Preparation of Polymer-Based Nano-Assembled Particles with Fe3O4 in the Core

Organic–inorganic nanocomposite particles, possessing defined morphologies, represent the next frontier in advanced materials due to their superior collective performance. In this pursuit of efficient preparation of composite nanoparticles, a series of diblock polymers polystyrene-block-poly(tert-butyl acrylate) (PS-b-PtBA) were initially synthesized using the Living Anionic Polymerization-Induced Self-Assembly (LAP PISA) technique. Subsequently, the tert-butyl group on the tert-butyl acrylate (tBA) monomer unit in the diblock copolymer, yielded from the LAP PISA process, was subjected to hydrolysis using trifluoroacetic acid (CF3COOH), transforming it into carboxyl groups. This resulted in the formation of polystyrene-block-poly(acrylic acid) (PS-b-PAA) nano-self-assembled particles of various morphologies. The pre-hydrolysis diblock copolymer PS-b-PtBA produced nano-self-assembled particles of irregular shapes, whereas post-hydrolysis regular spherical and worm-like nano-self-assembled particles were generated. Utilizing PS-b-PAA nano-self-assembled particles that containing carboxyl groups as polymer templates, Fe3O4 was integrated into the core region of the nano-self-assembled particles. This was achieved based on the complexation between the carboxyl groups on the PAA segments and the metal precursors, facilitating the successful synthesis of organic–inorganic composite nanoparticles with Fe3O4 as the core and PS as the shell. These magnetic nanoparticles hold potential applications as functional fillers in the plastic and rubber sectors.

For example, Yoshinaga et al. [19] synthesized poly(tert-butyl acrylate)-b-poly(methyl methacrylate) (PtBA-b-PMMA) diblock copolymer by living anionic polymerization. This was then hydrolyzed to obtain poly (acrylic acid)-b-poly(methyl methacrylate) (PAA-b-PMMA) and doped with titanium dioxide (TiO 2 ) nanoparticles using the sol-gel method. The resulting PAA@TiO 2 -b-PMMA organic-inorganic composite film material exhibited high transparency in the visible region, and the content of TiO 2 in the composite film material was adjusted by changing the ratio of PAA segments, which in turn changed the refractive index of the film material. In a separate study, Ryu et al. [20] synthesized polystyrene-b-poly(2, 2, 2-propenoic acid trifluoroethyl ester) (PS-b-PTFEAs) from

Preparation of the Macromolecular Initiator PS
Firstly, 84.70 mL cyclohexane (66.07 g), 1.1 mL THF (1.00 g) and 7.6 mL styrene (6.93 g) were added to a dry and clean ampoule in turn, stirred and protected by nitrogen; then, n-Bu − Li + (1.60 mmol/mL) was slowly added dropwise to the mixed system to remove impurities until the color of the mixture changed to golden yellow, indicating that the impurities were removed; finally, 1 mL of n-Bu − Li + (1.60 mmol/mL), which was used to initiate styrene polymerization, was immediately added to the ampoule, and the reaction was stirred at 0 °C for 30 min to obtain a macromolecular initiator PS with active species at the end, and a 5 mL sample was left for characterization.

Conversion of the Active Centre of the Macromolecular Initiator PS
First, 5.0 mL of cyclohexane (3.90 g) and 0.8 mL of DPE (1.11 g) were added sequentially to a 25 mL dry, clean, nitrogen-protected round-bottom flask; then, n-Bu − Li + (1.60 mmol/mL) was slowly added to the flask dropwise with stirring to consume impurities until the color of the mixture changed to orange; finally, the mixture was added to the ampoule of macromolecular initiator PS, the color of the system changed to deep red, and the reaction was stirred for 20 min at 0 °C to prepare the macromolecular initiator PS with DPE-Li as the active center.

Preparation of the Diblock Copolymer PS-b-PtBA
First, 6.2 mL of tBA (5.54 g) was added to 25 mL of a dry, clean round-bottom flask

Preparation of the Macromolecular Initiator PS
Firstly, 84.70 mL cyclohexane (66.07 g), 1.1 mL THF (1.00 g) and 7.6 mL styrene (6.93 g) were added to a dry and clean ampoule in turn, stirred and protected by nitrogen; then, n-Bu − Li + (1.60 mmol/mL) was slowly added dropwise to the mixed system to remove impurities until the color of the mixture changed to golden yellow, indicating that the impurities were removed; finally, 1 mL of n-Bu − Li + (1.60 mmol/mL), which was used to initiate styrene polymerization, was immediately added to the ampoule, and the reaction was stirred at 0 • C for 30 min to obtain a macromolecular initiator PS with active species at the end, and a 5 mL sample was left for characterization.

