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polymer chemistry question?

perhaps this question is a little "elementary" - but I don't know the answer- the shape of polymers can be linear, branched, combed..., but i always read them as being solvent like substances prior to polymerization. can someone explain how these solvent (liquid) mers change to a "strand" (solid) when lengthened?

Public Comments

1. Well the starting molecules usually have some kind of active sites on the ends. You can pick molecules with mating reactive groups on each end to make linear polymers. example for reactive groups that react as follows RH + R'H = RR' +H2 or similar you can use R-polymer_part-R' which when reacted yields long strands of -R-polymer_part-R'-R-polymer_part-R'-R-polymer_part-R'-R-polymer_part-R'-R-polymer_part-R'-R-polymer_part-R' and so on
2. Are you asking why some monomers are liquids but the polymers are solids? Polystyrene for example is made of monomer units of styrene, which is a toxic gas. As you polymerize the monomer, it increases the length (which can attach thousands of monomers to do so) and thereby changing the properties of the material. Styrene has a molar mass of around 100 g/mol, so if you connect around 10 units (1,000 g/mol) or more, then it becomes a solid. Branched and linear forms of polymers have different physical properties depending on what monomers you are attaching.
3. I think what you're looking for here is molecular mobility. All molecules move around and the extent to which they interact with other molecules in their vicinty determines whether they will be a solid or liquid or gas at room temperature. Small monomers have a greater degree of mobility than their longer-chain polymer cousins. Imagine two bowls of pasta, one full of orzo and the other full of spaghetti. It's easier to stir the orzo because the pieces of pasta are much smaller. They slide past each other with ease. Monomers are like the orzo pasta - small and easily moved around independent Spaghetti, on the other hand, is stringy and gets tangled up with itself. Polymer chains are like spaghetti. They get tangled up in each other and can't move around as well. Hence, it's not unusual for monomers to be liquids or even gases, but the finished polymers are usually solids.