Polymers interpenetrating networks

An interpenetrating polymer network (IPN) (Sec. 2-13c-3) is obtained by carrying out a polymerization with crosslinking in the presence of another already crosslinked polymer [Klempner 

UPRs can form interpenetrating polymer networks (IPNs). High mechanical strength was achieved, if one of the components was a polyurethane [84]. Also hybrid networks consisting of UPRs and polyurethanes were investigated by many authors. In any case, an improvement of properties by incorporating polyurethanes into crosslinked UPR [24,85,86] was found. 

Polyurethane and UPR-hybrid IPN networks were studied by several authors [86-88]. The thermomechanical properties of the networks were investigated. Influence of hard domains on mechanical properties was the main factor studied [86]. DSC measurements were applied to evaluate the 

Type of SIN Composition [wt/wt] [°C] [°C] Tensile strength [MPa] Elongation Elastic at break modulus [%] [MPa]  

Although the elongation at break of SINs was seriously decreased, the BO-g-VER and 200-g-VER phases reinforced the PU phase. 

The inferior results obtained for the PU/390-VER systems were caused by the microphase separation of the 390-g-VER network. 

An interpenetrating polymer network (IPN) is defined as a material comprising two or more networks which are at least partly interlaced on a molecular scale, hut not covalently bonded to each other. These networks caimot he separated unless chemical bonds are broken. Two possible methods exist for preparing them, as follows  

An IPN has different properties from either a copolymer or a polymer blend. It may swell in solvents, but will not dissolve it will resist creep or flow to a greater extent than copolymers or blends. Some differences in the physical properties of IPNs compared with polymer blends can be seen in Table 10.3. The major reason for the differences in properties between polymer blends and IPNs is that the latter have greater adhesion and better mixing. 

The interconnection between the two different polymers can cause some essentially thermoplastic polymers to behave as thermosets when combined in an IPN. This arises because of chain entanglement between different polymers. The entanglements behave as crosslinks at lower temperatures but they can be broken by heat. 

The term IPN was first used in 1960 to describe the apparently homogeneous product obtained from styrene crosslinked with divinylbenzene. IPNs were prepared from this system by taking a crosslinked poly(styrene) network and allowing it to absorb a controlled amount of styrene and a 50% divinylbenzene-toluene solution containing initiator. Polymerisation of this latter component led to the formation of an IPN, the density of which was 

Since this pioneering work a number of IPNs have been prepared. Poly(styrene) has been used as the second network polymer in conjunction with several other polymers, including poly(ethyl acrylate), poly(n-butyl acrylate), styrene-butadiene, and castor oil. Polyurethanes have been used to form IPNs with poly(methyl methacrylate), other acrylic polymers, and with epoxy resins. 

It follows from. sections 3.5 and 3.7 that the conditions of the onivpha.se state (compatibility) of IPN and SIPN are more restricted in comparison with polymer networks and mixture s. On the other hand, chemical crosslinks hinder phase separation which, therefore, has to be realized on th( colloidal level of dispersion. As a rule, microphase separation begins to be observed even at the stage of polymerization and crosslinking of the second polymer. 

Superposition of proc( sses of different nature leads to a diverse iiiorphol gical pattern of polymer materials which, in turn, provides their wide technical applications. The seipiential th( rmodynamic d( scription of such systems presents significant difficulties one can test this with an example of the PIPN structure model from (Donalelly el al., 1977 Sperling, 1981). 

Morphologically, the turbidity spectrum method has great advantage.s to cliHrarteri/.e tlu microlieterogeneous structure of IPN and SIPN (see subsection 2.1.5) (Kleniii et al., 1977b). 

Simultaneous IPNs involve monomers or reactive oligomers and crosslinkers of two or more reactive systems. These systems are generally chosen such that the reaction of one component does not interfere with or is involved with the reactions of the second component. Otherwise, grafting reaction would compete with interlocking ring formation as the method of compatibilization. An example of a simultaneous IPN is the reaction of free radical polymers (such as polyacrylates) in the presence of condensation polymers such as polyurethanes, as has been the subject of many investigations [171-174]. A PU/PMMA simultaneous IPN exhibited transparency and showed only limited phase separation below 30% PMMA [171]. This IPN 

Vinyl ester/epoxy (50/50) simultaneous IPNs were prepared with styrene addition to crosslink the vinyl ester and aliphatic or cycloaliphatic diamines to crosslink the epoxy [176]. Single broad TgS were observed for the IPNs. Atomic force microscopy (AFM) showed compaction of the IPN structure with post-curing along with an increase in the Tg. Similar results were observed in unsaturated polyester/epoxy simultaneous IPNs, where miscibility was observed over the entire composition along with improved toughness [177]. 