Conversion of the Active Centre of the Macromolecular Initiator PS
First, 5.0 mL of cyclohexane (3.90 g) and 0.8 mL of DPE (1.11 g) were added sequentially to a 25 mL dry, clean, nitrogen-protected round-bottom flask; then, n-Bu − Li + (1.60 mmol/mL) was slowly added to the flask dropwise with stirring to consume impurities until the color of the mixture changed to orange; finally, the mixture was added to the ampoule of macromolecular initiator PS, the color of the system changed to deep red, and the reaction was stirred for 20 min at 0 • C to prepare the macromolecular initiator PS with DPE-Li as the active center.

Preparation of the Diblock Copolymer PS-b-PtBA
First, 6.2 mL of tBA (5.54 g) was added to 25 mL of a dry, clean round-bottom flask filled with nitrogen, stirred and DPE-Li was slowly added dropwise to consume impurities until the color of the mixture changed to pale yellow; then, tBA monomer was added to the ampoule after the removal of impurities to start the LAP PISA process, and the red color of the reaction system immediately faded. The system gradually became turbid and the viscosity increased as the polymerization proceeded. After stirring the reaction for 1 h at room temperature, the diblock copolymer PS-b-PtBA was obtained; finally, the reaction system was exposed to air to terminate the polymerization.

Preparation of PS-b-PAA Nanoself-Assembled Particles
PS-b-PAA was obtained by hydrolyzing the tBA monomer unit on the diblock copolymer PS-b-PtBA obtained by LAP PISA using CF 3 COOH. Specific experimental steps: the polymer PS-b-PtBA (7.50 g) was added to a 20 mL round bottom flask and stirring was started, 0.6 mL CF 3 COOH (0.90 g) was slowly added dropwise to the flask with a syringe and the hydrolysis reaction was carried out at room temperature for 24 h. During the hydrolysis, the system was observed to become more turbid, and finally the product PS-b-PAA was obtained and dispersed in cyclohexane for characterization.

Preparation of PS-b-PAA@Fe 3 O 4 Nanocomposite Particles
Using the carboxyl group on the PAA chain segment to complex with the metal precursors FeCl 3 ·6H 2 O and FeCl 2 , Fe 3+ and Fe 2+ were introduced into the core of PSb-PAA nano-self-assembled particles, and NH 3 ·H 2 O was used as the reducing agent to generate PS-b-PAA@Fe 3 O 4 organic-inorganic nanocomposite particles in situ ( Figure 1). The specific experimental steps are as follows. First, 0.3012 g of PS 34 -b-PAA 20 diblock copolymer nano-assembled particles were dispersed in 10 mL DMF, 0.3962 g of FeCl 2 and 0.8434 g of FeCl 3 ·6H 2 O (25 equivalents of carboxyl group) were added, and stirred under nitrogen protection for 24 h; subsequently, 9 mL of NH 3 ·H 2 O (in excess) was added and reacted at 50°C or 30 min, and then aged at 80 • C for 1 h, followed by centrifugation at 1000 rpm for 5 min to remove the larger size of the aggregated nanoparticles to obtain PS 34 -b-PAA 20 @Fe 3 O 4 nanocomposite particles.
5, x FOR PEER REVIEW 4 of 15 the viscosity increased as the polymerization proceeded. After stirring the reaction for 1 h at room temperature, the diblock copolymer PS-b-PtBA was obtained; finally, the reaction system was exposed to air to terminate the polymerization.

Preparation of PS-b-PAA Nanoself-Assembled Particles
PS-b-PAA was obtained by hydrolyzing the tBA monomer unit on the diblock copolymer PS-b-PtBA obtained by LAP PISA using CF3COOH. Specific experimental steps: the polymer PS-b-PtBA (7.50 g) was added to a 20 mL round bottom flask and stirring was started, 0.6 mL CF3COOH (0.90 g) was slowly added dropwise to the flask with a syringe and the hydrolysis reaction was carried out at room temperature for 24 h. During the hydrolysis, the system was observed to become more turbid, and finally the product PS-b-PAA was obtained and dispersed in cyclohexane for characterization.

