Swelling Behavior and Microstructure of Poly(12-acryloyloxydodecanoic acid-co-acrylic acid) Gels in the Ethanol/Water System

Abstract

The swelling behavior and hierarchical structures of poly(acrylic acid) (AA) homopolymer gels and poly(12-acryloyloxydodecanoic acid (ADA)-co-AA) gels carrying ionizable groups as well as hydrophobic groups have been investigated by equilibrium swelling measurement, dynamic light scattering (DLS), and small-angle neutron scattering (SANS). The equilibrium swelling degree (Sv) and the structure factors of the copolymer gels were obtained as a function of the ethanol (EtOH)/water (W) solvent composition, x () vol % of EtOH). Sv showed a convex-upward function of x. That is, the gels swelled with increasing x until x ) 50-60 vol % for AA gels and x ) 70-80 vol % for ADA/AA gels and then decreased gradually. This phenomenon is explained by hydrophobic association of long alkyl chains of ADA and a cosolvency effect of poly(AA) in EtOH and W. The DLS results also indicated that the major component of light scattering was frozen inhomogeneities. SANS intensity functions, I(q), for the copolymer gels when x ) 25 vol % showed the presence of an ordered structure in water with a long spacing of ca. 46 Å. These experimental pieces of evidence suggest a strong correlation between the macroscopic properties, such as Sv, and the microscopic structure as well as the dynamics. The diffusion coefficients were obtained by DLS as well as SANS, of which physical meanings are discussed by comparing the x dependence of S v.

Volume transition and internal structures of small poly(N‐isopropylacrylamide) microgels

“…The previous SANS works on larger neutral/ionic colloidal nanoparticles and bulk gels, however, suggest an inhomogeneous gel structure in different solvents or in response to the external mechanical/osmotic pressures. This may be associated to the changing reaction rate and uncertain preference to the crosslinker during the free radical polymerization 12, 14, 52–54. The uniform structure of the small gel nanoparticle, as we concluded in this work, lead us to believe that the growth of the larger particles may also have experienced a similar constant reaction ratio of crosslinker to monomers at the initial phase of the polymerization.…”

Polymers with upper critical solution temperature behavior in alcohol/water solvent mixtures

“…For example, poly(12-acryloyloxydodecanoic acid-co-acrylic acid) gels were reported to swell with increasing content of ethanol (x) in ethanol/water binary solvent until x = 50-60 vol%. [72] In addition, solubility maxima have been reported for thermoresponsive polymeric gels based on 2-hydroxyethyl methacrylate and acetoacetoxyethyl methacrylate in ethanol/water solvent mixtures with around 40-50 mol-% ethanol. [63] In the latter system, the co-solvency effect was ascribed to the formation of water-alcohol-polymer contacts in the solution lowering the free energy of the system (as shown in Figure 2).…”

Mechanism of UV‐Induced Gelation of Acryloyl‐Type Monomer and Polymer Solutions Using Persulfate as Photoinitiator

“…Chemically cross-linked polymer gels have been synthesized using various methods, such as low-temperature redox, [1][2][3][4][5] heat-, [1,[6][7][8][9] high-energy electron beam-, [10][11][12] g-ray-, [13][14][15][16][17][18][19][20] and UV- [21][22][23][24][25] induced polymerizations. Heat-induced polymerization is a simple method in which heating to temperature higher than ca.…”