Poly crystal modification

Ichikawa Y, Suzuki J, Washiyama J, Moteki Y, Noguchi K, Okuyama K (1994) Strain-induced crystal modification in poly(tetramethylene succinate). Polymer 35 3338... 

The crystal polymorphism of the chiral but racemic P5MH1 is, to some extent, very reminiscent of that of isotactic polypropylene. It exists in two crystal modifications. One crystal modification is stable at high temperature, and was observed early on by Corradini et al [39]. Its structure has been redefined as a chiral, frustrated one based on a trigonal cell with three threefold helices per cell. We have also discovered a second crystal modification produced from solution. It has an orthorhombic unit cell that contains four chains in - again - three-fold helical conformation, for which one must assume coexistence of two right- and two left-handed helices. Contrary to the a and ft phases of iPP, the frustrated structure of poly( 5-methyl-hexene-1) is the more stable one [40]. 

Crystalline poly(oxymethylenes) with peculiar morphologies were produced via y-initiated topochemical polymerization of trioxane. Depending on the crystal modification of the trioxane, porous poly(oxymethylene) crystals, showing cylind-... 

These crystal modifications differ in their molecular and crystal structures as well as in their physical properties. Many types of crystalline modifications are reported, including a stable orthorhombic phase and metastable monoclinic phase for PE a, and y forms for isotactic polypropylene (/-PP) trigonal and orthorhombic phases for polyoxymethylene a and y forms for Nylon 6 and others. Poly(vinylidene fluoride) (PVF), for example, appears in at least four types of crystalline modification (Lovinger, 1985 Dunn Carr, 1989). 

Kojima M, Satake H, Masuko T, Magill JH Crystal modifications of poly[bi phenoxy)phospha-zene]. PBPP. J. Materials Sci., to be published, 1988... 

Haraguchi K, Kajiyama T, Takayanagi M (1979) Effect of coagulation conditions on crystal modification of poly(p-phenylene terephthalamide). J. Appl. Polymer Sci. 23 915... 

The phenomenon by which various monomer units can replace each other in the lattice is termed isomorphism. Isomorphism is possible in copolymers if the corresponding unipolymers show analogous crystal modifications, similar lattice constants, and the same helix type. For example, according to Table 5-5, the y form of it-poly(propylene) and modification 1 of it-poly (butene-1) possess triclinic crystal form, similar lattice constants for the c dimension, and the same helix type. The copolymers of propylene and butene-1 therefore show isomorphism. Isomorphism occurs particularly readily in helix-forming macromolecules, since the helix conformations lead to channels in the crystal lattice, which can easily accommodate different substituents. 

Pan, R, Zhu, B., Kai, W. et al. (2008) Effect of crystallization temperature on crystal modifications and crystallization kinetics of poly(L-lactide). Journal of Applied Polymer Science, 107, 54-62. 

Zhang, J., Duan, Y, Sato, H. et al. (2005) Crystal modifications and thermal behavior of poly(L-lactic acid) revealed by infrared spectroscopy. Macromolecules, 38, 8012-8021. 

NMR STUDIES ON CONFORMATION OF POLY (VINYLIDE] 5E FLUORIDE) IN SOLUTION AND ITS RELATION WITH CRYSTAL MODIFICATION... 

Poly(vinylidene fluoride) (hereafter,the acronym PVDF will be used) has been considered to have three crystal modifications depending on the crystallization condition such as the species of precipitation solvent,the concentrations of polymer and the annealing temperature in crystallization (1 5). These suggest that the conformations in solution-grown crystals are closely related to those in solution used for the growth of the crystal. 

In some cases, vibration bands are also conformation-sensitive. In particular, when a polymer exists in several crystal forms, different chain conformations may exist in these crystal modifications one example is poly(vinyhdene fluoride) (PVDF). At least four types of crystal modifications are known forms I, II, Hpoiar, and III (26). Form I has nearly a zig-zag chain conformation. Forms II and Ilpoiar exhibit the glide-type TGTG conformation, while form HI has a TTTGTTTG conformation. The ir spectra of these crystal modifications are shown in Fig. 9 (27). For example, the intensive bands observed in the spectra of form I are 1275, 840, and 510 cm and others correspond to the vibration modes intrinsic to long trans sequences of. .. TTTT. The bands at 800, 766, 610, and 530 cm and others in the spectra of form II are attributed to the conformation sequence of TG. On the other hand, in form III, the TG and TT bands coexist in addition to the bands characteristic of the TTTG sequence (27). 

