Smart inorganic polymer

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Ibuprofen is encapsulated within the hydrogen bonding network of a smart polysiloxane above LCST, and then released when temperature falls below LCST and the polymer becomes water-soluble. Ibuprofen Delivery via Smart Polysiloxane.png
Ibuprofen is encapsulated within the hydrogen bonding network of a smart polysiloxane above LCST, and then released when temperature falls below LCST and the polymer becomes water-soluble.

Smart inorganic polymers (SIPs) are hybrid or fully inorganic polymers with tunable (smart) properties such as stimuli responsive physical properties (shape, conductivity, rheology, bioactivity, self-repair, sensing etc.). [1] While organic polymers are often petrol-based, the backbones of SIPs are made from elements other than carbon which can lessen the burden on scarce non-renewable resources and provide more sustainable alternatives. Common backbones utilized in SIPs include polysiloxanes, polyphosphates, and polyphosphazenes, to name a few.

Contents

SIPs have the potential for broad applicability in diverse fields spanning from drug delivery and tissue regeneration to coatings and electronics. [2] [3] As compared to organic polymers, inorganic polymers in general possess improved performance and environmental compatibility (no need for plasticizers, intrinsically flame-retardant properties). The unique properties of different SIPs can additionally make them useful in a diverse range of technologically novel applications, such as solid polymer electrolytes for consumer electronics, molecular electronics with non-metal elements to replace metal-based conductors, electrochromic materials, self-healing coatings, biosensors, and self-assembling materials. [1]

Role of COST action CM1302

COST action 1302 is a European Community "Cooperation in Science and Technology" research network initiative that supported 62 scientific projects in the area of smart inorganic polymers resulting in 70 publications between 2014 and 2018, with the mission of establishing a framework with which to rationally design new smart inorganic polymers. [4] [5] This represents a large share of the total body of work on SIPs. [1] The results of this work are reviewed in the 2019 book, Smart Inorganic Polymers: Synthesis, Properties, and Emerging Applications in Materials and Life Sciences. [4]

Smart polysiloxanes

A generic polysiloxane Silicone monomere.png
A generic polysiloxane

Polysiloxane, commonly known as silicone, is the most commonly commercially available inorganic polymer. [1] The large body of existing work on polysiloxane has made it a readily available platform for functionalization to create smart polymers, with a variety of approaches reported which generally center around the addition of metal oxides to a commercially available polysiloxane or the inclusion of functional side-chains on the polysiloxane backbone. The applications of smart polysiloxanes vary greatly, ranging from drug delivery, to smart coatings, to electrochromics.

Drug delivery

Synthesis of smart stimuli responsive polysiloxanes through the addition of a polysiloxane amine to an α,β-unsaturated carbonyl via aza-Michael addition to create a polysiloxane with N-isopropyl amide side-chains has been reported. [6] This polysiloxane was shown to be able to load ibuprofen (a hydrophobic NSAID) and then release it in response to changes in temperature, showing it to be a promising candidate for smart drug delivery of hydrophobic drugs. [6] This action was attributed to the polymer's ability to retain the ibuprofen above the lower critical solution temperature (LCST), and conversely, to dissolve below the LCST, thus releasing the loaded ibuprofen at a given, known temperature.

Coatings

Commercial polysiloxane coatings are readily commercially available and capable of protecting surfaces from damaging pollutants, but the addition of TiO2 gives them the smart ability to degrade pollutants stuck to their surface in the presence of sunlight. [7] This particular phenomena is promising in the field of monument preservation. Similar hybrid textile coatings made of amino-functionalized polysiloxane with TiO2 and silver nanoparticles have been reported to have smart stain-repellent yet hydrophilic properties, making them unique in comparison to typical hydrophobic stain-repellant coatings. [8] Smart properties have also been reported for polysiloxane coatings without metal oxides, namely, a polysiloxane/polyethylenimine coating designed to protect magnesium from corrosion that was found to be capable of self-healing small scratches. [9]

Poly-(ε-caprolactone)/siloxane

Poly-(ε-caprolactone)/siloxane is an inorganic-organic hybrid material which, when used as a solid electrolyte matrix with a lithium perchlorate electrolyte, paired to a W2O3 film, responds to a change in electrical potential by changing transparency. [10] This makes it a potentially useful electrochromic smart glass.

