Inorganic polymer, also known asInorganic polymerIt belongs to an old and emerging cross discipline between inorganic chemistry and polymer chemistry.General inorganic polymer is defined as: the main chain is composed of noncarbon atomCovalent bondmolecule。Inorganic polymers are composed of non carbon atoms (N, P, O, S and other heteroatoms)Macromolecular substances, atoms are mainly combined with covalent bonds to formCarbon chainSimilar heteroatom backbone.Compared with organic polymers, inorganic polymers have many unique properties, which have attracted people's attention.[1]
The chemical composition of inorganic polymer materials is polymerization likeAluminosilicate, with Si, AI, O, P, N as the main chain, and introduced into CH3-、C-CsixHsix-、NHtwo-, CH=CH element or group and other chain links are formed by covalent bond or ionic bond, and the polymer is condensed into polymer,Degree of polymerizationHigher.By focusing on new inorganicPolymerResearch on the synthesis law and performance, using nano cage technology design, using inorganic compounds with high chemical activity as precursors, under the action of alkali (acid) catalyst, dissolving complexation, dispersion migration, self-assembled coordination bridging in liquid chemistry, and separating and characterizing a large number of intermediate products in the process of energy dynamic reaction mechanism control,So as to obtain good mechanical properties and three-dimensional network structure in physical formchemical stability。[1]
characteristic
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Inorganic polymer materials are made of nanometer sized particles by stacking, bridging, polymerization and curing, which can achieve densification at a lower temperature. At the same time, due toSmall size effect, surface and interface effectsquantum size effect And quantum tunnel effect, which makes it have unique properties, will help to solve the problem of strengthening and toughening the bond.Specifically, inorganic polymer materials have the following unique properties:
(1) Small particle size, large specific surface area and high chemical bonding can improve product performance;Reactive low temperature consolidation, saving energy;
(2) Densify and homogenize the composition and structure of the material, improve the structure and performance, and improve the reliability of use;
(3) The composition and structure of materials can be controlled from the quantum level, which makes it possible to design the structure and properties of inorganic polymer materials directionally.[1]
classification
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Classified according to the main chain structure
Homogeneous chain polymer material: the main chain is composed of atoms of the same element.For example,
Chain sulfur... － S － S － S －
H H H
Polysilane... － Si － Si － Si －
H H H
Heterochain polymer material: The main chain is composed of atoms of different elements.For example,
Polyphosphazene compounds... - P=N - P=N -
According to the spatial dimension of polymer materials
One dimensional polymer material: structural units are connected in a linear way, so it is also called chain inorganic polymer material.
Two-dimensional polymerSubstance: structural units are connected on a plane to form planar macromolecules.Planar molecules overlap each other to form crystals according to certain rules, so they are also called layered polymer substances.
Three dimensional polymer materials: structural units are connected in three-dimensional space, so they are also called skeleton (or network) polymer materials.
Examples of substances
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Homogeneous chain inorganic polymer
(1) Chain sulfur
The chain like sulfur molecule is a long chain composed of many S atoms by covalent bond
…－S－S－S－…
"- S -" is the structural unit.
Chain sulfur in nitrogen or otherinert gasThe sulfur is heated at 300 ℃ for 5 min, and then poured into ice water to form fibrous elastic sulfur, which is composed of spiral long chain sulfur (S) n.Chain sulfur is insoluble in CStwoWhen placed at room temperature, it will harden and lose elasticity, and slowly depolymerize into S8. Light can promote depolymerization.If phosphorus, halogen or alkali metal are added to the molten sulfur, the stability of chain sulfur can be improved.This is because they react with the sulfur at the end of the sulfur chain to form an end group, which can stabilize the end of the sulfur chain.For example, potassium polysulfide K [S] nK and iodine polysulfide I [S] nI are relatively stable.
(2) Polysilane and polyhalosilane
When calcium silicide is reacted with alcohol solution containing glacial acetic acid or hydrochloric acidrelative molecular massChain polysilane [SiHtwo]n. Its structure is similar to polyethylene;
Diluted with inert gasSilicon tetrachlorideOr silicon tetrabromide is fed into a reactor at 1000~1100 ℃ to generate polyhalosilane [SiX] similar to [SiH2] ntwo]n。
Replace (CHthree)twoSiCltwoReact with molten metal sodium to form polyDimethylsilane：
The cured polydimethylsilane is obtained by heating the polydimethylsilane in air at 200 ℃ for 16 h.Polydimethylsilane is very stable to waterChemical ReagentsIt also has good stability. For example, it can be soaked for a long time in NaOH aqueous solution, and its properties and shape do not change.
