Polyethylene chain-extended

Fig. 8. Superheating of polyethylene extended chain crystals. Curves 1) at 421.7 K, 2) at 419.2, 3) at 417.7 K, 4) at416.7K, 5) at 414.7 K. The equilibrium melting temperature is 414.6 K. Drawn after Ref.40). "w is the weight fraction molten, obtained by isothermal calorimetry...

Wunderlich, B. and Melillo, L. (1966) Surface recrystallization of polyethylene extended-chain crystals, Science, 154, 1329-1330. 

Pak J, Wunderlich B (2002) Reversible Melting of Polyethylene Extended-chain Crystals Detected by Temperature-modulated Calorimetry. J Polymer Sci, Part B Polymer Phys 40 2219-2227. 

DSC melting curves of (I) polyethylene extended chain-type crystals prepared by crystallization at 470 K under 500 MPa pressure and (II) folded chain-type polyethylene crystals prepared under atmospheric pressure... 

Annis B K, Noid D W, Sumpter B G, Reffner J R and Wunderlich B 1992 Application of atomic force microscopy (AFM) to a block copolymer and an extended chain polyethylene Makromol. Chem., Rapid. Commun. 13 169 Annis B K, Schwark D W, Reffner J R, Thomas E L and Wunderlich B 1992 Determination of surface morphology of diblock copolymers of styrene and butadiene by atomic force microscopy Makromol. Chem. 193 2589... 

Another subclass of substituted amides that is of great commercial value is the ethoxylated amides. They can be synthesized from alkanolamides by chain extending with ethylene or propylene oxide or by ethoxylation directly from the primary amide (46—48). It was originally beheved that the stepwise addition of ethylene oxide (EO) would produce the monoethano1 amide and then the diethanolamide when sufficient ethylene oxide was added (49), but it has been discovered that only one hydrogen of the amide is substituted with ethylene oxide (50—53). As is typical of most ethylene oxide adducts, a wide distribution of polyethylene oxide chain length is seen as more EO is added. A catalyst is necessary to add ethylene oxide or propylene oxide to a primary or an ethoxylated amide or to ethoxylate a diethoxy alkanolamide synthesized from diethanolamine (54). 

Hence, the extension of an isotropic unoriented partially crystalline polymer leads to the formation of a highly organized material with a characteristic fibrillar structure. The anisotropy of the sample as a whole is expressed by a higher modulus, tenacity and optical anisotropy. It would seem that the increase in strength in the drawing direction suggests that the oriented samples consist of completely extended chains. However, while the strength of such perfect structure for polyethylene has been evaluated as 13000 MPas), the observed values for an oriented sample are 50 to 30 MPa. 

Extended chain crystal (ECC) Folded chain crystal (FCC) Growth Growth rate Induction period Melt relaxation Molecular weight Nucleation Nucleation rate Nucleus Optical microscope (OM) Polyethylene Polymer Power law ... 

A) is much smaller than the lamellar length of ordinary PE crystals ( 100A), thus the PE chains are prevented from folding. In this manner, extended-chain crystalline nanofibers of linear polyethylene with an ultrahigh molecular weight (6,200,000) and a diameter of 30 to 50 nm are formed. 

Brown, J.R., P.J.C. Chappell, Z. Mathys (1992b). Plasma surface modification of advanced organic fibers, part III. Effects on the mechanical properties of aramid/vinylester and extended chain polyethylene/ vinylester composites. J. Mater. Sci. 27. 6475-6480. 

By variation of the conditions of crystallization (see Sect. 1.3.3.3) polyethylene can be obtained either as folded lamellae, as extended chain crystals (high strength fiber), or as so-called shish kebabs (fibrils with a morphology similar to cellulose). All these variants differ in properties. 

Figure 1.60 Schematic illustration of extended chain crystallinity in polymers (a) polyethylene and (b) polypropylene.

If groups A and B are methyl groups (butane), the steric hindrance between A and B leads to a rotational barrier of 25 kj ( 6 kcal) per mole. The consequence of this simple fact is that in fatty acids and related substances and in polyethylene the chains of CH2 groups tend to assume fully extended zigzag conformations. 

Fig. 19. Fracture surface of extended chain polyethylene crystallized at about 480 MPa pressure at 493 K (21 h) followed by slow cooling (96 % cryst.). Weight average molecular weight 24,100. Electron micrograph of a replica. Scale bar 1 micrometer. R. B. Prime, unpublished...

Fig. 20. Phase diagram of polyethylene. The difference between folded and extended chain crystal melting temperatures is largely a size effect (1 kbar = 100 MPa). Curve based on data of Ref. I19>...

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... 

The polyethylene samples examined are shown in Table III slowly cooled or quenched from melt, original monofilament, annealed, over drawn, cold drawn, single crystal, cast film, extended chain crystal, etc. The sample-probe distance can be chosen from TO to 260 mm. The setting angle is defined as the angle between the molecular plane and the be plane according to Bunn (1 1) as shown in Figure 12. 

Fig. 22 Ratio of growth rates Gioo/Gno vs. crystallization temperature for extended-chain crystals of Ciggfbgg from 2% (w/v) solution in octacosane (diamonds) and for linear polyethylene from 0.05% solutions in hexane (squares). The polyethylene crystal at Tc = 70.0 °C and the C198H398 crystals above Tc = 110 °C are non-truncated lozenges these form for any Guo/ cos( /2) > G100, where cp/2 = tan 1(flo/ o) and ao, b0 are unit cell parameters (cf Fig. 10). Data for PE are from [32] (from [45])...

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