Download Classification of polymers

DEFINITION

A Polymer is a substance composed of molecules
with a large molecular mass of repeating structural
units or monomers connected by covalent chemical
bonds.
Linear Polymers:

A polymer in which the molecules form long chains without branches or cross-linked
structures.
examples: nylon, polyester, PVC etc.

Branched Polymer:
A polymer chain having branch points that connect three or more
chain segments.
Examples: polythene, glycogen, starch etc

Cross linked Polymer:
Cross-links are bonds that link one polymer chain to another. They
can be covalent bonds or ionic bonds.
Examples: malamine formaldehyde resin etc

Linear & Branched Polymers are know as thermoplastic
materials.

Cross linked Polymer are know as thermosetting materials.
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Polymer classes include
Vinyl
polymer
Synthetic
rubber
silicone
Bio
polymer
Conductive
polymer
Polymer
classes
include
Co
polymer
Fluoro
polymer
In organic
polymer
rubber
Poly ester
Classification of polymers
A. Depending on response to heat
a. Thermoplastic : linear or slightly branched
Solid
melt solid
resolidification
Weak attractive forces hence, can be remolded.
Eg :PE, PVP,PVC etc.
Classification of polymers
a.Depending on response to heat
b.Thermosetting: Extensive cross linking covalently
Solid
Decomposed solid
Chains cannot be easily broken.
Eg : Epoxy resin, Poly urethane.
Classification of polymers
(b)Based on chemical reaction
Condensation polymerisation
Addition polymerisation
Classification of polymers
Addition polymerization
Condensation polymerisation
Classification of polymers
(C.) Based on repeating units
Homo polymer: [A-A-A-A]
Co polymer :
Alternating copolymers :
[A-B-A-B-A-B]
Random copolymers
[A-B-A-A-B-A-B-B]
Block copolymers:
[A-B-B-B-A-B-B-B]
Classification of polymers
(D.)Based on origin of polymer
(i )Natural polymers
Eg:Gelatin, Xantum gum , Sodium alginate etc.
(ii.)Semi synthetic polymers
Eg: Methyl cellulose, HPC, HPMC, etc.
(iii.)Synthetic polymers
Eg ;carbopol, PVA, PVP, PEG,etc.
Classification of polymers
(E). Based on degradation properties


Non bio degradable Eg:EC, PVC.
Bio degradable
 Bulk eroding polymer eg:PLGA
 Surface eroding polymers eg:Polyanhydrides
Classification of polymers
cotton., silk ,wool
Natural and
synthetic polymers
PVC, nylon
ethylene
Organic and
inorganic
polymers
Glass , silicone,
rubber
Thermoplastic &
Thermoplastic
Poly ethylene,
sealing wax.
polymers
Plastics,Elastomers,
Fibers, Liquid
Resins
PVC,
polystyrene,PMC
Nylon terelene
Molecular weight

There are different ways that molecular weights of a polymer
can be expressed:




By number of chains
By the weight of chains
By viscosity
The two most common ways are
1. Number(Mn)
2.
And weight average calculations
•Molecular weight determination
1. Number Average Molecular Weight

Molecular weight is determined by calculating the total
molecular weight of monomer and total number of
monomer.
NM

Mn 
N
i
i
i



Mi- total molecular weight of monomer.
Ni- number of monomer molecules.
Mn- number average molecular weight.
•Molecular weight determination
2. Weight Average Molecular Weight
NM M

Mw 
N M
i
i.
i



i
i
M w - weight average molecular weight.
Mi- total molecular weight of monomer.
Ni- number of monomer molecules.
Characteristics of ideal polymer
Inert
Easily
administered
polymer
Good
mechanical
strength
Non toxic
CRITERIA FOLLOWED IN POLYMER SELECTION

The polymer should be soluble and easy to synthesis

It should have finite molecular weight

It should be compatible with biological environment

It should be biodegradable

It should provide good drug polymer linkage
Preparation of polymer solution
Upon contact , the solvent molecules diffuses into the solid
particles swell them and then into gel particles
The solvated polymer molecule diffuses out into the solvent
. By stirring it reduces the thickness of the stagnant liquid
layer surrounding each particle
Powders or grains are added to solvent. Stirring done
inorder to prevent aggregation that forms lumps.
Eg: MC should be dispersed with high shear in about 1/4th
the total amount of water heated to 80 oCto 90o c
If particles are wetted and dispersed the rest of water is
added cold to about 50 oc. Swells and dissolves the
dispersed paticles fast with moderate shear.Eg:HPC,HPMC
Conti……………….
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
Eg:PVA &SCMC are soluble in hot than in cold water.
So dipersed in ice cold water followed by dissolution at
90oc
Eg: Dissolved in 80% toulene &20%ethyl alcohol . First
toulene is added , the alcohol is then added to effect
prompt dissolution.
Cellulose derivatives are stored for 48 hours after
dissolution to promote full hydration , viscosity, & clarity.
Thermodynamics of polymer solutions

For the dissolution of a polymer in the solvent at a temperature T , the
Gibbs free energy of mixing is
ΔG = ΔH - TΔS
The important points to be considered in thermodynamics of polymer
solution are
1)
2)
3)
Heat of mixing
Entropy of mixing
Free energy of mixing
Phase seperation



This technique is used in micro encapsulation of
drugs by using high molecular weight long chain
flexible polymers.
These polymers are used for their rate retarding
properties
Phase seperation-coacervation
1) Core(drug)
2) Coat(polymer)
3) LMV(liquid manufacturing vehicle)
Cont………………

