Formation of Mesoglobular Phase of Amphiphilic Copolymer Chains in Dilute Solution:  Effect of Comonomer Composition

Abstract

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.

Metastable cluster intermediates in the condensation of charged macromolecule solutions

“…28 For example, Wu and co-workers have reported stable aggregates with aggregation number ranging from 10 to several thousands ͑depending on temperature and concentration͒ in aqueous solutions of the nonionic hydrophobically modified poly ͑N-isopropylacrylamide͒, between single-chain globules and macroscopic precipitation. 29,30 It is quite probable that these mesoglobules can also exist in a metastable state relative to the dilute single-globule solution phase and macroscopically condensed phase, in which case condensation will occur through a two-step mechanism similar to the one proposed in our work.…”

Non-ionic Thermoresponsive Polymers in Water

“…Protein-like copolymers are a special case of thermosensitive copolymers capable of forming small colloidally stable aggregates in solutions heated above their LCST [177][178][179][180][181][182]. In globular proteins, the hydrophilic units mainly cover the waterexposed surface of the globule, thus preventing interprotein association, whereas hydrophobic units mainly form the core of the globule.…”

“…The theoretical model of protein-like copolymers ascribes the term "memory" to amphiphilic copolymers, stating that a polymer chain tends to reassume the conformation in which it was synthesized, due to the unique distribution of repeating units along this chain. The synthesis of protein-like copolymers from typical synthetic monomers is difficult, and only few reports on successful synthesis are available [181,182]. PiPAAm-graft-PEO copolymers in water close to the demixing temperature of the backbone turned out to be able to remember the original conformation in which they had been grafted [183,184].…”

Folding and Formation of Mesoglobules in Dilute Copolymer Solutions

“…Recently, Siu et al [139] studied the effect of comonomer composition on the formation of the mesoglobular phase of amphiphilic copolymer chains in dilute solutions. The copolymer used was made of monomers, N,Ndiethylacrylamide (DEA) and N,N-dimethylacrylamide (DMA).…”

“…35 Time dependence of average aggregation number (N agg ) of P(DEA-co-DMA) mesoglobules formed under different heating rates [139] 156 G. Zhang · C. Wu Fig. 36 Time dependence of average hydrodynamic radius ( R h ) of P(DEA-co-DMA) mesoglobules formed under different heating rates [139] mation of stable mesoglobules, where N agg was calculated from the ratio of the weight-average molar masses of the interchain aggregates and individual copolymer chains measured in static LLS. Note that for larger particles, the following Guinier plot instead of the Zimm plot (Eq.…”