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Polymers > final exam > Flashcards

final exam Flashcards

1
Q

What is a polymer?

A

A large molecule comprised of many repeat units called monomers.

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2
Q

What is an oligomer?

A

A low molecular weight polymer, about 100 - 1000s monomers.

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3
Q

Who is Hermann Staudinger?

A

The father of polymer chemistry, he proved the existence of macromolecules.

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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.

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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.

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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.

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7
Q

How many years did it take Staudinger to finally prove his theory?

A

10 years.

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8
Q

Who received the first Nobel prize in the field of polymers?

A

Hermann Staudinger

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9
Q

Definition of a thermoplastic?

A

Able to soften and liquify, reformable. A reversible and repeatable process.

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10
Q

Definition of a thermoset?

A

Permanently solid upon heating, crosslinked networks, brittle.

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11
Q

Weighted averages from greatest to least?

A

Mz > Mw > Mn

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12
Q

What is PDI?

A

The measure of breadth of distributions of the molecular weights in a polymer, always greater than 1.

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13
Q

PDI equation?

A

PDI = Mw/Mn

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14
Q

What is the PDI of a monodisperse polymer?

A

1 (or very close)

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15
Q

What are the two relative measurement methods of determining molecular weight?

A

Intrinsic viscosity & Size exclusion chromatography

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16
Q

What are the 7 types of Structural Isomers?

A

Linear, branched, star, ladder, network (crosslinked), hyper-branched, and dendrimer.

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17
Q

What 2 structural isomers have a common growth point?

A

Star & Dendrimer

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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.

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19
Q

What defines a cross linked polymer?

A

The polymers are covalently linked together by points other than their ends.

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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.

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21
Q

What are the 3 different Stereoisomers?

A

Isotactic, Syndiotactic, and Atactic

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22
Q

Which Stereoisomer is not crystalline?

A

Atactic, it’s amorphous

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23
Q

What are the 2 Geometric Isomers?

A

Cis & Trans

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24
Q

What are the 4 types of copolymers?

A

alternating, random, block, and graft

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25
Q

ABABABABAB

A

Alternating, property of -AB- monomer

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26
Q

AABABABBBABABA

A

Random, average property of A and B

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27
Q

AAAAABBBBB

A

Block, regions of property A and property B

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28
Q

AAAAAAAA
B B
B B
B

A

Graft, regions of property B surrounding property A

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29
Q

The degree of crystallinity can vary from completely amorphous to _% crystalline?

A

95

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30
Q

What 2 things increase crystallinity?

A

Slow cooling and stretching.

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31
Q

Crystalline = ?

A

Melting

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32
Q

Amorphous = ?

A

Liquify

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33
Q

What is the semicrystalline state?

A

Crystalline regions are dispersed throughout amorphous regions.

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34
Q

What is the fringed-micelle model?

A

Small crystalline regions with precise chain alignment are embedded within an amorphous matrix of randomly oriented molecules.

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35
Q

What is the chain-folded model?

A

Folds occur on platelet faces. Longer the polymer, more instability and more amorphous. Crystallinity minimizes entropy.

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36
Q

What is the spherulite model?

A

Lamellar crystal faces separated by amorphous regions.

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37
Q

What are the 3 orders of Liquid Crystals?

A

Nematic, Smectic, and Cholesteric.

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38
Q

Nematic LC?

A

No alignment of chain ends.

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39
Q

Smectic LC?

A

Chain ends are aligned.

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40
Q

Cholesteric LC?

A

Oriented chain planes rotate. Used for tv and computer monitors.

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41
Q

Thermotropic?

A

Liquid crystalline phase in temperature range.

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42
Q

Lyotropic?

A

Liquid crystalline phase in concentration range.

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43
Q

What are 2 advantages of liquid crystals?

A

Lower viscosity and higher mechanical strength.

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44
Q

How many principles of Green Chemistry are there?

A

12

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45
Q

It is better to prevent waste than to treat or clean up waste after is has been created.

A

Prevention

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46
Q

Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product.

A

Atom Economy

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47
Q

Growth by a reaction between two
oligomers.

A

Step Polymerization

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48
Q

Rapid loss of monomer species.