Preparation of PS-b-PAA@Fe3O4 Nanocomposite Particles
Using the carboxyl group on the PAA chain segment to complex with the metal precursors FeCl3·6H2O and FeCl2, Fe 3+ and Fe 2+ were introduced into the core of PS-b-PAA nano-self-assembled particles, and NH3·H2O was used as the reducing agent to generate PS-b-PAA@Fe3O4 organic-inorganic nanocomposite particles in situ ( Figure 1). The specific experimental steps are as follows. First, 0.3012 g of PS34-b-PAA20 diblock copolymer nano-assembled particles were dispersed in 10 mL DMF, 0.3962 g of FeCl2 and 0.8434 g of FeCl3·6H2O (25 equivalents of carboxyl group) were added, and stirred under nitrogen protection for 24 h; subsequently, 9 mL of NH3·H2O (in excess) was added and reacted at 50 ℃ or 30 min, and then aged at 80 °C for 1 h, followed by centrifugation at 1000 rpm for 5 min to remove the larger size of the aggregated nanoparticles to obtain PS34-b-PAA20@Fe3O4 nanocomposite particles.
Gel permeation chromatography (GPC, THF, Agilent-1260, San Diego, CA, USA): The G1310B pump, G1362A differential detector, G1314F UV detector and gel column (500 Å, molecular weight detection range 500 to 4 × 10 6 Da) were connected. The calibration standard was polystyrene (PS), the test temperature was 35 • C, and the mobile phase was chromatographic grade THF at a flow rate of 0.5 mL/min. The relative molecular weights and distributions of polymers soluble in THF were measured.
Dynamic light scattering (DLS, Malvern Zetasizer Nano ZS90, Sydney, Australia): the measurement range was from 0.3 to 5000 nm and the scattered light detection angle was 173 • . The solvents used for the measurements were cyclohexane and THF. The size of the nanoparticles was measured.
Transmission electron microscopy (TEM, JEOL JEM-1230, Tokyo, Japan): accelerating voltage of 80 kV, line resolution of 0.2 nm, and point resolution of 0.36 nm. The diblock copolymer nanoassembled particles were formulated into a mixture with a concentration of 0.1~0.3% w/w. A drop of the mixture was placed on the copper web coated with carbon film and dried in air for 24 h to remove the solvent for TEM characterization. The solvent used was cyclohexane.
Thermogravimetric analyzer (TGA, Pyris 1, East Lyme, CT, USA): temperature range from room temperature to 1000 • C, sample capacity: 60 mL/1.3 g, balance sensitivity: 0.1 mg, temperature rise/fall rate range from 0.1 • C/min to 200 • C/min. The thermal decomposition temperature of the material was characterized in a nitrogen atmosphere at a rate of 10 • C/min from 50 • C to 700 • C.
X-ray Diffractometer (XRD, D/max2200PC, Tokyo, Japan): used for the measurement of the samples. Cu target Kα radiation, tube voltage of 40 kV, tube current of 30 mA, scanning speed of 5 • C/min, and scanning angle of 5 to 80 • .

Characterization of PS-b-PtBA in LAP PISA
In the LAP PISA based on St and tBA, n-Bu − Li + was used as the initiator, cyclohexane as the solvent, and trace amounts of THF as the polarity modifier. In the first stage of the polymerization reaction, the St monomer was first polymerized via LAP to produce the macromolecular initiator PS with reactive species at the end. In the second stage of the polymerization, DPE with large site resistance was added for the conversion of the reactive center to reduce the initiation activity of the macromolecular initiator PS, and then the tBA monomer was added to the system for the LAP PISA process. Due to the poor solubility of PtBA segments in cyclohexane, with the polymerization of tBA monomer, the solubility of the resulting diblock copolymer PS-b-PtBA gradually decreased, and the diblock copolymer PS-b-PtBA started to assemble to form nano self-assembled particles, thus realizing the LAP PISA process. A series of LAP PISA formulations based on PS-b-PtBA were designed by varying the ratio of molecular weight of PtBA and PS segments (M n,tBA /M n,PS ), solids content, and other factors. The assembly morphology of the obtained nano self-assembled particles was investigated, and the polymerization formulations and data were summarized as shown in Table 1.   1 The M n and M w /M n were obtained by GPC measurement. 2 DP of macro-initiator PS (DP PS ) was calculated according to the M n,PS from GPC measurement. 3 DP of PtBA (DP PtBA ) and the conversion of tBA (Conv. tBA ) were calculated according to the DP PS and 1 H NMR spectra. 4 The morphology was observed by TEM image.