Heterochain inorganic polymer
(1) Sulfur nitrogen compound
Several S/N compounds are known, the most important of which is SfourNfourAnd long chain polymer (SN) n polymerized from it.
SfourNfourThere is a cradle shaped structure, which is an 8-membered heterocycle with DtwoD Symmetry.The S-N distance is 162 pm, which is shorter than the sum of their covalent radii (176 pm). In addition, the distance of each S-N in the molecule is equal. This fact is believed to be caused by the role of non localized electrons in the heterocycle of the molecule.The distance of S... S across the ring (258 pm) is between
The distance between the S-S bond (208 pm) and the unbound van der Waals distance (330 pm) indicates that there is a very weak but still obvious bonding between the trans ring S atoms.
Put SfourNfourSteam is heated to 300 ℃ to generate StwoNtwo。StwoNtwoIt is very unstable and can be polymerized at room temperature to synthesize (SN) n.
(SN) n is the only known chain inorganic polymer with superconductivity.(SN) n is a long chain structure, each chain is arranged in parallel with each other in the crystal, and adjacent molecular chains are combined by van der Waals force.(SN) n crystal is anisotropic in electrical properties.At room temperature, the conductivity along the bond direction is close to Hg and other metals, about hundreds of thousands of S · m－1, while the conductivity perpendicular to the bond direction is only 1 000 S · m－1。Up to 5 × 107 S · m at 5 K－1Below 0.26 K is superconductor.
The acquisition of superconductor (SN) n proves for the first time that the system without metal atoms may also have superconductivity.(SN) n is also the first achievement in the synthesis and research of one-dimensional anisotropic compounds with superconductivity.
The structure of As4S4 is similar to that of S4N4, but the elements of Group V and Group VI exchange positions with each other.
(2) Phosphorus nitrogen compound
① Chlorophosphazenes with low degree of polymerization
Chlorophosphazenes with low degree of polymerization (PNCltwo）N (n=3-8) has a ring structure.In which, trimer (PNCltwo)threeAnd tetramer (PNCltwo)fourMost important.The former is planar, while the latter has two configurations of "chair" and "boat".
In chlorophosphazene, the nitrogen atom is considered to haveSp2 hybrid, three hybrid orbitals are occupied by four electrons, one of which is a lone pair electron, and the other two sp2 hybrid orbitals with one electron areSp3 hybridOrbit generates P-N bond;The remaining pz orbital occupied by the fifth electron on the N atom is used to form the p bond.The four electrons of the phosphorus atom in the sp3 hybrid orbital are approximately arranged in the s bond according to the tetrahedron. These bonds are two P-Cl bonds, two P-N bonds, and the remaining fifth electron in the d orbital is used to form the p bond.So the p bond in chlorophosphazene is d (P) - p (N) p bond.
Due to the conjugation of d-pp bond, the framework of phosphazene compounds is stable and has high thermal stability.However, due to the existence of active P-X bonds in phosphazenes, it is easy to carry out chemical reactions.amongNucleophilic substitution reactionIt is the main reaction of phosphoronitrile compounds, whenNucleophileWhen attacking the phosphorus atom, the halogen atom on the phosphorus atom can be partially or completely replaced to generate corresponding substituents.For example:
[PNCltwo]three+6NaOR —→[PN(OR)two]three+6NaCl
② Phosphoronitrile compounds with high degree of polymerization
Replace the ring (PNCltwo)threeHeat it to 250~350 ℃ in a closed container, that is, open the ring to generate long chain polydichloroadiphosphazene with high polymerization degree (hereinafter referred to as chlorophosphazene):
n[PNCltwo]three——→ －[PNCltwo]threen－
It is widely believed that [PNCltwo]threeThe polymerization of is (cation) ion polymerization.That is, [PNCltwo]threeFirst generate a Cl－Ions and phosphorus containing cations.
Polychlorinated phosphazenes are colorless, transparent, and insoluble in any organic solvent elastomers with large relative molecular weight. They are called inorganic rubbers.hisGlass transition temperatureIt is about - 63 ℃, the plasticity limit temperature is - 30~30 ℃, the tensile strength is up to 18 kg · cm - 2, the elongation is 150~300%, it has good thermal stability, and it will not be depolymerized until it is above 400 ℃.However, due to the presence of highly active P-Cl bonds, polychlorinated phosphazenes are easy to hydrolyze:
Therefore, it is difficult to be practical.In recent years, the introduction of alkoxy groups and other groups has eliminated the instability of water, which makes the future development of polychlorinated phosphazenes and their applications promising.
