Natural rubber is made up of macromolecules. The natural rubber molecule is made up of thousands of repeating units called isoprene units (see image), hence, we call this polyisoprene. The molecular formula for the isoprene unit is C5H8. These units are strung together as a "chain" to form the molecule and the correct formula for polyisoprene (the entire molecule) is (C5H8)X where X equals from 10,000 to 20,000.

With tens of thousands of carbon and hydrogen atoms, it is obvious why they are called macromolecules. However, while this molecule is thousands of times larger than the molecules of an ordinary chemical substance (i.e. H2O) it is still much too small to be visible in the most powerful microscopes available.

Structure of Natural Rubber [Cis - poly isoprene]

Disadvantages of Natural Rubber:

Natural rubber does not perform well when exposed to chemicals and petroleum derivatives, including petrochemicals. It is not recommended for outdoor applications where maximum resistance to sunlight, ozone, oxygen or heat aging is major factors.

Its plasticity is greater than elasticity. It cannot sustain stress. Thus, when stretched to a great extent, it undergoes deformation permanently.

It has large water absorption tendency, which makes it weak.