Mesoglobular phase

Formation of a Stable Mesoglobular Phase in Dilute Solutions. 154... 

After accumulating sufficient experience in the preparation of narrowly distributed long homopolymer chains and in the study of individual homopolymer chains in dilute solutions, we gradually moved into the direction of the folding and formation of the mesoglobular phase of amphiphilic... 

In this review, hydrophilically and hydrophobically modified poly(N-iso-propylacrylamide) (PNIPAM) copolymers are mainly used to illustrate how amphiphilic copolymer chains can fold from an extended random coil to a collapsed globule in extremely dilute solutions and associate to form a stable mesoglobular phase which exists between single-chain globules and macroscopic precipitation. The copolymers used can be prepared by free-radical reaction. 

Using PNIPAM ionomers as a bridge, we will shift our discussion from the folding of individual copolymer chains in extremely dilute solutions to the formation of the mesoglobular phase of hydrophilically and hydrophobically modified copolymer chains in dilute solutions. The synthesis of PNIPAM-co-xKAA ionomers has been described before. 

The above discussion clearly shows that the increase of anionic copolymer concentration or the strength of chain interaction can lead to a transition from intrachain contraction to interchain association. It can result in a mesoglobular phase in which a limited number of copolymer chains are associated together to form polymeric colloidal particles stable between microscopic single-chain globular phase and macroscopic phase separation (precipitation). It is not a surprise to see the formation of such stable mesoglob-... 

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,N-diethylacrylamide (DEA) and N,N-dimethylacrylamide (DMA). like PNI-PAM, PDEA is also a thermally sensitive polymer with a similar LCST, but PDMA remains water-soluble in the temperature range (< 60 °C) studied. At room temperature, copolymers made of DMA and DEA are hydrophilic, but become amphiphilic at temperatures higher than 32 °C. Before the association study, each P(DEA-co-DMA) copolymer was characterized by laser light scattering to determine its weight average molar mass (Mw) and its chain size ( Rg) and (R )). The copolymer solutions (6.0 x 10 A g/mL) were clarified with a 0.45 xm Millipore Millex-LCR filter to remove dust before the LLS measurement. 

As the polymer concentration increases, interchain association inevitably occurs, but some amphiphilic chains can undergo a limited interchain association to form a stable mesoglobular phase that exists between microscopic single-chain globules and macroscopic precipitation. As expected, when the solvent quality changes from good to poor, intrachain contraction and interchain association occur simultaneously and there exists a competition between these two processes. Such a competition depends on the comonomer composition and distribution on the chain backbone and also depends on the rate of micro-phase separation. When intrachain contraction happens quickly and prior to interchain association, smaller mesoglobules are formed. A proper adjustment of the rates of intrachain contraction and interchain association can lead to polymeric colloidal particles with different sizes and structures. 

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