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Article

Thermoresponsive Star Dendronized Polymers as Smart Nanoboxes

by
Ze Qiao
,
Yi Yao
*,
Afang Zhang
and
Wen Li
*
International Joint Laboratory of Biomimetic and Smart Polymers, School of Materials Science and Engineering, Shanghai University, Nanchen Street 333, Shanghai 200444, China
*
Authors to whom correspondence should be addressed.
Molecules 2026, 31(5), 834; https://doi.org/10.3390/molecules31050834
Submission received: 25 January 2026 / Revised: 26 February 2026 / Accepted: 27 February 2026 / Published: 2 March 2026
(This article belongs to the Special Issue Topological Polymers for Advanced Materials)
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Abstract

Star polymers with dense shell structures exhibit unique advantages in molecule encapsulation. The incorporation of dendronized polymers as arms into star polymers enables the formation of spherical core–shell structures with high-density chain stacking, which is of great significance for enhancing their encapsulation capabilities. Here, we report on the synthesis of a new type of star dendronized polymer consisting of oligoethylene glycol (OEG)-based dendronized polymers as the arms and gold nanoparticles (AuNPs) as the core. Due to the thickness of individual dendronized polymer arms, the morphology of star dendronized polymers was directly visualized by an atomic force microscope (AFM). These star polymers inherit characteristic thermoresponsiveness from the OEG-based dendronized linear polymers, and their thermoresponsive behavior depends mainly on the grafting density of polymer chains on the AuNP cores and the molecular weights of the polymer arms. More importantly, these star dendronized polymers exhibit a tunable encapsulation capacity to guest molecules, which can be modulated through thermally induced aggregation. By virtue of these peculiarities, these thermoresponsive star dendronized polymers with tailorable release properties hold promise as smart nanoboxes for bio-applications, including drug delivery and biosensing.

Graphical Abstract

1. Introduction

Star polymers are a type of topological macromolecule consisting of multiple linear polymer arms fused at a central core [1,2,3]. Compared to conventional linear polymers, star polymers show significantly different physicochemical properties, including rheological behavior, molecular dynamics, and thermal characteristics [1,4,5]. Moreover, the diversity of polymer arms not only imparts functionalities such as stimuli responsiveness and architectural versatility but also creates segregated compartments with distinct chemical environments for guest molecule encapsulation [5,6,7]. These features allow star polymers to be used as drug carriers or nanoreactors in various applications [1,2,8,9].
Star polymers are generally prepared through one of the following three methods [10]: (i) First is the core-first approach. A multifunctional core is pre-synthesized and used to initiate the polymerization of monomers to achieve well-defined star polymers with linear homopolymer or copolymer arms [11,12]. This method is attractive because of its high yield and simple purification procedure; however, the resulting polymers typically have low arm numbers and a considerably smaller core domain [2]. (ii) Second is the arm-first approach. Star polymers are prepared from crosslinking linear polymers through coupling or polymerization reactions [13,14,15]. The arm polymers can be synthesized and characterized prior to star formation, which is beneficial to achieve high-level control over the arm structure, but the resulting star polymers often exhibit broader arm number distributions [13,16]. (iii) Third is the grafting-onto approach. Coupling of the cores and arm polymers is employed to prepare star polymers [17,18]. The core and arms can be synthesized and characterized independently before formation of the star polymers, which is conducive to obtaining more perfect structures [2,19]. Multitudinous star polymers with different cores and arms have been prepared through the above three methods [10,20].
It has been previously demonstrated that polymers prepared by reversible addition–fragmentation chain transfer (RAFT) polymerization that contain either thiol or trithiocarbonate terminals can chemisorb onto gold substrates via sulfur atoms with the formation of an Au-S bond [21,22]. This method has been efficiently applied to construct polymer–gold nanoparticles and multi-armed star polymers with a gold nanoparticle (AuNP) as the core [6,23,24]. In particular, linear thermoresponsive polymers such as poly(N-isopropylacrylamide) and poly(ethylene glycol) were grafted onto AuNP to afford the complexes thermoresponsive behaviors [6,25,26,27]. However, the encapsulating ability of star polymers with linear polymer arms remains insufficient for many applications [10,28,29]. In addition, visualizing the morphology of the star polymers is still a challenge due to the limited thickness of linear polymers. Alternatively, dendronized polymers, featuring densely packed dendritic pendants along polymer backbones, exhibit a crowding effect in nanometer dimensions, which has been proven to offer distinct advantages for encapsulating guest molecules [30,31,32,33,34]. Moreover, their enhanced thickness and rigidity enable individual polymer chains to be visualized by an atomic force microscope (AFM). However, thermoresponsive star polymers comprising dendronized polymer arms have rarely been reported due to synthetic challenges.
Recently, we have been dedicated to developing a homologous series of oligoethylene glycol (OEG)-based dendronized polymers, and we found that these dendronized polymers not only exhibited unprecedented thermoresponsiveness but also showed advantages in forming confined microenvironments at molecular levels for the efficient encapsulation of dyes [35,36], metal ions/nanoparticles [33], and proteins [34]. They also show low toxicity to cells and have been proven as promising materials for drug delivery and tissue engineering [37,38]. In addition, structures of these dendronized polymers can be rationally designed, which provides a wide choice for constructing star dendronized polymers [30,36]. Herein, the trithiocarbonate-terminated OEG-based dendronized polymers were synthesized through RAFT polymerization and were used as arm polymers. AuNPs with a size around 20 nm were selected as the core [6]. Star dendronized polymers were prepared by using the “grafting onto” strategy from the dendronized polymer and the AuNPs, as shown in Figure 1. Influential factors such as molecular weight of the arm polymer, feed ratios of the arm polymer to AuNPs, polymer concentration, and washing cycles on the morphology and thermoresponsive behavior of these star polymers were investigated. Furthermore, their thermally tunable encapsulation capacity for guest molecules (fluorescent probes) was explored by fluorescence spectroscopy.