The development of crystal modifications of poly-1-butene has been followed using DSC [15]. 

Isotactic poly(butene-l), PBl, may exist in at least three distinct crystal modifications. The crystallographic data of PBl are reported in Table 4. The different modifications are commonly referred to as I, II, and III. 

Y. Tbiila and R. Chtt o, High-resohitioa NMR spectra and oottfbttnalion of poly(viny)idBOc fluoride) and their relation with crystal modifications. Polymer J. 6 191 (1 4). 

Zhang J, Duan Y, Sato H, Tsuji H, Noda I, Yan S, Ozaki Y. Crystal Modifications and Thermal Behavior of Poly(l-lactic acid) Revealed by Infrared Spectroscopy. Macromolecules 2005 38 8012. 

It should be pointed out here that the epitaxy caused by special crystallographic interaction provides another efficient way to control the crystal modification of semicrystalline polymers together with molecular chain orientation [83,88,139-142]. As examples, while the crystal structure of isotactic poly(l-butene) (iPB-1) is successfully controlled through using substrates with different crystal structures... 

Note that a similar duality of crystal phases is observed when hexamethylbenzene is used as a substrate for the crystallization of poly(L-lactic acid) (PLLA). Two different crystal modifications are produced at ==120°C and 140°C that differ by the helix conformation (32 and 10 ) but have very similar interchain distances [74],... 

An example of cocrystallization among vinyl copolymers can be found in copoly(styrene/ p-fluorostyrene). The stable crystal modifications of the homopolymers polystyrene and poly (p-fluorostyrene) are quite different. In the former case the ordered chain conformation is a threefold helix while in the latter it is a four-fold one. Nevertheless, the copolymers are crystalline over the complete composition range, and the melting temperature is essentially a linear function of composition. These data by themselves provide adequate evidence of cocrystallization. 

Takahashi Y, Osaki Y and Tadokoro H (1980) Structures of three crystal modifications of poly(3,3-dimethyloxacyclobutane), J Polym Sci Polym Phys Ed 18 1863-1878. Miyasaka K and Ishikawa K (1968) Effects of temperature and water on the -y —>a crystalline transition of nylon 6 caused by stretching in the chain direction, J Polym Sci Part A-2 6 1317-1329. 

Zinc sulfide, with its wide band gap of 3.66 eV, has been considered as an excellent electroluminescent (EL) material. The electroluminescence of ZnS has been used as a probe for unraveling the energetics at the ZnS/electrolyte interface and for possible application to display devices. Fan and Bard [127] examined the effect of temperature on EL of Al-doped self-activated ZnS single crystals in a persulfate-butyronitrile solution, as well as the time-resolved photoluminescence (PL) of the compound. Further [128], they investigated the PL and EL from single-crystal Mn-doped ZnS (ZnS Mn) centered at 580 nm. The PL was quenched by surface modification with U-treated poly(vinylferrocene). The effect of pH and temperature on the EL of ZnS Mn in aqueous and butyronitrile solutions upon reduction of per-oxydisulfate ion was also studied. EL of polycrystalline chemical vapor deposited (CVD) ZnS doped with Al, Cu-Al, and Mn was also observed with peaks at 430, 475, and 565 nm, respectively. High EL efficiency, comparable to that of singlecrystal ZnS, was found for the doped CVD polycrystalline ZnS. In all cases, the EL efficiency was about 0.2-0.3%. 

Fig. 23. Crystal structure of /Worm (modification-/) poly (vinylidene fluoride). Figures in broken lines represent chain rotation to avoid the steric hindrance between F atoms (Hasegawa and others, 1970)...

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