Order-disorder transition homopolymer

Ruokolainen J, Torkkeli M, Serimaa R, Komanschek E, ten Brinke G, Ikkala O. Order-disorder transition in comblike block copolymers obtained by hydrogen bonding between homopolymers and end-functionalized oligomers poly(4-vinylpyridine)-pentadecylphenol. Mactomolecules 1997 30 2002-2007. 

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.

Fig. 6.30 Order-disorder transition in a binary homopolymer/diblock blend as a function of volume fraction of homopolymer computed using SCFT (Whitmore and Noolandi 1985a). The symmetric diblock has N = 100. Curves are shown for different values of /3 = NJNC. The temperature scale on the left-hand side was calculated for PS-PB/PB blends.

Fig. 6.36 Phase diagram calculated using SCFT for a blend of a symmetric diblock with a homopolymer with fl = 1 (see Fig. 6.32 for a blend with a diblock with / = 0.45) as a function of the copolymer volume fraction

In the case of diblock copolymer melts, which are the simplest model system for the elucidation of structure formation processes involving BCPs in nanoporous hard templates, only the two immiscible blocks have to be considered as components. Self-consistent field methods were applied to study the morphologies of liquid diblock copolymer/homopolymer mixtures that were considered as a model system for triblock copolymers in sol solutions [182], of pure diblock copolymer melts [200-202], and of order-disorder transitions in diblock copolymer melts [203]. For example, Li et al. found for a model diblock copolymer that forms cylinders in the bulk... 

The groups of Kramer and Hawker provided an example where the target polymer could be made using sequential CFR polymerizations, but CuAAC simplified the process and made it possible to obtain the polymer with a precise molecular weight and a low polydispersity index (PDl). Attempts to make poly(benzyl methacrylate)-b-poly(butyl acrylate) with equal volume fractions of each block to be used for the determination of order-disorder transition (ODT) led to materials with imprecise volume fractions and PDls higher than 1.3. Instead, by using preformed homopolymers that were then coupled by CuAAC, the authors were able to make a small library of covalent diblock copolymers with low PDIs, while also performing fewer total reactions. 

For instance, order-disorder transitions of BCP blends (typically related to macrophase separation processes) in thin films have been studied by Jeong et al. [48]. They used mixtures of PS-b-PMMA having PMMA cylindrical microdomains with homopolymers of either PMMA or poly(ethylene oxide) (PEO) and studied the morphological transitions and the formation of macrophase-separated domains in thin films (Fig. 6.7). Whereas the microdomains in all thin films are oriented perpendicular to the film surface, they found that the miscibility between PMMA homopolymer and PMMA block in thin film was enhanced compared with that in bulk at a given molecular weight of PMMA homopolymer. Equally, the PMMA homopolymer chains in thin films were more localized to the center of PMMA microdomains than in the bulk, which results in a larger increase of the lattice spacing (D) in the former. 

If the noise term is turned off, the system is driven towards the nearest saddle point. Therefore, the same set of equations can be used to find and test mean-field solutions. The complex Langevin method was first applied to dense melts of copolymers [74], and later to mixtures of homopolymers and copolymers [80] and to diluted polymers confined in a slit under good solvent conditions [77]. Figure 2 shows examples of average density configurations (p ) for a ternary block copolymer/homopolymer system above and below the order/disorder transition. 

Fig. 2 Averaged densities across the order-disorder transition in a two-dimensional ternary system with A, B homopolymers and A-B copolymers (20% homopolymer volume fraction), as obtained from Complex Langevin simulation runs...

Fig. 4 Snapshots of (j) for the same ternary A + B + AB system as in Fig. 2, at 70% homopolymer volume fraction, for different above and below the order-disorder transition, as obtained from Monte Carlo simulations with o> switched off (EP theory). From [83]...

Fig. 9 Anisotropy parameters 2 (solid) and 5 4 (dashed) vs. xN for different homopolymer volume fractions

Consider now a block copolymer composed of two chemically dissimilar blocks each of which is noncrystalline. The same factors that are involved in homopolymer mixing will still be operative so that phase separation would be a priori expected. However, since the sequences in the block copolymer are covalently linked, macrophase separation characteristic of binary blends is prevented. Instead, microphase separation and the formation of separate domains will occur. The linkages at the A-B junction points further reduce the mixing entropy. There has to be a boundary between the two species and the junction point has to be placed in this interphase. The interphase itself will not be sharp and will be composed of both A and B units. Mixing of the sequences, and homogeneity of the melt, will be favored as the temperature is increased. There is then a transition temperature between the heterogeneous and homogeneous melt, known as the order-disorder transition. 

SAXS measurements have also been useful in studies of the morphology and phase behavior of block copolymer/homopolymer blends. SAXS data on PS blends with SB diblock copolymers showed the presence of microdomains, which disappeared as the order-disorder transition was approached with increased temperature [162]. The order-disorder transition and the order-order transition (change in gyroid to cylinder morphology) was investigated with SAXS for PS/SI diblock copolymer blends [163]. The interfacial thickness of PS/PMMA samples with... 

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... 

An A-B diblock copolymer is a polymer consisting of a sequence of A-type monomers chemically joined to a sequence of B-type monomers. Even a small amount of incompatibility (difference in interactions) between monomers A and monomers B can induce phase transitions. However, A-homopolymer and B-homopolymer are chemically joined in a diblock therefore a system of diblocks cannot undergo a macroscopic phase separation. Instead a number of order-disorder phase transitions take place in the system between the isotropic phase and spatially ordered phases in which A-rich and B-rich domains, of the size of a diblock copolymer, are periodically arranged in lamellar, hexagonal, body-centered cubic (bcc), and the double gyroid structures. The covalent bond joining the blocks rests at the interface between A-rich and B-rich domains. 

Y. Zhou, C. K. Hall and M. Karplus. First-order disorder-to-order transition in an isolated homopolymer model. Physical Review Letters, 77 (1996), 2822. 

In present study, we employed both SAXS and theological measurements to investigate the order-disorder and order-order transitions in a series of SIS triblock copolymer/low molecular weight PS homopolymer mixtures, which did not show macrophase separation in the whole temperature and composition range covered in this experiment, Phase diagrams obtained from both measurements were compared with the predictions based on the Whitmore-Noolandi theory. The difference between the theory and the experiment was discussed in terms of the change in homopolymer distribution and microdomain morphology by the addition of homopolymer to block copolymer. 

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