Polymers

What is a polymer?

A large molecule (macromolecule) composed of repeating structural units connected by covalent bonds (can be natural or synthetic)

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What are the four main differences between polymers and small molecules?

State of matter, dissolution, solution properties and mechanical properties

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What is dissolution?

A substance which forms a solution (solute dissolved in solvent)

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What is the difference between small molecules and polymers in terms of state of matter?

Small molecules can take the form of a solid, liquid or gas. Polymers can only take the form of solid or liquid (gas molecules are too large to form polymers)

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What is the difference between small molecules and polymers in terms of dissolution?

Small molecules undergo a faster rate of dissolution compared to polymers (first stage of polymers dissolution - swelling)

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What is the difference between small molecules and polymers in terms of solution viscosity?

Small molecules have a low Mw (low viscosity) but polymers have a high Mw (high viscosity) at the same concentration

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What is the difference between small molecules and polymers in terms of mechanical properties?

Polymers have more elasticity - application of pressure/stress causes expansion but retains original form (reversible deformation)

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What is a monomer?

Units which make up a long chain polymer molecule

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What is an oligomer?

Substances with short chains containing relative few monomers

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What is an elementary unit?

The repeating unit in the polymer chain

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What is an end (terminal) group?

Units at the end of polymer chains (used for detection in techniques e.g. MS)

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How do you calculate the molecular weight of a polymer?

Mw of polymer = Mw of repeating unit x degree of polymerisation

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What is the degree of polydiversity?

Mw/Mn, Mw > Mn if polymer is polydisperse (monodisperse = 1)

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What is configuration?

The order (determined by chemical bonds). The configuration of a polymer cannot be altered unless chemical bonds are broken or reformed

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What are homopolymers?

Polymers in which all the monomeric units are identical

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What are copolymers?

Polymers consisting of more than one type of monomer

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What is molecular mass?

How much a substance weighs (depends on polymer chain length)

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What does the polydiversity index show?

How broad the Mw distribution is (polydispersed/monodispersed, normal distribution/straight line)

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How is the number average molecular mass determined?

By using MS (MALDI-TOF) or osmotic pressure measurements

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How do you calculate the number average molecular mass?

Sum of moles of Mw x mass of fragments / sum of fragments (normal distribution)

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How is the weight average molecular weight determined?

By light scattering and ultracentrifugation (biased towards larger molecules)

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How do you calculate the weight average molecular weight?

Sum of moles x (mass)^2 / sum of moles x mass

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Describe the nomenclature of synthetic polymers?

Polymer name = poly(monomer name)

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What are the types of copolymers (4)?

Statistical (random) copolymers, alternating copolymers, block copolymers, graft copolymers (drug interaction)

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Give examples of copolymers

Statistical copolymer of sytrene and methylmethacrylate. Alternating copolymer of styrene and methylmethacrylate

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Give examples of molecular architecture (6)

Linear, branched, ladder, star, dendrimer and cross-linked

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Give examples of natural polymers (3)

Proteins (BSA), polynucleotides (DNA), polysaccharides (cellulose, starch)

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Give examples of synthetic polymers (2)

Thermoplastic (polystyrene/polyethylene, polycarbonate), thermosetting (phenolformaldehyde)

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What is a thermoplastic?

A material that is plastic or deformable, melts to a liquid when heated and freezes to a brittle, glassy state when cooled sufficiently

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What is a thermosetting plastic?

Polymer materials that cure, through the addition of energy to a stronger form

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Give examples of important synthetic polymers

Polyethylene, polypropylene, polystyrene, polytetrafluoroethylene (Teflon), polymethylmethacrylate, polyethyleneterephtalate

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Give examples of important synthetic polymers in pharmacy

Polylactic acid, polyethylene glycol, polyvinylpyrrolidine

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Give examples of important natural polymers

Collagen, chitosan, sodium alginate, cellulose, methylcellulose

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The properties of polymers depend on which factors (3)?

Chemical identity, molecular weight, type of monomers (synthetic polymers can be designed to produced desired properties, natural polymers can be chemically modified)

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What are the physical phases in polymers?

Crystalline (ordered) and amorphous region (disordered). Amorphorous - no long range order, state depends on temperature and Mw, rigid, glassy, rubber is flexible (bond rotations)

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Describe the diagram for polymer phase behaviour

Changes from mobile liquid, crystalline solid, viscous liquid, partially crystalline, tough plastic, rubber

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Give examples of polymers and the solvents

Microspheres/capsules in solution (good/poor solvent/micellar aggregate). Hydrogel and microgel in gel state. Solid state includes amorphous/crystalline regions

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Give the features of a water soluble polymer (7)

Increase viscosity of solvents, swell in solution, absorb at surfaces, form gels, form films, stabilise drug formulations, control release

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Give features of an insoluble polymer (6)

Form films, film coating materials, surgical dressings, membranes for dialysis or filtration, matrices to envelop drugs, packaging materials

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Describe the stages of dissolution

Diffusion of solvent molecules into polymer, swollen gel and dissolution of gel

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Is the dissolution process for a polymer more complex than small chemical entities?

