11 Polymer Synthesis Flashcards
what is a polymer?
macromolecules made covalently bonded repeating subunits (monomer)
what does a monomer need?
2 (bifunctional) or more (polyfunctional) bonding sites
bi/polyfunctional produce
bi: linear
poly: branched
2 types polymer
Homopolymer: one species of monomer
Copolymer: two or
more monomers.
4 types copolymers
- Statistical copolymer. Two + monomers
randomly distributed.
– Alternating copolymer: alternate
throughout the chain.
– Block copolymer: Blocks of one monomer
followed by a second monomer.
– Graft copolymer: One monomer is grafted on to
the backbone of another polymer.
how to draw polymers
- repeat unit in square brackets, n
repeat units
– end group is
known/relevant, it can be
shown bonded to the repeat
unit
how to name a polymer
bad standardized
use poly(monomer) or hypothetical monomer
2 ways to grow polymers
- step growth: add to growing chain, can combine chains, free for all
- chain growth: monomers add to growing chain
chain growth mech
initiation
propagation
termination
Initiation
- monomer react with initiator
types initiators: radical, anionic, cationic
Propogation
initiator monomer react with monomer
Termination
2 radicals recombine
random process
reason why broad MW distribution
disproportionation
type termination
involves transfer of H ?
Chain transfer
- active and chain attacks another chain that NOT unsaturated
- original chain terminated new chain activated
Free radical initiator
- makes azo cmpd can decompose under mild/moderate conditions
- AIBN, VAZO
- characteristic of rad polymerization
- accelerate as T increases
- generally need heating/UV
anionic initiators
n-bu li or naphthalide
characteristic of anionic initiators
need to cool rxn
- can’t touch water
- said to be living: w/o terminating all chains active even if all monomers consumed
Living polymerization
chain polymerization with no transfer or termination
characteristic of living polymerization
1) chains similar lengths
2) length depends on amount initiator
3)can make block co-polymers
4)can add funtional groups
Narrow MW
distribution
because rate of
__________»_space; rate of ___________
initiation, propagation
Characteristic of living polymerization
- need to suppress chain transfer
- no termination until add a terminating species (work up)
- rate initiation»_space; propagation
- polymer chain length can be increase by adding more monomer
- can form block copolymers
- can add functional group
cationic initiator
Strong acid/ some Lewis acid
HCl, H2SO4, BF3, TiCl4
- can result in living chains
- stabilized by EWG in chains
Step growth polymerization
- NO 3 steps
- Polymerization from polyfunctional monomers
- producing repeating units connected by
ester, amide, urethane, sulfide, and ether
linkages. - Upon reaction, a small molecule
(generally water) is produced.
structure polymer classification
- Condensation polymers: Contain ester, ether,
urethane, sulfide linkages.
– Addition polymers: Do NOT contain linkages
above
polymerization clasification
- Step growth: A small molecule is released.
Reactivity of monomers is the same as that of
polymers.
– Chain growth: No small molecule is released.
Monomers are added to growing chain.
What is PET
polyethylene terephthalate: made from terephthalic acid
and ethylene glycol.
in water bottles
characterization of condensation polymerization
- Removal water/ another small
molecule drives the reaction forward. - Broad molecular weights
- Chain length controlled by adding
monofunctional reagents. - Highest molecular weights
when equimolar amounts of reagents
used. - Chain branching is possible if for example
triols or triamines are used.
Step growth polymerization & chain length
Broad size distribution
Low MW until close to
completion
Secondary reactions – Modifying polymer structure
- modifying side groups.
- used when polymerization with unsuitable side group
secondary rxn - crosslinking
-Two polymer chains can bond along their length
- can
occur via covalent bonding between
neighbouring chains, or via ionic bonding where
a single counter ion links two charged groups on
neighboring chains.
- helps reduce
solubility, improve strength, and increase
thermal stability.
Types of crosslinking
1) Between polymers with unsaturated side groups. Or between polymers with saturated
side-groups which undergo hydrogen radical
abstraction using peroxides or UV-light.
2) Between polymers that produce water or
other stable by-products and form a covalent
bond between chains.
3) Between polymers that have monovalent
cations upon exposure to divalent and
trivalent cations. (weaker)
Secondary reactions – Surface reactions
Sometimes the chemical properties of a solid
polymer surface must be different than the bulk.
