Cross-linked polymers hydrogen bonding

It may also be argued that plasticised PVC may be considered as a thermoplastic elastomer, with the polymer being fugitively cross-linked by hydrogen bonding via the plasticiser molecules. These materials were, however, dealt with extensively in Chapter 12 and will not be considered further here. The ionomers are also sometimes considered as thermoplastic elastomers but the commercial materials are considered in this book as thermoplastics. It should, however, be kept in mind that ionic cross-linking can, and has, been used to fugitively crosslink elastomeric materials. 

Cellulose, an important constituent of wood, has long chains of glucose molecules linked by glycoside bonds. These chains are cross-linked by hydrogen bonds. Many biological polymers have unusual mechanical properties, not at present matched by the properties of artificial macromolecules. For instance, arteries are... 

A massive polymer molecule that contains all the genetic information of the cell. It has a complicated structure containing many thousands of smaller units of amino acids, proteins, bases and sugars. It forms a double-twisted helix string-like molecule. The strands are held in position by cross links of hydrogen bonds from matching pairs of base materials on opposite chains. 

Chitin is a suitable material for the exoskeleton of invertebrates because of its mechanical strength. Individual polymer strands are cross-linked by hydrogen bonding, accounting for the strength. Cellulose is another polysaccharide cross-linked in the same way, and it can play a similar role. 

The mole fiaetion of 2-propanol in the liquid mixture, xc, is given for the polymer-free solvent mixture. The copolymer was considered to be a physical gel, i.e., cross-linked by hydrogen bonds. 

In contrast to the few examples of synthetic polymers that can be transiently cross-linked by hydrogen bonding, there is a huge variety of biopolymers that form supramolecular gels via hydrogen bonding. The most important representatives are polysaccharides such as cellulose [159, 160], starch [161], agarose [162, 163],... 

Pahnans and Meijer have reported wholly organic supramolecular materials the phase segregation of benzene-1,3,5-tricarboxamide (BTA)-based helical nanorods within an amorphous polymer such as poly(ethylene butylene) (PEB) resulted in elastomeric behavior (Figure 8). The BTA motif has two binding sites (top and bottom face of the discotic), which provide the basis for both supramolecular chain extension and simultaneous cross-linking. Furthermore, hydrogen-bonding interactions and order in the nanofibers were studied via infrared (IR) spectroscopy and circular dichroism (CD). The materials are liquid crystalline at room temperature, which leads to their elastomeric properties. 

Polymers frequently do not form stable mixtures. When solutions of incompatible polymers are mixed, they separate (Tables 3.3 and 3.4). On drying, the solutions dry in patches. Although this would be disfiguring if it occurred on objects, no problems seem to have been noticed. Mixtures of incompatible water-soluble polymers can cross-link by hydrogen bonding to form gels or precipitates. 

All the polyrotaxanes discussed thus far are based on linear backbones. Viewing new properties and applications of branched and cross-linked polymers, three-dimensional polyrotaxanes will surely be interesting in terms of both topology and potential applications. Gong and Gibson extended the hydrogen-bonding theo-... 

Because LHC is a complex of interpenetrating polymers, hydrogen bonds and ester cross-links can reestablish themselves unless further processing occurs promptly. Therefore, in practice, this disruption of the LHC phase may not be distinguishable from the subsequent stages. 

Physical entrapment This is often used in sandwich membranes, the enzyme is trapped in a cross linked polymer or adsorpted onto a gel matrix when constructing a sensor. It relies on weak hydrogen bonding and electrostatic interactions between the... 

---