Sequential IPNs properties

IPNs are also attractive for development of materials with enhanced mechanical properties. As PDMS acts as an elastomer, it is of interest to have a thermoplastic second network such as PMMA or polystyrene. Crosslinked PDMS have poor mechanical properties and need to be reinforced with silica. In the IPNs field, they can advantageously be replaced by a second thermoplastic network. On the other hand, if the thermoplastic network is the major component, the PDMS network can confer a partially elastomeric character to the resulting material. Huang et al. [92] studied some sequential IPNs of PDMS and polymethacrylate and varied the ester functionalities the polysiloxane network was swollen with MMA (methyl methacrylate), EMA (ethyl methacrylate) or BuMA (butyl methacrylate). Using DMA the authors determined that the more sterically hindered the substituent, the broader the damping zone of the IPN (Table 2). This damping zone broadness was also found to be dependant on the PDMS content, and atomic force microscopy (AFM) was used to observe the co-continuity of the IPN. 

As can be seen from all of these works, sequential IPNs have been extensively used with silicone with various crosslinking reactions and polymers. As a result, attention must be paid to the influence of processing conditions, of the chemical nature of components (silicone and the other polymer), of the evolution of the material at each step of the IPN synthesis etc. Depending on the mastering of these parameters, reactivity, morphology and entanglement can be controlled and consequently targeted properties can be reached. 

There are at least four general types of combinations of crosslinked (x) and linear (1) polymers in a two-component system both components crosslinked (xx), one or the other component crosslinked (lx or xl), and both components linear (11). Where at least one of the components has been polymerized in the presence of the other, the xx forms have often been called interpenetrating polymer networks (IPN), the lx and the xl forms termed "semi-IPNs", and the last, linear or in situ blends. There are also a number of ways in which the components can be formed and assembled into a multicomponent system. Sequential IPNs are prepared by swelling one network polymer with the precursors of the second and polymerizing. Simultaneous IPNs are formed from a mixture of the precursors of both components polymerization to form each component by independent reactions is carried out in the presence of the other precursors or products. Usually, the simultaneous IPNs that have been reported are extremes in the component formation sequence the first component is formed before the second polymerization is begun. Sequential IPNs and simultaneous IPNs of the same composition do not necessarily have the same morphology and properties. 

For sin s, monomer II or (prepolymer II) is added before step (b). Thus to a greater or lesser extent, the two networks are formed simultaneously. Network I chains are stretched and diluted by network II in a sequential IPN, but only diluted in an SIN, altering many morphological and physical properties. Of course it is required that the two polymerizations be non-interfering reactions, such as by stepwise and chain kinetics. 

Let us consider the Young s modulus, E, of a sequential IPN having both polymers above their respective glass transition temperatures. A simple numerical average of the two network properties results in (21) ... 

Amongst the above mentioned compatibilization methods, the obtaining of IPNs and SIPNs often proved to be a promising and very efficient route. An IPN is a polymer alloy comprised of two or more chemically crosslinked polymers. The difference between polymer blends and IPNs is that the latter ones swell instead of dissolving in solvents and do not creep or flow. Types of IPNs include sequential, simultaneous, latex and gradient IPNs and may also be thermoplastic (i.e. when physical crosslinks are imphed). Thermoplastic IPNs behave as thermosets at ambient temperature, but usually flow when heated at certain temperatures, possess IPN properties and often exhibit dual phase behavior [1]. 

Further electron micrographs will be found elsewhere in this book, particularly in Chapter 2. Certainly not all of the possible IPN morphologies have been discovered yet. While equation (6.36) describes the phase domain size in sequential IPNs, the correlation between synthetic detail and morphology is still in its infancy. Nonetheless, the experimentally known morphologies provide an important link between synthesis and properties. 

While the dielectric properties of a polymer system clearly have engineering value, changes in dielectric behavior with composition yield fundamental information. The behavior of the dielectric loss factor, tan 5, for the polyurethane/polystyrene sequential IPN was investigated by Lipatov et al Employing a frequency of 300 Hz, they studied the effect of filler over the temperature range -130 to 20°C. In this temperature range, the polystyrene does not exhibit a maximum in tan S however, the polyurethane does, at a temperature just below 0°C. Figure 7.1 shows the effect of Aerosil content on the loss peak. For convenience, the maxima in tan 8 are collected in Table 7.1. 

