Porosity Inherent to Chemically Crosslinked Polymers. Poly(N-vinylimidazole) Hydrogels
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- 作者：V. Calvino-Casilda ; A. J. Ló ; pez-Peinado ; E. Vaganova ; S. Yitzchaik ; I. E. Pacios ; I. F. Pié ; rola
- 刊名：Journal of Physical Chemistry B
- 出版年：2008
- 出版时间：March 13, 2008
- 年：2008
- 卷：112
- 期：10
- 页码：2809 - 2817
- 全文大小：970K
- 年卷期：v.112,no.10(March 13, 2008)
- ISSN：1520-5207
文摘
Swollen polymer networks exhibit multiscale pores filled with solvent. Such porosity, inherent to cross-linked polymers, determines some of their most relevant physical properties and applications. In this research,several samples of chemically crosslinked poly(N-vinylimidazole) were synthesized with the same permanentcrosslinking density at two different conversions, and their inherent porosity was characterized on freeze-dried specimens by SEM, TEM and nitrogen physisorption. It was thus found that all of the samples showedpores, both on the nanometer and the micrometer scales, whose dimensions were mostly equal to or largerthan the mesh size of the primary polymer network (22 nm) and whose volume and specific surface decreasedwith increasing conversion. Micropores have, in all cases, a very minor contribution. Samples synthesizedwith the largest comonomer concentrations show quasi-spherical mesopores (90 nm average diameter at anyconversion) and macropores (from 5 to 10 
m with increasing conversion), whereas the mesopores of samplessynthesized with the largest crosslinker ratios were channel-like (150 nm) and the macropores wereinterconnected contiguous voids (3 m). Samples with intermediate compositions exhibit the lowest porositydue, mostly, to interconnected mesopores. The differences in shape were ascribed to the mechanism of phaseseparation, taking place during polymerization, even for samples that are transparent following polymerization.The inherent porosity is a significant source of spatial inhomogeneity, which contributes to the increase inturbidity. Light scattering decreases with increasing ionization when the degree of protonation is greater than10%. An important consequence of the inherent porosity is that the degrees of swelling determined eithergravimetrically or through size measurements are not equivalent.
m with increasing conversion), whereas the mesopores of samplessynthesized with the largest crosslinker ratios were channel-like (150 nm) and the macropores wereinterconnected contiguous voids (3 m). Samples with intermediate compositions exhibit the lowest porositydue, mostly, to interconnected mesopores. The differences in shape were ascribed to the mechanism of phaseseparation, taking place during polymerization, even for samples that are transparent following polymerization.The inherent porosity is a significant source of spatial inhomogeneity, which contributes to the increase inturbidity. Light scattering decreases with increasing ionization when the degree of protonation is greater than10%. An important consequence of the inherent porosity is that the degrees of swelling determined eithergravimetrically or through size measurements are not equivalent.