Blend/block mixtures

In this paper, we have reviewed some recent applications of the HPTMC method. We have attempted to demonstrate its versatility and usefulness with examples for Lennard-Jones fluids, asymmetric electrolytes, homopolymer solutions and blends, block copolymer and random copolymer solutions, semiflexible polymer solutions, and mixtures. For these systems, the proposed method can be orders of magnitude more efficient than traditional grand canonical or Gibbs ensemble simulation techniques. More importantly, the new method is remarkably simple and can be incorporated into existing simulation codes with minor modifications. We expect it to find widespread use in the simulation of complex, many-molecule systems. 

We can exploit mixtures of per-deuterated and per-hydrogenated polymers in small-angle neutron scattering measurements to reveal information on the configuration of individual chains as well as assemblies of chains in the case of phase separating blends, block copolymers, and other inhomo-... 

Walsh, D. J. Higgins, J. S Maconnachie, Eds. Polymer Blends and Mixtures Nato ASI Series E No. 89 Martinus Nijhoff Publishers Boston, 1985 Noshay, A. McGrath, J. E. Block Copolymers Academic Press New York, 1977. 

What is usually defined as multiscale modeling at this time is far less ambitious. It can best be characterized as a serial approach. It involves the physically robust use of parameters obtained as output in one scale of simulation, as input parameters in simulations at a more coarse-grained scale. There has obviously already been sufficient progress to enable one to combine the same types of modeling techniques quite effectively to predict the morphologies and properties of many types of mixtures, solutions, dispersions, blends, block copolymers and composites as well as to characterize the interfaces between different phases in such systems. 

Polymer comprising two or more polymer networks which are at least partially interlaced on a molecular scale (Figure 1.16) but not covalently bonded to each other and cannot be separated rmless chemical bonds are broken [206,411]. A mixture of two or more preformed polymer networks is not an IPN. An IPN may be further described by the process by which it is synthesized e. g. when an IPN is prepared by a process in which the second component network is polymerized following the completion of polymerization of the first component network, the IPN may be referred to as a sequential IPN. In contrast, a process in which both component networks are polymerized concurrently, the IPN may be referred to as a simultaneous IPN. An IPN is distinguished from other multipolymer combinations, such as polymer blends, blocks, and grafts, in two ways (1) an IPN swells, but does not dissolve in solvents and (2) creep and flow are suppressed. 

Sonnier et al. have compared physical polymer blends, block, and random copolymers synthesized from MMA and MAPCl. The content of both comomomers ranged over a large extent. The heat release rate and total heat release measured in a PCFC followed the rule of mixture for physical polymer blends. On the other hand, the block copolymers exhibited lower heat release rate values than expected from the rule of mixture. Similar results and even better performances need to be confirmed for random copolymers. It is noteworthy that to the best of our knowledge the comparison between random and block copolymers was not carried out. 

Characterization of polymer mixtures is also of interest due to the wide use of polymer blend systems. Mixtures of homopolymers are relatively a simple form of chemical heterogeneity compared to copolymers. Even in this case, precise characterization is often non-trivial since many of polymer blend systems contain various additives in addition to polymer resins. In this section, recent progress on the characterization of synthetic polymers having chemical heterogeneity is reviewed. For the sake of convenience, the content is divided into mixtures, block copolymers, random copolymers, and functionality distribution. 

To this group of blends belong mixtures of PP with st)oene-elastomer copolymers, styrene-diene blocks styrene-butadiene-st)a ene (SBS), sty-rene-ethylene/butylene- t30 ene (SEBS), st)rrene-isoprene-styrene (SIS), with acrylonitrile-butadiene-styrene terpol)nners (ABS), acrylonitrile-styrene-acrylate (ASA), or with EPR/EPDM grafted with styrene and acrylonitrile (AES or AXS). The first blends of this type date from the early 1960s. In these systems, PP is either the main component to be modified, or an additive to enhance performance of the styrenic matrix. 

