Synthesis of thermoresponsive hyperbranched polyamidoamine and the molecular weight, pH, and anion sensitive thermoresponsive properties thereof

Modeling Lower Critical Solution Temperature Behavior of Associating Dendrimers Using Density Functional Theory

We study the phase behavior of associating dendrimers in explicit solvents using classical density functional theory. The existence of association enables uptake of solvent inside the dendrimer even for unfavorable Lennard-Jones interaction between the solvent and dendrimer. Depending on the distributions of associating sites, the dendrimer conformation can be either dense-core or dense-shell. The conformation of the associating dendrimer is greatly affected by the temperature. Due to the interplay between association interaction and Lennard-Jones attractions, we find the lower critical solution temperature (LCST) behavior of dendrimer conformation and study how it changes as the dendrimer size or solvent size changes. The dendrimer in our study displays no LCST behavior at low generations, and it has a maximum LCST at G4. Moreover, increasing the solvent chain length decreases the LCST. For solvents with self-association, the competition between solvent-solvent association and solvent-dendrimer association also tends to reduce the LCST. Qualitatively consistent with experiments, our results provide insight into the molecular mechanism of the LCST behavior of associating dendrimers.

Advances in thermosensitive polymer-grafted platforms for biomedical applications

Studies on "smart" polymeric material performing environmental stimuli such as temperature, pH, magnetic field, enzyme and photo-sensation have recently paid much attention to practical applications. Among of them, thermo-responsive grafted copolymers, amphiphilic steroids as well as polyester molecules have been utilized in the fabrication of several multifunctional platforms. Indeed, they performed a strikingly functional improvement comparing to some original materials and exhibited a holistic approach for biomedical applications. In case of drug delivery systems (DDS), there has been some successful proof of thermal-responsive grafted platforms on clinical trials such as ThermoDox®, BIND-014, Cynviloq IG-001, Genexol-PM, etc. This review would detail the recent progress and highlights of some temperature-responsive polymer-grafted nanomaterials or hydrogels in the 'smart' DDS that covered from synthetic polymers to nature-driven biomaterials and novel generations of some amphiphilic functional platforms. These approaches could produce several types of smart biomaterials for human health care in future.

Hyperbranched polyglycerol derivatives exhibiting normal or abnormal thermoresponsive behaviours in water: facile preparation and investigation by turbidimetry and fluorescence techniques

Polymers exhibiting an abnormal thermoresponsive behaviour, in which increase in the polymer concentration in water leads to an increase in the phase transition temperature, are few, and no plausible strategy has been addressed to prepare these polymers. For illuminating a feasible common strategy to prepare polymers with an abnormal thermoresponsive behaviour, in this study, we systematically prepared a series of hyperbranched polyglycerol (HPG) derivatives through a facile esterification reaction between HPG and aliphatic acids having different carbon numbers (X). Turbidimetry measurements demonstrate that thermoresponsive HPGs can be obtained only when HPGs are conjugated with aliphatic units of X ≤ 8. The conjugation of HPG with aliphatic units of X ≤ 4 resulted in thermoresponsive HPGs with a normal thermoresponsive behaviour. For the preparation of thermoresponsive HPGs with an abnormal thermoresponsive behaviour, X should be controlled in the range of 5-8. Fluorescence measurements with nile red as the fluorescent probe demonstrate that the existence of relatively strong hydrophobic interaction is a key factor to ensure that the polymer exhibits an abnormal thermoresponsive behaviour in water. Moreover, turbidimetry and fluorescence techniques are complementary for measuring the phase transition behaviour and suitable for different polymer concentration regions.

Stimuli-responsive hyperbranched poly(amidoamine)s integrated with thermal and pH sensitivity, reducible degradability and intrinsic photoluminescence

Stimuli-responsive HPA-C4s integrated with thermal and pH sensitivity, reducible degradability and intrinsic photoluminescence were successfully prepared and characterized.

