Multiresponsive Star-Graft Quarterpolymer Monolayers

Abstract

Multifunctional star-graft quarterpolymers PS n [P2VPb-(PAA-g-PNIPAM)] n with two different arm types, shorter PS arms and longer P2VP-b-PAA block copolymer arms with grafted PNIPAM chains, were studied in terms of their ability to form micellar structures at the air/water and air/solid interfaces. Because of the pH-dependent ionization of P2VP and PAA blocks, as well as thermoresponsiveness of PNIPAM chains, these multifunctional stars have multiple responsive properties to pH, temperature, and ionic strength. We observed that the molecular surface area of the stars is the largest at basic pH, when the PAA blocks are strongly charged and extended, and PNIPAM chains are spread at the interface. At acidic conditions, the molecular surface area is the smallest because the P2VP blocks submerge into the water subphase and the PAA blocks are contracted and form hydrogen bonding with grafted PNIPAM chains. The molecular surface area of the stars at the air/water interface gradually increases at elevated temperature. We suggest that the transition across lower critical solution temperature (LCST) results in the emerging of PNIPAM chains from the water subphase to the interface due to the hydrophilic to hydrophobic transition. Moreover, at higher surface pressure, the stars tend to form intermolecular micellar aggregates above LCST. The graft density of PNIPAM chains as well as the arm number was also found to have strong effects on the thermo-and pH-response. Overall, this study demonstrates that the star block copolymer conformation and aggregation are strongly dependent on the intramolecular interactions between different blocks and spatial distribution of the arms, which can be controlled by the external conditions, including pH, temperature, ionic strength, and surface pressure.

A convenient synthesis of α,α′‐ homo‐ and α,α′‐hetero‐bifunctionalized poly(ε‐caprolactone)s by ring opening polymerization: The potentially valuable precursors for miktoarm star copolymers

“…Insightful discussion of thiol-ene reaction for polymer-polymer conjugation has been provided in the reported studies. 46,[61][62][63][64] It is now accepted that the thiol-ene reaction is far from being satisfactory to be considered as a click reaction. Based on several intricate studies reported in the literature, reaction conditions for thiol-ene reaction have been suggested under which the reaction is (4) Photoinitiator whose generated radicals are capable of only abstracting proton from thiol (5) Higher ratio of thiol to photoinitiator and (6) Longer reaction time.…”

Multi-Stimuli-Responsive Polymer Materials: Particles, Films, and Bulk Gels

“…Tsukruk et al prepared a star‐graft quarterpolymer PS n [P2VP‐ b ‐(PAA‐ g ‐PNIPAM)] n (PS: polystyrene, P2VP: poly(2‐vinylpyridine)), which was responsive to pH, temperature, and ionic strength due to the presence of ampholytic P2VP‐ b ‐PAA arms and grafted PNIPAM blocks. The star block copolymer conformation and micellar aggregation were strongly dependent on the intramolecular interactions between different blocks and spatial distribution of the arms, which could be controlled by the external stimuli 132…”

Multicompartmental Microcapsules with Orthogonal Programmable Two‐Way Sequencing of Hydrophobic and Hydrophilic Cargo Release

“…Themechanism for the pH controlled permeability of the (TA/SGQP) 6 microcapsules is acombination of changes in the conformation of the SGQP and the hydrogen bonding interactions between TA and SGQP (Figure 2g). [29] At al ow pH condition (pH 3), the P2VP blocks are highly charged and extended, the grafted PNIPAM chains interact with the PA A block via hydrogen bonding,s ot hat the terminal block are collapsed. Thefully extended inner block as well as the loose interaction between collapsed arm ends with TA gives the microcapsules high permeability.I nc ontrast, when pH is increased to 7, the inner P2VP blocks are neutral and hydrophobic,a nd tend to collapse instead.…”

“…[28] TheS GQP PS n [P2VP-b-(PAA-g-PNIPAM)] n (PS:p olystyrene,P 2VP:p oly(2-vinylpyridine), PA A: poly-(acrylic acid)) contain two classes of arms,o ne is as horter hydrophobic PS arm, the other is apHresponsive hydrophilic P2VP-b-PAA block copolymer arm with grafted PNIPAM chains on the PA Ablock ( Figure 1b;Supporting Information, Tables S1, S2). Thec enter of the SGQP consists of ah ydrophobic polydivinylbenzene (PDVB) core and short PS chains, [29] which means the SGQP have the potential to encapsulate hydrophobic molecules in the core.T he grafting of poly(N-isopropylacrylamide) (PNIPAM) chains on the corona effectively shields the charges in the inner blocks, which can significantly extend their in vivo circulation for biomedical applications. [30] TheS GQP precursors were synthesized via ao ne-pot/ four-step sequential "living" anionic polymerization procedure (an extended "in-out" method), which was described in detail elsewhere.…”

“…[32] Thedetailed molecular structure and their responsive behaviors at the air-water interface have also been studied earlier. [29] Because the SGQP have adense PNIPAM shell, which is able to form hydrogen bonding as acceptors,tannic acid (TA) was chosen as the hydrogen donor and ac omponent for hydrogen bonded shell assembly (Supporting Information, Figure S2). [33] TA is anatural polyphenol, which has attracted much attention as acoating material in recent years due to its versatile chemistry.…”