Homopolymer blend, three-component

Factor analysis can be used as a quantitative method to establish the existence of a measurable interaction spectrum [23]. To determine whether the interaction spectrum is a contributing factor to the spectrum of the blend, a series of polymer blends with different volume fractions of each homopolymer is prepared, and the spectrum of each blend is obtained. The number of components present in these blend spectra is then determined by factor analysis. In the case of compatible blends, three components are expected, but for incompatible blends, only two should be observed. 

We assume, now, that the three component blend considered in the previous section consists of a copolymer A/B (could be a diblock, triblock, etc, or an alternating copolymer) and a homopolymer C [11-15]. The notation and formalism of the previous section hold but now XAB(Q) + 0 (note that Xab(Q) shows a peak in the scattering function). The partial structure factors become ... 

Noolandi et al. developed a theory for the interfacial region in three-component polymeric systems comprising di-block copolymer. There are two aspects to consider the phase separation in block copolymer upon addition of one or two homopolymers, and the modification of the A/B blend properties upon addition of a block copolymer (either A-B or X-Y type). The second aspect is more pertinent for the polymer blend technology. In particular, the ternary blends comprising two homopolymers and a copolymer, either A/B/A-B, or A/B/X-Y are of industrial interest. 

A copolymer sample produced by reactive blending of two homopolymers is made of three components the two homopolymers and the copolymer formed. As the reaction goes on, the two homopolymer sequences disappear and the copolymer sequences become abundant. 

In the case of PO blends, compatibilization most frequently aims for improved ductility and/or transparency. The Z-N-LLDPE obtained using multi-sited catalyst constitutes a specific case - the homopolymer may have phase-separated morphology that requires compatibilization. It has been known that addition of 5-20 wt% LDPE needs to be used for improved performance. However, explanation for this is rather recent (Robledo et al. 2009). The relaxation spectrum of the blend may be decomposed into three components (1) Z-N-LLDPE matrix, (2) LDPE dispersed drops, and (3) a thick interphase with its own viscoelastic properties, obtained by interaction between the high-MW linear fraction of the LLDPE and the low-MW linear LDPE macromolecules. 

Copolymers can be mixed with other copolymers, homopolymers, or solvents. Broadly speaking, there are three general problems related to the phase behavior of these blends the microphase behavior, the interplay between microphase and macrophase separation, and micelle formation at low copolymer concentration. The mixtures sometimes form one phase, which can be either ordered or disordered, and sometimes they separate into two macrophases. In the latter case, each of the macrophases can be ordered or disordered. For example, there could be coexisting phases of spheres and cylinders. The phase behavior of a two component system can be summarized by a temperature-composition phase diagram [102,103], that of a three component system by a series of ternary phase diagrams, and so on. Space permits touching only briefly on a small sample of these possibilities in this chapter. Copolymers can also be used as surfactant in homopolymer-homopolymer blends, but that topic is beyond the scope of this chapter. 

Studied the time evolution of the interfacial tension when polyisobutylene (PIB)-b-PDMS was introduced to PIB/PDMS blend, with the copolymer added to the PIB phase in that study both homopolymers were poly disperse. The time dependence of the interfacial tension was fitted with an expression that allowed the evaluation of the characteristic times of the three components. The characteristic time of the copolymer was the longest, whereas the presence of the additive was found to delay the characteristic times of the blend components from their values in the binary system. The possible complications of slow diffusivities on the attainment of a stationary state of local equilibrium at the interface were thoroughly discussed by Chang et al. [58] within a theoretical model proposed by Morse [279]. Actually, Morse [279] suggested that the optimal system for measuring the equilibrium interfacial tension in the presence of a nearly symmetric diblock copolymer would be one in which the copolymer tracer diffusivity is much higher in the phase to which the copolymer is initially added than in the other phase because of the possibility of a quasi-steady nonequilibrium state in which the interfacial coverage is depleted below its equilibrium value by a continued diffusion into the other phase. 

Experimentally, there are many miscible polymer pairs in which at least one of the components is a random copolymer but specific interactions are not present [40]. This phenomenon is attributed to the so-called intramolecular repulsion effect. Within the familiar Flory-Huggins description, and in the case of a random copolymer A Bi blended with a homopolymer C, three interaction parameters, Xab,Xac and Xbc are required to describe the enthalpy of mixing. Using a mean field theory, the mixture can be described in terms of one parameter XeS given by ... 

These essentially comprise a mixture of a skin-forming component, which comprises two distinct phases blended together, a high zero-shear viscosity material and a low zero-shear viscosity material, and a foam core-foaming component, which includes a blowing agent, physically dry blended together. The three materials are preferably selected from suitable homopolymers and copolymers of ethylene. CANADA... 

The phase behaviour of a binary blend of a block copolymer and a homo-polymer is primarily governed by the length of the homopolymer chain compared to the copolymer. Experiments by the groups of Hashimoto and Winey have led to the identification of three regimes, depending on the degree of polymerization of the homopolymer A, NAti, and that of the same component of the copolymer, NAc. 

When a block copolymer is blended with a homopolymer that differs in composition from either block the usual result is a three-phase structure. Miscibility of the various components is not necessarily desirable. Thus styrene-butadiene-styrene block copolymers are recommended for blending with high density polyethylene to produce mixtures that combine the relative high melting behavior of the polyolefin with the good low temperature properties of the elastomeric midsections of the block polymers. 

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