Poly /polystyrene IPNs

Figure 4. Transmission electron microscopy morphology of 50/50 cro55-poly( -butyl acrylate)-/ ler-croM-polystyrene IPNs as a function of network I cross-link density. (Reproduced with permission from ref. 18. Copyright 1982 Polymer Engineering and Science.)...

Table II. Experimental and theoretical domain sizes for cross-poly(n-butyl acrylate)-Inter-cross-polystyrene IPN s... 

Figure 7. High magnification scanning electron micrograph of decrosslinked and extracted cross-poly(n-butyl acrylate)-inter-cross-polystyrene IPN (80/20). The poly(n-butyl acrylate) phase was extracted. (Reproduced from Ref. 2 . Copyright 1982 American Chemical Society.)...

Fig. 5. Poly(n-butyl acrylate)/polystyrene IPN s, Phase domain size as a function of network I crosslink level. ...

Before leaving off the discussion of morphology, two additional structures must be presented in order to appreciate the range of materials that can be prepared. In Figure 6.2b a poly (ethyl acrylate)/polystyrene IPN was shown, polymerized in that order. Its topological designation may be written... 

V. Huelck, D. A. Thomas, and L. H. Sperling, Interpenetrating Polymer Networks of Poly(ethyl acrylate) and Poly(styrene-co-methyl methacrylate). I. Morphology via Electron Microscopy, Macromolecules 5(4), 340 (1972). Polyacrylate/Polystyrene IPNs. Polymethacrylate/Polyacrylate IPNs. Morphology via electron microscopy. 

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. 

J. K. Yeo, Controlled Variation of Poly(n-Butyl Acrylate)/Polystyrene IPN Morphology and Behavior, Ph.D. thesis, Lehigh University, in preparation. 

Polyurethane + polystyrene IPNs Poly(hydroxyethyl methacrylate) -I-poly(ethylene glycol) semi-IPN Polypropylene -I- polyacrylamide mix Poly(vinyl alcohol) -I- poly(2-hydroxyethyl methacrylate)... 

Siloxane containing interpenetrating networks (IPN) have also been synthesized and some properties were reported 59,354 356>. However, they have not received much attention. Preparation and characterization of IPNs based on PDMS-polystyrene 354), PDMS-poly(methyl methacrylate) 354), polysiloxane-epoxy systems 355) and PDMS-polyurethane 356) were described. These materials all displayed two-phase morphologies, but only minor improvements were obtained over the physical and mechanical properties of the parent materials. This may be due to the difficulties encountered in controlling the structure and morphology of these IPN systems. Siloxane modified polyamide, polyester, polyolefin and various polyurethane based IPN materials are commercially available 59). Incorporation of siloxanes into these systems was reported to increase the hydrolytic stability, surface release, electrical properties of the base polymers and also to reduce the surface wear and friction due to the lubricating action of PDMS chains 59). 

Figure 1. Morphology of sequential IPNs. (a) Crois-poly (ethyl acrylate)-m/er-crojs-polystyrene, showing typical cellular structure and a fine structure within the cell walls, (b) Cross-poly (ethyl acrylate)-/ /cr-cross-polystyrene-s/a/-(methyl methacrylate), showing smaller domain structure. PEA structure stained with OsO. (Reproduced from ref. 5. Copyright 1972 American Chemical Society.)...

Figure 12. Radius of poly(dimethyl slloxane) phase as a function of weight fraction In cross-poly(dimethyl slloxane)-Inter-cross-polystyrene sequential IPN s with three different crosslink densities of network I. Broken lines are theoretical values from...

Figure 17. Logarithmic dependence of the scattered light intensity, I, on time, t, for polystyrene-inter-cross-poly(butyl methacrylate) Semi-II IPN s. Registration anglel 8F) 10 ...

Examples of known phosphazene polymer blends are those in which phosphazenes with methylamino, trifluoroethoxy, phenoxy, or oligo-ethyleneoxy side groups form blends with poly(vinyl chloride), polystyrene, poly(methyl methacrylate), or polyethylene oxide).97 100 IPNs have been produced from [NP(OCH2CH2OCH2CH2OCH3)2] (MEEP) and poly(methyl methacrylate).101-103 In addition, a special type of IPN has been reported in which a water-soluble polyphosphazene such as MEEP forms an IPN with a silicate or titanate network generated by hydrolysis of tetraethoxysilane or tetraalkoxytitanane.104 These materials are polyphosphazene/ceramic composites, which have been described as suitable materials for the preparation of antistatic layers in the manufacture of photographic film. 

The only single phase, miscible IPNs reported are homopolymer IPNs, in which both networks are composed of the same polymer, and IPNs based on poly (2,6-dime thy Iphenylene oxide) (PPO) and polystyrene (PS) (18). The corresponding blend of the latter system is miscible and does not undergo thermally induced phase separation below its degradation temperature (19). 

