Structural engineering of polyurethane coatings for high performance applications

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A review on the Mullins effect

Characterization of poly(vinyl alcohol)/poly(ethylene glycol) hydrogels and PVA-derived hybrids by small-angle X-ray scattering and FTIR spectroscopy

A constitutive model for the Mullins effect with permanent set in particle-reinforced rubber

Interpenetrating Polymer Networks for High-Performance Electroelastomer Artificial Muscles

The sol–gel polymerization of 3-glycidyloxypropyltrimethoxysilane (GTMS) was followed by size exclusion chromatography and 29Si NMR. Extensive non-random cyclization under formation of polyhedral cycles – cubic cages – predominates at the beginning of the reaction. Structure growth of polysilsesquioxanes proceeds by combining the incompletely condensed cage frameworks. The extent of the cage formation increases with dilution and the amount of water and depends appreciably on a catalyst. The cage fraction was isolated from a reaction mixture using preparative size exclusion chromatography and identified by 29Si NMR spectroscopy and electrospray ionization mass spectrometry (ESI-MS). High content of polyhedral cages prevents gelation of the trifunctional GTMS monomer. Reaction of pendant epoxy groups is much slower; however, at a late reaction stage the epoxy hydrolysis can be significant. Under some conditions, like base catalysis, polysilsesquioxane clusters are crosslinked by intermolecular condensation of SiOH with hydrolyzed epoxy groups and the system gels. The cage with epoxide functionalities may serve as a rigid precursor of crosslinking.

Cage-like structure formation during sol–gel polymerization of glycidyloxypropyltrimethoxysilane

Sol−gel polymerization of organotrialkoxysilanes RSi(OR‘)3 and formation of silsesquioxane (SSQO) structures was followed using SEC, 29Si NMR, and both small- and wide-angle X-ray scattering. Evolution of the SSQO structure is controlled by the competition between intermolecular polycondensation and cyclization. A strong tendency to buildup of polyhedral cyclic oligomersmainly octamer “cages” and larger cagelike structureswas found to grow with increasing size of substituent R. As a result, long substituents prevent gelation of the trifunctional system and increase stability of the SSQO. Because of incompatibility of the polyhedral SSQO framework and pendant organic chains, microphase separation takes place and spontaneous self-organization occurs. A micellar arrangement of compact SSQO domains with a correlation distance corresponding to the size of the substituent is formed, and the ordering is promoted by increasing length of the organic chain. The most organized arrangement was observed with the trial...

Cyclization and Self-Organization in Polymerization of Trialkoxysilanes

The organic-inorganic (O-I) hybrid networks were prepared from two types of O-I precursors: (a) alkoxysilane-end-capped oligomers (ASO) and (b) epoxy-functional silsesquioxane (SSQO) clusters (EC). ASO precursors were cross-linked by hydrolysis and condensation of alkoxysilane groups and the EC by the reaction of the epoxy groups with oligomeric diamine. Structure evolution and formation of the networks were followed by NMR, SAXS, and chemorheology. In addition, nongelling model systems were used to analyze the structure. Gelation mechanism and effects governing the structure evolution are discussed. Depending on catalysis of ASO polymerization, the compact SSQO cagelike structures or loose SSQO clusters are formed at the chain ends, serving as junction domains of the O-I network. In the EC-amine system, large SSQO cylinder-like domains are produced and interlinked with diamine chains. Decreasing the size or a content of the oligomeric amine results in percolation of the SSQO structure. During cross-linking a structure ordering occurs.

Block Copolymer Organic−Inorganic Networks. Formation and Structure Ordering

Tensile stress-strain behaviour of rubberlike networks up to break. Theory and experimental comparison

A series of segmented polyurethanes was prepared from the new commercial product KRASOL LBH (linear liquid polybutadiene terminated with secondary hydroxy groups), aromatic diisocyanates, and an aliphatic low-molecular-weight diol. Three types of networks were prepared, with the nature of the crosslinks varied from purely chemical to physical, with a continuous transition to "combined" networks containing both crosslink types. Potassium 2-ethyl hexanoate was used as a catalyst of the in situ formation of trifunctional isocyanurate groups (by cyclotrimerization of isocyanate groups). It was confirmed that mechanical, thermal, and swelling properties are considerably influenced by the ratio of chemical to physical crosslink concentration. The best balance of stress- strain properties was obtained for "combined" networks at a NCO-OH molar ratio of 1.10 when only a few chemical crosslinks are present in predominantly physically crosslinked networks. The presence of thermally stable isocyanurate groups mainly influences the storage shear modulus at elevated temperatures. Small-angle X-ray scattering confirmed the two-phase structure of polyurethanes with a periodicity of 6-8 nm. © 2000 John Wiley &

Bohumil Meissner

Papers

Cage-like structure formation during sol–gel polymerization of glycidyloxypropyltrimethoxysilane

Cyclization and Self-Organization in Polymerization of Trialkoxysilanes

Block Copolymer Organic−Inorganic Networks. Formation and Structure Ordering

Tensile stress-strain behaviour of rubberlike networks up to break. Theory and experimental comparison

Polybutadiene‐based polyurethanes with controlled properties: preparation and characterization