Hydrogen bonding thermoplastic elastomers

Fig. 4 Hydrogen-bonded thermoplastic elastomer based on self-complementary interactions of ureido-pyrimidinone (UPy). (a) Poly(ethylene-co-butylene) with OH end groups, (b) Poly(ethyl-ene-co-butylene) functionalized with UPy. (c, d) Lateral intraactions through tt—tt stacking of UPy and hydrogen bonding of urethane linkers, (e) AFM image of nanofibers formed through these lateral interactions. Reprinted with permission friun [90-92]. Copyright 2000, 2006, 2008 Wiley-VCH Verlag GmbH, Wiley Periodieals, Ine., and American Chemical Society...

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. 

Zinc salt of maleated EPDM rubber in the presence of stearic acid and zinc stearate behaves as a thermoplastic elastomer, which can be reinforced by the incorporation of precipitated silica filler. It is believed that besides the dispersive type of forces operative in the interaction between the backbone chains and the filler particles, the ionic domains in the polymer interact strongly with the polar sites on the filler surface through formation of hydrogen bonded structures. 

Figure 25.10 Example of hydrogen bonding between urethane linkages in a hard block of a thermoplastic polyurethane elastomer...

Kautz H, van Beek DJM, Sijbesma RP, Meijer EW. Cooperative end-to-end and lateral hydrogen-bonding motifs in supramolecular thermoplastic elastomers. Macromolecules 2006 39 4265-4267. 

Freitas LDL, Stadler R. Thermoplastic elastomers by hydrogen bonding. 3. Interrelations between molecular parameters and rheological properties. Macromolecules 1987 20 2478-2485. 

Most thermoplastics, such as PVC, have relatively high moduli at their useful temperatures, which are below the Tr The intermolecular forces of plastics are much stronger than those of elastomers and are usually weaker than the intermolecular hydrogen bonds characteristic of most fibers. Figure 5.2 describes the idealized behavior of a thermoplastic as a function of chain length and temperature. 

New crosslinked elastomers may be formed by self-aggregation of substituted functional units able to form directed hydrogen-bonds. 1,4-PB has been randomly substituted with about 4 mol% urazole units [94], The urazole units form hydrogen-bonded supramolecular, plate-like aggregates which act as effective crosslinking zones, thus creating a thermoplastic elastomer [95, 96, 97]. The system is deuterated either in the PB backbone or in the urazole units, which allows to investigate the molecular dynamics in... 

Because of their reversible chain extension and the subsequent formation of small crystalline domains, the functionalized polymers exhibit properties typical for thermoplastic elastomers. At low temperatures the hydrogen-bond interaction contributes to the properties comparable to covalent interactions, whereas at high temperatures these interactions disappear and the materials exhibit flow behavior typical for a low-molecular-weight polymer. DSC,72 73 light and X-ray scattering,7174 dynamical mechanical analy-... 

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