Formation of two-phase morphologies

More recently, St. Clair and co-workers176) reported the use of aromatic amine terminated polydimethylsiloxane oligomers of varying molecular weights in an effort to optimize the properties of LARC-13 polyimides. They observed the formation of two phase morphologies with low (—119 to —113 °C) and high (293 to 318 °C) temperature Tg s due to siloxane and polyimide phases respectively. The copolymers were reported to have improved adhesive strengths and better thermal stabilities due to the incorporation of siloxanes. 

In most of the studies discussed above, except for the meta-linked diamines, when the aromatic content (dianhydride and diamine chain extender), of the copolymers were increased above a certain level, the materials became insoluble and infusible 153, i79, lsi) solution to this problem with minimum sacrifice in the thermal properties of the products has been the synthesis of siloxane-amide-imides183). In this approach pyromellitic acid chloride has been utilized instead of PMDA or BTDA and the copolymers were synthesized in two steps. The first step, which involved the formation of (siloxane-amide-amic acid) intermediate was conducted at low temperatures (0-25 °C) in THF/DMAC solution. After purification of this intermediate thin films were cast on stainless steel or glass plates and imidization was obtained in high temperature ovens between 100 and 300 °C following a similar procedure that was discussed for siloxane-imide copolymers. Copolymers obtained showed good solubility in various polar solvents. DSC studies indicated the formation of two-phase morphologies. Thermogravimetric analysis showed that the thermal stability of these siloxane-amide-imide systems were comparable to those of siloxane-imide copolymers 183>. 

Tough, transparent, heat and flame resistant, multiblock (bisphenol fluorenone carbonate) (BPF)-dimethylsiloxane copolymers have been synthesized by interfacial polycondensation of phosgene with various mixtures of BPF end-capped siloxane oligomers and free BPF or its monosodium salt 232). Siloxane content of the copolymers were varied between 7 and 27%. Presence of two Tg s, one below —100 °C and the other as high as 275 °C, showed the formation of two-phase morphologies. 

Nauman and He (2001) considered the modeling of the formation of two-phase morphologies by the spinodal decomposition of the initially homogeneous polymer/polymer or polymer/solvent mixture that was thermally quenched into a two-phase region. Let us outline their modeling approach. 

Polymerization in such systems is based on the reaction of isocyanate with hydroxyl groups to form the urethane linkage-OrganometaI Iic compounds (especially organotin) are often used to catalyze this reaction in commercial applications such as Reaction Injection Molding. Formation of elastomers with good mechanical properties is dependent on both reaction kinetics and development of two phase morphology. 

The morphology of the internal oxidation zone and stabihty of transformation front were studied in [29]. Solid-state reactions with formation of two-phase zones were analyzed in [3, 30, 31]. 

A two-phase zone is formed if in some layer Vap (see illustration for mode III in Figure 10.2) the particles of both phases are in equilibrium. Here we should introduce the notion of volume fraction of phases, which is the main parameter when describing modes with formation of two-phase zones. However, to fuUy describe the case, one needs to know both the volume fraction of phases and the contact zone morphology, which cannot be predetermined. So far, there are no criteria for choosing the morphology of the two-phase zone in the general case. 

Since the start of modern interpenetrating polymer network (IPN) research in the late sixties, the features of their two-phased morphologies, such as the size, shape, and dual phase continuity have been a central subject. Research in the 1970 s focused on the effect of chemical and physical properties on the morphology, as well as the development of new synthetic techniques. More recently, studies on the detailed processes of domain formation with the aid of new neutron scattering techniques and phase diagram concepts has attracted much attention. The best evidence points to the development first of domains via a nucleation and growth mechanism, followed by a modified spinodal decomposition mechanism. This paper will review recent morphological studies on IPN s and related materials. 

Figure 3.16 Schematic illustration of mechanism of dual phase morphology formation, (a) bimodal UCST (b) two step temperature quenching in polymer blend...

We observed some differences in morphology between the samples prepared by these two ways. For the systems obtained in situ the formation of NiO phase proceeded both on the surface of the spheres of the silicate and inside its pores. The composite material obtained by the second (two-step) way differed from the in situ obtained material by preferable incorporation of the NiO inside mesoporous and nanotubes of the Ti-silicate (Fig. la). It is likely that microemulsion provides a uniform distribution of the chelated nickel ions Inside the micelles over the total surface of the silicate, whereas suspension guarantees higher completeness of a transfer and concentration of the NiO crystallites inside the pores of the silicate. 

PUs comprise a polyether, or polyester soft segment, and a diisocyanate-based hard segment. This can be characterized by a two-phase morphology, which is due to the fact that the hard and soft phases are immiscible, leading to the formation of a hard-segment domain, a soft-segment matrix, and an ill-defined interphase. 

Iwa] Iwase, K., Okamoto, M., Amemiya, T., On the Formation of Two Liquid Layers in Copper-Iron Alloys , Sci. Rep. Tohoku Imp. Univ, 26, 618-640 (1938) (Phase Diagram, Phase Relations, Morphology, Experimental, 32)... 

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