Polymers Flashcards
Ozonolysis
Cleaves double bonds.
Addition Polymer table
Poly(vinyl alcohol) - PVA
Produced by polymerization of vinyl acetate (small double-bonded carbon monomer with acetate group) to form polyvinyl acetate, followed by hydrolysis to clip the acetate groups.
Polymethyl Methacrylate (PMMA)
- Hard, transparent polymer
- Methyl methacrylate is a methacrylate ester in which the group attached (R in the figure below) can be any alkyl group or even aryl group
- PMMA is vinyl polymer, made by free radical vinyl polymerization from the monomer methyl methacrylate.
- Mostly atactic, not crystalline and behave like glassy materials
- If isotactic, chain twists to relieve the “steric strain,” the relatively big carboxy methyl groups bang into each other so the chain twists in a way to stop that - forms a helical conformation.
Teflon (polytetrafluoroethylene)
- Useful for medical - biocompatible
- Vinyl - similar to polyethylene in structure
- free radical vinyl polymerization
- Fluorine doesn’t like to interact with others, especially something other than F
- repel everything, non-stick
- less protein adhesion?
- High Tm
- Inert
- Really strong bonds to backbone
- Not even O2 reacts
- Really strong bonds to backbone
Poly(vinylidene chloride)
- Saran plastic wrap that food comes in at the grocery store.
- Monomer is vinyl chloride with and extra Cl on the alpha carbon.
PMMA with copolymer of PV-alcohol and PV-acetate
PMMA, is a hard, tough, and shiny plastic, but hydrophobic. It doesn’t dissolve in water, and a lot of paints are water based.
In hydrolysis of polyvinyl acetate to polyvinyl alcohol, leave 20% of acetate groups to form random copolymer (in image).
Hydrophobic acetate groups in center, while hydrophilic alcohol forms ring outside.
PMMA hides in the hydrophobic center of the coiled polymer. By doing this, it can stay suspended in water based paints. Latex.
Mn, Mw and PDI
Acrylates
Vinyl polymers from acrylate monomers (usually esters which contain vinyl groups, that is, two carbon atoms double-bonded to each other, directly attached to the carbonyl carbon of the ester group).
Because of the very polar nature of the carbonyl, pulling electron density away from the normally electron-rich vinyl group, the alpha carbon is more electron poor than the beta carbon. This has a huge effect on the reactivity of the monomer.
Anionic polymerization becomes possible for acrylates (and methacrylates as well), and this gives polymers with very different backbone tacticities and very different physical properties such as being more crystalline.
Poly(acrylic acid)
A polyelectrolyte.
- Each repeat unit has an ionizable group. In this case, it’s a carboxylic acid group.
- Superabsorber: they absorb many times their own weight in water with no problem, even hundreds of times more.
- In baby diapers!
- Scientists not sure exactly how they work
Polyacetate vs Polyacrylate
Acrylate:
-(COO-R)
Acetate:
-(OCO-R)
Polyacrylates with nitrogen
(Polyacrylamide and polyacrylonitrile)
Polyacrylamide
- Will dissolve in water and is used industrially in many applications needing this ability.
- Even crosslinked polyacrylamides can absorb water.
- Crosslinked polymers can’t really dissolve, if you think about it, but that doesn’t stop water from wanting to interact with it through hydrogen bonding.
- These gels of water-swollen crosslinked polymer are used to make things like soft contact lenses.
- It’s the absorbed water in them that makes them soft, but you need other comonomers or polymers mixed in with them to help with things like oxygen permeability.
Modifying polyacrylates
Modify the ester
- HEMA
- Monomer has reactive -OH attached as the R of the ester.
- Reactive and likes to bond with lots of other polar functional groupa
Modify the vinyl
- MHMA
- Monomer has reactive alcohol attached to alpha carbon of the vinyl.
- ECMA
- Monomer has reactive chloromethyl group attached to alpha carbon of the vinyl.
- Two functional groups extending from alpha carbon. More control over properties and chain linking, even ring structures.
Polyisobutylene (synthetic rubber)
- synthetic rubber, or elastomer
- should be crystalline but it’s not
- Most polymers with highly symmetrical backbones like PIB are crystalline. Take isotactic polypropylene or polystyrene. Both are high melting, crystalline polymers.
- Polymers with disubstituted carbons in backbone usually have higher Tgs (> room temp) b/c chain mobility decreases
- Ex: PMMA Tg > PMA Tg b/c methyl on alpha carbon makes it have less chain mobility, i.e. glass at room temp rather than rubber PMA
- only rubber that’s gas impermeable, can hold air for long periods of time
- fixed tires so they retain air for longer
- cationic vinyl polymerization
- copolymerize with isoprene
- small amount (1%) of isoprene is added to the isobutylene and reaction is fast, done at low temp to allow for control
- isoprene has double bond, can be crosslinked by vulcanization
Polyisoprene (natural rubber)
- Elastomer: recovers its shape after being stretched or deformed.
