Polymer Science Overview

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Questions and Answers

How do plasticizers affect the properties of polymers?

They make polymers more brittle.

They enhance the thermal stability of polymers.

They increase the strength of polymers.

They partially neutralize the secondary forces between polymers. (correct)

What happens to polymers at a high rate of loading?

They become softer and more malleable.

They behave in a ductile manner.

They behave in a brittle manner. (correct)

They exhibit elastic properties.

Which factor influences the degree of order in polymers' crystalline structure?

Temperature during cooling (correct)

Size of polymer chains

Concentration of fillers

Rate of expansion

What effect does increasing temperature have on polymers near their glass transition temperature?

Polymers become softer. Signup and view all the answers

Which of the following is NOT a use of polymers in dentistry?

High-stiffness components in machinery Signup and view all the answers

What is the smallest repeating unit in a polymer chain called?

Monomer Signup and view all the answers

Which type of polymer is synthesized by living cells?

Natural polymer Signup and view all the answers

Which classification refers to polymers with a thread-like structure without branches?

Linear polymer Signup and view all the answers

Thermoplastic polymers can be described as?

Polymers that can soften upon heating Signup and view all the answers

What type of polymer consists of multiple different types of monomers?

Co-polymer Signup and view all the answers

Which of the following is an example of an elastomer?

Silicone rubber Signup and view all the answers

Brittle polymers exhibit which of the following characteristics?

High modulus of elasticity and low deformation Signup and view all the answers

What type of polymer features covalent bonds between the main chains?

Cross-linked polymer Signup and view all the answers

How is the molecular weight (M.W) of a polymer molecule calculated?

Weight of mers multiplied by the number of mers Signup and view all the answers

What happens to the properties of a polymer as the molecular weight increases?

The degree of polymerization increases Signup and view all the answers

What is a defining characteristic of a copolymer?

It consists of two or more different types of monomers Signup and view all the answers

What effect does small degree of cross-linking have on polymer chains?

It limits the movement of chains past each other Signup and view all the answers

What is the role of a plasticizer in polymer chemistry?

To partially neutralize secondary van der Waals forces Signup and view all the answers

What is the result of extensive cross-linking in polymers?

Brittleness of the polymer increases Signup and view all the answers

Which type of plasticizer is incorporated by copolymerization?

Internal plasticizer Signup and view all the answers

What type of bonding is characteristic of cross-linking in polymers?

Primary covalent bonds Signup and view all the answers

What process stops the growth of polymer chains?

Termination Signup and view all the answers

Which of the following describes the 'Direct Coupling' method of termination?

Reaction between two growing chains to form one long chain Signup and view all the answers

What is a result of the polymerization process under normal conditions?

Incompletion of the polymerization reaction Signup and view all the answers

Which of the following compounds is used to inhibit premature polymerization?

Hydroquinone Signup and view all the answers

What effect does oxygen have on the polymerization reaction of resin composites?

Inhibits the reaction Signup and view all the answers

Which advantage is NOT associated with ring-opening polymerization?

Higher heat evolution Signup and view all the answers

What is the main characteristic of polymers as solids?

They are amorphous solids Signup and view all the answers

What occurs during chain transfer in polymerization?

Active chains are converted to inactive chains Signup and view all the answers

What is the main characteristic of alternating copolymers?

Different monomers are arranged regularly in an alternative pattern. Signup and view all the answers

Which type of copolymer involves one polymer forming a backbone with attached side chains?

Graft copolymers Signup and view all the answers

What type of polymerization reaction involves the formation of polymers with the elimination of by-products?

Condensation Polymerization Signup and view all the answers

In the activation stage of polymerization, what are the possible methods to activate initiators?

Heat, light, or chemical compounds Signup and view all the answers

What is the primary difference between addition polymerization and condensation polymerization?

Addition polymerization does not involve the elimination of small molecules. Signup and view all the answers

What characterizes block copolymers?

Formation of clusters of one monomer type arranged alternatively Signup and view all the answers

What happens in the initiation stage of polymerization?

Activated monomers are produced from the reaction with free radicals. Signup and view all the answers

Which property makes addition polymerization more accurate than condensation polymerization?

There is no elimination of by-products. Signup and view all the answers

Study Notes

Polymer Definition

A polymer is a high molecular weight molecule composed of many repeating units (poly- many, mer- units).

Monomer Definition

A monomer is the smallest repeating building unit of a polymer chain (mono- single).

Polymerization Reaction

It's the reaction where monomers form a polymer chain.

Polymer Classification by Origin

Natural polymers: Synthesized by living cells, examples include proteins, starch, and polysaccharides (agar & alginate).
- Includes polypeptides, polynucleotides, and polysaccharides
- There are issues with lack of pure material, difficult synthesis, and system flexibility, as well as branched structures for some types.
Synthetic polymers: Synthesized by chemical reactions in the lab, an example is acrylic resin.

