Poly melt crystallization

Crystallization from the melt often leads to a distinct (usually lamellar) structure, with a different periodicity from the melt. Crystallization from solution can lead to non-lamellar crystalline structures, although these may often be trapped non-equilibrium morphologies. In addition to the formation of extended or folded chains, crystallization may also lead to gross orientational changes of chains. For example, chain folding with stems parallel to the lamellar interface has been observed for block copolymers containing poly(ethylene), whilst tilted structures may be formed by other crystalline block copolymers. The kinetics of crystallization have been studied in some detail, and appear to be largely similar to the crystallization dynamics of homopolymers. 

Morphological changes, which are classified into four groups, have been correlated to the degree of topotactic control. Thermal analysis has been studied on DSP poly-DSP in some detail. Two main endothermic peaks of as-polymerized poly-DSP crystals are characterized as thermal depolymerization in the crystalline state and crystal melting point followed by thermal depolymerization in the molten state. From the results of the studies on the heat treatment of as-polymerized polymer crystals, a reversible topochemical processe has been established. 

Since two endothermic peaks, exemplified by the poly-DSP crystal in Fig. 1464 are generally observed for the as-prepared polymer crystals and since a weaker peak appears at the lower temperature which grows at the later stage of photopolymerization as shown in Fig. 1510, these two peaks are attributed to thermal depolymerization in the crystalline state and the processes involving degradation and/or crystal melting, respectively. 

Another motivation for measurement of the microhardness of materials is the correlation of microhardness with other mechanical properties. For example, the microhardness value for a pyramid indenter producing plastic flow is approximately three times the yield stress, i.e. // 3T (Tabor, 1951). This is the basic relation between indentation microhardness and bulk properties. It is, however, only applicable to an ideally plastic solid showing no elastic strains. The correlation between H and Y is given in Fig. 1.1 for linear polyethylene (PE) and poly(ethylene terephthalate) (PET) samples with different morphologies. The lower hardness values of 30-45 MPa obtained for melt-crystallized PE materials fall below the /// T cu 3 value, which may be related to a lower stiff-compliant ratio for these lamellar structures (BaM Calleja, 1985b). PE annealed at ca 130 °C... 

The distinct changes in morphology achieved by melt-crystallization of polymers in the presence of small amounts of their (n-s) polymer-CD-ICs results in changes in other physical properties as well. For example, in Table 2 a comparison of the properties of poly(3-hydroxy butyrate) (PHB) melt-spun with and without the presence of (n-s) PHB-a-CD-IC are compared [104], The mechanical properties of the PHB/( -s) PHB-a-CD-IC fibers are superior. In fact, their lower elongation at break likely contributes to the removal of the stickiness normally observed between melt-spun PBH fibers [104],... 

Information on how orientation during melt crystallization affects the transport properties of polymers is sparse however, increases in the permeability have been attributed to the "shish kebab" morphology (ill). Most of the work involving barrier properties of oriented semicrystalline polymers has dealt with materials drawn at temperatures well below the melting point. The transport properties of cold-drawn polyethylene (34f 42-46), polypropylene (42,42), poly(ethylene terephthalate) (12,42-4 9), and nylon 66 (22) among others have been reported. 

Liu, J., Sidoti, G., Hommema, J. A., Geil, P. H., Kim, J. C. andCakmak, M., Crystal structure and moiphology of thin film, melt-crystallized poly(ethyle-nenaphthalate), J. Macromol. ScL, Phys., B37, 567-586 (1998). 

Negative Ea values (Figure 8) have been obtained experimentally by Vyazovkin et al. [24] for the melt crystallization of poly(ethylene terephthalate), poly(ethylene oxide) [25], and poly(ethylene 2,6-naphthalate) [26]. Similar dependencies have also been reported by other workers... 

Figure 10. dependencies for the Figure 11. vs T data converted glass and melt crystallization of from Ea dependencies (Figure 10) poly(ethylene terephthalate) and fitted to equation (29) (dashed... 

