1. Polymers: a chemical point of view
Introduction: What is a polymer?
Examples of polymers
The synthesis of polymer
The morphology of polymer
The glass transition
Surface: Example with hydrophilic and hydrophobic properties

2. Definition
Molecules whose molecular weight (or size) is in the range of several thousand or more
Repetition of a unit
...-A-A-A-A-A-A-A-...
But We can have different arrangements!
Branched
and a lot of
others possibilities...
Linear

3. Mixing, Molecular weight
Many possibilities with polymers:
Alternating
-A-B-A-B-A-B-A-B-A-
Random
A-B-B-A-B-A-A-B-A-
Block
A-A-A-A-B-B-B-B-B-
And then various configurations (tacticity,...)
Different definitions of molecular weight

4. Types of polymers Thermosets Thermoplastics
chemical change during production that cannot be repeated or reversed : one big molecule!
Thermoplastics
can be processed many times without a chemical change between the chains of the polymer
can be melted again and again and reformed as many times as desired
cross-linking

5. Common polymers Example of polymers Polyethylene Polypropylene
Poly(vinyl chloride)
Polystyrene
Polyesters
Nylon
Vinyl polymers
with a C=C in monomer
There are two general classes of polymers:
thermosets 3
and thermoplastics. 2
They are
distinguished by how they behave with respect to
processing and their characteristics once they are
processed.
A thermoset is a type of plastic that undergoes
a chemical change during production that cannot
be repeated or reversed. The way that this happens
is called cross-linking. This process results in
permanent chemical bonding of the individual
polymer chains to one another. These materials can
never be reshaped into a new form with the same
chemical composition by heating and mixing as the
other type of polymers can. Some examples of
materials made of thermosets are fiberglass boats
or showers, foam insulation, and epoxy glues.
A thermoplastic is a material that can be
processed many times without a chemical change
in or bonding between the chains of the polymer.
Because there is no chemical change, these
Atom Number of bonds
Hydrogen (H) 1
Carbon (C ) 4
Oxygen (O) 2
Fluorine (F) 1
Chlorine (Cl) 1
Nitrogen (N) 3
Table 1. Standard bonds for atoms. H C
Repeat unit
Common
polymer name
Typical uses
-CH2-
Polyethylene
(PE)
Milk bottles,
plastic bags
-C(CH3)HPolypropylene
(PP)
Children’s toys,
candy labels,
bottle labels
Polyester (PET)
Extrusion coating
on paper, 2-liter
bottles, clothing
Nylon
Nylon stockings,
wire insulation
-CH2CHCl-
Polyvinyl chloride
(PVC)
Vinyl siding,
pipe
-CH2CHPolystyrene
Packaging
materials, TV
cabinets, toys,
jewel cases
Table 2. Repetitive units, common polymer name,
and typical uses.
-CHCOO
-NH2(CH2)5CO
Polymer Basics 69
materials can be melted again and again and
reformed as many times as desired. (There is one
flaw in this statement, in that many polymers
degrade during processing because of the high
temperatures used in the process. This
degradation is a chemical process that cannot be
reversed and is guarded against by the use of
stabilizers.) Because they can be processed many
times, these materials are the backbone of the
plastics recycling industry. Common examples of
thermoplastics are polyethylene, polyvinyl
chloride, and polypropylene, and some common
uses are vinyl siding, plastic grocery bags, and
milk bottles. T
HERMOPLASTIC P
OLYMERS
There are many different properties of a
polymer used to characterize a material in
determining the best choice for use in an
application. Some of these properties involve how
the material will handle during processing, others
describe the strength or toughness of the polymer,
and still others describe how the material will
look. All of these need to be understood at a
fundamental level to help choose the best material
for a specific purpose. Some basic things we need
to know to explain the behavior of a polymer are
chain length (and chain length distribution),
crystallinity, polarity, and stability.
Chain Length
The number of repeat units in a polymer
molecule is described as its chain length. 4
The
chain length of a single chain is important to
know, but not as important as the distribution of
all the chains in a polymer material. A distribution
describes the population of each chain length. An
example is the best way to show this. Imagine that
we can look through a magic microscope at a
polymer and are able to count the number of
“mers” found on each molecule and the number
of times this length of molecule occurs in the
sample. Below is a summary of what we see:

6. Synthesis of polymers (1)
Monomer?
Types of reactions:
Addition Polymerization
Entire monomer becomes part of the polymer
Condensation Polymerization
Some atoms of the monomer don't end up in the polymer
Molecule which react with other molecules of the same type to form a polymer
Repeat unit
Common
polymer name
Typical uses
-CH2-
Polyethylene
(PE)
Milk bottles,
plastic bags
-C(CH3)HPolypropylene
(PP)
Children’s toys,
candy labels,
bottle labels
Polyester (PET)
Extrusion coating
on paper, 2-liter
bottles, clothing
Nylon
Nylon stockings,
wire insulation
-CH2CHCl-
Polyvinyl chloride
(PVC)
Vinyl siding,
pipe
-CH2CHPolystyrene
Packaging
materials, TV
cabinets, toys,
jewel cases
Polymer
Monomer

7. Synthesis of polymers (2) Example of vinyl polymers
3 majors ways of synthesis
Anionic
Cationic
Free Radical (example of LDPE below)
Initiation
Propagation
Termination ?

8. Crystallised/Amorphous Zones
Proportion of Crystallized zones depend on polymer structure
Example LDPE/HDPE
Linear (HD) : Highly crystallized
Branched (LD) : lowly crystallized
Polymer is never 100% cristal

9. The glass transition Important parameter: viscosity
Some polymers can have a Tf and a Tg
2nd order transition
involves a change in heat capacity, but does not have a latent heat
thermal transition that involves a change in heat capacity, but does not have a latent heat
1 leads to amorphous state 2 leads to crystalline state

10. Length of the chain (mobility)
Surface
Relationships between surface chemical (or morphological) structure and surface properties:
Length of the chain (mobility)
Type of the groups
Chain Entanglement
Remember now that most polymers are linear polymers; that is, they are molecules whose atoms are joined in a long line to form a huge chain. Now most of the time, but not always, this chain is not stiff and straight, but is flexible. It twists and bends around to form a tangled mess. the chains tend to twist and wrap around each other, so the polymer molecules collectively will form one huge tangled mess.
Now when a polymer is molten, the chains will act like spaghetti tangled up on a plate. If you try to pull out any one strand of spaghetti, it slides right out with no problem. But when polymers are cold and in the solid state, they act more like a ball of string. We're not talking about a new ball of string neatly wrapped up, either. We're talking about that tangled up old ball of string that you've been collecting for years. Trying to pull one strand out of this mess is a little harder. You're more likely to end up making a big knot!
Solid polymers are like this. The chains are all tangled up in each other and it is difficult to untangle them. This is what make so many polymers so strong in materials like plastics, paint, elastomers, and composites.
Summation of Intermolecular Forces
Remember intermolecular forces? If you don't I'll fill you in. All molecules, both small ones and polymers, interact with each other, attracting each other through electrostatics. Some molecules are drawn to each other more than others. Polar molecules stick together better than nonpolar molecules. For example, water and methane have similar molecular weights. Methane's weight is sixteen and water's is eighteen. Methane is a gas at room temperature, and water is a liquid. This is because water is very polar, polar enough to stick together as a liquid, while methane is very nonpolar, so it doesn't stick together very well at all.
As I said, intermolecular forces affect polymers just like small molecules. But with polymers, these forces are greatly compounded. The bigger the molecule, the more molecule there is to exert an intermolecular force. Even when only weak Van der Waals forces are at play, they can be very strong in binding different polymer chains together. This is another reason why polymers can be very strong as materials. Polyethylene, for example is very nonpolar. It only has Van der Waals forces to play with, but it is so strong it's used to make bullet proof vests.
Time Scale of Motion
This is a fancy way of saying polymers move more slowly than small molecules do. Imagine you are a first grade teacher, and it's time to go to lunch. Your task is to get your kids from the classroom to the cafeteria, without losing any of them, and to do so with minimal damage to the territory you'll have to cover to get to the cafeteria. Keeping them in line is going to be difficult. Little kids love to run around every which way, jumping and hollering and bouncing this way and that. One way to put a stop to all this chaotic motion is to make all the kids join hands when you're walking them to lunch. This won't be easy rest assured, as there's always going to be a lot of little boys who are too macho to hold the hands of the girls next to them in line, and some who are too insecure in their manhood to hold anyone's hand. But once you get them to do this, their ability to run around is severely limited. Of course, their motion will still be chaotic. The chain of kids will curve and snake this way and that on its way to eat soybean patties disguised as who knows what. But the motion will be a lot slower. You see, if one kid gets a notion to just bolt off in one direction, he or she can't do it because he or she will be bogged down by the weight of all the other kids to which he or she is bound. Sure, the kid can deviate from the straight path, and make a few other kids do so, but the deviation will be far less than you'd bet if the kids weren't all linked together.
It's the same way with molecules. A bunch of small molecules can move around a lot faster and a lot more chaotically when they're not all tied to each other. Tie the molecules together in a big long chain and they slow down, just like kids do when you join them into a chain.
So then how does this make a polymeric material different from a material made of small molecules? This slow speed of motion makes polymers do some very unusual things. For one, if you dissolve a polymer in a solvent, the solution will be a lot more viscous than the pure solvent. In fact, measuring this change in viscosity is used to estimate polymer molecular weight. Click here to find out how.
The pendant groups

