Copolymer, block

In block copolymers, the individual components are joined at their ends. Block copolymers have been synthesized by several methods, but perhaps the most elegant procedure follows the living polymer anionic polymerization process (Henderson and Szwarc, 1968). The unusual features of this reaction include simultaneous nucleation and uniform growth rates of all chains, and lack of termination reactions. After exhaustion of a first monomer the polymer chains remain alive, and addition of a second monomer results in a block copolymer of the form 

In general, block copolymers are heterogeneous (multiphase) polymer systems, because the different blocks from which they are buUt are incompatible with each other, as for example, in diene/styrene-block copolymers. This incompatibility, however, does not lead to a complete phase separation because the polystyrene segments can aggregate with each other to form hard domains that hold the polydiene segments together. As a result, block copolymers often combine the properties of the relevant homopolymers. This holds in particular for block copolymers of two monomers A and B. 

The simplest dependency exists between composition and glass transition temperature Independent from the ratio A/B one finds two values for Tg, one for the block from monomer A and one for the block of B. More complex are the dependencies with the mechanical properties. Here, parameters like the ratio A/B, number of blocks, block length, and alternation of the blocks play a decisive role. This is shown in Examples 3.47 and 3.48 with triblock copolymers of butadiene or isoprene with styrene. If the content of the diene blocks is around 20%, a stiff and elastic, transparent thermoplastic material is obtained. Instead, if the diene content is raised to about 70%, a highly elastic but still rather stiff thermoplastic elastomer is obtained. It has to be stressed that these properties can only be reached, when the polystyrene blocks are the terminal ones. 

Block copolymer is a type of copolymers, which has a chain structure of homopolymer blocks connected in series by a chemical bond. These block copolymers are commonly synthesized by either end coupling of two different polymers or growing different chains in a sequential manner. The precise analysis of diblock copol- 

Major effort has been made on LCCC separation at the critical condition of one block. It is based on the assumption that a block can be made chromatographi-cally invisible at its critical condition and the retention of the block copolymer is determined solely by the other block that is not under critical condition [55,128, 129). This assumption is only valid if the retention of the homopolymer of the invisible block is indeed independent of molecular weight at the critical condition and if the retention of the visible block is not affected by the presence of the invisible block. If these conditions were satisfied, LCCC would undoubtedly be a powerful tool for the characterization of selected blocks within block copolymers. The applications of LCCC for the characterization of block copolymers made so far can be divided into two categories. 

The other LCCC separation mode is to elute block copolymers in the SEC regime (eluting before injection solvent peak) if the visible block is less interactive 

AH of these works appear to support the applicability of LCCC for the characterization of selected block of block copolymers, but the precision of the method was not tested rigorously. A 10% error in the accuracy of an individual block molecular weight would not be uncommon in the characterization of block copolymers with conventional characterization methods. Therefore the apparent consistency found with several independent block copolymers would not constitute the validity of the method. In order to test the method rigorously, it is highly desirable to use a custom-made set of block copolymers. 

Lee at al. further extended the study using a single solvent, 1,4-dioxane to establish the LCCC condition for PI with the C18 bonded silica stationary phases [21]. Employment of single solvent for LCCC experiments is highly desirable. It improves the reproducibility of the LCCC experiments since the polymer retention changes very sensitively with eluent composition in mixed solvents. Also it elimi- 

While the simplest vinyl-type block copolymer is a two-segment molecule represented by 

ABA block copolymer ABC block copolymer Multiblock copolymer Stereoblock copolymer 

In the simplest case, block copolymers consist of successive series (blocks or segments) of A and B units. Depending on the number of linked blocks, one distinguishes diblock, triblock and multiblock copolymers  

For the synthesis of block copolymers chain addition polymerization (ionic or radical) as well as condensation polymerization and stepwise addition polymerization can be used. 

