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What is produced as a side product during the condensation polymerization of nylon?
What is produced as a side product during the condensation polymerization of nylon?
Bulk polymerization is the most complex technique for polymer synthesis.
Bulk polymerization is the most complex technique for polymer synthesis.
False
What kind of reaction is characterized by the fast growth of macroradicals?
What kind of reaction is characterized by the fast growth of macroradicals?
Addition reaction
The process of creating nylon involves the condensation polymerization of a diamine and a _____ chloride.
The process of creating nylon involves the condensation polymerization of a diamine and a _____ chloride.
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Match the following polymerization techniques with their characteristics:
Match the following polymerization techniques with their characteristics:
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Which polymerization technique results in lower yield and requires a solvent removal step?
Which polymerization technique results in lower yield and requires a solvent removal step?
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Dispersion polymerization requires the use of only one phase.
Dispersion polymerization requires the use of only one phase.
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What limitation is associated with bulk polymerization?
What limitation is associated with bulk polymerization?
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What are the two main factors that control the nature of the dispersion system?
What are the two main factors that control the nature of the dispersion system?
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Copolymers can only be formed from monomers with different reactivities.
Copolymers can only be formed from monomers with different reactivities.
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What is the term used for a polymer made from a single type of monomer?
What is the term used for a polymer made from a single type of monomer?
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A polymer blend can change its properties by mixing one or two different _______ in a molten or solution state.
A polymer blend can change its properties by mixing one or two different _______ in a molten or solution state.
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Match the following terms with their definitions:
Match the following terms with their definitions:
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Which type of copolymer is formed when one monomer is added preferentially to another?
Which type of copolymer is formed when one monomer is added preferentially to another?
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Pluronic surfactants are composed solely of ethylene oxide.
Pluronic surfactants are composed solely of ethylene oxide.
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What is the role of a surfactant in dispersion polymerization?
What is the role of a surfactant in dispersion polymerization?
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Which type of polymer is formed from cross-linking and cannot be reshaped after curing?
Which type of polymer is formed from cross-linking and cannot be reshaped after curing?
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Amorphous polymers display a sharp melting point.
Amorphous polymers display a sharp melting point.
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Name two examples of crystalline polymers mentioned in the content.
Name two examples of crystalline polymers mentioned in the content.
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Crystallinity increases the ______ properties of polymers, which is important for packaging.
Crystallinity increases the ______ properties of polymers, which is important for packaging.
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Match the following polymers with their respective melting ranges:
Match the following polymers with their respective melting ranges:
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Which statement correctly describes thermosets?
Which statement correctly describes thermosets?
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Small molecules like drugs can easily penetrate crystalline domains of a polymer.
Small molecules like drugs can easily penetrate crystalline domains of a polymer.
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What effect does increased crystallinity have on polymer strength?
What effect does increased crystallinity have on polymer strength?
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What effect do bulky side groups have on the glass transition temperature (Tg) of polymers?
What effect do bulky side groups have on the glass transition temperature (Tg) of polymers?
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Polar side groups decrease the glass transition temperature of polymers.
Polar side groups decrease the glass transition temperature of polymers.
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Name one factor that contributes to lowering the glass transition temperature (Tg) of a polymer.
Name one factor that contributes to lowering the glass transition temperature (Tg) of a polymer.
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Adding __________ to linear polymer chains limits chain movement and results in a higher Tg.
Adding __________ to linear polymer chains limits chain movement and results in a higher Tg.
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Match the type of molecular weight with its description:
Match the type of molecular weight with its description:
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Which of the following statements is true regarding plasticizers?
Which of the following statements is true regarding plasticizers?
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If all polymer chains in a sample are similar in size, then the number-average molecular weight (Mn) is equal to the weight-average molecular weight (Mw).
If all polymer chains in a sample are similar in size, then the number-average molecular weight (Mn) is equal to the weight-average molecular weight (Mw).
