Formation, Structure, and Temperature Behavior of Polyelectrolyte Complexes between Ionically Modified Thermosensitive Polymers

Abstract

Thermosensitive polymers such as poly(N-isopropylacrylamide) (PNIPAM) have a lower critical solution temperature in water in a temperature range between 32 and 35 °C. Micro-and macrogels of such polymers show a temperature-controlled reversible swelling behavior. Therefore, they are of great interest for a variety of applications (e.g., the controlled drug delivery and accessibility of enzymes). Up to now such gels were prepared by covalent cross-linking. A new and promising route for the preparation of microgels down to the nanometer scale consists of the formation of polyelectrolyte complex particles between ionically modified thermosensitive polymers. The formation, structure, and temperature behavior of complexes between PNIPAM with differing contents of anionic and cationic groups was studied by viscometry and static and dynamic light scattering. The level of aggregation of such complexes increases with increasing mixing ratio, while the polymer concentration has only a marginal effect. The complexes were highly swollen at 25 °C and collapsed in a temperature range up to 50 °C, where the swelling-deswelling process is completely reversible. Even complexes between copolymers of higher contents of ionic groups (up to about 30%) and complexes between copolymers and pure polyelectrolytes showed a pronounced temperature dependence of the structural density. † Part of the special issue "Colloid Science Matured, Four Colloid Scientists Turn 60 at the Millennium".

Complex coacervate core micelles

“…Recently, other copolymer architectures, such as graft and random or statistical copolymers [46,47,56,[59][60][61][62]89,[169][170][171][172][173][174]211,[235][236][237][238][239][240][241][242][243] have also been incorporated into C3Ms. Self-assembled C3Ms [48] and flowerlike C3Ms [221] are rare (see also Section 3.2).…”

“…The polyelectrolyte blocks of the neutral-ionic copolymers constitute the grey core, whereas the neutral blocks (blue and green) reside in the micellar corona. S-b-A PEO-b-PAsp + PEO-b-PLys bcp [1,90,91] PiPrOx-b-PAsp + PiPrOx-b-PLys bcp [92] PAAm-b-PAA + PGMA-b-PDMAEMA bcp [93] PVOH-b-PAA + PEO-b-P2MVP bcp [94] PNIPAAm-b-PAA + PEO-b-P2MVP bcp [95] [175] (continued on next page) [190,191] [194,195] PEO(Lactose)-b-PDMAEMA + pDNA DNA [196] PEO(Acetal)-b-PDMAEMA + pDNA DNA [197,198] PEO-b-PLys + pDNA DNA [199][200][201][202][203][204][205] [194,195] S-co-C P(NIPAAm-co-MADAMB) + P(NIPAAm-co-AMPS) cp [169] P(EO-co-DADMAC) + P(EO-co-AMPS) cp [ Colloidal stability of S-C3Ms depends on the copolymer block length ratio, the total block length of the copolymer, the chemical structure of the corona monomers, and the molecular weight and type of ionic groups of the homopolymer (see also Section 5.6). The differences between D-C3Ms and S-C3Ms have been investigated by several groups [44,90,98].…”

“…Furthermore, temperature sensitivity can be incorporated by using a neutral block with LCST behaviour, such as PNIPAAm [61,79,81,95,124,169,172,173] and PiPrOx [92]. The downside of the near-equilibrium and responsive nature of C3Ms is their relatively low stability as compared to their amphiphilic counterparts.…”

Externally Induced Thermal Actuation of Polymer Nanocomposites

“…[40] For example, poly(N-isopropylacrylamide) (PNIPAAm) has a LCST at which it undergoes a reversible volume phase transition. [41] Thermal expansion is regarded as one of the intrinsic properties of materials. Almost all materials have this property.…”

Grafting of thermoresponsive polymer from the surface of functionalized multiwalled carbon nanotubes via atom transfer radical polymerization

“…PNIPAM has an LCST, at which it undergoes a reversible volume phase transition caused by the coil-to-globule transition [34] . Intermolecular collapse occurs before intermolecular aggregation through LCST and the collapse of individual polymer chains increases the scatting of light in solution (cloud point), phase separation between the collapsed polymer molecules and the expelled water follows this cloud point [35] .…”