2. INTRODUCTION TO POLYMERS
Polymers are macromolecules composed of multiple
repetitive units called monomers linked by covalent bonds.
They are of mainly two origins, natural or synthetic.
By definition, polymers are large molecules made by
bonding; (covalent bond) a series of building blocks. The
word polymer comes from the Greek word stand for “many
parts.” Each of those parts is called monomer (which in
Greek means “one part”).
3. Anatomy/Structure of Polymer
Polymer structures can have two different components. All start
with a basic chain of chemically bonded links. This is sometimes
called its backbone.
Some may also have secondary parts that dangle from some (or all)
of the chain’s links. One of these attachments may be as simple as a
single atom. Others may be more complex and referred to as
pendant groups.
4. CLASSIFICATION OF POLYMERS
1. Classification of Polymers based on the Source of
Availability
2. Classification of Polymers based on the Structure of the
Monomer Chain
3. Classification Based on Polymerization
4. Classification Based on Monomers
5. Classification Based on Molecular Forces
5. 1. Classification of Polymers based on
the Source of Availability
Natural Polymers: They occur naturally and are found in
plants and animals. For example proteins, starch, cellulose,
and rubber.
Structure of cellulose
6. 1. Classification of Polymers based on
the Source of Availability
Semi-synthetic Polymers: They are derived from
naturally occurring polymers and undergo further chemical
modification. For example, cellulose nitrate, cellulose
derivatives such as hydroxypropyl methyl cellulose
(HPMC).
Structure of Hydroxy propyl methyl cellulose
7. 2. Classification of Polymers based on
the Structure of the Monomer Chain
Linear Polymers: The structure of polymers containing long
and straight chains fall into this category. These are long chain of
skeleton atoms to which substituent group are attached. They
are soluble in some solvents.
E.g. Polyethene.
Structure of Linear Polymer
8. 2. Classification of Polymers based on
the Structure of the Monomer Chain
Branched Polymers: These are linear polymers containing
branches. It occurs by replacement of any substituent such as
hydrogen atom, monomer subunit etc. For example, low
density polythene.
Structure of Branched Polymer
9. 2. Classification of Polymers based on
the Structure of the Monomer Chain
Cross-linked Polymers: There is a chemical linkage in
between the chains. They have a stronger covalent bond in
comparison to other linear polymers.
Structure of Cross-linked Polymer
10. Special types of polymers based on the
Structure of the Monomer Chain:
Star shaped polymers:Star-shaped polymers are the simplest
class of branched polymers with a general structure consisting of
several (at least three) linear chains connected to a central core.
Structure of Star-shaped Polymer
11. Special types of polymers based on the
Structure of the Monomer Chain:
Dendrimers: These are repetitively branched molecules. It is three
dimensional and the overall structure resembles like a sphere. It has
lower intramolecular entanglement which leads to lower the
viscosity.
Structure of Dendrimer Polymer
12. Special types of polymers based on the
Structure of the Monomer Chain:
Cyclolinear polymers: These are Special type of linear polymer
formed by linking together of ring system such as benzene ring,
heterocyclic rings. They differ from linear with respect to lower
solubility and higher crystallization tendency.
Structure of Cyclolinear Polymer
13. Special types of polymers based on the
Structure of the Monomer Chain:
Cyclomatrix Polymer: These are polymers in which ring systems are
linked together to form a 3 dimensional matrix of connecting units. E.g.
silicon minerals and silicon resins. They possess very high rigidity and
stability.
Structure of Cyclomatrix Polymer
14. Special types of polymers based on the
Structure of the Monomer Chain:
Ladder Polymer: A ladder polymer is a type of double
stranded polymer with the connectivity of a ladder. These are linear
molecule in which two skeleton strands are linked together in a regular
sequence by cross linking units. Due to rigidity in the structure have low
solubility and have very good thermal stability.E.g spiropolymers
Structure of Ladder Polymer
15. 3. Classification Based on Polymerization
Addition
Polymerization: An
addition polymer is a
polymer that forms by
simple linking of monomers
(that posses double or triple
bonds) without the co-
generation of other
products. The process of
formation of addition
polymer is referred as
addition polymerization.
Example: Polyvinyl
chloride (PVC),
Polypropylene, Polystyrene.
16. 3. Classification Based on Polymerization
Condensation Polymerization: Condensation polymers are the
polymers formed by a condensation reaction where different monomers
(bi-functional or tri-functional) joined together losing small molecules as
byproduct such as water or methanol. The process of formation of
condensation polymer is referred as condensation polymerization.
Example, Nylon -6, 6, perylene, polyesters.