③ Organic derivatives of polychlorinated phosphazenes and their applications
Various types of reactions can introduce different organic groups on phosphorus atoms to generate a wide range of organic derivatives.
Alkoxy substituents of polychlorinated phosphazenes have attracted great attention due to their low glass transition temperature, good thermal stability and non combustion characteristicsnew materials Key points of development and research.
Such as {NP (OCHtwoCFthree)[OCHtwo(CFtwo)threeCFtwoH] } n has been commercialized, and the trade name is PNF.PNF has excellent low temperature characteristics (glass transition temperature is - 68 ℃). After treatment with sulfur, it also has good flexibility at a very low temperature;Add appropriate amount of SiOtwo, MgO and other oxides, which can quickly solidify to form PNF rubber.PNF rubber has excellent properties such as oil resistance, high temperature resistance, aging resistance, low temperature elasticity and non combustion.
When the organic substituent in polyphosphazene contains active ammonia, it canDiazotization reactionThe polymer dye is prepared.They have the characteristics of high temperature resistance and non combustion, which are inferior to other dyes.
Polychlorophosphazene derivatives are being studied asMedical polymer materials, macromolecular drugs and efficient catalysts, which have attractive prospects.
The B-N group formed by connecting the B atom and the N atom is isoelectronic with the C-C group in structure. The similarity between them is mainly due to the fact that - B=N+In the double bond, the polarity of the p bond is just opposite to that of the s bond and mutually cancels out, so that the B=N bond generally does not show polarity, so it is very similar to the C=C bond.Because of the similarity between B=N bond and C=C bond, boron nitrogen hexacyclic BthreeNthreeHthree(Inorganic benzene) and benzene C in electronic structure and geometrysixHsixExactly the same.
BthreeNthreeHsixIt also has the property of aromatic hydrocarbon and can participate in various aromatic substitution reactions and addition reactions.
In addition reaction, boron nitrogen ring is more active than benzene ring, because electron deficient B is more inclined to accept foreign electrons.For example, B3N3H6 can react rapidly with HX (X=Cl -, OH -, - OR, etc.), but benzene does not:
BthreeNthreeHsix+3HX —→－[HtwoN－BHX]3－
Boron nitrogen six ring decomposes slowly during storage, and it can be hydrolyzed to NH at elevated temperaturethreeAnd B (OH)three。Their substituted derivatives have certain stability.
flocculant
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As an important method of wastewater treatment, flocculation is the most widely used, economical and simple water treatment technology.The key to achieve high flocculation efficiency is to add flocculants with excellent performance.Due to organic synthesisPolymer flocculantIts application in China is limited due to its toxicity and high price.Inorganic polymer flocculant(IPF) has been widely used in the treatment of various sewage and wastewater due to its high efficiency, strong adaptability, non-toxic and low price.The widely used inorganic polymer flocculants are developed on the basis of traditional aluminum salt and iron salt flocculants, which can be divided into three categories: cationic, anionic and composite.The traditional aluminum salt and iron salt flocculants have a long history of use, but there are many problems in the water treatment process. In the late 1960s, they were gradually replaced by the rapidly developing inorganic polymer flocculants.Inorganic polymer flocculant has better flocculation effect and lower price than the original traditional flocculant.
Cationic inorganic polymer flocculant
Cationic inorganic polymer flocculants mainly include polyaluminum chloride (PAC), polyaluminum sulfate (PAS), polymeric ferric sulfate (PFS), polymeric ferric chloride (PFC)Polymeric ferric chloride sulfate(PFCS) and polyphosphate ferric chloride (PPFC), etc.
Anionic inorganic polymer flocculant
Anionic inorganic macromolecular flocculant mainly refers to active silicic acid flocculant, which was applied in water treatment as a flocculant in the late 1920s. Under normal conditions, the components are negatively charged. Flocculation of colloidal particles is completed by binding colloidal particles through adsorption bridging. Activated silicic acid is usually made by adding sodium silicate (water glass) to acid,Because the gelling time and pH are not easy to control, the product cannot be stored for a long time, and needs to be prepared on the site of water treatment, so it is not widely used.However, since activated silicic acid has the characteristics of wide source of raw materials, low cost, non-toxic, simple preparation, and special effect in treating low temperature and low turbidity water, a lot of research work on modified activated silicic acid has been carried out at home and abroad in recent years[2]