2. Results and Discussion

2.1. Synthesis and Characterization of Polymer Ligands

An OEG-based first-generation dendronized polymer PG1S carrying three-fold dendritic OEG pendants and trithiocarbonate-terminal groups was synthesized via RAFT polymerization (Scheme S1). This polymer was used as the macromolecular ligands (the arms) to fabricate AuNP-cored star polymers in aqueous solutions. The ethoxyl-terminated dendritic OEG-based macromonomer MG1 was selected to afford the corresponding polymers with a cloud point temperature (Tcp) around the physiological temperature [35]. The trithiocarbonate end groups at PG1S from RAFT polymerization were used as binding sites for the polymers to AuNPs. To obtain polymer ligands (arms) with different lengths for the star polymers, two dendronized polymers (PG1S120 and PG1S65) with distinct molecular weights were designed and synthesized by varying the molar feed ratio of the macromonomer to the chain transfer agent ([MG1]/[DDMAT] = 300:1 or 120:1). For comparison, the OEG-based dendronized homopolymer PG1 (Scheme S1A) was synthesized by free radical polymerization of MG1. The chemical structures of PG1S120 and PG1S65 were characterized by proton nuclear magnetic resonance (1H NMR) spectroscopy (Figures S1 and S2). The observed proton signals corresponding to the dendritic OEGs (a, b, c, d, e) and the polymer backbone (f and g) confirmed successful synthesis of the polymers. The average molecular weights (Mn) of the polymers were determined by size exclusion chromatography (SEC), and the results are summarized in Table 1. The theoretical Mn of the two polymers was also calculated based on the assumption that every RAFT agent participated in chain growth. The obtained PG1S120 and PG1S65, which have different molecular weights, are suited for the subsequent preparation of star polymers with varying arm lengths.
The thermoresponsive behavior of PG1, PG1S120, and PG1S65 was investigated with ultraviolet–visible (UV-vis) spectroscopy, and their turbidity curves are shown in Figure S3. PG1S120 and PG1S65 showed similar turbidity curves as that of PG1 with sharp phase transitions and small hysteresis (<1.5 °C). The Tcps of PG1S120 and PG1S65 were found to be 33.0 and 33.8 °C, respectively, which are close to that (33.4 °C) of PG1, indicating that the trithiocarbonate end group exhibits negligible influence on the thermoresponsive behavior of the dendronized polymers.