NMR and GPC Characterization
The crude products of the polymers obtained from the two polymerization stages of the LAP PISA process were characterized using NMR. As shown in Figure 2

NMR and GPC Characterization
The crude products of the polymers obtained from the two polymerization stages o the LAP PISA process were characterized using NMR. As shown in Figure 2  We performed GPC characterization of the two polymerization stages of the LAP PISA process based on the diblock copolymer PS-b-PtBA. The GPC curves of the macro molecular initiator PS prepared in the first polymerization stage showed a single peak and a narrow molecular weight distribution (Mw/Mn < 1.10), which proved that the macromo lecular initiator PS was successfully synthesized (Figure 3a-c)). The diblock copolyme PS-b-PtBA was prepared in the second polymerization stage, and the molecular weigh and molecular weight distribution of the block polymer could not be characterized by We performed GPC characterization of the two polymerization stages of the LAP PISA process based on the diblock copolymer PS-b-PtBA. The GPC curves of the macromolecular initiator PS prepared in the first polymerization stage showed a single peak and a narrow molecular weight distribution (M w /M n < 1.10), which proved that the macromolecular initiator PS was successfully synthesized (Figure 3a-c). The diblock copolymer PS-b-PtBA was prepared in the second polymerization stage, and the molecular weight and molecular weight distribution of the block polymer could not be characterized by GPC because the resulting PS-b-PtBA was insoluble in THF, N,N-Dimethylformamide (DMF) and other solvents. This can be attributed to the cross-linking side reaction of the tBA monomer during the second stage of LAP PISA.
GPC because the resulting PS-b-PtBA was insoluble in THF, N,N-Dimethylformamide (DMF) and other solvents. This can be attributed to the cross-linking side reaction of the tBA monomer during the second stage of LAP PISA.

DLS and TEM Characterization
In order to demonstrate that the diblock copolymer PS-b-PtBA formed cross-linked nanoparticles during LAP PISA, we dispersed the diblock copolymer PS-b-PtBA nanoself-assembled particles in cyclohexane and THF (a good solvent for PS and PtBA blocks), respectively, for DLS characterization. The DLS results of PS-b-PtBA nano-self-assembled particles dispersed in cyclohexane are shown in Figure 4a. When the solid content was 15% w/w, the molecular weight of the macromolecular initiator PS was kept in the range of 3500~4000 g/mol, and the Mn,tBA/Mn,PS were designed to be 0.4/1, 0.8/1, and 1.2/1 to obtain PS35-b-PtBA11、PS34-b-PtBA20 and PS36-b-PtBA32, respectively. It can be observed in the corresponding DLS curves that the average size of the diblock copolymer nano-self-assembled particles PS-b-PtBA increases with the increase in Mn,tBA/Mn,PS. The DLS results of the diblock copolymer PS-b-PtBA nanoself-assembled particles dispersed in THF are shown in Figure 4b, and the size distribution of the PS-b-PtBA nanoself-assembled particles synthesized by LAP PISA in THF was in the range of 90-1100 nm. Since both PS and PtBA segments have good solubility in THF, the DLS results of PS-b-PtBA nano-self-assembled particles dispersed in THF should theoretically be less than 10 nm, but the PS-b-PtBA nano-self-assembled particles prepared by LAP PISA exhibited larger size in THF, which further proved that the tBA monomer was cross-linked in situ in the second polymerization stage of LAP PISA and formed cross-linked stable nano-assembled particles. The morphology of the diblock copolymer PS-b-PtBA nanoassemblies obtained by LAP PISA was characterized using TEM. As shown in Figure 4c-e, the diblock copolymers PS35-b-PtBA11 and PS34-b-PtBA20 were obtained by the LAP PISA process when the solid content was 15% w/w and the designed Mn,tBA/Mn,PS was 0.4/1 and 0.8/1, and their TEM images were shown in Figure 4c

