final exam Flashcards
1
Q
What is a polymer?
A
A large molecule comprised of many repeat units called monomers.
2
Q
What is an oligomer?
A
A low molecular weight polymer, about 100 - 1000s monomers.
3
Q
Who is Hermann Staudinger?
A
The father of polymer chemistry, he proved the existence of macromolecules.
4
Q
It was generally believed that the molecules in polymers were interacting with secondary intermolecular forces, what was the truth?
A
The molecules were connected by covalent bonds.
5
Q
What was Staudinger’s first approach, why didn’t it work?
A
He tried to measure the colligative properties of polyindene using hydrogenation. This method only works for low molecular weight polymers.
6
Q
What was Staudinger’s second approach?
A
He used intrinsic viscosity to measure the molecular weight of cellulose. This was repeatable on many polymers.
7
Q
How many years did it take Staudinger to finally prove his theory?
A
10 years.
8
Q
Who received the first Nobel prize in the field of polymers?
A
Hermann Staudinger
9
Q
Definition of a thermoplastic?
A
Able to soften and liquify, reformable. A reversible and repeatable process.
10
Q
Definition of a thermoset?
A
Permanently solid upon heating, crosslinked networks, brittle.
11
Q
Weighted averages from greatest to least?
A
Mz > Mw > Mn
12
Q
What is PDI?
A
The measure of breadth of distributions of the molecular weights in a polymer, always greater than 1.
13
Q
PDI equation?
A
PDI = Mw/Mn
14
Q
What is the PDI of a monodisperse polymer?
A
1 (or very close)
15
Q
What are the two relative measurement methods of determining molecular weight?
A
Intrinsic viscosity & Size exclusion chromatography
16
Q
What are the 7 types of Structural Isomers?
A
Linear, branched, star, ladder, network (crosslinked), hyper-branched, and dendrimer.
17
Q
What 2 structural isomers have a common growth point?
A
Star & Dendrimer
18
Q
What is the distinction between short and long chain branching?
A
In short chain branching it is easy to identify the polymer main chain.
19
Q
What defines a cross linked polymer?
A
The polymers are covalently linked together by points other than their ends.
20
Q
For Sequence Isomers, is head-to-head or head-to-tail preferred?
A
Head-to-tail is preferred because it has the least steric hindrance.
21
Q
What are the 3 different Stereoisomers?
A
Isotactic, Syndiotactic, and Atactic
22
Q
Which Stereoisomer is not crystalline?
A
Atactic, it’s amorphous
23
Q
What are the 2 Geometric Isomers?
A
Cis & Trans
24
Q
What are the 4 types of copolymers?
A
alternating, random, block, and graft
25
ABABABABAB
Alternating, property of -AB- monomer
26
AABABABBBABABA
Random, average property of A and B
27
AAAAABBBBB
Block, regions of property A and property B
28
AAAAAAAA
B B
B B
B
Graft, regions of property B surrounding property A
29
The degree of crystallinity can vary from completely amorphous to _% crystalline?
95
30
What 2 things increase crystallinity?
Slow cooling and stretching.
31
Crystalline = ?
Melting
32
Amorphous = ?
Liquify
33
What is the semicrystalline state?
Crystalline regions are dispersed throughout amorphous regions.
34
What is the fringed-micelle model?
Small crystalline regions with precise chain alignment are embedded within an amorphous matrix of randomly oriented molecules.
35
What is the chain-folded model?
Folds occur on platelet faces. Longer the polymer, more instability and more amorphous. Crystallinity minimizes entropy.
36
What is the spherulite model?
Lamellar crystal faces separated by amorphous regions.
37
What are the 3 orders of Liquid Crystals?
Nematic, Smectic, and Cholesteric.
38
Nematic LC?
No alignment of chain ends.
39
Smectic LC?
Chain ends are aligned.
40
Cholesteric LC?
Oriented chain planes rotate. Used for tv and computer monitors.
