Papers by Author: M. Ilavsky

Abstract: The aim of this contribution was to study the rubber elasticity of dry and swollen networks obtained by cyclotrimerization crosslinking reaction of isocyanate groups located at a linear telechelic network precursor. Telechelic diisocyanates were prepared in the undiluted state from 2,4-tolylene diisocyanate, α,ω,dihydroxypoly(oxypropylenes) and different contents of the monool component 2-(2-metoxyetoxy) ethanol. The network synthesis proceeded in a bulk. Detailed network topology was calculated by the theory of branching processes. The equilibrium swelling degree of prepared samples was related to the parameters, which are experimentally accessible for a network arising from an end-linking process using the Flory-Rehner theory. The experimental data for network modulus were compared with those arising from the "affine" model, "phantom’ model" and the model of constrained junctions.

Abstract: This paper describes DSC, dielectric and dynamic mechanical behavior of linear and crosslinked liquid crystalline (LC) polyurethanes based on LC diols with a mesogenic group in the side chain, diisocyanates of various flexibility and two triols. From our investigations it follows: a) Linear polymers prepared from diols with simple end side chain substituents (as hydrogen, nitro and nitril group) exhibit only amorphous behavior regardless of the structure of used diisocyanate; generally, the most pronounced LC behavior exhibited polymers prepared from a diol with phenyl substituent. b) Investigation of the curing reaction showed that rheological power-law parameters, which are characteristic of the structure at the gel point, are dependent on the initial ratio of the reactants (amount of LC diol in EANCs). c) Strong physical interactions between the mesogens support the cyclization in the course of crosslinking reaction. d) Introduction of chemical junctions (amount of triols) suppresses LC ordering in the networks.

Abstract: Here, as part of our experimental investigations dealing with poly(urethane-isocyanurate) networks, we investigate model irregular networks with increasing amount of dangling chains. In our study such an irregular network topology was obtained by partial substitution of a diol for a monohydroxy component during the preparation of isocyanate terminated precursors. Telechelic diisocyanates were synthesized from aromatic diisocyanate (2,4-TDI), α,ω-dihidroxypoly (oxypropylene) (PPG 2000), and diethyleneglycolmonomethylether (an aliphatic low-molecularweight monool component). The networks in undiluted state were prepared by cyclotrimerisation, in the presence of a catalyst. The network properties were estimated by multiple extraction in solvent, differential scanning calorimetry and photoelastical measurements. Independently of mechanical testing, the fraction and concentration of dangling and elastically active network chains were evaluated by the theory of branching processes (cascade theory). The influence of dangling chains on the mechanical properties was analyzed.

Abstract: This paper deals with the control of the adhesion strength in metal-elastomer joints by fillers and the use of rubber blends to produce advanced high performance adhesive systems. The curing behavior of rubber compounds and dynamic mechanical properties of crosslinked rubber composites were considered in this technologically applicable study. The effects of two types of reinforcing filler, used to increase the adhesion strength between steel and rubber matrix based on acrylonitrile-butadiene rubber (NBR) and chlorosulfonated polyethylene rubber (CSM) was investigated. Precipitated silica (with the average size of primary particle 15 nm) and diatomaceous earth (with the average size of primary particle 28 µm) were used for both rubber and its blend (NBR/CSM). The filler loading range was from 0 to 35 phr. The determination of curing characteristics was estimated by Monsanto Rheometer. The crosslink density of the rubber composites was determined by swelling measurement. Dynamic mechanical behavior was measured by mechanical spectroscopy (in a single cantilever bending mode).