Constrained thermoresponsive polymers – new insights into fundamentals and applications

• Patricia Flemming,
• Alexander S. Münch,
• Andreas Fery and
• Petra Uhlmann

Beilstein J. Org. Chem. 2021, 17, 2123–2163, doi:10.3762/bjoc.17.138

• turbidimetry (determination of the cloud point) is available. For thermoresponsive interfaces in the form of polymer brushes on a flat substrate or on nanoparticles, however, there are only very limited comparable analytical characterization methods, which consequently leads to a distortion of terminologies

• for any real polymer solution. Every polymer always exhibits a molar mass distribution. Therefore, a quasi-binary mixture is usually considered. It is possible to measure the cloud-points, but the obtained cloud-point (Tcp) curve differs from a simple bimodal. Thus, the critical point (LCST or UCST

• ) of one specific polymer with distinct Pn is not the extremum and is found at higher polymer concentrations in practice. The maximum of the cloud-point curve shifted to higher temperatures and to the solvent-rich region. The theoretical model was accordingly extended to account for polydispersity [80

An amphiphilic pseudo[1]catenane: neutral guest-induced clouding point change

• Tomoki Ogoshi,
• Tomohiro Akutsu and
• Tada-aki Yamagishi

Beilstein J. Org. Chem. 2018, 14, 1937–1943, doi:10.3762/bjoc.14.167

• -ECA500 spectrometer. UV–vis absorption spectra were recorded with a JASCO V-670 using 1 cm quartz cuvettes. Cloud points were determined by transmission changes (at 650 nm) of the solutions heated at 0.1 °C/min; cloud point values were defined as the temperature at which the transmission decreases by 50

Supramolecular polymer assembly in aqueous solution arising from cyclodextrin host–guest complexation

• Jie Wang,
• Zhiqiang Qiu,
• Yiming Wang,
• Li Li,
• Xuhong Guo,
• Duc-Truc Pham,
• Stephen F. Lincoln and
• Robert K. Prud’homme

Beilstein J. Org. Chem. 2016, 12, 50–72, doi:10.3762/bjoc.12.7

• consequences. Thus, turbidity measurements in aqueous solution show the cloud point for (a) to be 309.2 K whereas those of (b) and (c) are 316.2 K and 326.2 K, respectively. These increases are attributed to an increase in hydrophilicity caused by the anionic carboxylate and sulfonate groups protruding from

• the β-CD annuli and interacting with water. However, in (d) the negative charge is located in the centers of the β-CD annuli and there is no enhancement of interaction with water and the cloud point occurs at 307.2 K. Light-scattering studies show the hydrodynamic diameters of (a)–(d) to be 15.1, 11.5

Influence of cyclodextrin on the UCST- and LCST-behavior of poly(2-methacrylamido-caprolactam)-co-(N,N-dimethylacrylamide)

• Alexander Burkhart and
• Helmut Ritter

Beilstein J. Org. Chem. 2014, 10, 1951–1958, doi:10.3762/bjoc.10.203

• were performed. As shown in Figure 1, copolymer 6a has a typical LCST-behavior in water. The cloud point upon heating is 34 °C and upon cooling 37 °C, respectively. The hysteresis effect is a result of insoluble to soluble transition which depends on the shape and size distribution of dispersed polymer

• particles [16][17]. The more hydrophilic copolymer 6b has a higher cloud point at 67 °C whereas copolymer 6c is completely soluble in water up to >95 °C. Complexation of copolymer 6a with a 1.5 molar excess of CD, based on monomer 4, was carried out to yield the complexed copolymer 6aCD. Due to that

• complexation, the cloud point in the heating curves increases from 34 °C (6a) up to 47 °C (6aCD) with a sharp phase transition. Obviously, the complexation of the attached caprolactam ring with CD leads to a higher hydrophilicity of the copolymer and therefore to a better solubility in water. The postulated

Supercritical carbon dioxide: a solvent like no other

• Jocelyn Peach and
• Julian Eastoe

Beilstein J. Org. Chem. 2014, 10, 1878–1895, doi:10.3762/bjoc.10.196

• built on by Zhang et al. along with another low molecular weight, CO2-philic polymer; poly(vinyl ethyl ether), (PVEE, Figure 5, compound 38) [98][99]. Viscosities of the polymer-thickened CO2 were measured by capillary viscometry across a range of pressures along with cloud point pressures. Higher

• factor of around 5 to 400 through the addition of fluoroacrylate and styrene copolymers at a range of polymer concentrations (1–5 w/w %) and styrene:fluoroacrylate molar ratios [100]. Cloud point pressures indicated that polymer solubility decreased with increased concentrations of styrene in the polymer

• 1) [27][58][68]. Subsequently both surfactant development and the understanding of applications of scCO2 have advanced considerably. Surfactant solubility has been previously expressed in a range of ways based on pressure and temperature phase behaviour studies. The phase instability Ptrans (cloud

