24-04-2014, 12:40 PM
Polymer Structures
[attachment=62208]
Introduction
3⁄4 Polymers – materials consisting of polymer molecules
that consist of repeated chemical units (`mers') joined
together, like beads on a string. Some polymer
molecules contain hundreds or thousands of monomers
and are often called macromolecules.
3⁄4 Polymers may be natural, such as leather, rubber,
cellulose or DNA, or synthetic, such as nylon or
polyethylene.
Hydrocarbon molecules (I)
3⁄4 Most polymers are organic in their origin and are
formed from hydrocarbon molecules
3⁄4 Each C atom has four e- that participate in bonds,
each H atom has one bonding e-
Chemistry of polymer molecules (I)
3⁄4 Ethylene (C2H4) is a gas at room temp and pressure
3⁄4 Ethylene transform to polyethylene (solid) by forming active
mer through reaction with initiator or catalytic radical (R.)
3⁄4 (.) denotes unpaired electron (active site)
Chemistry of polymer molecules (III)
3⁄4 When all mers are the same, the molecule is called a
homopolymer
3⁄4 When there is more than one type of mer present, the
molecule is a copolymer
3⁄4 Mer units that have 2 active bonds to connect with other mers
are called bifunctional
3⁄4 Mer units that have 3 active bonds to connect with other mers
are called trifunctional. They form three-dimensional
molecular network structures
Properties of polymers depend on molecular weight
• Melting/softening temperatures increase with molecular
weight (up to ~ 100,000 g/mol)
• At room temperature, short chain polymers (molar
weight ~ 100 g/mol) are liquids or gases, intermediate
length polymers (~ 1000 g/mol) are waxy solids, solid
polymers (sometimes called high polymers) have
molecular weights of 104 - 107 g/mol
Geometrical isomerism
Geometrical isomerism: consider two carbon atoms
bonded by a double bond in a chain. H atom or radical R
bonded to these two atoms can be on the same side of the
chain (cis structure) or on opposite sides of the chain
(trans structure).
[attachment=62208]
Introduction
3⁄4 Polymers – materials consisting of polymer molecules
that consist of repeated chemical units (`mers') joined
together, like beads on a string. Some polymer
molecules contain hundreds or thousands of monomers
and are often called macromolecules.
3⁄4 Polymers may be natural, such as leather, rubber,
cellulose or DNA, or synthetic, such as nylon or
polyethylene.
Hydrocarbon molecules (I)
3⁄4 Most polymers are organic in their origin and are
formed from hydrocarbon molecules
3⁄4 Each C atom has four e- that participate in bonds,
each H atom has one bonding e-
Chemistry of polymer molecules (I)
3⁄4 Ethylene (C2H4) is a gas at room temp and pressure
3⁄4 Ethylene transform to polyethylene (solid) by forming active
mer through reaction with initiator or catalytic radical (R.)
3⁄4 (.) denotes unpaired electron (active site)
Chemistry of polymer molecules (III)
3⁄4 When all mers are the same, the molecule is called a
homopolymer
3⁄4 When there is more than one type of mer present, the
molecule is a copolymer
3⁄4 Mer units that have 2 active bonds to connect with other mers
are called bifunctional
3⁄4 Mer units that have 3 active bonds to connect with other mers
are called trifunctional. They form three-dimensional
molecular network structures
Properties of polymers depend on molecular weight
• Melting/softening temperatures increase with molecular
weight (up to ~ 100,000 g/mol)
• At room temperature, short chain polymers (molar
weight ~ 100 g/mol) are liquids or gases, intermediate
length polymers (~ 1000 g/mol) are waxy solids, solid
polymers (sometimes called high polymers) have
molecular weights of 104 - 107 g/mol
Geometrical isomerism
Geometrical isomerism: consider two carbon atoms
bonded by a double bond in a chain. H atom or radical R
bonded to these two atoms can be on the same side of the
chain (cis structure) or on opposite sides of the chain
(trans structure).