Networks, polyurethane characterization

Similar effects have been observed in interpenetrating networks (IPN) characterized by an exceptionally wide distribution of relaxation times, with (3 —> 0. For example, the DSC traces of an IPN consisting of 25 % polyurethane and 75 % PMMA measured by Sartor et al. (1994) did not provide evidence of a step-like change that could be attributed to the Tg. However, aging experiments revealed aging peaks with onset close to the aging temperature, an effect that was attributed to the existence of a very broad distribution of relaxation times. 

Siloxane containing interpenetrating networks (IPN) have also been synthesized and some properties were reported 59,354 356>. However, they have not received much attention. Preparation and characterization of IPNs based on PDMS-polystyrene 354), PDMS-poly(methyl methacrylate) 354), polysiloxane-epoxy systems 355) and PDMS-polyurethane 356) were described. These materials all displayed two-phase morphologies, but only minor improvements were obtained over the physical and mechanical properties of the parent materials. This may be due to the difficulties encountered in controlling the structure and morphology of these IPN systems. Siloxane modified polyamide, polyester, polyolefin and various polyurethane based IPN materials are commercially available 59). Incorporation of siloxanes into these systems was reported to increase the hydrolytic stability, surface release, electrical properties of the base polymers and also to reduce the surface wear and friction due to the lubricating action of PDMS chains 59). 

Polyurethane-acrylic coatings with interpenetrating polymer networks (IPNs) were synthesized from a two-component polyurethane (PU) and an unsaturated urethane-modified acrylic copolymer. The two-component PU was prepared from hydroxyethylacrylate-butylmethacrylate copolymer with or without reacting with c-caprolactonc and cured with an aliphatic polyisocyanate. The unsaturated acrylic copolymer was made from the same hydroxy-functional acrylic copolymer modified with isocyanatoethyl methacrylate. IPNs were prepared simultaneously from the two-polymer systems at various ratios. The IPNs were characterized by their mechanical properties and glass transition temperatures. 

Values of Au qQ 3 calculated from stress relaxation of the swollen networks agreed fairly well with those derived from swelling of polyurethane networks. The anomalous behavior of polyurethanes has been reported (12). Swelling at different solvent activity and stress relaxation of swollen networks are valuable techniques for network characterization. Other networks such as crosslinked polystyrene will be examined by these methods. The role of the Gaussian approximation in rubber elasticity will be evaluated in calculating Mc for highly swollen networks. 

Unsaturated resins are usually mixtures of vinyl monomers and prepolymers, such as unsaturated polyesters, polyurethane acrylates, and ac-rylated epoxides of the bisphenol A type. Polymerization of styrene-based resins involves the formation of a three-dimensional network via the cross-linking of prepolymer chains by styrene radicals. These standard thermoset resins are therefore characterized by great hardness (Shore D over 80, DIN 53505, arbitrary scale 0-100 based on the penetration of a needle point in the tested material), do not melt, and are not soluble in organic solvents. 

Muneera, B., and Siddaramaiah. 2004. Synthesis and characterization of polyurethane/polybutyl methacrylate interpenetrating polymer networks. Journal of Materials Science 39(14) 4615-4623. 

T. W. Pechar, G. L. Wilkes, B. Zhou and N. Luo, Characterization of soy-based polyurethane networks prepared with different diisocyanates and their blends with petroleum-based polyols , J Appl Polym Sci, 2007,106,2350-62. 

Merlin, L.M., Sivasankar, B. Synthesis and characterization of semi-interpenetrating polymer networks using biocompatible polyurethane and acrylamide monomer. Eur. Polym. J. 45, 165-170 (2009)... 

The formulations used in the manufacture of polyurethane elastomers are critical, as variations in the chemical composition of raw materials seriously affect properties. In particular, trace impurities can catalyze or inhibit the various reactions, changing network structures and hence final elastomer properties. For these reasons analytical tests to quantify the quality and reactivity of urethane intermediates have been developed and their use in urethane technology is essential. Additionally, characterization and identification of unknown polymers is frequently necessary. Finally, it is necessary to have procedures which characterize the structure and degree of crosslinking (where this applies) of polyurethane elastomers. 

Prochazka, F., Nicolai, T., and Durand, D. (1996) Dynamic viscoelastic characterization of a polyurethane network formation. Macromoiecules, 29, 2260 2264. 

Marija Pergal, MSc, works at the Department for Polymeric Materials, Institute for Chemistry, Technology and Metallurgy since 2003 as Research Scientist. Since 2007 she is also Teaching Assistant for the course Chemistry of Macromolecules at Department of Chemistry, University of Belgrade. Her research interests are focused on synthesis and characterization of siloxane homopolymers and copolymers, especially thermoplastic elastomers based on poly(butylene terephthalate) and polyurethanes, as well as polyurethane networks based on hyperbranched polyester. In addition to physico-chemical, mechanical and surface properties of polymers, her particular interest is directed towards the study of biocompatibility of polymer materials. 

Mahesh K.P.O., Alagar Muthukaruppan, and Jothibasu S. A comparative study on the preparation and characterization of aromatic and aliphatic bismaleimides-modified polyurethane-epoxy interpenetrating polymer network matrices. J. Appl. Polym. Sci. 99 no. 6 (2006) 3592-3602. 

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