A

Step Polymerization

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49
Q

Driving force: removal of condensation product.

A

Step Polymerization

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50
Q

Molar mass increases slowly throughout.

A

Step Polymerization

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51
Q

Ends remain active.

A

Step Polymerization

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52
Q

No initiator.

A

Step Polymerization

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53
Q

At any stage a range of molecular species are present.

A

Step Polymerization

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54
Q

Xn?

A

Number average degree of polymerization.

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55
Q

Xn Equation?

A

Xn = No/N
No = number of molecules initially
N = final number of molecules

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56
Q

Xn equation for a stoichiometric rxn?

A

Xn = 1/(1-p)
stoichiometric (r = 1)
p = extent of reaction

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57
Q

Reactant ratio (r) equation?

A

r = Na/Nb
r is always less than or equal to 1!

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58
Q

General Carother’s equation?

A

Xn = (1+r)/(1+r-2rp)

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59
Q

Growth by monomer addition at chain ends.

A

Addition Polymerization

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60
Q

Monomer concentration is never zero.

A

Addition Polymerization

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61
Q

Molar mass increases rapidly.

A

Addition Polymerization

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62
Q

Chain ends are not reactive after termination.

A

Addition Polymerization

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63
Q

Driving force: 1 double bond to 2 single bonds.

A

Addition Polymerization

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64
Q

Initiator is required.

A

Addition Polymerization

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65
Q

Small number of polymer chains growing at a time.

A

Addition Polymerization

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66
Q

What is the first step in the reaction of a polymer chain?

A

Initiation, a free radial is formed.

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67
Q

What is the second step in the reaction of a polymer chain?

A

Propagation, monomers are added one at a time to the growing polymer chain.

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68
Q

What is the final step in the reaction of a polymer chain?

A

Termination, the free radicals are consumed.

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69
Q

What is combination termination?

A

Two reactive polymer chains combine to form one extremely large chain.

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70
Q

What is disproportionation termination?

A

A hydrogen atom is extracted by the free radical leading to the creation of two separate polymer chains.

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71
Q

Equation for kinetic chain length (v)?

A

v = Rp/Ri
Rp = rate of propagation
Ri = rate of initiation

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72
Q

What is the relationship between kinetic chain length (v) and molecular weight?

A

v = k’([M]/[I]^1/2)
Xn = v by disproportionation
Xn = 2v by combination

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73
Q

What is the equation for rate of propagation (Rp)?

A

Rp = [M][I]^1/2
[M] = concentration of monomer
[I] = concentration of initiator

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74
Q

As concentration of monomer increases?

A

Rp increases
Xn increases

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75
Q

As concentration of initiator increases?

A

Rp increases
Xn decreases

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76
Q

What is Autoacceleration (Trommsdorff-Norrish effect)?

A
  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
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77
Q

When does chain transfer occur?

A

When one polymer chain is terminated, but a new growing chain is initiated.

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78
Q

What are the 2 main types of chain transfer?

A

Intramolecular and Intermolecular

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79
Q

Intramolecular?

A

Across, leads to short chain branching (backbiting mechanism.

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80
Q

What is the progression of intramolecular chain transfer?

A

linear -> butyl branch -> 2 ethyl branches

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81
Q

Intermolecular?

A

Between, long chain branching. NOT a termination step.

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82
Q

What is an inhibitor?

A

Prevents polymerization from taking place until all of the inhibitor is used up.

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83
Q

What does an inhibitor do to the free radical species?

A

Consumes

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84
Q

What type of chain transfer does an inhibitor have?

A

Intramolecular

85
Q

What does a retarder do?

A

Slows the polymerization process.

86
Q

What does a retarder do to free radicals?

A

Converts them into more stable free radicals.

87
Q

What type of chain transfer does a retarder have?

A

Intermolecular

88
Q

How does ionic polymerization differ from free radical?

A

Much faster, and uses ions.

89
Q

Why can’t coupling (termination) occur between two growing chains in ionic polymerization?

A

The active centers are of the same charge, thus repulsion occurs.

90
Q

Why is Cationic polymerization used?

A

To make stereospecific polymers.

91
Q

What are 4 important facts about cationic polymerization?

