Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Note
  • Published:

A surprisingly narrow particle size distribution for polyacrylic acid nanospheres produced by precipitation polymerization and revealed by small-angle X-ray scattering

Polymer Journal volume 55, pages 1387–1391 (2023)Cite this article

Subjects

Narrow size distributions of spherical polyacrylic acid (PAA) particles can be formed through precipitation polymerization initiated by a conventional radical initiator in a specific solvent without the use of stabilizers or emulsifiers [1, 2]. As pointed out by Nakano et al. and Downey et al., as well as by analogy with dispersion polymerization, particle formation may be divided into three phases with different mechanisms of growth [2, 3]: (1) Immediately after acrylic acid polymerization starts, PAA chains grow and eventually become insoluble once their molecular weights exceed a certain value, and they form small globular particles or nuclei compromising one PAA chain (formation of the primitive nucleus). (2) The primitive nuclei are too unstable to aggregate with each other until a certain size is reached. After reaching that size, aggregation is impeded by electrostatic repulsions between the particles (nucleation and stabilization). (3) As new PAA is prepared via polymerization, the nuclei grow into larger particles by absorbing the PAA chains from the solution or polymerization occurs on the surfaces or interiors of the particles (particle growth). In several previous papers, the second step was not mentioned; however, as far as we know, there is no experimental evidence to rule out the possibility of aggregation and primitive nuclei formation. Furthermore, the discussion of nucleation in the 1st and 2nd steps can be carried forward by replacing the spinodal decomposition mechanism [4]. In this case, it would be more appropriate to refer to the formation of droplets in the concentrated phase rather than nucleation. To examine the proposed mechanisms and understand why such narrow distributions are obtained, we need to know the number of particles in the solution, the particle sizes, and their distribution as a function of the reaction time. In the past, most studies were focused on qualitative size distribution analyses based on microscopic observations made after drying the particles [5,6,7,8]. It is better to have an in situ observations of particle growth in solution. Virtanen et al. carried out small-angle neutron scattering during precipitation polymerization of N‑isopropylacrylamide and found that the particle growth rate followed first-order kinetics, meaning that the growth rate depended only on the monomer concentration [9]. Peng et al. successfully used static light scattering during the dispersion polymerization of poly(methyl methacrylate) and evaluated the dispersity of the particles using scattering theory [10]. These works motivated us to measure PAA particle formation via small-angle X-ray scattering (SAXS), and Nakano et al. already observed the formation of extremely uniform particles [2]. During this work, we found that the particle size distribution was much smaller than expected, and thus, here, we report our result as a note.

Here, \(\sigma\) is the standard deviation. The best-fit curves are illustrated in the figures with red lines, and the resulting \({R}_{{{\mbox{av}}}}\) and \(\sigma\) values are summarized in Table 1. Figure 2B illustrates the theoretical curves with the \({R}_{{av}}\) vibration. When \({R}_{{av}}\) was varied by ±5%, it was no longer possible to reproduce the experimental data with the theoretical curve. The error seen in calculating the particle sizes with the theoretical model would be within 2.5%. The scattering intensity of the minimum value in the low-angle region did not match, which indicates a problem with the number of data points, and in fitting, the important factors are the q values of the maximum and minimum values and the number of maximum and minimum values that can be observed. The number of observable maximum and minimum values is directly related to the particle distribution, and when \(\sigma\) is increased to 6% of \({R}_{{{{{{\rm{av}}}}}}}\) (i.e., CV 6%), the number of observable maxima becomes mismatched. It can be asserted that the precision of particle size analysis with SAXS is exceedingly high. The calculated sizes of PAA particles were approximately 5–20% larger than that observed by SEM. This is because the PAA particles contained a small amount of solvent and swelled when dispersed in a liquid. In the case of nonswelling polystyrene latex particles, the particle sizes observed by SEM and calculated by SAXS were in complete agreement (data not shown). The two methods can be used together to obtain a more complete understanding of the particle sizes and distribution.

Table 1 Radii and standard deviations determined by SEM or SAXS
Full size table

This is a preview of subscription content, access via your institution

Access options

Buy this article

  • Purchase on Springer Link
  • Instant access to full article PDF
Buy now

Prices may be subject to local taxes which are calculated during checkout

Fig. 1
Fig. 2
Fig. 3

References

  1. Minami H, Kimura A, Kinoshita K, Okubo M. Preparation of poly (acrylic acid) particles by dispersion polymerization in an ionic liquid. Langmuir. 2010;26:6303–7.

    Article  CAS  PubMed  Google Scholar 

  2. Nakano T, Saito N, Minami H. Preparation of cross-linked monodisperse poly (acrylic acid) particles by precipitation polymerization. Langmuir. 2020;36:11957–62.

    Article  CAS  PubMed  Google Scholar 

  3. Downey JS, Frank RS, Li W-H, Stöver HD. Growth mechanism of poly (divinylbenzene) microspheres in precipitation polymerization. Macromolecules. 1999;32:2838–44.

    Article  CAS  Google Scholar 

  4. Abyzov AS, Schmelzer JW. Nucleation versus spinodal decomposition in confined binary solutions. J Chem Phys. 2007;127:114504.

    Article  Google Scholar 

  5. Huang H, Ding Y, Chen X, Chen Z, Kong XZ. Synthesis of monodisperse micron-sized poly (divinylbenzene) microspheres by solvothermal precipitation polymerization. Chem Eng J. 2016;289:135–41.

