Polymer Science

Neha P. Dave

DEFINITION

The word ‘polymer’ comes from the Greek words poly(meaning ‘many’) and meros (meaning ‘parts’).

Example: POLYBUTADIENE =(BUTADIENE+ BUTADIENE+......)nWhere n = 4,000

Polymers are very large molecules made when hundreds of monomers join together to form long chains.

INTRODUCTION

• Polymers are complex and giant molecules usually with carbons building the backbone, different from low molecular weight compounds.

• The small individual repeating units/molecules are known as monomers(means single part).

• Imagine that a monomer can be represented by the letter A. Then a polymer made of that monomer would have the structure:

-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A

• This kind of polymer is known as HOMOPOLYMER.

(According to their properties &

characteristics.)

1. Natural and Synthetic Polymers

Polymers which are isolated from natural materials, are called as ‘natural polymers’.

E.g. : Cotton, silk, wool, rubber.

natural rubber Polymers synthesized from low molecular weight compounds, are called

as, ‘synthetic polymers’.E.g. polyethylene, nylon, terylene.

Polyethylene

Semi synthetic polymers :• Geletin , fibrinogen chitin &chitoson , dextran, alginate

NATURAL RUBBER-

Hevea brasiilensis

A Polymer whose backbone chain is essentially made ofcarbon atoms is termed an ‘Organic polymer’.

Examples- cellulose, proteins, polyethylene, nylons.

A Polymer which does not have carbon atom in their chain istermed as ‘Inorganic polymer’ .

Examples- Glass and silicone rubber

2)BASED ON PRESENCE OF CARBON ATOM:

3. Classification by Monomer Composition

Homopolymer Copolymer

Block Graft Alternating Statistical

HomopolymerConsist of only one type of constitutional repeating unit (A)

AAAAAAAAAAAAAAACopolymerConsists of two or more constitutional repeating units (A.B )

Statistical copolymer (Random)ABAABABBBAABAABB

two or more different repeating unitare distributed randomly Alternating copolymer

ABABABABABABABABare made of alternating sequencesof the different monomers Block copolymer

AAAAAAAAABBBBBBBBBlong sequences of a monomer are

followedby long sequences of another monomer

Graft copolymerAAAAAAAAAAAAAAAAAA

B B BB B B

(d)

4. Based on Microstructure

5. Based on Chain structure (molecular architecture)

Linear chains :a polymer consisting of a single continuous chain of repeatunitsBranched chains :a polymer that includes side chains of repeat unitsconnecting onto the main chain of repeat unitsHyper branched polymer :consist of a constitutional repeating unitincluding a branching groupsCross linked polymer :a polymer that includes interconnections betweenchainsNet work polymer :a cross linked polymer that includes numerousinterconnections between chains

Linear Branched Cross-linked Network

Direction of increasing strength

6. Based on physical property related to heating

Some polymer are soften on heating and can be converted into any shape that they can retain on cooling.

Such polymer that soften on heating and stiffen on cooling are termed as `thermoplastic’ polymers.

Ex. Polyethylene, PVC, nylon, sealing wax.

Polymer that become an infusible and insoluble mass on heating are called ‘thermosetting’ polymers. Plastics made of these polymers cannot be stretched, are rigid and have a high melting point.

7. Classification by applications

Polymer is shaped into hard and tough utility articles byapplication of heat and pressure, is known as ‘plastics’.

E.g. polysterene, PVC, polymethyl methacrylate.

When plastics are vulcanised into rubbery products exhibitinggood strength and elongation, polymers are known as‘elastomers’.

E.g. silicone rubber, natural rubber, synthetic rubber, etc.

Long filament like material whose length is atleast 100 times it’sdiameter, polymers are said to be ‘fibres’.

E.g. Nylon, terylene.

Polymers used as adhesives, potting compounds, sealants, etc., ina liquid form are described as ‘liquid resins’.

E.g. Epoxy adhesives and polysulphides sealants.

8. Classification Based on Kinetics or Mechanism

A) Step-growth B) Chain-growth

9. BASED ON DEGRADATION OF POLYMER:

Biodegradable polymers:It can be defined as polymers comprised of monomers linked toone another through functional group and have unstable linkage inthe backbone.

eg. Collagen, Albumin,Casein etc.