Smart phosphorus polymers

There exist a sizable number of phosphorus polymers with backbones ranging from primarily phosphorus to primarily organic with phosphorus subunits. Some of these have been shown to possess smart properties, and are largely of-interest due to the biocompatibility of phosphorus for biological applications like drug delivery, tissue engineering, and tissue repair. [11] [12]

Polyphosphates

Polyphosphate (PolyP) is an inorganic polymer made from phosphate subunits. It typically exists in its deprotonated form, and can form salts with physiological metal cations like Ca2+, Sr2+, and Mg2+. [11] When salted to these metals, it can selectively induce bone regeneration (Ca-PolyP), bone hardening (Sr-PolyP), or cartilage regeneration (Mg-PolyP) depending on the metal to which it is salted. [11] This smart ability to attenuate the kind of tissue regenerated in response to different metal cations makes it a promising polymer for biomedical applications.

Polyphosphazenes

A generic polyphosphazene PolyphosphazeneGeneralStructure.png
A generic polyphosphazene

Polyphosphazene is an inorganic polymer with a backbone consisting of phosphorus and nitrogen, which can also form inorganic-organic hybrid polymers with the addition of organic substituents. Some polyphosphazenes have been designed through the addition of amino acid ester side chains such that their LCST is near body temperature and thus they can form a gel in situ upon injection into a person, making them potentially useful for drug delivery. [12] They biodegrade into a near-neutral pH mixture of phosphates and ammonia that has been shown to be non-toxic, and the rate of their biodegradation can be tuned with the addition of different substituents from full decomposition within days with glyceryl derivatives, to biostable with fluoroalkoxy substituents. [12]

Poly-ProDOT-Me2

Poly-ProDOT-Me2 is a phosphorus-based inorganic-organic hybrid polymer, which, when paired to a V2O5 film, provides a material that changes color upon application of an electrical current. This 'smart glass' is capable of reducing light transmission from 57% to 28% in under 1 second, a much faster transformation than that of commercially available photochromic lenses. [13]

Smart metalloid and metal containing polymers

While metals are not typically associated with polymeric structures, the inclusion of metal atoms either throughout the backbone of, or as pendant structures on a polymer can provide unique smart properties, especially in relation to their redox and electronic properties. [14] These desirable properties can range from self-repair of oxidation, to sensing, to smart material self-assembly, as discussed below.

Polystannanes

A generic polystannane Kette12.jpg
A generic polystannane

Polystannane, a unique polymer class with a tin backbone, is the only known polymer to possess a completely organometallic backbone. [15] It is especially unique in the way that the conductive tin backbone is surrounded by organic substituents, making it act as an atomic-scale insulated wire. Some polystannanes such as (SnBu2)n and (SnOct2)n have shown the smart ability to align themselves with external stimuli, which could see them become useful for pico electronics. [16] However, polystannane is very unstable to light, so any such advancement would require a method for stabilizing it against light degradation. [16]

Icosahedral boron polymers

Icosahedral boron is a geometrically unusual allotrope of boron, which can be either added as side chains to a polymer or co-polymerized into the backbone. Icosahedral boron side chains on polypyrrole have been shown to allow the polypyrrole to self-repair when overoxidized because the icosahedral boron acts as a doping agent, enabling overoxidation to be reversed. [17]

Polyferrocenylsilane

Polyferrocenylsilanes are a group of common organosilicon metallopolymer with backbones consisting of silicon and ferrocene. [14] Variants of polyferroceylsilanes have been found to exhibit smart self-assembly in response to oxidation and subsequent smart self-disassembly upon reduction, as well as variants which can respond to electrochemical stimulation. [14] One such example is a thin film of a polystyrene-polyferrocenylsilane inorganic-organic hybrid copolymer that was found to be able to adsorb and release ferritin with the application of an electrical potential. [18]

