Unit 4 Chapter 13: Macromolecules - polymers, proteins, and carbohydrates Flashcards
Polymer:
covalent molecular substance composed of many small molecules (monomers) joined together
Monomer:
smaller molecule that reacts with another monomer (either of the same or different compound) to form a polymer
Addition polymers:
must be unsaturated compounds (contain a double bond)
Low Density Polyethene (LDPE) properties (out of 8)
- Produced with high temperatures and pressure
- Polymer forms too rapidly for molecules to be neat and symmetrical
- More branching –> molecules cannot pack as closely together –> weaker dispersion forces
- Low density
- Relatively soft
- Low melting point
- Non-crystalline
- Opaque, non-conductor
High Density Polyethene (HDPE) properties (out of 7)
- Formed under low pressures using transition metal catalysts (Ziegler-Natta catalysts)
- Fewer branches –> more tightly packed –> stronger dispersion forces
- High density
- Hard
- Relatively high melting point
- Crystalline sections
Longer chain length =
higher melting point
Isotactic:
all side groups are on one side of the polymer chain
Atactic:
side groups are randomly distributed on either side of the polymer chain
Syndiotactic/Syntactic:
side groups are on regularly alternating sides
Common addition polymers:
Teflon, acrylic, polystyrene, Perspex
Condensation polymers:
formed when molecules with two functional groups meet and react together, eliminating a small molecule (usually water)
Common condensation polymers:
nylon, polyester, starch
Common characteristics of most polymers (out of 5):
- High resistance to chemicals
- Thermal and electrical insulators (non-conductors)
- High strength-to-weight ratio
- Can be moulded into variety of shapes
- Mostly derived from petroleum
Thermoplastic polymer:
softens when heated (can be reshaped and more easily recycled) as they have no strong bonds between polymer chains
Thermosetting polymer:
chars when heated due to strong covalent bonds between polymer chains (cross-links) which mean they do not melt and are difficult to reshape and recycle
Cross-links:
strong covalent bonds between polymer molecules, which overall limit movement, are rigid, hard, and heat-resistant
Elastomers:
have a few cross-links which allows the polymer chains to slide past each other when stretched, but return to its original position once released
Crystallinity:
percentage crystallinity is a measure of the relative amounts of crystalline (ordered) regions and amorphous (disordered) regions in the material
Factors affecting physical properties of polymers (out of 6):
- Polarity of side groups in the polymer chain
- Use of more than one monomer (copolymers)
- Polymer chain length
- Extent of branching (e.g., LDPE and HDPE)
- Arrangement of side groups in chain
- Inclusion of additives (e.g., plasticisers)
Copolymer:
polymer made from more than one different monomer
Plasticisers:
organic molecules used to soften plastic by forcing the molecules slightly further apart and weakening the dispersion forces which makes them more flexible
Advantages of polymers (out of 7):
- Available in large variety
- Biologically inert/chemically-resistant
- Easy to mould
- Low density
- Good mechanical strength
- Properties can be modified
- Many can be recycled
Disadvantages of polymers (out of 4):
- Many derived from petroleum
- Microorganisms cannot synthesise (breakdown) synthetic polymers
- Thermoplastic polymers have low thermal stability
- Thermosetting plastics are hard to recycle and may produce toxins when burnt
