The synthesis of thermoresponsive POSS-based eight-arm star poly(N-isopropylacrylamide): A comparison between Z-RAFT and R-RAFT strategies

Pang, B (Pang, Bo)^{[ 1 ]} ; Liu, R (Liu, Rui)^{[ 1 ]} ; Han, G (Han, Guang)^{[ 2 ]} ; Wang, W (Wang, Wei)^{[ 3 ]} ; Zhang, WQ (Zhang, Wangqing)^{[ 1,4 ]}

POLYMER CHEMISTRY, 2021, 12(14): 2063-2074

DOI: 10.1039/d1py00087j

摘要

POSS-based eight-arm star poly(N-isopropylacrylamide), POSS-(PNIPAM)(8), was synthesized via solution reversible addition-fragmentation chain transfer (RAFT) polymerization employing the core-first method via both a Z-RAFT strategy and an R-RAFT strategy. Well-defined Z-type POSS-(PNIPAM)(8) (POSS-(PNIPAM)(8)-Z) was obtained via employing the Z-RAFT strategy, in which side reactions, such as star-star coupling, linear-star coupling and intramolecular radical termination, were suppressed at moderate monomer conversion. However, when employing the general R-RAFT strategy, the RAFT polymerization was out of control at moderate monomer conversion, and polymers with a broad molecular weight distribution were obtained. The thermoresponse of star POSS-(PNIPAM)(8) was investigated via turbidity analysis, variable-temperature H-1 NMR analysis, DLS analysis, and TEM. It was found that the phase transition of star POSS-(PNIPAM)(8) occurred within a narrow temperature window and less significant hysteresis in the cooling process existed than that found for linear PNIPAM. Star POSS-(PNIPAM)(8) tended to form small-sized aggregates at temperatures above the phase transition temperature (PTT) of the PNIPAM arms. Star POSS-(PNIPAM)(8) could greatly decrease the oil/water interfacial tension, and oil-in-water emulsions, e.g., toluene-in-water, n-dodecane-in-water, cyclohexane-in-water, and n-hexane-in-water, could be prepared just by employing highly diluted star POSS-(PNIPAM)(8). Reversible emulsification-demulsification was triggered via increasing the temperature above the PTT or decreasing the temperature below the PTT.