Ferrocene biosensing

A number of ferrocene-organic inorganic-organic hybrid polymers have been reported to have smart properties that make them useful for application in biosensing. [19] Multiple polymers with ferrocene side-chains cross-linked with glucose oxidase have shown oxidation activity which results in electrical potential in the presence of glucose, making them useful as glucose biosensors. [20] This sort of activity is not limited to glucose, as other enzymes can be crosslinked to allow for sensing of their corresponding molecules, like a poly(vinylferrocene)/carboxylated multiwall carbon nanotube/gelatin composite that was bound to uricase, giving it the ability to act as a biosensor for uric acid. [21]

See also

Related Research Articles

Conductive polymer

Conductive polymers or, more precisely, intrinsically conducting polymers (ICPs) are organic polymers that conduct electricity. Such compounds may have metallic conductivity or can be semiconductors. The biggest advantage of conductive polymers is their processability, mainly by dispersion. Conductive polymers are generally not thermoplastics, i.e., they are not thermoformable. But, like insulating polymers, they are organic materials. They can offer high electrical conductivity but do not show similar mechanical properties to other commercially available polymers. The electrical properties can be fine-tuned using the methods of organic synthesis and by advanced dispersion techniques.

Polyacetylene (IUPAC name: polyethyne) usually refers to an organic polymer with the repeating unit (C2H2)n. The name refers to its conceptual construction from polymerization of acetylene to give a chain with repeating olefin groups. This compound is conceptually important, as the discovery of polyacetylene and its high conductivity upon doping helped to launch the field of organic conductive polymers. The high electrical conductivity discovered by Hideki Shirakawa, Alan Heeger, and Alan MacDiarmid for this polymer led to intense interest in the use of organic compounds in microelectronics (organic semiconductors). This discovery was recognized by the Nobel Prize in Chemistry in 2000. Early work in the field of polyacetylene research was aimed at using doped polymers as easily processable and lightweight "plastic metals". Despite the promise of this polymer in the field of conductive polymers, many of its properties such as instability to air and difficulty with processing have led to avoidance in commercial applications.

Polythiophene

Polythiophenes (PTs) are polymerized thiophenes, a sulfur heterocycle. The parent PT is an insoluble colored solid with the formula (C4H2S)n. The rings are linked through the 2- and 5-positions. Poly(alkylthiophene)s have alkyl substituents at the 3- or 4-position(s). They are also colored solids, but tend to be soluble in organic solvents.

Smart materials, also called intelligent or responsive materials, are designed materials that have one or more properties that can be significantly changed in a controlled fashion by external stimuli, such as stress, moisture, electric or magnetic fields, light, temperature, pH, or chemical compounds. Smart materials are the basis of many applications, including sensors and actuators, or artificial muscles, particularly as electroactive polymers (EAPs).

In materials science, the sol–gel process is a method for producing solid materials from small molecules. The method is used for the fabrication of metal oxides, especially the oxides of silicon (Si) and titanium (Ti). The process involves conversion of monomers into a colloidal solution (sol) that acts as the precursor for an integrated network of either discrete particles or network polymers. Typical precursors are metal alkoxides.

Ormosil is a shorthand phrase for organically modified silica or organically modified silicate. In general, ormosils are produced by adding silane to silica-derived gel during the sol-gel process. They are engineered materials that show great promise in a wide range of applications such as:

Nanocomposite is a multiphase solid material where one of the phases has one, two or three dimensions of less than 100 nanometers (nm) or structures having nano-scale repeat distances between the different phases that make up the material.

Polyphosphazene

Polyphosphazenes include a wide range of hybrid inorganic-organic polymers with a number of different skeletal architectures that the backbone P-N-P-N-P-N-. In nearly all of these materials two organic side groups are attached to each phosphorus center. Linear polymers have the formula (N=PR1R2)n, where R1 and R2 are organic (see graphic). Other architectures are cyclolinear and cyclomatrix polymers in which small phosphazene rings are connected together by organic chain units. Other architectures are available, such as block copolymer, star, dendritic, or comb-type structures. More than 700 different polyphosphazenes are known, with different side groups (R) and different molecular architectures. Many of these polymers were first synthesized and studied in the research group of Harry R. Allcock.