Non biodgradable polymers:

Polymerization mechanisms

- Step-growth polymerization

Forming large molecules from small molecules – Polymerization.There are two basic kinds of polymerization reactions:

A)condensation(example: curing of concrete) or step growthB)Chain growth (example, formation of PVC pipe)

Stage 1

Consumptionof monomer

n n

Stage 2

Combinationof small fragments

Stage 3

Reaction of oligomers to give high molecular weight polymer

Step-Growth Polymerization

Chain-growth polymerization

Chain growth polymerization involves an active chain site which reacts with an unsaturated (or heterocyclic) monomer such that the active site is recovered at the chain end.

Chain polymerization

Radical polym.The C=C is prefer the Polym. by R.P.and also can be used in the steric hindrance of the substituent

Ionic polym.

Anionic polym. Cationic polym.

X X X

radical cationic anionic

Electron with drawingsubstituent decreasingthe electron density on the double bond andfacilitate the attack of

anionic speciessuch as cyano andcarbonyl δ+ δ-

CH2=CH Y

Electron donatingsubstituent increasingthe electron density on the double bond andfacilitate the attack of

cationic speciessuch as alkoxy, alkyl, alkenyl, and phenyl

δ- δ+CH2 =CH Y

COMMON SYNTHESIS STEPS FOR DIFFERENT TECHNIQUES:

1)Initiation ;

2)Propagation;

3)Termination;

-Coupling ;

-Disproportionation ;

-Chain transfer;

-Inhibitor;

(1)INITIATION:

• Initiation in free radical polymerization involves first thegeneration of free radicals, which then attacks the double bond inthe monomer molecule, resulting in the following chemicalchange;

• R + CH2 = CH + R-CH2-CH! !

free radicals X Xmonomer

molecule

• The free radical site is now shifted from the initiator fragment tothe monomer unit.

• The monomer initiating polymerization is an exothermic process.

(2)PROPAGATION:

• In these step, the radical site at the first monomer unitattacks the double bond of a fresh monomer molecule.

• This results in the linking up of the second monomer unit tothe first and the transfer of the radical site from the firstmonomer unit to the second , by the unpaired electrontransfer process.

• This process involving a continuing attack in fresh monomermolecules.

(3)TERMINATION:

• In this process any further addition of the monomer unit to thegrowing chain is stopped & the growth of the polymer chain isarrested by one of the following reaction.

Coupling ;• The coupling of the lone electron present in each chain to form an

electron pair and, thus nullify their reactiveness.

Disproportionation ;• One H from one growing chain is abstracted by the other growing

chain & utilized by the lone electron for getting stabilized.

Inhibitor;• MH is known as a chain transfer agent, and addition of controlled

amounts of MH to the polymerization reaction can be used to controlmolecular weight of the polymers.

Characteristics of polymer

Low Density.

Low coefficient of friction.

Good corrosion resistance.

Good mould ability.

Excellent surface finish can be obtained.

Economical.

Poor tensile strength.

Low mechanical properties.

Poor temperature resistance.

Can be produced transparent or in different colours

Polymer properties

Physical Properties

• Specific Gravity

• Mold Shrinkage (in flow, cross-flow, and thickness directions)

Mechanical Properties

• Strength (Tensile and Flexural)

• Modulus (Tensile and Flexural)

• Elongation

• Hardness

• Impact Resistance

Environmental Properties

• Chemical Resistance

• UV Resistance

• Flame Resistance (UL Rating)

• Oxygen Index

• Water Absorption

Thermal Properties

• Heat Deflection Temperature

• VICAT Softening Temperature

• Glass Transition Temp

• Heat Capacity

• Thermal Conductivity

STRUCTURAL POLYMER PROPERTIES

• Mol. wt of polymer, this affect over all properties. theMol.wt increases with increased tensile strength &resistance.

• Force of attraction between polymer chain is high,crystals are formed.

• Secondary interaction between atom on side chainstiffing the chain and increase strength.

• Polymer appears translucent.• Heating of crystalline material above their melting

point cause individual polymer chain to become mobileand transparent.

• Density of polymer is increases by increasing crystallinecontent. Solubility decreases with the closer and morecloser and more regular packing of polymer chain.

CHEMICAL PROPERTIES

• Polymer undergo significant degradation in body.

• High crystallinity can increase polymer stability.

• Ingredient can be use to improve polymer formationand enhance the overall properties.

• Polymer properties may affect interaction withsurrounding.

