Inorganic Polymer In Chemistry

INORGANIC POLYMER

Polymer is a substance with high molecular weight containing large no. of repeating structural units. These units are called as monomer. The process of joining monomer to form polymer is called as polymerization.
Silica, clay, some mineral salts are the examples of inorganic polymer. It is defined as "The polymers are giant molecules formed by repeating structural units except carbon." Organic polymers have some limitations at higher temperature. These limitations are overcome by inorganic polymers.
Polymer containing same type of monomer is called as homopolymer & polymer containing more than one type of monomer is called as heteropolymer. The no. of monomers in a polymer molecule is specified by degree of polymerization. If no. of monomer is two it is called as dimer, if three – trimer , four-tetramer & so-on. If degree of polymerization is above hundred then it is known as high polymer.

Classification of polymer :
Polymers have linear, branched & cross-linked structure.
a) Linear polymer – If monomer is capable of forming two covalent bonds linear type of
polymer is formed.

b) Branched polymer – If linear structures develop side chains branched polymer is
formed.

c) Cross linked polymer – If short cross links are formed between linear structures these
polymers are formed.

Classification based on nature of origin:
a) Naturally occurring polymer – These are the polymers which obtains in nature directly.
eg. Cotton, silk, wool, starch etc.
b) Derived (modified) polymers – These polymers are derived from naturally occurring
polymers. eg. Nitrate & acetate ester of cellulose, terry cot, terry wool, etc.
c) Synthetic polymer – These are man made or artificially prepared polymers. eg.
polyethylene, polystyrene, epoxy resin, synthetic rubber, etc.
They are again classified as follows,
i) Synthetic fibers : They are capable of forming fibers of high strength &
flexibility. eg. Polyester, polyamide, etc.
ii) Elastomers : These polymers are having rubber like elasticity.
eg. polyurethanes, polyisoprene, etc.
iii) Plastic : Polymers neither forming nor elastic in nature comes under this
category. They have major applications in our daily life. eg. polyethelene,
polypropylene, etc.

Difference between organic polymer & inorganic polymer
Organic polymer Inorganic polymer
1) They have c-c linkage in their backbone. 1) They are having generally hetero type of
i.e. homopolymer. framework. i.e. heteropolymer.
2) They show tendency to form linear chain 2) They have tendency to depolymerise &
structure & do not depolymerise to form form cyclic monomer. i.e. four, six or
cyclic monomer. eight member ring structure.
3) These are three dimensional polymer may 3) They exit in highly stable crystalline
random structure & loose their structure form & maintain regularity even in
on heating. molten state.
4) They are having high degree of 4) They are having low degree of
Polymerization. Polymerization.
5) They are stable in atm upto 3000C. 5) They are stable at higher temp.than 300C
6) They are less resistant to acid, alkalies 6) They are comparatively more stable.
& other organic solvents.

Classification of Inorganic Polymers.
A] Classification based on type of atom forming skeleton.
(Korshak & Mozyora's classification)
i) Homoatomic polymer : These are the polymer containing same type of atom in
backbone. e.g. P4, S8, etc.
ii) Heteroatomic polymer : These are the polymer containing different type of atom in
backbone. e.g. silicones, phosphonitrillic compounds, etc.

B] Classification based on structure of polymer. (Mayers's classification)
According to this inorganic polymers are divided in three types- linear, sheet & three
dimensional structure. Many common inorganic polymers are not included in this
classification there fore it is not accepted.

C] Classification based on method of preparation.
i) Condensation polymers : These are formed by condensation polymerization, i.e. two or
more monomers are joined together by eliminating simple molecule like H2O, HCl,
NH3, H2. e.g. silicones, borazines.
ii) Addition polymers : These are formed by addition of monomers. e.g. phosphonitrillic
chloride is obtained by addition of PCl5 & NH4Cl.
iii) Co-ordination polymers : They are formed due to co- ordinate bond.
e.g. Dimer of Aluminium trichloride.


Cl Cl Cl
Al Al
Cl Cl Cl




Palladus chloride exists as a linear polymer.

