What is Polymethyl Methacrylate?
Polymethyl methacrylate, or PMMA, is a transparent organic polymer that is used as an alternative to glass. It is a rigid plastic that can find its application in a variety of industries. This synthetic resin is formed by the polymerization of methyl methacrylate.
Also referred to as plexiglass or acrylic glass, PMMA is used because it is easy to shape, tough and cost-effective. It has the ability to keep a light beam reflected within the surface and is also resistant to UV radiation. Acrylic glass can be used in a variety of products, including car windows, aquariums, screens of digital devices etc.
Polymethyl Methacrylate Structure
PMMA is formed by the free radical polymerization of monomer methyl methacrylate. The polymethyl methacrylate structure is a vinyl polymer which is an ester of methacrylic acid (CH2=C[CH3]CO2H).
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The pendant CH3 groups hinder the crystalline packing of the polymer chains. Since they are not allowed to rotate freely around the C-C bond, the resulting structure is quite rigid.
Production of PMMA
It is produced from propylene which is derived from the refining of crude oil. The process of formation of methyl methacrylate polymer involves the following steps:
Propylene reacts with benzene to form isopropylbenzene or cumene.
Cumene gets oxidized to form cumene hydroperoxide.
This reacts with an acid to form acetone.
Acetone forms methyl methacrylate (CH2=C[CH3]CO2CH3) in liquid form.
The polymerization of this compound in the presence of free-radical initiators forms PMMA in solid form.
Polymethyl Methacrylate Uses
Acrylic plastic or PMMA finds its application in a variety of industries due to its properties, easy processing and cost-effectiveness. PMMA is processed by injection molding, compression molding, extrusion or casting.
The extensive polymethyl methacrylate uses are a result of its advantageous properties and adaptability. This transparent plastic is used in a lot of markets. Some of the most common applications of PMMA are discussed below:
Glass Substitute
Acrylic glass is used as a shatterproof alternative for windows and skylights. It is also commonly used in aquariums and aircraft canopies. A lot of hockey rinks also use PMMA. Illuminated sign boards that display advertisements or directions are also usually made up of PMMA.
Construction and Design
Windows, doors, panels, canopies etc., all use polymethyl methacrylate due to its excellent properties such as heat insulation and light transmission. The polymer may also be used in the construction of sinks, baths, knobs or tap tops.
Automobile Industry
One of the most important industries that require PMMA is the transportation and automobile industries. From car windows to windshields, acrylic sheets can be found in a lot of spaces. It is used in the manufacturing of various automotive parts. The aviation and marine industry also require this polymer. Car indicator covers and panels are also made using plexiglass.
Healthcare Industry
PMMA polymer is also known as bone cement in the healthcare industry. It is used by orthopaedic surgeons for procedures like joint replacement or treating bone damages. It can also be used to fill in the gaps between bones. Optical fibres used for endoscopy also consist of PMMA.
Cosmetic Usage
PMMA has also found its usage in various beauty products and injectables. It is used in cosmetic procedures that treat ace, facial lines, wrinkles etc.
Lamps and Lighting
The light-emitting potential, transparency and other such properties allow PMMA to be used in LED lights and lamps. You can find PMMA being used in street and traffic lights. It is manufactured in various colour options, which adds to its usability in lamps and other lighting devices.
Electronic Devices
Acrylic glass can be used in the display of various electronic equipment, including tv screens, laptops and smartphones. This is due to its properties, such as transmittance and high optical clarity.
Solar Devices
The application of polymethyl methacrylate PMMA in solar panels is a result of its UV stability and light transmission ability. It can also be used in the construction of greenhouses, aquariums and marine centres.
Other products where this polymer finds its application include paint, furniture and
optical fibres used for telecommunication.
Advantages of PMMA
PMMA has several advantages over other polymers like polycarbonate (PC) and polystyrene etc. It doesn’t scratch easily or yellow over time. PMMA is used as an alternative to other transparent polymers in situations where extreme strength is not required.
