Polyurethanes ionomers

In comparison with the usual hydrophobic isocyanate polyaddition products, polyurethane ionomers are structurally much more suitable for the preparation of aqueous two-phase systems. These polymers, which show hydrophilic ionic sites between predominantly hydrophobic chain segments, are self-dispersing under favourable conditions. These products spontaneously form stable dispersions in water without the influence of shear forces and in the absence of dispersants. There are several techniques available  

If it is assumed that the water which was added is distributed homogeneously in the mixture of hydrophobic solvent and ionomer, then the hydration of the ionic segments prevents macroscopic precipitation of the polymer. However, since the hydrophobic segments (r. 50-98% of the polyurethane ionomer) cannot be hydrated, they form associates, which can eventually develop into a microscopic precipitation. As solvent is present this has a plasticizing effect on the nucleus of latex particles which thus form a film. The hydrated ionic segments provide the stabilizing surface changes. 

Prepolymer ionomers with isocyanate end-groups and of sufficiently low molecular weight can be mixed with water in the presence of hydrophobic organic solvents, such as methylene chloride or toluene, or, in the case of sufficiently low viscosities, even without solvent. The prepolymers form emulsions, which in turn form polymer dispersion after chain extension by reaction of the isocyanate. Such a process requires powerful high-shear mixing equipment in the presence or absence of solvents. Solutions of ionomers in hydrophilic solvents form emulsions spontaneously in the presence of water. The formation of the emulsion must be 

This procedure can also be used for prepolymers possessing other reactive groups, such as mercapto, chloromethyl, bromomethyl epoxy, amino, aziridine, vinyl, carboxyl, hydroxy or alkoxymethyl groups. Oligomer emulsions can also be obtained by mixing water into the dissolved or liquid ionomer, because these products are inert with respect to water. 

After coating on to a substrate the treated surface is cured by addition of a reactive component, e.g. by oxidation, change of pH or by heating. 

---

Polyurethane ionomers, 25 460 Polyurethane-modified isocyanurate (PUIR) foams, 25 455, 456 Polyurethanes (PUs), 9 564. See also Polyurethane (PU) antioxidant applications, 3 121-122 cardiovascular device applications, 3 720 CASE, 25 474-477 commercial block copolymers, 7 648t containing sulfur linkages, 23 742-745 dyeing, 9 204... 

Interest in polyurethane ionomers has increased in the last decade because of their growing uses in water-based coating, adhesives, medical, and semiconductor applications. However, relatively little information has been published regarding the synthesis and... 

As for ASAXS, we are currently using this technique to separate the crystallite and ionic "peak" scattering in the semicrystalline ionomers Nafion and Surlyn. Since these two scattering sources overlap in q-space, it has in the past proved difficult to separate and model these scattering sources, but with ASAXS this task becomes possible. Also, we are investigating the hlgh-q shoulder we have observed in the SAXS patterns of sulfonated polyurethane ionomers[45], which may be evidence of structural order within the ionic aggregates. 

These results confirm the observation that polyelectrolyte aqueous solutions show two separate decay modes in the autocorrelation function and support our contention that ionic polymer systems generally behave similarly in polar solvents [23], To support this, it may be added that similar dynamic scattering behavior was recently reported for another type of ionomer, polyurethane ionomer, dissolved in a polar solvent, dimethylacetamide (e = 38) [92], Finally, it should be stressed that the explanation given above for light scattering (both static and dynamic) behavior of salt-free polyelectrolytes is based on the major role of intermolecular electrostatic interactions in causing characteristic behavior. No intramolecular interactions are explicitly included to explain the behavior. This is in accord with our contention that much of the polyelectrolyte behavior, especially structure-related aspects, is determined by intermolecular interactions [23]. 

Nomula S, Cooper SL. Structural studies of polyurethane ionomer solutions. 1. Dynamic light scattering. Macromolecules 1997 30 1355—1362. 

H-S. Xu and C-Z. Yang, The ionic conductive properties of sulfonated polyethylene oxide polyurethane, J. Polym. Sci., Polym. Phys. Ed., 1995, 33, 745-751 G. Robila, T. Buruiana and E.C. Buruiana, Sulfonated polyurethane ionomers in solution, Angew. Makromol. Chem., 1995, 231, 25-33, etc. 

Because of interactions between the chains, the polyurethane ionomers are similar in properties to crosslinked elastomers. In solution they are strongly associated. 

Zhu, Y., Hu, J., and Yeung, K. (2009) Effect of soft segment crystallization and hard segment physical crosslink on shape memory function in antibacterial segmented polyurethane ionomers. Acta Biomaterialia, 5, 3346-3357. 

Pig. 16. Prepolymer-mixing Process for Polyurethane ionomer Dispersion... 

The general formula of an emulsified polyurethane or aqueous dispersion used for adhesive purposes is shown in Fig. 8.11. Aqueous polyurethane dispersions usually have 40% solids of a thermoplastic type (for aqueous inertness), aliphatic diisocyanate polymer (for light stability) and an anionic surfactant is used. However, if a polyurethane ionomer is prepared this does not contain added emulsifier, the polyurethane itself having its own emulsifier function. The incorporation of this function in the polyurethane chains as (a) sodium sulphonate or (b) sodium carboxylate groups is seen in Fig. 8.11. 

The strong stabilizing effect that polyurethane ionomers have on appropriately structured non-ionic polyurethanes, due to the formation of associated compounds, results in individual spherical particles instead of large jelly-like precipitations. This occurs when water is added to organic solutions of polyurethanes which contain 0 5-3% ionomers. 

Product before Non-ionic NCO Polyurethane ionomers Ionic biuret-... 

End-product Polyurethane-urea Polyurethane ionomer, po ly u ret ha n e-u rea ionomers Polyurethane-biuret ionomers... 

The thickening of SMC can be accelerated using hydroxy-terminated im-saturated polyesters in conjimction with isocyanate-terminated prepolymers. Polyurethane ionomer-based sizings for glass fibers used in RRIM applications are also known. 

Ding YS, Register RA, Yang C, Cooper SL. Synthesis and characterization of sulphonated polyurethane ionomers based on toluene diisocyanate. Polymer 1989 30(7) 1204-12. 

Zhao W, Zhang G, Jiang L, Lu T, Huang X, Shen J. Novel polyurethane ionomer nanoparticles displayed a good biosensor effection. Colloids SurfB Biointerfaces 2011 88 78-84. 

Dickinson RB, Nagel JA, Proctor RA, et al. Quantitative comparison of shear-dependent Staphylococcus aureus adhesion to three polyurethane ionomer analogs with distinct surface properties. J Biomed Mater Res Angast 1997 36(2) 152-62. 

Zhu, Y, Hu, J., Choi, K. F., Yeung, K. W., Meng, Q., Chen, S. (2008a) Crystallization and melting behavior of the crystalline soft segment in a shape-memory polyurethane ionomer, J. Appl. Polym. Sci., 107, 599-609. 

Piticescu, R. M., L. M. Popescu, and T. Bimiiana. 2012. Composites containing hydroxyapatite and polyurethane ionomers as bone substitution materials. Dig. J. Nanomater. Biostruct. 7 477 85. 

---