DLS and TEM Characterization
In order to demonstrate that the diblock copolymer PS-b-PtBA formed cross-linked nanoparticles during LAP PISA, we dispersed the diblock copolymer PS-b-PtBA nanoself-assembled particles in cyclohexane and THF (a good solvent for PS and PtBA blocks), respectively, for DLS characterization. The DLS results of PS-b-PtBA nano-self-assembled particles dispersed in cyclohexane are shown in Figure 4a. When the solid content was 15% w/w, the molecular weight of the macromolecular initiator PS was kept in the range of 3500~4000 g/mol, and the M n,tBA /M n,PS were designed to be 0.4/1, 0.8/1, and 1.2/1 to obtain PS 35 -b-PtBA 11 ,PS 34 -b-PtBA 20 and PS 36 -b-PtBA 32 , respectively. It can be observed in the corresponding DLS curves that the average size of the diblock copolymer nano-selfassembled particles PS-b-PtBA increases with the increase in M n,tBA /M n,PS . The DLS results of the diblock copolymer PS-b-PtBA nanoself-assembled particles dispersed in THF are shown in Figure 4b, and the size distribution of the PS-b-PtBA nanoself-assembled particles synthesized by LAP PISA in THF was in the range of 90-1100 nm. Since both PS and PtBA segments have good solubility in THF, the DLS results of PS-b-PtBA nano-self-assembled particles dispersed in THF should theoretically be less than 10 nm, but the PS-b-PtBA nanoself-assembled particles prepared by LAP PISA exhibited larger size in THF, which further proved that the tBA monomer was cross-linked in situ in the second polymerization stage of LAP PISA and formed cross-linked stable nano-assembled particles. The morphology of the diblock copolymer PS-b-PtBA nanoassemblies obtained by LAP PISA was characterized using TEM. As shown in Figure 4c-e, the diblock copolymers PS 35 -b-PtBA 11 and PS 34 -b-PtBA 20 were obtained by the LAP PISA process when the solid content was 15% w/w and the designed M n,tBA /M n,PS was 0.4/1 and 0.8/1, and their TEM images were shown in Figure 4c,d. The irregular morphology of the nano-assembled particles can be observed. The TEM image of the diblock copolymer PS 36 -b-PtBA 32 obtained by the LAP PISA process with a fixed solid content of 15% w/w and increasing M n,tBA /M n,PS to 1.2/1 was shown in Figure 4e, from which spherical micelles with a diameter of about 300 nm can be observed. It can be concluded that the LAP PISA system based on PS-b-PtBA was prone to the formation of irregularly shaped nano-self-assembled particles, which can be attributed to the lower glass transition temperature of the second segment PtBA (Tg = 40 • C) and the weaker ability of self-assembly to form the stable core [46]. We hydrolyzed the PtBA chain segment in PS-b-PtBA nano-self-assembled particles into the PAA segment to increase the glass transition temperature of the core block. be observed. It can be concluded that the LAP PISA system based on PS-b-PtBA was p to the formation of irregularly shaped nano-self-assembled particles, which can b tributed to the lower glass transition temperature of the second segment PtBA (Tg °C) and the weaker ability of self-assembly to form the stable core [46]. We hydrolyzed PtBA chain segment in PS-b-PtBA nano-self-assembled particles into the PAA segme increase the glass transition temperature of the core block.

Characterization of PS-b-PAA Nanoself-Assembled Particle
The PtBA segments in PS-b-PtBA nano-self-assembled particles were hydrolyze prepare nano-self-assembled particles with a core containing carboxyl functional gro The series of PS-b-PAA were prepared using CF3COOH hydrolysis of the tBA mono unit on the diblock copolymer PS-b-PtBA obtained from LAP PISA ( Table 2).

Characterization of PS-b-PAA Nanoself-Assembled Particle
The PtBA segments in PS-b-PtBA nano-self-assembled particles were hydrolyzed to prepare nano-self-assembled particles with a core containing carboxyl functional groups. The series of PS-b-PAA were prepared using CF 3 COOH hydrolysis of the tBA monomer unit on the diblock copolymer PS-b-PtBA obtained from LAP PISA ( Table 2).