Well developed is the anionic polymerization for the preparation of olefin/di-olefin - block copolymers using the techniques of living polymerization (see Sect. 3.2.1.2). One route makes use of the different reactivities of the two monomers in anionic polymerization with butyllithium as initiator. Thus, when butyl-lithium is added to a mixture of butadiene and styrene, the butadiene is first polymerized almost completely. After its consumption stryrene adds on to the living chain ends, which can be recognized by a color change from almost colorless to yellow to brown (depending on the initiator concentration). Thus, after the styrene has been used up and the chains are finally terminated, one obtains a two-block copolymer of butadiene and styrene  

Oxidative degradation by splitting off the double bonds in the butadiene blocks allows the styrene blocks to be isolated. The degradation of the chains 

A second route is termed sequential anionic polymerization. More recently, also controlled radical techniques can be applied successfully for the sequential preparation of block copolymers but still with a less narrow molar mass distribution of the segments and the final product. In both cases, one starts with the polymerization of monomer A. After it is finished, monomer B is added and after this monomer is polymerized completely again monomer A is fed into the reaction mixture. This procedure is applied for the production of styrene/buta-diene/styrene and styrene/isoprene/styrene triblock copolymers on industrial scale. It can also be used for the preparation of multiblock copolymers. 

Defined diblocks, triblock or multiblock copolymers find important applications in the areas of thermoplastic elastomers, data storage technology [126], and as compatibilizers (e.g. in polymer blends). In thin films these polymers may display different morphologies than in the bulk, which necessitates an accurate analysis. 

Magerle, Krausch and coworkers showed based on AFM data and simulations that the phase behavior at interfaces [127] and in thin films (interphases) [128] can be understood in terms of analogous to those of classic, inorganic crystals. In Fig. 3.55 thin triblock copolymer films of SBS on silicon are shown, which display a rich variety of morphologies depending on the local film thickness [129]. 

Similar experimental observations were reported by Lammertink and Vancso (Fig. 3.56). In this case, poly-(isoprene)-b-poly(ferrocenyl dimethylsilane) films 

The final topic we wish to consider in this section is block copolymers. These are fascinating materials at a number of levels. First, they are technologically important For example, triblock copolymers of styrene and butadiene are used to make thermoplas- 

FIGURE 8-66 Electron micrographs of styrene (S)/isoprene (I) block copolymers molecular weight of the blocks (S/T) are 68,000/12,000 g/mo] (left) and 30,000/11,000 g/mol (right) [images courtesy of C. K. Harrison, P. M. Chaikin, and R. A. Register, Princeton University]. 

FASCINATING POLYMERS—SUPER HIGH-STRENGTH PE FIBERS 

Stephanie Kwplek was assigned the task of featuring Stephanie Kwolek preparing fibers from completely para-substituted (Source Hagley Museum). aromatic polyamides. She succeeded in producing 

These are the principal morphologies found in diblock copolymers, but under certain conditions other periodic structures are formed. One snch morphology, where 

We have previously alluded to two major commercial applications of block copolymers the addition of AB diblock copolymers in blends of homopolymers, A and B, to improve the processability and mechanical properties of the mixture, and the use of ABA-type triblock copolymers as thermoplastic elastomers when block A (e.g., PS) is below its glass transition, whereas block B (e.g., polybutadiene) is above its glass transition at ambient temperature. Other products made from block copolymers include pressure-sensitive adhesives, oil additives, and automobile parts. 

FIGURE 3.27 Examples of oidered-state morphologies found in low polydispersity diblock copolymers. Shaded and unshaded regions represent the two different blocks. (Data from Bates, F. S. et al., Faraday Discuss., 1994, 98 7. Reprinted by permission from the Royal Society of Chemistry.) 

Most recent developments in block copolymer applications make use of the fact that the phase-separated microstructures are of nanometer length scales, periodic in nature, and in many cases porous if one of the phases is removed. The use of block copolymers is especially advantageous if these length scales cannot be readily accessed via other means. The following three examples will illustrate the opportunities and challenges in using block copolymers. 

In a block copolymer, long groups of one type of monomer are followed by long groups of the other within the backbone chain (Fig. 3.6). For example, some styrene-butadiene copolymers have a block copolymer structure. 

One way of forming block copolymers is to first polymerize each monomer separately to a low degree of polymerization, and then combine these small polymer molecules with each other (Fig. 3.7). 

Another option is to introduce the monomers into the reactor in an alternating sequence (Fig. 3.8). 

If two different polymeric species are coupled together by chemical links, one obtains block copolymers . These materials possess peculiar properties, and we will consider them in this section. 

The block architecture of the polymer chains significantly changes the physical properties, hi the case of poly(arylene ether ketone)s, for instance, it was shown that, while randomly sulfonated copolymers with lEC 1.6mmol/g 

The block copolymers exhibit conductivities up to 166mS/cm at 60 °C, fully hydrated, at a water uptake up to 250% in boiling water. Table 3 shows some properties of these materials. 