• Polymer has been found into shape suitable forintended, sterilization process.

Morphological Properties

•A synthetic polymer may be described as crystalline if it

contains regions of three-dimensional ordering on atomic

(rather than macromolecular) length scales, usually arising

from intramolecular folding and/or stacking of adjacent chains.

•Synthetic polymers may consist of both crystalline and

amorphous regions; the degree of crystallinity may be

expressed in terms of a weight fraction or volume fraction of

crystalline material.

•The driving force for crystallization is a closer packing of the

polymer chains with consequent enhancement of

intermolecular attractions.

Crystallinity

Bulk properties

Tensile Strength

The tensile strength of a material quantifies how much stress

the material will endure before failing. This is very important in

applications that rely upon polymer's physical strength or

durability. In general tensile strength increases with polymer

length.

Transport properties such as diffusivity relate to how rapidly

molecules move through the polymer matrix. These are very

important in many applications of polymers for films and

membranes.

Transport Properties

Young's modulus, E, can be calculated by dividing the tensile stress by the

tensile strain:

where

E is the Young's modulus (modulus of elasticity) measured in pascals;

F is the force applied to the object;

A0 is the original cross-sectional area through which the force is

applied;

ΔL is the amount by which the length of the object changes;

L0 is the original length of the object.

Youngs Modulus of Elasticity

This parameter quantifies the elasticity of the polymer. It is defined, for

small strains, as the ratio of rate of change of stress to strain. Like tensile

strength this is highly relevant in polymer applications involving the physical

properties of polymers

Pure Component Phase Behavior

Melting Point•The term "melting point" when applied to polymers

suggests not a solid-liquid phase transition but a transition

from a crystalline or semi-crystalline phase to a solid

amorphous phase.

•It is abbreviated as "Tm", is more properly called the

"crystalline melting temperature".

•Among synthetic polymers, crystalline melting is only

discussed with regard to thermoplastics, as thermosetting

polymers will decompose at high temperatures rather than

melt.

Glass Transition Temperature

•A parameter of particular interest in synthetic polymer

manufacturing is the glass transition temperature (Tg), which

describes the temperature at which amorphous polymers

undergo a second order phase transition from a rubbery,

viscous amorphous solid to a brittle, glassy amorphous

solid.

•The glass transition temperature may be engineered by

altering the degree of branching or cross-linking in the

polymer or by the addition of plasticizer.

Solution properties of polymersPolydispersityNearly all synthetic polymers and naturally occurring

macromolecules possess a range of molecular weights. The

exceptions to this are proteins and natural polypeptides. The

molecular weight is thus an average molecular weight and

depending on the experimental method used to measure it.

ViscosityThe viscosity of a polymer solution not only depends on its

concentration but also on polymer–solvent interactions, charge

interactions and the binding of small molecules.

The intrinsic viscosity of solutions of linear high-molecular

weight polymers is proportional to the molecular weight M of

the polymer as given by the Staudinger equation:

[η] = KMa

•A gel is a polymer–solvent system containing a three

dimensional network which can be formed by swelling of solid

polymer or by reduction in the solubility of the polymer in the

solution.

•When gels are formed from solutions, each system is

characterized by a critical concentration of gelation below

which a gel is not formed.

•Gels can be irreversible or reversible systems depending on

the nature of the bonds between the chains of the network.

Properties of polymer gels

Fabrication of polymers in pharmaceuticals

FABRICATION PROCESS

1) EXTRUSION

2) INJECTION MOULDING

3) COMPRESSION MOULDIND

4) PALTRUSION

5) SPINNING

6) TWO ROLL MILLING

7) INTERNAL MIXING

1. EXTRUSION• Extrusion is a process used to create objects of a fixed cross-

sectional profile. A material is pushed or drawn through a die ofthe desired cross-section. The two main advantages of thisprocess over other manufacturing processes is its ability tocreate very complex cross-sections and work materials that arebrittle, because the material only encounters compressive andshear stresses. It also forms finished parts with an excellentsurface finish.

• Extrusion may be continuous or semi-continuous.

• The extrusion process can be done with the material hot orcold.

• Commonly extruded materials include metals, polymers,ceramics, concrete and foodstuffs.

A. HOT EXTRUSION

• Hot extrusion is done at an elevated temperature to keep thematerial from work hardening and to make it easier to push thematerial through the die.

