Introduction to Polyisoprene

Polyisoprene is a polymer of isoprene (C5H8), which is the main chemical component of natural rubber, the naturally occurring resins balata and gutta-percha, and their synthetic equivalents. Polyisoprene may be a resilient, elastic polymer (elastomer) like natural rubber and isoprene rubber, or a tough, leathery resin-like natural and synthetic balata or gutta-percha, depending on its molecular structure. 


This article will study polyisoprene structure, trans polyisoprene, cis polyisoprene, rubber structure, isoprene synthesis and monomer of natural rubber in detail.


Polyisoprene Structure and Isoprene Formula

CH2=C(CH3)—CH=CH2 represents the chemical structure of isoprene. Polyisoprene, which is made up of multiple isoprene molecules linked together, can take on one of four spatial configurations, or isomers, each of which gives the polymers a different set of properties. The four isomers of polyisoprene have the following structures as repeating units:


Cis Polyisoprene for Formation of Natural Rubber

Do You Know What is the Monomer of Natural Rubber?

Natural rubber is almost entirely made up of the cis-1,4 polymer, which is formed by certain plants' milky latex, most notably the rubber tree (Hevea brasiliensis). Natural rubber is distinguished by its physical properties of extensibility and hardness, which are summed up by its capacity to be extended seven or eight times its original length. The polymer chains assume an amorphous, or disordered, arrangement in the absence of tensile (stretching) tension. The molecules, on the other hand, readily align into an ordered crystalline structure when extended. Natural rubber is called "self-reinforcing" because of its crystallinity, which gives it more power.


Natural rubber, on the other hand, is highly influenced by temperature in its natural state: it crystallizes on cooling, taking just a few hours at 25 °C (13 °F), and it becomes tacky and inelastic above 50 °C (120 °F). In addition, hydrocarbon oils swell and weaken it, and it reacts with oxygen and ozone in the atmosphere, causing polymer molecules to rupture at carbon-carbon double bonds, softening and cracking the substance over time. These drawbacks are mitigated to a large degree by vulcanization, a method that involves cross-linking polymer chains.


Isoprene Rubber

These are the elastomers that come from nature. Natural rubber is a mixture of solid particles suspended in a milky white liquid called latex that drips from the bark of tropical and subtropical trees. Brazil, India, Indonesia, Malaysia, and Sri Lanka are the largest producers of latex rubber. It is known as cis- 1, 4- polyisoprene and is produced by polymerizing isoprene (2 methyl-1, 3-butadiene) with the chemical formula (C5H8)n. They are rendered by loosely linking the monomers of isoprene (C5H8) in the form of a long tangled chain, in simple terms. Given below is rubber polymer structure and natural rubber formula.

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  1. Rubber Tapping – A small V-cut on the tree bark collects the milky white liquid latex from the rubber trees in a cup. To conceal the rubber particles, the collected latex is washed, filtered, and reacted with acids.

  2. Mastication – The rubber produced via the tapping process is still unfit for use. When it is cold, it is brittle, but once warmed up, it becomes very gluey. The rubber is allowed to pass through the rollers and pressed to soften to make it more durable to work with, removing its fragile nature and strong odor. This process is repeated depending on the properties of the rubber that are necessary. Extra chemical additives are also applied during this process to improve the properties of rubber.

  3. Calendaring - It is a rubber shaping method that uses rollers to give the rubber its shape (after proper mixing of the chemical ingredients).

  4. After that, the final product is extruded through hollow tubes by passing it through specially built holes in an extrusion system.

  5. Vulcanization – Performing any of the steps above would not result in rubber that is solid or hard enough to be used in car tyres or machinery. Sulfur is applied to the rubber, which is then heated between 373 and 415 degrees Celsius to improve both of these properties. Vulcanization is the term for this process. Sulfur serves as a cross-linking agent, and rubber becomes cross-linked and hard after vulcanization.


Trans Polyisoprene

Gutta-percha and balata, like natural rubber, are made from the milky exudate of some trees, and trans-1,4 polyisoprene is the dominant isomer. Since the trans-1,4 polymer is more crystalline than the cis-1,4 polymer, balata and gutta-percha are rugged, stiff, and leathery materials, which led to their use as sheathings for underwater cables and golf balls in the nineteenth century. With Ziegler-Natta catalysts, the trans-1,4 polymer can also be synthesized, producing a synthetic balata with similar properties that are used in golf ball covers as well as orthopedic devices like splints and braces.


The microstructure of natural and synthetic rubber differs; natural rubber is almost entirely made up of the cis-1,4 polymer, while synthetic isoprene is made up of a mix of cis-1,4, trans-1,4, and 3,4 polymers. The concentration of cis-1,4 is typically between 90 and 98 percent. In most cases, increasing cis-1,4 decreases the glass transition temperature increases crystallinity, and enhances mechanical power. As a result, synthetic polyisoprene's tensile strength and tear resistance are usually weaker than natural rubber.


Did You Know?

Rubber can be used for a variety of things and on a variety of platforms, some of which are mentioned below.

  • It's used to line chutes, containers, and industrial mixers, among other things. It can be used as a strong insulator due to its water-proof and durable properties.

  • It can be used as wetsuits and expandable garments in the clothing industry, such as gym and cycling shorts.

  • Rubbers are also used for flooring because they provide insulation, reduce fatigue, and are waterproof and slip-resistant.

  • Its use in the car industry can be seen in tyres, brake padding, airbags, seats, and roofs, among other places.

FAQs (Frequently Asked Questions)

Question1: in Chemistry, What is Natural Rubber?

Ans: Natural rubber is a polymer, which means it's a long, chain-like molecule with repeating subunits. Polymer is derived from the Greek words "poly" which means "many" and "mer" which means "pieces." Polyisoprene is the chemical term for natural rubber. Isoprene is the monomer (meaning "one part") from which it is produced.

Question2: What is the Composition of Polyisoprene?

Ans: Polyisoprene is a diene polymer and is a polymer made up of two carbon-carbon double bonds in a monomer. It has a carbon-carbon double bond in its backbone chain, like most diene polymers. The sap of the hevea tree can be used to make polyisoprene, but it can also be made using the Ziegler-Natta polymerization method.

Question3: Is Latex Present in Polyisoprene?

Ans: Polyisoprene is a rubber that is chemically similar to latex. Synthetic polyisoprene condoms, on the other hand, do not contain the natural proteins that cause most latex allergies.