Phase transition behavior copolymers

To further elucidate the structure of these copolymers, phase transition behavior of three copolymers of caprolactone and caprolactam (see Table IV) were determined. 

Liu, X.-M., Wang, L. S., Wang, L., et al. The effect of salt and pH on the phase-transition behaviors of temperature-sensitive copolymers based on IV-isopropylacry-lamide. Biomaterials 25 5659-5666, 2004. 

LC copolymers were prepared, and their photochemical phase transition behavior was examined (Tsutsumi et al., 1998a Sasaki et al., 1992 Ikeda et al., 1990b,c). One of the important factors of the photoresponsive LCs is their responses to optical stimuli. In this respect, the response time of the photochemical phase transition has been explored by time-resolved measurements (Sasaki et al., 1992 Ikeda et al., 1991 Kurihara et al., 1990). 

Very recently, the first examples of hybrid block copolymers comprising in the same macromolecule both main-chain and side-chain LC blocks (7) have also been described. To gain a better insight into the effects of the macromolecular architecture on the phase transition behavior of this last class of block copolymers, in the present contribution we report on the synthesis and properties of three series of main-chain and side-chain LC block copolymers 1-3, characterized by the following general structure ... 

Zhang J, Duan Y, Domb AJ, Ozaki Y (2010) PLLA mesophase and its phase transition behavior in the PLLA—PEG—PLLA copolymer as revealed by infrared spectroscopy. Macromolecules 43 4240 246... 

Interesting phase transition behavior was observed in copolymers of PVCL, which include PVCL-PEO (poly(ethylene oxide) hydrophilic) block copolymer, and copolymers of PVCL with (VA -dimethyl amino) ethyl methacrylate (DMAEMA), hydrophilic co-monomers like ethylacrylamide, polyacrylamide-PVA, or polyacrylamide-PEO copolymers. All of these combinations showed decrease in LCST of the PVCL copolymer system. The LCST behavior observed was not in accordance with conventional theory of increase/decrease in LCST with copolymerization with hydrophilic/hydrophobic... 

SUMMARY OF STUDIES OF PHASE TRANSITION BEHAVIOR OF COPOLYMERS... 

In this chapter a detailed description of the structure and phase-transition behavior of PVDF and its copolymers with TtFE, TFE, etc., will be given on the basis of experimental results of X-ray diflraction, infrared and Raman spectroscopy, neutron scattering. NMR, thermal analysis, electric measurements, etc. The phase-transition mechanism will be discussed experimentally and theoretically from various points of view. The ferroelectric behavior of other types of polymers, Le., odd nylons, VDCN copolymers, FLCP, etc. will also be discussed based on experimental data of X-ray diftaction and vibrational spectroscopy. 

In order to interpret the phase-transition behavior of fluorine polymers including PVDF, VDF-1YFE copolymers, and VDF-TFE copolymers, several theories have been reported. Some of them wUl be reviewed here. 

The photochemical phase transition behavior of copolymers that contained mesogens and azobenzene in the side chains has been extensively investigated. The molecular weight (Mn) of the polymer significantly affected the photochemical phase transition behavior in polymers with smaller Mn, the photochemical phase transition was induced more effectively [21,23]. Furthermore, the spacer between the main chain and mesogen also influenced the phase transition behavior to a great extent [21]. 

The GIXS technique can be extended to the investigation of phase transition behavior of miaodomains in block copoly-mers. In situ phase transition of microdomains was observed with an interesting amphiphilic diblock copolymer system, poly(ethylene oxide)-b-poly(ll-[4-(4-butylphenylazo) phenoxy]undecylmethacrylate) (p(EO)-b-p(MAAZ))... 

Phase behavior in complex fluids such as polymer blends and block copolymers has been a rich area of the chemical sciences. Near-critical and other transitional phenomena are frequently prominent. Since molecular movement in viscous systems such as these is comparatively slow, phase transitions can be studied more easily in time, and manipulated by quenching and other external influences. Processes for controlled growth of ordered materials are often readily influenced by diffusion, a variety of external fields, and the influence of interacting boundaries, or flow. 

In fact, even in pure block copolymer (say, diblock copolymer) solutions the self-association behavior of blocks of each type leads to very useful microstructures (see Fig. 1.7), analogous to association colloids formed by short-chain surfactants. The optical, electrical, and mechanical properties of such composites can be significantly different from those of conventional polymer blends (usually simple spherical dispersions). Conventional blends are formed by quenching processes and result in coarse composites in contrast, the above materials result from equilibrium structures and reversible phase transitions and therefore could lead to smart materials capable of responding to suitable external stimuli. 

Yamada et al. [9,10] demonstrated that the copolymers were ferroelectric over a wide range of molar composition and that, at room temperature, they could be poled with an electric field much more readily than the PVF2 homopolymer. The main points highlighting the ferroelectric character of these materials can be summarized as follows (a) At a certain temperature, that depends on the copolymer composition, they present a solid-solid crystal phase transition. The crystalline lattice spacings change steeply near the transition point, (b) The relationship between the electric susceptibility e and temperature fits well the Curie-Weiss equation, (c) The remanent polarization of the poled samples reduces to zero at the transition temperature (Curie temperature, Tc). (d) The volume fraction of ferroelectric crystals is directly proportional to the remanent polarization, (e) The critical behavior for the dielectric relaxation is observed at Tc. 

Tong X, Cui L, Zhao Y. (2004) Confinement effects on photoahgnment, photochemical phase transition and thermochromic behavior of liquid crystahine azobenzene-containing diblock copolymers. Macromolecules 37 3101-3112... 

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