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Complete summary of the Course Polymer Chemistry.
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Summary lecturesPart 1. General introduction
- The melting temperature increases, when the molecular weight increases.
- Low molecular weight molecules → no entanglements
- High molecular weight molecules → entanglements
- Longer chains: replace weak Van der Waals forces by strong covalent bonds
General stress-strain behavior
→ area = energy required for fracture (toughness)
Amorphous and crystalline polymers
- Amorphous: no order
- (semi-)crystalline: order
Thermal behavior
➔ The viscosity decreases when the temperature increases
,Summary lectures
Degree of polymerization = number of monomer (residue) units in the chain.
Molar mass of the chain = n x mass of repeat unit ( + masses of end groups)
Functionality = number of bonding sites per monomer molecule
- Monofunctional (chain stop)
- bifunctional (linear chains)
- multifunctional (network), etc.
Classifying polymers
1. According to origin
Natural, artificial, synthetic
2. According to polymerization mechanism
- Polycondensation/step
All chains react with each other; new chains have combined chain length
- Addition/chain (forms due to addition to a double bond)
Active chain adds to monomer
Grow one unit at the same time
3. According to structure
a. Composition
Backbone: flexibility (Tg) and stability (chemical and thermal)
Side groups determine: solubility, crystallinity, surface chemistry, etc.
b. Stereochemistry/tacticity → addition to double bonds via two ways.
c. Architecture
,Summary lectures
Effect of cross-linking:
4. According to mechanical properties
Fibers: resistant to deformation
Plastics: Thermoplastics: soft when heated above Tg (reversible)
Thermosets: hard when heated above a critical T (irreversible)
Elastomers: easily undergo deformation (large reversible elongations)
Part 2. Molar mass distributions and their determination
- Thermal transitions (melting point, glass transition) move to higher temperatures with
increasing molar mass
- The higher molar mass (and the more entangled), the more difficult for the chains to
escape
, Summary lectures
State diagram of amorphous polymers:
Mc = critical mass at which slope changes.
Mc ~ 2*Me (entanglement molecular weight)
Biological polymers
- Biosynthesis: step-wise addition of monomer units via enzymatic routes
- Chemical synthesis: step-wise addition of units: protection/deprotection, add excess
monomer, separate polymer
Monodisperse: all chains of the polymer have the same chain length.
There is always a distribution of chain lengths. Average chain length depends on functional
group conversion.
Molar mass distribution → all reactions occur simultaneously.
i = degree of polymerization = chain length
Molar mass = Mi
The (average) mass of a monomer unit = m0
Mi = i x m0
Ni = number of that specific chain length
Total mass: wi = Ni x Mi
Types of MMD:
- Number distribution ni
- Weight distribution wi
- Differential distribution w(log M)
M w = xw * m 0
M n = xn * m 0
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