2.2. Preparation of the Star Polymer Au-PG1S

AuNPs were synthesized according to a previously reported citrate-ligand method [39]. A transmission electron microscope (TEM) confirmed their uniform size of 20.9 ± 1.0 (Figure S4), making them suitable as cores for the synthesis of star polymers, as they possess a high surface-area-to-volume ratio (S/V). In addition, AuNPs of approximately 20 nm are commonly employed for forming polymer–nanoparticle composites due to their narrow size distribution and ease of purification by centrifugation [6]. The star polymer Au-PG1S was then synthesized by grafting the trithiocarbonate-terminated OEG-based dendronized polymers onto a AuNP core through the chemisorption of trithiocarbonate groups onto the gold surfaces via sulfur atoms. The star polymer Au-PG1S65 was prepared with a fixed Au-PG1S65-to-AuNPs mass feed ratio of 1:1. To investigate the effect of the feed ratio on the resulting architecture, Au-PG1S120 star polymers were prepared at varied PG1S120-to-AuNPs mass feed ratios (1:1, 2:1, 10:1). Unless otherwise specified, Au-PG1S120 prepared with a mass feed ratio of 2:1 was used for all of the following experiments.
The formation of the star polymer Au-PG1S was followed by UV-vis measurements. The color of Au-PG1S solutions showed a slight change after the reaction, and the maximum absorbances (λmax) from AuNPs, AuNP/PG1, Au-PG1S120, and Au-PG1S65 were found to be 518, 524, 522, and 522 nm, respectively (Figure 2A). The λmax of AuNP/PG1, Au-PG1S120, and Au-PG1S65 showed a red-shift when compared to the parent AuNPs, indicating that the surface plasmon resonance (SPRs) bands of the AuNPs were affected by the interaction between the OEG segments of the polymers. Therefore, changes in the absorbance at 522 nm were followed during the reaction between the polymers and AuNPs, and it was found that the absorbance from the Au-PG1S120 solution increased rapidly to reach an equilibrium within 20 min (Figure 2B). Differently, the absorbance of the Au/PG1 (without trithiocarbonate end groups) solution increased gradually and reached an equilibrium state after about 200 min. We suppose that the chemisorption between the trithiocarbonate terminals from the polymer and AuNP surface was greatly reduced after 20 min, but physical adsorption of polymers onto the gold sphere continued. To verify this, the interaction of a gold surface (conveniently modeled by a 58-atom cluster) with benzene or 1,2-dimethoxyethane (OEG segment) was investigated using density function theory (DFT). It was found that the adsorption enthalpies of OEG segments and benzene from dendrons on gold clusters were determined to be −15.4 kcal·mol−1 and −19.1 kcal·mol−1, respectively (Figure S5), indicating the presence of physical adsorption between the gold surface and the polymer arms.
Subsequently, the hydrodynamic radii (Rhs) of Au-PG1S120 and Au-PG1S65 in aqueous solutions were measured by dynamic light scattering (DLS) and found to be 42 and 36 nm, respectively (Figure S6A). Zeta potentials (ζ) of the samples were then measured (Figure S6B) and were found to be −35.8, −19.7, and −12.7 mV for AuNPs, Au-PG1S120 and Au-PG1S65, respectively. The increase in Rh and ζ after the reaction between PG1S and AuNPs proves the successful preparation of the star polymer. In addition, thermal gravimetric analyzer (TGA) measurement showed that Au-PG1S120 contained approximately 35 wt% of PG1S120 (Figure S6C).
Morphology of the star dendronized polymers was investigated by AFM. The wormlike chains were observed from PG1S120 (Figure S7A), and their average length was 44 nm. Differently, when grafted onto AuNPs, the same polymers adopted an “entangled” conformation, “lying down” on the particle surface (Figure 2C,D). Both the AuNP core and the dendronized polymer arms were clearly visualized in the AFM images, confirming the star-shaped architecture of the polymer–AuNP complexes. Moreover, different morphologies were observed in star polymers prepared with different PG1S120-to-AuNPs mass feed ratios. At a 1:1 feed ratio, the polymers were grafted unsaturated on the surface of the gold sphere (Figure 2C). With the ratio increased to 2:1, the surface-grafted chains became stretched and closely packed (Figure 2D). When the feed ratio was further increased to 10:1, the peripheral polymer chains even became densely packed (Figure S7B). The washing treatment through centrifugation also had an effect on the morphology of the star polymers. When increasing the washing treatment to three cycles, the density of polymer chains on the particle surface decreased significantly (Figure S7C). This means that centrifugation washing treatment could release a certain amount of physically adsorbed polymer chains. In addition, the morphology of star polymers was also influenced by the molecular weight of arm polymers. Different from Au-PG1S120, Au-PG1S65 with much shorter polymer arms was observed as a three-dimensional spherical shape wrapped by a polymer layer (Figure S7D). The above results suggest that morphologies of the star polymers are determined by both grafting density and molecular weights of the polymer arms.

