Completely miscible polymer blends

In the future we will witness a drive towards more complexity. In this review, we have discussed a number of preliminary experiments pointing in this direction. In polymer blends, the question of dynamic mixing on a local scale was addressed and the Rouse dynamics in miscible polymer blends was studied. How the tube confinement evolves in blends where the two components have different tube diameters is a completely open question. Also, the question of how... 

A number of miscible polymer blends are only completely miscible and form one-phase systems over a limited concentration, temperature and pressure range. Under certain conditions of temperature, pressure and composition, miscible binary blends may phase separate into two liquid phases with different compositions. Important characteristics of this type of blends are the overall blend composition, the morphology and the composition of the different phases as well as the nature of the interface between the phases. 

Elastomers with similar polarities and solubility characteristics can be easily combined to produce miscible polyblend (18). Miscible polymer blend is a polymer blend, which is homogeneous down to the molecular level and associated with the negative value of the free energy of mixing and the domain size is comparable to the dimensions of the macromolecular statistical segment. Complete miscibility in a mixture of two polymers requires that the following condition be fulfilled (19) ... 

For a mixture of low molecular constituents, n-propanol and u-nonane, it was observed not only negative deviation of surface tension from linear variation with composition, but also a minimum in surface tension (Gaman et al., 2005). Figure 6 shows variation of surface tension with composition of the mixture. Similar behaviour was found for the miscible blend of poly(methyl acrylate) (PMA) and poly(ethylene oxide) (PEO) (Pefferkometal., 2010). As far as the author is aware, this is first time that an extreme value for surface tension was found in a miscible polymer blend. The polymers used had number average molecular masses of A/ 5000 g/mol. Blends of PMA and PEO of those low molecular masses are completely miscible (Pedemonte and Buigisi, 1994). The Flory-Huggins interaction parameter was determined from PVT data io x 003 at 120 °C (Pefferkom et al., 2010). 

Nuclear magnetic resonance (NMR) has been applied to the study of homogeneity in miscible polymer blends and has been reviewed by Cheng [11a] and Roland [11b]. When the components of a blend have different Tg s, proton NMR can be used to assess the phase structure of the blend by taking advantage of the rapid decrease of proton-proton coupling with nuclear separation [lie]. For blends containing elastomers of almost identical Tg, proton MAS NMR is applied to blends where one of the components is almost completely deuterated [12], Another technique is crosspolarization MAS NMR [13], The transfer of spin polarization from protons to the atoms of... 

Table 3.4 refers to a number of crystaUizable miscible polymer blends for which the sphemhte growth rate as a function of the crystallization temperature has been investigated. For most blends, only a part of the bell-shaped curve could be measured. In Fig. 3.8, the complete bell-shaped spherulitic growth rate curve of iPS in iPS/PS blends containing 0,15, and 30 wt% PS is shown. Due to the addition of impurity (e.g., the amorphous PS), a suppression of the growth rate is observed, which is greater than the concentration of the impurity added. Important parameters of the impurity added to the crystaUizable component are the type, concentration, and molecular weight (Keith and Padden 1964). 

The morphologies of the miscible, immiscible, and partially miscible polymer blends are distinct from each other. In an immiscible blend, two phases are present the discrete phase (domain), which is lower in concentration, and the continuous phase, which is higher in concentration. The miscible polymer blends exhibit singlephase morphology. Partially miscible polymer blends may form completely miscible blends at a different composition. The two phases may not have a well-dehned boundary. Each component of the blend penetrates the other phase at a molecular level. The molecular mixing that occurs at the interface of a partially miscible two-phase blend can stabilize the domains and improve the interfacial adhesion. A compatible blend that has commercial possibilities may be immiscible, and a miscible polymer blend may lack commercial applications due to other factors such as cost, source of raw materials, safety, and environmental issues such as recyclability. 

The two prime predictions of Flory theory are as follows (i) T < N due to the nearly complete loss of ideal entropy of mixing due to chain connectivity constraints. Hence, it is correctly predicted to be generally very difficult to create a miscible polymer blend. " " (ii) Immlsclbility is promoted as the A and B monomers become more chemically distinct as quantified by their intermolecular tail potentials (e.g., London dispersion interactions). 

A comprehensive review of miscible polymer blends can be found in [ 1150], listing many of the systems noted in this chapter as well as many others not specifically noted. This review is the most complete listing of miscible polymer blends existing in the literature. 

In the case of vinyl chloride polymerisation in polyfbutyl acrylate) these materials are completely miscible but a two phase region exists within the phase diagram as shown in Fig. 4 Polymerisation from A to B produces a homogeneous blend whereas from E to F produces a two phase structure. Composition B can be reswollen to C with vinyl chloride which can then be polymerised to D to producea homogeneous blend. This route avoids the two phase region in the phase diagram and in principle all compositions of polymer blend can be prepared in a series of steps. 

What is necessary with a polymer blend in order to achieve the desired breadth of transition is partial miscibility. Complete immiscibility leads to two Tgs unshifted with respect to the Tgs of the components, and complete miscibility leads to the same relatively narrow transitions observed for homopolymers. Of course, with immiscible blends, it is possible to mix two or more polymers with relatively close Tgs and achieve broad damping transitions in that way. Hourston and Hughes (33) have reported broad transitions for polyether ester-polyvinyl chloride (PVC) blends where specific interactions occur between the ether oxygens and the chlorines in the PVC leading to partial miscibility. 

The miscibility of poly(4-vinylpyridine) (P4VP) with poly(4-vinylphenol) (PVPh) blends was investigated over a wide range of compositions by other techniques and high-resolution solid-state NMR. ° Relaxation times were studied as a function of blend composition. Ti(H) and Tip(H) results demonstrate that the spin diffusion can completely average out the entire relaxation process. It was also found that the intimate mixing of the polymer blends restricts the local chain mobility. 

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