• Most hot extrusions are done on horizontal hydraulic pressesthat range from 250 to 12,000 tons. Pressures range from 30 to700 MPa (4,400 to 102,000 psi), therefore lubrication is required,which can be oil or graphite for lower temperature extrusions, orglass powder for higher temperature extrusions.

B. COLD EXTRUSION

• Cold extrusion is done at room temperature or near room temperature.

• The advantages of this over hot extrusion are the lack of oxidation, higher strength due to cold working, closer tolerances, good surface finish, and fast extrusion speeds if the material is subject to hot shortness.

• Examples of products produced by this process are: collapsible tubes, fire extinguisher cases, shock absorber cylinders, automotive pistons, and gear blanks.

C. WARM EXTRUSION

• Warm extrusion is done above room temperature, but belowthe recrystallization temperature of the material thetemperatures ranges from 800 to 1800 °F (424 to 975 °C).

• It is usually used to achieve the proper balance of requiredforces, ductility and final extrusion properties.

Schematic diagram of a simple extrusion machine

2. INJECTION MOULDING

• Injection molding is a manufacturing process for producingparts from both thermoplastic and thermosetting plasticmaterials.

• Material is fed into a heated barrel, mixed, and forced into amold cavity where it cools and hardens to the configuration ofthe mold cavity.

• After a product is designed, usually by an industrial designer oran engineer, molds are made by a moldmaker (or toolmaker)from metal, usually either steel or aluminium, and precision-machined to form the features of the desired part.

• Injection molding is widely used for manufacturing a variety ofparts, from the smallest component to entire body panels ofcars.

INJECTION PROCESS

• Small injection molder showing hopper, nozzle and die areaWith Injection Molding, granular plastic is fed by gravityfrom a hopper into a heated barrel.

• As the granules are slowly moved forward by a screw-typeplunger, the plastic is forced into a heated chamber, where itis melted.

• As the plunger advances, the melted plastic is forcedthrough a nozzle that rests against the mold, allowing it toenter the mold cavity through a gate and runner system.The mold remains cold so the plastic solidifies almost assoon as the mold is filled.

A. INJECTION MOLDING CYCLE

• The sequence of events during the injection mold of aplastic part is called the injection molding cycle.

• The cycle begins when the mold closes, followed by theinjection of the polymer into the mold cavity.

• Once the cavity is filled, a holding pressure is maintained tocompensate for material shrinkage.

• In the next step, the screw turns, feeding the next shot tothe front screw. This causes the screw to retract as the nextshot is prepared. Once the part is sufficiently cool, the moldopens and the part is ejected

B. TIME FUNCTION

• The time it takes to make a product using injection molding can be calculated by adding:

•Twice the Mold Open/Close Time (2M)

+Injection Time (T)

+Cooling Time (C)

+Ejection Time (E)

Where T is found by dividing:Mold Size (S) / Flow Rate (F)

Total time = 2M + T + C + ET = V/R

V = Mold cavity size (in3)R = Material flow rate (in3/min)

The total cycle time can be calculated using tcycle = tclosing + tcooling + tejection

• Schematic diagram of injection-molding machine

Schematic diagram of injection-molding machine

3. COMPRESSION MOULDING A method of molding in which the molding material,

generally preheated, is first placed in an open, heatedmold cavity.

The mold is closed with a top force or plug member,pressure is applied to force the material into contact withall mold areas, and heat and pressure are maintaineduntil the molding material has cured.

The process employs thermosetting resins in a partiallycured stage, either in the form of granules, putty-likemasses, or preforms.

Compression molding is a high-volume, high-pressuremethod suitable for molding complex, high-strengthfibreglass reinforcements.

Advanced composite thermoplastics can also be compressionmolded with unidirectional tapes, woven fabrics, randomlyorientated fiber mat or chopped strand.

The advantage of compression molding is its ability to moldlarge, fairly intricate parts.

Compression molding produces fewer knit lines and less fiber-length degradation than injection molding.

4. PALTRUSION

• Paltrusion is a continuous process of manufacturing ofcomposite materials with constant cross-section wherebyreinforced fibers are pulled through a resin, possibly followed bya separate preforming system, and into a heated die, where theresin undergoes polymerization. Many resin types may be usedin paltrusion including polyester, polyurethane, vinylester andepoxy.