End-group-functionalized poly(N,N-diethylacrylamide) via free-radical chain transfer polymerization: Influence of sulfur oxidation and cyclodextrin on self-organization and cloud points in water

• Sebastian Reinelt,
• Daniel Steinke and
• Helmut Ritter

Beilstein J. Org. Chem. 2014, 10, 680–691, doi:10.3762/bjoc.10.61

• 3-(4-(2,4,4-trimethylpentan-2-yl)phenoxy)propane-1-thiol, poly(N,N-diethylacrylamide) (PDEAAm) with well-defined hydrophobic end-groups is obtained. These end-group-functionalized polymers show different cloud point values, depending on the degree of polymerization and the presence of randomly

• methylated β-cyclodextrin (RAMEB-CD). Additionally, the influence of the oxidation of the incorporated thioether linkages on the cloud point is investigated. The resulting hydrophilic sulfoxides show higher cloud point values for the lower critical solution temperature (LCST). A high degree of

• indication for further oxidation of the polymer chain or additional oxidized structures, e.g. of the methine groups in the main chain. Impact of the degree of polymerization and structure of the end-group on the cloud point values. Aqueous solutions of poly(N,N-diethylacrylamide) (PDEAAm) exhibtit a coil to

Oligomeric epoxide–amine adducts based on 2-amino-N-isopropylacetamide and α-amino-ε-caprolactam: Solubility in presence of cyclodextrin and curing properties

• Julian Fischer and
• Helmut Ritter

Beilstein J. Org. Chem. 2013, 9, 2803–2811, doi:10.3762/bjoc.9.315

• the solution properties of 9 and 10 in water, turbidity measurements were performed (Figure 1). It was observed, that 9 was soluble in cold water and exhibited a cloud point of about 27 °C due to heating. To evaluate the effect of CD complexation on the solubility of that oligomer 9, 150 mol % of

• randomly methylated β-cyclodextrin (RAMEB-CD) were added (9β). After that, the cloud point shifted significantly up to 36 °C, which is remarkable since PNIPAM does not interact with β-CD [14]. Explanation for this can be steric effects, since the isopropyl group in our system 9 is placed not so close at

• the backbone as in PNIPAM. For further confirmation of these findings, the solution of 9 with RAMEB-CD was treated with potassium 1-adamantylcarboxylate (AdCOO−K+) in some excess, which should displace 9 from RAMEB-CD due to its high complexation properties [6][24][25]. As predicted, the cloud point

Polymeric redox-responsive delivery systems bearing ammonium salts cross-linked via disulfides

• Christian Dollendorf,
• Martin Hetzer and
• Helmut Ritter

Beilstein J. Org. Chem. 2013, 9, 1652–1662, doi:10.3762/bjoc.9.189

• -dependent solubilities with lower critical solution temperatures (LCST) of 32 and 50 °C, respectively, in neutral media [50][51]. Therefore, the temperature-dependent behavior of poly(DEAAm-co-DMAEMA) and the influence of thiol side-chains on the cloud point temperatures (Tc) was investigated. Samples 3, 4a

• differed slightly with temperatures Tc of 23.0 and 25.6 °C and only 4c showed an elevated cloud point in the range of 27.9 to 31.0 °C. Under basic conditions the thiol side-chains are deprotonated, leading to betaine structures. Thus, the negatively charged thiolate groups can interact with the cationic

• transition temperature Tg for samples 3–6. Cloud point temperatures Tc of poly(DEAAm-co-DMAEMA) bearing thiole side chains after disulfide cleavage with DTT in dist. H2O and pH 10 buffer solution. Supporting Information Supporting information features experimental procedures, descriptions of

Influence of cyclodextrin on the solubility and the polymerization of (meth)acrylated Triton^® X-100

• Melanie Kemnitz and
• Helmut Ritter

Beilstein J. Org. Chem. 2012, 8, 2176–2183, doi:10.3762/bjoc.8.245

• °C due to a typical LCST effect. By addition of 1 equiv of RAMEB-CD (1a) the cloud point is shifted from 66 to 71 °C. This can be attributed to the increasing hydrophilicity. Figure 2 shows the changes of the transmittance as a function of the temperature. After the addition of a second equiv of

• total complexation of the hydrophobic component is required to prevent the intermolecular aggregation of the coil, which results in a higher rigidity of the polymer chain. The addition of 2 equiv of RAMEB-CD to 8 leads to a water soluble polymer with a cloud point of 11 °C. For the single and double

• . Above this temperature, the polymer precipitates (Figure 3, III). Similar curves were determined for different shear rates and the solution showed shear-thinning behavior. The results found by rheometer were confirmed by DLS and turbidity measurements. The cloud point was around 56 °C. Figure 3 shows

Cyclodextrin-induced host–guest effects of classically prepared poly(NIPAM) bearing azo-dye end groups