Even higher conductivities were found for block copolymers consisting of sulfonated poly(aryl ether sulfone) blocks alternating with fluorinated aromatic polyether blocks (Fig. 13), although they had relatively high water uptake even at room temperature. Table 4 shows conductivites and water uptake data. 

Polymer Molar mass hydrophilic block (g/mol) Molar mass hydrophobic block (g/mol) lEC (mmol/g) Conductivity at room temperature (mS/cm) Water uptake at room temperature (%) 

Clearly, separation of the requirements of high lEC and good mechanical properties in different blocks by combining segments with high degree of sulfonation with totally unsulfonated, hydrophobic segments is an attractive concept, despite the increased synthesis effort. 

Similarly, a polymeric medium characterised by strong cohesion, is also obtained from di- or tri-block copolymers made by linking two or three chemically homogeneous sequences which are incompatible with one another usually, the Tg of one of the two sequences is above room temperature while it is below for the other sequence [10]. There is a phase separation glassy segments are connected to one another by amorphous segments and they play the role of ordered domains formed in semi-crystalline polymers. 

One of the main reasons for the interest in living polymerization is its potential for the synthesis of block copolymers. 

ABA-type block copolymers are available if VFc is added after the polymerization of styrene (PSt) has reached 100%  

AB-type block copolymers can be synthesized by adding a second monomer (B) to preformed polyvinylterrocene anion (A), wdiich was synthesized as described above. Styrene, methyl methacrylate, and propylenesulfide have been appbed as monomer B. Typical results are given in Tab. 15.2 and Fig. 15.8. 

It is interesting to note that the block copolymers show only one instead of two glass transition temperature (Tab. 15.3). This might be due to the fact that the molar mass of segment A is still too small for being able to establish its own phase. 

Monomer A Monomer B Homopolymer A/°C Homopolymer B/°C Block copolymers AB/°C 

The sequential coupling of functionally terminated chains of different chemical structure can be used to make block copolymers, - including 

In a number of cases, the block used with the PDMS is sufficiently polar to give an amphiphilic block copolymer. Such materials form interesting structures in polar or nonpolar solvents. In the first case, the polar chains act like a corona around the nonpolar core, and in the latter, the nonpolar chains are a corona around the polar core. Examples include blocks of poly(ethylene oxide), acrylamides, sugars, glucono-lactone, hydrolysable siloxanes, and maleic anhydride—vinyl ethyl ethers.  

In related work, NMR studies have been carried out on PDMS chains onto which octyl groups had been grafted. Other examples of grafted systems include poly(ethylene oxide), polyurethanes, polyfbutyl methacrylate), and gelatin.  

In this type of material, two networks are formed, either simultaneously or sequentially, in such a way as to interpenetrate one another. The networks thus communicate with one another through interchain physical forces and entanglements, rather than through covalent bonds. A particularly simple example is the simultaneous formation of two PDMS networks, one by a condensation end-linking reaction and the other by an addition end-linking reaction, with the two types of chains mixed at the molecular level. -  

Warrick, E. L. Pierce, O. R. Polmanteer, K. E. Saam, J. C., Silicone Elastomer Developments 1967-1977. Rubber Chem. Technol. 1979,52,437-525. 

In most cases the different constituent blocks are incompatible, giving rise to intramolecular phase separation, but the chemical connectivity restricts the special dimension of phase segregation to the nanoscale. As a result, at sufficiently high molecular weight, monodisperse block copolymers form a rich variety of self-assembled structures or an array of periodic nanostructures with a periodicity of 10-100 nm, commonly referred to as microphase-separated structures. By changing the relative composition, the compatibility between the component polymers, and the architecture of the copolymer molecules, the size and type of nanostructures can be precisely controlled [1-6]. 

In the following Section 3.1.1, the morphology is discussed for block copolymer nanostructures via self-assembly (Section 3.1.1.1), in dependence on the chain architecture (Section 3.1.1.2), for blends of block copolymers with a constituent homopolymer (Section 3.1.1.3), for processing-induced influences (Section 3.1.1.4), and for block copolymer nanocomposites (Section 3.1.1.5). Section 3.1.2 gives an overview of nano- and micromechanical deformation effects. 

This is reflected in the rj, T2 values (see Table 8.3). For example, the styrene/MMA pair has rj = 0.02, V2 = 20.0 when initiated by QHsMgBr in ether at —78°C. Thus the polymerization of the mixture in this case will cause homopolymerization of MMA followed by that of styrene. However, excess MMA will add to living polystyrene producing a block copolymer of the two monomers. 