- Treated to enable crosslinks, better elastomer
- diene polymer: two C=C bonds (C=C-C=C)
- Ziegler-Natta polymerization
- polybutadiene: same but without the methyl on C2
Polybutadiene
(elastomer)
- Synthetic elastomer, diene
- isoprene without methyl on C2
- Very low Tg
- good in cold temps, used as copolymer element
- chains are mobile, linked to absence of the methyl
Poly(styrene-butadiene-styrene)
SBS hard rubber
- Durable and rubbery
- 3 segments in backbone
- Block copolymer with polystyrene(long)-polybutadiene-polystyrene(long)
-
Polystyrene
- tough and hard - gives it durability
-
Polybutadiene
- elastomer, very low Tg - gives it rubbery
- Polystyrene chains clump together
- When one styrene group of one SBS molecule joins one clump, and the other polystyrene chain of the same SBS molecule joins another clump, the different clumps become tied together with rubbery polybutadiene chains.
- This gives the material the ability to retain its shape after being stretched.
- Thermoplastic
- Most types of rubber are difficult to process because they are crosslinked.
- But SBS and other thermoplastic elastomers manage to be rubbery without being crosslinked, making them easy to process into nifty useful shapes.
Thermoplastic
- These are materials that behave like elastomeric rubbers at room temperature, but when heated, can be processed like plastics.
- Most types of rubber are difficult to process because they are crosslinked. But SBS and other thermoplastic elastomers manage to be rubbery without being crosslinked, making them easy to process into nifty useful shapes.
Poly(vinyl chloride)
PVC
- plastic for piping
- resists fire (chlorine atoms released inhibit combustion)
- water-resistant
- vinyl polymer
- free radical polymerization
-
semi-crystalline domains
- regions that have a much higher softening point (Tm) than the other amorphous domains (Tg) that make up the solid polymer.
- The crystalline domains act as physical crosslinks to give the product you make toughness and strength.
- This means you can process PVC as a thermoplastic to make all those wonderful pipes and clear plastic seals around stuff you buy that you can’t tear or cut easily.
- So what kind of crystallinity does PVC have?
- Think about size: chlorine atoms have many more electrons than hydrogen and that makes it bigger.
- As a vinyl chloride monomer approaches the radical chain end during polymerization, the bigger chlorine wants to be further away from the chlorine already there.
- That leads to more syndiotactic placement than atactic or even isotactic.
- Those syndiotactic segments (3, 4, 5 or more repeat units) can get together with similar segments on other polymer chains and form small domains of crystalline material. Good properties.
- Increase syndiotacticity?
- Lower the temperature and the steric effects during monomer addition increase.
- Chain twists to achieve a conformation that will minimize the steric strain caused by larger side groups.
- Or you can do the polymerization like normal but add a “complexing agent” (aldehyde) that makes the chlorines look even bigger than they are.
Semi-crystalline
Semi-crystalline domains or regions have a much higher softening point (Tm) than the other amorphous domains (Tg) that make up the solid polymer.
Polyethylene
Vinyl polymer (ethylene monomer)
Linear = HDPE (200k
- Stronger
- Ziegler-Natta polymerization
- UHMWPE (3mil
- Kevlar fibers
- Metallocene catalysis polymerization
Branched = LDPE
- Cheaper, easier to make
- Flexible
- free radical vinyl polymerization
- linear-LDPE can also be made with Ziegler
- copolymerize ethylene with alkyl-branched comonomer
Nylon
- Polyamide (just like silk protein)
- Very polar amide groups that H-bond to each other
- Also, backbone is regular and symmetrical
- Crystalline, make fibers
- Thermoplastic
- Nylon 6,6 means one repeat unit has 6 C stretches on each side separated by the amide group in the middle
- Condensation polymerization
- Made from diacid chloride (or adipic acid - switch Cl for OH) and diamine
- Nylon 6 is made from ring opening polymerization
- Hydroxy bonds with carbocation, nitrogen steals H from carbonyl and breaks off
- Then, next round acid loses its H, and the N in NH2 from broken chain bexome nucleophile, bonding to carbocation, giving ammonium.