Semi-IPNs involve one crosslinked polymer with a non-crosslinked polymer. Two variations of this class of IPNs involve  

Semi-IPNs include the early polymer blend of phenolic resin combined with natural rubber to yield improved toughness for phenolic based compositions. With the addition of sulfur, simultaneous IPNs have also been reported. The addition of engineering polymers (PSF, PES, PPO, PEI) to epoxy illustrates a more recent area of research, involving systems classified as semi-IPNs. The phase separation and morphology of PEI/epoxy semi-IPNs was reported by 

PU PMMA Simultaneous IPN prepared under high pressure increasing pressure decreased domain size 184 

In more recent work, Mandal and Mandal [382] described unique IPNs of P(Py) and poly(methyl acrylate) or poly(styrene-c( -butyl acrylate) which showed very low percolation thresholds for conductivity, ca. 0.023 volume fraction of P(Py). 

Define the terms Composite, Blend, Host Polymer, Matrix and Percolation Threshold. If the density of a host polymer matrix alone is 1.3 g/cc and 2.5 g/cc at atmospheric pressure and at 1 KBar respectively, what is the maximum possible Percolation Threshold, in w/w%, in this host polymer for a CP with density 1.25 g/cc Identify approximate percolation thresholds in all relevant figures cited in this chapter. 

Outline the five major types of synthesis of CP composites, and give one detailed example of each. Which are more likely to give each of the following monophasic blends CP coated nanospherules simple biphasic admixtures  

What kinds of characteristics and affinities (e.g. hydro(phil/phob)icity, void space) in a host polymer do you expect to be more important in determining sorption of FeClj and Fe(III)-Tosylate (as oxidant-cum-dopants) sorption of Py, Ani and 3-MeT monomers What physical parameters would govern sorption efficiencies  

200 mL of a FeClj solution in a hypothetical protic solvent has an redox potential of +0.4 V vs. SCE. Using the Nemst equation, compute the redox potential as the solvent slowly evaporates from the solution (e.g. at 100 mL, 50 mL, 10 mL and 2 mL). 

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Peroxides or other additives, eg, chlorinated paraffin, may also cause the thermoplastic resin to cross-link with the siloxanols. In this case, a tme interpenetrating polymer network forms, in which both phases are cross-linked. 

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). 

Where the polyurethane comprises <30% of the blend, the polyurethane remains in discrete droplets within the polyacetal matrix. In this range the particle size and particle size distribution of the elastomer particles are of importance. Where the elastomer component is in excess of 30%, interpenetrating polymer networks exist in the sense that there are two interpenetrating continuous phases (as opposed to two cross-linked interpenetrating polymer systems). 

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. 

Sheu and coworkers [111] produced polysty-rene-polydivinylbenzene latex interpenetrating polymer networks by the seeded emulsion polymerization of styrene-divinylbenzene in the crosslinked uniform polystyrene particles. In this study, a series of uniform polystyrene latexes with different sizes between 0.6 and 8.1... 

Interpenetrating Polymer Network (IPN) A subclass of PBs reserved for the mixture of two polymers where both components form a continuous phase and at least one is synthesized or crosslinked in the presence of the other [8]. 

L. H. Sperling, Interpenetrating Polymer Networks and Related Materials, Plenum Press, New York (1981). 

To prepare an interpenetrating polymer network (IPN) structure, PU networks having ACPA units were immersed with MMA and polymerized. PU-PMMA semi-lPN thus formed was given improved interfacial strength between PU and PMMA phases and showed flexibility with enforced tear strength [65,66]. 

