Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Polyurethanes phase-separated systems

In this case of three-monomer polyurethane synthesis, there is no thermodynamic driving force for phase separation. The formation of clusters is fully controlled by the initial composition of the system, the reactivity of functional groups, and the network formation history (one or two stages, macrodiol or triol reacted with diisocyanate first, etc.). [Pg.224]

The substantial work on polystyrene/polybutadiene and polystyrene/ polyisoprene blends and diblock and triblock copolymer systems has lead to a general understanding of the nature of phase separation in regular block copolymer systems (5,6). The additional complexities of multiblocks with variable block length as well as possible hard- and/or soft-phase crystallinity makes the morphological characterization of polyurethane systems a challenge. [Pg.38]

Several studies have been published in recent years on the properties of RIM polyurethanes and polyurethane-ureas (1-7). Unlike most studies, however, we have restricted our attention to simplified linear systems in order to establish the effect of reaction rates and mold temperatures on the phase separation and molecular weight of segmented polyurethane elastomers produced by RIM(6). [Pg.27]

Crystalline Systems. Lower Tqs, flatter rubbery plateau modulus, higher hard segment crystallinity, all support the view that phase separation is more complete MDI-BDO and MDI-ED0 based polyurethanes as catalyst concentration decreases. [Pg.45]

A polyurethane (PU)/poly(n-butyl methacrylate) (PBMA) system has been selected for an investigation of the process of phase separation in immiscible polymer mixtures. Within this system, studies are made of the XX, lx, xl, and the 11 forms. In recognition of the incompatibility of PBMA with even the oligomeric soft segment precursor of the PU, no attempt was made to equalize the rates of formation of the component linear and network polymers. Rather, a slow PU formation process is conducted at room temperature in the presence of the PBMA precursors. At suitable times, a relatively rapid photopolymerization of the PBMA precursors is carried out in the medium of the slowly polymerizing PU. The expected result is a series of polymer mixtures essentially identical in component composition and differing experimentally only in the time between the onset of PU formation and the photoinitiation of the acrylic. This report focuses on the dynamic mechanical properties cf these materials and the morphologies seen by electron microscopy. [Pg.247]

The use of chelate complexes with PAR and derivative spectrophotometry allows selective determination of Ni in mixture with Co and Cu [2]. Flow-injection spectrophotometry and PAR were used to determine Ni in silicates and alloys [3]. The detection limits of 77 ng ml was achieved. An online solid-phase extraction system with polyurethane foam was used for separation of Ni from interfering metals (Fe, Cu, Zn and Co). Online analysis of Ni and Cu in industrial effluents using the complexes with PAR has been described [4]. [Pg.501]

If one also considers phase separation for a reacting polyurethane system with gel effects, Malkin and Kulichikin (1991) showed that the chemoviscosity could then be described by... [Pg.352]

Polyurethane elastomers derive their elastomeric properties from phase separation of the hard and soft copolymer segments, such that the hard (urethane) segment domains serve as crosslinks between the amorphous soft segment domains, which are usually polyesters or polyethers. We are interested in the systems in which the hard segments are prepared from diphenyl-methane 4,4 -diisocyanate (MDI) with a linear diol as the chain extender ... [Pg.179]

As compared to the systems discussed in the previous section, due to the absence of a chain extender (EDA) in the synthesis of these polyurethanes, the length of the carbamate units is not sufficient to enable phase separation consequently, the small amount of photochromic hard segments here exist in a medium similar to isolated hard segments in the soft-phase of two-phase polyurethanes. [Pg.235]

Another metaflo-supramolecular system, on the basis of 2,6-bis(l,2,3-triazol-4-yl)pyridine (BTP) as well as Zn and Eu ", respectively, was introduced by Weng and coworkers [95], The approach is quite different from the majority of mechanically responsive metaflo-supramolecular polymers heretofore described the ligands were designed to be part of the polymer backbone instead of being located at the end of the polymer chains. Telechelic pTHF was thus copolymerized with the dUiydroxy-functionalized BTP ligand and hexamethylene diisocyanate to produce a polyurethane that was further cross-linked through the addition of metal ions (Fig. 28a). The metal-rich domains phase-separate from the pTHF soft... [Pg.370]

To further advance the knowledge on swelling of these systems, a study was conducted using elastomers with a limited phase separation. Polyurethanes were made by a two-step process. Polybutadiene diol (M. 2500) polytetramethylene oxide diol (M. 1400 and 2100) were used. Prepolymers were prepared by reaction of one mole of diol and two moles of 2,4-tolnene diisocyanate. Polypropylene glycol triol, Laprol 373 (M. 370) was... [Pg.257]

A process in which melted plastic is injected into a mold cavity, where it cools and takes the shape of the cavity. Bosses, screw threads, ribs, and other details can be integrated, which allows the molding operation to be accomplished in one step. The finished part usually does not require additional work before assembling. Any IPN in which the individual polymers are thermoplastic. The polymers may contain physical cross-links as in ionomers where ionic clusters join two or more chains together. Nowadays, phase-separated polymeric systems, e.g., block and graft copolymers or thermoplastic polyurethanes, are frequently considered thermoplastic IPNs. [Pg.2272]


See other pages where Polyurethanes phase-separated systems is mentioned: [Pg.459]    [Pg.576]    [Pg.291]    [Pg.344]    [Pg.377]    [Pg.65]    [Pg.66]    [Pg.205]    [Pg.20]    [Pg.37]    [Pg.115]    [Pg.21]    [Pg.39]    [Pg.59]    [Pg.323]    [Pg.158]    [Pg.429]    [Pg.367]    [Pg.381]    [Pg.183]    [Pg.47]    [Pg.70]    [Pg.306]    [Pg.151]    [Pg.226]    [Pg.235]    [Pg.624]    [Pg.639]    [Pg.827]    [Pg.841]    [Pg.115]    [Pg.459]    [Pg.591]    [Pg.606]    [Pg.23]    [Pg.372]    [Pg.3762]    [Pg.8276]    [Pg.564]   
See also in sourсe #XX -- [ Pg.547 ]




SEARCH



Phase-separable system

Polyurethane systems

Separable systems

© 2024 chempedia.info