11. Hydrophobic/ Hydrophilic
Type of pending chain:
Hydrophobic
CH3, C2H5, Cl, F,...
Hydrophilic
Groups with oxygen (acids, =O),....
Fluor: decrease the surface energy, the polymer becomes very hydrophobic (example: Teflon)
Polymers are in general hydrophobic. This necessitates their surface modification/treatment to render them adhesionable.

12. Conclusion Things that makes polymers different : Chain Entanglement
Summation of Intermolecular Forces
Time Scale of Motion
Surface properties depend on the pendants groups
hain Entanglement
Remember now that most polymers are linear polymers; that is, they are molecules whose atoms are joined in a long line to form a huge chain. Now most of the time, but not always, this chain is not stiff and straight, but is flexible. It twists and bends around to form a tangled mess. the chains tend to twist and wrap around each other, so the polymer molecules collectively will form one huge tangled mess.
Now when a polymer is molten, the chains will act like spaghetti tangled up on a plate. If you try to pull out any one strand of spaghetti, it slides right out with no problem. But when polymers are cold and in the solid state, they act more like a ball of string. We're not talking about a new ball of string neatly wrapped up, either. We're talking about that tangled up old ball of string that you've been collecting for years. Trying to pull one strand out of this mess is a little harder. You're more likely to end up making a big knot!
Solid polymers are like this. The chains are all tangled up in each other and it is difficult to untangle them. This is what make so many polymers so strong in materials like plastics, paint, elastomers, and composites.
Summation of Intermolecular Forces
Remember intermolecular forces? If you don't I'll fill you in. All molecules, both small ones and polymers, interact with each other, attracting each other through electrostatics. Some molecules are drawn to each other more than others. Polar molecules stick together better than nonpolar molecules. For example, water and methane have similar molecular weights. Methane's weight is sixteen and water's is eighteen. Methane is a gas at room temperature, and water is a liquid. This is because water is very polar, polar enough to stick together as a liquid, while methane is very nonpolar, so it doesn't stick together very well at all.
As I said, intermolecular forces affect polymers just like small molecules. But with polymers, these forces are greatly compounded. The bigger the molecule, the more molecule there is to exert an intermolecular force. Even when only weak Van der Waals forces are at play, they can be very strong in binding different polymer chains together. This is another reason why polymers can be very strong as materials. Polyethylene, for example is very nonpolar. It only has Van der Waals forces to play with, but it is so strong it's used to make bullet proof vests.
Time Scale of Motion
This is a fancy way of saying polymers move more slowly than small molecules do. Imagine you are a first grade teacher, and it's time to go to lunch. Your task is to get your kids from the classroom to the cafeteria, without losing any of them, and to do so with minimal damage to the territory you'll have to cover to get to the cafeteria. Keeping them in line is going to be difficult. Little kids love to run around every which way, jumping and hollering and bouncing this way and that. One way to put a stop to all this chaotic motion is to make all the kids join hands when you're walking them to lunch. This won't be easy rest assured, as there's always going to be a lot of little boys who are too macho to hold the hands of the girls next to them in line, and some who are too insecure in their manhood to hold anyone's hand. But once you get them to do this, their ability to run around is severely limited. Of course, their motion will still be chaotic. The chain of kids will curve and snake this way and that on its way to eat soybean patties disguised as who knows what. But the motion will be a lot slower. You see, if one kid gets a notion to just bolt off in one direction, he or she can't do it because he or she will be bogged down by the weight of all the other kids to which he or she is bound. Sure, the kid can deviate from the straight path, and make a few other kids do so, but the deviation will be far less than you'd bet if the kids weren't all linked together.
It's the same way with molecules. A bunch of