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BME 312 Exam 2 > Week 7 Polymers I > Flashcards

Week 7 Polymers I Flashcards

1
Q

Why choose a polymer for medical applications? (6)

A
  1. ability to degrade
  2. properties can be easily adjusted
  3. large spectrum of mechanical properties
  4. inexpensive
  5. alter physical appearance (color)
  6. manufacture in large quantities quickly with little variability
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2
Q

Recall the 6 bulk properties of materials

A
  1. chemical
  2. mechanical
  3. electrical
  4. dielectric
  5. magnetic
  6. optical
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3
Q

What is the primary bond in polymers?

A

covalent bonds

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4
Q

When are covalent bonds found in materials?

A

When the atoms have small differences in electronegativity - they share valence electrons

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5
Q

Covalently bonded materials have __________ melting and boiling points compared to ionic compounds.

A

lower melting and boiling points compared to ionic bonds

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6
Q

Lower melting and boiling points makes them __________ (not hard) and electrical ___________

A

softer and electrical insulators

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7
Q

What are the secondary bonding in polymers?

A
  1. Van der Waal’s
  2. Hydrogen
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8
Q

Van der Waal’s bonding

A

bonds between adjacent molecules and there are attractive forces between dipoles

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9
Q

What forces are between linear polymer molecules?

A

permanent dipoles

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10
Q

Hydrogen bonding

A

attractive forces between hydrogen and a highly electronegative atom (N, O, or F)

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11
Q

“poly” =

A

many

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12
Q

“mer” =

A

repeat units

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13
Q

oligomer

A

short polymer chain

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14
Q

Polyethylene (PE) repeat unit contains:

A

2 Carbon and 4 Hydrogen
each C has 2 H on top and bottom

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15
Q

Poly (vinyl chloride) (PVC) repeat unit contains:

A

2 Carbon, 3 Hydrogen, and 1 Chlorine atom
1 C has 2 H and the other C has 1 H and 1 Cl

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16
Q

Polypropylene (PP) repeat unit contains:

A

2 Carbon, 3 Hydrogen, and 1 CH3

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17
Q

Addition (chain) Polymerization

A

monomer units attached one at a time in chain-like fashion to form a linear macromolecule
- the composition of the resultant product is an exact multiple of the original reactant monomer

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18
Q

Internal factors that impact mechanical properties (4)

A
  1. chemical structure
    a. cross-linking and branching
    b. copolymerization
  2. molecular weight
  3. crystallinity
  4. additives
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18
Q

Based on the stress-strain behavior of polymers, can you explain the difference in elastic modulus, fracture strength, and deformation strains of polymers compared to metals?

A
  1. elastic modulus = much less than metals
  2. fracture strengths = about 10% of metals
  3. deformation strains > 1000%, but for most metals < 10%
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18
Q

Condensation (step) Polymerization

A

two monomers are combined to form a polymer with the loss of a small molecule, such as water

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18
Q

What are the 3 polymeric structures?

A
  1. linear - made of identical units repeated
  2. branched - main chain with side chains branched
  3. cross-linked - looks like ladder or grid
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19
Q

What are the different properties of each polymeric structure?

A
  1. linear = flexible and low melting point
  2. branched = more rigid and medium melting point
  3. cross-linked = very rigid and highest melting point
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19
Q

What are the three cross-linking techniques? (with examples)

A
  1. physical - temperature, pH, electrostatic interaction
  2. chemical - crosslinker molecules, photoinitiators
  3. enzymatic
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20
Q

What are the advantages and disadvantages of physical cross-linking?