Anionic polymerization utilizing the living polymer technique is particularly well suited to preparing block copolymers. The simplest vinyl-type block copolymer is a two-segment molecule illustrated by 

Other common block copolymer structures are shown below  

The properties of block copolymers differ from those of a blend of the correponding homopolymers or a random copolymer (Chapter 7) with the same overall composition. An important practical example is the ABA-type styrene/butadiene/styrene triblock copolymer. These behave as thermoplastic elastomers. Ordinary elastomers are cross-linked by covalent bonds, e.g., vulcanization (see Chapter 2) to impart elastic recovery property, as without this there will be permanent deformation. Such cross-linked rubbers are therraosets and so cannot be softened and reshaped by molding. However, solid thermoplastic styrene/butadiene/styrene triblock elastomers can be resoftened and remolded. This can be explained as follows. At room temperature, the triblock elastomers consist of glassy, rigid, polystyrene domains 

Most interesting from the standpoint of commercial development is the formation of block copolymers by the living polymer method. Sequential addition of monomers to a living anionic polymerization system is at present the most useful method of synthesizing well-defined block copolymers. Depending on whether monofunctional or difunctional initiators are used, one or both chain ends remain active after monomer A has completely reacted. Monomer B is then added, and its polymerization is initiated by the living polymeric carbanion of polymer A. This method of sequential monomer addition can be used to produce block copolymers of several different types. 

Polymers are not usually mutually miscible. Even polymer mixtures with other substances (fillers, dyes, stabilizers, softeners, etc.) are not always stable. At the same time, materials are often required to have the properties of a mixture of two or more components. Mutually insoluble, incompatible components can be held together by the addition of a compound exhibiting affinity to all components. Block and graft copolymers often possess the required property to affect the van der Waals force distribution at phase boundaries. 

Block copolymers themselves are also finding rapidly expanding applications on an industrial scale. A sandwich copolymer (triblock) with an elastomeric core (polybutadiene, polyisoprene, etc.) and plastomeric ends (polystyrene, etc.) represents a physically vulcanizing rubber (plastomeric elastomer). It can be processed above the glass transition temperature of the plastomeric blocks by work-efficient technologies (injection molding, extrusion, etc.). At temperatures below the Tg of the plastic blocks, the copolymer behaves as vulcanized rubber. 

The above sentences should indicate the reasons why block copolymers are the subject of increasing attention. They can be prepared by any of the known polymerization techniques. The problems of their synthesis have been treated in several large monographs [262-268]. 

Mechanochemical preparation of block copolymers is of historic interest. In a polymer blend, mechanical stress causes degradation, producing macroradicals which in turn lead to the formation of a large number of block and graft copolymers. Berlin assumes [269] that the radicals predominantly attack stress-activated backbone C—C bonds. Radical combination is not regarded as important as radical concentration in the system is negligible. 

The radical mechanism generates block copolymers mainly by means of multifunctional or polymeric initiators [270] or by the combination of radical chain ends produced by the separation of two propagating monomers into an aqueous and a micellar phase (in emulsion) [271], 

The one-prepolymer method involves one of the above prepolymers with two small reactants. The macrodiol is reacted with a diol and diisocyanate 

The block lengths and the final polymer molecular weight are again determined by the details of the prepolymer synthesis and its subsequent polymerization. An often-used variation of the one-prepolymer method is to react the macrodiol with excess diisocyanate to form an isocyanate-terminated prepolymer. The latter is then chain-extended (i.e., increased in molecular weight) by reaction with a diol. The one- and two-prepolymer methods can in principle yield exactly the same final block copolymer. However, the dispersity of the polyurethane block length (m is an average value as are n and p) is usually narrower when the two-prepolymer method is used. 

The prepolymers described above are one type of telechelic polymer. A telechelic polymer is one containing one or more functional end groups that have the capacity for selective reaction to form bonds with another molecule. The functionality of a telechelic polymer or prepolymer is equal to the number of such end groups. The macrodiol and macrodiisocyanate telechelic prepolymers have functionalities of 2. Many other telechelic prepolymers were discussed in Sec. 2-12. (The term functional polymer has also been used to describe a polymer with one or more functional end groups.) 

In the first step strictly living conditions have to be obeyed. 