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. 

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. 

G. M. Yenwo, J. A. Manson, J. Pulido, L. H. Sperling, A. Conde, and N. Devia, Castor Oil Based Interpenetrating Polymer Networks, Synthesis and Characterization, J. Appi Polym. ScL 21(6), 1531 (1977). Castor oil-urethane/PS sequential IPNs. Physical properties. 

Simultaneous and sequential IPNs based on various polymeric systems have been prepared using polydimethylsiloxane (PDMS) as the host network (3-8). These systems include poly(ether-urethane), polystyrene, poly(2,6-dimethyl-1,4-phenyleneoxide), polyacrylic acid, PDMS, polymethylmethacrylate, polyethylene oxide (PEO)... as the guest network. Some semi-interpenetrating networks (s-IPNs) based either on a linear polymer embedded in a polysiloxane network (5,9,10) or on a linear polysiloxane combined with a PEO network (8) have also been described. In some cases, PDMS has been replaced by polyaromatic siloxanes such as polydiphenyl or polymethylphenylsiloxanes (10-12). The focus of this paper concerns the preparation and properties of IPNs and s-IPNs based on polysiloxanes and poly(diethyleneglycol bis-allylcarbonate) (13,14). 

PVOH Poly(N- isopropyl acrylamide) Samples prepared by sequential IPN procedure hydrogel properties determined 189... 

The study of viscoelastic properties of sequential IPNs based on PU and styrene-DVB copolymer [192] has shown that increasing the content of the second network affects nonmonotonously the position and the shape of the curves of temperature dependence of the elastic characteristics. This dependence is shown in Figs. 36 and 37. The modulus diminishes only in a narrow... 

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). 

This is a theoretical study on the entanglement architecture and mechanical properties of an ideal two-component interpenetrating polymer network (IPN) composed of flexible chains (Fig. la). In this system molecular interaction between different polymer species is accomplished by the simultaneous or sequential polymerization of the polymeric precursors [1 ]. Chains which are thermodynamically incompatible are permanently interlocked in a composite network due to the presence of chemical crosslinks. The network structure is thus reinforced by chain entanglements trapped between permanent junctions [2,3]. It is evident that, entanglements between identical chains lie further apart in an IPN than in a one-component network (Fig. lb) and entanglements associating heterogeneous polymers are formed in between homopolymer junctions. In the present study the density of the various interchain associations in the composite network is evaluated as a function of the properties of the pure network components. This information is used to estimate the equilibrium rubber elasticity modulus of the IPN. 

Because the unique properties of IPNs arise from the intimate mixing of the component polymer systems, the synthetic methodology used to produce these materials is critical. Presently, there are three main routes utilized to produce IPNs simultaneous, sequential and latex. The method employed is determined by the component polymers selected, polymerization mechanisms, miscibility and the anticipated end use of the IPN. 

In our laboratory, much attention has been devoted to the investigation of in situ sequential polyurethane/poly(methyl methacrylate) interpenetrating polymer networks (SEQ PUR/PAc IPNs) (2- ) in which the elastomeric polyurethane network is completely formed in the presence of the methacrylic monomers before the onset of the radical copolymerization which leads to the second network. To each polymerization process corresponds a typical kinetics, which however is not completely independent from each other ( -8). The results obtained with such SEQ IPNs show that the properties do in... 

Das and coworkers studied the morphology and mechanical properties of NR/PMMA IPNs. Mathew studied solid NR and PS, intimately mixed by the sequential method of IPN synthesis. Semi-IPNs based on NR/PS where only the NR phase is crosslinked offer a binary polymer system network having the elastomeric properties of NR imparted to the hard brittle properties of PS. Schematically, the morphology of semi-IPNs can be represented as shown... 

The present chapter will review the pH/temperature-sensitive properties of novel PVA/PAAc IPN hydrogels synthesized by a unique sequential method through UV irradiation and a freezing-thawing process. 

The authors of references [52, 53] have synthesized new sequential and in-situ sequential polycyanurate-polyurethane full IPNs and studied their structure-properties relationship. PCN based on l,l-bis-4-cyanatopheny 1-ethane (CPE) and CPU synthesized from an adduct of 1,1,1-trimethylolpropane with 2,4-toluene diisocyanate (1 3, mol) and poly(tetramethylene) glyeol were used as the components for IPNs. 

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