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 Syndiotactic – two groups alternate Atatactic – displays no regular pattern Every other carbon in the chain is a steriocenter Isotactic and Syndiotactic forms are more crystalline in nature and are stronger and more resistant to solvents

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 under-water 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 MMA 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