NMR Characterization
We purified the samples of the macromolecular initiator PS, the diblock copolymer PS-b-PtBA and the diblock copolymer PS-b-PAA obtained by hydrolysis and characterized them using 1 H NMR. Figure 5a showed the 1 H NMR spectrum of the purified treated macromolecular initiator PS, Figure 5b was the 1 H NMR spectrum of the purified treated PS-b-PtBA, and Figure 5c was the 1 H NMR spectra of PS-b-PAA after purification treatment. The area of peak 'j' at 2.10-2.40 ppm was used as the reference, and the peaks at 1.00-2.00 ppm in the 1 H NMR spectra before Figure 5b and after hydrolysis Figure 5c were integrated and compared, respectively, and it was calculated that the PtBA segment had been completely hydrolyzed into the PAA segment, and the hydrolysis conversion rate was 100%. them using 1 H NMR. Figure 5a showed the 1 H NMR spectrum of the purified treated macromolecular initiator PS, Figure 5b was the 1 H NMR spectrum of the purified treated PSb-PtBA, and Figure 5c was the 1 H NMR spectra of PS-b-PAA after purification treatment. The area of peak j at 2.10-2.40 ppm was used as the reference, and the peaks at 1.00-2.00 ppm in the 1 H NMR spectra before Figure 5b and after hydrolysis Figure 5c were integrated and compared, respectively, and it was calculated that the PtBA segment had been completely hydrolyzed into the PAA segment, and the hydrolysis conversion rate was 100%.

TEM and DLS Characterization
The diblock copolymers PS35-b-PtBA11, PS34-b-PtBA20 and PS36-b-PtBA32 were hydrolyzed to obtain PS35-b-PAA11, PS34-b-PAA20 and PS36-b-PAA32 nano-self-assembled particles containing carboxyl groups in their cores, respectively. The morphology of the hydrolyzed nano-self-assembled particles was characterized using TEM. The results were shown in Figure 6. The TEM image of PS35-b-PAA11, from which regular spherical micelles with a size of about 20 nm can be observed in Figure 6a; Figure 6 b,b was the TEM image of PS34b-PAA20, from which regular spherical micelles with a size of about 35 nm can also be observed. Increasing the degree of polymerization of PAA, a mixture of short worm-like micelles and spherical micelles with a size of about 50 nm can be observed in the TEM images of PS36-b-PAA32 (Figure 6 c,c ). The TEM characterization results illustrate that when the solids content was 15% w/w and the molecular weight of the macromolecular initiator PS was kept in the range of 3500~4000 g/mol, the size of the PS-b-PAA diblock copolymer nanoparticles gradually becomes larger and the morphology changed from spherical micelles to short worm-like micelles as the polymerization degree of the core