A

A - reversible and non-toxic

D - unstable and easily disrupted with changes in temperature, pH, or ionic concentrations

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21
What are the biomaterials used for physical cross-linking? (4)
1. alginate 2. agarose 3. collagen 4. Matrigel
21
What are the advantages and disadvantages of chemical cross-linking?
A - extremely stable and allows for control of mechanical strength D - cross-linkers may induce cellular toxicity or may require additional composition to be activated (e.g. Iracure only activated by UV light)
22
What are the biomaterials used for chemical cross-linking? (4)
1. chitosan 2. gelatin methacrylate 3. hyaluronic acid 4. silk
23
What are the advantages and disadvantages of enzymatic cross-linking?
A - this cross-linking is always carried under physiological conditions and majority of enzymes used are common to those that catalyze in vivo reactions and can be used to cross-link opaque materials. Enzymes do not require light to be activated. D - this cross-linking is not tunable
24
What are the biomaterials used in enzymatic cross-linking? (4)
1. fibrin 2. gelatin 3. elastin 4. PEG
25
What is important to note about the difference between lengths of polymers?
large molecular or macromolecules have VERY different properties than small molecules
26
chain entanglement
occurs in large molecules when long polymers chain gets tangled with each other
27
small changes in the number of ______________ can cause significant differences in material properties: (4)
side branches 1. modulus 2. creep resistance 3. toughness 4. degradation
28
Copolymers and the 4 types
2 or more monomers polymerized together 1. random 2. alternate 3. block 4. graft
29
Molecular weight
mass of a mole of chains
30
Molecular Weight is a ________________ of values
distribution
31
Polydispersity Index
PDI = Mw / Mn < 0.05 common to monodisperse > 0.7 common to polydisperse distribution of particles
32
What is the main importance of molecular weight?
As the chains become longer (by polymerization), mobility decreases = more entanglements
33
The higher the molecular weight the (3) properties:
1. less mobility 2. greater strength 3. greater thermal stability
34
Hydrolysis is used to _________________
decrease MW of polymers
35
Degree of Polymerization
average number of repeat units per chain DP = Mn / m
36
Polymer Crystallinity
the packaging of molecular chains to produce an ordered atomic array
37
amorphous region occurs from (2)
chain disorder or misalignment
38
The density of a crystalline polymer is ___________ to an amorphous polymer of the same material and MW
greater
39
Heat treatment causes _________________ in % crystallinity.
increase
40
The rate of crystallization on cooling from melt depends on (2):
1. rate of nucleation 2. rate of crystalline growth
41
For semi-crystalline structures the _______________________ increases with % crystallinity
tensile modulus
42
Increasing crystallinity ___________________ what 3 properties?
increases 1. strength 2. hardness 3. modulus
43
Longer chains are _________________ to be crystallized
more difficult
44
Describe a semi-crystalline sructure
1. most common structure for linear polymers 2. contains ordered and disordered regions 3. branched polymers can't easily be crystallized due to steric hinderances
45
How do you determine crystallinity?
X-ray Diffraction sharp, scattered, and short bands = crystalline sharp, long arcs/ellipses = amorphous
46
What are 3 examples of linear, semi-crystalline polymers?
1. polyvinyls 2. polyamides 3. polyesters
47
How can you alter crystallinity?
annealing and quencing
48
What effect (3) does slow cooling have on the crystallinity of a structure?
1. increases the amount of crystallinity 2. decreases the free volume 3. increases density
49
What effect (2) does quenching have on the crystallinity of a structure?
1. less crystallization 2. more ductility - less rigid
50
What does the effect (3) of copolymerization have on crystallinity?
copolymerization decreases: 1. crystallinity 2. stiffness and hardness 3. effects side groups
51
What are the 6 Additives for polymers?
1. fillers 2. plasticizers 3. stabilizers 4. lubricants 5. colorants 6. flame retardants
52
Fillers are used to improve what 4 properties?
1. tensile and compressive strengths 2. abrasian resistance 3. toughness 4. dimensional thermal stability
53
What are examples of fillers?
1. carbon black 2. silica gel 3. wood flour 4. glass 5. limestone 6. talc
54
Plasticizers
Liquids with low vapor pressure and molecular weight to be used in polymers that are brittle to improve flexibility, ductility, and toughness
55
Plasticizers are added to what polymer since it is known to be very brittle?
PVC
56
Stabilizers
counteract deteriorative processes like UV or oxidation
57
Lubricants
added to allow easier processing; polymer "slides" through die easily
58
What is an example of a lubricant for polymers?
sodium stearate
59
Colorants
depends on the application, but may be needed.
60
Flame retardants
reduce combustibility and typically contain F, Cl, and B

BME 312 Exam 2 (6 decks)

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