• But the technology isn't limited to thermosetting resins. Morerecently, pultrusion has also been successfully used withthermoplastic matrices such as polybutylene terephthalate (PBT)either by powder impregnation of the glass fiber or bysurrounding it with sheet material of the thermoplastic matrixwhich is then molten up.

1 - Continuous roll of reinforced fibers/woven fiber mat2 - Tension roller

3 - Resin bath4 - Resin soaked fiber

5 - Die and heat source6 - Pull mechanism

7 - Finished hardened fiber reinforced polymer

5. SPINNING• Spinning is manufacturing process for creating polymer

fibers. It is a specialized form of extrusion that uses aspinneret to form multiple continuous filaments. Thereare four types of spinning: wet, dry, melt, and gelspinning.

• Wet spinning is the oldest of the four processes. Thisprocess is used for polymers that need to be dissolved in asolvent to be spun. The spinneret is submerged in achemical bath that causes the fiber to precipitate, andthen solidify, as it emerges. The process gets its namefrom this "wet" bath. Acrylic, rayon, aramid, modacrylic,and spandex are produced via this process.[1]

• Dry spinning is also used for polymer that must be dissolvedin solvent. It differs in that the solidification is achieved throughevaporating the solvent. This is usually achieved by a stream ofair or inert gas. Because there is no precipitating liquid involved,the fiber does not need to be dried, and the solvent is moreeasily recovered. acetate, triacetate, acrylic, modacrylic,polybenzimidazole fiber, spandex, and vinyon are produced viathis process.

• Melt spinning is used for polymers that can be melted. Thepolymer solidifies by cooling after being extruded from thespinneret. Nylon, olefin, polyester, saran, and sulfar areproduced via this process.

Direct spinning

• The direct spinning process is avoiding the stage of solidpolymer pellets. The polymer melt is produced from the rawmaterials and from polymer finisher diretly pumped to thespinning mill. Direct spinning is mainly applied duringproduction of polyester fibers and filaments and is dedicatedto high production capacity (> 100 t/day).

• Gel spinning, also known as dry-wet spinning, is used toobtain high strength or other special properties in the fibers.The polymer is in a "gel" state, only partially liquid, whichkeeps the polymer chains somewhat bound together.

• The fibers are first air dried, then cooled further in a liquidbath. Some high strength polyethylene and aramid fibers areproduced via this process.

TWO ROLL MILLING

Pharmaceutical Applications of polymers Polymers are used extensively in drug delivery,

• e.g., for rheology control, control of drug release rate,stabilization of colloidal drug carriers, and solubilizationof sparingly soluble drugs.

• Many of the properties used in drug delivery rely onthe chain-like nature of polymers.

• The pharmaceutical applications of polymers rangefrom their use as binders in tablets to viscosity andflow controlling agents in liquids, suspensions andemulsions.

• Polymers can be used as film coatings to disguise theunpleasant taste of a drug, to enhance drug stabilityand to modify drug release characteristics

• Pharmaceutical excipients

• Drug delivery

• Hydrogels

• Adhesive biomaterials

Pharmaceutical applications

• Coat tablets: Microcrystalline cellulose (MCC), sodium carboxyl

methylcellulose (NaCMC), hydroxypropylmethycellulose (HPMC),hydroxyethylcellulose (HEC), Hydroxypropylcellulose (HPC), PEG, povidone

• Binder: acacia, gelatin, sodium alginate, Microcrystalline cellulose

• Disintegrants: Starch, carboxymethylstarch, micro crystalline

cellulose, Na-carboxymethyl cellulose, cross linked pvp

• Plasticizer :PEG, propylyn glycol

• Thickening agents: xanthene gum (a natural gum polysaccharide

used as a food additive and rheology modifier )

• Suspending agents: acacia, tragacanth, ethylcellulose, gelatin

and sodium carboxymethylcellulose

Pharmaceutical excipients

Solid Dosage FormsTablets CapsulesFilm Coatings of Solid Dosage FormsDisperse SystemsGels

