Polymer Additive Binary Systems

Later Rytter et al. reported possible polymer chain exchange with polypropylene produced with a combination of 8 and 11 with TMA [32], The number of stereoerrors increased in the binary system at higher TMA levels. As discussed in the case of Przybyla and Fink (vida supra), pentad analysis is less compelling evidence for reversible chain transfer. In addition, the gel permeation chromatography (GPC) data showed bimodal peaks, indicating very limited reversible transfer. 

Typically, a binary system was selected as the base component of the recipe and the addition of polyelectrolytes to either side (core or receiving bath) was tested to evaluate the change in the capsule properties. The 33 successful multicomponent membrane systems are presented in Table 1. The components of the core material side (21 different chemical compositions) are listed in the first column, while the receiving bath components (20 different chemical compositions) are listed in the second column. With the exception of xanthan and CMC, the first polymer listed on the core side are gelling polymers which form beads with the appropriate ionotropic cation (salt). CMC can also be gelled by ions (alum), although they are considered to be non-compatible for cellular applications. The cations were tested both sequentially, usually with ionotropic cation first, and simultaneously. Walled capsules with adequate mechanical properties were often obtained through the simultaneous application of two polycations. Such a... 

In addition to protonic acids, Lewis acids are the most common initiators of carbocationic polymerizations. Two mechanisms are possible. Direct initiation is rare and usually slow. The more prevalent mechanism is by cocatalysis in binary systems, with the Lewis acid acting as a coinitiator or catalyst rather than as initiator. Cationating or protonating species are the true initiators, which are therefore the species incorporated at the polymer s end group. The most common initiator is adventitious water in insufficiently dried systems. Thus, mechanistic studies should be performed under stringently dry conditions or in the presence of proton traps such as hindered pyridines. In addition to water, the protonating reagent may be an alcohol, carboxylic acid, amine, or amide [Eq. (28)]. 

As for low molecular weight surfactants, the superstructures are assumed to be formed by micellar aggregates [126], But it seems that the formation of lyotropic liquid crystals is supported by the additional presence of thermotropic mesogens [87,122-124,126], Lamellar, hexagonal, cubic and even nematic and cholesteric mesophases were reported for binary systems, the latter being exceptional. Lyotropic mesophases were also observed in non-aqueous solvents [240,400,401,405], If polymerizable surfactants are studied, not only the phase diagram but also the types of mesophases observed for the monomer and the polymer may be different. 

Within types of polymers the individual samples are ordered by their increasing average molar mass, and, when necessary, systems are ordered by increasing tertqreratirre. In ternary systems, ordering is additionally made subsequently according to the name of the third component in the system. Each data set begins with the lines for the solution components, e g., in binary systems... 

Fillers and additives may also interact with the solvent, with the polymer, or with both. The electrospinnability of tbe solution may change as a result of these interactions, but it may also remain imcbanged, regardless of tbe additive. It has, for example, been shown that conductive solutions can form different kinds of three-dimensional loose structures on the substrate, instead of a tbin coating layer attached to the substrate surface. Tbe form of these structures can vary from fibrils perpendicular to the substrate surface to a layer with a fluffy cotton-like structure. Fibrils can even extend to cover tbe entire electrospinning zone. If this kind of conductive fibrous structure connects tbe nozzle and collector plate, the electric field discharges and the process stops. The optimisation of the process parameters for ternary systems can be even more challenging than for binary systems composed only of polymer and solvent. 

In addition to the considerations based on morphology that have been analyzed above, further strategies for improving mechanical properties are similar to those employed in binary systems, and include filler treatment, addition of compatibilizers, and functionalization of the polymers. These are briefly reviewed below. 

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