• Gero Maatz,
• Arkadius Maciollek and
• Helmut Ritter

Beilstein J. Org. Chem. 2012, 8, 1929–1935, doi:10.3762/bjoc.8.224

• [4-(4’-aminophenylazo)phenyl]amine. This dye-end-group-labeled polymer showed acidochromic effects, depending on the pH and the presence of randomly methylated β-cyclodextrin (RAMEB-CD). Also higher cloud-point values for the lower critical solution temperature (LCST) in the presence of RAMEB-CD were

• to the hydrophobic azo-dye end group of 6, a slight reducing effect on the cloud point in comparison to pure PNIPAM, from 32 down to 29.5 °C is detected. As a result of complexation of the hydrophobic azo-dye end group by RAMEB-CD, the cloud point increases from 29.5 back to 32 °C (Figure 2). This is

• -responsive behavior in aqueous solution was analyzed by absorption and cloud-point measurements. In addition, the influences of RAMEB-CD on both effects were investigated. The intermolecular interaction between the dye end group and RAMEB-CD was proven by absorption and 2D ROESY NMR experiments. Furthermore

Influence of cyclodextrin on the solubility of a classically prepared 2-vinylcyclopropane macromonomer in aqueous solution

• Helmut Ritter,
• Jia Cheng and
• Monir Tabatabai

Beilstein J. Org. Chem. 2012, 8, 1528–1535, doi:10.3762/bjoc.8.173

• ß-cyclodextrin in water. Via radical ring-opening copolymerization of 5 and NiPAAm a graft copolymer 8 with a clouding point of 32 °C was synthesized. The branched unsaturated polymer was treated with ozone to cleave the double bonds of the main chain. Keywords: branched poly(NiPAAm); cloud point

• voluminous vinylcyclopropane unit 5 possesses a slightly larger dn than 3 (by ca. 0.9 nm, Table 1). In general, the cloud point of poly(NiPAAm) with relative low molecular weight can be influenced by the structure of end groups. The relatively hydrophobic vinylcyclopropane end group hampers the aqueous

Chiral recognition of ephedrine: Hydrophilic polymers bearing β-cyclodextrin moieties as chiral sensitive host molecules

• Sabrina Gingter and
• Helmut Ritter

Beilstein J. Org. Chem. 2011, 7, 1516–1519, doi:10.3762/bjoc.7.177

• outer water phase. Figure 2 shows the results of cloud-point measurements performed on a turbidity photometer. However, the turbidity measurements only showed the inclusion of ephedrine, and no significant enantiomeric effect was observed. However, the supposed enantiomeric differences due to

• copolymer 1 and 60 mg of β-CD in alkaline D2O. Turbidity experiments were performed on a Tepper cloud-point photometer TP1. The relative transmission of a laser beam with a wavelength of 670 nm was recorded for each experiment. The measurements were performed within a temperature range between 5 and 40 °C

Hybrid biofunctional nanostructures as stimuli-responsive catalytic systems

• Gernot U. Marten,
• Thorsten Gelbrich and
• Annette M. Schmidt

Beilstein J. Org. Chem. 2010, 6, 922–931, doi:10.3762/bjoc.6.98

• biomolecules [33]. In this respect it is of interest to note, that the cloud point temperature can be adjusted by copolymerization in a wide range, including temperatures acceptable for biomolecules and biological species (Figure 3a) [34]. Furthermore, it has been shown that thermoflocculation of core–shell

• temperatures up to 80 °C depending on the FeOx content. A higher Fe3O4 content leads to faster heating, and a specific heat power (SHP) = 86.5 W·g−1 of the particle cores can be extracted from the data. The generated heat flux is strong enough to reach the cloud point temperature Tc of 61 °C in the dispersions

• general purpose mode (non-negative least-squares) algorithm included in the DTS software. Each experiment was performed at least three times. Cloud point photometry of aqueous particle dispersions was performed on a Tepper TP1 cloud point photometer at 1 K·min−1 in HEPES buffer. From the turning point of

Calix[4]arene-click-cyclodextrin and supramolecular structures with watersoluble NIPAAM-copolymers bearing adamantyl units: “Rings on ring on chain”

• Bernd Garska,
• Monir Tabatabai and
• Helmut Ritter

Beilstein J. Org. Chem. 2010, 6, 784–788, doi:10.3762/bjoc.6.83

• be ascribed to the existence of the hydrophobic adamantyl units in the copolymer. The host–guest effect of the coupled rings 4 on the cloud point of copolymer 5 was evaluated by turbidity measurements. Only a slight positive shift of the cloud point temperature from 29 °C to 30 °C was found (Table 1

• ). The temperature shift relative to the cloud point of poly(NIPAAM) itself, can be explained by the inclusion of the hydrophobic adamantyl units of 5 by the CD moiety of 4, which, in principal, should increase the cloud point temperature. In contrast to this, the unavoidable presence of the hydrophobic

• calixarene units of 4 leads to a reduction of the cloud point temperature. Repeating the turbidity experiment at pH of 12, the cloud point temperature of the copolymer 5 decreased from the original 29 °C to 23 °C due to salt and pH effects [18]. However, after adding the calixarene-click-cyclodextrin (4) to