Abstract
An UCST-type copolymer of acrylamide (AAm) and acrylonitrile (AN) (poly(AAm-co-AN)) was prepared by reversible addition fragmentation chain transfer (RAFT) polymerization and its temperature-induced phase transition and aggregation behaviour studied by turbidimetry, static and dynamic light scattering, small angle neutron scattering (SANS) and cryo-transmission electron microscopy (cryo-TEM) measurements. The phase transition temperature was found to increase with increasing AN content in the copolymer, concentration of the solutions and copolymer chain length. A significant effect was observed onto the phase transition temperature by addition of different electrolytes into the copolymer solution. The copolymer chains were aggregated below the phase transition temperature and disaggregated above it. The size of the aggregates increases with increasing AN contents and concentration of the copolymer solutions below the phase transition temperature. The copolymer chains were expanded and weekly associated in solution above the phase transition temperature. A model is proposed to explain such association-aggregation behaviour of poly(AAm-co-AN) copolymers depending on AN contents and concentration of the copolymer solutions as a function of temperature.
Highlights
There has been a recent increased interest in upper critical solution temperature (UCST) polymers
A robust UCST-type poly(AAm-co-AN) copolymer with different compositions was prepared through reversible addition fragmentation chain transfer (RAFT) polymerization
The temperature-induced phase transition and aggregation behaviour was systematically studied by a combination of turbidimetry, static and dynamic light scattering, small angle neutron scattering (SANS) measurements and cryo-TEM
Summary
There has been a recent increased interest in UCST polymers. to date, only few polymers exhibiting a UCST in water within a relevant temperature range (0 to 100 1C), have been reported, i.e. phase separate from solution upon cooling.[9,10,11] In addition, UCST type polymers based on ionic interactions such as polybetaines,[12,13,14,15] are difficult to use under physiological conditions (i.e. in the presence of salts etc.), which significantly restricts their potential applications. PNAGA and its derivatives display a significant hysteresis[20] and exhibit a slow phase transition,[19] preventing their use in many applications where sharp and fast transitions are required Another example of non-ionic UCST polymer is acrylamide based poly(methylacrylamide) (PMAm).[21] the UCST behaviour of PMAm is affected by the presence of ionic groups during synthesis. The phase transition temperature of this copolymer can be adjusted or tuned by varying the composition of the copolymer and the concentration of the solution.[21] the UCST type poly(AAm-co-AN) based derivatives show potential applications as microactuators[25] and drug delivery systems.[26] Very recently Pineda-Contreras et al.[27] investigated the pH dependent thermoresponsive behaviour of the poly(AAm-co-AN) in aqueous media. Based on the observed results, we propose a model for the phase transition and aggregation behaviour of poly(AAm-co-AN) depending on the AN fraction in the copolymer and the concentration of the solution
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