A polymer-based battery uses organic materials instead of bulk metals to form a battery. Currently accepted metal-based batteries pose many challenges due to limited resources, negative environmental impact, and the approaching limit of progress. Redox active polymers are attractive options for electrodes in batteries due to their synthetic availability, high-capacity, flexibility, light weight, low cost, and low toxicity. Recent studies have explored how to increase efficiency and reduce challenges to push polymeric active materials further towards practicality in batteries. Many types of polymers are being explored, including conductive, non-conductive, and radical polymers. Batteries with a combination of electrodes are easier to test and compare to current metal-based batteries, however batteries with both a polymer cathode and anode are also a current research focus. Polymer-based batteries, including metal/polymer electrode combinations, should be distinguished from metal-polymer batteries, such as a lithium polymer battery, which most often involve a polymeric electrolyte, as opposed to polymeric active materials.

An inorganic polymer is a polymer with a skeletal structure that does not include carbon atoms in the backbone. Polymers containing inorganic and organic components are sometimes called hybrid polymers, and most so-called inorganic polymers are hybrid polymers. One of the best known examples is polydimethylsiloxane, otherwise known commonly as silicone rubber. Inorganic polymers offer some properties not found in organic materials including low-temperature flexibility, electrical conductivity, and nonflammability. The term inorganic polymer refers generally to one-dimensional polymers, rather than to heavily crosslinked materials such as silicate minerals. Inorganic polymers with tunable or responsive properties are sometimes called smart inorganic polymers. A special class of inorganic polymers are geopolymers, which may be anthropogenic or naturally occurring.

Silsesquioxane

A silsesquioxane is an organosilicon compound with the chemical formula [RSiO3/2]n. Silsesquioxanes are colorless solids that adopt cage-like or polymeric structures with Si-O-Si linkages and tetrahedral Si vertices. Silsesquioxanes are members of polyoctahedral silsesquioxanes ("POSS"), which have attracted attention as preceramic polymer precursors to ceramic materials and nanocomposites. Diverse substituents (R) can be attached to the Si centers. The molecules are unusual because they feature an inorganic silicate core and an organic exterior. The silica core confers rigidity and thermal stability.

An Ion gel is a composite material consisting of an ionic liquid immobilized by an inorganic or a polymer matrix. The material has the quality of maintaining high ionic conductivity while in the solid state. To create an ion gel, the solid matrix is mixed or synthesized in-situ with an ionic liquid. A common practice is to utilize a block copolymer which is polymerized in solution with an ionic liquid so that a self-assembled nanostructure is generated where the ions are selectively soluble. Ion gels can also be made using non-copolymer polymers such as cellulose, oxides such as silicon dioxide or refractory materials such as boron nitride.

Poly(dichlorophosphazene)

Poly(dichlorophosphazene), also called dichlorophosphazine polymer or phosphonitrilechloride polymer, is a chemical compound with formula (PNCl2)n. It is an inorganic (hence carbon-free) chloropolymer, whose backbone is a chain of alternating phosphorus and nitrogen atoms, connected by alternating single and double covalent bonds.

Polysilazanes are polymers in which silicon and nitrogen atoms alternate to form the basic backbone. Since each silicon atom is bound to two separate nitrogen atoms and each nitrogen atom to two silicon atoms, both chains and rings of the formula occur. can be hydrogen atoms or organic substituents. If all substituents R are H atoms, the polymer is designated as Perhydropolysilazane, Polyperhydridosilazane, or Inorganic Polysilazane ([H2Si–NH]n). If hydrocarbon substituents are bound to the silicon atoms, the polymers are designated as Organopolysilazanes. Molecularly, polysilazanes are isoelectronic with and close relatives to Polysiloxanes (silicones).

