Blends of Amorphous Polymers

In order to further highlight the capabilities of tapping mode AFM imaging for the structural elucidation of polymer blends, the morphology of an acrylonitrile- 

Studying other systems, Noland et al (1971) presented data based on differential thermal analysis (DTA), thermomechanical analysis, and dilatometry to show that mechanical blends of poly(methyl methacrylate) and poly(ethyl acrylate) are compatible with poly(vinylidene fluoride) 

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After having studied in our laboratory, polymer blends of amorphous polymers poly-c-caprolactone and poly (vinyl chloride) (1,2) (PCL/ PVC), blends with a crystalline component PCL/PVC (3,4), poly(2,6-dimethyl phenylene oxide) (PPO) with isotactic polystyrene (i-PS) (5) and atactic polystyrene (a-PS) with i-PS (6), we have now become involved in the study of a blend in which both polymers crystallize. The system chosen is the poly(1,4-butylene terephthalate)/poly(ethylene terephthalate) (PBT/PET) blend. The crystallization behavior of PBT has been studied extensively in our laboratory (7,8) this polymer has a... 

Polymer blends, including blends of amorphous polymers, amorphous and semicrystalline polymers, semicrystalline polymers, and rubber blends... 

There are only a few compatible polymer blends without a pronounced morphology, such as PS/PPO or SAN/PMMA. The morphology of the other blends of amorphous polymers is determined by their incompatibility and processing conditions. Occasionally it can be difficult to reveal the morphology of an amorphous polymer blend in detail if there are no clear interface boundaries or the components show no different staining abilities in such cases some special preparation techniques are used. 

Two-component one-phase systems (miscible blends of amorphous polymers)... 

Blends of amorphous polymers with crystaUine polymers (Fig. 6.3) also show differences between miscible and immiscible components. In this comparison, the crystaUine polymer has a lower Tg than the amorphous polymer and exhibits a crystalline modulus plateau between the Tg and the Tm- The phase separated blend shows both TgS, with a modulus plateau between... 

The rather unexpected properties described above seem to be peculiar to PVN, for none of the blends with polystyrene, poIy-4-vinylbiphenyl, and polyacenaphthylene contained significant amounts of amorphous PEO. The modulus curves for these systems are characteristic of blends of incompatible polymers. The photomicrograph in Figure 12 illustrates the different morphologies of PVB and PEO blends. The reason for the apparently different behavior for these polymers as compared with PVN is not yet understood. But there is strong evidence from dilute solution-studies that the conformational properties for these polymers differ markedly. 

As a route for improving the melt-elongational properties of semicrystalline polymers, Siripurapu et al. [7] proposed the blending of amorphous and semicrystalline blends of PS and PVDF nevertheless, their approach showed only limited success. In contrast, Reichelt et al. [29] successfully developed blends of HMS-PP and PP-fe-PE block copolymers. As could be shown, the melt strength increases with the HMS-PP content, while blends rich in HMS-PP also show the lowest densities. 

The phase behavior of polymer blends comprising amorphous polymers is experimentally well accessible in a window which is bounded at high temperatures by the thermal decomposition temperature of the polymer components and at low temperatures by the glass transition temperature of the system (cf. Fig. 1). Below the glass transition temperature the phase behavior can be estimated only tentatively. 

Wilkinson, S. P., et al., Reactive Blends of Amorphous Functionalized Engineering Thermoplastics and Bismaleimide/Diallyl Bisphenol A Resins for High Performance Composite Matrices, Polymer Preprints, vol. 33, no. 1, 1992, p. 425. 

Modulus-temperature behavior of amorphous polymers is also affected by admixture with plasticizers. These are the soluble diluents described briefly in Section 12.3.2. As shown in Fig. 11-11, the incorporation of a plasticizer reduces Tg and makes the polymer more flexible at any temperature above Tg. In polyfvinyl chloride), for example, T can be lowered from about 85°C for unplaslicized material to —30°C for blends of the polymer with 50 wt % of dioctyl phthalate plasticizer. A very wide range of mechanical properties can be achieved with this one polymer by variations in the type and concentration of plasticizers. 

Novel Composites from Blends of Amorphous and Semicrystalline Engineering Thermoplastics with Liquid-Crystalline Polymers... 

Grafting of functional side-groups without forming long polymer chains may be achieved in a similar way by the reaction of activated polymeric materials with low molecular weight compounds carrying functional groups of appropriate reactivity. The physical stabilization of unstable blends of amorphized starch with reactive plasticizers has been achieved by EB-irradiation [11 ]. 

