Advanced Polymers and Applications Flashcards
Polymers
Polymers are long-chain molecules made up of a repeated pattern of monomers
Not all polymers are plastics but all plastics are polymers
Molecular weight
Sum of all atomic mass of the atoms in the chain
Rarely have a sample that contains only one chain length/molecular weight
Monodisperse: equal chain lengths
Polydisperse: unequal chain length
Classification
Thermoplastics: polymers which become plastic (flexible/mouldable) upon heating and solidifying after cooling
Thermosets: polymers which form irreversible bonds after polymerisation/curing
Elastomers: polymers which display elasticity, they are ‘rubber-like’
Chain Structure
Linear: Weak interchain interactions, Typically thermoplastics
Branched: Stronger interchain interactions, Typically thermoplastics
Network: Strong covalent bonds, thermosets
Crosslinked: Thermoset behaviour
Plasticiser: alters the mobility of polymer chains, increases the flexibility and decreases Tg
Substituents
Atatic: substitutes arranged randomly
Isotactic: on one side
Syndiotatic: alternate sides
Morphology and microstructure
Tend to be semi-crystalline
Crystals grow in the direction of fields (temperature or applied stress)
Polymer spherulites: radial growth upon nucleation in absence of fields
Glass Transition Temperature
Tg is the T at which amorphous solid loses its glasslike properties (hard/brittle) and becomes soft and flexible
All polymers have one
Increase in motion above Tg
Any factor which increases the interactions between polymer chains will increase Tg
Solubility
Depends on the chemistry and structure
Polar: tends to dissolve in water
Non-polar: can dissolve in non-polar solvents
Mechanism:
Solvent diffuses into a network and gel forms
Gel breaks up and the true solution forms
Low Mw polymers are easier to dissolve
High crystallinity ones are harder
Branched polymers dissolve easily
Smaller solvents are more effective at dissolving
In a good solvent, the bond between the solvent and the polymer should be stronger than the bond between the polymers
Identifying Polymers
Density
solubility
wettability
burning
machanical tests
optical properties: transparancies decreases with increasing Mw
Chemical compatibility
Mw
Gel Permeation Chromatography
chromatographic technique used for separating macromolecules based on their size. It involves passing a sample through a column filled with a porous gel matrix, where larger molecules move more quickly through the column, and smaller molecules experience a more tortuous path.
Measures molecular weight distribution and structure (branching etc.)
Pores exclude larger species so they move faster through the column
separates based on the hydrodynamic volume of the polymer → increases with higher MW,
Pore size should be chosen carefully
The most common detection by refractive index
Larger particles will elute first
Can be difficult to differentiate if the radius is similar
If there are more orientations where it will not fit, than when it will, it will come out first
Viscosity
Depending on structure and Mw
Viscosity of polymer solutions with known concentrations
Rheology: The rheometer measures flow or deformation of materials (including viscosity) in response to controlled shear/stress
Yield point: lowest shear stress above which a material will behave like a fluid
Thixotropy - time-dependent viscosity behaviour for shear thinning fluids
Other tests:
Characterising temperature-dependent behaviour
Gelation/cross-linking/curing characterisation
Crystallisation measurements
Thermogravimetric Analysis
a sample is heated or cooled at a constant rate, and the resulting weight loss or gain is recorded. This information provides insights into various material properties, including composition, thermal stability, and decomposition kinetics
measures thermal stability of a sample heated in air or inert gas
mass of a sample is monitored as a function of temperature
Can identify material composition and presence of contaminants
Differential Scanning Calorimetry
measures the heat flow associated with a sample’s physical or chemical changes as a function of temperature. By comparing the heat flow of a sample to a reference material, DSC provides insights into processes such as phase transitions, melting, crystallization, and chemical reactions.
thermal energy of a sample is monitored as a function of temperature
Measures thermal energy of phase transitions (crystallisation, melting point, Tg)
usually under inert atmosphere
Absorption Spectroscopy
measuring the absorption of electromagnetic radiation as it passes through a sample. The absorption spectrum obtained provides information about the chemical composition, molecular structure, and concentration of the absorbing species in the sample.
Measures absorbance of light by the sample at different wavelengths (λ)
Absorbance measured with respect to reference sample
UV Spectroscopy
Most organic molecules have some absorbance in UV/visible range → particularly those with double bonds * Absorbance proportional to concentration
IR Spectroscopy
Absorption of infrared light causes vibrations in a polymer
Unique fingerprint for each substance with a different structure and chemistry
Absorbance not directly proportional to concentration