41
Thermotropic?
Liquid crystalline phase in temperature range.
42
Lyotropic?
Liquid crystalline phase in concentration range.
43
What are 2 advantages of liquid crystals?
Lower viscosity and higher mechanical strength.
44
How many principles of Green Chemistry are there?
12
45
It is better to prevent waste than to treat or clean up waste after is has been created.
Prevention
46
Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product.
Atom Economy
47
Growth by a reaction between two
oligomers.
Step Polymerization
48
Rapid loss of monomer species.
Step Polymerization
49
Driving force: removal of condensation product.
Step Polymerization
50
Molar mass increases slowly throughout.
Step Polymerization
51
Ends remain active.
Step Polymerization
52
No initiator.
Step Polymerization
53
At any stage a range of molecular species are present.
Step Polymerization
54
Xn?
Number average degree of polymerization.
55
Xn Equation?
Xn = No/N
No = number of molecules initially
N = final number of molecules
56
Xn equation for a stoichiometric rxn?
Xn = 1/(1-p)
stoichiometric (r = 1)
p = extent of reaction
57
Reactant ratio (r) equation?
r = Na/Nb
r is always less than or equal to 1!
58
General Carother's equation?
Xn = (1+r)/(1+r-2rp)
59
Growth by monomer addition at chain ends.
Addition Polymerization
60
Monomer concentration is never zero.
Addition Polymerization
61
Molar mass increases rapidly.
Addition Polymerization
62
Chain ends are not reactive after termination.
Addition Polymerization
63
Driving force: 1 double bond to 2 single bonds.
Addition Polymerization
64
Initiator is required.
Addition Polymerization
65
Small number of polymer chains growing at a time.
Addition Polymerization
66
What is the first step in the reaction of a polymer chain?
Initiation, a free radial is formed.
67
What is the second step in the reaction of a polymer chain?
Propagation, monomers are added one at a time to the growing polymer chain.
68
What is the final step in the reaction of a polymer chain?
Termination, the free radicals are consumed.
69
What is combination termination?
Two reactive polymer chains combine to form one extremely large chain.
70
What is disproportionation termination?
A hydrogen atom is extracted by the free radical leading to the creation of two separate polymer chains.
71
Equation for kinetic chain length (v)?
v = Rp/Ri
Rp = rate of propagation
Ri = rate of initiation
72
What is the relationship between kinetic chain length (v) and molecular weight?
v = k'([M]/[I]^1/2)
Xn = v by disproportionation
Xn = 2v by combination
73
What is the equation for rate of propagation (Rp)?
Rp = [M][I]^1/2
[M] = concentration of monomer
[I] = concentration of initiator
74
As concentration of monomer increases?
Rp increases
Xn increases
75
As concentration of initiator increases?
Rp increases
Xn decreases
76
What is Autoacceleration (Trommsdorff-Norrish effect)?
1. as time increases the solution gels, MW and viscosity increase dramatically
2. mobility of polymer chain radicals almost go to zero, kt is reduced and steady state conditions no longer hold
3. small molecules diffuse to free radicals
4. Rp and Xn both increase
77
When does chain transfer occur?
When one polymer chain is terminated, but a new growing chain is initiated.
78
What are the 2 main types of chain transfer?
Intramolecular and Intermolecular
79
Intramolecular?
Across, leads to short chain branching (backbiting mechanism.
80
What is the progression of intramolecular chain transfer?
linear -> butyl branch -> 2 ethyl branches
81
Intermolecular?
Between, long chain branching. NOT a termination step.
82
What is an inhibitor?
Prevents polymerization from taking place until all of the inhibitor is used up.
83
What does an inhibitor do to the free radical species?
Consumes
84
What type of chain transfer does an inhibitor have?
Intramolecular
85
What does a retarder do?
Slows the polymerization process.
86
What does a retarder do to free radicals?
Converts them into more stable free radicals.