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What happens to the Tg of a plasticized polymer as the concentration of plasticizer increases?
What happens to the Tg of a plasticized polymer as the concentration of plasticizer increases?
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What does the area under the stress/strain curve represent?
What does the area under the stress/strain curve represent?
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Polymers only exhibit either elastic behavior or viscous behavior, never both.
Polymers only exhibit either elastic behavior or viscous behavior, never both.
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What is the significance of molecular weight in polymers?
What is the significance of molecular weight in polymers?
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Silicone rubber is an excellent candidate for _____ in biomedical applications.
Silicone rubber is an excellent candidate for _____ in biomedical applications.
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Match the following types of polymers with their characteristics:
Match the following types of polymers with their characteristics:
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Which of the following is a characteristic of elastic behavior in viscoelastic materials?
Which of the following is a characteristic of elastic behavior in viscoelastic materials?
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Elastomers have a Tg that is typically above room temperature.
Elastomers have a Tg that is typically above room temperature.
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What type of testing can evaluate the stress relaxation in polymers?
What type of testing can evaluate the stress relaxation in polymers?
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What type of interactions can cross-link hydrogels?
What type of interactions can cross-link hydrogels?
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Chemical gels can dissolve in water without breaking covalent cross-links.
Chemical gels can dissolve in water without breaking covalent cross-links.
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What is the primary driving force for swelling in ionic polymer structures?
What is the primary driving force for swelling in ionic polymer structures?
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Hydrogels are formed from __________ polymers that can swell rapidly in water.
Hydrogels are formed from __________ polymers that can swell rapidly in water.
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Match the following polymers with their characteristics:
Match the following polymers with their characteristics:
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Which of the following is a characteristic of physical gels?
Which of the following is a characteristic of physical gels?
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Hydrogels behave like elastic solids that can return to their original form after deformation.
Hydrogels behave like elastic solids that can return to their original form after deformation.
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The driving force for the swelling of nonionic polymer structures is __________ interactions.
The driving force for the swelling of nonionic polymer structures is __________ interactions.
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Study Notes
Introduction to Pharmaceutical Polymers
- Polymers are made of repeating units.
- Macromolecule refers to any large molecule, not necessarily made of repeating units.
- Polymers are a subset of macromolecules.
Monomers, Dimers, Trimers, Oligomers, and Polymers
- A monomer is a small molecule combining with others to form a polymer.
- If two, three, four, or five monomers are attached, the product is a dimer, trimer, tetramer, or pentamer, respectively.
- An oligomer contains 30 to 100 monomeric units.
- Products containing over 200 monomers are polymers.
- Polymers cannot exist as gases due to high molecular weight; they exist as liquids or solids.
Polymer Synthesis
- Monomers interact to form polymers.
- Polymerization mechanism is dependent on the monomer's structure.
Addition Polymerization
- Unsaturated monomers with double or pi bonds require low energy to break.
- Polymerization begins at the site of the double bond, with the addition of a free radical.
- Typically used for monomers with double bonds (ethylene-based) or sterically strained cyclic monomers.
- Fast, high MW chains are formed at the beginning of the reaction (e.g., Styrene and acrylic acid derivatives).
- Polymerization involves three steps:
- Initiation: Radical is transferred to monomer, forming a monomer radical.
- Propagation: Monomer radical attacks another monomer, creating macroradicals (repeating units).
- Termination: Macroradicals react with each other or an inert compound, stopping the chain reaction.
Condensation Polymerization
- Monomers without double bonds but with reactive functional groups (e.g., hydroxyl, carboxyl, or amines) interact via condensation.
- Slower, high MW polymer is formed near the end of polymerization when most of the monomer is depleted.
- Examples include nylon and polyester.
- A monomer containing reactive hydrogen from an amine residue can react with another monomer containing a reactive hydroxyl group to form an amide group and water.