The active species of the first block have to add the second monomer without side reactions. 

The first requirement is obvious the second one is of key importance in the preparation of block copolymers. It has been shown that the original anionic species 

A number of papers describe the alleged formation of block copolymers by cationic ring-opening polymerization. Some of these claims are insufficiently substantiated, mostly because it was not shown without doubt that block copolymers have been obtained. 

In our opinion, to make sure that block copolymer resulted, three products have to be obtained and their GPC traces compared, namely the first block, which has to be killed and isolated for this purpose, the alleged block copolymer, and the second block, prepared independently, and with the length (DPn) close to this, which has been assumed to be linked in the block copolymer. 

A theoretical expression giving the scattering intensity I(q) through the full range of q can be derived by using the same random phase approximation method used for a polymer blend. Again, we can only quote the final result here, which was obtained by Leibler,9 under exactly the same assumptions as those used for the derivation of 

Equation (6.47). The system considered consists of diblock copolymer molecules of volume v each, in which the volume fractions of the two types of blocks are/i and f2 (== 1 — /i), respectively. It is assumed that the flexibilities of the two block chains are similar, such that 

The intensity therefore approaches zero as q 0, and this is a consequence of the incompressibility assumption. For qRg 1, on the other hand, the structure factor S(q) can be approximated by 

For a homopolymer blend with equal numbers of molecules of type 1 and type 2, Equation (6.47) reduces, in the limit q 1, to 

The effect of a second component in the phase structure is treated in this chapter in several stages. First, it was assumed that both components were of identical size and behaved ideally, i.e., they do not interact. Assuming further that there is no cocrystallization, the typical eutectic phase diagram of Fig. 2.27 results. The discussion of the experimental evaluation of phase diagrams indicated the effect of formation of solid solutions, as seen in Fig. 7.2. The deviation from an ideal solution can be treated by introduction of an activity as in Fig. 7.3. Next, in Sect. 7.1.2 the shape-difference of two components was treated using the free-volume argument of Hildebrandt, and finally, the interaction parameter % was introduced to treat real solutions in Fig. 7.4-6. The examples treated in Sects. 7.1.3-5 dealt then with components that were isolated molecules. 

Typical phase morphologies of block copolymers are illustrated in Figs. 5.38 0 and 5.79. In the classification of phases, the phase-separated block copolymers are considered to be amphiphilic liquid crystals despite the fact that inside the phase areas the typical liquid-crystalline order is missing (see Sect. 5.5). In this section the question will be addressed what happens when the usually micro- or nano-phase separated block copolymers show solubility, i.e., when the amphiphilic liquid crystal becomes thermotropic, i.e., dissolve at a given temperature. 

In the copolymers described in Sect. 3.4, the multiple components of the system are joined by chemical bonds and demixing, needed for complete phase separation of the components, is strongly hindered and may lead to partial or complete decoupling from crystallization. The resulting product is then a metastable micro- or nanophase-separated system with arrested, local equilibria. In some cases, however, it is possible to change the copolymer composition during the crystallization or melting by chemical reactions, such as trans-esterification or -amidation. In this case, the chemical and physical equilibrium must both be considered and a phase separation of the copolymer into either crystalline homopolymers or block copolymers is possible. 

The thermodynamics of macromolecular solutions with small molecules is described in Sect. 7.1. A term frequently used to describe solutions of macromolecules is blend. The word is obviously derived from the mixing process and should only be used when the resulting system is not fully analyzed, i.e., one does not know if a dissolution occurred or the phases remained partially or fully separated. The term blend should best be used only if a phase-separated system has changed by vigorous mixing to a finer subdivision, containing micro- or nanophases. The differences between nanophase separation and solution can be rather subtle, as is seen, for example, in the thermodynamic description of block copolymers (see Sect. 7.1). Micro- and nanophase-separated systems can often be stabilized by compatibilizers that may be block copolymers of the two components. Their properties can be considerably different from macrophase separated systems or solutions and, thus, of considerable technical importance. 

The problems of nonequilibrium crystallization and melting discussed in Chap. 6 and Sect. 7.1 for single-component systems, are even more pronounced for multi-component systems. The additional problem of separating the components by diffusion into phases of different concentration complicates the description of multi-component systems even further. Usually equilibrium concentrations cannot be achieved at the moment of crystallization or melting, i.e., the processes of component diffusion and crystallization/melting are not molecularly coupled. One must thus always consider two deviations from equilibrium. One is the formation of non- 

FIGURE 12. Dynamic mechanical properties of Kraton samples. 

