Csaba Fodor

Unexpected thermal decomposition behavior of poly(N-vinylimidazole)-l-poly(tetrahydrofuran) amphiphilic conetworks, a class of chemically forced blends

The underlying chemical processes of the unexpected thermal decomposition behavior of poly(N-vinylimidazole)-l-poly(tetrahydrofuran) (PVIm-l-PTHF) amphiphilic conetworks (APCNs) as chemically forced blends of the otherwise immiscible components in broad composition ranges were investigated by thermogravimetric analysis (TG) and thermogravimetry-mass spectrometry (TG-MS). Surprisingly, the thermal decomposition of these conetworks occurs not by an expected two-stage but an apparently single-stage process. The homolytic scission of the PTHF cross-linkers is preceded by a less significant volatile product evolving by a non-radical reaction, presumably related to the well-known cis-elimination of the methacrylate ester linkages. The temperatures of the highest weight loss rate (Td(max)) were found to fall between that of the pure PVIm and PTHF homopolymers, and a universal correlation exists between Td(max) and the composition of the conetworks. The main thermal decomposition reactions of the polymer components in the PVIm-l-PTHF APCNs remain the same as in the corresponding homopolymers. However, among the two main degradation reactions of PVIm, the free radical depolymerization is promoted by PTHF macroradicals of molecular vicinity via hydrogen abstraction, which results in PTHF chains with improved stability. In contrast to expectations, this leads to a single-stage decomposition process of the two chemically interacting polymers in the conetworks. These results are expected to contribute to designing a variety of bi- and multicomponent polymeric materials with predictable thermal behavior composed of chemically and physically interconnected polymer chains, ranging from polymer blends to networks, block copolymers, composites and hybrids of the nanoscale to macroscopic objects.

Poly(: N -vinylimidazole)- l -poly(propylene glycol) amphiphilic conetworks and gels: Molecularly forced blends of incompatible polymers with single glass transition temperatures of unusual dependence on the composition

A series of macroscopically homogeneous poly(N-vinylimidazole)-l-poly(propylene glycol) (PVIm-l-PPG) (“l” stands for “linked by”) amphiphilic conetworks (APCNs) composed of otherwise incompatible polymers were successfully synthesized in a broad composition range (34–88 wt% PPG) by free radical copolymerization of hydrophilic N-vinylimidazole (VIm) and hydrophobic poly(propylene glycol) dimethacrylate (PPGDMA) macromolecular cross-linkers. Strikingly, while PVIm and PPGDMA homopolymers are immiscible and their blends have two distinct glass transition temperatures (Tg), the PVIm-l-PPG conetworks possess only one Tg indicating the absence of considerable phase separation in the conetworks, which was also confirmed by AFM measurements. This is in sharp contrast to the two Tgs of APCNs reported so far in the literature, on the one hand. On the other hand, the Tg values do not follow known correlations between Tg and composition, like the Fox equation or additive rule, widely applied for compatible polymers. These results indicate a strong interpolymer interaction on the molecular level between the PVIm and PPG chains in these new APCNs resulting in single Tg. Thermogravimetric analysis (TGA) shows that degradation of the conetworks occurs at high temperatures in two stages without sharp changes, but with a transition period in between. The DTG curves indicate that the components retain their chemical integrity to certain extent in these APCNs. The amphiphilic nature of the PVIm-l-PPG conetworks was confirmed by their composition dependent swelling in both polar (water, ethanol) and nonpolar (THF) solvents, that is in spite of the lack of phase separation, these new materials behave as either hydrogels or hydrophobic gels (organogels) depending on the swelling medium in a broad composition range.

Nanophasic morphologies as a function of the composition and molecular weight of the macromolecular cross-linker in poly(N-vinylimidazole)-l-poly(tetrahydrofuran) amphiphilic conetworks: bicontinuous domain structure in broad composition ranges

Macroscopically homogeneous poly(N-vinylimidazole)-linked by-poly(tetrahydrofuran) (PVIm-l-PTHF) amphiphilic conetworks (APCNs) were investigated to reveal the effect of conetwork composition in a broad composition range between 25–91 wt% PTHF content and the molecular weight of the components on phase separation and the formation of different morphological features. No macroscopic phase separation was found in these conetworks with semicrystalline PTHF phase, but the segregation of the various covalently connected phases occurs in the nanoscale. The nanophase separated APCNs possess compositionally asymmetric morphology with spherical and elongated domains together with a bicontinuous (cocontinuous) domain structure having ∼7–19 nm average domain sizes. The molecular weight of the PTHFDMA cross-linker, varying between 2170 and 10 030 g mol−1, also influences the size and distance between the phases. Moreover, morphology dependent interactions with polar and non-polar solvents, as well as amphiphilic swelling behavior were found. These nanostructured materials, due to their unique nanophasic morphology and swelling properties possess significant importance and have numerous potential applications in various fields from medicine to material science and engineering.

Crystal structure of di­aqua­tris­(1-ethyl-1H-imidazole-κN3)(sulfato-κO)nickel(II)

The NiII ion atom is octahedrally coordinated in diaquatris(1-ethyl-1H-imidazole)sulfatonickel(II). There are three organic ligands, two water and the sulfate anion coordinated around the NiII centre. Two complex molecules form an inversion dimer via two pairs of O—H⋯O hydrogen bonds between the coordinating sulfate anion and a water molecule in the unit cell.