Transcript Polymethyl%20Methacrylate[

Polymethyl
Methacrylate
(PMMA)
Monomer

Methyl Methacrylate (MMA)
Formula : H2C = CHCOOCH3
Structure :
Formation

Free Radical Polymerization

Step 1 :
→
Free radical (R*) plus methyl methacrylate
Step 2 : Polymerization - MMA radical
plus MMA :repeated many, many times
Step 3 : Termination – occurs
when two radicals join
Catalysts

Multiple catalysts can be used in
production of PMMA. Some of these are:



Butyl Lithium
Highly active catalysts based on group 4
metallocenes
An aluminum system supported by salen
ligands
Why Use Different Catalysts?

Different catalysts result in different
versions of the polymer

Variation is due to the placement of the ester
(R-O-R) and methyl (CH3) groups along the
polymer backbone

Isotactic – similar groups on same side of chain
COOME
ME

ME
COOME
ME
COOME
ME
COOME
ME
Syndiotactic – two groups alternate
COOME
ME

COOME
ME
COOME
COOME
ME
ME
COOME
ME
Atatactic – displays no regular pattern
COOME
ME

COOME
ME
ME
COOME
COOME
ME
ME
COOME
Every other carbon in the chain is a steriocenter
History of PMMA

Developed by three companies at
approximately the same time in 1928




Röhm and Haas
Du Pont
ICI (Imperial Chemical Industries)
First came on market 1933
Historical uses of PMMA


Du Pont first used PMMA primarily for cast
products (rods, tubes, and blocks)
ICI and Röhm and Haas focused on
producing sheets of PMMA to be used as
safety glass

Röhm and Haas introduced Plexiglass to
market in 1936 and ICI followed with Perspex
later that same year
Properties of PMMA






Lighter than glass (density is about half that of glass)
Shatter proof
Softer and easier to scratch than glass (scratch resistant
coatings may be applied)
Transmits more light than glass (92% of visible light)
Does not filter UV light (may be coated with UV film)
More transparent than glass, so windows can be made
thicker
Current uses for PMMA

Include many uses similar to those for
which it was first developed but include
many things never imagined by the
inventors! A partial list of the uses for
PMMA includes:

Safety glass such as Plexiglass and Lucite – uses
range from windows for aquariums and underwater restaurants to safety shields at hockey
rinks to skylights in your home to simple
paperweights
Medical Uses


Used as bone cement for use in
arthroplastic procedures of the hip, knee,
and other joints for the fixation of polymer
or metallic prosthetic implants to living
bone
Used in Pacemakers
Dentures!


Artificial eye lenses used for cataract
surgery
Suspended in collagen and implanted to
reduce wrinkles in cosmetic procedures
Acrylic Paints

Acrylic “latex paints” often contain PMMA
suspended in water
Blacklight Tattoo Ink


Made of 97.5% PMMA and 2.5%
microspheres of fluorescent dye suspended
in UV sterilized, distilled water with no
preservatives or other additives
The ink received USFDA approval in 1995 for
use in animals, plants and fish for the
purpose of tracking migration, growth
patterns; breeding habits etc.
Breakdown of PMMA


Autoignites at 445° C (833° F)
Burns cleanly to produce H2O and CO2


Virtually smokeless combustion
Has superior recyclability


Can be reground and reused
Can be depolymerized back to monomer,
purged of impurities, and reploymerized back
to PMMA
Potential Toxicity

PMMA is an essentially non-toxic material


No workplace exposure limits
MMA


Respiratory effects may result from chronic
low level exposure or from short term acute
exposure
Exposure primarily occupational (production
of monomer and its polymers, doctors,
nurses, dentists, and dental technicians)
Ingestion of PMMA/MMA


Oral LD50 (in rats) PMMA = 11,700 mg/kg
Oral LD50 (in rats) MMA – 7,872 mg/kg