Type Structure % Styrene Plateau modulus (psi) Mid-block Tg (°C) Tensile strength (psi) Elongation (%) 

Monc-directional chain growth potyoondonsahon by soquonllal monomar addttlotr 

The weight average number of polypropylene oxide units for the propylene oxide units (i.e., h,j,PO) obtained by this method was found to be 16.55 which was in good agreement with the value of 16.4 supplied by the polymer manufacturer. 

Pyrograms will differentiate between random copolymers and block polymers or polymer mixtures [35-38]. Presence of foreign monomer may interrupt chain transfer processes involved in the degradation. Similar products result but their quantities as determined from peak heights are different. Voigt demonstrated that even for closely related polyolefins the pyrograms will distinguish between polyethylene-propylene block and random copolymers of the same composition [36]. 

Monge and Haddleton [39] reported on the use of on-line NMR in the analysis of poly(n-hydroxysuccinamide methacrylate) - f -poly(methylmethacrylate AB) type block copolymer. 

Priorr in Surfactants in Consumer Products Theory, Technology and Application, Ed., J. Falbe, Springer Verlag, Heidelberg, Germany, 1987, p.5-22. 

Ryan and J.L. Stanford, Comprehensive Polymer Science, Eds., G. Allen and J.C. Bevington, Pergamon Press, Oxford, UK, 1989, p.427-455. 

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Gaines [13] has reported on dimethylsiloxane-containing block copolymers. Interestingly, if the organic block would not in itself spread, the area of the block polymer was simply proportional to the siloxane content, indicating that the organic blocks did not occupy any surface area. If the organic block was separately spreadable, then it contributed, but nonadditively, to the surface area of the block copolymer. 

Several studies have concerned the microstnicture of lamellae in materials such as the block copolymers polystyrene-h/oc/r-poly-l-vinylpyridine [139] and polystyrene-h/oc/r-polybutadiene [140], as well as single crystals of poly-para-xylylene [139], and reveal features (such as intersecting lamellae (figure Bl.19.29)) that had not been previously observed. 

Annis B K, Noid D W, Sumpter B G, Reffner J R and Wunderlich B 1992 Application of atomic force microscopy (AFM) to a block copolymer and an extended chain polyethylene Makromol. Chem., Rapid. Commun. 13 169 Annis B K, Schwark D W, Reffner J R, Thomas E L and Wunderlich B 1992 Determination of surface morphology of diblock copolymers of styrene and butadiene by atomic force microscopy Makromol. Chem. 193 2589... 

Shi A C, Noolandi J and Desai R C 1996 Theory of anisotropic fluctuations in ordered block copolymer phases Macromolecules 29 6487... 

Fraai]e J G E M 1993 Dynamic density functional theory for micro-phase separation kinetics of block copolymer melts J. Chem. Phys. 99 9202... 

In block copolymers [8, 30], long segments of different homopolymers are covalently bonded to each otlier. A large part of syntliesized compounds are di-block copolymers, which consist only of two blocks, one of monomers A and one of monomers B. Tri- and multi-block assemblies of two types of homopolymer segments can be prepared. Systems witli tliree types of blocks are also of interest, since in ternary systems the mechanical properties and tire material functionality may be tuned separately. 

Figure C2.1.11. Morjrhologies of a microphase-separated di-block copolymer as function of tire volume fraction of one component. The values here refer to a polystyrene-polyisoprene di-block copolymer and ( )pg is tire volume fraction of the polystyrene blocks. OBDD denotes tire ordered bicontinuous double diamond stmcture. (Figure from [78], reprinted by pemrission of Annual Reviews.)...

Bates F S and Fredrickson G FI 1999 Block copolymers—designer soft materials Phys. Today 52 32- 8... 

Wanka G, Floffman FI and Ulbrict W 1990 The aggregation behavior of poly-(oxyethylene)-poly(oxypropylene)-poly-(oxyethylene)-block copolymers in aqueous solutions Colloid Polym. Sc/. 268 101-17... 

Waldman D A, Kolb B U, McCarthy T J and Hsu S L 1988 Infrared study of adsorbed monolayers of poly(styrene-propylene sulphide) (PS-PPS) block copolymers Polym. Mater. Sc/. Eng. 59 326-33... 