TEM and DLS Characterization
The diblock copolymers PS 35 -b-PtBA 11 ,PS 34 -b-PtBA 20 and PS 36 -b-PtBA 32 were hydrolyzed to obtain PS 35 -b-PAA 11 ,PS 34 -b-PAA 20 and PS 36 -b-PAA 32 nano-self-assembled particles containing carboxyl groups in their cores, respectively. The morphology of the hydrolyzed nano-self-assembled particles was characterized using TEM. The results were shown in Figure 6. The TEM image of PS 35 -b-PAA 11 , from which regular spherical micelles with a size of about 20 nm can be observed in Figure 6a; Figure 6b,b' was the TEM image of PS 34 -b-PAA 20 , from which regular spherical micelles with a size of about 35 nm can also be observed. Increasing the degree of polymerization of PAA, a mixture of short worm-like micelles and spherical micelles with a size of about 50 nm can be observed in the TEM images of PS 36 -b-PAA 32 (Figure 6c,c'). The TEM characterization results illustrate that when the solids content was 15% w/w and the molecular weight of the macromolecular initiator PS was kept in the range of 3500~4000 g/mol, the size of the PS-b-PAA diblock copolymer nanoparticles gradually becomes larger and the morphology changed from spherical micelles to short worm-like micelles as the polymerization degree of the core block PAA increased. The size of the nano-assemblies was characterized using DLS. Figure 6d shows the DLS measurements of the nano self-assembled particles PS-b-PAA obtained after hydrolysis. The average diameter of the nano self-assembled particles was about 20 nm in the DLS curve of the spherical micelle PS 35 -b-PAA 11 , about 50 nm in the DLS curve of the spherical micelle PS 34 -b-PAA 20 , and the average diameter of the nano-self-assembled particles was about 80 nm in the DLS curves of the mixed system of worm-like micelles and spherical micelles PS 36 -b-PAA 32 . These DLS characterization results showed a variation trend that was in good agreement with the TEM results.
Based on the above characterization results, we can conclude that PS-b-PAA was prepared by CF 3 COOH hydrolysis of the tBA monomer unit on the diblock copolymer PS-b-PtBA obtained from LAP PISA, and due to the high glass transition temperature of PAA (T g = 106 • C) [47], the diblock copolymer PS-b-PAA can all form regular-shaped nano-self-assembled particles. The assembly morphology of the nano-self-assembled particles obtained from PS-b-PAA could be adjusted by changing the degree of polymerization of PAA at a solid content of 15% w/w, and the molecular weight of the macromolecular initiator PS was kept in the range of 3500-4000 g/mol.
Polymers 2023, 15, x FOR PEER REVIEW 10 of 15 block PAA increased. The size of the nano-assemblies was characterized using DLS. Figure 6d shows the DLS measurements of the nano self-assembled particles PS-b-PAA obtained after hydrolysis. The average diameter of the nano self-assembled particles was about 20 nm in the DLS curve of the spherical micelle PS35-b-PAA11, about 50 nm in the DLS curve of the spherical micelle PS34-b-PAA20, and the average diameter of the nanoself-assembled particles was about 80 nm in the DLS curves of the mixed system of wormlike micelles and spherical micelles PS36-b-PAA32. These DLS characterization results showed a variation trend that was in good agreement with the TEM results. Based on the above characterization results, we can conclude that PS-b-PAA was prepared by CF3COOH hydrolysis of the tBA monomer unit on the diblock copolymer PS-b-PtBA obtained from LAP PISA, and due to the high glass transition temperature of PAA (Tg = 106 °C) [47], the diblock copolymer PS-b-PAA can all form regular-shaped nano-selfassembled particles. The assembly morphology of the nano-self-assembled particles obtained from PS-b-PAA could be adjusted by changing the degree of polymerization of PAA at a solid content of 15% w/w, and the molecular weight of the macromolecular initiator PS was kept in the range of 3500-4000 g/mol.

Characterization of PS-b-PAA@Fe3O4 Nanocomposite Particles
Using the complexation between the carboxyl group on the PAA segment and FeCl3·6H2O and FeCl2 metal precursors, Fe 3+ and Fe 2+ were introduced into the core region of PS-b-PAA nano-self-assembled particles, and then NH3·H2O was used as the reducing agent to generate PS-b-PAA@Fe3O4 organic-inorganic nanocomposite particles in situ.

Characterization of PS-b-PAA@Fe 3 O 4 Nanocomposite Particles
Using the complexation between the carboxyl group on the PAA segment and FeCl 3 ·6H 2 O and FeCl 2 metal precursors, Fe 3+ and Fe 2+ were introduced into the core region of PS-b-PAA nano-self-assembled particles, and then NH 3 ·H 2 O was used as the reducing agent to generate PS-b-PAA@Fe 3 O 4 organic-inorganic nanocomposite particles in situ.

