Inorganic polymer

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The inorganic polymer (SN)x Polythiazyl-2D-dimensions.png
The inorganic polymer (SN)x

An inorganic polymer is a polymer with a skeletal structure that does not include carbon atoms in the backbone. [1] Polymers containing inorganic and organic components are sometimes called hybrid polymers, [2] and most so-called inorganic polymers are hybrid polymers. [3] 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. [4] 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.

Contents

Main group backbone

Traditionally, the area of inorganic polymers focuses on materials in which the backbone is composed exclusively of main-group elements.

Homochain polymers

Homochain polymers have only one kind of atom in the main chain. [5] One member is polymeric sulfur, which forms reversibly upon melting any of the cyclic allotropes, such as S8. Organic polysulfides and polysulfanes feature short chains of sulfur atoms, capped respectively with alkyl and H. Elemental tellurium and the gray allotrope of elemental selenium also are polymers, although they are not processable.

The gray allotrope of selenium consists of helical chains of Se atoms. Selenium trigonal.jpg
The gray allotrope of selenium consists of helical chains of Se atoms.

Polymeric forms of the group IV elements are well known. The premier materials are polysilanes, which are analogous to polyethylene and related organic polymers. They are more fragile than the organic analogues and, because of the longer Si–Si bonds, carry larger substituents. Poly(dimethylsilane) is prepared by reduction of dimethyldichlorosilane. [6] Pyrolysis of poly(dimethylsilane) gives SiC fibers.

Heavier analogues of polysilanes are also known to some extent. These include polygermanes, (R2Ge)n, and polystannanes, (R2Sn)n.

Heterochain polymers

Si-based

Heterochain polymers have more than one type of atom in the main chain. Typically two types of atoms alternate along the main chain. Of great commercial interest are the polysiloxanes, where the main chain features Si and O centers: −Si−O−Si−O−. Each Si center has two substituents, usually methyl or phenyl. Examples include polydimethylsiloxane (PDMS, (Me2SiO)n), polymethylhydrosiloxane (PMHS (MeSi(H)O)n) and polydiphenylsiloxane (Ph2SiO)n). [5] Related to the siloxanes are the polysilazanes. These materials have the backbone formula −Si−N−Si−N−. One example is perhydridopolysilazane PHPS. Such materials are of academic interest.

P-based

A related family of well studied inorganic polymers are the polyphosphazenes. They feature the backbone −P−N−P−N−. With two substituents on phosphorus, they are structurally similar related to the polysiloxanes. Such materials are generated by ring-opening polymerization of hexachlorophosphazene followed by substitution of the P−Cl groups by alkoxide. Such materials find specialized applications as elastomers. [5]

General structure of polyphosphazenes. Gray spheres represent any organic or inorganic group. PolyphosphazeneGeneralStructure.png
General structure of polyphosphazenes. Gray spheres represent any organic or inorganic group.

B-based

Boronnitrogen polymers feature −B−N−B−N− backbones. Examples are polyborazylenes, [7] polyaminoboranes. [8] [9]

S-based

The polythiazyls have the backbone −S−N−S−N−. Unlike most inorganic polymers, these materials lack substituents on the main chain atoms. Such materials exhibit high electrical conductivity, a finding that attracted much attention during the era when polyacetylene was discovered. It is superconducting below 0.26 K. [10]

Ionomers

Usually not classified with charge-neutral inorganic polymers are ionomers. Phosphorus–oxygen and boron-oxide polymers include the polyphosphates and polyborates.

Transition-metal-containing polymers

Inorganic polymers also include materials with transition metals in the backbone. Examples are Polyferrocenes, Krogmann's salt and Magnus's green salt.

Magnus's green salt, which is not a salt, features a one-dimension chain of weak Pt-Pt bonds. Magnus'-green-salt-from-xtal-1957-CM-3D-balls-horizontal.png
Magnus's green salt, which is not a salt, features a one-dimension chain of weak Pt–Pt bonds.