Polymer Synthesis Techniques
- Bulk polymerization
- Solution polymerization
- Suspension and inverse suspension polymerization
- Emulsion and inverse emulsion polymerization (dispersed systems)
Bulk Polymerization
- Advantages: simplest technique, highest polymer purity, high yield, and easy polymer recovery.
- Requirements: only a monomer, a monomer-soluble initiator, and sometimes a chain-transfer agent to control the molecular weight.
- Limitations: removing residual monomer, heat dissipation, especially in free-radical polymerization.
- If the monomer is water-soluble, a linear water-soluble polymer is prepared.
- If the monomer is oil-soluble, a linear oil-soluble polymer is prepared.
Solution Polymerization
- To solve the problem of exothermic heat in bulk polymerization, polymerization is conducted in solution.
- Solvent (diluent) molecules reside between monomer molecules, reducing interactions between neighboring monomers.
- Less heat is generated in a given time period.
- Solvent should dissolve monomer and initiator, and have suitable melting and boiling points for the reaction conditions and solvent removal.
- Disadvantages include relatively low yield and the need for a solvent removal step.
Dispersion Polymerization
- Two incompatible phases (water and oil) are dispersed into each other.
- The active material (monomer) can be water-soluble or oil-soluble.
- The monomer (dispersed phase) is dispersed into the continuous phase using a surface-active agent (surfactant).
- Surfactant should be soluble in the continuous phase.
- Factors controlling the dispersion system: surfactant concentration and surface tension.
- Emulsion systems using water as a continuous phase are known as latex.
Copolymers and Polymer Blends
- Polymer systems can be physically blended or chemically reacted if one system cannot meet the needs of the application.
- Copolymerization: polymerization reaction involving more than one monomer type.
- Homopolymer: polymerization process using one monomer type (e.g., polyethylene).
- Monomer sequence can range from random to perfectly alternating; sequence determined by relative reactivities of monomers.
- Examples: Eudragit polymers
Copolymers (Continued)
- If two monomers have similar reactivities, the result is a random copolymer.
- If one monomer is preferentially added to another, the result is an alternate copolymer.
- When monomers preferentially add to themselves, a block copolymer is formed.
- A monomer and a polymer are generally used to make graft copolymers.
- Pluronic surfactants (EO-PO-EO terpolymers) are composed of block units of ethylene oxide and propylene oxides.
Copolymer Examples
- Illustrative diagrams showing different copolymer structures (homopolymer, random copolymer, alternate copolymer, block copolymer, and graft copolymer).
Polymer Blends
- Polymer properties can be changed by mixing or blending two different polymers in a molten or solution state.
- Examples include making thermoplastic polymers rigid with the addition of flexible polymers like rubber.
Interpenetrating Polymer Networks (IPNs)
- Semi-IPNs are prepared by dissolving one polymer into a solution of another monomer.
- An initiator and cross-linker are added, and the monomer polymerizes and becomes cross-linked in the presence of the dissolved polymer.
- The result is a structure where one cross-linked polymer interpenetrates the non-cross-linked polymer.
- In complete IPNs, two different monomers and their respective cross-linkers polymerize and cross-link simultaneously.
Polymer Topology
- Topology of a polymer describes its structure as linear, branched, or cross-linked.
- Topology affects polymer properties.
- Linear polymers have non-covalent (weak) intermolecular forces holding chains together.
- Linear polymers show dual behavior:
- Linear chains move freely, resulting in low melting temperature.
- Linear chains have a higher chance of approaching each other, increasing crystallinity and melting temperature.
Polymer Topology (Continued)
- Branched polymers have chains moving with difficulty due to steric hindrance; weaker intermolecular forces help them move freely.
- In cross-linked polymers, chains are chemically linked, restricted from movement depending on cross-linking level, resulting in very rigid structures.
Polymer Isomerism
- Structural isomerism: occurs when there are unsaturated sites along a polymer chain, leading to cis and trans isomers, differing in glass transition and melting temperatures.
