Miscibility, poly molecular composites

The rotating-frame spin-lattice relaxation time for protons, Tip,( H), was measured indirectly from CPMAS/DD NMR to probe possible molecular scales of heterogeneity in the miscible poly(benzyl methacrylate)/poly(ethylene oxide) blend over the whole composition range. ... 

It was noted also that satisfactory compatibilization could be achieved by local miscibility (given by solubility parameters) rather than direct matching of the chemical and macro-molecular composition. This may require the copolymer to have several components, such as poly(styrene-co-ethylene)-b-poly(butene-co-styrene) (SEES), which has been found useful in compatibilization of HDPE and PET (Bonner and Hope, 1993). 

Recently, combinations of polymers meeting the basic concept of molecular composites have been reported. Poly-(p-phenylene terephthalamide) miscibility with PA-6 and PA-66 was reported [Kyu et al., 1989]. The blends were prepared by rapid coagulation of methane sulfonic acid solutions in water. Above 70% of the rigid rod polymer, polyamide crystallization disappears implying a level of intermixing of the blend constituents. However, thermal treatment results in phase separation thus indicating metastability for this combination. 

One of the basic problems confronting molecular composites is the difficulty of finding miscible combinations of rigid rod polymers with flexible chain polymers. Poly(p-phenylene benzobisthiazole)/poly(-2,5(6)-benzimidazole block copolymers have been reported by Tsai et al. [1985] and are noted to exhibit better processability and mechanical properties than the simple blends of the block copolymer constituents. Chang and Lee [1993] prepared poly(p-benzamide)/Pl block copolymers and reported on the liquid crystalline behavior. Such approaches would appear to have future implications. As an example PA e.g., PA-66) block copolymers with rigid rod polyamides could be prepared and used in blends with PA-66 to yield the desired molecular composite. 

Miscibility, Structure, and Property of Poly (biphenyl dianhydride perfluoromethylbenzidine)—Poly(ether imide) Molecular Composites... 

One promising approach to producing a true molecular composite is to make rod and coil components thermodynamically miscible by introducing attractive interactions, such as hydrogen bonds (16-18), between them. This method has proven useful for enhancing miscibility in flexible-flexible blends. Even more useful (stronger) interactions may be ionic interactions, such as ion-ion and ion-dipole interactions various studies on ionomer blends have demonstrated that ionic interactions can enhance the miscibility of otherwise immiscible polymer pairs (79). Polymers studied include polystyrene, poly(ethyl acrylate), poly(ethyleneimine), nylon, and poly (ethylene oxide) (20-22). 

Molecular composites by ion-ion interaction enhanced miscibility were described in the early 1990s for poly(2-acrylamido-2-methylpropanesulfonic acid)/poly(p-phenylene-benzobisthiazole) (PPBT) [50]. 

For systems of rigid poly diacetylenes with functional or ionic side groups and car-boxylated or sulfonated polystyrene or sulfonated polyester-urea urethanes, molecular composites could be achieved by ionic interactions [51]. The blends exhibited no microphase separation and the miscibility on a molecular length scale was proven by infrared spectroscopic, dynamic mechanical and differential scanning calorimetry analysis. The molecular reinforcement amounted to up to 1 order of magnitude in compliance with a Halpin Tsai description and was achieved by only a few weight percent of the rigid compound. 

Most of the polymer s characteristics stem from its molecular stmcture, which like POE, promotes solubiUty in a variety of solvents in addition to water. It exhibits Newtonian rheology and is mechanically stable relative to other thermoplastics. It also forms miscible blends with a variety of other polymers. The water solubiUty and hot meltable characteristics promote adhesion in a number of appHcations. PEOX has been observed to promote adhesion comparable with PVP and PVA on aluminum foil, cellophane, nylon, poly(methyl methacrylate), and poly(ethylene terephthalate), and in composite systems improved tensile strength and Izod impact properties have been noted. 

Chang et al. reported the miscibility of poly(vinylphenol) (PVPh) with poly(methyl methacrylate) (I MMA) Figure 1 shows the C CP/MAS spectra of pure PVPh, PMMA, PVPh-co-PMMA, PEG, and PVPh-co-PMMA/ poly(ethylene oxide) (PEO) blends of various compositions with peak assignments. VPh contents of PVPh-co-PMMA is 51 mol% and Mn of PEO is 20,000. The spin lattice relaxation time in the rotating frame (Tip ) was measured to examine the homogeneity of PVPh-co-PMMA/PEO blends on the molecular scale. 

Most polymers are not arbitrarily miscible with each other. Often a critical temperature exists, above which a phase separation into two mixtures of different compositions occurs. For mixtures of low molecular weight polymers the opposite effect can also be observed. Two incompatible polymers mix with each other, if a certain temperature is exceeded. An example for such a system are mixtures of polystyrene and poly butadiene. 

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). 

The composition dependence of the relative molecular mass for entanglement has been studied in the context of viscoelasticity for example polystyrene (PS) and poly(xylenyl ether) (PXE) are fully miscible but have very different values of Me, 19100 for PS and 4300 for PXE. Measurements of the plateau modulus of mixtures suggested that a simple harmonic mean blending law was followed (Prest and Porter 1972). 

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