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MSE 3611 > Lecture 20 - Polymers (B) > Flashcards

Lecture 20 - Polymers (B) Flashcards

1
Q

Natural Polymers

A
  • Chitosan
  • Collagen
  • Cellulose
  • DNA
  • Natural Rubber
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2
Q

Synthetic Polymers

A
  • PE
  • PS
  • PLA (Polylactic acid)
  • PGA (Polyglycolide)
  • PLGA
  • PCL (Polycaprolactone
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3
Q

Addition Polymerization

A
  • Chain reaction
  • Unsaturated monomers react (opens bond within)
  • Initiation, propagation, termination
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4
Q

Initiation

A
  • Activates monomer
  • Free radical, cation, anion
  • Opens double bond within monomer
  • Creates initiation site (site that wants to bond)
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5
Q

Propagation

A

Rapid chain growth

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6
Q

Termination

A
  • Reaction with another radical, solvent molecule, fragment of polymer chain
  • Depends on probability, more difficult to control
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7
Q

Condensation Polymerization

A
  • Stepwise growth
  • Two monomers react to form covalent bond
  • Elimination of small molecule (H2O, HCl, CO2)
  • Often carboxylic acid and amide
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8
Q

Synthesis Method

A
  • Strongly affects polymer obtained
  • Ex: free radical polymerization (MW difficult to control, MW distribution broad, branched products)
  • Ex: anionic polymerization (lower PI, regular linear chains, termination via addition of cation to neutralize process)
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9
Q

Homopolymer

A

All one mer

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10
Q

Copolymer

A
  • Alternating mers, no product of polymerization made
  • For Addition: random/alternating (blend of properties based on weight % of mers), or block (distinct properties of each)
  • For Condensation: depends on monomer used, properties depend on distribution of polymer
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11
Q

Solid State Properties

A
  • Determined from synthesis
  • Tacticity
  • Crystallinity
  • Thermal Properties
  • Mechanical Properties
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12
Q

Thermal Properties

A
  • Melt/Liquid State

- Measured by viscoelastic response (good for rank order, not great quantification), and DSC

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13
Q

Thermal Properties: Thermal Energy

A
  • Random chain motion (Brownian motion)
  • Cool-temp reached where all chain motion essentially ceases, glass transition temp (T_g), varies from polymer to polymer
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14
Q

Thermal Properties: Polymers Below T_g

A

Hard, glassy

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15
Q

Thermal Properties: Polymers Above T_g

A

Rubbery

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16
Q

Thermal Properties: Polymers With Crystallinity

A

Changes melting temp (T_m), melting of crystallinity phase

17
Q

Differential Scanning Calorimetry (DSC)

A
  • Can provide T_g —> heat capacity increases as energy is absorbed by chain rearrangement
  • Can provide T_m —> peak temperature, endothermic can be used to determine % crystallinity
  • Sample of known mass heated or cooled, changes in heat capacity tracked
  • Used to detect transitions in material —> melt, T_g, phase transformations, curing, loss of solvents, degradation
18
Q

DSC Type #1

A

Heat Flow

  • How much energy put in to raise temperature
  • Double oven (2 samples in separate ovens), maintain reference material/sample material @ same T
  • Measure difference in power to do this
  • During melting, heat absorbed into material
  • More power to sample to obtain equal T between sample/reference
19
Q

DSC Type #2

A

Heat Flux

  • Single oven
  • Measure T difference between sample and reference
  • Cheaper, less accurate
  • Sample absorbs heat, cooler than reference
20
Q

Mechanical Properties: Mechanical Testing

A
  • Highly dependent on test conditions
  • Temperature —> as T increases, increase in thermal energy results in chain motion and increase in free volume between chains
  • Rate —> fast rate means no time for chains to reorient and slide past one another, higher stiffness, shorter elongation to failure, brittle
21
Q

Mechanical Properties: Semi-Crystalline Polymers

A
  • Contains spherulites (ordered structure, polymer chains tightly packed with amorphous regions in between)
22
Q

Mechanical Properties: Exposure to Tensile Force

A
  • Tie chains extend and lamellae slide past each other
  • Lamellae become reoriented —> chain folds aligned along axis of loading
  • Blocks of crystalline phase become separated from one another (extra energy)
  • Blocks and tie molecules oriented along axis of applied tensile force
23
Q

Classes of Polymers

A
  • Homopolymers
  • Copolymers
  • ——> Non-resorbable and Bioresorbable
24
Q

Non-Resorbable Homopolymers

A
  • PMMA (polymethylmethacrylate)
  • HEMA (2-hydroxyethyl methacrylate)
  • HDPE (high density polyethylene)
  • PP (polypropylene)
  • PTFE (polytetrafluoroethylene)
  • PVC (polyvinylchloride)
  • PDMS (poly(dimethysiloxane))
25
Q

PMMA (polymethylmethacrylate)

A
  • AKA plexiglass, lucite
  • Hydrophobic
  • Clear
  • Tough
  • Applications: hard contact lenses (not very flexible/comfortable for eye), bone cements (hold in place)
26
Q

HEMA (2-hydroxyethyl methacrylate)

A
  • Hydrophilic
  • Clear
  • Soft
  • Cross-linked to resist degradation
  • Applications: soft contact lenses (wettable and easy movement along eye, but susceptible for protein deposition)
27
Q

HDPE (high density polyethylene)

A
  • Hydrophobic
  • Tough
  • Inexpensive
  • Applications: tubing, drains, catheters, UHMWPE acetabular cups (articulating surfaces)
28
Q

PP (polypropylene)

A
  • High rigidity (semi-crystalline form)
  • Chemical resistance
  • Good tensile strength
  • Applications: similar to HDPE, storage containers (tubes)
29
Q

PTFE (polytetrafluoroethylene)

A
  • AKA gortex
  • Very stable
  • Difficult to process
  • Very hydrophobic
  • Low coefficient of friction (don’t want protein adsorption)
  • Applications: vascular grafts
30
Q

PVC (polyvinylchloride)

A
  • Hard
  • Brittle
  • Can be softened with plasticizers (plasticizers can be eluted into body, give space between adjacent chains)
  • Applications: tubing
31
Q

PDMS (poly(dimethysiloxane))

A
  • Extremely flexible (Si-O-Si)
  • Lower T-g (remain rubbery to lower T)
  • Applications: catheters, tubing, insulation, blood vessels, heart valves, cosmetic surgery —> comfortable
32
Q

Non-resorbable Copolymers

A
  • FEP (tetrafluoroethylene-hexafluoropropylene)

- Polyurethane

MSE 3611 (16 decks)

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