Week 7 Flashcards
What are 6 advantages of polymers?
- ease of manufacturability to produce different shapes
- cost
- desired mechanical and physical properties
- modification of surfaces to make them bioactive to body of biological processes
- low density
- biodegradeable
These are the largest molecules made of repeating parts
polymers
What does polymer mean when broken up?
poly = many
mer = part
a long chain molecule made up of many small identical units
polymer
the smallest repeating unit of a polymer
monomer
What is an example of a monomer?
ethylene in polyethylene
What is the reaction that occurs to allow bonds between monomers to form polymers?
polymerization
Polymers are primarily held by what two types of bonding
- primary covalent –> forces to form a chain and crosslinks between chains
- secondary bonding (van der waals & hydrogen)
What bond properties are represented by covalent bonds?
mechanical, thermal, photochemical
What bond properties are represented by secondary bonds?
physical, melting, flow, dissolution
How is the molecular weight of polymers determined?
calculated from the molecular weights of all the chains
What happens as molecular chains become longer?
mobility decreases
What happens as molecular weight increases?
less mobility of the chains (more entangled) –> higher strength –> greater thermal stability
What are the 4 ways which polymer chains can be arranged?
- linear
- branched
- cross-linked
- three-dimensional
In these type of polymers, the repeating units are joined end to end. There may also be extensive van der Waals and hydrogen bonding between chains
linear polymers
These type of polymers have branched side chains connected to the backbone which result from side reactions during polymersynthesis.
branched polymers
What happens to the chain packing efficiency when branches are formed within polymers?
reduced –> lower polymer density
How are cross-linking polymers obtained?
by adding a cross-linking agent
What three things can crosslinking of polymers change?
- melting temperature, strength, flexibility
- increase wear resistance
- degradation from solvents (i.e., alcohol)
This type of polymer has 3 active covalent bonds which forms 3-D networks and may be highly crosslinked
network polymer
How are polymers classified?
by type of polymers
- homopolymers
- copolymers
one type of monomer is used to form the polymer
homopolymers
if two types of monomers (a and B) are used in the polymerization reaction
copolymers
process which takes chemical bonds of monomer to form chains
polymerization
Not all monomers react during polymerization, so what is the result of this?
residual monomers trapped in the polymer
True or false: Polymerization may produce byproducts
true
What two things happen during polymerization?
- polymer chains with different lengths formed
- number of monomers per chain are different
the extent to which monomer is converted into polymers
degree of polymerization
This type of polymerization leads to more rigid, less soluble polymer netowrks
high degree
This type of polymerization has fewer longer polymer chains
high degree
What are the 3 chemical stages to obtain the monomer’s bonding?
- initiation –> activation of monomer
- propogation –> chain growth
- termination –> reaction completion
When does an addition polymerization begin?
when a free radical is formed
True or false: In addition polymerization, there is co-generation of byproducts.
False, there is no co-generation of by-products
What are 3 reasons why addition polymerization is preferred clinically?
- no risk of leaching of the by-product intraorally
- prevents increase shrinkage
- toxic reactions to the patient
What is an example of polymerization?
PMMA
a chemical species that reacts with a monomer to form an intermediate compound
initiator
What do the most widely used initiators produce?
free radicals
What are the 3 types of initiators?
- photo –> light
- chemical –> chemistry
- thermal –> heat
increases the speed of polymerization
accelerator
chemicals modify the interactions between the polymer strands
plasticizers
solid particles that change their optical or physical properties
fillers
What two things can happen when fillers are added into the polymer?
- increase wear resistance
- decrease shrinkage
What do the physical states of polymers depend on?
phase, configuration and alignment of molecular chains
- amorphous
- crystalline
- semi-crystalline
True or false: polymers are rarely 100% crystalline
True
The temperature at which a significant loss of modulus (stiffness) or volume occurs
glass transition temperature (Tg)
What are 5 properties of thermoplastic polymers?
- linear and branched structures (easy to fabricate)
- soften when heated, harden when cooled
- reversible
- reheating and reforming do not significantly change properties
- very long main chain of carbon atoms covalently bonded
What are 5 properties of thermoset polymers?
- heat required to permanently set
- formed by temporary disabling of crosslinking
- once hardened, structure will not soften upon heating
- degrades or decomposed if heated at high temperature
- harder and stronger than thermoplastics
Compare and contrast thermoplastics vs. thermoset polymers. Give 3 examples of each type.
Polyethylenes are available commercially as what 5 things? Which is the most common? Which is implantable?
What is the colour of polyethylene?
clear to whitish translucent thermoplastic
What are the 3 different types of polyethylene?
low = short branches
high = long chain, long branches
linear low = like low density, but longer branches
Compare and contrast HPDE (high density) and LPDE (low density)
What are the applications of HDPE?
pharmaceutical bottles, nonwoven fabrics, caps
What are the applications of LPDE?
flexible container, nonwoven disposabal and laminated foil, polymers for packaghing
What are the applications of LLDPE
pouches and bags due to its excellent puncture resistance
What are the applications of VLDPE
extruded tubes
This has been used for orthopaedic implant fabrications because it has superior wear properties
UHMWPE
What are the 3 load-bearing applications of UHMWPE?
- acetabular cup of total hip
- tibial plateau
- patellar surfaces of knee joints
What are 5 specific properties of UHMWPE?
- low cost
- easy to process
- excellent electrical insulator
- excellent chemical resistance
- tough and flexible (even at low temps)
bone loss in the vicinity of total joint prostheses caused by wear particles shed by the UHMWPE
osteolysis
What does osteolysis result in?
loosening of implants
True or false: Crosslinking has led to significantly reduced wear and osteolysis
True
Polymethylmetacrylate (PMMA) is best known for what 4 things?
- biocompatibility
- light
- transparency
- good weathering properties
What are the 4 medical applications of PMMA?
- bone cement
- bone pump
- IV systems
- contact lens
How is PMMA formed?
free radical polymerization
- no by products, exothermic
acrylic or acrylic glass as well as by the trade names Crylux, Plexiglas, Acrylite, Lucite, Perspex
poly (methyl methacrylate) - PMMA
What are the chemical stages for PMMA initiated by?
benzoyl peroxide
What are 8 PMMA properties?
Comonomers such as ____ are often added to improve impact strength
butyl acrylate
Comonomers such as ___ can be added to increase the glass transition temperature
methacrylic acid
Crosslinking ____ and ____ can increase strength, hardness, stiffness, and creep resitance
ethylene glycol
dimethacrylate
____ can be used to add translucency, inorganic pigments for colour and small coloured fibers to mimic blood vessels
ceramic oxide
Traces of _____ can be used to prevent inappropriate polyermization by room light
inhibitor (hydroquinone)
