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Microemulsion Polymerization: Creating clean and green nano-size polymers

Photo: Siddharth Kankaria

Nano-size polymers have made headlines in the recent years for their biological and medical applications. With dimensions of less than 100 nanometers (nm), they can carry drugs and pharmaceuticals in the body due to their subcellular size, sustained release properties and biocompatibility with our tissues and cells. But how are these nano-size polymers synthesized? In a recently written book chapter in the book, ‘Nano-size polymers: preparation, properties, application’, Prof. Manas Chanda, a retired faculty from the Indian Institute of Science, Bangalore and an expert in the field of polymers, has enunciated the direct synthesis of these tiny polymers by a method called microemulsion polymerization.

Microemulsions are liquid mixtures of water, oil and a surfactant that lowers the surface tension between water and oil. They are isotropic and thermodynamically stable with each droplet size varying between 1 to 100 nm. Because of this small size, microemulsions possess unique properties like large surface area, thermodynamic stability and low surface tension that have made them immensely useful in areas such as oil recovery, immune-assays, protein adsorbents, enzyme immobilization, drug delivery systems and also as a reaction media for polymerization. Many commercially available polymers like polyvinyl acetate (PVA), polyvinyl chloride (PVC) and butadiene-styrene copolymers used in coatings, adhesives, paints and biomedical equipment, are produced in bulk by microemulsion polymerization.

The prime focus of a polymerization reaction is to produce high molecular weight polymer that imparts desirable mechanical properties to the polymer, like elasticity and tensile strength. Studies have shown that microemulsion polymerization technique with a polymerizable surfactant provides better compatibility and stability to the polymer matrix by becoming a part of it. This technique also results in an increased rate in which monomers are converted to polymer by a factor of 20 - 25 percent as compared to conventional emulsion processes. In addition, this also results in an increased molecular weight to about 106-107grams per mole for the polymer.

Another advantage of microemulsion polymerizations is the generation of solid, porous materials, which would then be converted to porous membranes. These membranes are used in controlled separation of mixtures to obtain fragments with better utility than the original mixture. The size of the pore defines the utility of the membrane to separate dust or micro-particles such as the virus, bacteria, pigments and colloidal particles.They are also used in medicines and in biotechnology for culturing living cells and enzymes since they can support high cell density per unit bed volume. Apart from this, they can also be used to separate gases and are thus applied to produce oxygen-enriched air to be used for applications in medicine and industry.

Hydrophobic polymers produced through microemulsions promise an exciting breakthrough in drug release and drug delivery methods. These hydrophobic polymers contain water microdroplets, are insoluble, and have a large surface area that is chemically active and electrophilic, helping in entrapment of drugs. During the synthesis of such hydrophobic polymers, the required drug is entrapped in water microdroplets and then polymerized to encapsulate the drug in a droplet microcapsule within the polymer. The drug is slowly released through diffusion, once inside the body.

These versatile nano-size polymers are biocompatible and biodegradable and hence environmentally friendly. “Since the polymers generated by microemulsion polymerization find its application mainly in oil recovery technology where they are injected into oil-bearing structures underground to flush out petroleum, they do not add to the current environmental problem put forth by littering of plastics”, says Prof. Chanda. In an era where climate change, environmental degradation and waste handling are growing concerns, innovations such as these are our hope towards a sustainable living.

About the scientist

Prof. ManasChanda is a retired faculty from the Department of Chemical Engineering, Indian Institute of Science, Bangalore. He can be reached at profmanas@gmail.com.

About the article

This article is based on a chaptertitled “Direct Synthesis of Nano-size Polymers by Microemulsion Polymerization” published in the book “Nano-size polymers: preparation, properties, application”.