Main features of the polymerization process

The poly­mer­iza­tion process is a re­ac­tion in which a poly­mer mol­e­cule is formed from a low-molec­u­lar sub­stance with­out the dis­charge of byprod­ucts.

Main char­ac­ter­is­tics

In the poly­mer­iza­tion process, the links of a poly­mer con­nect, and by its com­po­si­tion the poly­mer it­self does not dif­fer in any way from the orig­i­nal monomers. The el­e­men­tal com­po­si­tion of the poly­mer and monomer are ab­so­lute­ly iden­ti­cal.

Poly­mers, in their turn, can be di­vid­ed into 2 large groups de­pend­ing on the num­ber of monomers tak­ing part in poly­mer­iza­tion:

1. ho­mopoly­mers (only one type of monomer takes place in for­ma­tion);
2. copoly­mers (sev­er­al monomers take part in their for­ma­tion si­mul­ta­ne­ous­ly).

An in­ter­est­ing fea­ture of poly­mers is that un­like var­i­ous low-molec­u­lar sub­stances, poly­mers do not have a pre­cise melt­ing point, al­though at high tem­per­a­tures they grad­u­al­ly soft­en.

In melt­ing, a poly­mer pass­es through 3 stages of dif­fer­ent states:

• glass-like;
• high­ly elas­tic
• vis­cous-flow­ing.

Poly­mers can be di­vid­ed into 3 main groups by elec­tri­cal con­duc­tiv­i­ty: di­electrics, semi­con­duc­tors and con­duc­tors. The con­duc­tiv­i­ty of di­electrics in­creas­es as a poly­mer is heat­ed to melt­ing point. The heat shrink­age of poly­mers is around 15 times greater than for any met­al. Click here to find out more in­ter­est­ing facts about poly­mers.

Mech­a­nism of form­ing poly­mers

Poly­mer­iza­tion usu­al­ly takes place ac­cord­ing to a chain rad­i­cal mech­a­nism. This mech­a­nism is used in ob­tain­ing poly­mers for in­dus­tri­al pur­pos­es. The process con­sists of sev­er­al stages. It is eas­i­est to ex­am­ine the whole mech­a­nism based on the ex­am­ple of the poly­mer­iza­tion of eth­yl­ene.

1. Ini­ti­a­tion. In this sit­u­a­tion rad­i­cals strive to at­tach some sub­stances to them­selves, as they have free elec­trons.

2. Growth of the chain. Ini­tial­ly the process starts with the monomer at­tach­ing a rad­i­cal par­ti­cle to it­self. As a re­sult, a new rad­i­cal par­ti­cle forms, then it once more bonds with the monomer. These trans­for­ma­tions may take place many times. At this mo­ment the ac­tive cen­ter moves to oth­er links in the chain, and there is also a for­ma­tion of sev­er­al ac­tive cen­ters at once.

3. Break in the chain. This may take place at any mo­ment. This phe­nom­e­non is ex­plained by the fact that rad­i­cals in­ter­act with one an­oth­er at this time. At this mo­ment the de­struc­tion of ac­tive cen­ters takes place.

If the ac­tive cen­ters are free rad­i­cals, then this poly­mer­iza­tion is called rad­i­cal. If they are lo­cat­ed in ions or po­lar­ized mol­e­cules, then this will be ion­ic poly­mer­iza­tion. As a re­sult, a macro­molecule of the sub­stance forms. Its main dis­tin­guish­ing fea­ture is that it con­sists of the most var­ied mol­e­cules of sub­stances, and not of nu­mer­ous iden­ti­cal small mol­e­cules. This phe­nom­e­non is called poly­dis­per­si­ty of a poly­mer. This fea­ture is dis­played by all poly­mers, re­gard­less of the way they are formed.

Main prop­er­ties of poly­mers

In ex­am­in­ing this top­ic, it is also im­por­tant to pay at­ten­tion to the main func­tions of poly­mers, which must be tak­en into ac­count when work­ing with these sub­stances:

• poly­mers are usu­al­ly ei­ther in a sol­id or liq­uid state. Gaseous states are not char­ac­ter­is­tic for them;
• poly­mers are a very durable ma­te­ri­al. Many or­gan­ic poly­mers dis­play dura­bil­i­ty even in such medi­ums as al­ka­lis and con­cen­trat­ed acids;
• un­like met­als, they are far less sub­ject to cor­ro­sion. They dis­play more prom­i­nent and lengthy dura­bil­i­ty to cor­ro­sion, both in chem­i­cal form and in elec­tric form;
• the greater the molec­u­lar mass of a poly­mer, the worse it dis­solves. Large mol­e­cules prac­ti­cal­ly do not dis­solve in sol­vents, not even in sol­vents of an or­gan­ic na­ture. Poly­mers with a spa­tial struc­ture are bare­ly sub­ject to the im­pact of or­gan­ic sol­vents;
• com­pared with ma­te­ri­als made of iron, poly­mers have greater plas­tic­i­ty, but they are less strong;

• poly­mers have the great­est heat ca­pac­i­ty and low­est heat con­duc­tiv­i­ty com­pared with oth­er ma­te­ri­als used in in­dus­try;
• from lengthy stress, the dura­bil­i­ty of poly­mers grad­u­al­ly de­te­ri­o­rates;
• usu­al­ly the pro­cess­ing of all poly­mers takes place in the pe­ri­od when they are in a vis­cous flow­ing state;
• when poly­mers are used over a long time, cer­tain chem­i­cal and phys­i­cal changes takes place in them, as a re­sult of which poly­mers age, i.e. they un­der­go a par­tial grad­u­al loss of their main prop­er­ties. Pro­vok­ing fac­tors ca­pa­ble of ac­cel­er­at­ing ag­ing are light, and also fre­quent change of tem­per­a­tures;
• to slow down the ag­ing of poly­mers, sta­bi­liz­ers are usu­al­ly added to them. This makes the ma­te­ri­al more durable to the im­pact of the en­vi­ron­ment;
• be­fore start­ing man­u­fac­ture of poly­mers, they are test­ed for var­i­ous kinds of dura­bil­i­ty. Only af­ter this can prop­er man­u­fac­ture be­gin.

Here is how to make a poly­mer us­ing re­sor­ci­nol and formalde­hyde:

In con­clu­sion, poly­mers are one of the most im­por­tant ma­te­ri­als used in ev­ery­day life and in­dus­try. Rub­ber is also a poly­mer which is used in the most var­ied spheres of ac­tiv­i­ty. The ma­te­ri­al is pop­u­lar be­cause un­like met­als, poly­mers are more durable to the im­pact of the en­vi­ron­ment. They are there­fore a more uni­ver­sal ma­te­ri­al for out­door work, and also for ap­pli­ca­tion in places with ag­gres­sive weath­er con­di­tions. The prop­er­ties of poly­mers also make it pos­si­ble to use them as in­su­la­tion ma­te­ri­al in places with high volt­age.