    Article  CAS  Google Scholar 

  6. Onita K, Onishi M, Omura T, Wakiya T, Suzuki T, Minami H. Preparation of monodisperse bio-based polymer particles via dispersion polymerization. Langmuir. 2022;38:7341–5.

    Article  CAS  PubMed  Google Scholar 

  7. Bai F, Huang B, Yang X, Huang W. Synthesis of monodisperse poly (methacrylic acid) microspheres by distillation–precipitation polymerization. Eur Polym J. 2007;43:3923–32.

    Article  CAS  Google Scholar 

  8. Kurozuka A, Onishi S, Nagano T, Yamaguchi K, Suzuki T, Minami H. Emulsion polymerization with a biosurfactant. Langmuir. 2017;33:5814–8.

    Article  CAS  PubMed  Google Scholar 

  9. Virtanen OL, Kather M, Meyer-Kirschner J, Melle A, Radulescu A, Viell JR, et al. Direct monitoring of microgel formation during precipitation polymerization of N-isopropylacrylamide using in situ SANS. ACS Omega. 2019;4:3690–9.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  10. Peng B, Van Der Wee E, Imhof A, Van Blaaderen A. Synthesis of monodisperse, highly cross-linked, fluorescent PMMA particles by dispersion polymerization. Langmuir. 2012;28:6776–85.

    Article  CAS  PubMed  Google Scholar 

  11. Akiba I, Sakurai K. Characterizing block-copolymer micelles used in nanomedicines via solution static scattering techniques. Polym J. 2021;53:951–73.

    Article  CAS  Google Scholar 

  12. Jiang J, Zhang Y, Guo X, Zhang H. Narrow or monodisperse, highly cross-linked, and “living” polymer microspheres by atom transfer radical precipitation polymerization. Macromolecules. 2011;44:5893–904.

    Article  CAS  Google Scholar 

  13. Elliott JE, Macdonald M, Nie J, Bowman CN. Structure and swelling of poly (acrylic acid) hydrogels: effect of pH, ionic strength, and dilution on the crosslinked polymer structure. Polymer. 2004;45:1503–10.

    Article  CAS  Google Scholar 

  14. Khanlari S, Dubé MA. Effect of pH on poly (acrylic acid) solution polymerization. J Macromol Sci A. 2015;52:587–92.

    Article  CAS  Google Scholar 

  15. Hashimoto T, Tanaka H, Koizumi S, Naka K, Chujo Y. A combined small-angle scattering study of a chemical reaction at specific sites and reaction-induced self-assembly as a problem in open non-equilibrium phenomena. Appl Crystallogr. 2007;40:s73–7.

    Article  CAS  Google Scholar 

  16. Ruland W. Small-angle scattering of two-phase systems: determination and significance of systematic deviations from Porod’s law. J Appl Crystallogr. 1971;4:70–3.

    Article  Google Scholar 

  17. Chalal M, Ehrburger-Dolle F, Morfin I, Bley F, Aguilar de Armas M-R, Lopez Donaire M-L, et al. SAXS investigation of the effect of temperature on the multiscale structure of a macroporous poly (N-isopropylacrylamide) gel. Macromolecules. 2010;43:2009–17.

    Article  CAS  Google Scholar 

  18. Asai H, Fujii K, Ueki T, Sakai T, Chung U-I, Watanabe M, et al. Structural analysis of high performance ion-gel comprising tetra-PEG network. Macromolecules. 2012;45:3902–9.

    Article  CAS  Google Scholar 

  19. Malo de Molina P, Lad S, Helgeson ME. Heterogeneity and its Influence on the properties of difunctional poly (ethylene glycol) hydrogels: structure and mechanics. Macromolecules. 2015;48:5402–11.

    Article  CAS  Google Scholar 

  20. Winters A, Cheong FC, Odete MA, Lumer J, Ruffner DB, Mishra KI, et al. Quantitative differentiation of protein aggregates from other subvisible particles in viscous mixtures through holographic characterization. J Pharm Sci. 2020;109:2405–12.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

Download references

Acknowledgements

The SAXS measurements were carried out at SPring-8 BL40B2 (proposal no. 2022B1713, 2022B1277, 2022A1106). This work was supported by the JSPS KAKENHI: Grant-in-Aid for Scientific Research A (20H00668), the Grant-in-Aid for Challenging Exploratory Research (20K20449), the Grant-in-Aid for Scientific Research (19K15394), and the Grant-in-Aid for Scientific Research B (22H01913). We also acknowledge the support from the Kitakyushu Innovative Human Resource and Regional Development Program (JST grant code: JPMJSP2149).

Author information

Authors and Affiliations

  1. Department of Chemistry and Biochemistry, The University of Kitakyushu, 1-1 Hibikino, Kitakyushu, Fukuoka, 808-0135, Japan

    Shin Takano, Ryohei Ono & Kazuo Sakurai

Authors
  1. Shin Takano
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Ryohei Ono
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Kazuo Sakurai
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

ST and RO contributed equally to this work. The manuscript was written with contributions from all authors. All authors approved the final version of the manuscript.

Corresponding author

Correspondence to Kazuo Sakurai.

Ethics declarations

Conflict of interest

The authors declare no competing interests.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Takano, S., Ono, R. & Sakurai, K. A surprisingly narrow particle size distribution for polyacrylic acid nanospheres produced by precipitation polymerization and revealed by small-angle X-ray scattering. Polym J 55, 1387–1391 (2023). https://doi.org/10.1038/s41428-023-00836-y

Download citation

  • Received:

  • Revised:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/s41428-023-00836-y

Search

Advanced search

Quick links