Homopolymer blend-diblock copolymer

Fig. 26 Critical exponent of the susceptibility y versus diblock content of two homopolymer blend-diblock copolymer melts. The crossover to the renormalized Lifshitz critical behavior with y = 1.62 is clearly visible. Differences of the two blends are remarkable In PEE PDMS a plateau of y = 1.62 and a further crossover to a renormalized Lifshitz behavior is found. In PB PS, on the other hand a double critical point with the Lifshitz critical exponent y = 1.62 is observed...

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 2. Transmission electron micrographs of (a) a blend of polybutadiene (25 vot %) and polyisoprene (75 wt %) (b) polyisoprene homopolymer (c) diblock copolymer 2143. Magnifications as indicated.

The LC LC separation mode that employs narrow zone of retention promoting substance is easy to employ because the retention volume of interacting polymer can be adjusted by the time delay between barrier and sample injection. The longer time delay, the lower retention volume of interacting macromolecules because the extended time is allowed for their fast elution in the exclusion mode, before their impact with the barrier. As indicated, multiple barriers can be employed to separate three or more sample constituents such as multicomponent polymer blends, statistical copolymers of different compositions or parent homopolymers from diblock copolymers. 

The expressions presented above comprise a complete set for the NSCFT of polymers and polymer-solvent blends, applicable to both homopolymers and diblock copolymers. The generalizations to other architectures are generally straightforward. In all cases, one must solve a diffusion equation for polymer propagators, from which the polymer volume fractions are calculated. When solvent is present, its distribution is then calculated from the incompressibility condition. However, in order to solve the diffusion equation, the potential fields tup(r) are needed, and they depend on the volume fraction profiles. As a result, the problem must be solved self-consistently. 

Bodycomb J, Yamaguchi D, Hashimoto T (1996) Observation of a discontinuity in the value of Ijjj-i at the order-disorder transition in diblock copolymer/homopolymer and diblock copolymer/diblock copolymer blends. Polym J 28 821-824... 

Figure B3.6.5. Phase diagram of a ternary polymer blend consisting of two homopolymers, A and B, and a synnnetric AB diblock copolymer as calculated by self-consistent field theory. All species have the same chain length A and the figure displays a cut tlirough the phase prism at%N= 11 (which corresponds to weak segregation). The phase diagram contains two homopolymer-rich phases A and B, a synnnetric lamellar phase L and asynnnetric lamellar phases, which are rich in the A component or rich in the B component ig, respectively. From Janert and Schick [68].

A diblock copolymer, 71% polyisoprene (1) by weight and 29% polybutadiene (B), was blended in different proportions into a 71%-29% mixture of the individual homopolymers. The loss tangent was measured as a function of temperature for various proportions of copolymer. Two peaks are observed ... 

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. 

Diblock copolymers, as illustrated in Fig. 5.8 c), comprise homopolymer sequences of the two monomers linked together. The homopolymer blocks may be either compatible or incompatible, depending on their chemical structure. If the sequences are compatible, they will mix to form a material with characteristics similar to those of a blend of the two homopolymers. On the other hand, if the blocks are incompatible, they will tend to segregate from one another to form distinct phases. Each phase will display properties characteristic of the homopolymer, modified by the constraints placed on them by having one end attached... 

NSE measurements at zero average contrast conditions on a symmetric diblock copolymer of H-PS and D-PS dissolved in an appropriate mixture of proto-nated and deuterated benzene are reported [171,172]. The measurements were performed at different concentrations c > c. For comparison, the interdiffusion of a corresponding blend of H-PS and D-PS homopolymers dissolved in deuterated benzene was studied, too [171]. Owing to the relatively low molecular masses, only the regime Q1/2 < 1 was accessible, and the internal modes could not be probed. 

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.

With the discussion above in mind, it is now possible to provide a similar semi quantitative framework in which to view the results obtained on ternary systems (homopolymer A, homopolymer B, diblock AB) and on binary blends of one homopolymer and a diblock copolymer. Of particular importance is the need for an explanation of the fact that the diblock copolymer may serve either as an emulsifying agent (9,25) or as a homogenizing agent (1, 4 ) in ternary blends. 

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 effect of blending an AB diblock copolymer with an A-type homopolymer has been the subject of many research activities. On a theoretical basis the subject was investigated e.g. by Whitmore and Noolandi [172] and Mat-sen [173]. If a diblock exhibiting lamellae morphology is blended with a homopolymer of high molecular weight, macrophase separation between the... 

A phase diagram of the symmetric PS-fc-PI blended with PS homopolymer of shorter chain lengths was constructed by Bodycomb et al. [ 174]. The effect of blend composition on the ODT is shown in Fig. 56 along with the results of mean-field calculations. In analogy to MFT the addition of homopolymer decreases the ODT temperature for the nearly symmetric diblock copolymer. 

Fig. 6 a DSC cooling scans (10°Cmin ) for poly(e-caprolactone) (PCL) and poly(p-dioxanone) (PPDX) homopolymers, diblock copolymers and a 50/50 blend, b Subsequent heating scans (10 °Cmin 1). (From [103], Reproduced with permission of the Royal Society of Chemistry)... 

Chen et al. [92] also performed self-nucleation experiments by DSC in PB-fr-PEO diblock copolymers and PB/PB-b-PEO blends. The cooling scans presented in their work showed that a classical self-nucleation behavior was obtained for PEO homopolymer and for the PB/PB-b-PEO blend where the weight fraction of PEO was 0.64 and the morphology was lamellar in the melt. For PB/PB-fr-PEO blends with cylinder or sphere morphology, the crystallization temperature remained nearly constant for several self-seeding temperatures evaluated. This observation indicates that domain II or the self-nucleation domain was not observable for these systems, as expected in view of the general trend outlined earlier. 

One can have the same type of situation in a blend of two mutually immiscible polymers (e.g., polymethylbutene [PMB], polyethylbutene [PEB]). When mixed, such homopolymers form coarse blends that are nonequilibrium structures (i.e., only kinetically stable, although the time scale for phase separation is extremely large). If we add the corresponding (PEB-PMB) diblock copolymer (i.e., a polymer that has a chain of PEB attached to a chain of PMB) to the mixture, we can produce a rich variety of microstructures of colloidal dimensions. Theoretical predictions show that cylindrical, lamellar, and bicontinuous microstructures can be achieved by manipulating the molecular architecture of block copolymer additives. 

In binary blends of A homopolymer and AB diblock copolymer, the interplay between microphase separation and macrophase separation is controlled mainly by the relative length of the chains, in addition to the composition of the mixture. Homopolymers shorter than the corresponding block tend to be solubilized within the corresponding domain of a microphase-separated structure. As the homopolymer molecular weight increases to approach that of the corresponding... 

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