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Dual thermo- and light-responsive water-soluble copolymers that respond to exclusively non-invasive triggers are obtained by functionalising poly(N,N-dimethylacrylamide) with arylazopyrazole side chains. The light-induced E–Z (trans–Z) photo isomerisation of these dyes provides an exceptionally effective photo-switch, which can reversibly shift the LCST-type phase transition temperatures by almost 25 K. [ABSTRACT FROM AUTHOR]

Thermoresponsive polymers are being used increasingly in cell culture applications due to their temperature dependent surface properties. Poly(MEOMA-co-OEGMA) (PMO) brushes offer tunable physical properties via variation in the copolymer ratio, but the effects of composition on cell-substrate interactions is unclear. To this end, a series of PMO brushes (0-8% OEGMA) was fabricated and L-929 fibroblast adhesion and morphology was quantified in the presence of serum (FBS) or after functionalization via the adsorption of fibronectin (FN) and vitronectin (VN). Quantification of the adsorption of model proteins, bovine serum albumin and FN, revealed that the extent of adsorption was correlated to the amount MEOMA content, which represents the more hydrophobic component in PMO brushes. Cells exhibited delayed attachment and spreading on all PMO substrates in the presence of FBS. After 24 h, cell attachment was comparable; however, increased spreading was correlated with increased MEOMA content. Adsorption of FN significantly increased initial cell attachment to all PMO surfaces after 2 h. This was not observed with VN; however, both FN and VN increased cell spreading/decreased cell circularity for all PMO substrates relative to FBS. Pure MEOMA brushes with FN exhibited increased cell spreading/decreased cell circularity relative to other PMO substrates after 2 h, and elicited the highest cell density after 24 h. These results demonstrate that increased MEOMA content in PMO substrates facilitates cell attachment and spreading, which can be further enhanced by adsorbing FN in the absence of other proteins. [ABSTRACT FROM AUTHOR]

A concentrated solution of a symmetric triblock copolymer with a thermoresponsive poly(methoxy diethylene glycol acrylate) (PMDEGA) middle block and short hydrophobic, fully deuterated polystyrene end blocks is investigated in DO where it undergoes a lower critical solution temperature-type phase transition at ca. 36 °C. Small-angle neutron scattering (SANS) in a wide temperature range (15-50 °C) is used to characterize the size and inner structure of the micelles as well as the correlation between the micelles and the formation of aggregates by the micelles above the cloud point (CP). A model featuring spherical core-shell micelles, which are correlated by a hard-sphere potential or a sticky hard-sphere potential together with a Guinier form factor describing aggregates formed by the micelles above the CP, fits the SANS curves well in the entire temperature range. The thickness of the thermoresponsive micellar PMDEGA shell as well as the hard-sphere radius increase slightly already below the cloud point. Whereas the thickness of the thermoresponsive micellar shell hardly shrinks when heating through the CP and up to 50 °C, the hard-sphere radius decreases within 3.5 K at the CP. The volume fraction decreases already significantly below the CP, which may be at the origin of the previously observed gel-sol transition far below the CP (Miasnikova et al., Langmuir 28: 4479-4490, 2012). Above the CP, small, and at higher temperatures, large aggregates are formed by the micelles. [ABSTRACT FROM AUTHOR]

1H NMR relaxation is used to study the self-assembly of a double thermoresponsive diblock copolymer in dilute aqueous solution. Above the first transition temperature, at which aggregation into micellar structures is observed, the trimethylsilyl (TMS)-labeled end group attached to the shell-forming block shows a biphasic T2 relaxation. The slow contribution reflects the TMS groups located at the periphery of the hydrophilic shell, in agreement with a star-like micelle. The fast T2 contribution corresponds to the TMS groups, which fold back toward the hydrophobic core, reflecting a flower-like micelle. These results confirm the formation of block copolymer micelles of an intermediate nature (i.e., of partial flower-like and star-like character), in which a part of the TMS end groups folds back to the core due to hydrophobic interactions. [ABSTRACT FROM AUTHOR]

