Chain stabilisation

Figure 3.17 Alkaline chain stabilisation (stopping) reactions of cellulose.

The torsion angles predicted by conformational analysis agree closely with those of crystalline cellobiose as measured by X-ray diffraction, the conformation of which is restricted by two chain-stabilising intramolecular hydrogen bonds between 0(3 )-H and 0(5) and also between 0(2 )-H and 0(6) (Figure 4.3). These are also found in cellulose and they assist in maintaining the highly extended conformation which allows it to function as a structural polymer. 

Figure 11.2 Structural organisation (a-helix and P-sheet of proteins), a) structure of an a-helix (3.6 amino acids per turn, stabilised by H-bonds) and b) structure of a P-sheet (antiparallel linear chains, stabilised by H-bonds). Reproduced with permission from L.G. Phillips, D.M. Whitehead and J. Kinsella in Structure-Function Properties of Food Proteins, Eds., L.G. Phillips,...

Anodic resins are those which contain acid groups along the chain and which are made water dispersible by the addition of a base. The acid-base reaction produces carboxyl ions (COO ) along the chain, stabilising the aqueous dispersion. 

Similar ligand-ligand interactions have been reported for a large number of ternary -amino acid complexes, built up of two different amino acid.s. A compilation of 72 examples is presented in reference 39. The extra stabilisation due to ligand-ligand interactions in these complexes depends on the character of the amino-acid side chains and amounts to 0.34 - 0.57 kJ/mole for combinations of aromatic and aliphatic side chains and 0.11 - 6.3 kJ/mole when arene - arene interactions are possible. ... 

Phosphites Tris-(p-nonylphenyl) phosphite (X) No Widely used in conjunction with conventional stabilisers (q.v.) in PVC. Some types appear to be useful heat and light stabilisers in polyolefins. Function primarily as peroxide decomposers rather than chain-breaking antioxidants. 

Other additives that may be incorporated include sodium hydrogen phosphates as buffering agents to stabilise that pH of the reaction medium, lauryl mercaptan or trichlorethylene as chain transfer agents to control molecular weight, a lubricant such as stearic acid and small amounts of an emulsifier such as sodium lauryl sulphate. 

Introduction of some vinyl groups in a side chain enables vulcanisation to take place. It is claimed that when stabilised with ferric oxide the materials may be used operationally to 250°C and the possibility of short-term use up to 400°C has... 

The chloride ion is the most frequent cause of contact corrosion, since chlorine is present in the many chlorinated plastics, and is also frequently retained in residual amounts from reactive intermediates used in manufacture. Thus epoxides usually contain chloride derived from the epichlor-hydin used as the precursor of the epoxide. In addition to the contaminants referred to in Table 18.18, various metal and ammonium cations, inorganic anions and long-chain fatty acids (present as stabilisers, release agents or derived from plasticisers) may corrode metals on contact. 

Double helix involving two polysaccharide chains. The helix is stabilised by intermolecular hydrogen bonds... 

The intermolecular interactions stabilise the helices and greatly influence the properties of exopolysaccharides in solution, ie solubility, viscosity and gel-formation. A strong interaction or good-fit between molecules will lead to insolubility, whereas poor interaction will lead to solubility of exopolysaccharides. The interactions between molecules is influenced by the presence of side-chains. For example, cellulose is insoluble but introduction of a three monosaccharide side-chain into the cellulose chain gives the soluble xanthan. Small changes in the structure of the side-chains can alter the molecular interactions and thus properties of the exopolysaccharide. 

Emulsion polymerisation is initiated using a water-soluble initiator, such as potassium persulfate. This forms free radicals in solution which may initiate some growing chains in solution. These radicals or growing chains pass to the micelles and diffuse into them, which causes the bulk of the polymerisation to occur in these stabilised droplets. 

This highly conjugated molecule was stabilised with nitroxyl biradical side chains. The resulting material had sufficient ferromagnetism that a usable compass needle could be made from it. Despite the success of this demonstration, organic ferromagnetism remains a curiosity. Such polymers are not likely to replace conventional ferromagnetic metals in any application within the foreseeable future. 

The obvious Vfittig disconnection gives stabilised ylid (5fi) and keto-aldehyde (57). We have used many such long-chain dicarbonyl compounds in this Chapter and they are mostly produced from available alkenes by oxidative cleavage (e.g. ozonolysis). In this case, cyclic alkene (58) is the right starting material, and this can be made from alcohol (59) by elimination,... 

British Biotech has described co-crystal structures of both BB-3497 and actinonin bound in the active site of E. coli PDF [24]. The metal centre (Ni ) in both complexes adopts a pentacoordinate geometry, bound by the two oxygen atoms of the hydroxamate along with Cys-90, His-132 and His-136. This coordination pattern is consistent with the mechanism of de-formylation proposed by Becker et al. [56] and Jain et al. [67], in which a pentacoordinated metal centre stabilises the transition state during hydrolysis of the formamide bond. When compared to the co-crystal structure of a substrate hydrolysis product, Met-Ala-Ser, it is clear that the side chains of these two inhibitors bind into the active site pockets similarly to the substrate [56]. 

Phenyl iodide dissociates at Cu(110) to form a c(2 x 2) iodine layer, accompanied by coupling of phenyl groups which desorb as biphenyl but with evidence that some phenyl groups remain at the surface stabilised as chains at step-edges and on terraces as paired chains . Chemisorption of HC1 at Cu(110) is corrosive , with evidence for surface buckling. 

As already shown, it is technically possible to incorporate additive functional groups within the structure of a polymer itself, thus dispensing with easily extractable small-molecular additives. However, the various attempts of incorporation of additive functionalities into the polymer chain, by copolymerisation or free radical initiated grafting, have not yet led to widespread practical use, mainly for economical reasons. Many macromolecular stabiliser-functionalised systems and reactive stabiliser-functionalised monomers have been described (cf. ref. [576]). Examples are bound-in chromophores, e.g. the benzotriazole moiety incorporated into polymers [577,578], but also copolymerisation with special monomers containing an inhibitor structural unit, leading to the incorporation of the antioxidant into the polymer chain. Copolymers of styrene and benzophenone-type UV stabilisers have been described [579]. Chemical combination of an antioxidant with the polymer leads to a high degree of resistance to (oil) extraction. 

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