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Polymer
science
By Viraj Sukthankar.
F.Y m-pharm.
Pharmaceutics dept.

Contents..
➢ INTRODUCTION.
➢ POLYMER CLASSIFICATION.
➢ GENERAL MECHANISM OF
DRUG RELEASE FROM
POLYMER
➢ APPLICATION OF POLYMERS IN
FORMULATION OF CONTROLLED
DRUG DELIVERY SYSTEM.
➢ REFERENCES.

INTRODUCTION
Polymer Science
Polymer Science or Macromolecular Science is a subfield of
materials Science concerned with polymers, Primarily
synthetic polymers such as plastics and elastomers.
Polymer Science has been the backbone for the
development of new formulations for past few years and its
advances have led to development of several applications in
pharmaceutical science.

Polymers
Polymers are high molecular weight compounds or
macromolecules composed of many repeating subunits
called “MONOMERS”, connected by Covalent bonds or
chemical bonds. The reaction involving combination of two
or more monomer units to form a long chain polymer is
termed as polymerization.
These are widely used as Pharmaceutical aids like
suspending agents, Emulsifying agents, Adhesives, Coating
agents, Adjuvants etc. Packaging material and medical
devices both in conventional and controlled drug delivery
systems.

Other definitions-
A Polymer is like a thread that is joined by many coins
punched through the center, in the end we get a string of
coins, the coins would be the monomers and the chain with
the coins would be the polymer.
E.g. Polyethylene = Ethylene-ethylene-ethylene-ethylene-…
Polymers are long chain giant organic molecules assembled
from many smaller molecules called monomers. A polymer
is analogous to a necklace made from many small beads.

Historical Background
T h e work in polymer science was started in 1811 b
y
Henri braconnot.
T h e term polymer was coined in 1833 by Jon's Jacob
Berzelius to describe the relationship of ethylene to butane
and higher homologs.
Bakelite was introduced in market in 1909 by reacting
phenol and formaldehyde at precisely controlled
temperature and pressure.
Flory, Mark and other in 1940’s were responsible for
rapid expansion of polymers, including detailed studies of
materials of increasing commercial value.

Drugs Used Category Method Used Polymer Used
Zidovudine Anti-viral Direct Compression HPMC-K4M,
Carbopol-934, EC
Venlafexine Anti-depressant Wet Granulation Beeswax, Carnauba
wax
Domperidone Anti-emetic Wet Granulation HPMC-K4M,
Carbopol-934
Ibuprofen Anti-inflammatory Wet Granulation EC, CAP
Miconazole Anti-fungal Direct Compression/
Wet Granulation
Pectin, HPMC
Verapamil Ca+2 channel
blocker
Direct Compression HPMC-K100M,
HPMC-K4M, HPMC-
K15M
Diethyl
carbamazepine
citrate
Anti-filarial Wet Granulation Guar gum, HPMC-
E15LV
Amlodipine Anti- arrythmatic Direct Compression HPMC, EC

Chemical nature of some common polymers
1. Polyethylene (LDPE) (Addition polymer)
Formula- -(CH2-CH2)n-
Monomer- Ethylene (CH2=CH2)
Properties- Soft, Waxy Solid
Uses- Film Warp, Plastic bags etc.
2. Butyl Rubber (Copolymer)
Monomer A- H2C=C(CH3)2
Monomer B- H2C=C-CH-CH2
► Properties- Elastic Strong rubber material.
Uses- Inner tubes of tires.

3.Polyvinyl Chloride (PVC) (Addition Polymer)
Formula : -(CH2-CHCL)n-
Monomer : Vinyl Chloride (CH2=CHCL)
Properties : Strong rigid Solid
U s e s : Pipes, Siding, Flooring.
4.Polypropylene (Diff Grades) (Addition Polymer)
Formula : -[CH2-CH(CH3)]n-
Monomer : Propylene (CH2=CHCH3)
Properties : Atactic, Soft, Elastic solid
U s e s : Similar to LDPE carpet, upholstery etc.

