Yes it is! Each molecule gets 1 unit of thermal energy to kick about regardless if it's a small molecule or a superlong chain. For a large number of small molecules, the large entropy gain is usually the driving force for mixing. For high MW polymers there is hardly any entropy gain. So the driving force will have to come from a gain in enthalpy, i.e. a blend will only be thermodynamically stable if the polymers really like each other, e.g. if they have opposite charge.
Ferry Melchels is correct about the thermodynamic reasons for poor co-solubility of polymers. Entropy fights your blending. Like dissolves in like, and gets fussier about match as MW goes up. However, quite a large number of miscible polymer pairs are known. Two common miscible blends are poly(styrene) (PS)–poly(phenylene oxide) (PPO); and poly(styrene-acrylonitrile) (SAN)–poly (methyl methacrylate) (PMMA). See for example, Chapter Polymer Blends: State of the Art, New Challenges, and Opportunities
I also see this 2014 article from Polymer Blends Handbook, which is paywalled, but the abstract says:
"Miscible polymer blends were once considered a rarity. However, extensive research has led to the discovery of a large number of miscible polymer blends. This Chapter is a compilation of miscible polymer blends reported in literature up to 2012." -- Chapter Miscible Polymer Blends
So yes, thermodynamics make miscibility more difficult as chain length increases, but not at all impossible.
- Badges
- Science method
- Similar topics
- Methodology
- Crystallography
- X-ray Diffraction