- Now amine of one become an amide to the carbonyl of the other
- https://www.pslc.ws/mactest/nysix.htm
Polyester
- Plastics and fibers
- Hydrocarbon chains with ester linkages
Poly(ethylene terephthalate)
PET
- ester groups are polar (C+ : O-)
- +/- charges of different ester groups are attracted to one another, crystallization in chains - strong fibers
- Tg is low, is soft at higher temps
- Monomers
- dimethyl terephthalate and ethylene glycol
- OR, terephtalic acid and ethylene glycol with acid catalyst
Poly(ethylene naphthalate)
PEN
- Bulkier backbone, less mobile, Tg higher
- Higher Tg than PET
- Even mixing some in as a copolymer to PET increases the Tg
Transesterification for making polyester
Alcohol + ester
- O-CH3 of ester switches place with -O-CH2-CH2-OH of ethylene glycol
- then,
https://www.pslc.ws/mactest/petsyn.htm
Or, if done in lab can do with picture monomers instead
Polycarbonate of bisphenol A
- Clear plastic
- Monomers
- Bispenol A and phosgene
- Thermoplastic
Chains with carbonate-containing groups
Thermosets
- Light
- High refractive index
- Free radical vinyl polymerization
-
Crosslinked with allyl groups
- Very strong
-
Thermoset
- Strong and heat resistant
Polystyrene
- Inexpensive
- Hard, plastic
- Vinyl polymer
- Long HC chain with phenyl group on alpha C
- Free radical vinyl polymerization
- monomers = styrene
- Hard, durable component of SBS
- Syndiotactic state is crystalline (high Tm) because order allows the chains to arrange for maximum packing and minimal steric strain requiring bending
- $$$
- Metallocene catalysis polymerization
- Atactic normal state can be used to make high-impact
High-impact polystyrene
- Atactic state of polystyrene + polybutadiene undergoes free radical polymerization to form a graft copolymer
- Backbone is polystyrene and polybutadiene chains grow from it
- Polybutadiene chains
- rubbery
- doesn’t mix with polystyrene backbone
- phase separate and form globs
- absorb energy on impact: resilience
- stronger, not as brittle
- only some chains are branched, lots of plain for both
- immiscible blend
PET and PVA
- Sheets: lamellar morphology.
- PET makes the bottle strong.
- PVA keeps CO2 from passing.
Silicones
- Inorganic
- No carbon, rather silicone and oxygen backbone with organic groups branching from silicone
- Elastomers since backbone is flexible with Si-O bonds, angle opens easily
- Formation driven by entropy
Polyurethane
- Foams, spandex
- Versatile
- Elastomers, fibers, or adhesives
- Urethane linkage in backbone
- Monomers:
- diisocyanates and di-alcohols (ethylene glycol) like how PET does
- Hydrogen bond very well - crystalline
- Combined with soft rubbers to form block copolymers - thermoplastic elastomers
- Very rigid sections form fibers and clump
- Rubbery links
Chain-growth
- Monomers become part of polymer one at a time
- Ex: anionic polymerization of styrene to make polystyrene
- Only the monomer can react with the chain, growing chains cannot react with one another
MW with conversion
- conversion: how fast one or more of reactants is used up
- Step-growth
- Main reactant (monomer or reactive species) used up early, before high MW needed for useful properties
- Chain-growth
- chain growth to high molecular weight is fast for any GIVEN growing chain
- molecules that are present in a typical chain growth polymerization are only either monomer or high molecular weight polymer
- Radical polymerizations behave this way.
- And near the end of polymerization, when the rate of reaction (i.e., conversion of monomer to polymer) slows way down, you STILL have monomer around.
- It’s almost impossible to get rid of all of it.
Initiators for free radical poly
Branched polymer formation through free radical polymerization
Chain transfer to polymer by radical end pulling and H from middle of chain and occurs in polyethylene.
- This is why linear non-branched polyethylene can’t be made by free radical polymerization
Anionic vinyl polymerization
Living
https://pslc.ws/macrog/anionic.htm
vinyl monomers
initiator is anion (butyl lithium with carbanoin)
perpetuated carbanion formation by forcing electrons from double bond onto end carbon
stops when monomer runs out
polystyrene (add H2O to stop)
living polystyrene and butadiene to form SBS
Poly(vinyl ethers)
PVE
- Size of a side group can be so big that it promotes stereoregularity, which is done by the bend of the chain to allow for minimized steric strain, greater organization can allow for higher crystallinity (may be why but>meth for PMMA alternates)
Metallocene catalysis polymerization
- High MW polymers
- Specific tacticities: iso and syndio
- Metallocene is a positively charged metal ion sandwiched between two negatively charged cyclopentadienyl anions.
- https://pslc.ws/macrog/mcene.htm
- thermoplastic, elastomeric polypropylene
Tg graphs
In semi-crystalline, the crystalline regions will go straight to crystal formation below Tm, whereas the amorphous will gradually become less stiff as T increases above Tg.
Tg and Tm
Above Tg, the mobility is sufficient (if no crystals are present) that the polymer can flow as a highly viscous liquid.
The viscosity decreases with increasing temperature and decreasing molecular weight.
There can also be an elastic response if the entanglements cannot align at the rate a force is applied.
Semi-crystalline is viscoelastic above Tm
PLA, PGA, PCL