Cl Cl Cl Cl
----Pd Pd Pd Pd Pd----
Cl Cl Cl Cl

Nickel cyanide is two dimensional polymer.

CN CN

----CN Ni CN Ni CN----

CN CN

---- CN Ni CN Ni CN----

CN CN

Polymer Backbone :
The framework of atom in polymer is known as polymer backbone. In homopolymer backbone is made up of same atoms, while in heteropolymers it is made up of different atoms.
The formation of chain of same atoms is called as catenation. Elements having catenation power generally forms homopolymer. Carbon is having high catenation power hence forms backbone all organic polymers. Another elements having some catenation power are B, N, P, Si & S. They show low tendency of catenation may be due to poor bond strength between homoatomic chains. So in Inorganic polymer homopolymers are less. However strength (bond energy) of heteroatoms such as C-N, Bi-O, Si-O are even higher than C-C bond energy. Therefore heteroatomic backbone is major in Inorganic polymer & also explains thermal stability.


Homoatomic Polymer containing Phosphrous.
Phosphorous shows catenation power & exist in three allotropic forms such as white phosphorous, red phosphorous & crystalline black phosphorous.
P P P P


P P P P P P

P P P P
White Red Black
In all these allotropic forms phosphorous is linked with three other phosphorous atoms through covalent bond. In white phosphorous only four atoms are linked. In red phosphorous P4 tetrahydra are linked to form a long chain polymer. In black phosphorous layers of phosphorous are bonded to other three neighbours. Red phosphorous can be obtained by heating white phosphorous at 3000C for several days. When phosphorous is heated under high pressure at 20000C black phosphorous is obtained.
Self linked phosphorous compounds :
P2H4 (phosphorous dihydride), P2X4 (phosphorous dihalide)

H H X X
P P P P
H H X X

H4P2O6 (hypophosphoric acid)

OH OH

O P P O

OH OH

Phosphor benzene Phosphortetrafloromethane

C6H5 C6H5 CF3 CF3

P P P P

P P P P

C6H5 C6H5 CF3 CF3

These compounds are thermally stable because they form strong P-P bond due to Π
bonding effect. i.e. lone pair electron of one phosphorous atom empty 3d orbital of other phosphorous involves in Π bonding.


Heteroatomic Polymer
In heteroatomic polymer different types of atoms are present in polymer backbone. eg. silicones phosphonitrillic compounds & fluorocarbons.

1] Silicones :
These are organosilicone polymer containing alternate Si & O atoms. The remaining valencies of silicones are fulfilled by organic group like CH3, C2H5 etc.
They are also called as siloxanes. Depending upon degree polymerization & structure they are roughly classified as i) silicone fluids , ii) silicone resins, iii) silicone grease, iv) silicone rubber.
Preparation :- They are prepared in two steps. In first step intermediate is obtained by reacting silicon directly with alkyl halide or by aromatic silylation or by using Grignard's reagent. In second step the intermediate on hydrolysis undergoes polymerization.
i) SiCl4 + C6H5MgCl C6H5SiCl3 + MgCl2 using G.R.
ii) C6H6 + HSiCl3 C6H5SiCl3 + H2 aromatic silylation

iii) CH3Cl + 2HCl Si Cu CH3SiCl3 + H2 direct reaction
3000C
These monoalkyl silicon trichloride gives cross linked polymer.
RSiCl3 + 3HOH RSi(OH)3 + 3HCl

nRSi(OH)3
-H2O


O R O

-------O Si O Si O Si O------

R O R

-------O Si O Si O Si O-----

O R O
Similarly dialkyl silicon dichloride on hydrolysis gives along chain polymer.

R2SiCl2 + 2H2O R2Si(OH)2 + 2HCl

R R R R

HO Si OH + HO Si OH HO Si O Si OH

R R R R

Polymerization

R R R R

------- O Si O Si O Si O Si O-----

R R R R
Properties of silicones :-
1) They have high thermal stability. (-700 to 5000C)
2) They are water repellent & insulator.
3) They are resistant to chemical attack due to presence of Si-O-Si bond.
4) Some of them are soluble in organic solvents such as benzene, ether etc.