The previous two chapters briefly described a number of two-polymer combinations polymer blends, blocks, grafts, and IPNs. A few somewhat more complicated systems were alluded to blends of a homopolymer with a block copolymer, or a mixture of a graft copolymer with one or both homopolymers. This chapter will explore some of the more complex (and interesting) structures, and provide a nomenclature scheme where one now does not exist. ... 

Wilson DJ, Hurtrez G, Riess G (1985) Colloidal behavior and surface activity of block copolymers. In Walsh DJ, Higgins JS, Maconnachie A (eds) Polymer blends and mixtures. NATO Advanced Science Institute Series. Mortmus Nijhoff, Dordrecht, The Netherlands, p 195... 

Hyperbranched polyurethanes are constmcted using phenol-blocked trifunctional monomers in combination with 4-methylbenzyl alcohol for end capping (11). Polyurethane interpenetrating polymer networks (IPNs) are mixtures of two cross-linked polymer networks, prepared by latex blending, sequential polymerization, or simultaneous polymerization. IPNs have improved mechanical properties, as weU as thermal stabiHties, compared to the single cross-linked polymers. In pseudo-IPNs, only one of the involved polymers is cross-linked. Numerous polymers are involved in the formation of polyurethane-derived IPNs (12). 

The principle of blending a conduction fiber with a static-prone fiber has been known for years. A mixture of a substantial quantity (30—40%) of a hydrophilic fiber such as cotton or rayon with a hydrophobic static-prone fiber such as a polyester can produce a static-free blend under ordinary conditions. However, blocking the hydrophilic groups by cross-linking of the cotton with biflinctional reagents such as dimethylolethylene urea or addition of a water-repellent finish such as a sUicone resin increases the static propensity of such a blend. 

Blends with styrenic block copolymers improve the flexibiUty of bitumens and asphalts. The block copolymer content of these blends is usually less than 20% even as Httie as 3% can make significant differences to the properties of asphalt (qv). The block copolymers make the products more flexible, especially at low temperatures, and increase their softening point. They generally decrease the penetration and reduce the tendency to flow at high service temperatures and they also increase the stiffness, tensile strength, ductility, and elastic recovery of the final products. Melt viscosities at processing temperatures remain relatively low so the materials are still easy to apply. As the polymer concentration is increased to about 5%, an interconnected polymer network is formed. At this point the nature of the mixture changes from an asphalt modified by a polymer to a polymer extended with an asphalt. 

In contrast to two-phase physical blends, the two-phase block and graft copolymer systems have covalent bonds between the phases, which considerably improve their mechanical strengths. If the domains of the dispersed phase are small enough, such products can be transparent. The thermal behavior of both block and graft two-phase systems is similar to that of physical blends. They can act as emulsifiers for mixtures of the two polymers from which they have been formed. 

Instead of the familiar sequence of morphologies, a broad multiphase window centred at relatively high concentrations (ca. 50-70% block copolymer) truncates the ordered lamellar regime. At higher epoxy concentrations wormlike micelles and eventually vesicles at the lowest compositions are observed. Worm-like micelles are found over a broad composition range (Fig. 67). This morphology is rare in block copolymer/homopolymer blends [202] but is commonly encountered in the case of surfactant solutions [203] and mixtures of block copolymers with water and other low molecular weight diluents [204,205]. 

Hammer and coworkers prepared PEG-h-PCL polymersomes entrapping DXR (Fig. 11a). The release of DXR from the polymersomes was in a sustained manner over 14 days at 37 °C in PBS via drug permeation through the PCL membrane, and hydrolytic degradation of the PCL membrane [228]. The release rate of encapsulated molecules from polymersomes can be tuned by blending with another type of block copolymer [229]. Indeed, the release rate of encapsulated DXR from polymersomes prepared from mixtures of PEG- -PLA with PEG- -PBD copolymers increased linearly with the molar ratio of PEG- -PLA in acidic media (Fig. lib). Under acidic conditions, the PLA first underwent hydrolysis and, hours later, pores formed in the membrane followed by final membrane... 

---