Polymers

Its all about polymers its classification, method of preparation, properties and applications.

1. P olymers Presented by Ms. Aboli Malokar M. Pharm (pharmaceutics) 1 st sem Dadasaheb balpande college of pharmacy

2. CONTENTS INTRODUCTION CLASSIFICATION METHOD OF PREPARATION PROPERTIES APPLICATIONS REFERENCES

3. DEFINATION Polymers also known as macromolecules, are very large molecules consisting of many repeating units called monomers (smaller molecules) and are formed by a process called polymerization.

4. HISTORY In 1845, the first semisynthetic polymer ever made was guncotton(cellulose nitrate) by Christian F. Schonbein . In 1872, Backelite a strong and durable synthetic polymer based on phenol and formaldehyde was invented. In 1933, polyethylene, 1935 polyamide, 1938 Teflon, 1942 synthetic rubber were invented .

5. INTRODUCTION Polymers are very large molecules made when hundreds of monomers join together to form long chain. The word ‘polymer’ comes from the Greek words poly means ‘many’ and mer means ‘parts ’. The monomers can be linked together in various ways to give rise to various types of polymers are linear polymer, branched polymer and three dimensional crosslinked polymer .

6. a) linear polymer b) branched polymer c) crosslinked or network polymer

7. A polymer is a macromolecule composed of either Many repeating units of one type (same monomer) i.e. homopolymer . Many repeating units of several types (different monomers) i.e. copolymer. -A-A-A-A-A-A-A-A-A-A- Homopolymer -A-B-A-B-A-B-A-B-A-B- Copolymer A - B – B – A – B – A – A Random copolymer A – B – A – B – A – B – A Alternating copolymer A – A – A – B – B – B Block copolymer

8. IDEAL CHARACTERISTICS Should be inert Should be compatible with environment Should be non toxic Easy and inexpensive to fabricate dosage form should be biodegradable and biocompatible It should provide good drug polymer linkage It should be versatile and posses a wide range of mechanical, physical and chemical property.

9. Classification of Polymers Based on source N atural S ynthetic Based on Chemical nature O rganic I norganic Based on Thermal behavior T hermoplastic T hermosetting Based on their ultimate forms Plastics Elastomers Fibres Liquid resins

10. Based on source Natural Polymers :- Polymers which are isolated from natural materials are called as natural polymers. E.g. :- Cotton, silk, wool, rubber Cellophane, cellulose rayon, leather are chemical modifications of natural polymers. The Cellulose is another natural polymer which is a main structural component of the plants. Cotton Rubber Wool Silk

11. Synthetic Polymers :- polymers which are synthesized from low molecular weight compounds are called synthetic polymer. E.g. :- Polyethylene, PVC, nylon, terylene P olyethylene T erylene Nylon PVC

12. Based on Chemical Nature Organic Polymers :-Polymers whose backbone chain essentially made of carbon atoms is termed an organic polymers. Organic polymers are derived either from petroleum or from plants, animals, microorganisms. Hence, they are generally accessible in large quantities and at nominal cost. The majority of synthetic polymers are organic. E.g. :- Cellulose, Proteins Inorganic Polymers :- The molecules of inorganic polymers contain no carbon atom in their chain backbone. E.g. :- Glass, S ilicone, Rubber

13. Based on Thermal Behaviour Thermoplastic Polymers :- Polymers that soften on heating and stiffen on cooling are termed as thermoplastic polymers. The process of heating, reshaping and retaining on cooling can be repeated several times. When frozen, thermoplastics becomes glass like and subject to fracture. Popular uses of thermoplastic polymers include the manufacture of pipes, ropes, belts. E.g. :- polyethylene, PVC, nylon, sealing wax

14. Thermosetting polymers :- These polymers undergo some chemical change on heating and convert themselves into an infusible and insoluble mass. Once set, cannot be reshaped E.g. :- Backelite , epoxy resin, polyesters

15. Based on their ultimate forms Plastics :- A polymer is shaped into hard and tough utility articles by the application of heat and pressure is used as plastic. E.g. :- polystyrene, PVC, Polymethyl methacrylate Elastomers :- When vulcanized into rubbery products exhibiting good strength and elongation, polymer are used as elastomers. E.g. :- Natural rubber, synthetic rubber, silicon rubber. Fibers :- When drawn into long filament-like materials, whose length is at least 100 times its diameter, are called as fibers. E.g. :- Nylon, terylene

16. Liquid resins :- Polymers used as adhesives, plotting compounds , sealants in liquid form are described as liquid resins E.g. :- Epoxy adhesives, polysulphide sealants

17. Biodegradable polymers Non-biodegradable polymers They are degraded in the body to the simple molecules like water and co2 which are easily eliminated in the urine Mainly used for parentral drug delivery system and can also be used for oral drug delivery system Examples :- Natural polymers like gelatin, collagen and synthetic polymers like polycaprolactone and polyethylene glycol. They are not degraded in the body Only for oral administration, they cannot be used for parentral drug delivery of drugs Examples :- Semi synthetic polymers like ethyl cellulose.

18. Method of preparation of polymers Bulk polymerization This polymerization carried out by adding a soluble initiator to pure monomer. The mixture is constantly agitated and heated to polymerization temperature. Once the reaction starts, heating is stopped as the reaction is exothermic. The heat generated is dissipated by circulating water jacket. Viscosity increases dramatically during conversion. The method is used for the polymerization of liquid state monomers. It is usually adopted to produce free radical polymerization of methyl methacrylate or styrene and also for vinyl chloride to get PVC resin.