2.3. Thermoresponsive Behaviors of Au-PG1S

The thermoresponsive behavior of Au-PG1S was investigated by DLS at varied temperatures, and the results are plotted in Figure 3A,B. The molecular weight of the polymer arms was found to have an obvious effect on their thermally induced aggregation. For example, after the centrifugal washing treatment was performed once to remove the physically adsorbed polymers, Rh of Au-PG1S65 increased from 36 to 74 nm, whereas Au-PG1S120 with a higher molecular weight increased more obviously from 42 to 302 nm when the temperature was increased above the Tcp (Figure 3A), indicating collapse and aggregation of the star polymers. As the temperature increased, the OEG-based polymer chains collapsed because of dehydration and increased hydrophobicity. This collapse leads to the formation of aggregates through intermolecular interactions. Following a single washing cycle, the remaining higher amount of physically adsorbed polymers facilitates these intermolecular interactions among the collapsed star polymers, thereby forming large aggregates. Additionally, the grafting density of polymer arms on the AuNPs also showed a major influence. After two cycles of centrifugal washing to remove the redundant physically adsorbed polymers, the Rh of Au-PG1S65 and Au-PG1S120 decreased upon heating from 32 to 25 nm and 39 to 22 nm, respectively. This indicates that the polymer arms collapsed within individual star polymers, without inter-star aggregation. The concentration of the star polymers also showed obvious influence on their thermally induced aggregation. For the case of Au-PG1S120 after two cycles of washing treatment, its Rh at a concentration of 0.5 and 5 mg·mL−1 decreased from 43 to 25 nm and 47 to 38 nm, respectively (Figure 3B), when the temperature increased from 20 to 50 °C. Differently, when its concentration increased to 7.5 mg·mL−1, the Rh of Au-PG1S120 increased sharply from 44 to 986 nm, indicating the collapse and aggregation of the star polymers on an intermolecular level at a high concentration. A high concentration of polymer promoted intermolecular interactions among the collapsed star polymers, resulting in their aggregation to form large aggregates. All of the above results suggest that thermally induced aggregations of the star polymers were determined by the corresponding polymer arms, including their molecular weight, concentration, and grafting density on the cores.
The SPR transition of Au-PG1S during its thermally induced aggregations was monitored by UV-vis spectroscopy with Au-PG1S120 as the example. When the temperature increased from 25 to 50 °C, the absorbance at λmax of AuNPs within Au-PG1S120 increased from 0.57 to 0.59, and the corresponding λmax red-shifted from 522.5 to 524.5 nm (Figure 3C,D). This is usually attributed to the dehydration shrinkage of the dense OEG dendritic pendants, which restricts the intramolecular conformations of star polymers [40]. The changed hydrophobic properties and dielectric constant of the gold sphere surface afforded the star polymers better thermodynamic stability and caused an absorbance increase with a red-shift of the λmax [41,42].

