Ch. 10- Polymers Flashcards
polymer
a molecule with a large molecular mass that is formed by repeating smaller units (monomers)
monomer
a substance of relatively low molecular mass; the building blocks of polymers
polymerization
a process by which monomers are made into polymers
celluloid
cellulose nitrate, derived from natural cellulose by treating it with nitric acid; earliest synthetic attempt to improve on natural polymers
what do we use celluloid for?
as a substitute for more expensive materials like ivory, amber, and tortoise shell; used to make billiards balls, movie film, & stiff shirt collars
why don’t we use celluloid as much?
it’s highly flammable and difficult to preserve
what was the first truly synthetic polymer?
Bakelite, made from phenol & formaldehyde
what is the simplest and least expensive synthetic polymer?
polyethylene
why was polyethylene so important for the Battle of Britain?
it was invented just before the war, and was used as an electric insulator; without it, the British would have had to use what they had at the time (cotton braid + rubber paint) for electric wires, which was very ineffective for their radar; if their radar wasn’t as effective as it was with polyethylene, they could’ve lost the battle
what is the source of most synthetic polymers?
petroleum & natural gas
copolymer
a polymer formed by the combination of two (or more) different monomers
what are the 3 main types of polyethylene
- high-density polyethylene (HDPE)
- low-density polyethylene (LDPE)
- linear low-density polyethylene (LLDPE)
properties of high-density polyethylene (HDPE)
- has mostly linear molecules that pack tightly in a crystalline structure
- rigid & strong plastics
- have densities of 0.94-0.96 g/cm3
- hold shape in boiling water
how do we use HDPE?
- threaded bottle caps
- toys
- detergent bottles
- milk jugs
properties of low-density polyethylene (LDPE)
- has many side chains branching off the polymer molecules, preventing the molecules to tightly pack & assume crystalline structure
- waxy, bendable plastics
- have densities of 0.91-0.94 g/cm3
- severely deform in boiling water
how do we use LDPE?
- plastic bags & film
- squeeze bottles
- electric wire insulation
- common household products that require flexibility
how do we make linear low-density polyethylene (LLDPE)?
by polymerizing ethylene with a branched-chain alkene
how do we use LLDPE?
- plastic films for landfill liners
- trash cans
- tubing
- automotive parts
thermosetting polymer
a polymer that cannot be softened and remolded; very high temperatures cause them to discolor and decompose
thermoplastic polymer
a polymer that can be heated and reshaped
addition polymerization (chain-reaction polymerization)
a polymerization reaction in which all the atoms of the monomer molecules are included in the polymer
vulcanization
the process of making naturally soft rubber harder by reacting it with sulfur
vulcanization
the process of making naturally soft rubber harder by reacting it with sulfur
cross-linking
connecting long chains of molecules through covalently bonded atoms or small groups of atoms
Charles Goodyear
discovered vulcanization & was issued a patent for it
elastomer
a polymeric material that returns to its original shape after being stretched
what is natural rubber a polymer of?
isoprene
condensation polymerization (step-wise polymerization)
a polymerization reaction in which not all the atoms in the starting monomers are incorporated in the polymer because water (or other small) molecules are formed as by-products
polyamide
a polymer that has monomer units joined by amide linkages
polyester
a polymer that has monomer units joined by ester linkages
thermosetting resins
polymeric materials that harden irreversibly
polycarbonates
“clear as glass”, tough polymers that have carbonate groups
polyurethanes
polymers that are similar to nylon polymers in structure, but have (–NHCOO) bonds, which are formed by an isocyanate group (–N=C=O) reacting with an alcohol group (–OH)
epoxies
polymers that are powerful adhesives due to cross-linking
silicone
a polymer whose chain consists of alternating silicon and oxygen atoms
important properties of silicone
- can be linear, cyclic, or cross-linked networks
- heat-stable and resistant to most chemicals
- excellent waterproofing materials
crystalline polymers
polymers composed of molecules that line up neatly to form long, strong fibers
amorphous polymers
polymers composed of molecules that are randomly oriented & intertwined with one another
glass transition temperature (Tg)
the temperature of a polymer that states if the polymer measures above that temperature, it’s rubbery & tough, and if the polymer measures below that temperature, it’s hard, stiff, & brittle, like glass
why do we use synthetic fibers instead of natural fibers for everyday use?
- synthetic fibers can replicate many liked properties of natural fibers, like appearance & how they feel
- less expensive
- easier to care for
- last longer
- more useful (i.e. microfibers’ ability to either absorb or repel water)
of the 55% of solid waste produced by the U.S. annually, how much of it is plastic?
about 13%
name two degradable plastics & their sources
- polylactic acid (PLA) made from corn or sugar cane
- polyhydroxyalkanoates (PHAs) made from microorganisms
which plastics are currently recycled on a large scale in the U.S.?
- polyethylene terephthalate - PET (28% recycled)
- high-density polyethylene - HDPE (29% recycled)
how have we developed flame-retardant fibers? how do we use them?
- we add chlorine & bromine atoms to polymeric fibers which results in flame-retardant fibers (required for children’s sleepwear)
- development of Nomex (meta-aramid) which is a synthetic fiber that does not react with flames/high heat (used for protective clothing, like firefighting gear)
plasticizer
a substance added to some plastics to make them more flexible and easier to work with by lowering their glass transition temperature
how can plasticizers be harmful to the environment?
plasticizers get lost by diffusion & evaporation as a plastic ages, spilling into the environment & degrading very slowly, leading to their becoming concentrated in the food chain
what used to be a popular plasticizer that is now banned, and why is it banned?
polychlorinated biphenyls (PCBs); derived from biphenyls, when PCBs are exposed to other compounds, the hydrogen atoms of biphenyl get replaced with chlorine atoms, creating substances that have similar psychological effects as DDT (insecticide)
what is the most popular plasticizer currently & why?
- phthalate esters which are derived from phthalic acid
- they’re safer to use & degrade rapidly