Olson et al. [2003] carried out PALS studies of 22 poly(ethylene terephthalate) (PET) specimens with varying degrees of crystallinity 11 specimens were melt-crystallized at 210°C and 11 were made via cold crystallization at 110°C. Each sample was characterized thoroughly by DSC and WAXD in terms of Tg, Tm, and Xc, and, in fact, prior to the PALS investigation, were employed in a study of oxygen permeability at room temperature, which demonstrated that the O2 solubility in the melt-crystallized PET is higher than in the cold-crystallized PET [Lin et al., 2002]. This earlier work further established that the observed decreases in solubility and diffusion coefficient of oxygen in semicrystalline PET could be explained by the three-phase model of semicrystalline polymers, in which the RAF is considered in... 

Figure 5-19. Lamellae of melt-crystallized poly(ethylene) (after P. H. Lindenmeyer, V.

Abe H, Doi Y (1996) Enzymatic and environmental degradation of racemic poly(3-hydroxybutyric acid)s with different stereoregularities. Macromolecules 29 8683-8688 Abe H, Doi Y, Aoki H, Akehata T (1998) Solid-state structures and enzymatic degradabilities for melt-crystallized films of copolymers of (f )-3-hydroxybutyiic acid with different hydroxyal-kanoic acids. Macromolecules 31 1791-1797... 

Voigt-Martin LG., E.W. Fisher, and L. Mandelkern. 1980. Morphology of melt-crystallized linear polyethylene fractions and its dependence on molecular weight and crystallization temperature. / Poly Sci (Poly Phys) 18 2347-2367. 

As suggested in Sect. 3.6.1, TMDSC, detailed in Sect. 4.4, is a new and effective tool to analyze the nature of the melting/crystallization transition [34]. Figure 3.88 shows with quasi-isothermal measurements that melting/crystallization is largely irreversible for well-crystallized, extended-chain poly(oxyethylene) molecules of 5,000 molar mass. Such results are expected from Fig. 3.76. In the quasi-isothermal... 

A similar analysis of a melt-crystallized poly(ethylene terephthalate), PET, of the typical molecular mass of a polyester showed a surprising reversing melting peak, as seen in Fig. 3.92. On comparison with an amorphous PET, one finds that the reversing peak depends on crystallization history, as is shown in Fig. 4.136. The change of the glass transition with crystallization is typical for polymers. It shows a... 

Twin crystals based on the lattice of the repeating unit are also common in the growth of macromolecular crystals, as shown, for example, in the poly(oxyethylene) crystal of Fig. 5.55. It grew out of a small droplet of a melt. The multiple twin has its chain axis tilted to the a-axis by 126°, so that the axis shown in the figure is the... 

Poly(butylene terephthalate), PBT, is the next member of the homologous series of polyterephthalates with its thermodynamic properties listed in Fig. 6.40. Figine 6.45 presents the crystallinity for a semicrystalline, melt-crystallized PBT sample, calculated with the method of Fig. 4.80, Eq. (3). Below the glass transition, the crystallinity reaches 36.2%. With this crystallinity function, the expected heat capacity without latent heat effects is given in Fig. 6.46. 

Melting Temperature of Melt-crystallized Poly(vinylidene Fluoride) as a Function of Crystallization Temperature... 

Hu WB (2005) Molecular segregation in polymer melt crystallization simulation evidence and unified-scheme interpretation. Macromolecules 38 8712-8718 Hu WB, Cai T (2008) Regime transitions of polymer crystal growth rates molecular simulations and interpretation beyond Lauritzen-Hoffman model. Macromolecules 41 2049-2061 Jeziomy A (1971) Parameters characterizing the kinetics of the non-isothermal crystallization of poly(ethylene terephthalate) determined by DSC. Polymer 12 150-158 Johnson WA, Mehl RT (1939) Reaction kinetics in processes of nucleation and growth. Trans Am Inst Min Pet Eng 135 416-441... 

Yu, J. and Qiu, Z. (2011) Effect of low octavinyl-polyhedral oligomeric silsesquioxanes loadings on the melt crystallization and morphology of biodegradable poly(L-lactide). Ther-mochim. Acta, 519, 90-95,... 

Yasuniwa, M. and Satou, T. (2002) Multiple melting behavior of poly(butylene succinate). I. Thermal analysis of melt-crystallized samples. /. Polym. Sci. Polym. Phys., 40, 2411-2420. 

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