2.4. Star Dendronized Polymer as Nanocarrier for Fluorescent Probe Release

The encapsulation capacity of these star polymers was checked by using a typical fluorescent dye, 2-p-toluidinylnaphthalene-6-sulfonate (TNS), as a model guest. TNS is a widely recognized probe characterized by its solvatochromic effect. It is found to be almost fluorescence-silent in aqueous solutions, whereas it shows a high quantum yield in organic solvents [43]. The fluorescence spectra of TNS within Au-PG1S120 and Au-PG1S65 were recorded at different temperatures for exploration of their encapsulation and release capability during the thermally induced aggregation of star polymers. At 20 °C, TNS showed negligible fluorescence in water [44], while the Au-PG1S120/TNS solution showed strong fluorescence, as shown in Figure 4A, indicating the effective encapsulation of TNS within the star polymers. Similar to our previously reported OEG-based linear dendronized polymers, the star polymer with a high density of dendritic OEG groups exhibits multiple weak hydrophobic interactions between OEG chains and the hydrophobic dyes [44]. When the temperature was increased from 20 to 50 °C, the maximum fluorescence intensity (Imax) of TNS within Au-PG1S120 decreased from 0.84 to 0.19 × 105 CPS, and maximum emission (λmax) blue-shifted from 446 to 437 nm (Figure 4A,B). Similarly, for the cases of Au-PG1S65, Imax decreased from 16 to 0.20 × 105 CPS, and λmax blue-shifted from 446 to 436 nm (Figure 4C,D). This behavior is attributed to the de-complexation and release of TNS from the hydrophobic microenvironment of the star polymers. As the polymer arms collapse and aggregate, TNS is expelled into the aqueous solution, resulting in significant fluorescence quenching and a blue-shift of λmax. With the increase in temperature, the interaction among OEG-based polymer chains was enhanced due to their increased hydrophobicity. This results in diminished interactions between the polymers and the dyes, consequently leading to the release of TNS from the star polymers. A similar phenomenon has also been reported for OEG-based linear dendronized polymers [35]. Moreover, the fluorescence intensity of TNS within Au-PG1S65 was more than 19 times higher than that of Au-PG1S120 below their Tcps, indicating that shorter polymer arms impart the better encapsulation capability of star dendronized polymers. This should be due to the higher polymer density on Au-PG1S65, which was calculated and is summarized in Table S1. The above results indicate that Au-PG1S possesses a tunable encapsulation capacity to TNS during its thermally induced aggregation, enabling it to act as a “smart nanobox” for encapsulation and the controlled release of guests.

3. Materials and Methods

3.1. Materials

An OEG-based first-generation dendronized homopolymer (PG1) was synthesized according to our previous report through free radical polymerization of macromonomer MG1 [35]. Chloroauric acid (HAuCl4·3H2O, 99.9%) and RAFT agent S-dodecyl-S′-(a, a′-dimethyl-a′′-acetic acid) trithiocarbonate (DDMAT, 98%) were purchased from Sigma-Aldrich Co., Ltd. (Shanghai, China). Trisodium citrate dehydrate (≥99.0%), tris(hydroxymethyl)-amino-methane (TB, GR), 2, 2′-Azobis(2-methylpropionitrile) (AIBN), and sodium 6-(p-tolylamino) naphthalene-2-sulfonate (TNS) were purchased from Tokyo Chemical Industry, Co., Ltd. (Shanghai, China). Deionized water was used throughout the experimental process.

