Swelling polyurethane networks

The network polyurethane obtained by reacting a diisocyanate R(N=C=0)2 vvith pen-taerythritol C(CH20H)4 contains, according to an elemental analysis, 0.2% (w/w) nitrogen and has a density of 1.05 g/cm. The network polymer swells to 6 times its original volume when equilibrated with chlorobenzene (p= 1.10 g/cm, mol. wt. 

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. 

It was determined that a dense physical network having ciosslinking points forming hard domains is characteristic of segmented polyurethane ureas. This physical network limits swelling of SPUU in organic liquids that carmot dissolve hard domains. 

Network Synthesis (4) Solid MDI was weighed into a flask and an equivalent amount of polyol added. The mixture was heated to about 40°C to dissolve the MDI. The mixture was then cooled to room temperature and degassed for several minutes under vacuum in order to remove dissolved air. Catalyst was then added and the contents of the flask mixed under vacuum to ensure uniformity and then poured into a mold. All operations were carried out in a dry glove bag to minimize reaction with atmospheric water. The cross-linking process was also carried out in dioxane solution at 70% volume fraction of solids. Polyurethane networks with different crosslink densities were prepared by varying the ratio of difunctional and trifunctional polyols. All samples were extracted with dioxane to remove unreacted and uncrosslinked materialbefore swelling. 

Stress Relaxation Polyurethane networks were also polymerized in a mold with a cylindrical cavity. Uniform rings were cut from the cylinders and weighed. The cross sectional area was then derived from the sample diameter and polymer density and approximated 0.05 cm2. Stress relaxation was measured at several strains between 10 and 43% with an Instron tensile tester. During stress relaxation, the samples were immersed in dioxane and swelled to equilibrium. 

The Flory-Rehner equation (2,13) was used to interpret the swelling of the polyurethane networks in pure dioxane in order to calculate, the molecular weight between crosslinks. Here, we set qQ= 1 and x the network-solvent interaction parameter, constant and assumed equal to 0.35 (3). Networks with degrees of swelling (q ) of 6.41, 11 and 21.1 yielded Mc values of 7,700,... 

Figure 1. The degree of swelling fqj of polyurethane networks in dioxane vapor over polystyrene solutions of various volume fractions ( s).

Swelling of Polyurethane Networks over Polystyrene Solutions in Dioxane... 

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. 

Swelling of polyurethane networks. Proceeding from the general conception of the role of surfactants in the formation of the secondary structure of polyurethanes, studies of the influence of KEP-2 on the distribution of hydrogen bonds in polyurethane networks were required. The literature on the thermodynamic properties of polymer solutions and gels was searched and, in particular, the work of the authors of [117] is of direct interest in this context. This work... 

Figure 3.27 Dependence of equilibrium swelling on the solubility parameter in a number of solvents (I) diethyl ether (11) diethylene glycol diethyl ether (III) butyl acetate (IV) ethyl acetate (V) tetrahydrofdran (VI) dioxane. Polyurethane networks based on PTMG and PPG mixture without additives (4) and containing various KEP-2 mass fractions (1) 1.5 x 10 (3) 5 X 10- (2) 7.5 X 10- (5) 1.5 x 10 ...

Let us consider the data from swelling studies in polyurethanes based on two incompatible ohgoglycols. Figure 3.28 shows dependences found for poljmier networks synthesized from PPG and ODA... 

As a result of increase in molecular weight of prepolymer from 1400 (SPU-1) to 2100 (SPU-4) or partial replacement of MOCA by polypropylene oxide diol (SPU-2) the amount of hard segments and common density of network decreased. But the equilibrium swelling in plasticizers increases (Table 10.15). The SPU modulus of elasticity decreases. The increase in the number of oxygen atoms in a polyether chain (SPU-4) results in decreased swelling in less polar plasticizers (TO, DOS, DOP). The elasticity modulus of the material in these plasticizers varies slightly. A large value for polyurethane SPU-5... 

Yu. S. Lipatov, L. V. Karabanova, T. S. Khramova, and L. M. Sergeeva, Study of Physicochemical Properties of Interpenetrating Polyurethane and Poly(urethane acrylate) Polymer Networks, Vysokomol. Soedin. Ser. A 20(1), 46 (1978). Thermodynamics and Swelling of IPNs and PU-based IPNs. 

Figure 3.1 The swelling coefficient, Q, reaches a maximum when the solubility parameter of the solvent nearly matches that of the polymer, for several cross-linked systems polyurethane ( ), polystyrene (A), and a polyurethane-polystyrene interpenetrating polymer networks ( ) (9). Solvents having solubility parameters near 2 x 10 (J/m ) will swell the IPN best.

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