17. 4. Classification Based on Monomers
Homomer: In this type, a single type of monomer unit is present. For
example, Polyethene.
Structure of Polyethene (Homomer)
18. 4. Classification Based on Monomers
Copolymers or Heteropolymer: These are the polymers which are
made from different monomer units. Copolymerization refers to a
polymerization reaction in which more than one type of monomer is
involved. According to the method and mechanism of synthesis, different
types of sequence arrangement are found.
19. 5. Classification Based on Molecular Forces
Elastomers: These are rubber-like solids weak interaction forces
are present. For example, Rubber.
Fibres: Strong, tough, high tensile strength and strong forces of
interaction are present. For example, nylon -6, 6.
Thermoplastics: These have intermediate forces of attraction.
For example, polyvinyl chloride.
Thermosetting polymers: These polymers greatly improve the
material’s mechanical properties. It provides enhanced chemical
and heat resistance. For example, phenolic, epoxies, and silicones.
20. PROPERTIES OF POLYMERS
Properties of polymers can be widely classified as
Physical properties
o Polymer Crystallinity: Crystalline andAmorphous polymers
o MolecularWeight
Thermal properties
o Melting point and glass transition temperature
Mechanical properties
o Plasticity
o Strength
o Percent elongation to break
o Young’s modulus
o Toughness
o Viscoelasticity
21. Physical properties
Polymer Crystallinity: Crystalline and
Amorphous Polymers
The polymeric chains being very large are found in the
polymer in two forms as follows: crystalline form in which
the chains are arranged in the regular manner and amorphous
form in which the chains are in the irregular manner.
Examples of amorphous polymers:polystyrene and poly (methyl
methacrylate).
Examples of crystalline polymers:polyethylene, and PET
polyester.
22. Physical properties
Polymer Crystallinity: Crystalline and
Amorphous Polymers
A typical range of crystallinity can be defined as amorphous (0%)
to highly crystalline (>90%).
The polymers having simple structural chains as linear chains and
slow cooling rate will result in higher crystallinity. In slow cooling,
sufficient time is available for crystallization to take place.
Polymers having high degree of crystallinity are rigid and have
high melting point.
Amorphous structure is formed due to either rapid cooling of a
polymer melt and they are soft.
Amorphous or glassy polymers do not generally display a sharp
melting point; instead, they soften over a wide temperature range.
23. Physical properties
Polymer Crystallinity: Crystalline and
Amorphous Polymers
Polymer strength and stiffness increases with crystallinity as a result of
increased intermolecular interactions.
With an increase in crystallinity, the optical properties of a polymer
are changed from transparent (amorphous) to opaque (semi-
crystalline).
From a pharmaceutical prospective, good barrier properties are
needed when polymers are used as a packaging material or as a
coating. Crystallinity increases the barrier properties of the polymer.
Small molecules like drugs or solvents can penetrate the amorphous
part more easily than the crystalline part.
Therefore, crystalline polymers display better barrier properties and
durability in the presence of attacking molecules.
On the other hand, a less crystalline or an amorphous polymer is
preferred when the release of a drug or an active material is intended.
24. Physical properties
Molecular Weight
There are different ways that molecular weights of a polymer can be
expressed; by the number of the chains, by the weight of the chains (the
chain size), or by viscosity.
However, the two most common ways are number (Mn) and weight (Mw)
average calculations. If all polymer chains are similar in size, then the number
and weight average values will be equivalent. If chains are of different sizes,
then weight average is distancing itself from the number average value.
The term polydispersity (PD) represents the ratio of Mw/Mn. It indicates
how far the weight average can distance itself from the number average.
A PD value closer to 1 means the polymer system is close to monodispersed
and all of the polymer chains are almost similar in size. The farther the value
from 1 indicates that the polymer system is polydispersed and chains are
different in size.
It is well-known that colligative properties such as osmotic pressure and
freezing point depression are dependent on the number of particles in the
solution. These techniques are very appropriate for calculating the average
Mn of a given polymer. On the other hand, the weight average relies on the
size of the molecules.
25. Thermal properties
Melting point and Glass transition
temperature
In the amorphous region of the polymer, at lower temperature,
the molecules of the polymer are in, say, frozen state, where the
molecules can vibrate slightly but are not able to move
significantly.This state is referred as the glassy state.
In this state, the polymer is brittle, hard and rigid like a glass.
Hence the name glassy state.
Now, when the polymer is heated, the polymer chains are able to
move around each other, and the polymer becomes soft and
flexible similar to rubber.This state is called the rubbery state.
The temperature at which the glassy state makes a transition to
rubbery state is called the Glass transition temperatureTg.
