Introduction to polymers Definition, classifications, chemical/physical properties, some structures, applications Rheolo

1. Introduction to polymers Definition, classifications, chemical/physical properties, some structures, applications Rheology Viscosity, newtonian and non-newtonian flow, rheograms, application in pharmaceutics Colloids Lyophilic, lyophobic, association

2. Introduction to polymers Poly = many, mer = unit, many units Classification: Homochain polymers Heterchain polymers

3. Polymerization • Addition • Condensation Initiation: R-CO-O-O-CO-R  2 R-CO-O* R-CO-O* + H2C=CH-C6H5 R-CO-O-CH2-C*H-C6H5 Propagation: Mn-CH2-CHR* + H2C=CHR  Mn-CH2-CHR-CH2-CHR* Termination: Mn-1-CH2-CHR* + Mm-1-CH2-CHR*  Mn-1-CH2-CHR-CHR-CH2-Mm-1

4. Polymers • Homopolymers (A-A-A-A-A-A) • Copolymers -- Random copolymer A-A-B-A-B-B-B-A-A-B-A-B- -- Alternating copolymer A-B-A-B-A-B-A-B -- Block copolymer A-A-A-A-B-B-B-B-B-A-A-A

6. Types of polymers • Thermoplastics (material that is plastic or deformable, melts to a liquid when heated and freezes to a brittle, glassy state when cooled sufficiently), polystyrene, polyethylene • Thermosets (cannot be melted and remolded) phenolic resins, urea-formaldehyde resin • Elastomers Rubbers

7. Chemical, physical properties • Molecular weight: Number average Mw = ∑ Xi Mwi Weight average Mw = ∑ wi Mwi • Conformation of polymers dissolved in solutions (molecular interactions) -- Randomly coiled linear polymer -- Very dilute polymer solution -- Gel state of polymers (elastmers)

8. Intramolecular interactions

9. Diluted polymer solution and gel

10. Polymer blend Poly (Vinyl alcohol)-(vinyl pyrrolidone), PVA-PVP

11. Structures of selected polymers Sodium alginate Sodium carboxylmethycellulose methylcellulose Carbopol hydroxypropylmethylcellulose

12. Pharmaceutical applications • Pharmaceutical excipients • Drug delivery (PLGA microparticles) • Hydrogels • Adhesive biomaterials

13. Pharmaceutical excipients • Coat tablets: Microcrystalline cellulose (MCC), sodium carboxylmethylcellulose (NaCMC), hydroxypropylmethycellulose (HPMC), hydroxyethylcellulose (HEC), Hydroxypropylcellulose (HPC), PEG, povidone • Binder: acacia, gelatin, sodium alginate • Disintegrants: Starch, carboxymethylstarch, povidone • Plasticizer, PEG • Thickening agents: xanthan gum (a natural gum polysaccharide used as a food additive and rheology modifier )

14. PLGA microparticles

16. Prolonged release Leuprolide release from PLGA microparticles Treat endometeriosis Prostate cancer Treat growth deficiency

17. Rheology • Rheo = flow • Viscosity (h, poise) is an expression of the resistance of a fluid to flow (1 p = 0.1 Pa.s) • Fluidity (f) = 1/h • Newton’s theory

18. Newton’s theory • F’/A = h dn/dr; h = F/G; G = dn/dr = velocity gradient/rate of shear F = F’/A = shear stress • Rate of shear is directly proportional to shearing stress. • Kinematic viscosity = h/ ( is density) • Effect if temperature on viscosity h = A e EvRT (A is a constant, Ev is the activation energy required to initiate flow between molecules

19. Newtonian and non-newtonian systems

20. Rheograms of different fluids

21. Viscosity vs. Shear rate

22. Non-newtonian systems 1. Bingham plastic flow • does not begin to flow until a shear stress corresponding to the yield value is exceeded. • Flocculated colloid particles 2. Pseudoplastic flow • Typically exhibited by polymers in solution (tragacanth, sodium alginate, methylcellulose, NaCMC) • Viscosity decreases with the increase of shear rate/shear thinning • Caused by the re-alignment of polymer and/or the release of solvents associated with the polymers. • Dilatant flow • Volume increases when sheared • Shear-thickening • Suspension containing a high concentration of small, deflocculated particles

23. Thixothropy and anti-thixotropy

24. Thixotropy in formulation • Procaine benzylpenicillin • Procaine benzylpenicillin, also known as procaine penicillin, is a combination of benzylpenicillin with the local anaesthetic agent procaine. Following deep intramuscular injection, it is slowly absorbed into the circulation and hydrolysed to benzylpenicillin – thus it used used where prolonged low concentrations of benzylpenicillin are required. • This combination is aimed at reducing the pain and discomfort associated with a large intramuscular injection of penicillin. It is widely used in veterinary settings.

25. Colloids • a mixture in which one substance is divided into minute particles (called colloidal particles) and dispersed throughout a second substance. • Size: 1 nm to 0.5 mm • Visible under electron microscope • Not resolved by ordinary microscope • Do not pass through semipermeable membrane

26. Type of colloid systems 1. Lyophilic colloids (solvent-loving) • Systems containing colloidal particles that interact to an appreciable extend with the dispersion medium. • Acacia in water or celluloid in amyl acetate lead o the formation of a sol. • Solvation, hydration, hydrophilic sols (gelatin, acacia, insulin, albumin in water), lipophilic sols (rubber, polystyrene in non-aqueous solvents) • Lyophobic colloids (solvent-hating) • Colloids are composed of materials that have little attraction, if any, for the dispersion medium. • No solvent sheath around the particles • Gold, silver, arsenous sulfide, silver oxide in water 3. Association colloids

28. Classification of colloids