POLYMERS

DEFINITIONS

Monomer• A small molecule with a relatively low molar

mass. When many monomers are bonded together, a polymer is formed.

Polymer• Larger than a monomer with a higher molar

mass. A polymer is formed by many monomers bonded together in a chain or network

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C==C + C==C —C—C—C—C—

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MONOMERS POLYMERS

POLYMERIZATION

1. Addition Polymerization

2. Condensation Polymerization

Addition PolymerizationStage 1:

• Initiation– The initiating molecule forms a bond to a

carbon atom in a double bond– The unpaired electron that forms the bond

shifts to the other end of the original double bond.

Addition Polymerization

Stage 2:

• Propagation– The unpaired electron is now available to

form a covalent bond with another atom– The term used when the chain adds more

atoms or groups is propagates

Addition Polymerization

Stage 3:

• Termination– Occurs when two unpaired electron ends

combine and form a covalent bond– Two growing chains are linked and can no

longer grow

Condensation Polymerization

Condensation polymers are formed when monomer units bond through a condensation reaction such as:

– Carboxylic acids reacting with alcohols to form esters

– Monomer units reacting with amines to form amides

• Esters form when a carboxylic acid reacts with alcohol. When this process is repeated to form multiple esters, that form a long chain, and a polyester is produced. This occurs when dicarboxylic acid is added to a diol to form the polyester and water molecule

• Di-methanoic acid + 1,2-ethenediol polyester + water

A—A + B—B + A—A + B—B

A—[AB]—[BA]—[AB]—B + water

=A—A (acid) =B—B (alcohol) =AB (ester link)

POLYAMIDES

Formed when condensation reactions result in the formation of amide bonding between monomers. They are formed by condensation reactions between a carboxylic acid and an amide, with the removal of the water molecule

O O || ||

n[—C—N—C—N—]n

| | H H

CROSS LINKAGE

Cross links are bridges which are formed between two separate polymer chains, connecting the polymers together. Cross links help to strengthen polymers. The more cross links that are formed, the stronger the attraction holding the chain together, due to covalent bonding.

CH=CH2 + CH=CH2 CH—CH2—CH—CH2

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BIOLOGICAL POLYMERS

Protiens: Amino Acids

Amino acids contain a carboxylic acids and an amine which are both attached to a central atom. The amino acids both combine as monomers to form the larger polymer, the protein. The amino acids can arrange and form various structures of proteins, with varying properties. The varying properties and arrangement leads to the many different proteins, found in living organisms. All amino acids can form two different isomers, therefore known as ‘chiral molecules’. A chiral molecule is able to exist in two forms, which mirror each other.

The amino acids are linked together by addition reactions. An amine group from one amino and the acid group from the other amino bond to form a chain of amino acids, this is know as a peptide bond. When a peptide bond forms, a polypeptide is created. A peptide is a polymer made up of amino acids joined by peptide bonds. When an amino acid joins at a peptide bond, a dipeptide is formed.

H O H O | || | ||H2N—C—C—[OH + H]N—C—C—OH | |

R’ R” Amine 1 Amine 2

H O H O

| || | || H2N—C—C—N—C—C—OH + H2O | |

R’ R” Dipeptide

PROTEIN STRUCTURE

The protein molecule’s structure depends on the electron attraction and repulsion of the amino acid. There are four different protein structures:– Primary– Secondary– Tertiary– Quaternary

PRIMARY

The original structure known as a polypeptide, which is the long strings of amino acids arranged in a certain order.

SECONDARY

• The amino acids, which are either polar or non-polar, that interact within the polypeptide

• This forms the ‘coils’ or ‘pleated sheets’ through forces such as Van der Waals, hydrogen bonding, etc.

TERTIARY

• Pleated sheet sections and hetical sections are found together within the same protein molecule

• They attract each other forming shapes that are spherical or globular

QUARTERNARY

• Van der Waal forces join two or more protein subunits together

• Example: in hemoglobin four protein subunits are joined in a tetrahedral shape

POLYMERS OF SUGARS

MONOSACCHARIDE

• Carbohydrate consisting of a single sugar unit

• Arranged in a carbon backbone, usually 6 carbons long

• Some sugars, such as glucose, have a carbonyl group on the first carbon to form an aldehyde

• Other sugars, such as fructose, have a carbonyl group on the second carbon keytone

• Glucose is a aldose. Fructose is a keytose

GLUCOSE:

O

||

CH2—CH—CH—CH—CH—C—H

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OH OH OH OH OH

FRUCTOSE:

O

||CH2—CH—CH—CH—CH—C—CH2

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OH OH OH OH OH OH

Polymethylmethacrylate (PMMA)

[also known as Plexiglas]

PMMA

• PMMA is a acrylate polymer• Other acrylate include; Poly(butylenes

terephthalate) and Poly(methyl acrylate)• PMMA is also found in acrylic paint.• PMMA was first discovered in the 1870's, but

was first commercialized by Rohm and Haas in 1935 as Plexiglas. DuPont brought out PMMA as Lucite in 1937

Structural Diagram of PMMA:

SYNTHESIS

• Free radical polymerization of the monomer methyl methacrylate.

• The carbon-carbon double bond is broken and the free radical electrons create bonds more of the methyl methacrylate monomer in an addition reaction creating a chain of methyl methacrylate, known as poly(methyl methacrylate).

PROPERTIES

• State: Solid• Melting point: 490° F (254.5° C)• Tensile Strength: 7000 psi• Compression Strength: 11500 psi• Flexural Strength: 10500 psi• Chemical Restance:

– Acids: Resistant– Alkalis: Very Resistant– Solvents: Poorly Resistant

• Forms: Sheets, blocks, moldings, etc. (basically can be molded into any shape)

USAGE

• PMMA is used as a glass substitute. Known commonly as Plexiglas it is used in hockey arenas to shield fans from speeding pucks. Other sports uses include basketball backboards and helmet visors. PMMA is found in many common items such as acrylic paint, and various figurines, or even a chess set. Its strong and versatile, as well as fairly inexpensive, so many companies use it for toy components. It was once used as a corrective lens but due to it’s poor gas permeability, PMMA caused the eyes to become irritated and swollen. Today polymers that allow oxygen to pass through are used.