26. Thermal properties
Melting point and Glass transition
temperature
The glass transition temperature is the property of the amorphous
region of the polymer, whereas the crystalline region is characterized
by the melting point.
In thermodynamics, the transitions are described as first and second
order transitions. Glass transition temperature is the second order
transition, whereas the melting point is the first order transition.
The semi-crystalline polymer shows both the transitions
corresponding to their crystalline and amorphous regions. Thus, the
semi-crystalline polymers have true melting temperatures (Tm) at
which the ordered phase turns to disordered phase, whereas the
amorphous regions soften over a temperature range known as the glass
transition (Tg).
27. Thermal properties
Melting point and Glass transition
temperature
It should be noted that amorphous polymers do not possess the
melting point, but all polymers possess the glass transition
temperature.
The polymer melting point Tm is increased if the double bonds,
aromatic groups, bulky or large side groups are present in the
polymer chain, because they restrict the flexibility of the chain.
The branching of chains causes the reduction of melting point, as
defects are produced because of the branching.
28. Thermal properties
Melting point and Glass transition
temperature
At temperatures well below the Tg, amorphous polymers are hard,
stiff, and glassy although they may not necessarily be brittle. On the
other hand, at temperatures above the Tg, polymers are rubbery and
might flow.
The value of glass transition temperature is not unique because the
glassy state is not in equilibrium. The value of glass transition
temperature depends on several factors such as molecular weight,
measurement method, and the rate of heating or cooling.
From a pharmaceutical standpoint, Tg is an important factor for solid
dosage forms. For example, a chewable dosage form needs to be soft
and flexible at mouth temperature of about 37◦C. This means the
polymer used as a chewable matrix should be softened at this
temperature.
29. Thermal properties
Melting point and Glass transition
temperature
Factors affectingTg
Tg and the length of the polymer chain:
Long polymer chains provide smaller free volume than their
shorter counterparts. So, in general long polymer chain relates
to highTg values.
Tg and polymer chain side group:
A side group may be bulky or polar. Because of its steric
hindrance, higher temperature is needed to induce segmental
motion in polymers containing bulky groups. On the other hand,
polar side groups provide stronger intermolecular interactions
that significantly affectTg.
30. Thermal properties
Melting point and Glass transition
temperature
Factors affectingTg
Tg and polymer chain flexibility:
Flexible polymer chains display higher entropy (desire to move) than
rigid chains. Groups such as phenyl, amide, sulfone, and carbonyl in
backbone or side chain increases polymer flexibility. With more
flexibilityTg moves to lower side of temperature range.
Tg and polymer chain branching:
Linear polymer chains possess smaller free volume as opposed to their
branched counterparts. Therefore, higher Tg values are expected for
linear polymers.
Tg and polymer chain cross-linking:
Compared to cross-linked chains, linear chains have higher entropy
and the desire to move; hence, they display lowTg values.
31. Thermal properties
Melting point and Glass transition
temperature
Factors affectingTg
Tg and processing rate:
In order to prepare polymer products, the polymer needs to be
processed at different temperatures or pressures that can significantly
affect the molecular motion in polymers. Therefore, the rate of
processes such as heating, cooling and loading might be considered
when evaluating the Tg value of a given polymer. Kinetically speaking,
if the rate of the process is high (fast cooling, fast loading), the
polymer chains cannot move to the extent that they are expected to.
They virtually behave like rigid chains with lower tendency to move,
which results in reading highTg values.
Tg and plasticizers:
Plasticizer molecules can increase the entropy and mobility of the
polymer chains. This is translated to lower Tg values for plasticized
polymers compared with their non-plasticized counterparts.
32. Mechanical properties
Plasticity
A plasticizer is added to a polymer formulation to enhance its
flexibility and to help its processing. It facilitates relative
movement of polymer chains against each other. The addition of a
plasticizer to a polymer results in a reduction in the glass
transition temperature of the mixture. Since plasticizers increase
molecular motion, drug molecules can diffuse through the
plasticized polymer matrix at a higher rate depending on the
plasticizer concentration.
33. Mechanical properties
Polymer Strength
In simple words, the strength is the stress required to break the
sample. There are several types of the strength, namely tensile
(stretching of the polymer), compressional (compressing the
polymer), flexural (bending of the polymer), torsional (twisting of the
polymer), impact (hammering) and so on. The polymers follow the
following order of increasing strength:
Linear < branched < cross-linked < network
FactorsAffecting the Strength of Polymers:
o Molecular Weight: The tensile strength of the polymer rises with
increase in molecular weight and reaches the saturation level at some
value of the molecular weight.
o Cross-linking: The cross-linking restricts the motion of the chains and
increases the strength of the polymer
o Crystallinity: The crystallinity of the polymer increases strength,
because in the crystalline phase, the intermolecular bonding is more
significant.
