Lecture 5 Flashcards
polymerization methods
example of crosslinked polymers
alkyd polyesters, bakelite, crosslinked polydimethyloxanes
In chain growth polymerization MW distribution will be relatively ____
narrow
In chain growth large polymers will form at _____ stages
early
types of chain growth
free radical, anionic, cationic
free radical polymerization
initiator, propagation, and termination
is exothermic
kinetics of free radical polymerization
Ro = Rp = kp[IMx][M]
thermodynamics of chain growth
dGp = dHp-TdSp
what happens at the ceiling temp?
polymerization reaches equilibrium
ceiling temp equation
Tc = (dHp/dSp)
Step vs. Chain (step growth)
- occurs by reaction between monomers and polymers
- MW increases slowly
- no initiator
- no termination
- poly. rate decreases as groups are consumed
Step vs. Chain (chain growth)
- growth is successive addition of monomer units
- MW increases rapidly
- initiation and propagation
- has termination
- poly. rate increases then remains constant as monomers are depleted
Living polymerization (look at graph comparing methods)
Xn linearly increases with time
Xn = [M]o/[I]o
Bulk Polymerization Pros
-simplest technique
-only monomer, monomer-soluble initiators, and chain transfer agent
can be applied to FR poly, and step poly
Bulk Polymerization Cons
-auto acceleration
-high viscosity at high conversions
-heat transfer problems
Suspension polymerization
-initiator is soluble in monomer
-no monomer transfer between droplets
emulsion polymerization
-initiator is soluble in continuous solvent
-monomer transfer between droplets
-surfactants are involved
precipitation polymerization
-water soluble monomers and initiators
-surfactants if needed
-makes hydrogels
How do we find chemical composition?
FTIR and NMR
FTIR probes transition between molecular __________ levels
vibrational
for _______________ there are many vibrations, some overlap
macromolecules
transmittance
%T = l/lo
absorbance
A = -logT
Beers law
A = ecl
NMR spectroscopy
when put in an external magnetic field, a spinning nucleus splits and a nucleus with I = 1/2 has two states
NMR can be used to examine:
stereoisomerism and composition
