Chapter 1 Flashcards
What is a polymer?
A polymer is a large molecule consisting of at least five repeated chemical units (monomers) joined together, often forming chains with hundreds or thousands of monomers.
What are the three major classes of polymers?
The three major classes are thermoplastics, thermosets, and elastomers.
What distinguishes thermoplastics from thermosets?
Thermoplastics can be reshaped upon reheating, while thermosets are crosslinked polymers that do not melt or reshape after curing.
Why are thermoplastics easier to recycle compared to thermosets?
Thermoplastics can be melted and reshaped, while thermosets are chemically crosslinked, making them infusible (not able to melt upon reheating).
What happens during the crosslinking process in thermosets?
Crosslinking materials are covalently tied together, creating a network that is infusible and insoluble.
What is the significance of side groups in polymers?
Side groups influence the polymer’s properties such as flexibility, crystallinity, and melting point.
How does molecular weight affect polymer properties?
Higher molecular weight leads to increased toughness, melt temperature, melt viscosity, and resistance to stress but can difficult processing.
What is the glass transition temperature (Tg)?
Tg is the temperature at which an amorphous polymer transitions from a hard, glassy state to a soft, rubbery state.
(DSC) Differential Scanning Calorimetry
Why are branched polymers like low-density polyethylene (LDPE) more flexible?
Branched structures allow the structure bend more easily, reducing density and increasing flexibility.
What makes high-density polyethylene (HDPE) different from LDPE?
HDPE has a linear structure, resulting in higher density, stiffness, and tensile strength.
LDPE is branched structure, resulting lower density, increased flexibility and lower tensile strength.
List the industrial techniques for polymer production.
Bulk, solution, suspension
What is bulk polymerization?
Bulk polymerization is a process where the polymerization reaction occurs in the absence of any solvent, using only the pure monomer and an initiator. Simplest method.
What are the advantages of bulk polymerization?
Simple formulation and equipment are required.
High-purity polymer is obtained directly.
Suitable for creating large castings.
What are the disadvantages of bulk polymerization?
- Heat evolved during the reaction can make it difficult to control.
- Viscosity increases as the reaction progresses, complicating stirring and heat transfer.
- Broad molecular weight distribution due to autoacceleration.
What is solution polymerization?
In solution polymerization, monomers and initiators are dissolved in a suitable solvent, and the polymerization reaction occurs in this solution. Have to choose solvent that not undergo chain transfer.
Advantages of solution polymerization?
- Improved heat transfer, making it easier to control the reaction.
- Solutions much easier to stir than bulk.
- Suitable for applications where the presence of a solvent is required, such as in varnishes and adhesives.
What are the disadvantages of solution polymerization?
- Separation of the polymer product from the solvent can be challenging.
- Difficult to remove solvent completely.
- Chain transfer to the solvent can affect polymer properties.
What is suspension polymerization?
Suspension polymerization involves dispersing monomers in a liquid (usually water) using vigorous stirring and stabilizers. Polymerization occurs within the suspended droplets. To get granules, beads form
What are the advantages of suspension polymerization?
-Efficient heat transfer through the aqueous medium making it easier to control.
-The polymer product can be easily separated by filtration.
- Good control over particle size and distribution.
What are the disadvantages of suspension polymerization?
- It is not suitable for water soluble monomers.
- Limited to the preparation of granular polymers like polystyrene, PVC, and PMMA.