To achieve this phase seperation different methods employed are
Changing in temperature
Addition of incompatible polymer
Non solvent addition
Salt addition
Polymer polymer interactions
How the deposition of coat over core materials occurs?
Rigidisation of micro capsules

Formed embryo microcapsules are gets hardened by various
methods like
Thermal linking
Cross linking
Polymers in solid state



Solid polymers depends on:
Mechanical ,
permeability,
electric,
thermal,
optical properties.
These factors determine the flexibility and strength of
the polymers
For amorphous polymers cross linking or the fillers
may be desirable.
Properties of polymers

A.Physical properties of polymers

The properties of polymer depends on many
factors including
inter and intrachain bonding
Presence of additives
Chain size and geometry
Molecular weght distribution

Polymers do not boil
a.Physical properties

Glass transition temperature(Tg)
Vinyl
polymers
Condensation
polymers
(Tg)Below
room
temperature
flexible
(Tg) above
room
temperature
(Tg)
Rubber
&plastic
Hard plastics
Many polymers brittle at room temperature.
To become liable plasticizers added that allow segmental mobility
Eg:
PVC, & poly styrene
a. Physical properties conti…………

Inflexible region
Hard
Poly urethanes

Flexible region
Soft

Urethane portion
Hydrogen bonding
Room
temperature

Polyether portion
Flexible
Soft
Hard
b.Chemical properties

Different side groups on the polymer can lend to:





Ionic bonding
Hydrogen bonding
Polymers containing amide or carbonyl groups can form
hydrogen bonds between adjacent chains.
Polyesters have dipole –dipole bonding between the oxygen
atoms in C=Ogroups and the hydrogen ato.ms in C-H groups.
Dipole bonding is not as strong as hydrogen bonding
c. Mechanical properties





Depending on their structure , molecular weight , and
intermolecular forces, polymers resist differently
when they are stressed.
For elastic materials the stress and strain correlation
is linear upto the failure point
For fibres and highlt cross linked polymers the slope
of the stress and strain line is steeper.
Energy is needed to break the polymer . The area
under the stress/strain measures it.
The larger the area, is the tougher the polymer.
Tacticity

Tacticity describes the relative steriochemistry of chiral
centers in neighbouring structural units within a
macromolecule. There are three types :
 Iso tactic
 A tactic
 Syndiotactic
Thermal characterisation

Thermal analysis of the polymers is the important
phenomenon to study the stability and degradation
of polymers.
Method :a) TGA
b) DSC
c) Thermo mechanical analysis
THERMOGRAVIMETRICAL ANALYSIS
(TGA)
•
This method provides indication for thermal stability and
upper limit of thermal degradation where loss of
sample begins.
•
This method only measures loss of volatile content from
the polymer.
•
This method has limitation that it can not detect
temperature at chain cleavage of chain takes place.
Differential Scanning Calorimetry
(DSC)
parameters measured1.
Glass transition temperature (Tg)
2.
Crystalline melting point
3.
Heat of fusion
4.
Heat of crystallization

It requires placing of Reference and test sample for
the continuous monitoring in the heating chamber.
Differential scanning calorimetry
Thermo Mechanical Analysis
(TMA)
•
This method is used for determination of deformation of
polymer sample as a function of temperature placed on
platform in contact with probe.
•
It measures transition from glassy to a rubbery polymer
and gives idea about softening temperature.
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Pharmaceutical applications of polymers
1.Biomaterials for delivery systems
 Polyurethanes
 Polysiloxanes
 Poly methyl methacrylate
 Poly vinyl alcohol
 Polyethylene
 Poly vinyl pyrrolidone
Biomaterials for delivery systems
Currently being used polymers




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poly (2-hydroxy ethyl
methacrylate).
Poly( acrylic acid)
Poly(N-vinyl pyrrolidone)
Poly(methyl methcrylate)
Poly vinyl alcohol
Poly acryl amide
Poly(methacrylic acid).
PEG
Polyethylene-co-vinyl acetate
Polymers which degrade in body

Poly actides

Polyglycolides

Poly (lactide-co-glycolides)

Poly anhydrides

Poly orthoesters
Polymers in controlled drug delivery

Micrograph of particles used to

Drug levels in the blood with
carry drugs to the lung
a.
Traditional drug dosing
b.
Controlled delivery dosing
Controlled release mechanisms
Drug delivery from a typical matrix drug delivery system
Drug delivery from typical reservoir devices:
a. Implantable or oral systems
b. Trans dermal systems
Bio degradable systems

Drug delivery from :
a.
Bulk eroding and
b.
Surface eroding bio degradable systems
Bio degradabl micro particles of
60:40 lactide :glycolide PLGA
Bio degradable micro particle of 75:25
lactide:glycolide PLGA after 133 days
of degradation in water
Applications of polymers
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Dental
Ophthalmic
orthopedic
Sutures
Drug delivery
Drugs
Tablets
Liquids
For controlling the flow semi solids
References

Bio pharmaceutics and pharmacokinetics by: D.M.Bharmankar,
Sunil.B. Jaiswal.

Govariker V. R., Viswanathan N. V., Sreedhar J., “Polymer
Science”, New age publications, 263 .

Jain N.K., Controlled and novel drug delivery, CBS
Publisher,New delhi, 27-49.

Martin A., Swarbrick J., Commarata A., Physical pharmacy,
K.M.varghese company, Bombay,

Sinko P.J.,Physical pharmacy and pharmaceutical sciences, fifth
edition, lippincot williams & wikins co., 585-627.

http://en..wikipedia.org/wiki/Polymers.