An amphiphilic linear ternary block copolymer was synthesised in three consecutive steps via reversible addition-fragmentation chain transfer polymerisation. Oligo(ethylene glycol) monomethyl ether acrylate was engaged as a hydrophilic building block, while benzyl acrylate and 3-tris(trimethylsiloxy)silyl propyl acrylate served as hydrophobic building blocks. The resulting 'triphilic' copolymer consists thus of a hydrophilic (A) and two mutually incompatible 'soft' hydrophobic blocks, namely, a lipophilic (B) and a silicone-based (C) block, with all blocks having glass transition temperatures well below 0 °C. The triphilic copolymer self-assembles into spherical multicompartment micellar aggregates in aqueous solution, where the two hydrophobic blocks undergo local phase separation into various ultrastructures as evidenced by cryogenic transmission electron microscopy. Thus, a silicone-based polymer block can replace the hitherto typically employed fluorocarbon-based hydrophobic blocks in triphilic block copolymers for inducing multicompartmentalisation. [ABSTRACT FROM AUTHOR]

We investigate concentrated solutions of poly(styrene- b-N-isopropyl acrylamide) (P(S- b-NIPAM)) diblock copolymers in deuterated water (DO). Both structural changes and the changes of the segmental dynamics occurring upon heating through the lower critical solution temperature (LCST) of PNIPAM are studied using small-angle neutron scattering and neutron spin-echo spectroscopy. The collapse of the micellar shell and the cluster formation of collapsed micelles at the LCST as well as an increase of the segmental diffusion coefficient after crossing the LCST are detected. Comparing to our recent results on a triblock copolymer P(S- b-NIPAM- b-S) [], we observe that the collapse transition of P(S- b-NIPAM) is more complex and that the PNIPAM segmental dynamics are faster than in P(S- b-NIPAM- b-S). [ABSTRACT FROM AUTHOR]

Imidazolium-based ionic liquids are used as new solvents for the synthesis of statistical copolymers from methacrylates of strongly differing polarities and solubilities, namely of n-butylmethacrylate and 3-( N-2-[methacryloyloxyethyl]- N,N dimethyl-3-ammonio)propane sulfonate. Though difficult to prepare in classical solvents, true copolymers of these monomers can be obtained in ionic liquids, providing zwitterionic amphiphilic polymers. The relative reactivity of the monomers and thus the copolymer composition is influenced by the ionic liquid used. Analysis of the copolymers using 1H NMR spectroscopy, elemental analysis, and asymmetrical flow field-flow fractionation (AF4) shows the influence of both the length of the alkyl chain bound at the nitrogen atom of the imidazolium ring and the anion of the ionic liquid on the structure of the copolymers. Furthermore, the highly polar methacrylate with a sulfobetaine moiety is only slightly preferred in copolymerization if ionic liquids are used as solvents for copolymerization. The ratio of monomer segments in the copolymer can be influenced by the selection of the ionic liquid used as a solvent for polymer synthesis and by the variation of the monomer ratio selected for copolymerization if it is carried out in an ionic liquid. This opens new possibilities for a broad variation of amphiphilic copolymer structures obtained through free radical copolymerization of differently polar monomers. Copyright © 2008 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Free radical homo- and copolymerization of the highly polar 3-(N-[2- methacryloyloxyethyl]-N,N-dimethylammonio)propane sulfonate with the nonpolar n-butylmethacrylate was investigated in the ionic liquids 1-butyl-3-methyl imidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium hexafluoro phosphate, and compared to analogous polymerizations in standard solvents. Higher molar masses are obtained for the zwitterionic homopolymer when the polymerization is carried out in an ionic liquid compared to the classical reaction in water. Although homopolymerization of the sulfobetain monomer as well as of n- butylmethacrylate results in phase separation during the polymerization process, copolymerization of a stoichiometric ratio of the two monomers in the ionic liquids produced transparent gels indicating that no macrophase separation occurs. The use of ionic liquids as reaction medium improved the copolymerization behavior of the two methacrylates significantly. Whereas only minor amounts of n-butyl methacrylate were incorporated in the copolymer when synthesized in acetonitrile, the content of the non-polar monomer units in the zwitterionic copolymer approached increasingly its content in the polymerization mixture when ionic liquids were employed as solvents. [ABSTRACT FROM AUTHOR]

