Interpenetrating polymer network Glass transition

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. 

A random co-polymer or a blend of compatible polymers will have a single glass transition temperature intermediate between those of the two homopolymers. An example is shown in Figure 14 for nitrile-butadiene-rubber (22). The specific weight percents shown are those of commercial interest for NBR. In contrast, most polymer blends, graft and block copolymers, and interpenetrating polymer networks (IPN s) are phase separated (5) and exhibit two separate glass transitions from the two separate phases. Phase separated systems will not be considered here. 

The second growing trend is the impact modification of polyolefin blends using styrenic block copolymers, which are known to be clear, strong, have low glass transition, compatible with PP, form interpenetrating polymer networks, and very efficient in contrast to maleic anhydride-grafted polyolefins. 

If the domain sizes are small, only a veiy broad glass transition of the interpenetrating polymer network ean be observed that stretches across the range between the two polymers. In contrast to this, two distinct glass transitions are found when the domains are larger and the two polymers are better separated. In many cases, the two or more polymers of the interpenetrating network form phases that are continuous on a macroscopic scale. 

A. FIPN s, PDIPN s and linear blends of poly(2,6-dimethy1-1,4-phenylene oxide) and polystyrene all exhibited single phase behavior as evidenced by glass transition analysis and electron microscopy. Thus, for the first time, true interpenetrating polymer networks have been produced, i.e., homogeneous morphology with little or no possibilities of covalent bonds between the component pol3nners. 

Characterisation of Glass Transition Behaviour in Interpenetrating Polymer Networks The multi-phase nature of IPNs results in complicated glass transition behaviour [101]. Figure 3.46 shows that heat capacity changes with temperature for a series 60 40 polyurethane (PU)/ polystyrene (PS) IPNs (see Table 3.5 for the compositional details) [131,132]. It is, however, not possible to obtain much detailed information from these heat capacity signals. 

A. J. Curtius, M. J. Covitch, D. A. Thomas, and L. H. Sperling, Polybutadiene/Polystyrene Interpenetrating Polymer Networks, Polym. Eng. Sci. 12(2), 101 (1972). Polybutadiene/Polystyrene Network. Interpenetrating polymer network. Impact resistance and glass transition studies. 

H. L. Frisch, K. C. Frisch, and D. Klempner, Glass Transition of Topologically Interpenetrating Polymer Networks, Polym. Sci. 14(9), 646 (1974). Topological IPN. Glass Transitions. Polyurethane-based SIN. 

S. C. Kim, D. Klempner, K. C. Frisch, and H. L. Frisch, Polyurethane Interpenetrating Polymer Networks II. Density and Glass Transition Behavior of Polyurethane-Poly(methyl methacrylate) and Polyurethane-Polystyrene IPNs, Macromolecules 9(2), 263 (1976). Polyurethane/Polymethacrylate SIN Polystyrene/Polyurethane SIN. Glass transition and density studies. 

L. H. Sperling, T. W. Chiu, and D. A. Thomas, Glass-Transition Behavior of Latex-Interpenetrating Polymer Networks Based on Methacrylic-Acrylic Pairs, J. Appl. Polym. Sci. 17(8), 2443 (1973). Polyacrylate/polymethacrylate latex IPNs. Glass transition and damping behavior. 

L. H. Sperling, V. Huelck, and D. A. Thomas, Morphology and Mechanical Behavior of Interpenetrating Polymer Networks, in Polymer Networks Structure Mechanics and Properties, A. J. Chompff and S. Newman, eds.. Plenum, New York (1971). PEA/PS and PEA/PMMA sequential IPNs. Glass transitions. 

L. H. Sperling, J. A. Manson, G. M. Yenwo, A. Conde, and N. Devia, Castor Oil Based Interpenetrating Polymer Networks, Polym. Prepr. Am. Chem. Soc. Div. Polym. Chem. 16(2), 604 (1975). Castor oil-urethane/PS IPNs. Glass transitions and morphology. 

G. M. Yenwo, Synthesis, characterization, and Behavior of Interpenetrating Polymer Networks and Solution Graft Copolymers Based on Castor Oil and Polystyrene, Diss. Abstr. Int. B 37(11), 5788, (1977). Castor oil-urethane/PS sequential IPNs. Synthesis, morphology, glass transitions, mechanical properties. Ph.D. thesis. 

Interpenetrating Polymer Networks IV. Mechanical Behavior, Polym. Eng. Sci. 17(4), 251 (1977). Castor oil-urethane/PS IPNs. Glass transition and mechanical behavior ... 

Most polymer blends, as well as their related graft and block copolymers and interpenetrating polymer networks, are phase-separated (122) (see Section 4.3). In this case each phase will exhibit its own Tg. Rgure 8.29 (123,124) illustrates two glass transitions appearing in a series of triblock copolymers of different over l compositions, lie intensity of the transition, especially in the loss spectra "), is indicative of the mass fraction of that phase. 

In this case, an apparent activation energy is determined, and it has higher values than secondary relaxations 100-300 kJ/mol for urethane-soybean oil networks (Cristea et al. 2013), 200-300 kJ/mol for polyurethane-epoxy interpenetrating polymer networks (Cristea et al. 2009), more than 400 kJ/mol for semicrystalline poly(ethylene terephtalate) (Cristea et al. 2010), and more than 600 kJ/mol for polyimides (Cristea et al. 2008, 2011). The glass transition temperature is the most appropriate reference temperature when applying the time-temperature correspondence in a multifrequency experiment. The procedure allows estimation of the viscoelastic behavior of a polymer in time, in certain conditions, and is based on the fact that the viscoelastic properties at a certain tanperature can be shifted along the frequency scale to obtain the variation on an extended time scale (Brostow 2007 Williams et al. 1955). The shift factor is described by the Williams-Landell-Ferry (WLF) equation ... 

Frisch HL, Frisch KC, Klempner D. Glass transitions of topologically interpenetrating polymer networks. Polym Eng Sci 1974 14(9) 646-50. 

When the blend is prepared with a linear polymer and a crosslinkable monomer, a semi-interpenetrated polymer (semi-IPN) network is obtained and this concept has been applied to a linear heterocyclic polymer and a crosslinkable thermostable oligomer [111]. The linear heterocyclic polymers exhibit high glass transition temperatures, good fracture toughness (Table 6), but the high viscosity above Tg make them difficult to process. 

The highest sonic damping is obtained in transition zones. The glass transition can be used for this purpose if cross-linked polymers are applied, with a rubbery solid state until far above Tg. Very interesting work in this field was done by Sperling and his coworkers (1987,1988) who studied the damping behaviour of homopolymers, statistical copolymers and interpenetrating networks (IPNs) of polyacrylics, polyvinyls and polystyrenes. 

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