Uses of silicones
1) Silicone fluid : They are used as hydraulic fluids. They are also used as lubricants,
antifoam agent, grease, polish additive, liquid spring, etc.
2) Silicone rubber : As they retain their elasticity even at low temp & also resistance to
oil, heat they are used in sealing joints & seams of jet aircrafts.
3) Silicone grease : As they are having wide temp range (-100 to 5000C) they are used for
ball bearings operating at high speed & high temp in aircrafts.
4) Silicone resins : They are used in all type of resins such as coating, laminating, water
repellent, moldings, electrical resins, etc.
5) In general they are used in paints, enamels, medical & surgical appliances.

2] Phosphonitrillic compounds : (Inorganic rubber)
They are cyclic or linear polymer with –N=P – repeating units in their structure. They are represented by general formula (PNX2)n, where X may be Cl, F, Br, SCN, CH3, C6H5, etc. Among the phosphonitrillic haides chlorides are well known, out of which trimer & tetramer are very important. They can prepared easily by following method.
nPCl5 + nNH4Cl (PNCl2)n + 4nHCl
Structure : A trimer of (PNX2)3 has planer six membered ring structure like benzene, where P & N are at alternate position. PNP bond angle is 1200 i.e. N is is SP2 hybridized.
Tetrahedral valency of phosphorous shows SP3 hybridization. All P-N bonds in a ring have equal bond length 1.61 A0 which is less than normal bond length 1.81 A0 i.e. it posses Π bond & some aromatic character.

Cl

P N Cl

N P

P N Cl

Cl

7N - 1S2 2S2 2P3



15P - 3S2 3P3 3d


dΠ orbital of phosphorous overlap laterally pΠ orbital of nitrogen to form a Π bond & hence it posses aromatic character.
Tetramer of (PNCl2)4 has puckered ring structure.

Linear phosphonitrillic chlorides can be prepared by heating trimer at 250-3500C in CCl4 with excess of oxygen. This polymer may have higher molecular weight (20000).
Properties : 1) They are thermally stable elastomers.
2) These polymer decomposes in presence of moisture.
3) On exposing to air they form long spiral chains which gradually changes
into horny solids.
4) Above 3500C they undergo depolymerization to form cyclic
phosphonitrillic compound.
These compounds are used in laboratory & their applications are restricted due to their carcinogenic nature.

3] Florocarbons :
Though fluorocarbons belongs to organic polymer they are different from their hydrocarbon homologue & posses outstanding properties such as toughness, thermal stability, high resistance to chemical attack & insolubility. These properties are mainly due to fluorine content. Therefore their study is included here.
The hydrocarbon in which all hydrogen atoms are replaced by fluorine atom are called as fluorocarbon. Carbon monofluoride is the simplest & important polymer. It is prepared by heating graphite at 420-4600C in a stream of fluorine. It is solid having different colors from grey to white depending on fluorine content.
n C + n/2 F2 420-4600C (CF)n
They conduct electricity & conducting decreases with increase in fluorine content. They are not attacked by conc. acids, alkalies & not wetted by water.
Chlorofluorocarbons are heated to get monomer C2F4
2CHClF2 600-8000C C2F4 + 2HCl

F F F F

n C C C C

F F F F
Polytetrafluoroethylene (Teflon)



Fluoroaromatic polymer can be prepared as

Uses :
Due to their outstanding properties they are used in lubricants, adhesives, coating, bearings, tubing, non sticking cooking appliances & elastic material. Also used in aircraft industries.

The structure of carbon monofluoride is made up of puckered layers. Each carbon in the layer undergoes SP3 hybridization & forms three covalent bond with other three carbon in same layer. Fourth orbital is linked with fluorine atom.

Que.
1. What are inorganic polymer? Give their types & comparison between organic polymer & inorganic polymer.
2. What are phosphonitrillic compounds? Give method of preparation & uses.
3. Explain silicones w.r.t. definition, preparation & uses.
4. Types of polymer backbone.
5. Distinguish between organic polymer & inorganic polymer.