Degradable Polymers

3 ways to make progress in waste

1. use monomers derived from biomass to make biodegradable polymers

2. introduce small amt of monomer into traditional polymers causing chain cleavage

3. use polymers that can depolymerize when treated with acid or base

why are biodegradable polymers expected to break down more quickly in environment?

they can be hydrolyzed 

• unlike C-C bonds of polyolefins

oftentimes, biodegradable polymers include __________ bonds in the polymer backbone

polar C-O or C-N

• such as esters, carbonates, amides, phosphoesters

biodegradable polymers are often ________ and have __________ applications

nontoxic / biomedical

degradation studies in labs have not been __________ and thus are hard to _________ to environmental conditions

standardized / translate

most common biodegradable polymer

poly(lactide)

how is L-lactic acid produced?

from biomass: fermented plant starch (corn, sugar starch)

how is poly(L-lactide) turned into corn cups?

thermoforming

how are dissolvable stitches made from poly(L-lactide)

spinning

L-lactide structure

L-lactic acid structure

will poly(lactide) ever be able to replace polyolefins? why/why not?

no — has inferior material properties even for high MW samples

• low Tm

polyolefins

high MW hydrocarbons

• polyethylene

• polypropylene

how long does it take poly(lactide) to degrade fully in body?

b/w 6 months and 2 years

do poly(lactides) degrade/compost well in landfills?

no

what temp is required for poly(lactides) to degrade?

above 55 C or 130 F

why are such high temps required to degrade poly(lactide)?

need to kick off hydrolysis

there is concern that wide-scale use of poly(lactide) will cut into _______ supply

food (corn)

biodegradable polymers are _________ to match commercial polymer properties

unlikely

thionolactones

promising monomer → can be radically polymerized with olefins like styrene & methyl acrylate

triggered degradation

add small amount of monomer that degrades easily, causing chain cleavage/scission at special monomer site more rapidly due to weak bond

thionolactone product with desirable properties produced in article via computational chem predictions

POT

benefits of POT

• reactivity ratios

• styrene

• acrylate derivatives

• RAFT copolymerization

once POT was synthesized, what was the additive?

5% of polymerized styrene & methyl acrylate

describe steps of example triggered degradation

1. synthesize POT

2. use Lawesson’s reagent to replace ester =O with =S

3. add radical growing polymer chain

4. C-S bond formation (b/w radical C and =S)

5. ring opens

6. stabilized radical reacts with more olefin

7. degrade poly(styrene) using TBD in THF for hydrolysis

8. degrade poly(methyl acrylate) using KOH and iPrNH2 in water for hydrolysis

overall, triggered degradation likely requires _________ of used polyolefins & hydrolysis to break the thionolactone links

dissolution

what does triggered degradation degrade into?

oligomers

• could still lead to microplastics

does depolymerization take it back to monomers?

no - oligomers

poly(carbonates)

can be synthesized from epoxides (oil-based) and CO2 (from atm)

requirements for depolymerization

1. high pressure

2. catalyst

products of depolymerization depolymerize fully into ____________

cyclic carbonates

mechanism used in depolymerization

back-biting

depolymerization is especially fast with a ________ but not with the metal catalyst used in the paper

base

5-membered cyclic carbonates are very _________ due to _____________

stable / bond angles

depolymerization is driven by __________

thermodynamics

it is very hard to _________ a 5-membered cyclic carbonate

repolymerize

are 5-membered cyclic carbonates toxic?

no

• ok as waste

describe which R groups in depolymerization led to fastest yield of cyclic carbonate from fastest to slowest

1. Ph and Me (tied)

2. CH2Cl

cyclic carbonate structure

polycarbonate structure