Yes

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What are the factors that affect the solubility of polymers (4)?

Polymer-solvent interactions (chemical nature), presence of cross-links/strong intramolecular interactions, Mw of macromolecules, temperature

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How do cross-links in a polymer affect dissolution?

If there are cross-links, dissolution does not take place

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How do polymer-solvent interactions affect solubility?

Strong polymer-solvent interactions (good affinity) favour solubility (polar polymers are soluble in polar solvents, non-polar polymers in non-polar solvents)

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Give examples for the conformation of macromolecules in solution

Globule, ramdom coil, rigid rod and helix

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What does conformation depend on?

Chain flexibility and polymer-solvent interactions

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Do covalently cross-linked polymers dissolve?

No (crystallinity and strong intramolecular interactions act as physical cross-links/unfavourable for polymer solubility)

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Give examples of hydrophilic substituents

OCH3, NO2, CHO, COOH, NH2, COO-, NH3+, OH (hydrophobic - alkane chains)

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Give examples of fully hydrophobic polymers which become water soluble polymers

PMMA, PMA, PHEMA, PHEA

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Give examples of synthetic water soluble non-ionic polymers

PEO/PEG, PVA, PAAM, PVP, PEG-PPG-PEG

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What is done to cellulose to make it water soluble?

Add hydrophobic groups (breaks H bonding between chains) - cellulose ethers e.g. MC, HEC, HPC, HPMC, NaCMC

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Describe features of dextran

Water soluble non-ionic polysaccharide, soluble in cold and hot water, used as volume expander to treat hypovolemia (decreased blood volume)

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Describe features of starch

Water soluble non-ionic polysaccharide, native starches are mixtures of branched/unbranched derivates, dissolved in water upon heating, used in tablets as filler, disintegrant, binder

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What are polyelectrolytes?

Polymers which have ionisable functionable groups (charged groups) eg. cationic (polybases), anionic (polyacids), amphoteric (polyampholytes)

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Give examples of cationic polyelectrolytes

Chitosan/PEI (weak), Poly(') ethyltrimethylammonium chloride (strong) - protonation of chitosan (insoluble to soluble in water)

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Give examples of anionic polyelectrolytes

Polyacrylic acid/polymethacrylic acid (weak), heparin (strong) - (ionisation of polyacrylic acid)

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Give examples of polyampholytes

Synthetic polyampholyte (copolymer), carboxymethylchistosan, gelatin, proteins (BSA)

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What is viscosity?

The measure of a material's resistance to flow. It is a result of the internal friction of the material's molecules

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What is relative viscosity?

Viscosity of solute compared to solvent (equation). Viscosity with respect to the solvent

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What is specific viscosity?

Relative viscosity -1 (take off solvent from solute before dividing by solvent).

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What is reduced viscosity?

Applies to ideal systems (colloids, volume fraction), relationship between specific viscosity and concentration is not constant. Specific viscosity divided (reduced) by concentration C

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By plotting reduced viscosity vs concentration, we get an estimate of what?

k1 ~ [n] (use of Huggins constant) - gives a relationship between volume and concentration e.g. information on how big the molecule is

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What is intrinsic viscosity?

A characteristic of the material obtained by plotting the reduced viscosity as a function of concentration and extrapolating at a concentration of zero

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How is the relative viscosity of Newtonium liquids measured?

Measuring the flow time of polymer solution against the flow of solvent

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What can be intrinsic viscosity be used to estimate?

The Mw and shape (Mark-Houwink equation, [n] = KM^alpha)

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What does an alpha value of 0.5 indicate?

Flexible polymer chain in 'ideal' solvent

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What does an alpha value between 0.5 and 0.8 indicate?

Flexible polymer chain in 'good' solvent

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What does an alpha value > 0.8 indicate?

'Stiff' chain

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The value of alpha gives information about what?

The conformation of the polymer

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What is a hydrogel?

A 3D cross-linked network of a hydrophilic polymer which is able to swell and retain significant amounts of water

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What are the features of a hydrogel (3)?

~90% is water, soft/wet/porous material, similar to living tissue (scaffold for tissue regeneration)

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How do you calculate the degree of swelling for a hydrogel?

(m of swollen sample - m of dry sample) / m of dry sample, graph has linear increase which levels off due to equilibrium being reached

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What are the types of stimuli-response hydrogels (5)?

Temperature, pH/ionic strength, electric field, light, additives (graph for pH for anionic hydrogels/broad sigmoid shape due to swelling/shrinking)

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What is a type I gel?

Chemically cross linked, irreversible covalent bonds. Polymer swells when in presence of solvent. Swelling decreases as degree of cross linking increases and depends on solvent-polymer interactions

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What are the uses of type I gels (4)?

