Simultaneous IPNs

Silicone co-polymer networks and IPNs have recently been reviewed.321 The development of IPNs is briefly described, and the definitions of the main (non-exclusive) classes of the IPNs are cited. Examples of latex IPNs, simultaneous and sequential IPNs, semi-IPNs, and thermoplastic IPNs are provided. The use of silicone-silicone IPNs in studies of model silicone networks is also illustrated. Networks in which siloxane and non-siloxane components are connected via chemical bonds are considered co-polymer networks, although some other names have been applied to such networks. Today, some of the examples in this category should, perhaps, be discussed as organic-inorganic hybrids, or nanocomposites. Silicone IPNs are discussed in almost all of the major references dealing with IPNs.322-324 Silicone IPNs are also briefly discussed in some other, previously cited, reviews.291,306... 

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. 

Simultaneously IPN Simultaneously IPN system is formed by the simultaneous polymerization of both components of polymer [69]. 

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). 

The first type, termed sequential IPN s, involves the preparation of a crosslinked polymer I, a subsequent swelling of monomer II components and polymerization of the monomer II in situ. The second type of synthesis yields materials known as simultaneous interpenetrating networks (SIN s), involves the mixing of all components in an early stage, followed by the formation of both networks via independent reactions proceeding in the same container (10,11). One network can be formed by a chain growth mechanism and the other by a step growth mechanism. 

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). 

Figure 1. The synthesis of sequential IPN above and simultaneous interpenetrating networks, SIN, below. For the synthesis of SIN, two different reactions operate simultaneously such as condensation polymerization and addition polymerization. Reproduced with permission from Ref. 23. Copyright 1981, Plenum Publishing.

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. 

Simultaneous IPN. According to the statistical theory of rubber elasticity, the elasticity modulus (Eg), a measure of the material rigidity, is proportional to the concentration of elastically active segments (Vg) in the network [3,4]. For negligible perturbation of the strand length at rest due to crosslinking (a reasonable assumption for the case of a simultaneous IPN), the modulus is given by ... 

Because v, is a fractional quantity. Equation 18 always predicts modulus values larger than the corresponding expression for a simultaneous IPN(Equation 13). For the special case of a network with no defects or trapped entanglements (i)) 1, "), an earlier... 

Interpenetrating polymer networks are defined in their broadest sense as an intimate mixture of two or more pol)Mners in network form [1,2]. Ideally, they can be synthesized by either swelling the first crosslinked polymer with the second monomer and crosslinker, followed by in-situ polymerization of the second component (sequential IPN s) or by reacting a pair of monomers and crosslinkers at the same time through different, non-interfering reaction mechanisms, simultaneous interpenetrating networks, SIN s. In fact, many variations of these ideas exist in both the scientific and the patent literature. In any case, at least one of the two components must have a network structure, as an IPN prerequisite. ... 

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. 

IPNs can be prepared by either the "sequential" or the "simultaneous" technique. IPNs synthesized to date exhibit varying degrees of phase separation depending primarily on the compatibility of the component polymers (4-7). 

This paper describes two types of novel urethane-acrylic IPNs for coating applications. The mode of preparation used was the simultaneous or SIN technique. In order to examine the effect of the soft segment on the properties and morphology of IPN coatings, the pendant hydroxy group in the hydroxyethylacrylate-butylmethacrylate copolymer was reacted with caprolactone to increase the chain length of the pendant hydroxy group. 

Note 2 An IPN may be further described by the process by which it is synthesized. When an IPN is prepared by a process in which the second component network is formed following the completion of formation of the first component network, the IPN may be referred to as a sequential IPN. When an IPN is prepared by a process in which both component networks are formed concurrently, the IPN may be referred to as a simultaneous IPN. 

We synthesized [13] IPNs composed of polyethylene oxide) (PEO) (polymer A) and poly(N-acryloylpyrrolidine) (PAPy) (polymer B). The IPN was synthesized by simultaneous crosslinked polymerization of APy and PEO. The overall reaction scheme for IPN synthesis by radical polymerization for APy (polymer A) and addition polymerization for PEO (polymer B) is shown in Fig. 3. This pair shows simple coacervation behavior in water. The IPN is constructed from PEO and PAPy networks as shown in Fig. 4. Chemically independent networks of polymer A and polymer B are interlocked and macroscopic phase separation in water swollen states is avoided. 

Physical hybrids containing silica and polymer are typically interpenetrating networks (IPNs). They can be subdivided into simultaneous or sequential IPNs. The terminology of... 

IPNs are fabricated along several general pathways. In one, a linear or slightly crosslinked polymer is swollen by a monomer, followed by polymerization of the monomer. Another method is the utilization of simultaneous graft polymer-... 

Semi-IPNs are obtained by simultaneous polymerization of styrene and polycyclo-trimerization of BPA/DC (Sect. 2) [52, 53], IPNs consisting of two separate networks are formed, if unsaturated monomers with two or more polymerizable double bonds are used. 

Heat resistant IPN systems were obtained by simultaneous radical polymerization of divinylbenzene with benzoyl peroxide as an initiator and Zn acetate as cyclotri-merization catalyst [122], Hot-curing composition contains BPA/DC, BMI, epoxide resin, Zn acetate and divinylbenzene [123]. Crosslinked compositions consisting of BPA/DC and BPA bis(vinylbenzyl) ether show Tg values above 240 °C [124]. 

Simultaneous IPN was obtained by dissolving BPA/DC in an unsaturated polyester resin (UPR) and crosslinking at elevated temperature using benzoyl peroxide and a zinc compound as cyclotrimerization catalyst. Prolonged post-curing at 180 °C was needed to reach elevated Tg values [132, 133],... 

The detection of the IPNS-activity was first described by Kupka et al. [53], this method is for simultaneous measurement of IPN and PEN. The assay contained ACV as substrate and DTT, FeS04, KCl, MgS04, ascorbic acid and TRIS/HCl as buffer. After a reaction time of 20 min, 25 °C the reaction was stopped with cool methanol. The determination of the PEN-concentration, which was created during the test, could be done by using a similar method as described in Sect. 2.3.1. 

An interpenetrating polymer network (IPN) consisting of an epoxy and an elastomer has been developed by Isayama.29 This is a two-component adhesive-sealant where the components are simultaneously polymerized. It consists of the MS polymer, developed in Japan by Kanegafuchi and commonly used in sealant formulations, with the homopolymerization of DGEBA using a phenol catalyst and a small amount of silane as a graft site to connect the MS polymer and epoxy homopolymer networks. 

First, PDMS network was combined to a cellulose acetate butyrate (CAB) network into an IPN architecture in order to improve the thermomechanical properties of PDMS network (Scheme 1). The linear CAB can be cross-linked through its free OH groups with a Desmodur N3300 pluri-isocyanate. The alcohol/isocyanate reaction is catalyzed by DBTDL leading to urethane cross-links. Simultaneously, PDMS oligomers must be cross-linked independently in order to form the PDMS network. In order to carry out independent cross-linking reactions. 

Similarly, the crosslinking operation C may be broadened by also considering that it represents the addition of a monomer capable of being crosslinked in a later reaction. For example, when one of the polymers is crosslinked (semi-IPN s), the picture becomes interesting. Assuming first that G12 is simultaneous with P2, as in Equation 7, a number of... 

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