Separation copolymers

Applying a chromatographic method it is sometimes possible to separate copolymer molecules according to their size Z and composition [5]. The SCD found in such a way can be compared with that calculated within the framework of the chosen kinetic model. The first- and second-order statistical moments of SCD are of special importance. 

We will then examine other flexible polymer crystallization instances which may be interpreted, at least qualitatively, in terms of the bundle model. We will concentrate on crystallization occurring through metastable mesophases which develop by quenching polymers like isotactic polypropylene, syndiotactic polypropylene etc. In principle also hexagonal crystallization of highly defective polymers, and order developing in some microphase-separated copolymer systems could be discussed in a similar perspective but these two areas will be treated in future work. A comparison between the bundle approach and pertinent results of selected molecular simulation approaches follows. 

There have been many studies directed at using adsorption and re versed-phase HPLC to separate copolymers by composition (1.-3) interacting problems associated with these approaches ares o The presence of one property distribution interferes with separation on the basis of the other. For example, in adsorption chromatography, the degree of adsorption can be affected by both the molecular weight and by the composition of the molecule. For a linear copolymer, adequate fractionation requires that the ccmposltlon differences completely dominate. 

This section deals with the effect of monomeric sequences in copolymer chains upon TLC separation. A possibility of separating copolymers by the difference in their chain architectures was first demonstrated by Kamiyama et al. S9 For the preliminary TLC experiment they used copolymers composed of styrene and methyl methacrylate, for the reason that this comonomer pair is endowed with the possibility of being polymerized to three different chain architectures, namely, alternating61 , statistical, and block. 

Fig. 6.3 Schematic phase diagram for lamellar PS-PB diblocks in PS homopolymer (volume fraction 0h). where the homopolymer Mv is comparable to that of the PS block (Jeon and Roe 1994). L is a lamellar phase, I, and I2 are disordered phases, M may correspond to microphase-separated copolymer micelles in a homopolymer matrix. Point A is the order-disorder transition.The horizontal lines BCD and EFG are lines where three phases coexist at a fixed temperature and are lines of peritectic points. The lines BE and EH denote the limit of solubility of the PS in the copolymer as a function of temperature.

Considering the competition between intrachain contraction and interchain association, we have to discuss an overlooked viscoelastic effect in the formation of stable mesoglobules in dilute solutions. Otherwise, it would be difficult to understand why copolymer chains with a high content of hydrophobic comonomers could form smaller interchain aggregates. In the micro-phase separation, copolymer chains in solutions contract and associate. The collision between contracted and associated chains would not be effective if the collision (or contact) time (rc) is much shorter than the time (re) needed to establish a permanent chain entanglement between two ap-... 

Needless to say, the best established architecture which can be designed by the macromonomer technique has been that of graft copolymers. With this technique we now have easy access to a variety of multiphased or microphase-separated copolymer systems. This expanded their applications into a wide area including polymer alloys, surface modification, membranes, coatings, etc. [5]. 

Modern polymerization techniques, such as sequential iodine transfer polymerization of fluoroalkenes [11,12], lead to novel thermoplastic elastomers (TPEs). These triblock copolymers can be produced in a process, which can be emulsion, suspension, microemulsion, or solution polymerization [13], Using pseudo-living technology or branching and pseudo-living technology, A-B-A phase separated copolymers with soft (amorphous) and hard (crystalline) domains can be produced. The hard domains can be composed from the following ... 

Techniques such as SEC-LC (liquid chromatography other than the size exclusion separation mode) are required to characterize copolymers in accurate detail. Several techniques for nonexclusion liquid chromatography (NELC) to separate copolymers according to composition have been developed and reported within the past several years. These techniques can give the information on chemical heterogeneity of copolymers thus, SEC-NELC is required to determine both distributions. 

An obvious advantage of this strategy is that copolymer is made only as needed and a separate copolymer commercialization process need not be developed. 

A number of parameters determine whether or not the morphology of interest is adopted by a microphase separating copolymer melt. Of these, most important are the interaction parameter, the volume ratio of the blocks, the degree of polymerization, the individual block molecular weight distributions, the overall polydispersity, the interactions with the interfaces, and last but not least, the temperature. Only the latter two parameters are experimentally accessible and can be altered after the synthesis of the copolymer (disregarding polymer blends). Control over the self-assembly at the film interfaces becomes essential when the polymer films are intended to be used as templates. Meuler et al. recently published a comprehensive review on how these various parameters affect the formation of gyroid-like morphologies in polymeric materials [47]. 

Microdomain size in phase-separated copolymers plays a fundamental role in determining various macroscopic physical properties in the solid state. The difference in segmental mobility between the hard and soft domains governs the physical properties of microphase-separated polyurethane elastomers [7]. In this respect, the development of structure-property relations at the molecular level which relate directly to macroscopic behavior is the focus of this sub-section. One can exploit the well-documented difference between domain mobility [7-10] and the i3C NMR chemical shift distinction between the 0 .H2 resonances in the hard and soft segments to probe the microdomain morphology of polyether-... 

Figure 6.12 Dependence of impact parameters on material composition for group III filled PP oomposites. (a) CNIS/G/ (b) scale factor. O, MPP/EPR/ Mg(OH)2-filler 1 complete separation , PP/MEPR no adhesion , MPP/EPR no adhesion PP/EPR no adhesion , MPP/EPR/Mg(OH)2 complete separation-copolymer matrix A, MPP/EPR/Mg(OH)2-filler 2 complete separation , PP/MEPR/CaCOa complete encapsulation H, PP/MEPR/Mg(OH)2-filler 1 complete encapsulation Jt, PP/MEPR/Mg(OH)2-filler 2 complete encapsulation. (From Ref. 86, courtesy of SPE.)...

In summary, Helfands NIA theory predicts molecular weight dependencies of domain size, separation and other parameters of the phase separated copolymers with the presumption of an interface of constant thickness at the-domain boundary. 

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