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Poly crystallization rate constants

The effect of poly(methyl methacrylate), PMMA, on the crystallization kinetics of poly(ethylene oxide) has been investigated using the Avrami equation to analyze the results (80). The crystallization-rate constant, k, decreased as the concentration of PMMA increased. This and other results indicated that, in the blends, crystallization proceeds by a predetermined nucleation and this is followed with a two-dimensional growth. There has been evidence of melt compatibility for these two polymers (81-84) see Section V. Crystallization behavior of blends of poly(ethylene oxide) with poly(propylene oxide) (85) and with poly(vinyl acetate) (83) have been studied, as well as star and block copolymers of ethylene oxide and styrene (86). [Pg.169]

Fig. 11.19 Plot of crystallization rate constants of poly(ethylene terephthalate) in blends with poly(butylene terephthalate) as a function of crystallization temperature. Composition poly(butylene terephthalate)/poly(ethylene terephthalate) X 0/100 V 10/90 20/80 O 40/60. (From Elscala and Stein (36))... Fig. 11.19 Plot of crystallization rate constants of poly(ethylene terephthalate) in blends with poly(butylene terephthalate) as a function of crystallization temperature. Composition poly(butylene terephthalate)/poly(ethylene terephthalate) X 0/100 V 10/90 20/80 O 40/60. (From Elscala and Stein (36))...
An interesting observation associated with crystallization under uniaxial deformation is the marked enhancement of the crystallization rate at constant tempera-tures.(43,44,55,56) For example, the crystallization rate constant of natural rubber increases by six to nine orders of magnitude with extension ratio at constant temper-atures.(43) This enhancement is also reflected in the crystallization half-time, which also increases by several orders of magnitude.(44,46,47,55,56) This enhancement of crystallization rate is not limited to rubber-like polymers. It is also observed in poly(pentenamer) (50) and in poly(ethylene terephthalate) (47 9,57,57a) when crystallized under uniaxial deformation. The change in rate can be attributed in part... [Pg.365]

The self-seeded crystallization of high-molecular-weight poly(ethylene oxide) from dilute toluene solutions by static and dynamic light-scattering techniques indicated that the radii of the crystals grow in a linear manner (77). The rate constant. [Pg.168]

Other polymers, as typified by poly(3,3-dimethyl thietane), show maxima in the overall crystallization rate.(218) The data can be analyzed in a manner comparable to that described for spherulite growth rates and the conclusions are the same. Whether a transition from Regime II to III is discerned depends on the values taken for the Vogel constants. [Pg.136]

The crystallization rate of poly(cis-isoprene) displays a maximum with crystallization temperature under atmospheric pressure (Fig. 9.6). As is illustrated in Fig. 12.3 this maximum is still maintained for crystallization under applied pres-sure.(2) Here the rate constant, from the derived Avrami expression, is plotted... [Pg.350]

Fig. 12.3 Plotoflogfcs (Avrami rate constant) for poly(cis-isoprene) against crystallization temperature at indicated applied hydrostatic pressure.(2)... Fig. 12.3 Plotoflogfcs (Avrami rate constant) for poly(cis-isoprene) against crystallization temperature at indicated applied hydrostatic pressure.(2)...
An analysis of the overall crystallization rate with composition requires that the comparison be made either at constant undercooling or at one of the nucleation temperature quantities, T / T AT or T /T(AT). This requirement is essential because of the importance of nucleation to the crystallization process. The overall crystallization kinetics of a variety of polymer-diluent systems have been reported. Many different relations between the overall crystallization rate and composition have been observed. For example, as is shown in Fig. 13.17 there is a continuous decrease in the crystallization rate with dilution for linear polyethylene-a-chloronaphthalene mixtures.(42) The results for poly(trans-1,4-isoprene) in methyl oleate follow a similar pattem.(80) In contrast, the rates for poly(dimethyl siloxane) crystallizing from toluene, at compositions V2 = 0.32 to 0.79, are the same at all undercoolings, but are faster than that of the pure polymer.(78) Another example is found with poly(ethylene oxide)-diphenyl ether mixtures.(77) In this case the crystallization rates for the pure polymer and composition = 0.92 to 0.51 are the same. However, the rates for the more dilute mixtures, V2 = 0.04 and 0.30 are lower. For poly(decamethylene adipate)-dimethyl formamide mixture the rates for the pure polymer and V2 = 0.80 are the same.(77) The mixture of isotactic poly(propylene) with dotricontane shows interesting behavior.(81) At all undercoolings studied, the crystallization rate initially decreases with dilution, reaches a minimum in the range V2 — 0.7 (a maximum in ti/2) and then slowly increases with further dilution, up to V2 = 0.10. [Pg.418]

Additions of small amounts of poly(D-lactic acid) to poly(L-lactic acid) accelerated overall PLEA crystallization, which was confirmed by the effect of additive on nncleation constant. Similarly addition of 3 wt% UHMWPE to HOPE decreased nncleation constant from 3.04x10 to 2.27x10, indicating that UHMWPE increased nncleation rate in HDPE.20... [Pg.81]

Fig. 13.7. Heat flux during heating of poly(ethylene terephthalate) (PET) at a constant rate in a differential scanning calorimeter (DSC), showing changes in specific heat at Tg, crystallization exotherm at Tc, and melting endotherm at I m. Fig. 13.7. Heat flux during heating of poly(ethylene terephthalate) (PET) at a constant rate in a differential scanning calorimeter (DSC), showing changes in specific heat at Tg, crystallization exotherm at Tc, and melting endotherm at I m.

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See also in sourсe #XX -- [ Pg.307 , Pg.308 ]




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