Three-Component Supramolecular System with Multistimuli-Responsive Properties in Water

Hyperbranched polyethylenimine terminated with isobutyramide groups (HPEI-IBAm), 4-(phenylazo)benzoic acid (PABA), and α-cyclodextrin (α-CD) were assembled together at pH≈7 to form the three-component supramolecular complexes that were verified by (1) H and 2D ROESY (1) H NMR spectroscopy. UV/Vis spectrometric titration experiments showed that the content of α-CD in the three-component complexes was less than the feed amount and it was difficult for all the PABA units in the complexes to further form complexes with α-CD. The obtained three-component supramolecular complexes exhibited thermoresponsive properties in water. Increasing the α-CD concentration led to a sharp increase in the cloud point temperature (Tcp ) at the beginning, but after the [α-CD]/[PABA] ratio was in the region of 1.3-1.6, the Tcp increased gradually When the concentration of α-CD was low, a higher concentration of PABA led to a lower Tcp , however, the opposite was observed when the concentration of α-CD was high. For the three-component complex, increasing the α-CD concentration at pH≈7 or at pH≈9 led to different Tcp temperatures. In the low α-CD concentration range, adjusting the pH from ≈7-≈9 resulted in an increase in the Tcp , similar but not so pronounced as that of the two-component system of HPEI-IBAm/[PABA]. When the concentration of α-CD was high, adjusting the pH from ≈7-≈9 decreased the Tcp ; this observation is different to that of the two-component system of HPEI-IBAm/[PABA]. Reversible trans-to-cis photoisomerization of azobenzene units in the complexes occurred, following irradiation with UV or visible light. Trans-to-cis isomerization of azobenzene units decreased the Tcp . However, this result differed to that of the two-component system of HPEI-IBAm/PABA.

Influence of hydrophilic dyes on the phase transition of a thermoresponsive hyperbranched polymer

The influences of hydrophilic dyes on the phase transition behaviors of HPEI-IBAm in the neutral and charged state were different.

Thermo-, pH-, and Light-Responsive Supramolecular Complexes Based on a Thermoresponsive Hyperbranched Polymer

Hyperbranched polyethylenimine terminated with isobutyramide groups (HPEI-IBAm) was mixed with 4-(phenylazo)benzoic acid (PABA) to form supramolecular complexes through the neutralization reaction between the amino groups of HPEI-IBAm and the carboxylic acid group of PABA, which was verified by ¹H and 2D NOESY ¹H NMR spectroscopy. The obtained supramolecular complexes with a molar ratio of PABA to HPEI-IBAm of ≤8 were soluble in water and exhibited thermoresponsive properties. Their cloud point temperature (T_cp) was sensitive to PABA content, and PABA molecules were exchanged between HPEI-IBAm hosts. The topology of the polymer affected the change in T_cp of the complexes. At pH ∼7, increasing the PABA content decreased T_cp, whereas it caused T_cp to increase at pH ∼9. Reversible trans-to-cis photoisomerization of azobenzene units in the complexes occurred following irradiation with UV or visible light. At pH ∼7, trans-to-cis isomerization of azobenzene units increased T_cp, whereas the opposite occurred at pH ∼9.

Hyperbranched polymers with thermoresponsive property highly sensitive to ions

The salt effects on the water solubility of thermoresponsive hyperbranched polyethylenimine and polyamidoamine possessing large amounts of isobutyramide terminal groups (HPEI-IBAm and HPAMAM-IBAm) were studied systematically. Eight anions with sodium as the counterion and ten cations with chloride as the counterion were used to measure the anion and cation effects on the cloud point temperature (T(cp)) of these dendritic polymers in water. It was found that the T(cp) of these dendritic polymers was much more sensitive to the addition of salts than that of the traditional thermoresponsive linear polymers. At low anion concentration, the electrostatic interaction between anions and the positively charged groups of these polymers was dominant, resulting in the unusual anion effect on the T(cp) of these polymers in water, including (1) T(cp) of these dendritic polymers decreasing nonlinearly with the increase of kosmotropic anion concentration; (2) the chaotropic anions showing abnormal salting-out property at low salt concentration and the stronger chaotropes having much pronounced salting-out ability; (3) anti-Hofmeister ordering at low salt concentration. At moderate to high salt concentration, the specific ranking of these anions in reducing the T(cp) of HPEI-IBAm and HPAMAM-IBAm polymers was PO(4)(3-) > CO(3)(2-) > SO(4)(2-) > S(2)O(3)(2-) > F(-) > Cl(-) > Br(-) > I(-), in accordance with the well-known Hofmeister series. At moderate to high salt concentration, the specific ranking order of inorganic cations in reducing the T(cp) of HPEI-IBAm polymer was Sr(2+) ≈ Ba(2+) > Na(+) ≈ K(+) ≈ Rb(+) > Cs(+) > NH(4)(+) ≈ Ca(2+) > Li(+) ≈ Mg(2+). This sequence was only partially similar to the typical Hofmeister cation series, whereas at low salt concentration the cation effect on T(cp) of the dendritic polymer was insignificant and no obvious specific ranking order could be found.