Polymeric Materials Flashcards
Types of Polymers
- Linear polymers
- Branched polymers
- Star polymers
- Dendrimers
Polymer
large molecule comprised of repeating structural units joined by covalent bonds
Polymeric biomaterals used for
- syringes
- tubings
- wound dressing
- drug delivery system, wafer for brain tumor ( last picture )
Major nondisposable market
- testing/diagnostic equipment
- surgical instruments and related equipment
- prostheses/implants
- dental/ophthalmic devices
Disposable products
syringes, kits, labware, tubing, blood bags, utensils, gloves, trays, catheters, thermometers, etc.
What polymers represent 80% of the medical field?
PVC, polypropylene and polystyrene.
successful product design requires knowledge of:
- requirements of final product
- behavior of polymeric materials
- commercial polymer processing technology
- relevant cost and market factors
Molecular arrangement of polymers
- most polymers are large linear macromolecules
- this chain is called the backbone
- normally, some of these atoms in the chain will have small chains of atoms attached to them called pendant groups
- pendant chains normally have a few atoms but the backbone chain usually has hundreds of thousands of atoms
Polyethylene
simplest polymer structure, containing carbon and hydrogen
Polypropylene
backbone chain is made up of just two carbon atoms repeated over and over again.
Hydrocarbons
contain only carbon and hydrogen
Polymers vs. organic compounds
molecular weight and dimension
Structure of Polymers
many polymers made of carbon and hydrogen, Oxygen, chlorine, fluorine, nitrogen, silicon, phosphorous, and sulfur are other elements found in the molecular makeup of polymers.
Polyvinyl chloride (PVC) contains
chlorine
Nylon contains
nitrogen
Teflon contains
fluorine
Polyester and polycarbonates contain
oxygen
Inorganic polymers
skeletal structure that does not include carbon atoms in the backbone
ex. Polysiloxanes (Silicones) and Polyphosphazenes
Vinyl Polymers
Made from vinyl monomers, small molecules containing carbon-carbon double bonds
- make up the largest family of polymers.
Polymer conformation
refers to the three- dimensional arrangement of atoms within a polymer chain.
Polymer Structure
- carbon to carbon bond allows full rotations of molecules, or conformations
- refers to the 3D arrangement of atoms within a polymer
Consequences Random coil model
- prevents crystallization, dispersed in liquid
- entanglement gives rise to very high viscosity of polymer melts
- elasticity of elastomers
Branched polymers
large branches compared to the linear structure
Linear Polymers
Proteins are linear polymers that consist of all levo-isomers of amino acids.
Star polymers
- ends of several polymer chains are joined together at a common center
- often used as additives or as coating materials
- at least 3 arms joined
- homo star polymer if arms are the same
Dendrimer
- sometimes no backbone chain at all
- built in a way that branches just keep growing out of branches
- precise branches
- different generations
- tree like structure
- finding number generations can find molecular weight
Cross-linked polymers
- both ends of the branch chains are attached to the backbone chains of separate polymer molecules
- 3D network can be formed
Types of polymers classification based on
Processing: Thermosets, Thermoplastics
Mechanical properties: elastomers
Chemical properties: hydrogels, polyelectrolyes
Origin: natural
Biostability: biodegradable
Polymerization starts with monomers
large number of monomers react to form polymer, addition and condensation polymerization
Addition polymerization or Chain Growth Polymerization
entire monomer molecule becomes part of the polymer one at a time, involves the sequential addition of monomer units containing double or triple bonds, without the loss of small molecules.
Addition polymerization example
ethylene is polymerized to polyethylene
Condensation polymerization or condensation elimination polymerization
reaction where part of the monomer molecule is kicked out when the monomer becomes part of the polymer, part that gets kicked out is usually a small molecule like water or hcl gas
Nylon 6,6
Because there is less mass in the polymer than in the original monomers, we say that the polymer is condensed with regard to the monomers.
Condensation polymerization, Step Growth polymerization
multiple reaction products are possible
ex. terephthaloyl chloride and ethylene glycol, to make a polyester called poly(ethylene terephthalate).
