance of the different backbone structures. 

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