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Localized Thermoresponsive Behavior in P(NIPAm-co-AAc) Copolymers : Structural Insights From Rheology and Small Angle X-Ray Scattering

Fernandez Bordín, S. P. LU ; Rufeil Fiori, E. ; Padró, J. M. ; Galván Josa, V. M. ; Plivelic, T. S. LU and Romero, M. R. (2025) In Journal of Polymer Science 63(2). p.393-405
Abstract

Stimuli-responsive polymers stand out for their ability to respond to small environmental changes. One of the most representative thermo-sensitive materials is poly(N-isopropyl acrylamide) (PNIPAm), which presents reversible phase transitions close to the human body temperature. However, previous studies observed that the copolymerization of NIPAm with small quantities of different monomers like acrylic acid (AAc) results in copolymers with reduced or lost thermo-responsivity. In this study, thermo-sensitive PNIPAm, pH-sensitive poly(acrylic acid) (PAAc), and various proportions of their copolymers P(NIPAm-co-AAc) were obtained by free radical polymerization and thoroughly characterized. Rheological and structural studies reveal the... (More)

Stimuli-responsive polymers stand out for their ability to respond to small environmental changes. One of the most representative thermo-sensitive materials is poly(N-isopropyl acrylamide) (PNIPAm), which presents reversible phase transitions close to the human body temperature. However, previous studies observed that the copolymerization of NIPAm with small quantities of different monomers like acrylic acid (AAc) results in copolymers with reduced or lost thermo-responsivity. In this study, thermo-sensitive PNIPAm, pH-sensitive poly(acrylic acid) (PAAc), and various proportions of their copolymers P(NIPAm-co-AAc) were obtained by free radical polymerization and thoroughly characterized. Rheological and structural studies reveal the remaining thermosensitivity of the copolymers manifested at short molecular ranges. These alterations in short-range interactions are observed in all samples containing NIPAm, and they are evidenced by changes in the fractality of their structure and flow index behavior of the Viscosity Ostwald–de Waele Model. Particularly, when the copolymer proportion of NIPAm/AAc is about 40/60, the Beaucage model reveals two structural levels, ~200 and ~10 nm. Furthermore, the model exhibits a thermal response of the lower-size substructures, indicating possible segregation of NIPAm-rich regions from copolymer chains. The evidence found in this work could contribute to the development of nanosystems, in which local thermoresponsive effects are sought, such as for active drug targeting.

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author
; ; ; ; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Beaucage model, fractality, Ostwald–de Waele model, PNIPAm, PNIPAm copolymers, small-angle x-ray scattering, thermo-sensitive polymers
in
Journal of Polymer Science
volume
63
issue
2
pages
13 pages
publisher
John Wiley & Sons Inc.
external identifiers
  • scopus:85208816239
ISSN
2642-4150
DOI
10.1002/pol.20240799
language
English
LU publication?
yes
id
8fed52f4-b186-48b4-bff2-bbf7639478e9
date added to LUP
2025-02-17 14:32:21
date last changed
2025-04-04 14:36:45
@article{8fed52f4-b186-48b4-bff2-bbf7639478e9,
  abstract     = {{<p>Stimuli-responsive polymers stand out for their ability to respond to small environmental changes. One of the most representative thermo-sensitive materials is poly(N-isopropyl acrylamide) (PNIPAm), which presents reversible phase transitions close to the human body temperature. However, previous studies observed that the copolymerization of NIPAm with small quantities of different monomers like acrylic acid (AAc) results in copolymers with reduced or lost thermo-responsivity. In this study, thermo-sensitive PNIPAm, pH-sensitive poly(acrylic acid) (PAAc), and various proportions of their copolymers P(NIPAm-co-AAc) were obtained by free radical polymerization and thoroughly characterized. Rheological and structural studies reveal the remaining thermosensitivity of the copolymers manifested at short molecular ranges. These alterations in short-range interactions are observed in all samples containing NIPAm, and they are evidenced by changes in the fractality of their structure and flow index behavior of the Viscosity Ostwald–de Waele Model. Particularly, when the copolymer proportion of NIPAm/AAc is about 40/60, the Beaucage model reveals two structural levels, ~200 and ~10 nm. Furthermore, the model exhibits a thermal response of the lower-size substructures, indicating possible segregation of NIPAm-rich regions from copolymer chains. The evidence found in this work could contribute to the development of nanosystems, in which local thermoresponsive effects are sought, such as for active drug targeting.</p>}},
  author       = {{Fernandez Bordín, S. P. and Rufeil Fiori, E. and Padró, J. M. and Galván Josa, V. M. and Plivelic, T. S. and Romero, M. R.}},
  issn         = {{2642-4150}},
  keywords     = {{Beaucage model; fractality; Ostwald–de Waele model; PNIPAm; PNIPAm copolymers; small-angle x-ray scattering; thermo-sensitive polymers}},
  language     = {{eng}},
  number       = {{2}},
  pages        = {{393--405}},
  publisher    = {{John Wiley & Sons Inc.}},
  series       = {{Journal of Polymer Science}},
  title        = {{Localized Thermoresponsive Behavior in P(NIPAm-co-AAc) Copolymers : Structural Insights From Rheology and Small Angle X-Ray Scattering}},
  url          = {{http://dx.doi.org/10.1002/pol.20240799}},
  doi          = {{10.1002/pol.20240799}},
  volume       = {{63}},
  year         = {{2025}},
}