Polymers 2

Flashcards about polymers in pharmacy

What factors affect the solubility of polymers?

Polymer-solvent interactions

Presence of cross-links or strong intramolecular interactions

Molecular weight of macromolecules

Temperature.

What generally happens when a cross-linked polymer is exposed to water?

The polymer hydrates, swells, resulting in a gel structure that immobilizes water.

What is the first step when a cross-linked polymer absorbs water?

Water Penetration

What happens during the 'swelling' phase of a cross-linked polymer in water?

Chains expand but can't separate due to cross-links.

How do polymer-solvent interactions affect solubility?

Chemical similarity between the polymer and the solvent is important for solubility. Polar polymers dissolve in polar solvents, non-polar polymers in non-polar solvents.

What happens to covalently cross-linked polymers when placed in a solvent?

Covalently cross-linked polymers do not dissolve.

How do crystallinity and strong intramolecular interactions affect polymer solubility?

Act as physical cross-links and are unfavorable for polymer solubility

Give examples of hydrophobic substituent groups.

-CH3, -CH2-, C6H5- , -Cl, -F, -Br, -OCH2CH3 , -N(CH3)2

Give examples of slightly hydrophilic substituent groups.

-OCH3, -NO2 , -CHO

Give examples of hydrophilic substituent groups.

-COOH, -NH2

Give examples of very hydrophilic substituent groups.

-COO- , -NH3 + , -OH

What are the properties of Poly(methylmethacrylate) (PMMA)?

Very hydrophobic and insoluble in water

What are the properties of Poly(methyl acrylate) (PMA)?

Hydrophobic and insoluble in water

What are the properties of Poly(2-hydroxyethyl methacrylate) (PHEMA)?

Hydrophilic and swells in water

What are the properties of Poly(2-hydroxyethyl acrylate) (PHEA)?

Very hydrophilic and soluble in water

Give an example of an important synthetic water-soluble non-ionic polymer.

Poly(ethylene oxide) or Poly(ethylene glycol) (PEO or PEG)

What are the properties ofPoly(ethylene oxide) or Poly(ethylene glycol) (PEO or PEG)?

Extremely hydrophilic; forms hydrogen bonds with water

Give an example of an important synthetic water-soluble non-ionic polymer.

Poly(vinyl alcohol) (PVA)

Give an example of an important synthetic water-soluble non-ionic polymer.

Poly(acrylamide) (PAAM)

Give an example of an important synthetic water-soluble non-ionic polymer.

Poly(N-vinyl pyrrolidone) (PVP)

Give an example of an important synthetic water-soluble non-ionic polymer.

Pluronics (block-copolymers of polyethylene glycol and polypropylene glycol) (PEG-PPG-PEG)

What causes cellulose to be insoluble in water?

The presence of crystalline domains and strong intermolecular hydrogen bonding

How does interchain hydrogen bonding contribute to cellulose's insolubility?

-OH groups form strong H-bonds between adjacent chains, creating rigid, crystalline regions.

What should be done to cellulose to make it water-soluble?

Replace -OH with -OCH₃ (hydrophobic).

How does adding -OCH₃ groups to cellulose increase water solubility?

Disrupts H-bonding, increasing water solubility despite being a hydrophobic modification.

What are some uses of methylcellulose (MC)?

Tablet binder and food thickener.

Why is native cellulose insoluble?

Native cellulose’s -OH groups form strong H-bond networks causing insolubility.

How does adding hydrophobic groups (e.g., -OCH₃) to cellulose increase water solubility?

Adding hydrophobic groups (e.g., -OCH₃) disrupts this order, increasing water solubility

How do hydrophobic modifcations increase solubility?

Breaks Crytallinity by disrupting the hydrogen bond network.

Name another water-soluble cellulose ether.

Sodium carboxymethylcellulose (NaCMC)

Give examples of water-soluble non-ionic polysaccharides.

Dextran and Starch

What are the properties of Dextran?

Soluble in cold and hot water, used as volume expander to treat hypovolemia (= decreased blood volume)

What are the properties of Starch?

Dissolves in water upon heating. Used in tablets as filler, disintegrant, binder.

What is viscosity?

The measure of a material's resistance to flow.

