Material microphase structure

Of the microphase-structure dependent physical properties of ionomers, perhaps the most widely studied are glass transition temperatures, (Tg), and dynamic mechanical response. The contribution of the Coulombic forces acting at the ionic sites to the cohesive forces of a number of ionomeric materials has been treated by Eisenberg and coworkers (7). In cases in which the interionic cohesive force must be overcome in order for the cooperative relaxation to occur at Tg, this temperature varies with the magnitude of the force. For materials in which other relaxations are forced to occur at Tg, the correlation is less direct. 

Bonart was amongst the first to identify the orientation of the periodic microphase structure under tensile deformation. Bonart suggested that the hard domains are composed of laterally stacked HS. It was noted that in MDI polyether copolymers, the SS become fully extended along the stretch direction and begin to crystallize at strains of about 150%. In contrast, the HS were found initially to orient transverse to the stretch direction and ultimately to break up to allow orientation of the HS in the stretch direction [14], Similar observations were made by us on DBDI based materials [67], as shown in the following section. 

There is considerable interest in the properties of new mesomorphic materials, which are composed of molecules with novel architectures. These include rod-coil molecules [1], polyphilic molecules [2, 3], block-copolymers [4] and dendritic molecules [5]. In many of these systems microphase separation can be used to build new materials containing structures that are ordered on the nanoscale. Examples include the formation of spheres or rods within a uniform matrix of dififerent chemical... 

If techniques based upon fluorescence and phosphorescence spectroscopy are going to gain acceptance as routine tools in the industrial laboratory, they must prove their merit by establishing that they can provide important information about typical polymeric industrial materials. Such materials are frequently prepared from recipes, where the recipes themselves have been optimized for product performance and not for structural simplicity. This means that one is dealing with complex materials composed of mixtures of homopolymers and various kinds of copolymers. These may generate microphase structures, interfaces and interphase regions. One normally believes that the microscopic structure of the material and its dynamic response are somehow responsible for its desirable properties. 

The formation of nanopattemed functional surfaces is a recent topic in nanotechnology. As is widely known, diblock copolymers, which consist of two different types of polymer chains cormected by a chemical bond, have a wide variety of microphase separation structures, such as spheres, cylinders, and lamellae, on the nanoscale, and are expected to be new functional materials with nanostructures. Further modification of the nanostructures is also useful for obtaining new functional materials. In addition, utilization of nanopartides of an organic dye is also a topic of interest in nanotechnology. 

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. 

D.W. Schaefer, J.E. Mark, D.W. McCarthy, L. Jian, C.-C. Sun and B. Farago, Structure of microphase-separated silica/siloxane molecular composites. In D.W. Schaefer and J.E. Mark (Eds.), Polymer-Based Molecular Composites, Materials Research Society, Pittsburgh, 1990, Vol. 171, p. 57. 

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