The next step in precipitation polymerization of N-isopropylacrylamide: particle number density control by monochain globule surface charge modulation

Virtanen, Otto L. J.; Brugnoni, Monia; Kather, Michael; Pich, Andrij; Richtering, Walter

doi:10.1039/c6py01195k

Cited by 30 publications

(40 citation statements)

References 41 publications

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“…The power law exponent with respect to NIPAM concentration, determined here as 1.54 ± 0.07, is higher than expected based on the earlier results of 0.94 ± 0.08 36 and 1.05 ± 0.08. 35 However, given the limited amount of experimental data, the value is in reasonable agreement with previous work. As expected for radical solution polymerization, the power law exponent of 0.42 ± 0.03 in respect to APS concentration is close to half an order of magnitude lower than for the NIPAM concentration.…”

Section: Resultssupporting

confidence: 91%

“…Earlier studies have shown the polymerization rate to be close to the power law behavior of radical solution polymerization with R p ∝ [monomer][initiator] 1/2 shortly after initiation. 35,36 This is not surprising, given the abundant solubility of NIPAM in water, which implies that significant conversion takes place in the water phase during early reaction stages.…”

Section: Resultsmentioning

confidence: 99%

“…In a series of batches with increasing NIPAM concentration, the end particle concentration first increases, goes through a maximum, and then decreases. 34,35…”

Section: Resultsmentioning

confidence: 99%

“…Using the heat of polymerization of NIPAM, determined to be 84.5 ± 0.3 kJ mol –1 in one of our previous reports, 35 it is possible to calculate the conversion depending on the reaction time (Figure 7A). Performing a single exponential fit of the conversion data with eq 11 on the NIPAM synthesis without BIS shows a good agreement with corresponding fits of the scattering data (Figure 5).…”

Section: Resultsmentioning

confidence: 99%

“…32,33 Recently, it has been shown that the principles of radical solution polymerization can be effectively used to regulate the stabilization and final particle volume of PNIPAM particles. 34,35…”

Section: Introductionmentioning

confidence: 99%

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Direct Monitoring of Microgel Formation during Precipitation Polymerization ofN-Isopropylacrylamide Using in Situ SANS

et al. 2019

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Poly( N -isopropylacrylamide) microgels have found various uses in fundamental polymer and colloid science as well as in different applications. They are conveniently prepared by precipitation polymerization. In this reaction, radical polymerization and colloidal stabilization interact with each other to produce well-defined thermosensitive particles of narrow size distribution. However, the underlying mechanism of precipitation polymerization has not been fully understood. In particular, the crucial early stages of microgel formation have been poorly investigated so far. In this contribution, we have used small-angle neutron scattering in conjunction with a stopped-flow device to monitor the particle growth during precipitation polymerization in situ. The average particle volume growth is found to follow pseudo-first order kinetics, indicating that the polymerization rate is determined by the availability of the unreacted monomer, as the initiator concentration does not change considerably during the reaction. This is confirmed by calorimetric investigation of the polymerization process. Peroxide initiator-induced self-crosslinking of N -isopropylacrylamide and the use of the bifunctional crosslinker N , N ′-methylenebisacrylamide are shown to decrease the particle number density in the batch. The results of the in situ small-angle neutron scattering measurements indicate that the particles form at an early stage in the reaction and their number density remains approximately the same thereafter. The overall reaction rate is found to be sensitive to monomer and initiator concentration in accordance with a radical solution polymerization mechanism, supporting the results from our earlier studies.

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Section: Resultssupporting

confidence: 91%

Section: Resultsmentioning

confidence: 99%

“…In a series of batches with increasing NIPAM concentration, the end particle concentration first increases, goes through a maximum, and then decreases. 34,35…”

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Direct Monitoring of Microgel Formation during Precipitation Polymerization ofN-Isopropylacrylamide Using in Situ SANS

et al. 2019

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On the Thermoresponsivity and Scalability of N,N‐Dimethylacrylamide Modified NIPAM Microgels