TEM and DLS Characterization
Inorganic-organic nanocomposite particles PS 34 -b-PAA 20 @Fe 3 O 4 , obtained from the hydrolysis product PS 34 -b-PAA 20 with a solid content of 15% w/w as a template, were used as an example. The morphology was characterized by TEM by dispersing the inorganicorganic nanocomposite particles into cyclohexane. Figure 7a  about 100 nm, again demonstrating that the size of the nano self-assembled particles after the modification of Fe 3 O 4 was larger than that before the modification, which was consistent with the TEM measurements.
as an example. The morphology was characterized by TEM by dispersing the inorganicorganic nanocomposite particles into cyclohexane. Figure 7a shows the TEM image of PS34-b-PAA20, where spherical micelles with an average diameter of about 50 nm can be observed; the TEM image of PS34-b-PAA20@Fe3O4 after modification of Fe3O4 nanoparticles in the core region of the micelles is shown in Figure 7b,b , and spherical self-assembled particles with a larger size of about 100 nm can be observed. The size of PS34-b-PAA20@Fe3O4 was significantly larger compared to PS34-b-PAA20 without Fe3O4 modification, and the PS shell layer on the surface of the spherical micelles can be observed in the magnified Figure 7b of PS34-b-PAA20@Fe3O4. The DLS characterization results are shown in Figure 7c. The DLS curves of PS34-b-PAA20 nano-assembled particles show an average size of about 50 nm, and the DLS curves of PS34-b-PAA20@Fe3O4 nano-assembled particles show an average size of about 100 nm, again demonstrating that the size of the nano selfassembled particles after the modification of Fe3O4 was larger than that before the modification, which was consistent with the TEM measurements.

TGA Characterization
TGA was utilized to separately analyze nano-assembled particles pre-and post-Fe3O4 modification. As shown in Figure 8, the weight loss was 45.2% in the TGA curve of the organic-inorganic nanocomposite particles PS34-b-PAA20@Fe3O4, while the weight loss was 99.7% in the TGA curve of the diblock copolymer nanoassemblies PS34-b-PAA20, which was almost all thermally decomposed at 485 °C. Obviously, this was due to the introduction of Fe3O4 in polymer nanoassemblies.

TGA Characterization
TGA was utilized to separately analyze nano-assembled particles pre-and post-Fe 3 O 4 modification. As shown in Figure 8, the weight loss was 45.2% in the TGA curve of the organic-inorganic nanocomposite particles PS 34 -b-PAA 20 @Fe 3 O 4 , while the weight loss was 99.7% in the TGA curve of the diblock copolymer nanoassemblies PS 34 -b-PAA 20 , which was almost all thermally decomposed at 485 • C. Obviously, this was due to the introduction of Fe 3 O 4 in polymer nanoassemblies.

XRD Characterization
The nanoassemblies before and after modification of Fe 3 O 4 were characterized separately using XRD. As shown in Figure 9, the characteristic peaks of Temperature( o C) Figure 8. TGA curves of the crosslinked nanoassemblies of diblock copolymer PS34-b-PAA20 and the corresponding organic-inorganic nanoparticles PS34-b-PAA20@Fe3O4 (in the air, 10 °C/min).

Conclusions
In summary, utilizing the LAP PISA technique, diblock copolymer nano-self-assembled particles PS-b-PtBA were synthesized. The employed methodology incorporated cy-

Conclusions
In summary, utilizing the LAP PISA technique, diblock copolymer nano-self-assembled particles PS-b-PtBA were synthesized. The employed methodology incorporated cyclohexane as a solvent, n-Bu − Li + as an initiator, trace tetrahydrofuran as a polarity modifier, DPE as the active species conversion agent, St as the first monomer and tBA as the second monomer. The nano-assembled particles were insoluble in THF, DMF and other solvents, and the DLS results in THF showed a large size, demonstrating that the tBA monomer undergoes cross-linking side reactions during LAP PISA to form cross-linked stable nanoparticles with irregular morphology. Subsequently, CF 3 COOH was used to hydrolyze the tert-butyl group on the tBA monomer unit in the diblock copolymer PS-b-PtBA obtained by LAP PISA into the carboxyl group, and the prepared diblock copolymer PS-b-PAA could self-assemble into spherical and short worm-like micelles with the core containing carboxyl functional groups. The morphology of the nano-self-assembled particles formed by PS-b-PAA gradually evolved from spherical micelles to a mixture of spherical micelles and short worm-like micelles as the degree of polymerization of the core block PAA increased. Finally, the nano-self-assemblies containing carboxyl groups were used as polymer templates, and the PS-b-PAA@Fe 3 O 4 organic-inorganic composite nano-assembled particles were prepared by introducing Fe 3 O 4 into the core of the polymer nanoassemblies using the complexation between the carboxyl group and the metal precursors. It is expected that PS-b-PAA@Fe 3 O 4 spherical nanoparticles can be dispersed uniformly in an elastomer and used as magnetic functional fillers to prepare an electromagnetic shielding elastomer.