3.2. Instrumentation and Measurements

1NMR spectra were recorded on a Bruker AV 500 (Billerica, MA, USA, 1H:500 MHz) spectrometer at 25 °C. Samples were prepared in CDCl3 with a concentration of 10 mg·mL−1.
SEC measurements were performed on a Waters GPC e2695 instrument (Milford, MA, USA) at 45 °C with 3 columns set (Styragel HR3 + HR4 + HR5) equipped with a refractive index detector (Waters 2414) and DMF (containing 1 g·L−1 of LiBr) as the eluent. The calibration was performed with poly(methylmethacrylate) standards in the range of Mp = 2540–936,000 (Polymer Standards Service-USA, Inc., Santa Clara, CA, USA).
Zeta potential measurements were carried out on a Zetasizer Nano ZS90 (Malvern Panalytical Instruments, Worcestershire, UK) at 25 °C using a laser at 633 nm.
UV-vis absorption spectra (between 400 and 800 nm) and turbidity measurements were performed on a PE UV-Vis spectrophotometer (PerkinElmer, Waltham, MA, USA, Lambda 35) with a thermo-controlled bath. Polymer solutions were placed in the quartz cell (path length 1 cm) and heating or cooling took place at a rate of 0.2 °C·min−1. Tcp was determined when the transmittance reached 50% of its initial value at λ = 700 nm. The concentration of polymers was 2.5 mg·mL−1.
DLS measurements were performed using a multi-angle light scattering detector (Wyatt Technology Corporation, Goleta, CA, USA, Dawn EOS 243-E). Sample solutions were placed in a quartz cell in temperature range of 20–50 °C and with a heating or cooling rate of 1 °C·min−1.
Fluorescence measurements were carried out on a Horiba Jobin Yvon Fluorolog®-3 spectrofluorometer equipped with FluorEssenceTM 3.5 and a Peltier temperature controller (Edison, NJ, USA). Spectra were recorded for all samples containing TNS, with excitation at 340 nm and emission scanned between 350 and 650 nm. The excitation and emission slits were both set to a band-pass of 3 nm. For comparison, Au-PG1S120 and Au-PG1S65 were prepared at identical molar concentrations, with the molar ratio of the star polymer to the TNS fluorescent probe maintained at 1:100. A representative procedure for a 1 mL sample preparation was as follows. After two cycles of centrifugation, the Au-PG1S was resuspended in a mixture of pre-cooled aqueous TNS solution (50 μL, 2.00 × 10−4 M, stored at ca. 4 °C) and 950 μL of pre-cooled deionized water (ca. 4 °C), with final concentrations of CAu-PG1S = 1.0 × 10−7 M and CTNS = 1.0 × 10−5 M. All samples were equilibrated at the predetermined temperature for 5 min before data collection.
AFM measurements were carried out in air on a Bruker Nanoscope MultiMode VIII (Billerica, MA, USA) with an “E” scanner (scanning range 10 mm × 10 mm) and operated in Peak Force mode for 3D morphology of the nanocomposites. All samples were prepared on a mica slice from their solutions (0.002 mg·mL−1) through spinning coating at a rate of 2000 r·min−1 and dried in N2 atmosphere for 3 h. The statistical analysis was carried out using the open-source software FiberApp (version updated October 12, 2016).
TEM images were taken on a JEM-200CX electron microscope (JEOL, Akishima-shi, Japan) operating at 200 kV. The average size and standard deviation of AuNPs based on particle size analysis were generated by digitizing statistics of TEM images with Image Tool.
TGA measurements were performed on a TGA 550 (TA instruments, New Castle, DE, USA) from 50 to 600 °C with a heating rate of 10 °C·min−1 in N2 flow.

3.3. Simulation Method

The calculations were carried out with the ORCA 5.0.4 [45]. Geometrical optimizations were performed at the level of PBE0-D3(BJ, ABC)/def2-SV(P) [46]. The single point energies were further estimated using a larger basis set of def2-QZVP [47]. Independent Gradient Model based on the Hirshfeld partition (IGMH) was performed with the Multiwfn 3.8 program [48].

