Importance of compositional homogeneity of macromolecular chains for UCST-type transitions in water: Controlled versus conventional radical polymerization

Abstract

The change of polymerization method from conventional free radical polymerization to the reversible addition fragmentation chain transfer (RAFT) method provided thermoresponsive behavior of upper critical solution temperature (UCST)‐type in water to copolymers of styrene (St) and acrylamide (AAm). Sample preparation conditions (temperature and time of dissolution) for turbidity measurements could also significantly influence the thermoresponsive behavior of polymers based on AAm. Poly(AAm‐co‐St)s made by RAFT method till high conversions showed sharp cloud points ranging 50–62 °C with low hysteresis in water depending upon the copolymer composition. Samples for turbidity measurements were prepared under optimized conditions, that is, 70 °C for 1.5 h. In contrast, the copolymers made by conventional radical polymerization in all copolymer composition range were not thermoresponsive. The example [poly(AAm‐co‐St)] emphasizes the importance of compositional homogeneity of macromolecular chains for showing UCST‐type transitions in water for a system with wide difference in reactivity ratios of the comonomers. Since, examples of polymeric systems showing UCST in water are not too many, this work highlights how compositional homogeneity would help in developing many more systems with tuned cloud points. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1878–1884

Tunable, concentration‐independent, sharp, hysteresis‐free UCST phase transition from poly(N‐acryloyl glycinamide‐acrylonitrile) system

“…The self‐assembly of the poly(NAGA‐AN) copolymers to micellar structures above a critical temperature appears to be responsible for thermoresponsivity with sharp transitions. Moreover, the polymers in the present work are made by RAFT showing low (1.2–1.3) molar mass dispersity and expected to have compositional homogeneity leading to sharp transitions …”

pH dependent thermoresponsive behavior of acrylamide–acrylonitrile UCST-type copolymers in aqueous media

“…Similar controlled polymerization behavior was observed for UCST-type polymers of poly(AAm-co-St). 13 The synthesized samples of poly(AAm 87 -co-AN 12 ) and poly(AAm 70 -co-AN 16 ) with molar masses M n = 20 300 Da and M n = 24 700 Da, respectively, were used for further hydrolysis experiments. Turbidity curves at pH 3 and 9 (buffer solutions) of poly(AAm 87 -co-AN 12 ) are compared to the obtained curve in Millipore water in Fig.…”

“…AAm with additional contents of hydrophobic AN or styrene (St) units. 12,13 Recently, we showed that free radical polymerization of AAm and AN with benzophenone acrylamide as a cross-linker could be used for the preparation of thermophilic films and fibers, with promising applications for wound dressings, micro-actuators and biofabrication. 14 The responsivity of non-ionic UCST polymers is based on reversible hydrogen bonding, which enables stability against pH and salt changes in their environment.…”

Smart polymers in drug delivery systems on crossroads: Which way deserves following?

“…For polymeric drug delivery systems discussed in this article, only water-based solvents are applicable. There exist a certain number of water-soluble polymers that exhibit a UCST behavior [18][19][20][21][22], i.e. the polymer becomes insoluble on cooling.…”

“…Another problem is molecular heterogeneity [22], especially if relatively large hydrophobic moieties [33,34] (e.g., anticancer drugs doxorubicin and paclitaxel) are used as comonomeric units. Copolymers with usual molecular weight of tens of kDa may contain only few monomeric units of such type to remain water-soluble at room temperature, which however has large influence on the overall CPT.…”