The concept of supramolecular polymer chemistry offers an interesting approach to tailoring very different polymers by using intermolecular bonds instead of covalent linkages. [1] The ability to combine polymeric materials with widely differing properties is an especially important tool for engineering tailored polymers for a wide range of applications. Thus, mixing extremely soft polymers (i.e., low glass-transition temperature (T g ) polymers exhibiting high chain flexibility) and stiff polymers (i.e., those characterized by inflexible, rod-type chains, usually with a high glass-transition temperature) is a technically important task with the potential for generating processable materials with high mechanical flexibility. In this communication, we report on the generation of tunable supramolecular materials made from two strongly phase separating polymeric fragments. Hydrogen-bonding elements (showing an A-B type structure) with a variable association strength (i.e., displaying an association constant K a of either 800 M -1 or ∼ 3 × 10 4 M -1 ) have been affixed onto strongly phase separating poly(isobutylene) (PIB) and poly(etherketone) (PEK) polymers, respectively, in order to combine these two remarkably different polymers through directed supramolecular interactions. As depicted in Figure 1, an unusual temperaturedependent switching between micro-and macrophase separated states is expected due to the competing effects of micro/ macrophase separation and the attractive hydrogen-bonding interactions between the telechelic PIB and PEK fragments. The complex interplay between microphase and macrophase separation in the resulting materials (pseudo block copolymers) has been studied by temperature-dependent smallangle X-ray scattering (SAXS) measurements. Supramolecular approaches to polymer chemistry offer the possibility of reversible or partially reversible combinations of materials due to the presence of non-covalent bonds whose association energies are within the thermal barrier of temperatures ranging between 25°C and 300°C. Certainly, it should be possible to generate tunable materials if these features are combined into polymeric structures held together by supramolecular bonds. In the past, heterospecific multiple-hydrogen-bonding (A-B) systems have been used to assemble different telechelic polymers in a sheet-type fashion, [2] generating the so-called pseudo block copolymers.[3] The tunability of the resulting materials has been demonstrated most impressively in terms of electrical [4] and optical [5] properties, as well as via reversible fiber formation [6] by the use of weak hydrogen-bonding interactions between side-chain-functionalized polymers. An important aspect of these weakly bound materials is that a high density of hydrogen-bonding interactions is necessary in order to achieve a measurable effect in terms of modulative behavior. [7] It is more difficult to achieve a combination of strongly phase-separating polymers by purely supramolecular interactions, since the energy of phase separat...
Supramolecular gels consisting of trivalent polyisobutylene and bivalent poly(ethylene oxide) are generated. Strong hydrogen bonding interactions, affixed to the end‐group moieties of the respective polymers (binding constant Kassn = 105 M–1), serve as molecular glue, leading to the formation of weak gels. Two different gels were prepared: one, with a short telechelic poly(ethylene glycol) (PEG) segment (gel A), and one with a longer PEG segment (number‐average molecular weight Mn = 2000 g mol–1) (gel B). Both gels show a significant increase in viscosity upon mixing of the two polymeric components, with a lag time of several minutes, indicative of nucleation mechanisms as the formation principle. However, only gel A displays classical gel‐like behavior, with a loss modulus G′ larger than the storage modulus G″ after formation. Both gels display microphase‐separated behavior with a spacing between 4–5 nm as probed via small‐angle X‐ray scattering (SAXS) and transmission electron microscopy (TEM) measurements. The incorporation of magnetic nanoparticles (Fe2O3; radius r = 3.5 nm) is successfully achieved, generating new magnetic gels with strongly thermoresponsive properties, displaying a strong temperature‐dependent release profile of included dye molecules. Magnetic measurements indicate a superparamagnetic behavior of the incorporated nanoparticles, prospecting the application as magneto‐sensitive delivery gels for pharmaceutical purposes.
New synthetic methodologies towards hydrogen bonded supramolecular polymers are described. Focus is directed on synthetic work towards telechelics with hydrogen bonds either as side chain moieties or as endgroups. Physical ordering effects related to polymers and particles are discussed citing own and related work in ∼60 references.
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