87
What type of chain transfer does a retarder have?
Intermolecular
88
How does ionic polymerization differ from free radical?
Much faster, and uses ions.
89
Why can't coupling (termination) occur between two growing chains in ionic polymerization?
The active centers are of the same charge, thus repulsion occurs.
90
Why is Cationic polymerization used?
To make stereospecific polymers.
91
What are 4 important facts about cationic polymerization?
Lots of side rxns
high MW = subzero temps
rapid (seconds)
issues with heat transfer and steady state
92
Why use Anionic polymerization?
Living polymerization, polymer chains permanently retain their active centers and continue to grow as long as there are monomers.
93
Equation for anionic polymerization (Poisson distribution)?
Mw/Mn = 1+1/(Xn)
94
What are 2 important facts about anionic polymerization?
Super reactive
Low concentration of reaction species
95
What are 3 other types of polymerization?
Photo-polymerization, radiation, and electrochemical
96
What are 3 advantages of photopolymerization?
No initiator contamination
Fast (seconds)
Photolithography can be used
97
What are 2 disadvantages of photopolymerization?
UV penetration into bulk
# of photo-cleavable monomers
98
What is important about radiation polymerization?
There are no contaminants, but it can give degradation.
99
What is important about electrochemical polymerization?
Used for corrosion protection
Can't be used for bulk polymerization
100
What is the end-to-end distance (R)?
The distance that connects two terminal ends of a polymer chain.
101
In a good solvent, is the R larger or smaller?
Larger
102
What is the equation for w/ no angle restriction?
103
What is the equation of w/ a fixed angle?
104
Why is the radius of gyration (S) used to determine ?
105
How is the radius of gyration (S) measured?
Using light scattering techniques.
106
What is the equation that relates the end-to-end distance to the radius of gyration?
107
What is the Flory-Huggins theory used for?
Calculating the deltaG of mixing.
108
What are the 4 assumptions of the Flory-Huggins theory?
1. polymer solution can be regarded as chemical repeat units of polymer unit occupying each lattice unit.
2. lattice units have equal size, can be occupied by polymer or solvent
3. number of neighboring chemical repeat units is called the valence number
4. change in volume due to mixing is zero
109
What are the 2 disadvantages of the flory-huggins theory?
doesn't allow for thermal expansion, and different solvent molecule sizes cannot be evaluated
110
What value of deltaG is necessary for mixing to occur?
Greater than zero
111
What is the equation for the flory-huggins parameter (X)?
Xc = 1/2*(1/sqrt(n1) + 1/sqrt(n2))^2
if X > Xc soln will not mix
112
theta-solvent -
X parameter = _?
0.5
113
What are the exceptions of molecules that show lower critical solution temperatures (LCST)?
They dissolve in cold solvents and precipitate in hot solvents.
114
What does viscosity mean?
Difficulty to flow.
115
What does the Doolittle equation tell us?
Viscosity is a function of temperature.
116
What is the Mark-Houwink-Saruda equation?
Intrinsic viscosity = K(M^a)
K and a are constants
M is the viscosity average molecular weight
117
What leads to molecular entanglement?
A polymer is a good solvent of itself.
118
How does the relationship between viscosity and MW change above the entanglement MW?
Viscosity goes from being proportional to MW^1 to proportional to MW^3.4
119
What is the reptation model?
Polymeric chains repeating through a tube, can move in the direction of the tube but not transversely bc of entanglement.
120
What are the first order transitions?
melting and evaporation discontinuous w/ respect to specific volume and entropy.
121
What are second order transitions?
Glass transition discontinuity in thermal expansion coefficient and heat capacity.
122
Does the glass transition temperature occur in both amorphous and semicrystalline polymers?
yes
123
What is the glass transition temperature?
The temperature at which the amorphous polymer or amorphous components of a polymer change from a glassy to rubbery state.
124
Free volume at Tg = _?