Some important Polymers used for drug delivery
► Hydroxyl propyl Methyl Cellulose
It is a semisynthetic, Inert, Viscoelastic polymer used as an
ophthalmic lubricant as well as an excipient and controlled
delivery component in oral medicaments. It is also found in
variety of commercial products.
Description- It is solid and slightly off-white to beige powder
in appearance and may be formed in granules.
Category- Suspending Agent, Viscosity enhancer, Tablet
binder, Coating agent, Film forming agent, Emulsion
stabilizer etc.

Method of Manufacture-
Cellulose fibers obtained from cotton linters or wood pulp
are treated with caustic soda. Alkali cellulose thus obtained
is in turn treated with methyl chloride and propylene oxide to
produce methyl hydroxyl propyl esters of cellulose. Fibrous
reaction product is than purified and ground to fine uniform
powder or granules.

► Micro crystalline cellulose (MCC)
MCC is a unique ingredient. In water with shear it forms
three dimensional matrix comprised of invisible
microcrystals that form an extremely stable, thixotropic
gel. It functions at any temp and provides superior freeze
and heat stability to finished products.
Category- Tablet and capsule diluent, Tablet disintegrate,
Suspending agent, Viscosity enhancer etc.
Description- Purified, Partially depolymerized cellulose
occurs as a white odorless crystalline powder composed of
porous particles. Available in diff particle size grades and
prop.

Method of manufacture –
MCC is manufactured by controlled hydrolysis of a-
cellulose, Obtained as a pulp from fibrous plant materials,
With dilute mineral oil and acids solutions. Following
hydrolysis, the hydrocellulose is purified by filtration and
aq. Slurry is sprayed dried to form dry, porous particles of
broad size distribution.

► Guar gum-
Guar gum is a natural polymer obtained from ground
endosperm of guar beans.
Category- Tablet binder, suspending and viscosity increasing
agent, Tablet disintegrating agent etc.
Chemistry- Chemically gaur gum consist of polysaccharides
composed of sugars galactose and mannose.
Description- White to yellowish-white powder. Odorless and
bland in taste.

Method of manufacture –
The gum consist of the pulverized endosperm of the seed of
gaur. The seed hull can be removed by grinding, After soaking
in Sulfuric acid or water or by charring. The separated
endosperm is ground into diff particles size depending on final
application.

Polyethylene Glycol (PEG)
Polyethylene glycol is a polyether compound with many
applications from industrial manufacturing to medicine.
Category- Suppository base, Solvent, Tablet and capsule
lubricant, Ointment base etc.
Diff grades of PEG-
PEG-200,
300,400,600,800,1000,1500,1540,2000,3000,4000,6000,8000,
20,000, 35,000.
Description- Clear, Colorless or Slightly Yellowish, Viscous
liq.

Method of manufacture-
Condensation polymers of ethylene oxide and water are
progressively formed under pressure in the presence of a
catalyst.

CHARACTERISTICS OF IDEAL
POLYMER SYSTEM
► Inert and compatible with environment.
► Nontoxic.
► Easily administrable.
► Easy and inexpensive to fabricate the dosage form.
► Good mechanical strength.

1. CLASSIFICATION OF POLYMERS
POLYMERS
NATURAL SYNTHETIC SEMI-SYTHETIC
Biodegradable Non biodegradable
Lactides, glycolides
and their copolymers,
polyanhydrides Acrolein, epoxy polymers
Proteins
Carbohydrates
Nucleic acids

a. Natural polymers: Natural polymers are derived
from natural sources and can be polysaccharides and
proteins in chemical nature.
E.g. Collagen, Albumin, Starch, Silk, Proteins, Wool,
Natural rubber etc.
b. Synthetic polymers: Synthetic polymers are of artificial
origin which consist of fibers like Teflon and Dacron,
Synthetic Rubbers, Plastics and PVC.
Synthetic polymers are further classified into two main
categories i.e.

1.Biodegradable polymers: E.g. Proteins, Collagen
Polysaccharides etc.
2.Non-biodegradable polymers: E.g. Acrolein, Epoxy
Polymers.
Bio- degradable polymers are further classified into
1. Natural bio-degradable polymers- These polymers are
very common in nature. Natural biodegradable polymers like
collagen, albumin, gelatin, hemoglobin etc. have been studied
for medical & pharmaceutical applications.
The use of these polymers is limited because of their high
costs and questionable purity.
Examples-Albumin, Collagen, Gelatin, Starch etc.