Polymer Classification by Spatial Configuration

Linear polymer: The polymer molecule forms a thread-like structure without branches.
Branched polymer: In the polymer molecule, shorter side chains are attached to the main backbone chain.
Cross-linked polymer: The main polymer chains are bonded by covalent bonds.

Polymer Classification by Thermal Behavior

Thermoplastic polymer: A polymer that softens when heated and hardens when cooled and can be molded repeatedly.
- Has the same chemical composition after heating and cooling
- Shows Glass Transition Temperature (Tg)
Thermoset polymer: A polymer that decomposes when heated and cannot be reshaped.
- The final product is chemically different than the original substances
- Doesn't exhibit Glass Transition Temperature (Tg)

Polymer Classification by Mechanical Properties

Elastomers (Elastic Polymers): Polymers with a wide range of elastic deformation and a low modulus of elasticity. Example: rubber base impression materials.
Plastic polymers: Polymers with a moderate range of elastic deformation and a moderate modulus of elasticity. Example: Acrylic resin.
Brittle polymers: Polymers with a small range of elastic deformation and a high modulus of elasticity.

Polymer Classification by Chemical Composition of Monomers

Homopolymers: A polymer consisting of a single type of monomer.
Copolymers: A polymer consisting of two or more different types of monomers.
- Alternating copolymers: Different monomers are arranged regularly in an alternative pattern.
- Random copolymers: Different monomers are arranged randomly.
- Block copolymers: Each monomer forms a cluster and the clusters are arranged alternatively.
- Graft copolymers: One polymer forms a backbone, and the other monomer is attached as side chains to the backbone.

Polymer Classification by Polymerization Reaction

Addition Polymerization reaction: The monomers react together to form the polymer chains without the elimination of by-products (e.g., water, gas).
- More accurate polymers than condensation polymers, due to no elimination of by-product.
Condensation Polymerization reaction: The monomers react together to form the polymer chains with the elimination of a small molecule (e.g., water, gas) as a byproduct.

Stages of Polymerization Reaction

Activation: The process of producing free radicals. Free radicals are the active forms of initiators.
Initiation: The reaction of free radicals with the first monomer. The free radical breaks the double bond of the monomer and reacts with one carbon atom.
- The other carbon atom in the monomer contains the unpaired electron, making it very reactive.
- Reactivity is transferred to the monomer.
Propagation: The process of adding monomers to the growing chains. Each activated monomer attacks the C=C of unreacted monomers, transferring the active part to it to extend the main chain.
Termination: The termination process stops the growth chain.
- Direct Coupling: Two growing chains react together to give one long stable chain.
- Hydrogen atom transfer: Hydrogen atom transfers from the active chain to another active chain, forming two stable chains.

Polymer Classification by Chain Transfer

Chain transfer is the transfer of reactivity from an active chain to an inactive chain.

Polymer Termination

The termination process occurs under normal conditions.
- Incomplete polymerization reaction results in residual monomers.

Ring Opening Polymerization Reaction

The terminal group of the monomer is a ring.

Ring Opening Polymerization Advantages

Less polymer shrinkage.
Less heat evolution.

Inhibition & Retardation

Inhibition: Stopping
Retardation: Lowering the rate
Hydroquinone: Added to monomers to inhibit premature polymerization during storage or accidental heat/light exposure.

Inhibition & Retardation Continued

Eugenol: Inhibits the polymerization reaction of resin composite. Bases containing eugenol should not be used as a base under composite resin restorations.
Oxygen: Inhibits the polymerization reaction of resin composite. The surfaces of restorations should be polished to remove the unreacted surface layer OR covered with a matrix band.

Factors Associated with Polymerization Reaction

Heat evolution due to the breaking of monomers.
Reduction in volume (polymerization shrinkage).
Presence of residual monomers (not all participate in the reaction).

General Properties of Polymers

Polymers are molecular solids.
Polymers are amorphous solids (unless specific arrangements of monomers form crystalline regions).

Factors Affecting Polymer Properties

Molecular weight (MW) and degree of polymerization (DP)
Copolymerization
Cross-linking
Plasticizer
- Internal plasticizers
- External plasticizers
Addition of inorganic fillers
Rate of loading
Degree of crystallinity
Spatial configuration
Temperature

Uses of Polymers in Dentistry

Denture base materials
Artificial teeth
Teeth restorative materials
Dental cements
Temporary crowns
Endodontic filling & sealers
Maxillo-facial prosthesis
Impression materials

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Description

This quiz covers the essential concepts of polymer science, including definitions of polymers and monomers, polymerization reactions, and classifications based on origin and spatial configuration. It aims to provide a foundational understanding of the types of polymers and their characteristics.