34. Mechanical properties
Percent Elongation to Break
It is the strain in the material on its breakage. It measures the
percentage change in the length of the material before fracture.
It is a measure of ductility. Ceramics have very low (<1%),
metals have moderate (1–50%) and thermoplastic (>100%),
have high value of elongation to break.
35. Mechanical properties
Young’s Modulus
Young’s Modulus is the ratio of stress to the strain in the linearly
elastic region. Elastic modulus is a measure of the stiffness of the
material.
E =Tensile Stress(𝜎) /Tensile Strain(𝜀)
36. Mechanical properties
Toughness
The toughness of a material is given by the area under a stress–
strain curve.
Toughness = ∫𝜎d𝜀
The toughness measures the energy absorbed by the material
before it breaks. The rigid materials possess high Young’s
modulus (such as brittle polymers), and ductile polymers also
possess similar elastic modulus, but with higher fracture
toughness. However, elastomers have low values of Young’s
modulus and are rubbery in nature.
37. Mechanical properties
Viscoelasticity
There are two types of deformations: elastic and viscous.
Usually, polymers show a combined behavior of elastic and
plastic deformation, depending on the temperature and strain
rate.
At low temperature and high strain rate, elastic behavior is
observed, and at high temperature but low strain rate, the
viscous behavior is observed. The combined behavior of viscosity
and elasticity is observed at intermediate temperature and strain
rate values. This behavior is termed as viscoelasticity, and the
polymer is termed as viscoelastic.
39. 1. ORAL DELIVERY SYSTEM
These techniques are capable of controlling the rate of drug
from the delivery systems that can be utilized for controlled
delivery of drugs.
Some of novel drug delivery system for oral controlled release
drug administration include:
o Osmotic pressure controlled GI delivery system.
o Diffusion controlled GI delivery system.
o Bio[muco]adhesive GI delivery system.
40. 1. ORAL DELIVERY SYSTEM
o Osmotic Pressure Controlled GI delivery system:
Semi permeable membrane made from biocompatible
polymers.
E.g. cellulose acetate
E.g. of such type of system include Acutrim tablet which
contains Phenylpropanolamine as a drug.
o Gel diffusion controlled GI delivery system:
Fabricated from gel forming polymers such as CMC.
o Bio adhesive GI drug delivery system: It is capable of
producing an adhesion interaction with a biological
membrane. E.g. Carbopol.
41. 1. ORAL DELIVERY SYSTEM
These techniques are capable of controlling the rate of drug
from the delivery systems that can be utilized for controlled
delivery of drugs.
Some of novel drug delivery system for oral controlled release
drug administration include:
o Osmotic pressure controlled GI delivery system.
o Diffusion controlled GI delivery system.
o Bio[muco]adhesive GI delivery system.
42. 2. TRANSDERMAL DRUG DELIVERY SYSTEM
Transdermal drug delivery system: Mostly used when the
medicaments are applied on topical route.
E.g. Transdermal patch of scopolamine, nitro glycerin etc.
Advantages:
They permits easy removal and termination of drug action in
situation of toxicity.
Problems encountered with oral administration like
degradation, gastric irritation etc. are avoided.
43. 3. OCCULAR DRUG DELIVERY SYSTEM
Ocular Drug Delivery System: It allows prolonged contact
of drug with the surface of the eye.
Highly viscous suspension and emulsion are prepared to
have such purpose but these preparations does not achieve
this purpose at controlled rate.
E.g. Pilocarpine ocular insert used in treatment of
glaucoma.
44. 3. OTHER APPLICATIONS
Drug delivery and the treatment of diabetes: Here
the polymer will act as a barrier between blood stream and
insulin.
E.g. Polyacrylamide or N,N-Dimethyl amino ethylmetha
acrylate.
Drug delivery of various contraceptives and
hormones: It consist of drug saturated liquid medium
encapsulated in polymeric layer which controls the
concentration and release of drugs into the blood stream.
E.g. Medoxy progesterone acetate, Progestasert,
Duromine
46. Various uses of Polymers in
pharmaceutical sciences:
Formulation of Matrix tablets.
Formulation of Nanoparticles.
Formulation of solid dispersion.
In targeted drug delivery systems.
In the preparation of Polypeptide vesicles for drug delivery.
In formulation of cross linked Polymers.
Micelles for cancer therapeutics.