The advances in polymer blending and alloying technology have occurred through three routes (1) similar-rheology polymer pairs, (2) miscible polymers such as polyphenylene oxide and polystyrene, or (3) interpenetrating polymer networks (IPNs). All these systems were limited to specific polymer combinations that have an inherent physical affinity for each other. However with... 

IPNs are found in many applications though this is not always recognised. For example conventional crosslinked polyester resins, where the polyester is unsaturated and crosslinks are formed by copolymerisation with styrene, is a material which falls within the definition of an interpenetrating polymer network. Experimental polymers for use as surface coatings have also been prepared from IPNs, such as epoxy-urethane-acrylic networks, and have been found to have promising properties. 

The ultimate goal of bulk modification endows with the polymer-specific surface composition or a specific property for a given application. The bulk modification can be classified into blending, copolymerization, interpenetrating polymer networks (IPNs), etc. 

Radio-chemical graft copolymerization with good efficiency on halogenated polyolefins has been carried out by contacting the substrate with monomer (styrene) vapor [158,159]. Interpenetrating polymer network (IPN) could be made by grafting the monomers on preirradiated substrates... 

Davis, P. A. Nicolais, L., Ambrosio, L., and Huang, S. J., Synthesis and characterization of semi-interpenetrating polymer networks of poly(2-hydroxyethyl methacrylate) and poly(capro-lactone), Polym. Mater. Sci. Eng., 56, 536-540, 1987. 

The use of interpenetrating donor-acceptor heterojunctions, such as PPVs/C60 composites, polymer/CdS composites, and interpenetrating polymer networks, substantially improves photoconductivity, and thus the quantum efficiency, of polymer-based photo-voltaics. In these devices, an exciton is photogenerated in the active material, diffuses toward the donor-acceptor interface, and dissociates via charge transfer across the interface. The internal electric field set up by the difference between the electrode energy levels, along with the donor-acceptor morphology, controls the quantum efficiency of the PV cell (Fig. 51). 

Polymers with Spatially Graded Morphologies Designed from Photo-Induced Interpenetrating Polymer Networks (IPNs)... 

Interpellet porosity, 25 294 Interpenetrated wall matrix, in hollow-fiber membranes, 76 15 Interpenetrating polymer networks (IPNs), 79 834... 

Semi-gloss alkyd paint formulation, 18 6 It Semi-interpenetrating network (IPN) approaches, 10 436 Semi-IPN (interpenetrating polymer network) hydrogels, 13 733 Semikilled steels, 23 291 Semimoist pet foods, 10 849 Semipermanent cells, 14 228 Semiphorone, 14 583 Semiportable mri system, 23 860-861 Semiregenerative reforming operations, 25 166... 

Klempner, D., Frisch, K. C., Eds. Advances in Interpenetrating Polymer Networks Technomic Publishing Lancaster, PA, 1994 Vol. IV. 

Frisch, H. L. Du, Y. Schultz, M. Interpenetrating Polymer Network (IPN) Materials. In Polymer Networks. Principles of Their Formation Structure and Properties-, Stepto, R. F. T., Ed. Blackie Academic London, 1998 pp 186-214. 

So, interpenetrating polymer networks (IPNs) with a weight ratio of vinyl alcohol residue in PVA to acrylic acid monomer 4 6 exhibit positive swelling changes with temperature but IPNs 6 4 evidence negative swelling ones [48],... 

Formation of industrially usable interpenetrating polymer networks derived from caster oil is described in Chapter 27. Products can vary from soft and flexible to hard and tough. 

Materials known as interpenetrating polymer networks, IPN s, contain two or more polymers, each in network form (6 9), A practical restriction requires that at least one of the polymer networks has been formed (i.e. polymerized or crosslinked) in the immediate presence of the other. Two major types of synthesis have been explored, both yielding distinguishable materials with different morphologies and physical properties. 

Simultaneous Interpenetrating Networks. An interpenetrating polymer network, IPN, can be defined as a combination of two polymers in network form, at least one of which was polymerized or synthesized in the presence of the other (23). These networks are synthesized sequentially in time. A simultaneous interpenetrating network, SIN, is an IPN in which both networks are synthesized simultaneously in time, or both monomers or prepolymers mixed prior to gelation. The two polymerizations are independent and non-interfering in an SIN, so that grafting or internetwork crosslinking is minimized (23-26). 

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