Miscibility, tacticity effect

Beaucage, G., Stein, R. S., Koningsveld, R. Tacticity effects on polymer blend miscibility. 1. Elory-Huggins-Staverman analysis. Macromolecules, 26, 1603-1608 (1993). 

The decrease of Todt or Ts for MA-g-SEBS means that the repulsive interaction between styrene and ethylenebutylene is decreased by the MA modification. Since the molecular weight is small enough for the tacticity effect to be neglected in the miscibility problem, it is supposed that also the interaction between SPS and modified EB chains will be reduced by MA modification. 

A complete quantitative description of the thermodynamics of polymer-polymer solutions also might need to include the effects of polymer tacticity. As demonstrated recently by Schurer et al. (50), changing the stereo configuration of poly (methyl methacrylate) from isotactic to syn-diotactic causes it to become miscible with PVC. These results suggest the importance of the spatial articulation of interacting segments in the polymer. 

If there are more than two components in a mixture (as in a blend of a homopolymer with a copolymer), binary interaction parameters can be combined into a composite % parameter to describe the overall behavior of the system. For example, Choi and Jo [11] showed how the effects of copolymer sequence distribution in blends of polyethylene oxide) with poly(styrene-co-acrylic acid) can be described by an atomistic simulation approach to estimate the binary intermolecular interaction energies which are combined into a total interaction parameter for the blend. Their paper [11] also provides a list of the many preceding publications attempting to address the effects of copolymer composition, tacticity, and copolymer sequence distribution on polymer blend miscibility. In addition to the advances in computational hardware and software which have made atomistic simulations much faster and hence more accessible, work in recent years has significantly improved the accuracy of the force fields [12] used in such simulations. 

The miscibility between several (meth)acrylate polymers and phenoxy (PHE) has been reported.[155,156] PEMA was noted to be partially miscible and PBMA to be phase separated in PHE blends. [155] An investigation of the effect of PMMA s tacticity on the phase behavior of PMMA/PHE blends showed aPMMA, sPMMA and iPMMA to all exhibit miscibility with PHE. [156] The miscibility of PMMA with a vinylidene chloride-acrylonitrile (20 wt% AN) copolymer was shown to be a function of the PMMA tacticity (aPMMA and iPMMA miscible with the copolymer and sPMMA immiscible). [157] Hsu et fl/.[158] reported the effect of tacticity of PMMA on the miscibility with PVAc. This study showed a limited effect of tacticity and solvent choice on the phase behavior of PMMA/PVAc blends and all blends were analyzed as being immiscible based on the observation of two Tgs. Modest areas of miscibility were established for MA, EA, nBA, and 2-ethylhexyl acrylate based acrylate-acrylic acid in the respective copolymers. No miscible combinations were found for MMA-AA or acrylate-MAA copolymers with vinyl acetateethylene (VAE) or PVAc. 

In addition to the isotope effects discussed above, the miscibility of polymers will depend on the stereochemical micro structure and the tacticity of the constituent polymers. The influence of microstructure on the thermodynamics... 

The effect of tacticity (i.e., the stereochemical arrangement of the units in the main chain of a polymer) on the properties of polymers and polymer blends has long been recognized with such basic differences as in the Tg, miscibility, crystallization, and blend characterization, including their mesoscale morphologies. In general, isotactic polymers (where all substituents are located on the same side of the polymer backbone) are semicrystalline in nature, whereas atactic polymers (where all substituents are placed randomly along the backbone) are amorphous. 

Blends of PMMA and polycarbonate based on hexafluoroBisphenol A (HFPC) were noted to be miscible as well as blends of PC copolymers based on HFBisphenol A and Bisphenol A PC [437]. Additionally, HFPC exhibited miscibility with PEMA and PnPMA. Bisphenol chloral polycarbonate (BCPC) exhibited miscibility only with PMMA. The effect of tacticity of PMMA was reported [438] on phase behavior with PC blends. Miscibility was shown to increase in PC blends in the order of atactic, isotactic, syndiotactic, with syndiotactic PMMA/PC showing no thermally induced phase separation up to 300 °C. 

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