Matrix for drug release, soft contact lenses (polyglycol dimethacrylate), expanding implants (hydrophilic polyglycol methadrylates loaded with drug/implanted into cavities in dry state/ swell), surgical dressings/nappies/laxatives (carbs/cellulose d)

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What are type II gels?

Physically cross linked due to chain entanglement and intermolecular bonding (electrostatic attraction forces, H bonding/hydrophobic interactions. Reversible. Can be formed by changing temperature/pH/adding salts (e.g gelatin)

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What are the uses of type II gels (2)?

In-situ gelling injectable formulation, poly(vinyl alcohol) gels: application of drugs to skin (upon drying, leaves a plastic film)

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Give examples of physical gels (3)?

Sodium alginate (divalent ions, Ca) for dressings, pluronics for micelles, gelatin (natural/from degradation of collagen/colourless gel on cooling/used in food industry, drug delivery, tissue engineering). Junction zones

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What can polymers do for pharmacy (9)?

Solubilise drugs, protect drugs, improve physio-chemical stability, adhere to biosurfaces, increase viscosity of solutions, form films/patches/depots, control release kinetics, target specific site, can be drugs themselves

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What are the pharmaceutical uses of polymers (4)?

Conventional dosage forms, controlled release by the oral route, adhesive polymer for skin delivery, controlled delivery through parenteral administration

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Describe the features of conventional dosage forms in tabletting (4)

Diluents (e.g. starch), binder (in wet granulation technique to provide cohesiveness/agglutinates particles to form grains that are easily compressed), disintegrant, lubricant to reduce friction between power and die wall (compression/ejection)

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Describe the features of conventional dosage forms in semi-solid preparations (2)

Thickeners, suspending agents (e.g. gels, creams, ointments, lotions, suspensions/syrup). Semi-synthetic cellulose ethers, carbomers, Carbopol etc

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Describe the features of controlled release by the oral route (5)

Control drug release profile, enhance patient compliance, extend lifecycle of a drug, target specific locations, minimise toxic effects. Matrix/used of reservoir. E.g. of formulation - microspheres.

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Describe insoluble polymers in matrices formulations

Matrix formed by tabletting or hot melt extrusion. Inertness - drug release governed by diffusion (e.g. polyalkylmethacrylates)

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Describe soluble polymers in matrices formulations

Matrix swollen by polymer, drug dissolves, further diffusion or matrix dissolved in GI tract and eroded (e.g. cellulose ethers - MC, HPMC)

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What is localised delivery (2)?

pH-dependent release (delivery in intestine), azopolymers target the colon (diazoic bond cleaved by enzymes present in colon bacterial flora)

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Describe the features for bioadhesive polymers in the controlled release for mucosal delivery (3)

Prolong activity, enhance permeation of a drug (better systemic delivery), protect drug from pH/enzymatic activity

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What are the routes of administration for bioadhesive polymers (6)?

Oral, buccal, vaginal, ocular, nasal, pulmonary (e.g. polyacrylic acid, PVP, PVA. cellulosic ethers, chitosan)

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Give examples of adhesive polymers for the skin (4)

Pressure sensitive adhesives (PSA), wound coverings, surgical drapes and transdermal delivery

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What is the glass transition temperature for adhesive polymers for the skin?

~ -20 to -60 degress Celsius (soft materials)

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What are the requirements for adhesive polymers for the skin (6)?

Adhere easily, be removable without pain/skin damage/residue, not irritating to skin, protects against loss of fluids, absorbs wound excretions, not allergenic

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What polymers are used in adhesive polymers for the skin (4)?

Natural rubber, poly(isobutene) (Vistanex), poly (acrylates), silicones

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What are the requirements for polymer implants for the controlled release by parenteral route (5)?

Biocompatible/non-toxic, easily delivered (liquid/soft), biodegradable, encapsulate drug/efficiently control release, specific mechanical properties e.g. poly-alpha-hydroxyacids, polylatic acid, etc

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What are the motivations for polymer-drug conjugates for controlled release by parenteral route (5)?

Increase drug shelf-life, decrease toxicity, control of drug biodistribution (targeting), protection against degradation, prolonged retention in blood

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What is the Enhanced Permeation and Retention effect (EPR)?

Drugs conjugate to a polymer and can passively be distributed in favour of tumour tissue

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Describe the features of polymeric nanoparticles (NPs) in controlled released by parenteral route (5)

50-1000 nm (nanospheres/capsules), injected intravenously, diffuse through capillary vessels/mucosae, high specific SA for oral/lympathic/pulmonary/ocular/subcutaneous/intramuscular admin, avoid phagocytes uptake/steric stab prolong blood circulation

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What are biomaterials?

All materials used in medical devices in with contact with tissues of patient (important/guiding feature of their use and performance) e.g. hydrogels, implants, adhesives

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Give examples of uses for polymeric biomaterials (8)

Intraocular lens, contact lens, vascular grafts, hip/knee prostheses, catheters, pacemakers, renal dialyzers, ventricular assist devices

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Polymers

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