Conjugated microporous polymer

Conjugated microporous polymers (CMPs) are a sub-class of porous materials that are related to structures such as zeolites, metal-organic frameworks, and covalent organic frameworks, but are amorphous in nature, rather than crystalline. CMPs are also a sub-class of conjugated polymers and possess many of the same properties such as conductivity, mechanical rigidity, and insolubility. CMPs are created through the linking of building blocks in a π-conjugated fashion and possess 3-D networks. Conjugation extends through the system of CMPs and lends conductive properties to CMPs. Building blocks of CMPs are attractive in that the blocks possess broad diversity in the π units that can be used and allow for tuning and optimization of the skeleton and subsequently the properties of CMPs. Most building blocks have rigid components such as alkynes that cause the microporosity. CMPs have applications in gas storage, heterogeneous catalysis, light emitting, light harvesting, and electric energy storage.

Conducting polymer metal nanocomposites are.

Electronic skin refers to flexible, stretchable and self-healing electronics that are able to mimic functionalities of human or animal skin. The broad class of materials often contain sensing abilities that are intended to reproduce the capabilities of human skin to respond to environmental factors such as changes in heat and pressure.

Prof. Dr. Dr. h.c. mult. Evamarie Hey-Hawkins is a German inorganic chemist and professor at Leipzig University. Her research has focused on main group and transition metal chemistry.

Polyferrocenes

Polyferrocenes are polymers containing ferrocene units. Ferrocene offers many advantages over pure hydrocarbons when used as a building block of macromolecular chemistry. The variety of possible substitutions at the ferrocene parent body results in a multitude of accessible polymers with interesting electronic and photonic properties. Many polyferrocenes are relatively easily accessible. Poly(1,1'-ferrocene-silane) can be prepared by ring-opening polymerization and has a variety of interesting properties, such as a high refractive index or semiconductor properties. Ring-opening polymerization usually leads to polymers containing ferrocene in the backbone. Besides the latter motif, ferrocene can be attached to the backbone as pendant unit as well.

Molecular layer deposition (MLD) is a vapour phase thin film deposition technique based on self-limiting surface reactions carried out in a sequential manner. Essentially, MLD resembles the well established technique of atomic layer deposition (ALD) but, whereas ALD is limited to exclusively inorganic coatings, the precursor chemistry in MLD can use small, bifunctional organic molecules as well. This enables, as well as the growth of organic layers in a process similar to polymerization, the linking of both types of building blocks together in a controlled way to build up organic-inorganic hybrid materials.