Zehm

Lieske

Stoll³

2020

Macro Chemistry & Physics

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versa. [1a,2a] The deswelling/swelling temperature is then referred to as volume phase transition temperature (VPTT), as opposed to an LCST. This reflects the fact that the particles undergo a volume collapse at the transition temperature, as opposed to the nearly complete desolvation observed in the case of linear homopolymer.The prime technique to synthesize such colloidal thermoresponsive microgels is precipitation polymerization (PP). [1c,h] Here, monomer, initiator, and optionally surfactant are all molecularly dissolved in the initially homogeneous reaction solution, which makes this process rather simple to conduct. Once a critical degree of polymerization is reached and the polymerization is performed above the LCST of the targeted polymer, the polymer chains become insoluble while the charges obtained from the initiator prevent particle precipitation. The precipitating chains agglomerate and serve as nuclei that are grown by further conversion of monomer and oligoradicals, leading to near-monodisperse particles in the range of 100 nm to ≈1 µm. Considering the simplicity of PP, it is hardly surprising that the body of proposed applications is vast: it ranges from waste water treatment, [3] enhanced oil recovery, [4] and thickening, [5] to more sophisticated technologies such as drug delivery, tissue engineering, sensing, and liquid chromatography (i.e., used as temperature-sensitive stationary phases for size exclusion, hydrophobic, ionic, and affinity chromatography), which are summarized in recent reviews. [1h,6] In addition to these proposed fields of application, colloidal microgels are valuable model systems in fundamental research to study soft matter physics. [1g] In this context, the usage of near-monodisperse particles of well controllable size and dispersity is essential to study effects on the microscopic scale (or less), which is perfectly fulfilled by particles obtained by PP.With this article, we want to present our contribution on the synthesis of thermoresponsive microgels. For a collaborative project, we were requiring significant amounts of such particles supposed to be embedded in films (or foams) for the reversible release/absorption of water at a critical temperature. More specifically, the following criteria were defined for the system to be used as the responsive material:1. The synthetic method to be used is scalable and provides at least 250 g pure thermoresponsive microgels per batch. N-isopropylacrylamide (NIPAM) and N,N-dimethylacrylamide (DMAAm) are prepared using either precipitation polymerization (PP) or inverse emulsion polymerization (IEP). The comparison of the volume phase transition temperature (VPTT) for PNIPAM n -co-PDMAAm m copolymer microgels prepared by PP or IEP reveals significant differences. Empirically, PP leads to lower VPTTs than IEP for identical monomer composition, whereby the observed difference in the VPTT becomes greater the higher the DMAAm content of the monomer mixture is. Presumably this is because IEP confers a higher homogeneity of the cros...

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A “Limited Aggregation Model” to Predict the Size of Acrylamide‐Based Microgels Synthesized with Ionic Surfactants

Brézault,

Schmitt,

Ravaine

et al. 2023

Macro Chemistry & Physics

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The size of acrylamide‐based microgels can be decreased by addition of ionic surfactants during the classical dispersion polymerization. Nevertheless, the mechanism of such syntheses is not well understood yet. Here, a “Limited Aggregation Model” is proposed by analogy with the limited coalescence mechanism occurring for Pickering emulsion stabilization. In such a model, nuclei aggregate until a constant, high enough surfactant surface coverage is reached, which ensures colloidal stability. Consequently, the total surface of the growing particles, linked to the inverse of their size, is linearly dependent on the surfactant concentration. This law is verified if the surfactant/polymer particle interaction is high enough to guarantee a “total adsorption” of the surfactants onto the particles. This simple model fits very well with all the data extracted from the literature, including very different synthesis conditions. Finally, it not only permits to predict the microgels size, but it is also an interesting tool to investigate the role of each synthesis parameter like initiator, solvent or polymer. For instance, it shows that the surfactant role is not linked to its charge, proving that a phenomenon complementary to the electrostatic repulsion, related to the surfactant tail, ensures the colloidal stability of the growing collapsed microgels.

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The next step in precipitation polymerization of N-isopropylacrylamide: particle number density control by monochain globule surface charge modulation

Abstract: Many applications of poly(N-isopropylacrylamide) microgels necessitate robust control over particle size.

Cited by 30 publications

References 41 publications

Direct Monitoring of Microgel Formation during Precipitation Polymerization ofN-Isopropylacrylamide Using in Situ SANS

Direct Monitoring of Microgel Formation during Precipitation Polymerization ofN-Isopropylacrylamide Using in Situ SANS

On the Thermoresponsivity and Scalability of N,N‐Dimethylacrylamide Modified NIPAM Microgels

A “Limited Aggregation Model” to Predict the Size of Acrylamide‐Based Microgels Synthesized with Ionic Surfactants

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