Abstract: A series of RAFT agents was synthesised, and used to prepare various ionic, non-ionic and zwitterionic water-soluble polymers, in organic as well as in aqueous media. The RAFT process proved to be a powerful method to prepare functional polymers of complex structure, such as amphiphilic diblock and triblock copolymers. This includes polymers containing one or even two stimuli-sensitive hydrophilic blocks. Switching the hydrophilic character of a single or of several blocks by changing the pH, the temperature or the salt content demonstrated the variability of the molecular designs suited for stimuli-sensitive polymeric amphiphiles, and exemplified the concept of multiple-sensitive systems. [Copyright &y& Elsevier]

Aqueousmixtures of a dye-labeled non-ionic thermoresponsive copolymerand a conjugated cationic polyelectrolyte are shown to exhibit characteristicchanges in fluorescence properties in response to temperature andto the presence of salts, enabling a double-stimuli responsiveness.In such mixtures at room temperature, i.e., well below the lower criticalsolution temperature (LCST), the emission of the dye is strongly quencheddue to energy transfer to the polycation, pointing to supramolecularinteractions between the two macromolecules. Increasing the concentrationof salts weakens the interpolymer interactions, the extent of whichis simultaneously monitored from the change in the relative emissionintensity of the components. When the mixture is heated above itsLCST, the transfer efficiency is significantly reduced, signalinga structural reorganization process, however, surprisingly only ifthe mixture contains salt ions. To elucidate the reasons behind suchthermo- and ion-sensitive fluorescence characteristics, we investigatethe effect of salts of alkali chlorides, in particular of NaCl, onthe association behavior of these macromolecules before and afterthe polymer phase transition by a combination of UV–vis, fluorescence,and 1H NMR spectroscopy with light scattering and small-angleneutron scattering measurements. [ABSTRACT FROM AUTHOR]

Abstract: Colloidal probe microscopy was employed to study forces between cellulose surfaces upon addition of a series of cationic copolymers in aqueous solution, as model compounds for wet strength agents. The content of quaternary ammonium groups and primary amines was systematically varied in the cationic polymers, to distinguish between the importance of electrostatical and H-bonding effects. Cellulose microspheres were glued at the apex of tipless microfabricated cantilevers and used as colloidal probes. Ultra thin cellulose films and cellulose fibres were employed as model surfaces. The cellulose films of a thickness of about 5 nm were spin-coated from cellulose solution onto silicon substrates. The root-mean-square-roughness (RMS) was 0.3–0.8 nm. The cationic model polymers were compared to Servamine, a polymer employed as standard wet strength resin in papermaking industries. Force versus separation measurements showed a detailed picture of adhesion and contact breaking. Relatively strong adhesion of the order of 0.3 mJ/m2 was observed with Servamine within a range of approximately 10 nm. At larger distances weak bond breaking and elastic chain pulling were identified. When approaching the surface one to two small jump-in''s possibly related to strong binding of Servamine and subsequent attraction could be found in the case of Servamine. In contrast, all the model copolymers showed only a weak adhesion of 8–30 μJ/m2, i.e., an order of magnitude less than that of Servamine and subsequent elastic rupture domains. The contour length, persistence length and characteristic rupture distances were calculated by means of applying the WLC model. Measurements against cellulose fibres obtained from the production process proved the relevance of the model systems. [Copyright &y& Elsevier]