0.025
125
What are 2 facts about Tg?
It increases with rigidity of backbone increasing. It has a strong molecular weight dependence.
126
What is the Fox equation?
1/Tg = (w1/Tg,1) + (w2/Tg,2)
127
How is the Gordan Taylor equation more specific than the Foz equation?
Takes thermal expansion coefficient into account and considers the volume fraction.
128
What is the melting temperature used for?
Characterizing the semicrystalline polymers.
129
What is the correlation between Tg and Tm for symmetric molecules?
Tg = 1/2 Tm
130
What is the correlation between Tg and Tm for asymmetric molecules?
Tg = 2/3 Tm
131
What are mechanical properties sensitive to?
Temperature and strain rate
132
What is stress?
pressure/area
133
What is strain?
chain in length/original length
134
What is Poisson's ratio (v) of an ideal rubber?
0.5
135
What is Poisson's ratio?
The decreased width/increased length upon stretching
136
What is the rubber elasticity theory?
Large deformation with extremely low modulus.
Lightly cross linked rubber.
Entropy decreases upon stretching.
137
What is stress relaxation?
If there is constant strain over time, material will relax.
ex- rubber band
138
What is the definition of viscoelastic?
Flows like a viscous material, elastic like a rubber band.
139
What is creep?
How a polymer responds to constant stress.
ex- plastic coat on a hook
140
In phase strain?
Elastic
141
Out of phase strain?
Viscous
142
G'?
Dynamic storage modulus, elastic
143
G"?
Dynamic loss modulus, viscous
144
Tan(δ) =_?
G"/G'
145
How does time temperature superposition work?
Tests properties to give an idea what will happen over a long period of time. Uses a bunch of curves to give a master curve. Only applies to thermorheologically simple materials.
146
What is the most dominant factor in processing, why?
Viscosity, it's difficult to process high viscosity materials.
147
What is rheology?
Study of flow.
148
What 5 things influence viscosity?
1. Temperature
2. shear rate
3. MW and distribution
4. molecular structure of polymeric change
5. heterogeneity
149
What is a composite?
A Heterogeneous substance consisting of two or more materials that do not
lose the individual characteristics.
150
What are reasons the composites are better?
Increased tensile strength, durability, size stability, improved fire retardancy, corrosion protection, coloring, etc.
151
What is a reinforced polymer?
composite with fibrous materials, improved composite properties.
152
What is a filled polymer?
polymers with particulate fillers, not necessarily improved composite properties.
153
What does an extender do?
Typically reduces cost without changing properties.
154
What is the hierarchy of reinforcing properties?
filament to strand to roving
thinnest -> bulkiest
155
Why do rigid rod materials have difficulty as Nano composites?
Need to have homogeneous dispersion.
156
What is nanoconfinement?
The change in structure and properties of a polymer due to the molecules being in nanospace. Surface effects become more significant.
157
Intercalated?
Not mixed well
158
Exfoliated?
Mixed well
159
What is Hand Lay-up Molding?
Laying down fabrics of reinforced fibers and painting on the resin layer until desired thickness is achieved.
160
Pros of Hand Lay-up Molding?
Fibers are easily aligned lending to very high strength.
Can create irregular shapes.
161
Cons of Hand Lay-up Molding?
Time and labor intensive.
162
Uses of Hand Lay-up Molding?
Aerospace
Airplane wings
163
What is Spray-up Molding?
Chopped fibers are sprayed on a mold with streams of resin mist and catalyst.
164
Pros of Spray-up Molding?
Large and complex objects.
Less time and labor consumption.
165
Cons of Spray-up Molding?
Short fibers, no high strength applications.
166
Uses of Spray-up Molding?
Life size statue of yourself.
Artificial rocks.
167
What is Compression Molding?
Hydraulic press to form composite into a shape.
168
Pros of Compression Molding?
Highly automated
169
Cons of Compression Molding?
Energy and labor intensive.
