Networks of polyurethanes

K.H. Hsieh, J.S.Tsai, K.W.Chang (1991). Interpenetrating Polymer Network of Polyurethane and Unsaturated Polyester. Journal of Materials Science, Vol. 26., pp. 5877-5882. 

T. Nakamura, Preparation Techniques for Interpenetrating Polymer Networks of Polyurethanes, Purasuchikkusu 27(7), 50 (1976). Review of polyurethane-based IPNs. 

V. F. Rosovizky, M. Ilavsky, J. Hrouz, K. Dusek, and Yu. S. Lipatov, Viscoelastic Behavior of Interpenetrating Networks of Polyurethane and Polyurethane Acrylate, /. AppL Polym. ScL 24, 1007 (1979). SINs of polyurethane diacrylate and polyurethane. Swelling, mechanical, and optical properties. Interfacial layer interpretation. 

Vatalis A, Delides C, Grigoryeva O, Sergeeva L, Brovko A, Zimich O, Shtompel V, Georgoussis G and Pissis P (2000) Thermoplastic apparent interpenetrating polymer networks of polyurethane and styrene/acrylic acid copolymer obtained by melt mixing. Structure-property relationships, Polym Eng Sci 40 2072-2085. 

Pandit S B and Nadkarni V M (1994) Sequential interconnected interpenetrating polymer networks of polyurethane and polystyrene. 1. S5mthesis and chemical structure elucidation, Macromolecules 27 4583-4594. 

Valero, M.E, Pulido, J.E., Ramirez, A., Cheng, Z., 2009. Simultaneous interpenetrating networks of polyurethane from pentaerythritol-modified castor oil and polystyrene structure-property relationships. 1. Am. Oil Chem. Soc. 86, 383-392. 

Hyperbranched polyurethanes are constmcted using phenol-blocked trifunctional monomers in combination with 4-methylbenzyl alcohol for end capping (11). Polyurethane interpenetrating polymer networks (IPNs) are mixtures of two cross-linked polymer networks, prepared by latex blending, sequential polymerization, or simultaneous polymerization. IPNs have improved mechanical properties, as weU as thermal stabiHties, compared to the single cross-linked polymers. In pseudo-IPNs, only one of the involved polymers is cross-linked. Numerous polymers are involved in the formation of polyurethane-derived IPNs (12). 

Over the years many blends of polyurethanes with other polymers have been prepared. One recent example is the blending of polyurethane intermediates with methyl methacrylate monomer and some unsaturated polyester resin. With a suitable balance of catalysts and initiators, addition and rearrangement reactions occur simultaneously but independently to give interpenetrating polymer networks. The use of the acrylic monomer lowers cost and viscosity whilst blends with 20% (MMA + polyester) have a superior impact strength. 

Thermosets consist of a network of interconnected chains whose positions are fixed relative to their neighbors. Such polymers do not flow when heated. Instead, when exposed to high temperatures, thermosets degrade into char. Examples of thermosets include some polyurethanes and epoxy resins. 

Table IV. Shear modulus and Tg of polyurethane networks prepared from bulk reactios (29). G(298K) - shear modulus at 298K, (a) from uniaxial...

The deviations from Gaussian stress-strain behaviour for the tetrafunctional polyurethane networks of Figure 9 are qualitatively similar to these found for the trifunctional polyester networks (Z5), and the error bars on the data points for systems 4 and 5 in Figure 9 indicate the resulting uncertainties in Mc/Mc. It is clear that such uncetainties do not mask the increases in Mc/Mc with amount of pre-gel intramolecular reaction. 

Figure 4. Theoretical curves for reduced moduli Gd/RT (mol/cm3) of polyurethane networks from polyoxypropylene triols versus the gel fraction w . Value of A indicated. Networks from LHT-240. Continued.

Another approach was attempted by Seppala and Kylma who reported the synthesis of poly(ester-urethane)s by condensation of hydroxyl terminated tel-echelic poly(CL-co-LA) oligomers with 1,6-hexamethylene diisocyanate (Scheme 33) [94]. The diisocyanate acts as chain extender producing an increase in molecular weight of the preformed oligomers. The authors claim that some of the copolymers present elastomeric properties. Using a similar method. Storey described the synthesis of polyurethane networks based on D,L-LA, GA, eCL,... 

Figure 9. Reduced equilibrium modulus of polyurethane networks from POP trlols and MDI in dependence on the sol fraction. networks from POP triol Mjj - 708, o networks from POP triol Mjj = 2630. C-) calculated dependence using Flory junction fluctuation theory for the value of the front factor A indicated. (Reproduced from Ref. 57. Copyright 1982 American Chemical Society.)...

The Tg of polyurethanes crosslinked with aromatic isocyanates shows no difference between the PEG-extended and the CEHPL networks. The Tg values for both types of networks follow the same relationship. Networks without soft segment content generally have a higher Ttf than those with... 

Tuerker and Mavituna immobilized Trichoderma reesei within the open porous networks of reticulated polyurethane foam matrices. Growth pattern, glucose consumption, and cellulase production were compared with those of freely suspended cells. The method of immobilization was simple and had no detrimental effect on cell activity. Hundreds of similar projects could be cited. Not all rated the use of polymethane as the preferred technique. If a statistical analysis were conducted on aU the immobilization literature, we are sure that no single technique would be dominant. However, the combination of ease of immobilization, cost of materials, flow-through properties, control of flux rate through the immobilizing membrane, high surface-to-volume ratio, and other factors make polymethane a viable substratum for the continuous production of proteins. 

Table 1. Dependence of the kinetic parameters of the reaction, the structural parameters of the network and the physico-mechanical properties of polyurethane elastomers on the molar fraction of OH groups in the monofunctional reagent21...

Blokland, R. Elasticity and structure of polyurethane networks. Rotterdam Universitaire Pers 1968. 

Figure 2.10. Temperature increase in adiabatic polymerization of polyurethane accompanied by the formation of interpenetrating networks in the polyurethane-unsaturated polyester system.

In discussing the formation of interpenetrating networks, we may reasonably assume as a first approximation that the synthesis of each component occurs irrespective of the others, and that the kinetics of the process is determined by the concentration of one or another component. However, this is a rather rough approximation, which is more or less valid at low concentrations of the polyurethane component. As was shown before,51 when the content of polyurethane exceeds 50%, its network begins to work as a cage, preventing polyester formation because the primary polyurethane network hampers diffusion of the ester. This means that in such systems, mutual interference of the components occurs even in the absence of chemical interactions between them. 

Fig. 6.3 shows the empirical Yg values of the different series of condensation polymers characterised by their functional groups as a function of the number of the CH2 groups in the structural unit (Nch2)- It is evident that for all series, except the polyamides, polyurethanes and polyurea s, the slope of the lines is constant, viz. 2.7, the increment of the CH2 group (Fig. 6.3a). Only for the polymers mentioned - all containing hydrogen bonding groups - the slope is 4.3. Networks of inter-molecular hydrogen bonds obviously cause an apparent increase of the CH2 increment from 2.7 to 4.3 (Fig. 6.3b).

Blokland R, "Elasticity and Structure of Polyurethane Networks", Thesis, Delft University of Technology, 1968. Blokland R and Prins W, J Polym Sci (A2) 7 (1969) 1595. 

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