Linear polyethylene crystals

The extended chain is another conformation which has been discussed often and proved to exist—e.g., in linear polyethylene crystallized at high pressures. It has also been assumed for amorphous polymers in the form of strands of parallel molecules [kink model (57)]. The maximum length L (x-ray) of a sequence of vinyl monomers of basic molecular weight M0 is 2.52 A. Straight strands of molecules can be... 

Linear Polyethylene Crystallized from Dilute Solution. 61... 

To elucidate the phase structure in detail it is necessary to characterize the molecular chain conformation and dynamics in each phase. However, it is rather difficult to obtain such molecular information, particularly of the noncrystalline component, because it is substantially amorphous. In early research in this field, broad-line H NMR analysis showed that linear polyethylene crystallized from the melt comprises three components with different molecular mobilities solid, liquid-like and intermediate molecular mobility [13-16]. The solid component was attributed to molecules in the crystalline region, the liquid component to... 

Figure 12.34 Loss compliance isotherms in the frequency domain of linear polyethylene crystallized from the melt. (From Ref. 44.)...

A preferentially and a sheaf-like aggregation with random in-plane orientation are observed for the thinner films (thicknesses of 0.1, 0.2 and 0.4 pm in panels a-c). By contrast thick films (0.6 pm and thicker, panel d) show a morphology that resembles the well known (bulk) spherulitic form with a banded structure, characteristic of linear polyethylene crystallized from the melt at moderately high undercooling. 

Lamellae within adjacent bands of a banded spherulite of linear polyethylene crystallized at 125 C. The specimen was cut open after crystallization, and lamellae are revealed by permanganic etching of the cut surface. The electron micrograph is of a carbon replica of the etched cut surface (after 0. C. BassetO. Scale bar=f 0 fim. 

Fig. 1. A truncated lozenge of linear polyethylene, crystallized from 0.01% solution in xylene, with boundaries delineating its six sectors and a step at the outer edge where the crystallization temperature was reduced from 90 to 76 = C. From Ref. 18.

Fig. 4.15 TEM micrograph of a chlorosulfonic acid stained linear polyethylene crystallized isothermally from the melt reveals the electron dense interlamellar surfaces typical of polyethylene.

Fig. 16-2. Relaxation spectrum in extension for single crystal mat of linear polyethylene, crystallized at 80°C as in Fig. 16-1, and subsequently annealed at two different temperatures Ta as shown. ...

Fig. 16-9. Storage and loss moduli in extension at 110 Hz, plotted against temperature, for single crystal mats of linear polyethylene crystallized at five different temperatures with the following lamellar thicknesses in A 1, 94 2, 104 3, 114 4, 137 5, 167. Dashed curves are for the polymer crystallized from the melt in bulk. (Takayanagi. )...

Figure 7.15 Lateral shape of crystals of linear polyethylene crystallized in dilute solutions with different solvents at different temperatures, as indicated in the figure. Drawn after data from Organ and Keller (1985) and Bassett, Olley and A1 Reheil (1988).

Blends of linear and branched polyethylene normally crystallize in two stages. The components crystallize separately provided that they are of similar molar mass. A diagram similar to that presented in Fig. 8.29 may also be constructed for mixtures of linear and branched polyethylene. The linear polyethylene crystallizes at the highest temperatures,... 

Figure 11.13 Cumulative melting and dissolution (in p-xylene) curves of a linear polyethylene crystallized at 401 K to completeness and then rapidly cooled to room temperature. Drawn after data horn Gedde, Eklund and Jansson (1983).

Miyaji H and Ceil P H (1981) Annealing of nodular linear polyethylene crystallized from the glass, Polymer 22 701-703. 

Dynamic Melt Properties of Polymer Blends," with A. S. Hill, VoZymoA EngZmcAZng and Science9 10.> 5 289, Sept. 1970. "Melting of Linear Polyethylene Crystallized from the Melt under Shear Stress," with T. W. Haas, J. 0 AppZZed PoZymeA Science, lU, 2I+07 (1970). 

Fig. 12.7 Plots of lateral growth rates as a function of the reciprocal undercooling for linear polyethylene crystallized at the indicated pressures. (From Rastogi et al. (22))...

It has been noted that the transformation is almost complete for linear polyethylene crystallized from dilute solution. For example, the crystallinity level that is attained at the isothermal crystallization temperature varies from about 85-90% at the lower molecular weights, < 1 x 10, to about 75-80% at higher molecular weights, including M = 3.1 x 10 .(28,38) These results can be contrasted with those for bulk crystallization. At the isothermal crystallization temperatures the... 

Fig. 13.15 Plot of Avrami n value for molecular weight fractions of linear polyethylene crystallizing from the pure melt and polymer-n-hexadecane mixtures. W2 is weight fraction of polymer n=4o n = 3A n = 2n. (From Chu (29))...

Fig. 13.16 Plotof time in minutes for 10% of the transformation to occur, ro.i, as a function of molecular weight for fraction of linear polyethylene crystallizing from dilute n-hexadecane solution. Crystallization temperatures are indicated. (From Chu (29))...

The influence of dilution on the crystallization rate is illustrated in Fig. 13.17 for an unfractionated linear polyethylene crystallizing from a-chloronaphthalene.(42) Here the crystallization rate is plotted according to three-dimensional nucleation... 

Fig. 13.17 Plot of log( 1 /T0.9) against temperature variable (FX1 / AT) for linear polyethylene crystallizing from Q -chloronaphtlialene mixture. Volume fraction of diluent in each mixture, ui, is indicated.(42)...

Growth rate studies of linear polyethylene from other solvents have also been re-ported.(51,53) The results obtained with decalin, a relatively good solvent, are very similar, at all concentrations, to those obtained with p-xylene.(51) In contrast, in a poorer solvent, n -octane, a maximum in the growth rate is observed at all concentrations studied, 0.001 % to 0.1 wt%.(48) However, the rate of decrease is much steeper in this case. Growth rates of linear polyethylene crystallizing from tetradeconol (0.05%), over the molecular weightrangeM = 1.4x 10" to 1.2x 10, are essentially constant at the lower crystallization temperatures. (5 3) However, as the temperature is raised the crystallization rate of the lowest molecular fractions decreases. 

Fig. 13.25 Plot of a against the weight average molecular weight for linear polyethylene crystallizing from different solvents, p-xylene o 86.0 °C and 86.6 °C 90.7 °C. Decalin 85.3 °C n-octane A 98.0 °C.

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