# About how long do polymer chains have to be for their physical properties to resemble the polymer more than the monomer? (Or are at least comparable)

For example: According to wikipedia, Styrene is a liquid at room temperature, whereas isotactic Polystyrene does not melt until the 200s celcius. This is a simple property but quite a large change. I am curious how long polymer chains have to be (how many monomer units are present) before you can just consider them to be functionally identical to the kind of Polystyrene generally used in practical situations? I know that there are different forms of polystyrene such as puffed/extruded, films etc, this is just an example.

The purpose behind this question is that I am considering doing some molecular dynamics/computational work on polymers and the longer the chains are, the more computer time is needed. So I'm wondering how large the molecules should be to reflect "real behavior".

Note: I'm sure it's a bit of a spectrum. You can probably make a smooth function between chain length and melting point, but I doubt it's a linear function... there's probably a point where it basically stops changing.

Edit: While I cited melting point I am actually more interested in electronic/orbital properties in case that helps.

• A thing of 2 units is pretty different from the monomer, but also very different from the polymer. 10 units is closer to the polymer than to the monomer, but not quite there yet. 100 units is a polymer all right. As for electronic properties, they barely change at all, unless you have a conductive polymer. – Ivan Neretin May 25 '18 at 14:38
• Great question. Regarding Ivan's comment, even if electronic properties don't change much past a certain number of units, what we would consider purely steric effects may still vary considerably, which should be relevant for most polymers. – pentavalentcarbon May 25 '18 at 23:47