A

Lots of side rxns
high MW = subzero temps
rapid (seconds)
issues with heat transfer and steady state

92
Q

Why use Anionic polymerization?

A

Living polymerization, polymer chains permanently retain their active centers and continue to grow as long as there are monomers.

93
Q

Equation for anionic polymerization (Poisson distribution)?

A

Mw/Mn = 1+1/(Xn)

94
Q

What are 2 important facts about anionic polymerization?

A

Super reactive
Low concentration of reaction species

95
Q

What are 3 other types of polymerization?

A

Photo-polymerization, radiation, and electrochemical

96
Q

What are 3 advantages of photopolymerization?

A

No initiator contamination
Fast (seconds)
Photolithography can be used

97
Q

What are 2 disadvantages of photopolymerization?

A

UV penetration into bulk
# of photo-cleavable monomers

98
Q

What is important about radiation polymerization?

A

There are no contaminants, but it can give degradation.

99
Q

What is important about electrochemical polymerization?

A

Used for corrosion protection
Can’t be used for bulk polymerization

100
Q

What is the end-to-end distance (R)?

A

The distance that connects two terminal ends of a polymer chain.

101
Q

In a good solvent, is the R larger or smaller?

A

Larger

102
Q

What is the equation for <R> w/ no angle restriction?</R>

A

<R> = b*sqrt(n)
</R>

103
Q

What is the equation of <R> w/ a fixed angle?</R>

A

<R> = sqrt(2)*b*sqrt(n)
</R>

104
Q

Why is the radius of gyration (S) used to determine <R>?</R>

A

<R> is difficult to measure.
</R>

105
Q

How is the radius of gyration (S) measured?

A

Using light scattering techniques.

106
Q

What is the equation that relates the end-to-end distance to the radius of gyration?

A

<S^2> = 1/6<R^2> = 1/6n(b^2)

107
Q

What is the Flory-Huggins theory used for?

A

Calculating the deltaG of mixing.

108
Q

What are the 4 assumptions of the Flory-Huggins theory?

A
  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
Q

What are the 2 disadvantages of the flory-huggins theory?

A

doesn’t allow for thermal expansion, and different solvent molecule sizes cannot be evaluated

110
Q

What value of deltaG is necessary for mixing to occur?

A

Greater than zero

111
Q

What is the equation for the flory-huggins parameter (X)?

A

Xc = 1/2*(1/sqrt(n1) + 1/sqrt(n2))^2
if X > Xc soln will not mix

112
Q

theta-solvent -
X parameter = _?

A

0.5

113
Q

What are the exceptions of molecules that show lower critical solution temperatures (LCST)?

A

They dissolve in cold solvents and precipitate in hot solvents.

114
Q

What does viscosity mean?

A

Difficulty to flow.

115
Q

What does the Doolittle equation tell us?

A

Viscosity is a function of temperature.

116
Q

What is the Mark-Houwink-Saruda equation?

A

Intrinsic viscosity = K(M^a)
K and a are constants
M is the viscosity average molecular weight

117
Q

What leads to molecular entanglement?

A

A polymer is a good solvent of itself.

118
Q

How does the relationship between viscosity and MW change above the entanglement MW?

A

Viscosity goes from being proportional to MW^1 to proportional to MW^3.4

119
Q

What is the reptation model?

A

Polymeric chains repeating through a tube, can move in the direction of the tube but not transversely bc of entanglement.

120
Q

What are the first order transitions?

A

melting and evaporation discontinuous w/ respect to specific volume and entropy.

121
Q

What are second order transitions?

A

Glass transition discontinuity in thermal expansion coefficient and heat capacity.

122
Q

Does the glass transition temperature occur in both amorphous and semicrystalline polymers?

A

yes

123
Q

What is the glass transition temperature?

A

The temperature at which the amorphous polymer or amorphous components of a polymer change from a glassy to rubbery state.

124
Q

Free volume at Tg = _?

A

0.025

125
Q

What are 2 facts about Tg?

A

It increases with rigidity of backbone increasing. It has a strong molecular weight dependence.

126
Q

What is the Fox equation?

A

1/Tg = (w1/Tg,1) + (w2/Tg,2)

127
Q

How is the Gordan Taylor equation more specific than the Foz equation?