19. Solution Polymerization This polymerization carried out by taking monomer along with initiator dissolved in solvent . The mixture is kept at polymerization temperature and constantly agitated. After the reaction is over, the polymer is used as such in the form of polymer solution or the polymer is isolated by evaporating the solvents. Polymer so formed can be used for surface coating. It is used for the production of polyacrylonitrile , block copolymers are also made exclusively by this technique.

20. Suspension Polymerization In this process monomer is dispersed in a dispersing medium. Initiators used are monomer soluble E.g. dibenzoyl peroxide. The dispersion is maintained by continuous agitation and the droplets are prevented to coalesce by adding suitable water soluble protective colloids, surface active agents and by stirring. polymerization occurs in the monomer droplets suspended in the dispersing medium and product formed being insoluble in water.

21. The product is separated out in the form of spherical pearls or beads of polymer. They can be used directly for some application or can be extruded and chopped to form large easily moulded pallets. This technique is used to form expandable polystyrene beads, styrene- divinyl benzene copolymer beads and polyvinyl acetate beads.

22. Emulsion polymerization This technique is used for the production of large number of platics and elastomers. The system consists of water soluble monomer, dispersion medium and emulsifying agents or surfactants. The monomer is dispersed in the aqueous phase, not as discrete droplets, but as a uniform emulsion. The size of monomer droplet is around 0.5 to10µm in diameter depending upon the polymerization temperature and rate of agitation. The emulsion of monomer in water is stabilized by a surfactant. A surfactant has a hydrophilic and hydrophobic end in its structure. When it is put into a water, the surfactant molecules gather together into aggregates called micelles.

23. The hydrocarbon tails (hydrophobic) orient inwards and head (hydrophilic) orient outwards into water. The monomer molecules diffuse from monomer droplets to water and from water to the hydrocarbon center of micelles This technique is used to produce polybutadiene , polychloroprene , polystyrene, acrylonitrile-butadiene-styrene terpolymer (ABS)

24. Polymer properties Molecular weight :- molecules within a given polymer mass will have different molecular weight. So that molecular weight of polymer are described in terms of average molecular weight. Polymer molecular weights can be defined in different ways, most common molecular weights are the number average molecular weight, Mn , the weight average molecular weight, Mw, and the viscosity average molecular weight, Mv .

25. The ratio of Mw/ Mn also known as the polydispersity index It indicated broadness of molecular weight distribution, and for Mw/ Mn = 1 the polymer is monodispersed i.e. all polymer molecules within a polymer mass have the same molecular weight.

26. Polymer hydrophobicity When a polymer is placed in an aqueous environment it will gradually absorb water, and the amount of absorb water is determined by the polymer structure. According to nature of polymer-water interaction, polymers can be classified into Hydrophobic polymer Hydrophilic polymer Water soluble polymer hydrogels

27. Glass transition temperature When a crystal melts, the polymer volume increases significantly as the solid turns to a liquid. The melting temperature(Tm) represents the first order thermal transition in polymers. The volume of an amorphous polymer gradually changes over a wide temperature range or so called glass transition temperature( Tg ). This behavior represents a second order thermal transition in polymers. At temperatures well below the ( Tg ) amorphous polymers are hard, stiff, and glassy. At temperature well above the Tg polymers are in the form of liquid or becomes rubbery.

28. Crystallinity Crystallinity is indication of amount of crystalline region in polymer with respect to amorphous content. With increased temperature, the crystal cells starts to melt and the whole polymer mass suddenly melts at a certain temperature Amorphous structure is formed due to either rapid cooling of a polymer melt in which crystallization is prevented. Polymer strength and stiffness increase with crystallinity . Crystallinity increases the barrier properties of a polymer packaging.

29. Pharmaceutical Applications Conventional dosage form Binder E.g. polyethylene, polyolefin Controlled release dosage form Transdermal patch E.g. polyethylene glycol Contraceptives E.g. medroxyprogesterone acetate- vaginal contraceptive ring It consists of a drug reservoir and polymer coating material. Through this layer the drug releases slowly.

30. Drug delivery and the treatment of diabetes Here the polymer will act as barrier between blood stream and insulin. E.g. polyacrylamide or N,N- dimethylaminoethylmethacrylate Application of polymers in solid dosage forms In Tablets Methyl cellulose, hydroxyl ethyl cellulose, hydroxyl ethyl methyl cellulose used as binders Cellulose derivatives used as coating materials CAP, hydroxyl propyl methyl cellulose phthalate, polyvinyl acetate phthalate are used as enteric coating material In capsule Gelatin a natural polymer which is the major ingredient in the manufacturing of capsules

31. Application of polymer in liquid dosage forms In suspension Acacia, tragacanth , cellulose derivative, xanthum gum are used as suspending agents They enhances dispersion of solids in liquids In emulsion Tragacanth , tweens are used as emulsifying agents Polymers can be used as film coating in tablets Hyaluronic acid is used in controlled release ophthalmic preperations Natural gums are used as thickening agents e.g. polyethylene glycol Some polymers are used as suppository bases e.g polyethylene glycol

32. References Gowariker V. R., Vishwanathan N. V., Sreedhar J., Polymer science, second edition, new age international publishers page no 6-14 Robinson J. R., Lee V. H. L, Controlled drug delivery systems, fundamentals and application, second edition, revised and expanded, page no. 152-155.