Homopolymers blends

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. 

F. S. Bates, W. Maurer, T. Lodge, M. F. Schulz, M. W. Matsen, K. Almdal, K. Mortensen. Isotropic Lifshitz behavior in block copolymer-homopolymer blends. Phys Rev Lett 75 4429-4432, 1995. 

Another example of favorable synergistic effects in ionomer/homopolymer blends is evident from a study of the tensile properties of blends of an SPS ionomer with PS. Over most of the composition range these two polymers are incompatible. For small additions of the SPS ionomer to PS, TEM studies of cast thin films show that... 

Table 1 lists some of the homopolymers and diblock copolymers which have been employed in our experimental investigations (1-8). Particular emphasis has been placed on blends containing 1,4 polybutadiene (1,4B). In one case, 1,4B was blended with various amounts of 1,2 polybutadiene (1,2B) and the corresponding 1,2B/1,4B diblock copolymer. A second major set of samples was constructed from various combinations of 1,4B and cis 1,4 polyisoprene (1,41) and 1, 41/1,4B diblock copolymers. A large number of ternary blends were studied, the preponderence of which contained either 25%, 50% or 75% (by weight) of a selected diblock copolymer, the remainder of the blend being comprised of one or both of the corresponding homopolymers. Homopolymer blends (0% diblock) and the pure copolymers (100% diblock) were also studied in detail. 

Figure 1. Phase diagram showing the three distinct regions discussed in the text. Key n, diblock copolymers O, homopolymer blends pip up, heterogeneous pip down, homogeneous solid points, 12B/1,4B open points, l,4l/l,4B half-open point, 1,4I/1,2B with the abscissa representing the weight fraction of 1,2B.

Figure 2. Schematic three-dimensional plot showing various planes of AB polymer/polymer composition. From left to right homopolymer blends blends containing 50 weight percent diblock copolymer diblock copolymers. 

The TEM (Fig. 44) and SAXS data clearly indicate that the structure is lamellar to the first order but modified by channels in the PI layers, leading to a PL pattern. However, Fredrickson s theoretical results indicate that in the SSL this structure is not the most favourable one [123]. In the WSL, similar PLs are to occur for equal weight fractions, even though lamellae are expected in that region [124]. A similar behaviour has been observed in the case of PI2PS homopolymer blends for the PL morphology [15]. 

Fig. 58 Lattice constants vs. volume fractions of PS phase for a blending a PI-0-PS-0-P2VP triblock terpolymer with PS homopolymer (blends I and II) and b blending a Pl-fr-PS-fr-P2VP triblock terpolymer with PI and P2VP homopolymers (blends III and IV). Arrows variations of ps with increasing volume fractions of added homopolymers. , , lattice constants of pure triblock terpolymers o, , A lattice constants of blends. Gray band between a and b expresses experimentally obtained microphase separation phase diagram for unblendend PI-6-PS-6-P2VP. From [159], Copyright 2002 Wiley...

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]. 

Phase ordering in block copolymers can be described by the same dynamic equation as in the case of homopolymer blends [Eqs. (53)—(55)] with the LG... 

There are relatively few entries in the non-fused dioxepin area, and most of these focus on reactions of these systems. For example the triflic acid-initiated polymerisation of 1,3-dioxepane in the presence of acetic acid and hexanedicarboxylic acid has been studied and mechanistic aspects discussed <00JPS(A)1232>. Biodegradable microspheres for the controlled delivery of drugs have been made from copolymers and homopolymer blends of L-lactide and l,5-dioxepan-2-one <00PP1628>. Ring contraction of 5-methylene-l,3-dioxepanes (eg. Ill) on reaction with trimethylsilyl trifluoromethanesulfonate in the presence of base afforded the exo tetrahydropyrans, in good yields <00TL2171>. 

Additionally, some properties unique to both systems may result. The majority of homopolymer blends are immiscible with one another and often experience poor interfacial adhesion between the separate phases. Since block copolymers are covalently linked together, macroscopic incompatibility at the interface is minimized. The macroscopic incompatibility of a two-polymer blend may be eliminated by the addition of a block copolymer derived from the two systems. Hence, copolymers can be used to strengthen blends of immiscible polymers by serving as emulsifiers (7-9). 

Microdomains of block copolymer/ homopolymer blends 25-A-diameter Pd clusters Metal-ion precursors, introduced into cast thin films of polymer microdomains, are reduced by high pressure hydrogen 60,61... 

Figure 4. Polarized optical micrographs of polymer blends, (a) two homopolymer blend with PE/PS = 50/50 (100x). (b) two homopolymers and PE-g-PS copolymer blend with PE/PE-g-PS/PS = 45/10/45 (lOOx).

This chapter is organized as follows. Section 6.2 is concerned with experiments on binary block copolymer/homopolymer blends, Section 6.3 deals with experiments on ternary blends containing a block copolymer and in Section 6.4 experiments on binary blends of block copolymers are reviewed. Theory for the corresponding type of blend is discussed successively in Sections 6.5 to 6.7. Finally, experiments on thin films are discussed in Section 6.8, separately from the work on bulk blends, in keeping with earlier chapters. 

Experiments on binary block copolymer/homopolymer blends... 

Table 6.1 Experimental studies of binary block copolymer/homopolymer blends. Adapted and extended from Roe and Rigby (1987)...

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