APPLICATIONS OF POLYMERS FOR CONVENTIONAL DOSAGE FORMS

Applications of polymers in Medical

COMMERCIAL SUTURES

PROSTHETIC ORGANS

SILICON IMPLANTS

ARTIFICIAL SKIN

In Packaging

• Container

• Bottles

• Closers

• Blisters

Criteria Categories Examples

Source Semi-natural/natural

Synthetic

Agarose, chitosan, gelatinHyaluronic acidVarious gums (guar, hakea, xanthan, gellan, carragenan, pectin, and sodiumalginate)Cellulose derivatives[CMC, thiolated CMC, sodium CMC, HEC, HPC, HPMC, MC,methylhydroxyethylcellulose]Poly(acrylic acid)-based polymers[CP, PC, PAA, polyacrylates, poly(methylvinylether-co-methacrylic acid),poly(2-hydroxyethyl methacrylate), poly(acrylic acid-co-ethylhexylacrylate),poly(methacrylate), poly(alkylcyanoacrylate), poly(isohexylcyanoacrylate),poly(isobutylcyanoacrylate), copolymer of acrylic acid and PEG]OthersPoly(N-2-hydroxypropyl methacrylamide) (PHPMAm), polyoxyethylene,PVA, PVP, thiolated polymers

polymers used in oral drug delivery

Aqueoussolubility

Charge

Potentialbioadhesive

forces

Water-soluble

Water-insoluble

Cationic

Anionic

Non-ionic

Covalent

Hydrogen bond

Electrostaticinteraction

CP, HEC, HPC (waterb38 8C), HPMC (cold water), PAA, sodium CMC,sodium alginateChitosan (soluble in dilute aqueous acids), EC, PC

Aminodextran, chitosan, dimethylaminoethyl (DEAE)-dextran, trimethylated chitosanChitosan-EDTA, CP, CMC, pectin, PAA, PC, sodium alginate, sodium CMC,xanthan gumHydroxyethyl starch, HPC, poly(ethylene oxide), PVA, PVP, scleroglucan

Cyanoacrylate

Acrylates [hydroxylated methacrylate, poly(methacrylic acid)], CP, PC, PVA

Chitosan

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To mask the taste, odor, color of the drug. To provide physical and chemical protection for the

drug. To control the release of the drug from the tablet. To protect the drug from the gastric environment of

the stomach with an acid resistant enteric coating. To incorporate another drug or formula adjuvant in

the coating to avoid chemical incompatibilities or to provide sequential drug release.

To improve the pharmaceutical elegance by use of special colors and contrasting

Tablet Coating Applications:

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• To enhance the solubility of poorly soluble drugs solid dispersion is prepare by using water soluble polymers

Examples:

• Poly ethylene glycols (PEG)

• Poly vinyl alcohol (PVA)

• Poly vinyl pyrrolidone (PVP)

• Mannitol etc…….

Disperse system

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The polymeric capsules and hollow particles can be prepared from either monomeric starting materials or from oligomers and preformed polymers.

Mostly, the process involves a disperse oil phase in an aqueous continuous phase.

The precipitation of polymeric materials at the oil-water interface causes each oil droplet to be enclosed within polymer shell.

Capsules

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The interfacial polycondensation is used to prepare :

poly(urea), poly(amide), or poly(ester) capsules by reaction between an oil-soluble monomer and water soluble monomers

Vinyl polymers such as polystyrene, acrylates and methacrylates have been used to prepare hollow or capsule polymer particles

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• Highly swollen hydro gels:

– cellulose derivatives

– poly(vinyl alcohol)

– poly(N-vinyl 2-pyrrolidone), PNVP

– poly(ethylene glycol)

• Moderately or poorly swollen hydro gels:

- poly(hydroxyethyl methacrylate), PHEMA and derivatives

• One may copolymerize a highly hydrophilic monomer with other less hydrophilic monomers to achieve desired swelling properties

Hydrogels

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PLGA microparticles

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• Over the last two decades more than 35 transdermal patch products have been approved globaly.

• Prescriptions for transdermal products have been used by ~12 million people worldwide for ailments ranging from bladder control to heart disease

Transdermal Drug Product

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Passive :• Matrix (Oxytrol, Vivelle Dot)• Reservior (Androderm, Duragesic)Active :• Iontophoresis• Electroporation• Sonophoresis• Heat or thermal energy• Microneedles

Transdermal Drug Delivery

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Matrix Transdermal Systems

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Reservoir System Design

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BIODEGRADABLE POLYMERS

Definition :

Biodegradable polymers are defined as polymerscomprised of monomers linked to one another throughfunctional groups and have unstable links in the backbone.

• They slowly disappear from the site of administration inresponse to a chemical reaction such as hydrolysis.