Miscible blends of poly(vinyl methyl ether) and polystyrene exhibit phase separation at temperatures above 100 C as a result of a lower critical solution temperature and have a well defined phase diagram ( ). This system has become a model blend for studying thermodynamics of mixing, and phase separation kinetics and resultant morphologies obtained by nucleation and growth and spinodal decomposition mechanisms. As a result of its accessible lower critical solution temperature, the PVME/PS system was selected to examine the effects of phase separation and morphology on the damping behavior of the blends and IPNs. 

Since this paper will be restricted to sequential IPN s based on cross-poly butadiene-inter-cross-polystyrene. PB/PS, it is valuable to examine the range of possible compositions, see Figure 2 ( ). The PB/PS IPN polymer pair models high-impact polystyrene, and in fact, many of the combinations made are actually more impact resistant than the commercial materials. In general, with the addition of crosslinks, especially in network I, the phase domains become smaller. The impact resistance of high-impact polystyrene, upper left, is about 80 J/ra. In the same experiment, the semi-I IPN, middle left is about 160 J/m, and the full IPN, lower left, is about 265 J/m (g). Since the commercial material had perhaps dozens of man-years of development, and the IPN composition was made simply for doctoral research with substantially no optimization, it was obvious that these materials warranted further study. 

Other synthetic approaches to the kinetic problem have been taken. Variations in catalyst concentration for the formation of each component network from linear polyurethanes and acrylic copolymers have been used along with a rough measure of gelation time (5) to confirm the earlier (2-3.) results. Kim and coworkers have investigated IPNs formed from a polyurethane and poly(methyl methacrylate) (6) or polystyrene (7) by simultaneous thermal polymerization under varied pressure increasing pressure resulted in greater interpenetration and changes in phase continuity. In a polyurethane-polystyrene system in which the polyurethane was thermally polymerized followed by photopolymerization of the polystyrene at temperatures from 0 to 40 C, it was found (8.) that as the temperature decreased, the phase-... 

Recent research on IPN s has emphasized thermoplastic IPN s based on physical crosslinks, and the factors controlling the variation of domain sizes in sequential IPN s. Most recently, decross linking and extraction studies on sequential IPN s has led to an improved understanding of the dual phase continuity sometimes present in these materials. The sequential IPN system poly(n-butyl acrylate)/polystyrene is emphasized. 

Sequential PnBA/PS IPN s were prepared with various compositions. Thus, the material was rigid where polystyrene was the major component, and soft when poly(n-butyl acrylate) dominated, confirming previous studies by Yeo et al. >. ... 

When the process involves two competitive reactions, some people prrfer to call those modified polymers interpenetrated polymer networks (IPNs) [5]. The formation of a polyether-urethane network in a loosely crosslinked poly(methyl methacrylate) matrix to increase its toughness can serve as one of the examples. From a general point of view, the analysis of the reaction-induced phase separation is the same (perhaps more complex) for IPNs than for rubber-modified epoxies or for high-impact polystyrene. 

Addition of AN to a level of 40% (NBR-40) destroys the phase boundaries entirely, resulting in the microheterogeneous system shown in Figure 3.10. The phase domains ( 100 A) shown in Figure 3.10 are clearly smaller than the polymer molecules themselves, yet the material is not totally compatible. Only a few cases are known in which the phase division in blends is so fine such cases include the IPN s discussed in Chapter 8 and the poly(2,6-dimethyl phenylene oxide)/polystyrene blend described in Section 9.7.1. 

This paper reports what we believe to be the first true IPN, i.e., no grafting between polymers and a single phase morphology (i.e., complete chain entanglement). In order to achieve this, pol3nners of known compatibility were used. Thus, IPN s, pseudo-IPN s (PDIPN s - only one polymer crosslinked), and linear blends of polystyrene (PS), and poly(2,6-dimethyl-l,4-phenylene oxide) (PPO) (whose compatibility has been reviewed elsewhere (14)) were prepared by the simultaneous interpenetrating network (SIN) technique. The polystyrene was crosslinked by incorporating divinylbenzene. Several methods have been reported to synthesize... 

Here, two polymers are caused to form one network through conterminous junctions of the ends of the polystyrene to the poly(vinyl trichloroacetate). An IPN of two different polymers is... 

In order to synthesize the IPN, the urethane elastomer was swelled with styrene containing 0.4% benzoin as initiator and 1% divinylbenzene (DVB) as crosslinker. Polymerization of the styrene was carried out by ultraviolet radiation at room temperature for 24 hr. The corresponding castor oil-poly ester/polystyrene SINs are discussed in Section 5.5. 

Figure 6.2. Electron micrographs of IPN s of (a) 75/25 poly(ethyl acrylate)/poly(methyl methacrylate), and (b) 50/50 poly (ethyl acrylate)/polystyrene. A small amount of butadiene was copolymerized with the poly(ethyl acrylate) to aid in osmium tetroxide staining.

In one of the few studies that employed more than one instrument to study the Tg s of IPNs and related materials, Kim et combined DSC and torsional pendulum to study a series of SINs. In Table 6.9, polyurethane is the low Tg network and poly(methyl methacrylate) or polystyrene is the high Tg network. Semi-SINs (Kim etal. prefer the term pseudo instead of semi ) and chemical blends are also shown. 

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