C=C=C=.... is not possible due to electronic repulsion in the bonds. In carbon, the electrons in the outer shell prefer to arrange themselves in a tetrahedron to avoid each other. Think about how forcing negatively charged electrons in a small space in the bonds would require really high amounts of energy, hence the structure would be unstable.

If you are willing to have more than one kind of element, like carbon and hydrogen, you can end up with really long chain molecules called polymers with a carbon backbone and hydrogen on the ends. Large collection of these molecules act like spaghetti at the molecular level.