what happens during the process of polymerisation?

Answer 1

Good you already have plenty of good answers.

Thing is that a chain of non-breakable molecules combine to become polymers. that's it.

Answer 2

Polymerization is a process of reacting monomer molecules together in a chemical reaction to form three-dimensional networks or polymer chains. There are many forms of polymerization and different systems exist to categorize them.

Answer 3

Many molecules of a compound unites chemically in a sequence.

Answer 4

Polymerization
Forming large molecules from small molecules - Polymerization

Just as a house can be constructed from building blocks, so too large molecules can be constructed from small ones. The building blocks, monomers are connected to form polymers. Just as houses can have many shapes depending on the shapes of the blocks used and how they are arranged, so too polymers can have many shapes depending on how the monomers are connected. The properties of the polymer depend on how the kinds of monomers and how they are connected together.

There are two basic kinds of polymerization reactions:

condensation (example: curing of concrete)
free radical (example, formation of PVC pipe)
Condensation Polymerization
In condensation reactions, covalent bonds are rearranged in such a way that two monomers are connected and water is "condensed" out. In the illustration, there are two molecules . "X" and "Y" are atoms of unspecified elements, "O" and "H" are symbols for oxygen and hydrogen. Each stick connecting atoms represents a covalent bond (consisting of shared electrons). Notice that both molecules have OH connected to some other element. It this reaction, the bond between X and OH is broken in one molecule and the bond between O and H is broken in the other. Two new molecules are formed. One is water formed by the OH from XOH and the H from HOY. The other new molecule is a "dimer" (two monomers) with the remaining O atom forming a bridge between X and Y. The diagram shows water being "condensed" out of the two reacting molecules.

The chemical reactions that occur in the curing of mortar or of concrete are complex, but condensation is an important feature. If you follow the links about concrete, you will discover that Portland cement is the material that, when mixed with water, holds aggregate (sand and pieces of rock or gravel) together. Portland cement contains, among other things, silicates. Silicates are minerals that contain some form of the silicate anion and various cations (e.g., calcium, sodium, magnesium, iron, aluminum ions). A simple silicate anion is represented here. Each of the four oxygens forms a covalent bond to an atom of silicon. The structure is like a triangular pyramid with silicon in the very center of the pyramid and with an oxygen is at each vertex. Each oxygen has a single negative charge (an extra electron). In the presence of water, silicates become hydrated. Some of the oxygens form a covalent bond with with a hydrogen nucleus from the water. One possible product of hydration is illustrated. The small black spheres represent hydrogens. There are now only two charged oxygens. Other possibilities for hydrated silicates would have just one or three or even four hydrogens attached.


Since the hydrated silicates contain Si-O-H bonds, condensation is possible:




form







The resulting structure is a silicate dimer. Note that the dimer contains OH groups. Further reactions are possible. The two monomers are connected by an oxygen bridge. In effect there are now two pyramids sharing one corner. Diagrammatically, the dimerization can be represented by pyramids being connected:



More complex structures can be formed in one, two, or three dimensions: A trimer might look like this:


A more extended two dimensional structure might look like:



One can imagine a huge structure extending not only in a sheet (as illustrated above) but extending up from the top vertices of the pyramids.

The essential ingredients of concrete are cement, water, and aggregate. When all are mixed together, the silicate polymers start to form. As water evaporates, the polymers can get quite large and can bind together and enclose the aggregate (gravel and sand) together. The polymerized silicate is the framework for this composite material. It is ironic that a process that starts by hydrating the silicates continues by condensing water out of the structure. This view of the chemistry involved is very simplistic but gives some idea of why concrete is very strong.


Free Radical Polymerization

The polymerization of vinyl chloride is typical of free radical polymerizations. Vinyl chloride molecules contain two carbon atoms, three hydrogens, and one chlorine. One of the chemical characteristics of carbon is that each carbon atom usually forms four covalent bonds. Remember that a covalent bond is a shared pair of electrons. In the structure above, each "stick" represents one bond. " _ is the same as .." Notice that in vinyl chloride, the bond between the two carbons is a double bond consisting of two shared pairs or four electrons.

During free radical polymerization, one of the two bonds between the two carbons ruptures, leaving one unshared electron on each carbon atom. An atom with an unpaired electron is very reactive. It is called a free radical. The vinyl chloride free radical is illustrated to the right. If two such free radicals meet, they can form a dimer with a new covalent bond linking the two vinyl chlorides:




This dimer can react with another vinyl chloride to form a trimer:



By repeating this process many times, a long polymer, hundreds or even thousands of monomer units long, can be formed. This polymer is then called polyvinyl chloride or simply, PVC.



--------------------------------------------------------------------------------

RETURN