170
Uses of Compression Molding?
iPhone case
Construction Helmet
Shin guards
171
Transfer Molding?
Fiber/resin mix is transferred into a mold by a press. Close mold can be uses so no flash. Improvement on compression molding.
172
Resin Transfer Molding?
Preformed fiber fabric placed into mold beforehand.
173
Vacuum Assisted RTM?
Vacuum helps pull viscous resin into the perform cavity, can mold much larger objects than RTM.
174
What is Injection Molding?
Resin from extruder injected into a closed mold.
175
Pros of injection Molding?
Very fact cycle time.
Intricate shapes.
176
Uses of Injection Molding?
Pokemon toy.
Small plastic gear.
177
What is Extrusion?
Mixture is fed into a hopper, moved along a heated barrel with a screw, high shear process, injected into a mold.
178
Pros of Extrusion?
Used for short fiber reinforced thermoplastics.
High productivity.
Automated process.
Produces little scrap.
179
Cons of Extrusion?
High shear means fibers can be easily damaged.
180
Uses of Extrusion?
PVC Pipe
Constant cross-sectional area products.
181
What is Pultrusion?
Fiber rovings passed through resin bath, squeezed into shape, passed
through heated die, cured into composite.
A continuously reinforced fiber technique.
182
Pros of Pultrusion?
High productivity
Low labor costs
Inexpensive
High mechanical properties
183
Cons of Pultrusion?
Only constant cross-sectional products can be made.
184
Uses of Pultrusion?
Arrows for archery
185
What is Reaction Injection Molding?
Reaction happens in the extruder barrel.
186
Pros of Reaction Injection Molding?
Low cycle time
Low amounts of power
187
Cons of Reaction Injection Molding?
Few polymers can be made thermosets.
188
Uses of Reaction Injection Molding?
Snowmobile
Jetski
189
What is Filament Winding?
Resin wet rovings wound with figure 8 pattern around a mandrel and cured, continuous reinforced fiber technique.
190
Pros of Filament Winding?
Extremely high mechanical properties.
Automated process.
191
Cons of Filament Winding?
Time consuming
Low productivity
192
Uses of Filament Winding?
20 m Boat
500 gallon chemical tank
Nuclear submarine
Golf shaft
193
What 4 things should you consider when determining a processing method?
Aspect ratio, shape of final product. fiber types, time necessary to form solid.
194
High Aspect ratio?
Hard to extrude or injection mold.
195
Continuous fibers?
Reaction injection molding and resin transfer molding.
196
A relative measurement that can determine Mn, Mw, Mz.
Size Exclusion Chromatography
197
Jacquinot's Advantage?
energy throughput advantage
198
Conne's Advantage?
frequency accuracy advantage
199
Fellgett's Advantage?
multiplex advantage
200
What 2 types of molecular vibrations are studied in Infrared Spectroscopy?
Stretches and bends
201
What is Nuclear Magnetic Resonance Spectroscopy?
Studies the properties of nuclear spin in a magnetic field. Highly specific. C^13, H^1
202
What is Chemical shift factor?
Resonant frequency of a nucleus relative to a standard in a magnetic field.
203
Differential Scanning Calorimetry (DSC)?
Measures the heat required to maintain the same temperature. Can determine Tg, degree of crystallinity, melting, crystallization temperature, and conversion.
204
Thermogravimetric Analysis (TGA)?
Uses a highly accurate quartz balance to measure the weight of a sample as a function of temperature.
Thermal decomposition as a function of temperature.
Char yield at 800 C
5% degradation temperature
205
Dynamic Mechanical Analysis (DMA)?
Determines viscoelastic properties (stretching, twisting, bending, etc.)
Determines cross linking density, Tg.
Determines G' and G"
206
G'
Storage modulus, stored energy
207
G"
Loss modulus, energy dissipated as heat
208
Tanδ
Phase angle between G' and G"
209