2. Synthetic Bio-degradable polymers -These type of
polymers are preferred rather than natural bio-degradable
polymers due to their inertness and easy and cheap
formulation.
Synthetic bio-degradable polymers have following
advantages over natural ones :
Localized delivery of drug.
Sustain delivery of drug.
Stabilization of drug.
Reduced side effects etc.
Examples- Poly lactide homopolymer, Polyester,
L-PLA etc.

c. Semi-Synthetic Polymers –
This type of polymers are derived from naturally occurring
polymers by means of chemical modifications.
E.g. Vulcanized rubber, Gun cotton, Cellulose diacetate,
HPMC etc.
Vulcanized rubber is used in making tires as the process
of vulcanization increases the mechanical strength of
natural rubber.
G u n cotton which is a cellulose nitrate is used in making
explosives.

► Cellulose on acetylation with acetic anhydride in the
presence of sulfuric acid forms cellulose diacetate which
is used in production of treads and materials like films,
glasses etc.
Vulcanization of rubber

2. Based on their interaction with water
Polymer
Non-Biodegradable Hydro gels Soluble Bio-Degradable
Polymer. Polymer. Polymer.
e.g. PVC, PVA .
PGA
E.g. PVP. E.g. HPMC, PEG. E.g. PAA,

3. Based upon linkage it can be classified
as:
a. Linear polymer: Molecules has definite backbone
and does not have long chain branches.
e.g. Polyformaldehyde,Polyesters,
Polycarbonates etc.

b. Branched polymers: It has long chain branches
that cannot be defined. It may also have short chain
branches.
E.g. Polyethylene, HPLD Polyethylene etc.

C. Cross-linking polymers:
In this type all molecules are chemically bonded together,
forming a three dimensional network. The bonding is usually covalent
but other types such as ionic bond are also possible.
Cross-linked polymers are produced from linear and branched
polymers or directly from chemical precursor.
E.g. Natural rubber, polyacrylamide gels,
epoxies, Alkyd resins etc.

4. Based on polymerization mechanisms:
a.Addition polymers:
Addition polymers are formed when monomer units
are separately added to form long chains without
elimination of any by-product molecules.
This polymers are formed by reactions between
monomer molecules possessing multiple bonds.
E.g. Polyethylene, Polypropylene, Styrene-
butadiene rubber etc.

b. Condensation polymers.
Condensation polymers are formed when the
monomers containing active functional groups react
together with the elimination of a small molecule like
water, ammonia, alcohol etc.
E.g. Nylon-66, Polyester, Bakelite etc.

5. Based on polymerization mechanisms:
1.Chain polymerized polymer:
Involves initiation, propagation, and
termination.
E.g. Polystyrene
2.Step growth polymerized polymer:
No discrete initiation, propagation takes place
but instead involves sp. Reaction b/w functional
group.
E.g. Nylon

Addition: one monomer at a time
Also called chain growth.
Condensation: Also called step growth.

6. Based on composition:
A. Homopolymer:
Polymers formed from one kind of monomer are
called a homopolymer like -A-A-A-A-
e.g. Polyethylene, polystyrene
B. Copolymer:
Polymers formed from more than one kind of
monomer unit is called a co-polymer or mixed
polymer like -A-B-A-B-A-B-
e.g. Silicone, Ethyl cellulose

► There are three primary mechanisms by which
active agents can be released from a delivery
system: namely,
► Diffusion, degradation, and swelling followed by
diffusion.
► Any or all of these mechanisms may occur in a
given release system. Diffusion occurs when a drug
or other active agent passes through the polymer
that forms the controlled-release device.
GENERAL MECHANISM OF DRUG
RELEASE FROM POLYMER

► The diffusion can occur on a macroscopic scale as
through pores in the polymer matrix or on a molecular
level, by passing between polymer chains.

► For the reservoir systems the drug delivery rate can
remain fairly constant.
► In this design, a reservoir whether solid drug, dilute
solution, or highly concentrated drug solution within a
polymer matrix is surrounded by a film or membrane of
a rate-controlling material.
► The only structure effectively limiting the release of the
drug is the polymer layer surrounding the reservoir.
► This polymer coating is uniform and of a no changing
thickness, the diffusion rate of the active agent can be
kept fairly stable throughout the lifetime of the delivery
system.

