Synthesis and Swelling Behavior of pH-Responsive Polybase Brushes

Abstract

We synthesize polybase brushes and investigate their swelling behavior. Poly(2-(dimethylamino)ethyl methacrylate)) (PDMAEMA) brushes are prepared by the "grafting from" method using surface-initiated Atom Transfer Radical Polymerization to obtain dense brushes with relatively monodisperse chains (PDI = 1.35). In situ quaternization reaction can be performed to obtain poly(2-(trimethylamino)ethyl methacrylate)) (PTMAEMA) brushes. We determine the swollen thickness of the brushes using ellipsometry and neutron reflectivity techniques. Brushes are submitted to different solvent conditions to be investigated as neutral brushes and weak and strong polyelectrolyte brushes. The swelling of the brushes is systematically compared to scaling models. It should be pointed out that the scaling analysis of different types of brushes (neutral polymer and weak and strong polyelectrolyte brushes) is performed with identical samples. The scaling behavior of the PDMAEMA brush in methanol and the PTMAEMA brush in water is in good agreement with the predicted scaling laws for a neutral polymer brush in a good solvent and a polyelectrolyte brush in the osmotic regime. The salt-induced contraction of the quaternized brush is observed for high salt concentration, in agreement with the predicted transition between the regimes of the osmotic brush and the salted brush. From the crossover concentration, we calculate the effective charge ratio of the brush following the Manning counterion condensation. We also use PDMAEMA brushes as pH-responsive polybase brushes. The swelling behavior of the polybase brush is intermediate with respect to the behavior of the neutral polymer brush in a good solvent and the behavior of the quenched polyelectrolyte brush, as expected. The effective charge ratio of the PDMAEMA brush is determined as a function of pH using the scaling law of the polyelectrolyte brush in the osmotic regime.

Water Soluble Responsive Polymer Brushes

“…The degree of swelling in PDMAEMA and PTMAEMA brushes decreased as the grafting density was increased, in accordance with the respective power law exponents of −2/3 and −1 predicted [50] by scaling theory. Measurements on the PTMAEMA strong polybase brushes also illustrated the turnover between osmotic brush regime and salted brush regime as the salt concentration is increased.…”

“…The form of the polymer volume fraction profiles is intriguing since no aspect of current polymer brush theory supports the notion of a non-monotonic brush profile, but the presence of entanglements could provide an explanation. A recent study from Sanjuan et al [50] used both PDMAEMA polybase brushes grown using ATRP, as well as PTMAEMA (poly(2-(trimethylamino)ethyl methacrylate) strong polyelectrolyte brushes produced by quaternisation of PDMAEMA samples. Ellipsometry and neutron reflectivity were carried out to measure the thickness of the brushes, expressed as a swelling ratio.…”

“…These vindications of the scaling approximations are particularly rewarding and difficult to obtain since real experimental systems rarely conform without ambiguity to the precisely defined regime behaviour. In the same study [50], the behaviour of PDMAEMA weak polybase brushes in response to changing pH was also presented, using data from both ellipsometry and neutron reflectivity. The brushes were fully swollen at low pH (at a size similar to that of the strong polyelectrolyte PTMAEMA in water).…”

Stimuli-Responsive Polyelectrolyte Brushes As a Matrix for the Attachment of Gold Nanoparticles: The Effect of Brush Thickness on Particle Distribution

“…Neutral polymer brushes and polyelectrolyte brushes are widely used for the modification of surfaces, due to their advantageous specific properties, such as mechanical and chemical stability, their adsorption behavior [1] and permeability [2] and the possibility to tune their structure by varying external stimuli. For instance, the structure of a weak polyelectrolyte brush depends on pH [3][4][5][6][7][8], temperature [9][10][11], salt [12][13][14][15] and solvent [16][17][18]. More precisely, the swelling/shrinking of the studied poly-(N,N-(dimethylamino ethyl) methacrylate) (PDMAEMA) brushes can be manipulated by adjusting the pH of the surrounding environment to values below and above the pK A .…”

Synthesis and characterization of poly(sodium-p-styrenesulfonate)/modified SiO2 spherical brushes

“…The grafting density of brushes formed is limited in this fashion because of the steric hindrance among the preformed polymers [11][12][13]. The latter strategy, the so-called 'grafting from' technique [14][15][16][17], is based on the surface modified by polymerization initiators. Due to bearing initiator functionalities on the surface of core, it can lead to a dense layer of chemically bound polyelectrolyte chains.…”