• Material progressively releasing dissolved or dispersed drug,with ability of functioning for a temporary period andsubsequently degrade in the biological fluids under a controlledmechanism, in to product easily eliminated in body metabolismpathway.

ADVANTAGES

• Localized delivery of drug

• Sustained delivery of drug

• Stabilization of drug

• Decrease in dosing frequency

• Reduce side effects

• Improved patient compliance

• Controllable degradation rate

BIODEGRADATION

ENZYMATIC

DEGRADATION COMBINATIONHYDROLYSIS

BULK EROSIONSURFACE EROSION

MECHANISM OF BIODEGRADABLE POLYMERS

Factors Influencing Biodegradation CHEMICAL STRUCTURE

(a) Functional Group

(b) Hydrophobicity

MORPHOLOGY

(a) Crosslink density

PARTICLE SIZE

TYPES OF BIODEGRADABLE POLYMERS POLY ESTERS

POLY PHOSPHO ESTERS

POLY ANHYDRIDES

POLY OLEFINS

POLY AMIDES

Pre Requisites of Bio degradable Polymers

BIO COMPATABILITY

MECHANICAL STRENGTH

STABILITY

BIO RESORBIBILITY

INERT

Biodegradation : It is the process of chain cleavage, Found out bychange in Mol.wt.

Bioerosion : It is the sum of all process, leading to los of mass froma polymer matrix.

Note : Hydrophobic polymers have to undergo degradation beforeErosion takes place.

Synthetic polymers used in pharmacy

Carboxypolymethylene (Carbomer, Carbopol):• It is a high-molecular-weight polymer of acrylic acid,

containing a high proportion of carboxyl groups

• It is used as a suspending agent in pharmaceutical

preparations, as a binding agent in tablets, and in the

formulation of prolonged-acting tablets.

Cellulose derivatives:Methylcellulose: It is slowly soluble in water.

• Low-viscosity grades are used as emulsifiers for liquid

paraffin and other mineral oils. High-viscosity grades are

used as thickening agents for medicated jellies and as

dispersing and thickening agents in suspensions.

Hydroxypropylmethylcellulose (hypromellose)

• It forms a viscous colloidal solution and is used in ophthalmic solutions to

prolong the action of medicated eye drops and is employed as an artificial tear

fluid.

• Ethylhydroxyethylcellulose

It is an ether of cellulose with both ethyl and hydroxyethyl substituents

attached via ether linkages to the anhydroglucose rings. It swells in water to

form a clear viscous colloidal solution.

• Ethylmethylcellulose

– contains ethyl and methyl groups, a 4% solution having approximately the

same viscosity as acacia mucilage.

• Hydroxyethylcellulose

– is soluble in hot and cold water but does not gel. It has been used in

ophthalmic solutions. More widely used for the latter, however, is

hydroxypropylmethylcellulose (hypromellose) which is a mixed ether of

cellulose containing 27–30% of –OCH3 groups and 4–7.5% of –OC3H6OH

groups. It forms a viscous colloidal solution. There are various

pharmaceutical grades.

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Polymer Characterization

The characterization of a polymer requires several parameters which

need to be specified. This is because a polymer actually consists of a

statistical distribution of chains of varying lengths, and each chain

consists of monomer residues which affect its properties.

A variety of lab techniques are used to determine the properties of

polymers. Techniques such as wide angle X-ray scattering, small angle

X-ray scattering, and small angle neutron scattering are used to

determine the crystalline structure of polymers. Gel permeation

chromatography is used to determine the number average molecular

weight, weight average molecular weight, and polydispersity. FTIR and

NMR can be used to determine composition. Thermal properties such as

the glass transition temperature and melting point can be determined by

differential scanning calorimetry and dynamic mechanical analysis.

Pyrolysis followed by analysis of the fragments is one more technique for

determining the possible structure of the polymer.

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Biocompatible evaluation techniques

i. Cytotoxic Testing

The degree of cytotoxicity is determined by two means

• Qualitative examination views cells microscopically for

change in general morphology, detachment or cell

lyses/membrane.

• Quantative evaluation measurement of cell death,inhibition of

cell growth,cell proliferation or colony formation.

ii. Homocompatibility

It is defined as the ability of the materials to coexist with blood

without producing any toxicity, coagulation effects or

complement activation. Materials should therefore neither initiate

nor deactivate the processes involved in and associated with

blood coagulation nor interfere with platelet morphology and

function.