Microdomain structure

Laser ablation of polymer films has been extensively investigated, both for application to their surface modification and thin-film deposition and for elucidation of the mechanism [15]. Dopant-induced laser ablation of polymer films has also been investigated [16]. In this technique ablation is induced by excitation not of the target polymer film itself but of a small amount of the photosensitizer doped in the polymer film. When dye molecules are doped site-selectively into the nanoscale microdomain structures of diblock copolymer films, dopant-induced laser ablation is expected to create a change in the morphology of nanoscale structures on the polymer surface. 

As aforementioned, diblock copolymer films have a wide variety of nanosized microphase separation structures such as spheres, cylinders, and lamellae. As described in the above subsection, photofunctional chromophores were able to be doped site-selectively into the nanoscale microdomain structures of the diblock copolymer films, resulting in nanoscale surface morphological change of the doped films. The further modification of the nanostructures is useful for obtaining new functional materials. Hence, in order to create further surface morphological change of the nanoscale microdomain structures, dopant-induced laser ablation is applied to the site-selectively doped diblock polymer films. 

Drug Release from PHEMA-l-PIB Networks. Amphiphilic networks due to their distinct microphase separated hydrophobic-hydrophilic domain structure posses potential for biomedical applications. Similar microphase separated materials such as poly(HEMA- -styrene-6-HEMA), poly(HEMA-6-dimethylsiloxane- -HEMA), and poly(HEMA-6-butadiene- -HEMA) triblock copolymers have demonstrated better antithromogenic properties to any of the respective homopolymers (5-S). Amphiphilic networks are speculated to demonstrate better biocompatibility than either PIB or PHEMA because of their hydrophilic-hydrophobic microdomain structure. These unique structures may also be useful as swellable drug delivery matrices for both hydrophilic and lipophilic drugs due to their amphiphilic nature. Preliminary experiments with theophylline as a model for a water soluble drug were conducted to determine the release characteristics of the system. Experiments with lipophilic drugs are the subject of ongoing research. 

Fig. 17 In situ SAXS (a) and SANS profiles (b) obtained at various temperatures and schematic models of microdomain structures in temperature ranges between room temperature and 72 °C (c), between 72 and 122 °C (d), and between 122 and 177 °C (e). From [74]. Copyright 2003 Wiley...

Fig. 56 Phase diagram of blend of PS-fi-PI with PS. T0dt. o TDMt, Toot- Vertical lines separating microdomain structures are obtained from total volume fraction PS in system. Dashed line results of mean-field calculation for ODT. The OOT line which exists at volume fractions ps 5 ub was obtained during a heating process. From [174]. Copyright 2000 American Chemical Society...

Polushkin E, Alberda van Ekenstein GOR, Knaapila M, Ruokolainen J, Torkkeh M, Serimaa R, Bras W, Dolbnya 1, Ikkala O, ten Brinke G. Intermediate segregation type chain length dependence of the long period of lamellar microdomain structures of supramolecular comb-coil diblocks. Macromolecules 2001 34 4917-4922. 

The most important structural features of these SPUs are the microphase-separated (or microdomain) structures which are formed in their molecular assembly systems. In 1972, Lyman [5] suggested that the antithrombogenic property of his PEUU may be brought about by its microarchitectural effect. In the same year (1972), Imai and Masuhara [6,7] reported that micro-heterogeneous surface structure was responsible for its antithrombogenicity. 

Since the 1970s, a number of reports on biomaterials other than SPU have also been presented, providing us with evidence which shows the important role played by microdomain structures in realizing excellent biomedical properties. For instance, an A-B-A type block copolymer (HEMA-St—HEMA) (See Sect. 4.2) was shown to form microdomain structure and to exhibit excellent blood compatibility in both in vitro and in vivo tests. 

A series of polyamine-graft copolymers (See Sect. 4.3) were found to form microdomain structure and to exhibit unique biomedical behavior at the interface with living cells, e.g. blood platelets or lymphocytes. Although a number of postulates were proposed to explain the unique behavior of microdomain-structured surface, mechanisms for the mode of interaction of living cells with any of the domain-structured materials have not been adequately explained. In Sect. 4, the author will review results on the biomedical behavior of SPUs, HEMA-STY, and polyamine-graft copolymers, and discuss their interfacial properties in terms of the random network concept of water molecules on the material s surface. 

As stated in Chapter 1, microdomain-structured surfaces are believed to play an important role in their interactions with cells, proteins, and other biological elements. In this Chapter, the author will discuss biomedical behavior of three types of microdomain-structured materials segmented polyurethanes, A-B-A block copolymers, and polyamine-graft copolymers. 

Yui et al. [86-89] have previously reported another type of microdomain-structured polymer, po y(propylene oxide) (PPO)-segmented nylon 610, which has a crystalline-amorphous microdomain structure ... 

A series of polymine-graft copolymers of styrene [92-95] and hydroxyethyl methacrylate [96-98] were found to form a microdomain structure and exhibit unique biomedical behavior at the interface with living cells, such as blood platelets and lymphocytes. The most intensive studies were made with poly(hydroxyethyl methacryIate)-0ra/t-polyamine copolymers (HA) ... 

The random-network concept discussed above may be applicable, in principle, to the surfaces of some microdomain-structured materials. As stated in Sect. 4.2, the HEMA-STY copolymer showed the best blood compatibility after... 

Khokhlov, A.R., Nyrkova, I.A. (1992). Compatibility enhancement and microdomain structuring in weakly charged polyelectrolyte mixtures. Macromolecules, 25, 1493-1502. 

On an even smaller scale is the microdomain structure at 0.01-. im spacing. This is interpreted as a structure where the crystallites of about 0.01-pm spacing arc tied together by molecules in the amorphous regions. Plasticizer swells llie amorphous regions without dissolving Hie crystallites. 

Helfand, E. and Wasserman, Z. R. (1982). Microdomain structure and the interface in block copolymers. In Developments in block copolymers,Nol. 1, (ed. I. Goodman), p. 99. Applied Science, London. 

Heteropolymers can self-assemble into highly ordered patterns of microstructures, both in solution and in bulk. This subject has been reviewed extensively [1,123-127]. The driving force for structure formation in such systems is competing interactions, i.e., the attraction between one of the monomer species and the repulsion between the others, on the one hand, and covalent bonding of units within the same macromolecule, on the other hand. The latter factor prevents the separation of the system into homogeneous macroscopic phases, which can, under specific conditions, stabilize some types of microdomain structures. Usually, such a phenomenon is treated as microphase separation transition, MIST, or order-disorder transition, ODT. 

When the block length becomes comparable with Ny distinctions between the behaviors of two copolymers practically disappear. At L > 200, one observes that T Ly with y = 4/3. In this case, the characteristic scale of the microdomain structure behaves as r Ls with <5 = 1/2. This dependence is caused by the fact that flexible chains in the melt have a Gaussian conformation, and the average size of any chain section of n units is proportional to ft1/2 [75]. Hence, for sufficiently large Vs, the spatial scale of microinhomogeneities in the system is determined only by the block size. However, the behavior of the random-block copolymer at L < 102 is more complicated. In particular, r has a minimum at L 10. 

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