Organic Polymers

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Almost all of the molecules we have studied so far have been relatively small with low molecular masses. But in nature and the world of synthetics, there are many substances with molecular masses in the thousands and hundred thousands containing hundreds or thousands of atoms. These molecules are called macromolecules.
Macromolecular substances are almost everywhere in nature and in synthetics. Synthetic macromolecules are examples of how chemists talk ordinary substances in nature, like coal, oil, air, and water, and make new materials with useful applications.
Some macromolecules have more structural order than others. A polymer is a macromolecule in which all of the molecules have a small characteristic structural feature that repeats itself again and again. For example, here is a molecule of polyethylene: 
etc.-CH2CH2-CH2CH2-CH2CH2-CH2CH2-CH2CH2-etc.
The strucutre has one structural unit, or monomer, that occurs repeatedly--ethylene (ethene), CH2CH2. The structure of the polymer can therefore be represented by: 
-(CH2CH2)n-
Where n can be several thousand. Polymers therefore do no consist of molecules identical in size but identical in kind.
The reaction that makes a polymer out of a monomer is called polymerization. If we let a be a repeating unit, then its polymer can be: 
etc.-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-etc.
But sometimes during polymerization, a long chain may develop branches that themselves are long. 
       a                 etc.
        \                |
         a               a       a-a-a-a-etc.
         |               |       |
etc.-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-etc.
       |           |             |             |
       a           a             a             a
       |            \                           \
       etc.          a-a-etc.                    a

Copolymers

Sometimes two monomers are mixed together and polymerized, providing a unit a and a unit b. For example, saran is a copolymer of CH2=CCl2 and CH2=CHCl, and its molecules have the following units in their structure: 
-CH2-CCl2-CH2-CHCl-
When copolymers form though, there are several possibilities when they are polymerizing: 
alternate copolymer
etc.-a-b-a-b-a-b-a-b-a-b-a-b-a-b-a-b-a-b-a-b-a-b-a-b-a-b-a-b-etc.

block copolymer
etc.-a-a-a-b-b-a-a-a-a-a-b-b-b-a-a-b-b-b-b-b-a-a-a-b-b-b-a-a-a-a-a-etc.

random copolymer
etc.-a-a-b-a-b-a-a-a-b-b-a-b-b-a-a-a-b-b-a-b-b-a-a-a-b-a-b-a-a-etc.

graft copolymer
etc.-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-etc.
         |       |       |       |       |       |       |
         b       b       b       b       b       b       b
         |       |       |       |       |       |       |
         b       b       b       b       b       b       b
         |       |       |       |       |       |       |
         etc.    etc.    etc.    etc.    etc.    etc.    etc.

cross-linked copolymer
      a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a
            |               |           |             |
            b               b           b             b
            |               |           |             |
            b               b     a-a-a-a-a-a-a-a-a-a-a-a-a-a
            |               |           |
a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a-a       b
    |                                   |
    b                                   b

Addition Polymers

Polymerization that make addition polymers general join the monomer molecules end to end. For example, in the addition polymerization of ethylene: 
etc. + CH2=CH2 + CH2=CH2 + CH2=CH2 + CH2=CH2 + CH2=CH2 + etc.
through addition polymeriztion gives: 
etc.-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-etc.
Chemicals called promoters initiate polymerizations, and pieces of their molecules become joined to the ends of the polymer systems (where "etc." has been written).

Condensation Polymers

Condensation polymers are copolymers, which have monomers having functional groups that can reacted with each other, usually spitting out water. The reaction between a carboxylic acid and an alcohol creates an ester. If the carboxylic acid and the alcohol were the monomers of the polymer, during polymerization, they would create polyester, and spitting out water in the process. The polymerization of a carboxylic acid and an amine similarly creates polyamides.

Effect of Size and Geometry on Properties

Polymers are very useful because they are very chemically inert. They are not attached by air or its pollutants. They are stable toward water. They must keep these properties under high temperatures, as Teflon does on a nonstick frying pan. Polyesters and polyamides have functional groups that water can attack, but this does not happen due to the enormous size of the molecule. They are completely insoluble in water and therefore makes a good storing container for food but bad for waste disposal since it does not decay.

Polymers and Physical Properties

Physical properties of polymers are the ones that are most sought-after for pratical use. For example, teflon (a polyolefin) has a slipperiness toward almost anything. Nylon (a polyamide) isn't eaten by moths and has superior tensile strength and the ability to be made into fibers and fabrics. Dacron (a polyester) does not mildew, and when made into fibers, it is superior to cotton, with greater strength and lower mass, and it doesn't stretch as much.
The best fiber-forming polymers have molecules have shapes that let the molecules align side by side and be twisted into cables. Because the molecules are large, substantial London forces of attraction occur between them. Hydrogen bonds are also present in some, like the polyamides.

Polyolefins

Polyolefins are polymers of alkenes and their halogen derivatives. They include saran, teflon, polystyrine, and many others.

Polyacrylates

Polyacrylates are like polyolefins, but made from derivatives of acrylic acid. 
CH2=CHCOOH
acrylic acid

    C(triple bond)N
    |
CH2=CCO2CH3
methyl alpha-cyanoacrylate
Methyl alpha-cyanoacrylate is an unusual monomer in that its polymerization is promoted by water. "Superglue" contains this monomer, and since there is a film of moisture on almost any surface wherever superglue would be used, the water promotes polymerization, making the substances it is bonding together stick.

Natural Rubber

Natural rubber is a contains monomers of a diene called isoprene (2-methyl-1,3-butadiene). It is part of a large family of polymers called elastomers because of its ability to recover its shape after being deformed. Natural rubber contains several alkene groups and makes it easily attacked by ozone though. This problems has largely been solved by adding antioxidant compounds to rubber products when they are made. 
    CH3
    |
CH2=C-CH-CH2
isoprene

Polyesters and Polyamides

Polyesters and polyamides are condensation polymers. Polyesters are created using two monomers--dicarboxylic acids (two carboxyl groups on each end) and diols (two alcohol groups on each end). As they create esters during polymeration, water molecules are spit out. A similar reaction happens with polyamides using diamines and dicarboxylic acids.
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