- Sequence isomerism: monomers with pendant groups can attach in head-to-tail, head-to-head, or tail-to-tail conformation.
- Stereoisomerism: applies to polymers with chiral centers, presenting three different configurations (isotactic, syndiotactic, atactic) based on the position of pendant groups.
Thermoplastics
- Polymers with linear or branched structures.
- Can be reversibly refabricated and reshaped with heat (undergo melting).
- Are originally solids that can flow upon heat application.
- The process of melting and solidifying can be repeated indefinitely (e.g., polystyrene, polyethylene, polypropylene, PVC).
Thermosets
- Formed from cross-linked polymers (combination of a cross-linker and heat or combination of heat and internal functional group reaction).
- Resist thermal softening and cannot be reshaped.
- Their flow behavior is temperature-independent.
- No reversible melting and solidifying (e.g., epoxy, fiberglass).
Crystalline and Amorphous Polymers
- Polymers have varying thermal, physical, and mechanical properties depending on structure, molecular weight, linearity, and interactions.
- In linear polymers, chains pack regularly, creating crystalline lattice and exhibiting sharp melting temperatures.
- Irregular polymer structures lead to glassy or amorphous regions.
- Amorphous polymers soften over a wide temperature range.
Thermal Transitions
- When a crystal melts, polymer volume significantly increases due to the liquid state.
- Melting temperature (Tm) represents a first-order thermal transition.
- Amorphous polymers undergo broad, continuous changes (glass transition, Tg) over a wide temperature range, representing a second-order thermal transition.
- Differential scanning calorimetry (DSC) can detect Tm and Tg as endothermic peaks and baseline shifts, respectively.
Glass Transition Temperature (Tg)
- Tg is not an absolute property but is influenced by factors, affecting polymer chain movement.
- Below Tg, amorphous polymers are hard, stiff, and glassy.
- Above Tg, polymers are rubbery and flow more easily.
- Tg value in linear organic polymers ranges from about -100°C to above 300°C.
Glass Transition Temperature (Tg) (Continued)
- Tg is an important factor for solid dosage forms, such that a chewable dosage form needs to be soft and flexible at mouth temperature (37°C).
- This implies that polymers used for chewable matrices should have Tg close to 37°C.
- Example: Nicotine gum (Nicorette® gum)
Glass Transition Temperature (Tg) (Continued)
- Segmental motion in polymers is facilitated by free volume between polymer chains.
- Free volume increases with chain length and affects segmental movement and thus Tg.
- Longer end-to-end distances obtained if chains are longer and have more interactions with the solvent.
- Hydrophilic polymers are better dissolved in water; lipophilic polymers in organic solvents.
Factors Affecting Tg
- Chain length: Shorter chains, lower molecular weights result in less restriction and lower Tg.
- Side groups: Bulky side groups hinder motion, increasing Tg. Polar groups lead to stronger intermolecular forces, again increasing Tg.
- Chain Flexibility: more flexibility lowers Tg.
- Cross-linking: cross-linking limits chain movement, increasing Tg; highly cross-linked polymers have very high Tg values.
- Plasticizers: plasticizer molecules increase polymer chain entropy and mobility, lowering Tg.
Molecular Weight of Polymers
- Typical polymer batches have chains of different lengths and molecular weight distributions.
- Narrow molecular weight distributions are desired for mechanically strong polymers.
- Polymer molecular weight is expressed as an average due to chain variations.
- Number-average MW (Mn), weight-average MW (Mw), and viscosity-average MW are common methods for polymer weight expression.
- Polydispersity (PD): the ratio Mw/Mn; this value indicates how homogeneous/heterogeneous the polymer is with regard to molecular weight.
Mechanical Properties
- Polymer mechanical properties depend on structure, molecular weight, and intermolecular forces.
- Important properties include tensile strength, compressive strength, flexural strength, impact strength, and fatigue.
- Flexible polymers perform better under stretching, while rigid ones are better for compression.