A

Takes thermal expansion coefficient into account and considers the volume fraction.

128
Q

What is the melting temperature used for?

A

Characterizing the semicrystalline polymers.

129
Q

What is the correlation between Tg and Tm for symmetric molecules?

A

Tg = 1/2 Tm

130
Q

What is the correlation between Tg and Tm for asymmetric molecules?

A

Tg = 2/3 Tm

131
Q

What are mechanical properties sensitive to?

A

Temperature and strain rate

132
Q

What is stress?

A

pressure/area

133
Q

What is strain?

A

chain in length/original length

134
Q

What is Poisson’s ratio (v) of an ideal rubber?

A

0.5

135
Q

What is Poisson’s ratio?

A

The decreased width/increased length upon stretching

136
Q

What is the rubber elasticity theory?

A

Large deformation with extremely low modulus.
Lightly cross linked rubber.
Entropy decreases upon stretching.

137
Q

What is stress relaxation?

A

If there is constant strain over time, material will relax.
ex- rubber band

138
Q

What is the definition of viscoelastic?

A

Flows like a viscous material, elastic like a rubber band.

139
Q

What is creep?

A

How a polymer responds to constant stress.
ex- plastic coat on a hook

140
Q

In phase strain?

A

Elastic

141
Q

Out of phase strain?

A

Viscous

142
Q

G’?

A

Dynamic storage modulus, elastic

143
Q

G”?

A

Dynamic loss modulus, viscous

144
Q

Tan(δ) =_?

A

G”/G’

145
Q

How does time temperature superposition work?

A

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
Q

What is the most dominant factor in processing, why?

A

Viscosity, it’s difficult to process high viscosity materials.

147
Q

What is rheology?

A

Study of flow.

148
Q

What 5 things influence viscosity?

A
  1. Temperature
  2. shear rate
  3. MW and distribution
  4. molecular structure of polymeric change
  5. heterogeneity
149
Q

What is a composite?

A

A Heterogeneous substance consisting of two or more materials that do not
lose the individual characteristics.

150
Q

What are reasons the composites are better?

A

Increased tensile strength, durability, size stability, improved fire retardancy, corrosion protection, coloring, etc.

151
Q

What is a reinforced polymer?

A

composite with fibrous materials, improved composite properties.

152
Q

What is a filled polymer?

A

polymers with particulate fillers, not necessarily improved composite properties.

153
Q

What does an extender do?

A

Typically reduces cost without changing properties.

154
Q

What is the hierarchy of reinforcing properties?

A

filament to strand to roving
thinnest -> bulkiest

155
Q

Why do rigid rod materials have difficulty as Nano composites?

A

Need to have homogeneous dispersion.

156
Q

What is nanoconfinement?

A

The change in structure and properties of a polymer due to the molecules being in nanospace. Surface effects become more significant.

157
Q

Intercalated?

A

Not mixed well

158
Q

Exfoliated?

A

Mixed well

159
Q

What is Hand Lay-up Molding?

A

Laying down fabrics of reinforced fibers and painting on the resin layer until desired thickness is achieved.

160
Q

Pros of Hand Lay-up Molding?

A

Fibers are easily aligned lending to very high strength.
Can create irregular shapes.

161
Q

Cons of Hand Lay-up Molding?

A

Time and labor intensive.

162
Q

Uses of Hand Lay-up Molding?

A

Aerospace
Airplane wings

163
Q

What is Spray-up Molding?

A

Chopped fibers are sprayed on a mold with streams of resin mist and catalyst.

164
Q

Pros of Spray-up Molding?

A

Large and complex objects.
Less time and labor consumption.

165
Q

Cons of Spray-up Molding?

A

Short fibers, no high strength applications.

166
Q

Uses of Spray-up Molding?

A

Life size statue of yourself.
Artificial rocks.

167
Q

What is Compression Molding?

A

Hydraulic press to form composite into a shape.

168
Q

Pros of Compression Molding?

A

Highly automated

169
Q

Cons of Compression Molding?

A

Energy and labor intensive.

170
Q

Uses of Compression Molding?

