Amorphous polymers miscibility

The glass transition temperature of poly(ether ether ketone) (PEEK), a semicrystaUine polymer, is 145°C, whereas that of poly(ether imide) (PEI), an amorphous polymer miscible with PEEK, is 215°C. What will be the of a blend of these two materials containing 10% by weight PEI Speculate on what the presence of the PEI in the blend might do to the rate of crystaUization of PEEK. 

Miscibility or compatibility provided by the compatibilizer or TLCP itself can affect the dimensional stability of in situ composites. The feature of ultra-high modulus and low viscosity melt of a nematic liquid crystalline polymer is suitable to induce greater dimensional stability in the composites. For drawn amorphous polymers, if the formed articles are exposed to sufficiently high temperatures, the extended chains are retracted by the entropic driving force of the stretched backbone, similar to the contraction of the stretched rubber network [61,62]. The presence of filler in the extruded articles significantly reduces the total extent of recoil. This can be attributed to the orientation of the fibers in the direction of drawing, which may act as a constraint for a certain amount of polymeric material surrounding them. 

Miscible blends are not as easy to achieve as immiscible blends. As noted above, entropy is the major driving force in causing materials to mix. Because polymer chains are already in a state of relatively high order, increases in randomness are not easily achieved so that immiscible blends are often more easily formed. To make matters worse, for amorphous polymers the amount of disorder in the unmixed polymer is often higher than for blends that tend to arrange the polymer chains in a more ordered fashion. 

The four curves have about the same shape they are shifted along the T-axis. C and D are typically amorphous polymers. They are wholly miscible. The pattern resembles the one of Noryl (PPE -i- PS). 

In blends composed of immiscible polymers, amorphous polymer does not affect the crystallization of crystallizable polymer, but if two polymers are miscible, amorphous polymer acts as diluent and affects crystallization of the second polymer. Poly(E-caprolactone) is a crystallizable component of the blend with poly( vinyl butyral), which is studied in compositions containing carbon black. Typically, blends of these two polymers form very large spherulites, and it is interesting to find out how carbon black affects crystallization and other properties of the blend as well as the distribution of carbon black in relationship to the spherulites. Figure... 

Model C is mostly found for a blend of crystalline and amorphous polymers. In general, the miscibility for the crystalline/amorphous blends would be better in an amorphous component-rich system than that of a crystalline-rich system. For example, when the crystalline PEO composition is more than 60 wt% in PEO/amorphous PVPh, PEO in the blend showed two Tip relaxation times (Table 10.2) [34]. One of the two Tip agrees well with Tip... 

The most complex types of interfaces are those between two amorphous polymer phases, as in immiscible or partially miscible blends and block copolymers. Such interfaces differ in a... 

This is due to the effects on nucleation and growth rates. Thus, blending method may have serious effects on crystaHizability and crystal size. Experimentally, the presence of a miscible, amorphous polymer in the blend usually slows down, or it even prevents, crystallization of the semicrystalline resin. The enhancement of crystallinity and increase in T on blending have also been reported [Harris and Robeson, 1987 Dumoulin et ai, 1987]. As a result, the T method is far from being fool-proof and the obtained values of Xi2 should be confirmed by other techniques [Utracki, 1989 Groeninckx et al., 1998]. 

And finally, the glass-transition temperature and the melting temperature can be influenced by addition of an amorphous polymer. As already mentioned in section 3.3.1, the T of miscible... 

It is well-known that the rate of crystallization of a crystalline polymer is often reduced by blending with a miscible amorphous polymer. Some typical examples are blends of PVDF/PMMA [Tanaka et al., 1985], PVDF/PEA [Alfonso and Russel, 1986], PEO/PMMA [Briber and lOioury, 1987] and PCL/SAN (19.2 wt% acrylonitrile) [ICressler et al., 1991]. 

To obtain a reasonable prediction of miscibility, the values of the solubility parameters are to be measured to an accuracy better than 5j - 82 < 0.2 (J/mL). The measured values of 8j (where i = 1 or 2) far exceeds the magnitude of the critical difference of these parameters, 8j - 82 < 2 (J/mL). The calculated values of 8. are claimed to be precise within 0.8 (J/mL)i/2 [Coleman et al, 1990]. The solubility parameter approach is applicable to amorphous polymer systems. In order to adopt to highly crystalline polymers, the heat and entropy of fusion (Ah j and As p respectively) is to be dealt with in free energy of mixing equation [Van Krevelen and Hoftyzer, 1976] ... 

SMP based on miscible blends of semicrystalline polymer/amorphous polymer was reported by the Mather research group, which included semicrystalline polymer/amorphous polymer such as polylactide (PLA)/poly vinylacetate (PVAc) blend [21,22], poly(vinylidene fluoride) (PVDF)/PVAc blend [23], and PVDF/polymethyl methacrylate (PMMA) blend [23]. These polymer blends are completely miscible at all compositions with a single, sharp glass transition temperature, while crystallization of PLA or PVDF is partially maintained and the degree of crystallinity, which controls the rubbery stiffness and the elasticity, can be tuned by the blend ratios. Tg of the blends are the critical temperatures for triggering shape recovery, while the crystalline phase of the semicrystalline PLA and PVDF serves well as a physical cross-linking site for elastic deformation above Tg, while still below T ,. 

Another miscible semicrystalline polymer/amorphous polymer blend SMP is a polyethylene oxide (PEO)/novolac-type phenolic resin blend [24]. The blend was found to be completely miscible in the amorphous phase when the phenolic content is up to 30 wt%, and the crystalline melting temperature (T,f) of the PEO phase working as a transition temperature can be tuned. 

Common examples of miscible blends are ethylene-propylene copolymers of different composition that result in an elastomer comprising a semicrystalline, higher ethylene content and an amorphous, lower ethylene content components. These blends combine the higher tensile strength of the semicrystaUine polymers and the favorable low temperature properties of amorphous polymers. Chemical differences in miscible blends of ethylene-propylene and styrene-butadiene copolymers can also arise from differences in the distribution and the type of vulcanization site on the elastomer. The uneven distribution of diene, which is the site for vulcanization in blends of ethylene-propylene-diene elastomers, can lead to the formation of two distinct, intermingled vulcanization networks. 

Polymer-polymer miscibility is usually characterised [1,5,6] by investigating the optical appearance, morphology, glass transition temperature or the crystalline melting behaviour of the blend [38,39]. A blend of two amorphous polymers with different refractive indices will be judged to be miscible if it is optically clear. Measurement of the glass transition temperature, or temperatures, of a polymer blend is the most convenient and popular way of investigating polymer-polymer miscibility. 

PBSA and PVPh are miscible crystalline/amorphous polymer blends. Miscibility of PBSA/PVPh blends was evidenced by the single composition-dependent glass-transition temperature over the entire blend compositions. The negative polymer-polymer interaction parameter, obtained from the melting depression of PBSA, indicates that PBSA/PVPh blends are thermodynamically miscible. 

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