The first case concerns particles with polymer chains attached to their surfaces. This can be done using chemically (end-)grafted chains, as is often done in the study of model colloids. Alternatively, a block copolymer can be used, of which one of the blocks (the anchor group) adsorbs strongly to the particles. The polymer chains may vary from short alkane chains to high molecular weight polymers (see also section C2.6.2). The interactions between such... 

Finally, we briefly mention interactions due to adsorbing polymers. Block copolymers, witli one block strongly adsorbing to tire particles, have already been mentioned above. Flere, we focus on homopolymers tliat adsorb moderately strongly to tire particles. If tliis can be done such tliat a high surface coverage is achieved, tire adsorbed polymer layer may again produce a steric stabilization between tire particles. 

Fig. 6. Snapshot from a dynamic density functional simulation of the self-organisation of the block copolymer PL64 (containing 30 propylene oxide rmd 26 ethylene oxide units (EO)i3(PO)3o(EO)i3) in 70% aqueous solution. The simulation was carried out during 6250 time steps on a 64 x 64 x 64 grid (courtesy of B.A.C. van Vlimmeren and J.G.E.M. Praaije, Groningen).

Fraaije, J.G.E.M., Van Vlimmeren, B.A.C., Maurits, N.M., Postma, M., Evers, O.A., Hoffmann, C., Altevogt, P., Goldbeck-Wood, G. The dynamic mean-field density functional method and its application to the mesoscopic dynamics of quenched block copolymer melts. J. Chem. Phys. 106 (1997) 4260-4269. 

The structure of a block copolymer consists of a homopolymer attached to chains of another homo-polymer. 

Poly butylene (PB) Styrene-butadiene block copolymer... 

Heterogeneous alloys can be formed when graft or block copolymers are combined with a compatible polymer. Alloys of incompatible polymers can be formed if an interfacial agent can be found. 

The desired form in homopolymers is the isotactic arrangement (at least 93% is required to give the desired properties). Copolymers have a random arrangement. In block copolymers a secondary reactor is used where active polymer chains can further polymerize to produce segments that use ethylene monomer. 

Styrene-Butadiene-Styrene Block Copolymers. Styrene blocks associate into domains that form hard regions. The midblock, which is normally butadiene, ethylene-butene, or isoprene blocks, forms the soft domains. Polystyrene domains serve as cross-links. 

Polyolefin Polyester Block copolymers of styrene and butadiene or styrene and isoprene Block copolymers of styrene and ethylene or styrene and butylene Poly(vinyl chloride) and poly(vinyl acetate) ... 

Cohen and Ramost describe some phase equilibrium studies of block copolymers of butadiene (B) and isoprene (I). One such polymer is described as having a 2 1 molar ratio of B to I with the following microstructure ... 

Table 3.4 Temperature Coordinate and Relative Height (in Parenthesis) for the Two Loss Tangent Maxima Observed in Mixtures of Isoprene-Butadiene Block Copolymers with Homopolymers of These Two Repeat Units in the Same Proportion ...

Amide interchange reactions of the type represented by reaction 3 in Table 5.4 are known to occur more slowly than direct amidation nevertheless, reactions between high and low molecular weight polyamides result in a polymer of intermediate molecular weight. The polymer is initially a block copolymer of the two starting materials, but randomization is eventually produced. 

On the basis of these observations, criticize or defend the following proposition The fact that the separate spots fuse into a single spot of intermediate Rf value proves that block copolymers form between the two species within the blend upon heating. 

Block copolymers are closer to blends of homopolymers in properties, but without the latter s tendency to undergo phase separation. As a matter of fact, diblock copolymers can be used as surfactants to bind immiscible homopolymer blends together and thus improve their mechanical properties. Block copolymers are generally prepared by sequential addition of monomers to living polymers, rather than by depending on the improbable rjr2 > 1 criterion in monomers. 

The successive repeat units in strucutres [VI]-[VIII] are of two different kinds. If they were labeled Mj and M2, we would find that, as far as microstructure is concerned, isotactic polymers are formally the same as homopolymers, syndiotactic polymers are formally the same as alternating copolymers, and atactic polymers are formally the same as random copolymers. The analog of block copolymers, stereoblock polymers, also exist. Instead of using Mj and M2 to differentiate between the two kinds of repeat units, we shall use the letters D and L as we did in Chap. I. 

Blister or strip packs Blister packaging Bloch walls Block copolymers... 

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