Chemical Reactions and Free Radicals

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Questions and Answers

What type of polymerization involves the linear growth of molecules and the shifting of free radicals?

Chain-growth polymerization (correct)

Step-growth polymerization

Ring-opening polymerization

Cross-linking polymerization

Which factor is NOT typically associated with polymerization reactions?

Evolution of heat

Monomer immobilization (correct)

Residual monomer

Shrinkage

What is the primary characteristic of the ring opening mechanism in polymerization?

Results in high thermal expansion

Involves only linear monomers

Utilizes cyclic monomers with terminal reactive groups (correct)

Leads to a frozen spatial configuration

Which method of termination in radical polymerization involves the direct coupling of two radicals?

Direct coupling Signup and view all the answers

What type of material is an example of a polymer formed via ring-opening polymerization?

Polyether rubber impression material Signup and view all the answers

What key aspect is affected by the thermal behavior of polymers during polymerization?

Mechanical properties Signup and view all the answers

What major disadvantage is associated with residual monomer in polymerization processes?

Potential toxicity Signup and view all the answers

During which stage of polymerization would shrinkage primarily occur?

Post-polymerization Signup and view all the answers

What is the term for a polymer composed of a single type of monomer?

Homopolymer Signup and view all the answers

Which of the following best describes an oligomer?

A short polymer composed of up to 10 mers Signup and view all the answers

In terms of spatial configuration, what does a branched polymer refer to?

A polymer where monomers branch off from the main chain Signup and view all the answers

What type of polymer consists of more than one type of monomer?

Copolymer Signup and view all the answers

Which of the following is a natural polymer?

Proteins Signup and view all the answers

What is the primary bond type in intermolecular forces within polymers?

Secondary (2ry) bond Signup and view all the answers

Which of the following is not a characteristic of the polymerization reaction?

Occurs at low temperature environments Signup and view all the answers

What is the result of a polymer that is classified based on its origin?

It distinguishes natural from synthetic polymers Signup and view all the answers

Which characteristic is true for thermoplasts?

They can be remelted and reshaped. Signup and view all the answers

What differentiates addition polymerization from condensation polymerization?

Addition polymerization has no by-products. Signup and view all the answers

Which type of polymerization is typically slower and produces shorter polymer chains?

Condensation polymerization Signup and view all the answers

Which of the following polymers is associated with condensation polymerization in clinical applications?

Polysulfide rubber Signup and view all the answers

What is the main reason condensation polymerization results in small molecular weight products?

Elimination of by-products. Signup and view all the answers

Which statement is true regarding thermosets?

They degrade upon exposure to high temperatures. Signup and view all the answers

What initiates the activation and initiation in addition polymerization?

Free radicals generated by an initiator. Signup and view all the answers

Which of the following properties is NOT typically associated with thermoplasts?

They can degrade under high temperatures. Signup and view all the answers

Study Notes

Free Radical Polymerization

Involves radical compounds with an unpaired electron, initiated using light or chemical means.
Initiation requires a radical generator like benzoyl peroxide to form free radicals.

Propagation

Characterized by linear growth of molecules through the addition of free radicals to the end of the growing chain.

Termination Mechanisms

Direct Coupling: Two free radicals combine to terminate the reaction.
Hydrogen Atom Transfer: Involves the transfer of hydrogen atoms between radicals, leading to new bond formation.

Factors Influencing Polymerization

Heat generation occurs during polymerization.
Shrinkage and the presence of residual monomer can affect the final product.

Ring Opening Mechanism

Utilizes terminal reactive groups within cyclic monomers.
Examples: Polyether rubber impression material and low shrinkage composites (Siloranes).

Types of Polymers

Thermoplasts: Physical reactions, soft, can be remelted and reformed. Sensitive to heat. Example: Acrylic resin.
Thermosets: Chemical reactions, cannot be remelted, degrades upon heating, high mechanical properties.

Polymer Preparation Reactions

Condensation Polymerization:
- Involves stepwise reactions with multiple monomer species.
- Produces low molecular weight due to by-product elimination.
- Slower with shorter polymer chains. Relevant in polysulfide rubber impression materials.
Addition Polymerization:
- Faster reaction without by-products.
- Results in high molecular weight polymers.

Polymer Structure

Polymers are long-chain organic molecules made of repeated units called monomers.
Monomer: Smallest repeating unit (single).
Oligomer: Short polymer composed of 10 monomers.

Bonding Types in Polymers

Intramolecular bonds (primary bonds) are covalent.
Intermolecular bonds (secondary bonds) connect individual polymer chains.

Polymerization Reaction

Process by which monomer units chemically link to form high molecular weight polymers.
Homopolymers: Comprised of one type of monomer.
Copolymer: Made from more than one type of monomer.

Classification of Polymers

By origin:
- Natural: Proteins, polysaccharides, DNA, RNA.
- Synthetic: Bakelite, nylon, PMMA, polyvinyl chloride.
By spatial configuration:
- Linear, branched, and cross-linked structures.

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Description

Explore the fascinating world of chemical reactions involving free radicals and initiators. This quiz will test your understanding of how these chemical groups with unpaired electrons interact under the influence of light and other factors. Get ready to dive into the complexities of radical compounds!