Classification of Inorganic Polymers

There are different ways of classifying them 

1^st classification:

Depending upon whether the polymer contains the atoms of only one element or of different elements in its backbone, they are classified into the following two groups.

[1] Homo-atomic polymers:

These polymers contain the atoms of only one element in their backbones Silicon, phosphorus, sulphur, germanium and tin from homo-atomic inorganic polymer. For example, sulphur has a tendency to form chains or rings in its elemental form (S₈) and in several compounds, like persulphides (H-S-S-H, H-S-S-S-H, H-S-S-S-S-H etc.)

[2] Hetero-atomic Polymers:

These contain the atoms of different elements in their backbones

2^nd Classification

Inorganic polymers can also be classified in another way, which is base on the type of reaction by which the polymers are formed. On this basis, inorganic polymers may be of the following types:

[1] Condensation (polymerisation) polymers.

Condensation polymers are those, which are formed by the condensation (polymerisation) process. In this process, two or more simple molecules of the same substance polymerise together and from the condensation polymer. One or more H₂O, NH₃, H₂, HCl etc., molecules are also eliminated.
Examples: (a) Cross-linked silicone is obtained by the polymerisation of many RSi(OH)₃ molecules.
(b) When PCl₅ is partially hydrolysed by water, dichloro phosphoric acid, PO(OH)Cl2 is obtained. When PO(OH)Cl2 is heated, many molecules of this substance get polymerized.

[2] Addition polymers:

These polymers are obtained, when many simple molecules (monomers) combine together.
Example: (a) many molecules of sulphur trioxide may be polymerised by the addition of a small amount of water. This gives additional polymer.
(b) When SO₂ reacts withh propylene, CH₂-CH=CH₂, in presence of benzoyl peroxide an addition polymer is obtained.

[3] Coordination polymers:

These are formed by the addition of saturated molecules to each other or by combining a ligand with a metal atom.

3^rd Classification.

According to this classification, the inorganic polymers can be classified into the following categories:
1. Polymers containing two bridging bonds per unit, e.g., homo-atomic sulphur, selenium and teturiurm polymers.
2. The alternating silicone-oxygen polymers. Examples are silicones and related compounds.
3. The alternating phosphorus- nitrogen polymers. Examples, phosphonitrilic halides (NPX₂)_n.
4. The alternating phosphorus-oxygen polymers. Examples are metaphosphates polyphosphates and cross-linked phosphates.
5. The alternating sulphur-nitrogen polymers. Examples are (i) polymeric nitrides of sulphur(e.g., S₂N₂, S₄N₄, S₅N₂,etc.) (ii) thiazyl halides, [e.g., (NSF)₃, (NSF)₄, (NSCl)₃] (iii) imides of sulphar[e.g., S₇(NH), S₆(NH)₂, S₅(NH)₃ and S₄(NH)₄].

4^th Classification. 

This classification is based on the element which forms inorganic polymers.
1. Polymers containing boron. Examples are, (a) Borazine. (BH)₃(NH)₃ or B₃N₃H₆. (b) substituted borazines like (i) B-trimethyl borazine, [B(CH₃)₃(NH)₃] (ii) Boroxine (BH)₃O₃, (iii) N-trimethyl borazine, (BH)₃ [N(CH₃)]₃ (c) Boron nitride, (BN)n 
2. Polymers containing silicon. These are called silicones. 
3. Polymers containing phosphorus. Examples are : (a) Metaphosphates, (b) Polyphosphates, (c) Cross-linked phosphates, (d) Phosphonitrilic halides, [PNX₂]n. 
4. Polymeric compounds of sulphur. Examples are nitrides of sulphur, thiazyl halides and imides of sulphur.