Phase Separation and pH-Dependent Behavior of Four-Arm Star-Shaped Porphyrin-PNIPAM₄ Conjugates

Abstract

Star-shaped porphyrin-PNIPAM 4 (PP) conjugates having four PNIPAM arms connected to a central tetraphenylporphyrin unit were synthesized using reversible addition−fragmentation chain-transfer polymerization. Temperature-induced phaseseparation behavior of the conjugates was investigated, and the lower critical solution temperature (type II)−composition phase diagram was constructed using Flory−Huggins theory. Interestingly, in contrast to PNIPAM homopolymers, the shorter PNIPAM arms of PP conjugates lead to a lower phase-separation temperature (T p ). The concentration dependency of the size of the cooperative domain was also determined. Below T p , experimental data indicate that PP behaves as a 1D supramolecular polymer with a concentration-dependent length, while above T p , PP globules adopt a larger spherical shape. Various temperature− pH reversible and irreversible interdependencies ("cross-effects") between phase separation and protonation were observed. The PP conjugates represent a dual temperature−pH-responsive model system possessing various aggregated states, making them candidates for visual indicators, pH or temperature sensors, or singlet oxygen generators for biomedical applications.

Thermoresponsive Properties of Poly[oligo(ethylene glycol) sorbate]s Prepared by Organocatalyzed Group Transfer Polymerization

“…In light of their specified structures or by incorporating some functional components, their thermoresponsive properties can be precisely tuned, and sometimes used in combination with other functions, such as pH detection and light sensing. 23 The phase-transition behavior of thermoresponsive polymers has been proven to be very complicated since it is affected by a lot of intrinsic factors of a thermoresponsive polymer, such as the constitution of monomeric unit, 1,5,7,13,[15][16][17][18][19][20][21]25 chain end, 24 chain length, 7,12,[14][15][16]25 polydispersity, 1 chain rigidity, 25 copolymer composition, 4,6,7,16,17 polymer architecture, 16−28 and so on, as well as many extrinsic experimental conditions, such as its concentration, 14,15,22,25 used solvent, 29−31 solvent composition, 6,22,31 heating or cooling rate, 32 wavelength of light used, 1 and so on. Many efforts have thus been dedicated to tuning thermoresponsive properties from the above aspects.…”

“…, poly­(ethylene glycol)/poly­(ethylene oxide), , and substituted polyethers, − polyacrylamides, ,,− polyoxazolines, poly­(meth)­acrylates, − polyphosphazes, poly­( N -vinylcaprolactam)­s, etc . In light of their specified structures or by incorporating some functional components, their thermoresponsive properties can be precisely tuned, and sometimes used in combination with other functions, such as pH detection and light sensing . The phase-transition behavior of thermoresponsive polymers has been proven to be very complicated since it is affected by a lot of intrinsic factors of a thermoresponsive polymer, such as the constitution of monomeric unit, ,,,,− , chain end, chain length, ,,− , polydispersity, chain rigidity, copolymer composition, ,,,, polymer architecture, − and so on, as well as many extrinsic experimental conditions, such as its concentration, ,,, used solvent, − solvent composition, ,, heating or cooling rate, wavelength of light used, and so on.…”