Polymerization methods

Inorganic polymers are formed, like organic polymers, by:

Reactions

Inorganic polymers are precursors to inorganic solids. This type of reaction is illustrated by the stepwise conversion of ammonia borane to discrete rings and oligomers, which upon pyrolysis give boron nitrides. [7]

Related Research Articles

<span class="mw-page-title-main">Boranes</span>

Boranes is the name given to compounds with the formula BxHy and related anions. Many such boranes are known. Most common are those with 1 to 12 boron atoms. Although they have few practical applications, the boranes exhibit structures and bonding that differs strongly from the patterns seen in hydrocarbons. Hybrids of boranes and hydrocarbons, the carboranes are also well developed.

<span class="mw-page-title-main">Diborane</span> Chemical compound

Diborane(6), generally known as diborane, is the inorganic chemical compound consisting of boron and hydrogen with the formula B2H6. It is a toxic, colorless and pyrophoric gas with a repulsively sweet odor. Synonyms include boroethane, boron hydride, and diboron hexahydride. Diborane is a key boron compound with a variety of applications. It has attracted wide attention for its electronic structure. Its derivatives are useful reagents.

In polymer science, the polymer chain or simply backbone of a polymer is the main chain of a polymer. Polymers are often classified according to the elements in the main chains. The character of the backbone, i.e. its flexibility, determines the properties of the polymer. For example, in polysiloxanes (silicone), the backbone chain is very flexible, which results in a very low glass transition temperature of −123 °C. The polymers with rigid backbones are prone to crystallization in thin films and in solution. Crystallization in its turn affects the optical properties of the polymers, its optical band gap and electronic levels.

In chemistry, catenation is the bonding of atoms of the same element into a series, called a chain. A chain or a ring shape may be open if its ends are not bonded to each other, or closed if they are bonded in a ring. The words to catenate and catenation reflect the Latin root catena, "chain".

<span class="mw-page-title-main">Polysulfide</span>

Polysulfides are a class of chemical compounds containing chains of sulfur atoms. There are two main classes of polysulfides: inorganic and organic. Among the inorganic polysulfides, there are ones which contain anions, which have the general formula S2−
n
. These anions are the conjugate bases of the hydrogen polysulfides H2Sn. Organic polysulfides generally have the formulae R1SnR2, where R = alkyl or aryl.

<span class="mw-page-title-main">Siloxane</span> Si–O–Si chemical bond

A siloxane is a functional group in organosilicon chemistry with the Si−O−Si linkage. The parent siloxanes include the oligomeric and polymeric hydrides with the formulae H(OSiH2)nOH and (OSiH2)n. Siloxanes also include branched compounds, the defining feature of which is that each pair of silicon centres is separated by one oxygen atom. The siloxane functional group forms the backbone of silicones, the premier example of which is polydimethylsiloxane. The functional group R3SiO− (where the three Rs may be different) is called siloxy. Siloxanes are manmade and have many commercial and industrial applications because of the compounds’ hydrophobicity, low thermal conductivity, and high flexibility.

Chlorosilanes are a group of reactive, chlorine-containing chemical compounds, related to silane and used in many chemical processes. Each such chemical has at least one silicon-chlorine bond. Trichlorosilane is produced on the largest scale. The parent chlorosilane is silicon tetrachloride.

<span class="mw-page-title-main">Borazine</span> Boron compound

Borazine, also known as borazole, is a non-polar inorganic compound with the chemical formula B3H6N3. In this cyclic compound, the three BH units and three NH units alternate. The compound is isoelectronic and isostructural with benzene. For this reason borazine is sometimes referred to as “inorganic benzene”. Like benzene, borazine is a colourless liquid with an aromatic smell.

In organic chemistry, hydroboration refers to the addition of a hydrogen-boron bond to certain double and triple bonds involving carbon. This chemical reaction is useful in the organic synthesis of organic compounds.