The system shown in Figure (a) is
representative of an implantable or
oral reservoir delivery system,
whereas the system shown in (b) is
transdermal system.

Bio degradation of polymers -
B i o degradation is the chemical changes that
alter t
h
emolecular weight or solubility of the polymers.
B i o erosion may refer to as physical process that
result i
n
weight loss of a polymer device.
T h e possibility for a polymer to degrade and to have i
t
s
degradation by products assimilated or excreted by
living system is designated as Bio Resorbable.
T h e erosion of polymers basically takes place
by t
w
omethods:-
1.Chemical erosion
2.Physical erosion

Chemical Erosion
Bio erosions through chemical mechanisms are explained
below-
Mechanism-I :It describes the degradation of water
soluble macromolecules that are cross-linked to form three-
dimentional network
Degradation in these systems can occur by
•Type (1A)- Degradation occur at crosslinks to form soluble
backbone polymeric chains. It provides high molecular
weight, Water soluble fragments.
•Type (1B)- Degradation occur to form water-soluble
fragments. Such type provides low molecular weight, water
soluble oligomers and monomers.

► Mechanism-II : Describes the dissolution of water
insoluble macromolecules with side groups that are
converted to water insoluble polymers as a result of
ionization, Protonation or hydrolysis of the groups.
► Molecular weight remains unchanged.
► Materials showing this type of erosion include
Cellulose acetate derivatives,
Co-polymers of maleic anhydride.

► Mechanism-III : Describes the degradation of insoluble
polymers with liable bonds. It forms low molecular
weight, water soluble molecules.
► Polymers undergoing this type of erosion include
Poly(lactic acids)
Poly(glycolic acid) and their co-polymers etc.

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Physical erosion
T h e physical erosion mechanisms can be characterized a
s
heterogeneous or homogeneous.
M o s t polymers undergo homogenous erosion that means
the hydrolysis occur at even rate through out the polymeric
matrix.
I n homogenous erosion, there is loss of integrity
of t
h
ematrix or polymer.
I n heterogeneous erosion, also called as Surface Erosion.
The polymer erodes only at the surface and maintains its
physical integrity as it degrades.
Highly crystalline polymers tend to undergo
heterogeneous erosion.

APPLICATIONS OF POLYMERS IN
CONTROLLED DRUG DELIVERY
1.ORAL DELIVERY SYSTEM:
These techniques are capable of controlling the rate o
f
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:
Osmotic pressure controlled GI delivery system.
Diffusion controlled GI delivery system.
Bio[muco]adhesive GI delivery system.

❑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.

❑ Gel diffusion controlled GI delivery system:
➢ Fabricated from gel forming polymers such as
CMC.
❑ Bio adhesive GI drug delivery system:
➢ It is capable of producing an adhesion interaction
with a biological membrane.
➢ E.g. Carbopol.

2.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.

3.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.

Other applications:
► Drug delivery and the treatment of diabetes:
blood
Here the polymer will act as a barrier between
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 etc.

Polymer Membrane Permeation-Controlled
Drug Delivery Systems
E.g. progestasert
Drug reservoir
Polymer layer

► Various uses of Polymers in pharmaceutical sciences:
1. Formulation of Matrix tablets.
2. Formulation of Nanoparticles.
3. Formulation of solid dispersion.
4. In targeted drug delivery systems.
5. In the preparation of Polypeptide vesicles for drug
delivery.
6. In formulation of cross linked Polymers.
7. Micelles for cancer therapeutics.

Imp. Questions from this topic -
Classify Polymers with examples?
Discuss imp. Polymers used in design o
f
controlled drug delivery system?
G i v e an account on pharmaceutical applications o
f
polymers?
Discuss biodegradable polymers usedi
n
formulation of controlled release systems?

REFERENCES
► Targeted and control drug delivery by S.P.Vyas and
R.K.Khar. Pg. no 417 to 422.
► The eastern pharmacist-august,1998, vol. no 41.
► Remington : The science and practice of pharmacy.
Vol.no 1 [20th edition]
► www.google.com
► Bio pharmaceutics and pharmacokinetics by
D.M.Brahmankar and Sunil.B.Jaiswal.

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