Methylene backbone

Electroreductive fixation of CO2 into formate can be efficiently performed by using Fe4S4 cubane clusters (276) bearing a 36-membered methylene backbone in a DMF-Bu4NBF4-(Pt/Hg) system... 

All but the polyurethane are characterized by methylene backbones with ligands that are sufficiently polar to make them water soluble. Thus, upon dissolution in water, the polarity of the water molecule associates with the polarity of the acrylic or acrylamide groups to form a shell. We discussed hydrophilic polyurethanes that are typically cross-linked and are not (but could be) considered effective thickeners. Nevertheless they too have hydration shells developed due to the influence of the polyethylene glycol backbone. The extent of that shell is determined by the hydro-philicity of the ligand the acrylic > acrylamide > alcohol > polyurethane. The volume... 

Novel -symmetric chiral arsepin 61 possessing the 1,1 -binaphthyl-2,2 -bis(methylene) backbone was prepared using (S)-(—)-l,l -bi-2-naphthol 84 as the chiral substrate. The dilithio derivative 86, generated from (S)-2,2 dimethyl-1,1 -binaphthyl 85 and Avy-biitvllithiuru, reacted with PhAsBr2 to give arsepin 61 (Scheme 7) <2002TA2187>. 

In the majority of cases, the cosolvent mixtures for PMMA contain either or acetonitrile as one of the liquid components. A study of the mixture formed by these two liquids and a comparison with the results obtained in the other cosolvents studied before has been also reported. The total sorption of the cod (PMMA) was calculated from second virial coefficient and intrinsic viscosity data. According to these authors, acetonitrile can interact favorably with the ester group of PMMA and is imfavorable with its methylene backbone. The role of these opposing interactions and of liquid order in acetonitrile are taken into account to explain the dilute solution properties of PMMA in this cosolvent system. ... 

The methine protons in isotactic polymers cure coupled to four methylene backbone protons and may be coupled to protons on the pendant R group as well. If we avoid the latter possibility, and remember that J for isotactic polymers, the methine resonance... 

The methylene backbone carbons are designated by Greek symbols. The first Greek letter gives the distance in carbon atoms to the nearest branch thus refers to a backbone CH2 two carbons away from a branch point. If two letters are given, the second refers to the distance from a second branch point in the opposing direction. /+ refers to methylenes three or more units away from a branch. The resonances are different and can be used to identify branch lengths up to six carbons, but a... 

Figure 42 Temperature dependence of the in-phase spectrum of polystyrene in the CH2-stretching vibration region of the methylene backbone groups.

The same system of notation can be extended further by focusing attention on the backbone substituents rather than on the methylenes. Consider bracketing a center substituent with a pair of monomers in which the substituents have either the same or opposite configurations as the central substituent. Thus the two bracketing units are either m or r with respect to the central unit and the probabilities of the resulting triads are obtained from the probabilities of the respective m or r additions. The following possibilities exist ... 

To investigate the triads by NMR, the resonances associated with the chain substituent are examined, since structures [XV] -[XVII] show that it is these that experience different environments in the various triads. If dyad information is sufficient, the resonances of the methylenes in the chain backbone are measured. Structures [XIII] and [XIV] show that these serve as probes of the environment in dyads. 

The hydrogens of the methylene group in the backbone of the poly (methyl methacrylate) produce a single peak in a racemic dyad, as illustrated by structure [XVI]. 

Properly end-capped acetal resins, substantially free of ionic impurities, are relatively thermally stable. However, the methylene groups in the polymer backbone are sites for peroxidation or hydroperoxidation reactions which ultimately lead to scission and depolymerisation. Thus antioxidants (qv), especially hindered phenols, are included in most commercially available acetal resins for optimal thermal oxidative stabiUty. 

Numerous diamines and aromatic dianhydrides have been investigated. WhoUy aromatic Pis have been stmctiirally modified by incorporating various functional groups, such as ether, carbonyl, sulfide, sulfone, methylene, isopropjlidene, perfluoroisopropyUdene, bipyridyls, sdoxane, methyl phosphine oxide, or various combinations of these, into the polymer backbone to achieve improved properties. The chemistry and apphcations of Pis have been described in several review articles (4). 

A waterborne system for container coatings was developed based on a graft copolymerization of an advanced epoxy resin and an acryHc (52). The acryhc-vinyl monomers are grafted onto preformed epoxy resins in the presence of a free-radical initiator grafting occurs mainly at the methylene group of the aHphatic backbone on the epoxy resin. The polymeric product is a mixture of methacrylic acid—styrene copolymer, soHd epoxy resin, and graft copolymer of the unsaturated monomers onto the epoxy resin backbone. It is dispersible in water upon neutralization with an amine before cure with an amino—formaldehyde resin. 

Thus, a polyester with the ring in the backbone can be prepared by the Friedel-Crafts polyalkylation of vinyl 2-furoate. BF3 Et20 gave similar results at room temperature in methylene chloride. Structure 30 was arrived at by spectroscopy and by alcoholysis of the polymers. 

PVAc is known to contain a significant number of long chain branches. Branches to the acetate methyl may arise by copolymerization of the VAe macromonomcr produced as a consequence of transfer to monomer (Section 6.2.6.2). Transfer to polymer may involve either the acetate methyl hydrogens (Scheme 6.34) or the methine (Scheme 6.35) or methylene hydrogens of the polymer backbone. 

Even in the absence of flow, a polymer molecule in solution is in a state of continual motion set forth by the thermal energy of the system. Rotation around any single bond of the backbone in a flexible polymer chain will induce a change in conformation. For a polyethylene molecule having (n + 1) methylene groups connected by n C — C links, the total number of available conformations increases as 3°. With the number n encompassing the range of 105 and beyond, the number of accessible conformations becomes enormous and the shape of the polymers can only be usefully described statistically. 

Homologs of yS-peptides with one additional methylene group inserted into the backbone of each residue, namely y-peptides (Fig. 2.33), also form well-defined... 

The effect of different backbones on ero.sion rates was demonstrated in a study of the homologous poly[ (p-carboxyphenoxy)alkane] series. As the number of methylene groups in the backbone increased from 1 to 6, thus decreasing the reactivity of the anhydride linkage and rendering the polymer more hydrophobic, the erosion rates underwent a decrease of three orders of magnitude (4). 

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