A

iPhone case
Construction Helmet
Shin guards

171
Q

Transfer Molding?

A

Fiber/resin mix is transferred into a mold by a press. Close mold can be uses so no flash. Improvement on compression molding.

172
Q

Resin Transfer Molding?

A

Preformed fiber fabric placed into mold beforehand.

173
Q

Vacuum Assisted RTM?

A

Vacuum helps pull viscous resin into the perform cavity, can mold much larger objects than RTM.

174
Q

What is Injection Molding?

A

Resin from extruder injected into a closed mold.

175
Q

Pros of injection Molding?

A

Very fact cycle time.
Intricate shapes.

176
Q

Uses of Injection Molding?

A

Pokemon toy.
Small plastic gear.

177
Q

What is Extrusion?

A

Mixture is fed into a hopper, moved along a heated barrel with a screw, high shear process, injected into a mold.

178
Q

Pros of Extrusion?

A

Used for short fiber reinforced thermoplastics.
High productivity.
Automated process.
Produces little scrap.

179
Q

Cons of Extrusion?

A

High shear means fibers can be easily damaged.

180
Q

Uses of Extrusion?

A

PVC Pipe
Constant cross-sectional area products.

181
Q

What is Pultrusion?

A

Fiber rovings passed through resin bath, squeezed into shape, passed
through heated die, cured into composite.
A continuously reinforced fiber technique.

182
Q

Pros of Pultrusion?

A

High productivity
Low labor costs
Inexpensive
High mechanical properties

183
Q

Cons of Pultrusion?

A

Only constant cross-sectional products can be made.

184
Q

Uses of Pultrusion?

A

Arrows for archery

185
Q

What is Reaction Injection Molding?

A

Reaction happens in the extruder barrel.

186
Q

Pros of Reaction Injection Molding?

A

Low cycle time
Low amounts of power

187
Q

Cons of Reaction Injection Molding?

A

Few polymers can be made thermosets.

188
Q

Uses of Reaction Injection Molding?

A

Snowmobile
Jetski

189
Q

What is Filament Winding?

A

Resin wet rovings wound with figure 8 pattern around a mandrel and cured, continuous reinforced fiber technique.

190
Q

Pros of Filament Winding?

A

Extremely high mechanical properties.
Automated process.

191
Q

Cons of Filament Winding?

A

Time consuming
Low productivity

192
Q

Uses of Filament Winding?

A

20 m Boat
500 gallon chemical tank
Nuclear submarine
Golf shaft

193
Q

What 4 things should you consider when determining a processing method?

A

Aspect ratio, shape of final product. fiber types, time necessary to form solid.

194
Q

High Aspect ratio?

A

Hard to extrude or injection mold.

195
Q

Continuous fibers?

A

Reaction injection molding and resin transfer molding.

196
Q

A relative measurement that can determine Mn, Mw, Mz.

A

Size Exclusion Chromatography

197
Q

Jacquinot’s Advantage?

A

energy throughput advantage

198
Q

Conne’s Advantage?

A

frequency accuracy advantage

199
Q

Fellgett’s Advantage?

A

multiplex advantage

200
Q

What 2 types of molecular vibrations are studied in Infrared Spectroscopy?

A

Stretches and bends

201
Q

What is Nuclear Magnetic Resonance Spectroscopy?

A

Studies the properties of nuclear spin in a magnetic field. Highly specific. C^13, H^1

202
Q

What is Chemical shift factor?

A

Resonant frequency of a nucleus relative to a standard in a magnetic field.

203
Q

Differential Scanning Calorimetry (DSC)?

A

Measures the heat required to maintain the same temperature. Can determine Tg, degree of crystallinity, melting, crystallization temperature, and conversion.

204
Q

Thermogravimetric Analysis (TGA)?

A

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
Q

Dynamic Mechanical Analysis (DMA)?

A

Determines viscoelastic properties (stretching, twisting, bending, etc.)
Determines cross linking density, Tg.
Determines G’ and G”

206
Q

G’

A

Storage modulus, stored energy

207
Q

G”

A

Loss modulus, energy dissipated as heat

208
Q

Tanδ

A

Phase angle between G’ and G”

209
Q
A

Polymers (1 decks)

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