Dimer
two monomers come together which form dimer
ex. Terephthaloyl chloride and ethylene glycol react to form an ester dimer
Monodiperse
defined structure and defined molecular weight (protein), molecules have the same degree of polymerization or relative molecular mass
average molecular weight of a polydisperse polymer is equal to
product of the DP (degree of polymerization) and the molecular weight of the repeating unit
Molecular weight districution
bell curve
polydispersity index
how wide the distribution is within a sample; value greater than or equal to one: it is equal to one only if all the molecules have the same weight (i.e. if it is monodisperse), and the further away it is, the larger the spread of molecular weights.
Number Average Molecular Weight (Mn)
defined as the total weight of polymer divided by the total number of molecules.
Weight Average Molecular Weight (Mw)
depends not only on the number of molecules present, but also on the weight of each molecule.
Gel permeation chromatography
separation of polymer based on size; small molecules move slower because it goes into all the cavities, takes longer to dilute out of system
Increasing molecular mass…
- high strength (higher interchain forces, more entanglement)
- higher impact strength
- higher chemical resistivity
- reduction in flowability and resistance to melt fracture
Interchain bonding of polymers are
covalent
intermolecular binding:
- permanent dipole (polar groups)
- induction forces: induced dipole
- hydrogen bonds
- repulsive forces
- van der waals interaction
Intermolecular interactions
forces between permanent dipoles
- different electronegativity of partners
- permanent dipole moment
Effect of polar groups
- increased intermolecular attraction
- influence on solubility (strong dipole forces tend to dissolve better in polar solvents)
Hydrogen bonds
FON
External dipole moment
almost none for symmetrical arrangement of dipoles
Thermoplastics vs. Thermosets
- two categories of polymers with distinct properties, applications, and processing techniques
- the difference lies in how they respond to heat and whether they can be reshaped after initial formation
Thermoplastic polymers
- soften, melt, and flow when heat applied, adhesives solidify when cooled
- can be reprocessed
- ideal for application that require flexibility in processing and reshaping
Forms of thermoplastics
- amorphous
- random stucture
- good clarity
- broad melt temperature
- low mold shrinkage
- ex: polycarbonate,
polystyrene, pvc
- semi-crystalline
- linear alignment of chains
- harder, less flexible
- unique melting point
- high mold shrinkage
- ex: polyethylene, polypropylene, PTFE, polyamide
Thermosets
- large number of crosslinking!!
- process of forming cross links between linear polymer molecules
- cant reprocess, become infusible and insoluble and rigid
- hard, strong rigid
- excellent heat resistance
Thermosets Amorphous Nature
The cross-linking that occurs during the curing process locks the polymer chains into a fixed position, preventing them from arranging into ordered, crystalline domains.
Thermosets Cross-linked Structure
The highly cross-linked structure of thermosets prevents significant movement of the polymer chains, making them rigid and giving them their high thermal stability, chemical resistance, and mechanical strength.
Thermosets characteristics
They are ideal when structural integrity, heat resistance, and chemical resistance are critical.
- not meltable, not soluble, not swellable, processing generally prior to crosslinking
80% of polymers used in the medical industry are represented by 3 polymers.
Which of these is not one of the 3 polymers?
PVC
Polypropylene
Polyamide
Polystyrene
Polyamide
True or false: All polymers have a backbone chain that is made of carbon.
False
At the heart of polymer science and technology is:
Processing properties
Molecular structure
Material properties
Application
Molecular structure
Which element is present in the polymer polyvinyl chloride (PVC)?
Oxygen
Chlorine
Flourine
Nitrogen
Chlorine
What is the key characteristic of vinyl monomers that form vinyl polymers?
They contain carbon-carbon double bonds.
Which of the following are consequences of the random coil model in polymers?
Crystallization is strongly impeded by chain entanglement.
Polymer melts exhibit very high viscosity due to entanglement.
There is an entropic restoring force when the chain is stretched.
What makes polymers different from each other?
Molecular Weight, Crosslinking, Crystallinity
What type of polymerization is used to turn ethylene into polyethylene?
Addition Polyermization
True or false: Nylon 6,6 undergoes addition polymerization.
False
Increasing molar mass leads to:
Higher Chemical Resistivity
Which of the following elements can form hydrogen bonds due to their
strong electronegativity?
Fluorine, Oxygen, Nitrogen
Which of the following is a characteristic of thermoplastic polymers?
They soften, melt, and flow when heat is applied and solidify when cooled
Which of the following is a key property of thermoset polymers?
They are hard, strong, and rigid with excellent heat resistance
Which of the following is an effect of polar groups on a polymer?
Lower solubility in non-polar solvents
