Thermosensitive Diblock Copolymer of Poly(N-isopropylacrylamide) and Poly(ethylene glycol) in Water:  Polymer Preparation and Solution Behavior

Abstract

This investigation focused on the self-assembly of poly(N-isopropylacrylamide)-block-poly-(ethylene glycol) (PNIPA-block-PEG) in water. A quasi-living radical polymerization technique including a Ce(IV) ion redox system enabled us to prepare block copolymers with relatively narrow molecular weight distributions. We distinguish five regions in the phase diagram: a transparent sol, opaque sol, transparent gel, opaque gel, and syneresis. By examining the extent of changes in the spectroscopic properties of a fluorescence probe, pyrene, as a function of block polymer concentration and/or temperature, we determined the critical association concentration as well as the partition coefficient K v for pyrene. The spectroscopic properties indicate that the hydrophobicity around the probe starts to increase far below the demixing line of the PNIPA-block-PEG, a remarkable finding which suggests that even in the temperature region below the LCST temperature of a PNIPA block (∼32 °C), this block copolymer provides more space for a preferential transfer of pyrene molecules than a bulk water medium at a higher temperature. This result may be attributed to the action of water, which starts to behave as a selective solvent for PEG blocks; the PEG chains are more swollen with water than are the PNIPA chains. Dynamic light scattering measurements also indicate that contraction of the PNIPA block starts to occur around 18 °C, which is consistent with results obtained by fluorescence measurements. By employing small-angle neutron scattering, it is also confirmed that microphase separation occurs above 17 °C to form disordered micelles, which includes a range of states from (i) asymmetric swelling to (ii) micelle formation with only shortrange liquidlike order. Above 30 °C, network domains are formed as a result of macrophase separation due to dehydration of PNIPA blocks. As the temperature increased up to 40 °C, the network domain is collapsed along a direction parallel to PNIPA-block-PEG interface, leading to increase in interfacial thickness and to macroscopic syneresis.

Fabrication and aggregation of thermoresponsive glucose-functionalized double hydrophilic copolymers

“…3) clearly indicate that an aggregate forms even below the LCST. This might arise because of a chemical potential effect: a similar phenomenon was found by Liang and Annaka when they studied the association and dissociation of PEO-b-PNIPAAm [31,32].…”

Advances in drug delivery systems based on synthetic poly(hydroxybutyrate) (co)polymers

“…Poly(N-isopropyl acrylamide) (PNIPAAM) (low critical solution temperature (LCST) = 32-34 °C) [172,173], poly(propylene glycol) (PPG) (LCST = 15-45 °C) [80], and poly(2- In addition, the micellization process is entropy driven, thus making it strongly dependent on the hydrophilic/hydrophobic balance of the copolymer [80,157]. Also, it is generally admitted that the micellization process is favored by a high hydrophobic content as it is mainly driven by hydrophobic interactions [178].…”

Study on the solution properties of ZnO QDs-embedded MEO2MA m –HEMA n –MEO2MA m triblock copolymers

“…It is well known that the emission spectrum of pyrene is sensitive to the polarity of an environment in which it is dispersed [27][28][29]. Specially, the intensity ratio (I 1 /I 3 ) of the first (0, 0) to the third (0, 2) bands is used in the study of micelles [30,31].…”