References

  1. 1 2 3 4 Caminade AM, Hey-Hawkins E, Manners I (September 2016). "Smart Inorganic Polymers" (PDF). Chemical Society Reviews. 45 (19): 5144–5146. doi:10.1039/C6CS90086K. PMID   27711697.
  2. ↑ Chivers T, Manners I (2009). Inorganic Rings and Polymers of the p-Block Elements. Cambridge, UK: RSC Publishing. ISBN   978-1-84755-906-7.
  3. ↑ Baumgartner T, Jaekle F (2018). Main Group Strategies towards Functional Hybrid Materials. Wiley. ISBN   978-1-119-23597-2.
  4. 1 2 Hey-Hawkins E, Hissler M, eds. (April 2019). Smart Inorganic Polymers: Synthesis, Properties, and Emerging Applications in Materials and Life Sciences. Wiley. ISBN   978-3-527-34484-0.
  5. ↑ "COST ACTION CM 1302". European Network on Smart Inorganic Polymers (SIPs) - STSMs-. Retrieved 2019-05-09.
  6. 1 2 Li S, Feng S (2016). "High-sensitivity stimuli-responsive polysiloxane synthesized via catalyst-free aza-Michael addition for ibuprofen loading and controlled release". RSC Advances. 6 (101): 99414–99421. doi:10.1039/C6RA20568B.
  7. ↑ Cappelletti G (2015). "Smart hybrid coatings for natural stones conservation". Progress in Organic Coatings. 78: 511–516. doi:10.1016/j.porgcoat.2014.05.029.
  8. ↑ Dastjerdi R, Montazer M, Stegmaier T, Moghadam MB (March 2012). "A smart dynamic self-induced orientable multiple size nano-roughness with amphiphilic feature as a stain-repellent hydrophilic surface". Colloids and Surfaces. B, Biointerfaces. 91: 280–90. doi:10.1016/j.colsurfb.2011.11.015. PMID   22138117.
  9. ↑ Zhao Y, Shi L, Ji X, Li J, Han Z, Li S, Zeng R, Zhang F, Wang Z (September 2018). "Corrosion resistance and antibacterial properties of polysiloxane modified layer-by-layer assembled self-healing coating on magnesium alloy". Journal of Colloid and Interface Science. 526: 43–50. Bibcode:2018JCIS..526...43Z. doi:10.1016/j.jcis.2018.04.071. PMID   29715614.
  10. ↑ Rodrigues LC (2012). "Poly (􏰀-caprolactone)/siloxane biohybrids with application in "smart windows"". Synthetic Metals. 161: 2682–2687. doi:10.1016/j.synthmet.2011.09.043. hdl: 1822/13824 .
  11. 1 2 3 Wang X, Schröder HC, Müller WE (2018). "Amorphous polyphosphate, a smart bioinspired nano-/bio-material for bone and cartilage regeneration: towards a new paradigm in tissue engineering". Journal of Materials Chemistry B. 6 (16): 2385–2412. doi: 10.1039/C8TB00241J . PMID   32254456.
  12. 1 2 3 Rothemund S, Teasdale I (October 2016). "Preparation of polyphosphazenes: a tutorial review". Chemical Society Reviews. 45 (19): 5200–15. doi:10.1039/C6CS00340K. PMC   5048340 . PMID   27314867.
  13. ↑ Ma C, Taya M, Xu C (2008). "Smart sunglasses based on electrochromic polymers". Polymer Engineering & Science. 48 (11): 2224–2228. doi:10.1002/pen.21169.
  14. 1 2 3 Hailes RL, Oliver AM, Gwyther J, Whittell GR, Manners I (October 2016). "Polyferrocenylsilanes: synthesis, properties, and applications" (PDF). Chemical Society Reviews. 45 (19): 5358–407. doi:10.1039/C6CS00155F. hdl:1983/02c9c1b8-8477-41e3-b9d7-c184785fc9ae. PMID   27348354.
  15. ↑ Caminade AM, Hey-Hawkins E, Manners I (September 2016). "Smart Inorganic Polymers" (PDF). Chemical Society Reviews. 45 (19): 5144–5146. doi:10.1039/C6CS90086K. PMID   27711697.
  16. 1 2 Caseri W (October 2016). "Polystannanes: processible molecular metals with defined chemical structures". Chemical Society Reviews. 45 (19): 5187–99. doi:10.1039/C6CS00168H. PMID   27072831.
  17. ↑ Núñez R, Romero I, Teixidor F, Viñas C (October 2016). "Icosahedral boron clusters: a perfect tool for the enhancement of polymer features". Chemical Society Reviews. 45 (19): 5147–73. doi: 10.1039/C6CS00159A . PMID   27188393.
  18. ↑ Eloi JC, Jones SE, Poór V, Okuda M, Gwyther J, Schwarzacher W (2012-08-07). "Electrochemically Triggered Selective Adsorption of Biotemplated Nanoparticles on Self-Assembled Organometallic Diblock Copolymer Thin Films". Advanced Functional Materials. 22 (15): 3273–3278. doi:10.1002/adfm.201200210.
  19. ↑ Yan Y, Zhang J, Ren L, Tang C (October 2016). "Metal-containing and related polymers for biomedical applications". Chemical Society Reviews. 45 (19): 5232–63. doi:10.1039/C6CS00026F. PMC   4996776 . PMID   26910408.
  20. ↑ Deng H, Shen W, Gao Z (2012-06-20). "Synthesis of water-soluble and cross-linkable ferrocenyl redox polymers for uses as mediators in biosensors". Sensors and Actuators B: Chemical. 168: 238–242. doi:10.1016/j.snb.2012.04.014.
  21. ↑ Erden PE, Kaçar C, Öztürk F, Kılıç E (March 2015). "Amperometric uric acid biosensor based on poly(vinylferrocene)-gelatin-carboxylated multiwalled carbon nanotube modified glassy carbon electrode". Talanta. 134: 488–495. doi:10.1016/j.talanta.2014.11.058. PMID   25618698.
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