Why do polymers increase viscosity?

Long polymer chains physically tangle, creating internal friction.

How does molecular weight affect viscosity?

Higher molecular weight (MW) = more entanglements = thicker solutions.

How does increasing viscosity impact drug suspensions?

Decreases the rate of sedimentation, maintaining dose uniformity

What factors generally increase viscosity?

The higher the concentration, branching, or molecular weight, the higher the viscosity.

What are hydrogels?

Hydrogels are three-dimensionally cross-linked networks of a hydrophilic polymer, which are able to swell and retain significant amounts of water.

Describe Type I gels.

Chemically cross-linked with covalent bonds and irreversible. Swelling decreases as degree of cross-linking increases and depends on solvent-polymer interactions.

What are the applications of Type I gels?

Used as matrix for drug release, soft contact lenses, expanding implants, and surgical dressings.

Describe Type II gels.

Physically cross-linked due to chain entanglement, electrostatic attraction forces, hydrogen bonds or hydrophobic interactions. These gels are usually reversible.

Give examples of Type II gels.

Gelatin, Methylcellulose, and Pluronic

How Type II gels be formed?

Changing the temperature, the pH or adding salts.

What are the uses of Type II gels?

in-situ gelling injectable formulations and poly(vinyl alcohol) gels applied to the skin form a plastic film upon drying.

Give an example of physical gels.

Sodium alginate

How does alginate form a gel?

Divalent Ions (Ca²⁺, Mg²⁺) bridge alginate chains by binding to -COO⁻ groups forming a 3D 'egg-box' structure.

How isalginate gel reversed?

Gel dissolves if ions are removed (e.g., by chelators like EDTA).

What is the mechanism of Pluronics gelation?

Increases (at high concentration of polymer), PEO blocks dehydrate and “connect” with PEO groups from other micelles, forming a long-range order “macro” crystal or lattice.

What happens when gelatin cools?

Forms a colorless, transparent gel upon cooling

What are the applications of Gelatin?

Food industry, drug delivery, tissue engineering

What is the purpose of triple helices at low temperatur in relation to gelatin?

They act as junction zonesfor the gel (= crosslinks)

What can polymers do for pharmacy?

solubilize drugs, protect drugs, improve physico-chemical stability, adhere to bio-surfaces, increase viscosity of solutions, form films, patches, depots, control release kinetics, target to specific site, and they can be drugs themselves!

Give pharmaceutical uses of polymers.

Tablets, semi-solid preparations, controlled release by the oral route, adhesive polymers for topical delivery and controlled delivery through parenteral administration

What is the purpose of tablets?

diluents, binder, disintegrant, lubricant

Give some examples of natural polymers.

Cellulose and derivatives

What are semi-solid preparations used for?

thickeners and suspending agents

List some benefits of controlled release.

control drug release profile, enhance patient compliance, extend lifecycle of a drug, target specific locations, minimise toxic effects

Name two types of controlled release.

Matrix, Reservoir

Describe Matrix Systems (Monolithic) Controlled release.

Drug is dispersed in a polymer matrix (e.g., PLGA, HPMC). Release via diffusion or erosion.

Describe Reservoir Systems (Membrane-Controlled) release.

Drug core surrounded by a polymer membrane (e.g., silicone, ethyl cellulose). Release via diffusion through membrane pores.

What forms a depot that releases the drug over the required time frame?

Combines drug (proteinor peptide) and a biodegradable polymer, delivered by injection.

What are the requirements for adhesive polymers for the skin?

adhere easily, be removable without pain/skin damage/residue, not irritating to the skin, protect against loss of fluids and Absorbs wound excretions

What are the benefits of bioadhesive polymers?

Extend drug activity, enhance permeationof the drug, protect drug from pH and enzymatic activity.

What are the routes of administration of bioadhesive polymers?

oral, buccal, vaginal, rectal, ocular, nasal

What are the characteristics of Polymeric nanoparticles (NPs)?

can be injected intravenously, can diffuse through capillary vessels and mucosae, very high specific surface area beneficial for oral, lymphatic, pulmonary routes and for ocular, subcutaneous and intramuscular administration

What are biomaterials?

Materials used in medical devices where there is a high contact with the tissues of the patient.