3.4. Synthesis Procedure

General Procedure for Synthesis of Dendronized Polymer PG1S. The trithiocarbonate-terminated dendronized polymer PG1S was prepared through RAFT polymerization. Firstly, the monomer MG1, DDMAT, and AIBN were dissolved in dry DMSO in a Schlenk tube. Then, the solution was deoxygenated and stirred at 65 °C for the polymerization. After 2.5–9.0 h, the mixture was cooled to room temperature. Subsequently, the polymers were purified by silica gel column chromatography with DCM as the eluent to yield the polymers as yellowish oils.
Synthesis of Gold Nanoparticles. AuNPs were prepared according to the previous report [32]. A trisodium citrate solution (10 mL, 33 mM) was added into boiling deionized water (140 mL) with vigorous stirring and continuous heating for 15 min. Then, fresh HAuCl4 (1 mL, 25 mM) and a TB solution (5 mL, 0.1 M) were added (time delay 60 s) into the boiling deionized water, which was maintained at 137 °C for 50 min. Subsequently, extra HAuCl4 (1 mL, 25 mM) was injected twice (interval of 30 min), and the mixture was heated for 50 min at 100 °C.
General Procedure for Synthesis of Au-PG1S. The star polymers Au-PG1S were prepared according to previously reported method [6]. The synthesized AuNPs were concentrated by centrifugation at 8500× g for 15 min first; then, the precipitate was dissolved in deionized water in a 5 min ultrasonic bath, and for 30 min it was stirred in an ice bath to generate a AuNP solution (10 mL, 0.05 mg·mL−1). In a typical procedure for synthesis of Au-PG1S, a PG1S aqueous solution (1 mL, 1.0 mg·mL−1) was dripped into the AuNP solution and stirred overnight under the conditions of an ice bath. The products were centrifuged at 8500× g for 20 min at 5 °C. The supernatant was carefully discarded, and the precipitate was subsequently resuspended in 1 mL of pre-cooled deionized water (ca. 4 °C). This washing procedure was repeated twice to yield purified Au-PG1S star polymers.

4. Conclusions

Star dendronized polymers with trithiocarbonate-terminated OEG-based dendronized polymers as the arms and AuNPs as the cores were successfully prepared. These star dendronized polymers exhibit characteristic thermoresponsive behavior and encapsulation capacity inherited from the OEG-based dendronized polymers. The grafting ratios of arm polymers on AuNP cores and the molecular weight of the polymer arms had significant effects on their thermoresponsive behavior and morphologies. Moreover, these dendronized star polymers exhibited a tunable encapsulation capacity to the dyes through their thermally induced aggregations. We therefore believe these stimuli-responsive star dendronized polymers can be used as promising nanoboxes to encapsulate and control the release of guest molecules for various applications.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/molecules31050834/s1, the molecular structures of all polymers and additional characterization data, including synthetic conditions, 1H NMR spectra, TEM images, DLS results, TGA results, results of Zeta potential, and AFM images (PDF).

Author Contributions

Conceptualization, W.L. and A.Z.; experiments, Z.Q.; original draft preparation, Y.Y.; review and editing, all authors; supervision, W.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China (22371179 and 21971161).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The original data presented in this research are included in the article. Further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest, and the funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