Some of the advantages of PMMA include:
Economical
Resistance to weathering
Various colouring options
Tensile strength
Easy to process and handle
Versatility
Biocompatibility
UV Stability
Durability
Transmittance and better optical clarity
Recyclable
Polishability
BPA-free, non-toxic
FAQs on Polymethyl Methacrylate
1. What is Polymethyl Methacrylate (PMMA) and what are its common trade names?
Polymethyl Methacrylate, abbreviated as PMMA, is a synthetic, transparent thermoplastic polymer of methyl methacrylate. It is often used as a lightweight and shatter-resistant alternative to glass. Due to its popularity, it is known by several trade names, including Plexiglas, Lucite, Perspex, and simply Acrylic.
2. What is the chemical formula and monomer unit of Polymethyl Methacrylate?
The monomer that forms PMMA is methyl methacrylate, which has the chemical formula C₅H₈O₂. Through a process called polymerisation, these monomers link together to form the polymer. The repeating structural unit of Polymethyl Methacrylate is represented by the formula (-[CH₂C(CH₃)(COOCH₃)]-)n.
3. What are the most important applications of Polymethyl Methacrylate (PMMA)?
Thanks to its transparency, durability, and light weight, PMMA has a wide range of applications. Some of the most important examples include:
- Automotive Industry: Used for rear lights, instrument panels, and indicator light covers.
- Electronics: Found in LCD/LED TV screens, mobile phone displays, and laptop screens.
- Medical and Dental: Used for making dentures, bone cement, and contact lenses.
- Construction: Used as shatterproof windows, skylights, and large public aquariums.
- Everyday Items: Used in signage, picture frames, and various decorative items.
4. What are the main drawbacks or limitations of using PMMA compared to glass?
While PMMA is a versatile material, it has some key limitations, especially when compared to traditional glass. The primary drawbacks include:
- Low Scratch Resistance: The surface of PMMA can be scratched more easily than glass.
- Lower Impact Strength: Although shatter-resistant, it is not as strong as other engineering polymers and can crack under a high load.
- Poor Chemical Resistance: It can be damaged by certain organic solvents like esters and ketones.
- Low Heat Resistance: It has a lower melting point and can deform at high temperatures.
5. How does the chemical structure of PMMA cause it to be highly transparent?
The high transparency of PMMA is a direct result of its amorphous structure. Unlike crystalline materials where molecules are in an ordered, repeating lattice that can scatter light, the polymer chains in PMMA are arranged randomly. The presence of the bulky methyl (-CH₃) group on the polymer backbone prevents the chains from packing closely together into an organised crystalline form. This random, non-crystalline arrangement allows light to pass through with minimal scattering, resulting in its excellent optical clarity.
6. Why is Polymethyl Methacrylate (PMMA) such a popular material in dentistry?
PMMA is widely used in dentistry, particularly for making dentures and temporary crowns, for several important reasons. Its biocompatibility means it does not harm oral tissues. It is lightweight, making dentures more comfortable for the wearer. Furthermore, it is easy to mould, repair, and polish, allowing dentists to create a perfect fit. Its ability to be coloured to match the patient's natural gum and tooth shade provides excellent aesthetic results, making it a preferred choice for dental prosthetics.
7. How is raw PMMA modified to improve its properties for commercial use?
To overcome its natural limitations like brittleness and low impact strength, raw PMMA is often modified by incorporating other substances. This process, known as copolymerisation or compounding, can involve:
- Adding rubbery comonomers like butyl acrylate to increase its impact strength and make it less brittle.
- Introducing comonomers like methacrylic acid, which can increase its glass transition temperature, allowing it to be used at higher temperatures.
- Using plasticizers to improve its flexibility and processing properties.
- Mixing in fillers to reduce the overall cost and improve specific mechanical properties.
8. Is Polymethyl Methacrylate (PMMA) considered safe for direct use in cosmetics and skincare products?
Yes, Polymethyl Methacrylate is generally considered safe for use in cosmetics and skincare. It is used in products as tiny spheres (microbeads) for a silky texture, or as a film-former to provide a smooth finish on the skin. The key to its safety is that the PMMA molecule is a large polymer, which is too big to be absorbed by the skin. It remains on the surface and does not penetrate into the body, therefore posing a very low risk of toxicity or irritation for topical applications.
