Introduction to polymersDefinition, classifications, chemical/physical properties, some structures, applications

RheologyViscosity, newtonian and non-newtonian flow, rheograms, application in pharmaceutics

ColloidsLyophilic, lyophobic, association

Introduction to polymersPoly = many, mer = unit, many units

Classification:

Homochain polymers

Heterchain polymers

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

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

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

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)

Intramolecular interactions

Diluted polymer solution and gel

Polymer blend

Poly (Vinyl alcohol)-(vinyl pyrrolidone), PVA-PVP

Sodium alginate

methylcellulose

Sodium carboxylmethycellulose

hydroxypropylmethylcellulose

Carbopol

Structures of selected polymers

Pharmaceutical applications

• Pharmaceutical excipients

• Drug delivery (PLGA microparticles)

• Hydrogels

• Adhesive biomaterials

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 )

PLGA microparticles

Prolonged release

Leuprolide release from PLGA microparticles

Treat endometeriosis

Prostate cancerTreat growth deficiency

Rheology

• Rheo = flow • Viscosity (poise) is an

expression of the resistance of a fluid to flow (1 p = 0.1 Pa.s)

• Fluidity () = 1/• Newton’s theory

Newton’s theory• F’/A = d/dr; = F/G; G = d/dr = velocity gradient/rate of shear F = F’/A = shear stress

• Rate of shear is directly proportional to shearing stress.

• Kinematic viscosity = / ( is density)

• Effect if temperature on viscosity = A e EvRT (A is a constant, Ev is the

activation energy required to initiate flow between molecules

Newtonian and non-newtonian systems

Rheograms of different fluids

Viscosity vs. Shear rate

Non-newtonian systems1. 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.

3. Dilatant flow• Volume increases when sheared• Shear-thickening• Suspension containing a high concentration of small, deflocculated particles

Thixothropy and anti-thixotropy

• 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.

Thixotropy in formulation

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 m

• Visible under electron microscope

• Not resolved by ordinary microscope

• Do not pass through semipermeable membrane

Type of colloid systems1. 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)

2. 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

Classification of colloids