Polymers Flashcards

Questions and Answers

What are polymers?

Plastics and natural materials such as rubber or cellulose are composed of very large molecules called polymers.

What are polymers made of?

Polymers are constructed from relatively small molecular fragments known as monomers that are joined together.

What are thermoplastics?

Thermoplastics soften at a specific temperature, allowing individual molecules to slide independently of their neighbors.

What are thermosets?

Thermosets do not melt and must undergo polymerization within molds. Signup and view all the answers

What is the primary difference between thermoplastics and thermosets?

Thermoplastics can be remelted into a liquid, while thermosets always remain in a permanent solid state. Signup and view all the answers

Name 2 general methods of polymer synthesis.

Condensation-Elimination and Addition. Signup and view all the answers

What is condensation-elimination?

Monomers react in a way that parts of their functional groups combine to form a small molecule which is eliminated. Signup and view all the answers

What is addition polymerization?

An initiator monomer starts a chain reaction by sharing its unpaired electron with another monomer, which then becomes reactive. Signup and view all the answers

Name 2 kinds of commercially important synthetic thermoplastics and specify some of their principal uses.

Polycarbonate (Lexan) used in compact disks; Nylon used in carpets and clothing. Signup and view all the answers

Name 2 kinds of commercially important synthetic thermosets and specify some of their principal uses.

Silicones (used in lubricants and medical implants) and Alkyd-Polyester resins (used in fibers for clothing and fiberglass). Signup and view all the answers

Name two kinds of commercially important natural polymers.

Starch and rubber. Signup and view all the answers

What are some of the concerns and sources of small-molecule release from polymers?

Small molecules can diffuse from unreacted monomers or added substances, potentially contributing to pollution. Signup and view all the answers

What are some of the problems connected with recycling or reuse of polymeric materials?

Energy-intensive processes for recycling, incompatibility issues with mixed plastics, and thermosets being non-recyclable. Signup and view all the answers

The physical properties of a polymer such as its strength and flexibility depend on:

Chain length, side groups, branches, and cross-linking. Signup and view all the answers

How does chain length affect the strength of a polymer?

In general, the longer the chains, the stronger the polymer. Signup and view all the answers

What role do side groups play in polymer strength?

Polar side groups increase attraction between polymer chains, making the polymer stronger. Signup and view all the answers

How does branching affect the density and strength of polymers?

Straight, unbranched chains pack more closely than branched chains, leading to higher density and strength. Signup and view all the answers

What is cross-linking in polymers?

Cross-linking occurs when polymer chains are linked extensively by covalent bonds, making them harder to melt. Signup and view all the answers

Study Notes

Polymers Overview

Polymers are large molecules composed of repeating structural units called monomers.
Common examples include plastics, rubber, and cellulose.

Composition of Polymers

Polymers are formed by joining smaller units (monomers) through chemical reactions.

Types of Polymers

Thermoplastics:
- Exhibit a softening point.
- Flexible at high thermal energy due to internal rotation and independent sliding of molecules.
Thermosets:
- Do not melt upon heating.
- Created through a complex process within molds, resulting in a more structured and crystalline form.

Key Differences

Thermoplastics can be remelted into liquid, while thermosets always remain solid.

Polymer Synthesis Methods

Condensation-Elimination:
- Involves monomers reacting to eliminate small molecules (like water) as new bonds form.
Addition Polymerization:
- Initiated by a monomer that starts a chain reaction by transferring an unpaired electron to another monomer.

Commercially-Important Synthetic Thermoplastics

Polycarbonate (Lexan):
- Strong and durable, used in compact disks.
Nylon:
- Offers erosion resistance, used in fabrics and engineering materials.

Commercially-Important Synthetic Thermosets

Silicones:
- Used in lubricants, medical devices, and non-stick cookware.
Alkyd-Polyester Resins:
- Used in textiles and fiberglass.

Important Natural Polymers

Starch and rubber are significant natural polymers with various applications.

Environmental Concerns & Release of Small Molecules

Small molecules from polymers (like unreacted monomers and additives) can leach into the environment.
These can contribute to indoor air pollution and aquatic contamination.

Recycling Challenges

Mixed plastics require energy-intensive processes for recycling.
Only a few condensation polymers can be depolymerized for reuse, while thermosets are often used as fillers in recycled materials.

Physical Properties Influencing Factors

Key properties like strength and flexibility depend on:
- Chain length: Longer chains generally yield stronger polymers.
- Side groups: Polar groups enhance hydrogen bonding, increasing polymer strength.
- Branching: Less branched chains pack tighter, increasing density and crystallinity.
- Cross-linking: Extensive covalent bonds create harder, heat-resistant polymers.

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Description

Explore essential concepts related to polymers through flashcards. This quiz covers definitions, components, and characteristics of different types of polymers. Perfect for anyone studying materials science or chemistry.