<span class="mw-page-title-main">Ammonia borane</span> Chemical compound

Ammonia borane (also systematically named amminetrihydridoboron), also called borazane, is the chemical compound with the formula H3NBH3. The colourless or white solid is the simplest molecular boron-nitrogen-hydride compound. It has attracted attention as a source of hydrogen fuel, but is otherwise primarily of academic interest.

<span class="mw-page-title-main">Binary silicon-hydrogen compounds</span>

Silanes are saturated chemical compounds with the empirical formula SixHy. They are hydrosilanes, a class of compounds that includes compounds with Si-H and other Si-X bonds. All contain tetrahedral silicon and terminal hydrides. They only have Si–H and Si–Si single bonds. The bond lengths are 146.0 pm for a Si–H bond and 233 pm for a Si–Si bond. The structures of the silanes are analogues of the alkanes, starting with silane, SiH
4
, the analogue of methane, continuing with disilane Si
2
H
6
, the analogue of ethane, etc. They are mainly of theoretical or academic interest.

A silicone oil is any liquid polymerized siloxane with organic side chains. The most important member is polydimethylsiloxane. These polymers are of commercial interest because of their relatively high thermal stability, lubricating, and dielectric properties.

<span class="mw-page-title-main">Silsesquioxane</span>

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.

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).

<span class="mw-page-title-main">E. D. Jemmis</span>

Eluvathingal Devassy Jemmis or E. D. Jemmis is a Professor of theoretical chemistry at the Indian Institute of Science, Bangalore, India. He was the founding Director of Indian Institute of Science Education and Research, Thiruvananthapuram (IISER-TVM). His primary area of research is applied theoretical chemistry with emphasis on structure, bonding and reactivity, across the periodic table of the elements. Apart from many of his contributions to applied theoretical chemistry, an equivalent of the structural chemistry of carbon, as exemplified by the Huckel 4n+2 Rule, benzenoid aromatics and graphite, and tetrahedral carbon and diamond, is brought in the structural chemistry of boron by the Jemmis mno rules which relates polyhedral and macropolyhedral boranes to allotropes of boron and boron-rich solids. He has been awarded Padma Shri in Science and Engineering category by the Government of India.

<span class="mw-page-title-main">Polysilane</span>

Polysilanes are organosilicon compounds with the formula (R2Si)n. They are relatives of traditional organic polymers but their backbones are composed of silicon atoms. They exhibit distinctive optical and electrical properties. They are mainly used industrially as precursors to silicon carbide. The simplest polysilane would be (SiH2)n, which is mainly of theoretical, not practical interest.

IUPAC Polymer Nomenclature are standardized naming conventions for polymers set by the International Union of Pure and Applied Chemistry (IUPAC) and described in their publication "Compendium of Polymer Terminology and Nomenclature", which is also known as the "Purple Book". Both the IUPAC and Chemical Abstracts Service (CAS) make similar naming recommendations for the naming of polymers.

Trihydridoboron, also known as borane or borine, is an unstable and highly reactive molecule with the chemical formula BH
3
. The preparation of borane carbonyl, BH3(CO), played an important role in exploring the chemistry of boranes, as it indicated the likely existence of the borane molecule. However, the molecular species BH3 is a very strong Lewis acid. Consequently, it is highly reactive and can only be observed directly as a continuously produced, transitory, product in a flow system or from the reaction of laser ablated atomic boron with hydrogen.

<span class="mw-page-title-main">Smart inorganic polymer</span>

Smart inorganic polymers (SIPs) are hybrid or fully inorganic polymers with tunable (smart) properties such as stimuli responsive physical properties. 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.

<span class="mw-page-title-main">Polymer derived ceramics</span>

Polymer derived ceramics (PDCs) are ceramic materials formed by the pyrolysis of preceramic polymers, usually under inert atmosphere.

References

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  2. IUPAC , Compendium of Chemical Terminology , 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006) " hybrid polymers ". doi : 10.1351/goldbook.HT07556
  3. Inorganic Two-dimensional Nanomaterials, Editor: Changzheng Wu, Royal Society of Chemistry, Cambridge 2017.
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