Crystallization of poly

Several studies have concerned the microstnicture of lamellae in materials such as the block copolymers polystyrene-h/oc/r-poly-l-vinylpyridine [139] and polystyrene-h/oc/r-polybutadiene [140], as well as single crystals of poly-para-xylylene [139], and reveal features (such as intersecting lamellae (figure Bl.19.29)) that had not been previously observed. 

The crystallization of poly(ethylene terephthalate) at different temperatures after prior fusion at 294 C has been observed to follow the Avrami equation with the following parameters applying at the indicated temperatures ... 

Large domains of oriented single crystals of poly(TCDU) and poly(DMDA) were produced on the alkali halide surface. Figures 1 and 2 show the typical elongated platelet morphology. Selected... 

The existence of two T2 relaxation times was also observed in the radiation cured photopolymers 99), and studies of tri- and tetra-functional network organosilicon polymers with rings at the network points 100). The effects of crystallization of poly-dimethylcarbosiloxane networks (PDMCS) I01), and water sorption and stoichio-metrical composition of the cured DGEBA/DETA resins on phase structure and mobility 102) were studied. 

Lieser, G. Polymer single crystals of poly(4-hydroxybenzoate). J. Polymer Sci., Polymer Phys. Ed., 27, 1611 (1983)... 

Figure 4. Single crystal of poly(t-caprolactone) and its electron diffractogram...

The tacticity of PLA influences the physical properties of the polymer, including the degree of crystallinity which impacts both thermo-mechanical performance and degradation properties. Heterotactic PLA is amorphous, whereas isotactic PLA (poly(AA-lactide) or poly (55-lac tide)) is crystalline with a melting point of 170-180°C [26]. The co-crystallization of poly (RR-lactide) and poly(55-lactide) results in the formation of a stereocomplex of PLA, which actually shows an elevated, and highly desirable, melting point at 220-230°C. Another interesting possibility is the formation of stereoblock PLA, by polymerization of rac-lactide, which can show enhanced properties compared to isotactic PLA and is more easily prepared than stereocomplex PLA [21]. 

Yuan B-L, Rybnikar F, Saha P, Geil PH (1999) Phase I and II crystals of poly(p-oxybenzoate). II. Effects of solution polymerization conditions on morphology and crystal structure. J Polym Sci Polym Phys Ed 37 3532... 

The polymerizability of a monomer is also influenced by the physical state of the polymerization. For example, crystallization of poly(oxy methylene) provides the driving force for trioxane polymerization. In this case, propagation occurs at active sites on the crystal lattice rather than in solution, and AGP includes the change in free energy of the phase transition as well as that of the solution polymerization [Eq. (19)]. 

From studies on the polymerization behavior of four-center photopolymerizations in the crystalline state, several remarkable features have been found which suggest significant participation of the crystal lattice in polymerization. For example, the plate-like crystals of DSP (a) obtained by recrystallization from solution photopolymerize in the crystalline state whereas DSP crystals (y) obtained through sublimation are needle-like and do not undergo any photochemical change20. Moreover, plate-like crystals of DSP and P2 VB, and crystals of poly-DSP and poly-P2 VB respectively are very similar to each other in their major X-ray diffraction peaks (Fig. 9)8,40). X-Ray analyses of the crystal structures of several diolefinic compounds, including photostable DSP (y) crystals, have been performed mostly by Nakanishi and Sasada26,4151). 

Most of the polymer crystals are thermally depolymerized to monomer and then degraded to undefinable materials64 68). For example, an exothermal oxidation effect has been observed above 200°C in the DTA of poly-DSP645. In aqueous solution, fine crystals of poly-DSP are readily oxidized with potasium parmanganate at 70 °C for 10 h, and 2,5-pyrazinedicarboxylic add is identified as one of the reaction products containing a certain amount of benzoic acid135. 

Figure 3.26. Polydiacetylene mesomers (a) and (b) with different energetic conformation. A single crystal of poly(2,4-hexadiyne-l,6-diol-bis-p-toluene-sulfonate) shows strong TP resonances at about 2.7 eV and 2.1 eV, and a weaker TP state that is centered at 1.8 eV when irradiated with a 2 1 ps Ti sapphire laser [405].

Interaction of Halogens with Single Crystals of Poly( 1,6-di-A -carbazolyl-2,4-hexadiyne)... 

Recently, we observed that the PDA from l,6-di-N-carbazolyl-2,4-hexadiyne (2a), i.e., poly-DCH (2), reacts with assorted gaseous and liquid species to give modified materials which appear homogeneous on microscopic examination (1). Our studies to date of the interaction of chlorine, bromine, and iodine with single crystals of poly-DCH are presented herein. 

Polydiacetylenes. Single crystals of poly(TCDU) and poly— (DMDA) were deposited on a variety of alkali halide crystals. The resultant morphology of both the monomers and polymers were identical and were elongated platelets oriented in the substrates <110> directions (Figures 5 and 6). 

A comfortable pathway for improvement of the crystallization of poly(3-hydroxybutyrate) in a melt-spinning process is the use of nucleating agents like electron-beam irradiated PHB [28] or the reactive extrusion with peroxide [29]. 

Besides the above conventional effects, Chapter 3 summarizes data suggesting the ability of some gases to sorb and diffuse inside the actual crystals of poly(4-methyl-l-pentene) (68,69). Finally, Chapter 3 considers liquid crystalline polymers, which seem to form a new class of materials in terms of barrier responses(57). The high barrier nature of liquid crystal polymers appears to be largely due to their unusually low solubility coefficients for typical penetrants. This is quite different from the case for most high barriers like EVOH, and polyacrylonitrile that typically function due to the unusually low mobilities of penetrants in their matrices (70). ... 

Of the many other ways of detecting phase transitions, including cloud points for systems with mixed phases, particular mention should be made of the use of dynamic-mechanical methods, and specifically measurement of the shear compliance to 1 kbar. When applied to columnar crystals of poly-diethylsiloxane) such a method was able to detect the melting point in conditions where the volume change was close to zero. 

Mena-Osteritz, E. et al.. Two-dimensional crystals of poly(3-alkylthiophene)s Direct visualization of polymer folds in submolecular resolution, Angew. Chem. Int. Ed. 39, 2680-2684, 2000. 

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