Side polymers, hydrogen-bonded

Another aspect of side-chain hydrogen-bonded polymers is related to the miscibility enhancement between immiscible polymers via (weak) hydrogenbonding interaction, generating polymer blends. This topic was described in Sect. 3.1, the interested reader is referred to this section within this review. 

Hydrophilic Groups. Water solubiUty can be achieved through hydrophilic units in the backbone of a polymer, such as O and N atoms that supply lonepair electrons for hydrogen bonding to water. SolubiUty in water is also achieved with hydrophilic side groups (eg, OH, NH2, CO2, SO3 ). 

Many synthetic water-soluble polymers are easily analyzed by GPC. These include polyacrylamide,130 sodium poly(styrenesulfonate),131 and poly (2-vinyl pyridine).132 An important issue in aqueous GPC of synthetic polymers is the effect of solvent conditions on hydrodynamic volume and therefore retention. Ion inclusion and ion exclusion effects may also be important. In one interesting case, samples of polyacrylamide in which the amide side chain was partially hydrolyzed to generate a random copolymer of acrylic acid and acrylamide exhibited pH-dependent GPC fractionation.130 At a pH so low that the side chain would be expected to be protonated, hydrolyzed samples eluted later than untreated samples, perhaps suggesting intramolecular hydrogen bonding. At neutral pH, the hydrolyzed samples eluted earlier than untreated samples, an effect that was ascribed to enlargement... 

Recently, it was shown that polydimethylcarbosiloxanes with a small content of side carbonyl groups (PDMS-C) exhibit increasing viscosity and formation of a physical network at elevated temperatures [88,89], This was attributed to a rearrangement of intramolecular hydrogen bonds, which formed between the carboxyls during the synthesis and isolation of the polymers, forming intermolecular hydrogen bonds. 

Helical columns of bifunctional ureidotriazines have also been created in water.40 In this solvent the aromatic cores of compound 39 stack and create a hydrophobic environment that favors the formation of intermolecular hydrogen bonds. The chiral side chains can express their chirality within the columnar polymer because of the helicity generated by the backbone. In contrast, for monofunctional 68 water interferes with the hydrogen bonding and 68 does not stack to form a column. As a consequence the chiral side chain does not express its chirality in the aromatic system. For 39, the bifunctional nature allows for a high local concentration of stacking units. A comparison might be made here to the individual DNA bases that also do not dimerize and stack in water, unless they are connected to a polymer backbone. 

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