- Some polymers do not have a breaking point; they deform and yield before breaking apart.
- Toughness relates to the energy needed to break the polymer (area under the stress-strain curve).
Viscoelastic Properties
- Polymers are viscoelastic, neither pure solids nor pure fluids; they store and dissipate energy (elastic and viscous behaviors).
- Examples include poly(vinyl chloride) (PVC), which behaves like a solid at temperatures below Tg (100°C) and like a fluid above.
- Viscoelasticity can be measured through creep tests (applied stress and deformation monitored over time) and stress relaxation tests (deformed polymer and observed stress decrease over time).
Varieties of Polymers-Rubbers
- Silicone rubber is a very inert rubber with low affinity to other materials.
- It is a good candidate for implants.
- Rubbers tend to be weak in their raw forms but can be crosslinked and cured under high pressure and temperature to improve strength.
- Tg of rubbery polymers (elastomers) are usually below room temperature.
Plastics
- Plastics generally have a Tg above room temperature.
- Plastics are manufactured through injection molding, extrusion, and thermoforming, requiring a molten state.
Plastics (Continued)
- Polymers like polyethylene, polypropylene, and polystyrene have only carbon in their backbone.
- Engineering plastics (polyesters, polyamides, and polyacetals) used in engineering applications resist impact, weather, and solvents and have high intermolecular forces, giving them high melting points.
Fibers
- Polymers used for fibers must have a crystalline structure with a sharp melting point—this allows them to be melt-spinnable.
- Examples of fiber-forming materials include cellulose acetate, rayon, polypropylene, nylon, polyesters, polyamides, and polyacrylonitrile.
Adhesives
- Polymers for adhesives need adhesive properties balancing cohesive forces (interaction within the material).
- Strength of adhesive forces (interaction with the second material) and cohesive forces (interaction within itself) increases with molecular weight due to increased interactions.
- Polar polymers adhere to polar surfaces (like dissolves like).
Coatings
- Coatings protect underlying materials from various environments (air, oxygen, water, stomach fluid, solvents).
- Examples include poly(vinyl acetate), acrylates, and ethyl cellulose.
Polymers as Rheology Modifiers
- Polymer chains coil when resting and extend when loaded.
- Increased solution viscosity is often desired; adding polymers to increase end-to-end chain distance under load is a common strategy.
- Loading of a polymer in dissolution/swelling processes depends on polymer interactions with solvents.
- Longer chains will interact more, creating greater viscosities.
- Hydrophilic polymers are excellent solvent candidates for water.
Hydrogels
- Hydrogels consist of hydrophilic polymers able to swell in water, holding large amounts of water.
- Cross-links (chemical bonds, cohesion forces) are important for maintaining hydrogel structure.
- Hydrogels behave like elastic solids, able to return to their original shapes after loading.
- Nonionic hydrogels rely on polymer-solvent interactions for swelling; ionic hydrogels rely on osmotic and electrostatic forces.
Chemical Gels
- Chemical gels are cross-linked by covalent bonds.
- Unlike physical gels, chemical gels do not readily dissolve in water or solvents unless the covalent cross-links are broken.
- Cross-linking via double bonds may be energetically favored compared to reactions between functional groups.
Physical Gels (Continued)
- Hydrogen bonding, hydrophobic interactions, and complexation are important methods in creating physical gels.
- Hydrogen bonding is important for some polymers (e.g., polyvinyl alcohol).
- Hydrophobic interactions play a role in thermoresponsive hydrogels (e.g., some cellulose derivatives).
- Complexation, e.g., alginate with chitosan, is also used to create gels, and the complex solubility is pH-dependent.
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Test your knowledge on polymer chemistry, specifically focusing on techniques like condensation polymerization, bulk polymerization, and dispersion polymerization. This quiz will challenge your understanding of polymer structures, reactions, and characteristics. Perfect for students studying advanced chemistry or materials science.
