Homopolymer poly(N,N-dimethylacrylamide) (PDMA) is soluble in water, but poly(N,Ndiethylacrylamide) (PDEA) and poly(N-ethylacrylamide) (PEA) are soluble only in cold water. The copolymers made of DEA and DMA or DEA and EA are hydrophilic at T < ∼32 °C, but become amphiphilic in the higher temperature range. The synthesis of two series of P(DEA-co-DMA) and P(DEA-co-EA) copolymers with a similar chain length, but different compositions (30 and 50 mol % of DMA and 40, 60, and 80 mol % of EA, respectively), enabled us to study the composition dependence of their association in water by laser light scattering. Our results showed that a limited number of these neutral copolymer chains could associate together to form stable mesoglobules existing between single-chain collapsed globules and macroscopic precipitation. Besides thermodynamical consideration, the formation of such mesoglobules can also be attributed to the competition between intrachain contraction and interchain association as well as the viscoelastic effect. Increasing the hydrophilic DMA or EA content leads to a larger average aggregation number, but increasing the heating rate results in smaller, but less dense, mesoglobules consisting of many loosely associated small single-or pauci-chain globules. For the copolymers with higher EA contents, we unexpectedly found that interchain association can gradually relax to intrachain association as time elapses.

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