Some may have Tg below zero such as polyethylene and polypropylene but still have plastic characteristics due to other factors such as crystallinity. Below their Tg these polymers become quite brittle. They may vary in processing or performance due to differences is molecular weight, additives, or other structural features. For example, a supplier of polycarbonate may have flame resistant grades, glass fiber reinforced grades, a conductive grade, and easy flowing grades. Wide and skewed distributions result significant variance in properties.
Narrow distributions are more consistent.
The number of atoms can range from two to millions. A molecule is the smallest unit of a substance which still retains the properties of that substance. Monomers are generally gases or liguids. When bonded together in long chains they form solid materials or polymers. Organic infers some relationship to materials which at some point in time were alive.