Lecture 20 - Polymers (B) Flashcards
1
Q
Natural Polymers
A
- Chitosan
- Collagen
- Cellulose
- DNA
- Natural Rubber
2
Q
Synthetic Polymers
A
- PE
- PS
- PLA (Polylactic acid)
- PGA (Polyglycolide)
- PLGA
- PCL (Polycaprolactone
3
Q
Addition Polymerization
A
- Chain reaction
- Unsaturated monomers react (opens bond within)
- Initiation, propagation, termination
4
Q
Initiation
A
- Activates monomer
- Free radical, cation, anion
- Opens double bond within monomer
- Creates initiation site (site that wants to bond)
5
Q
Propagation
A
Rapid chain growth
6
Q
Termination
A
- Reaction with another radical, solvent molecule, fragment of polymer chain
- Depends on probability, more difficult to control
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
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)
9
Q
Homopolymer
A
All one mer
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
11
Q
Solid State Properties
A
- Determined from synthesis
- Tacticity
- Crystallinity
- Thermal Properties
- Mechanical Properties
12
Q
Thermal Properties
A
- Melt/Liquid State
- Measured by viscoelastic response (good for rank order, not great quantification), and DSC
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
14
Q
Thermal Properties: Polymers Below T_g
A
Hard, glassy
15
Q
Thermal Properties: Polymers Above T_g
A
Rubbery
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
PMMA (polymethylmethacrylate)
- AKA plexiglass, lucite
- Hydrophobic
- Clear
- Tough
- Applications: hard contact lenses (not very flexible/comfortable for eye), bone cements (hold in place)
26
HEMA (2-hydroxyethyl methacrylate)
- Hydrophilic
- Clear
- Soft
- Cross-linked to resist degradation
- Applications: soft contact lenses (wettable and easy movement along eye, but susceptible for protein deposition)
27
HDPE (high density polyethylene)
- Hydrophobic
- Tough
- Inexpensive
- Applications: tubing, drains, catheters, UHMWPE acetabular cups (articulating surfaces)
28
PP (polypropylene)
- High rigidity (semi-crystalline form)
- Chemical resistance
- Good tensile strength
- Applications: similar to HDPE, storage containers (tubes)
29
PTFE (polytetrafluoroethylene)
- AKA gortex
- Very stable
- Difficult to process
- Very hydrophobic
- Low coefficient of friction (don't want protein adsorption)
- Applications: vascular grafts
30
PVC (polyvinylchloride)
- Hard
- Brittle
- Can be softened with plasticizers (plasticizers can be eluted into body, give space between adjacent chains)
- Applications: tubing
31
PDMS (poly(dimethysiloxane))
- 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
Non-resorbable Copolymers
- FEP (tetrafluoroethylene-hexafluoropropylene)
| - Polyurethane
