Adaptive polymer networks

Adaptive Polymer Networks Towards a Systems Materials/Polymer Science. 166... 

Modern concepts in polymer chemistry are based on complex molecular architectures. In this way, some new functions such as self-organisation, adaptability and self-healing can be realised in synthetic materials of different dimensions and complexity. Colloidal polymer networks (nano- or microgels) are unique 3-D polymer structures with tuneable properties and enormous application potential. 

The matrix polymer has to be rather rigid to conserve the empty imprinted sites after extraction of the template, this is achieved by extensive crosslinking. Generally, the crosslinker content of a mixture has to exceed a threshold value (>40%) to obtain selectivity [444,447]. Further, the chemical structure of the polymer network is of minor importance for the selectivity, though its polarity should be adapted to the imprinting molecule [444]. To obtain a maximum number of accessible sites,... 

Figure 16.2. SEM photographs of PP/EP blends, (a) PP/EP blend (b) PP/EP/talc blend with separated nucrostructure (c) PP/EP/talc blend with core-shell microstructure. [Adapted, by permission, from Shanks R A, Long Y, Polym. Networks Blends, 7, 1997, 87-92.]...

Polymer networks such as epoxies play an increasing role as adhesives in industry. Two properties are of special importance for their application (a) a strong adhesive bond is required between the solidified adhesive and the bonded object, which is often a metal (b) the mechanical stiffness of the adhesive has to be adapted to the desired level. As a consequence, the adhesive has to be selected according to its adhesion properties as well as its mechanical properties. Several studies have shown that both properties are linked as soon as the epoxy polymer layer is sufficiently thin the contact of the polymer with the substrate may induce in the polymer a broad interphase where the morphology is different from the bulk. Roche et al. indirectly deduced such interphases, for example from the dependence of the glass transition temperature on the thickness of the polymer bonded to a metal substrate [1]. Moreover, secondary-ion mass spectroscopy or Auger spectroscopy provided depth profiles of interphases in terms of chemical composition, which showed chemical variations at up to 1 pm distance from the substrate. 

Figure 9.6 Representation of a trifunctional monomer according to the classical theory of gelation. The monomer can hold four reactive states, from 0 to 3, which indicate the numher of functional groups that have been reacted, linking this unit with its neighbor. Source Adapted with permission from Dusek K, MacKnight WJ. Crosslinking and structure of polymer networks. In Labana SS, Dickie RA, Bauer RS, editors. CrossLinked Polymers. American Chemical Society 1988. p. 2 [88]. Copyright 1988 American Chemical Society.

F. 2.17 a Schematic representation of the formation of the nanoporous membrane based on smectic liquid crystals, b The chemical structure of the LCs. c Simplified artistic view of the nanopores in the layered network. To visualize the 2D pores the counter ion is not shown and the benzoic acid derivatives are drawn highly ordered, d A free-standing H-bonded polymer network, e TEM of the nanoporous polymer network filled with barium ions, scale bar 20 nm. f X-ray diffraction pattern of the alkaline treated network. Adapted from Ref. [76] by permission of John Wiley Sons Ltd... 

Fig. 2.19 Adsorption of MB in the polymer network as shown in Fig. 2.18. From left to right the MB solution without adsorbent, with adsorbent and with H-bonded adsorbent. Adapted from Ref. [76] by permission of John Wiley Sons Ltd...

Fig. 28 (a) Chemical structure of a poly(THF)-BTP polyurethane, (b) Schematic representation of structure and morphology of the metallo-supramolecular polymer network formed by combination of poly(THF)-BTP and Zn. (c) Pictures of a film of the metallo-supramolecular polymer network made from poly(THF)-BTP and Eu before and after stretching. Adapted with permission from [95]. Copyright 2013 The Royal Society of Chemistry... 

The collapse of polymer networks has recently attracted a lot of attention. This boom is partially due to some important applications, which all stem from the fact that you need only slightly change the quality of the solvent to make the network collapse rapidly. It is especially useful that the collapse is very sensitive to the presence of charged monomers and counterions in the solution. Thus collapsing networks can be adapt to detect small ion impurities in a solution, as well as to clear the impurities away. Besides all this, the collapse of networks can also serve as a good model for some other processes in biology (e.g., in the vitreous body in the eye). 

Chemomechanical systems based on a synthetic polymer network gel are the only artificial systems able to convert chemical energy directly into mechanical work. Gels are soft with respect to their environments. Machines made of metal or silicon operate as closed systems. They do not adapt to changes in their operating conditions unless a separate sensor system or a human operator is at the controls. 

Another use of the adaptive algorithm is in simulations of polymer melts " and highly cross-linked polymer networks, " which typically combine an atomistic to... 

Adapted, by permission, from La Mantia F.P., Ma Wenguang (1996) Recycling of post-consumer polyethylene greenhouse films monopolymer blends of recycled and virgin polyethylene , Polym. Networks Blends, 5, 173-179. Copyri t ChemTec Publishing. 

Cationic hydrogel swelling behavior at low pH the drug is released due to the swelling of the polymer network. (Source-. Reprinted and adapted from Reyes eta ., 2013, copyright 2013, with permission from Elsevier B.V.)... 

Figure 7.23. Temperature dependence ofme-chanical loss tangent in IPITs without filler (1-3), with 20% (4-6) and 40% (7-9) at various initiator concentrations a-0.74.10, b-2.96.10, c-5.4.10 mol/1. [Adapted by permission from Y. S. Lipatov, T. T. Alekseeva, V. F. Rosovitsky, and N. V. Babkina, Polym. Networks Blends, 4, 9 (1994)]...

Adapted, by permission, from N. Nakajima and J. L Liu, Polymer Network Blends,... 

In a gedanken experiment, a polymer is swollen with a liquid crystal and crosslinked. By swelling with the LC polymer chains lose their isotropic conformation due to the anisotropic environment. This leads to an anisotropic conformation of the network chains as well. The respective coil dimensions differ parallel and perpendicular to the director of the LC phase. Upon heating, the LC phase will lose its anisotropy and turn isotropic. The polymer network will follow this change, but due to the crosslinks, the adaption of an isotropic conformation will lead to a deformation of the elastomer (Figure 19). 

These four types of forces are responsible for the adaptive behavior of smart gels. The different forces come into play when the network of polymer chains composing a gel is disturbed, (a) Charged ionic regions can attract or repel each other, (b) Nonpolar hydrophobic regions exclude water, (c) Hydrogen bonds may form from one chain to another, (d) Dipole-dipole interactions can attract or repel chains. 

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