The remainder of this chapter will focus on the thermal conductivities of amorphous polymers (or the amorphous phase, in the case of semicrystalline polymers). See Chapter 20 for a discussion of methods for the prediction of the thermal conductivities of heterogeneous materials (such as blends and composites) in the much broader context of the prediction of both the thermoelastic and the transport properties of such materials. 

Compatible Polyblends. When the polymeric materials are compatible in all ratios, and/or all are soluble in each other, they are generally termed polyalloys. Very few pairs of polymers are completely compatible. The best known example is the polyblend of polyCphenylene oxide) (poly-2,6-dimethyl-l,4-phenylene oxide) with high-impact polystyrene (41). which is sold under the trade name of Noryl. It is believed that the two polymers have essentially identical solubility parameters. Other examples include blends of amorphous polycaprolactone with poly(vinyl chloride) (PVC) and butadiene/acrylonitrile rubber with PVC the compatibility is a result of the "acid-base" interaction between the polar substituents (1 ). These compatible blends exhibit physical properties that are intermediate to those of the components. 

To be able to measure the osmotic pressure n, a semipermeable membrane that permits passage of the solvent molecules but not the solute molecules is needed. This can, in practice, be realized only when there is a large disparity between the sizes of the solute and solvent molecules, as in a solution of a polymer in a small-molecule solvent. However, the existence of osmotic pressure can be envisioned, at least mentally, with any kind of solution, such as a solution of two small-molecule liquids or a miscible blend of two polymers. Equation (6.6) is thus valid for any two-component (amorphous) system, as long as it is in equilibrium and classical thermodynamics is applicable to it. For applications to these general cases, it is more convenient if Equation (6.6) is reformulated in terms of the free energy of mixing and no explicit reference to osmotic pressure is made in it. 

As has already been stated, the verified possibility of extending the reduced variables principles to ABS resins makes it possible to treat these typical heterophase systems as blends of amorphous homophase polymers and plasticizers. One possible explanation is that over the experimental y range it is not possible to separate the contributions of the two different phases, and the materials will behave as homophase polymer. In fact, long-time molten polymer rheology experiments measure viscoelastic processes over the entire molecule, and, as a consequence, molecular compatibility is evaluated (13). On the other hand, high frequency and/or low temperature tests involve the main chain as well as the side chains of the polymer system the segmental miscibility of the polymer-polymer system is then evaluated. It is important in experimental measurements of polymer compatibility to evaluate the actual size of the volume subject to the test. 

A miscible blend of amorphous and crystalline polymers usually means a single phase in the melt and a neat crystalline phase with a mixed amorphous region in the sohd. Because of chain folding during crystallization, the crystal lamellae are formed. Their radical growth usually lead to the formation of spheniUtes [Nadkami and Jog, 1991]. 

Molten polyesters show low viscosity and small extmdate swell. For these reasons, they have been blended with amorphous polymers to improve the latter s processability and chemical resistance. Elastomers have also been added to polyesters to improve impact resistance. Blends of polyester (either PET or PBT) with polycarbonate, PC, are the most popular (viz., Bay/oF, BCT4201, Calibre , Dialoy P, Ektar MB (with PCTG), Idemitsu SC, MakroblencT, MB4300, NovadoF, Pocan , R2-9000, Sabre , SC 600, Stapron E, Ultra-blencF KR, Valox , Xenoy 1000, etc.). Presence of PC in PET/PC increases crystallization rate of PET, which translates into faster injection molding cycle and lower part distortion upon demolding than those observed for neat PET. 

The primary motivations for blending the thermoplastic polyesters with other polymers are (a) to improve the solvent resistance and process-ability of amorphous polymers such as PC, styren-ics, PPE, etc., (b) to reduce the mold shrinkage of polyesters associated with their crystallization,... 

The majority of these studies has been done on homopolymers. A recent study using blends of two polymers reported [56] that blends of poly(3-octylthio-phene) and poly(3-hexylthiophene) have a characteristic temperature of thermochromism that correlates in a linear way with the lamellar distance found in x-ray diffraction. These blends are partially crystalline with a lamellar distance intermediate between that of the homopolymers, but not in a simple linear manner. It is argued that this indicates that the side chains act primarily as spacers between the chains, and that melting of the main chains is essential to the thermochromism. As thermochromism is not limited to the crystalline phase, the argument has certainly to be extended to the amorphous phase, where no such simple description of geometry can be given. 

Mather, P.T., Liu, C., 2011. Blends of Amorphous and SemicrystaUine Polymers Having Shape Memory Properties. Patent, PCX number PCT/US2003/032329. 

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