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Molecules 31 00834 g001
Figure 1. Schematic illustration for synthesis of star dendronized polymers and their applications in controlled release of guest molecules through thermally induced phase transitions.
Figure 1. Schematic illustration for synthesis of star dendronized polymers and their applications in controlled release of guest molecules through thermally induced phase transitions.
Molecules 31 00834 g001
Molecules 31 00834 g002
Figure 2. (A) UV-Vis spectra of AuNPs before and after addition of the polymers (inset: synthetic procedure of star dendronized polymers). (B) Absorbance of AuNP solutions with PG1 and PG1S120 at 522 nm over reaction time (inset: representative snapshot of dendrons interacting with AuNPs). AFM images of Au-PG1S120 prepared with PG1S120-to-AuNP mass feed ratios of (C) 1:1 and (D) 2:1, after two cycles of centrifugation and resuspension.
Figure 2. (A) UV-Vis spectra of AuNPs before and after addition of the polymers (inset: synthetic procedure of star dendronized polymers). (B) Absorbance of AuNP solutions with PG1 and PG1S120 at 522 nm over reaction time (inset: representative snapshot of dendrons interacting with AuNPs). AFM images of Au-PG1S120 prepared with PG1S120-to-AuNP mass feed ratios of (C) 1:1 and (D) 2:1, after two cycles of centrifugation and resuspension.
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Molecules 31 00834 g003aMolecules 31 00834 g003b
Figure 3. Rh of (A) Au-PG1S120 and Au-PG1S65 with 0.05 mg·mL−1 after different cycles of centrifugal washing treatment and (B) Au-PG1S120 with different concentrations after two cycles of centrifugation and resuspension at different temperatures. Absorbance of Au-PG1S120 solution at different temperatures (C). The maximal absorbance Amax and corresponding λmax of Au-PG1S120 at different temperatures (D). C = 0.05 mg·mL−1.
Figure 3. Rh of (A) Au-PG1S120 and Au-PG1S65 with 0.05 mg·mL−1 after different cycles of centrifugal washing treatment and (B) Au-PG1S120 with different concentrations after two cycles of centrifugation and resuspension at different temperatures. Absorbance of Au-PG1S120 solution at different temperatures (C). The maximal absorbance Amax and corresponding λmax of Au-PG1S120 at different temperatures (D). C = 0.05 mg·mL−1.
Molecules 31 00834 g003aMolecules 31 00834 g003b
Molecules 31 00834 g004
Figure 4. Fluorescence spectra of TNS aqueous solution in the presence of Au-PG1S120 and Au-PG1S65 (A,C), and Imax and λmax of Au-PG1S120 and Au-PG1S65 at different temperatures (B,D). Both Au-PG1S120 and Au-PG1S65 were purified via two cycles of centrifugation and resuspension. CTNS = 1.00 × 10−5 M, CAu-PG1S = 1.00 × 10−7 M.
Figure 4. Fluorescence spectra of TNS aqueous solution in the presence of Au-PG1S120 and Au-PG1S65 (A,C), and Imax and λmax of Au-PG1S120 and Au-PG1S65 at different temperatures (B,D). Both Au-PG1S120 and Au-PG1S65 were purified via two cycles of centrifugation and resuspension. CTNS = 1.00 × 10−5 M, CAu-PG1S = 1.00 × 10−7 M.
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Table 1. Conditions for and results from the polymerization of MG1.
Table 1. Conditions for and results from the polymerization of MG1.
SamplesPolymerization ConditionsYield
(%)		Molecular Weight (Mn kDa) ÐTcp d
(°C)
Feed Ratio a
[MG1]/[DDMAT]/[AIBN] 		Time
(h)		Theoretical bSEC c
PG1S120300:1:0.259571201301.3733.0
PG1S65120:1:0.252.57765501.4833.8
PG158:0:1560\3002.1033.4
a Polymerizations were performed with AIBN as the initiator at 65 °C in DMSO. b Mn (Theoretical) = [MG1]/[DDMAT] × polymerization yield × molecular weight of the repeating unit, based on the assumption that every RAFT agent participated in chain growth. c Determined by SEC with DMF as the eluent containing 0.1 wt.% LiBr. Đ represents dispersity of the polymers. d Tcp was determined as the temperature at which the transmittance had reached 50% of its initial value at λ = 700 nm.
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Qiao, Z.; Yao, Y.; Zhang, A.; Li, W. Thermoresponsive Star Dendronized Polymers as Smart Nanoboxes. Molecules 2026, 31, 834. https://doi.org/10.3390/molecules31050834

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Qiao Z, Yao Y, Zhang A, Li W. Thermoresponsive Star Dendronized Polymers as Smart Nanoboxes. Molecules. 2026; 31(5):834. https://doi.org/10.3390/molecules31050834

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Qiao, Ze, Yi Yao, Afang Zhang, and Wen Li. 2026. "Thermoresponsive Star Dendronized Polymers as Smart Nanoboxes" Molecules 31, no. 5: 834. https://doi.org/10.3390/molecules31050834

APA Style

Qiao, Z., Yao, Y., Zhang, A., & Li, W. (2026). Thermoresponsive Star Dendronized Polymers as Smart Nanoboxes. Molecules, 31(5), 834. https://doi.org/10.3390/molecules31050834

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