Polyethylene ethyl branching

Linear Polyethylene with Randomly Distributed Ethyl Branches (Hydrogenated Polybutadiene)... 

The half-widths of 37-39 and 78-88 Hz, respectively, for the crystalline and amorphous phases are significantly larger than 18 and 38 Hz for those of the bulk-crystallized linear polyethylene (cf. Table 1). This is caused by incorporation of minor ethyl branches. The molecular alignment in the crystalline phase is slightly disordered, and the molecular mobility in the amorphous phase will therefore be promoted. With broadening of the crystalline and amorphous resonances, the resonance of the interphase also widens in comparison to that of bulk-crystallized linear polyethylene samples. This shows that the molecular conformation is more widely distributed from partially ordered trans-rich, conformation to complete random conformation, characteristic as the transition phase from the crystalline to amorphous regions. 

Branching may be produced deliberately by copolymerizing the principal monomer with a suitable comonomer. Ethylene and 1-butene can be copolymerized with a diethylaluminum chloride/iitanium chloride (Section 9.5) and other catalysts to produce a polyethylene with ethyl branches ... 

Tirpak, G. a. Position of ethyl branches in conventional polyethylene made by the free radical process. J. Polymer Sci. 3B, 371 (1965). 

High-density polyethylene has less spurious branching than the low-density material, about 0.3-5 ethyl branches per 1,000 carbon atoms. The much lower extent of branching in HOPE enables closer packing of the polymer chains in the solid state. Closer packing explains both the higher density and the higher crystallinities observed for this material as compared to those of low-density polyethylene. 

LLDPE(2) Linear low density polyethylene with 17 ethyl branchings per 1000 carbon atoms... 

Despite these observations, analysing the SEC Rl-elution volume traces with a linear polyethylene calibration curve appears to be valid, in that the short-chain branches did not substantially alter the molecular dimensions. In particular, hydrogenated polybutadienes with 2-5% ethyl branches, an excellent model system for n-butene-1 copolymer systems, elute at the same retention volume as HDPE with the same molecular mass, and they have been used widely as molecular mass standards for HDPE. Unfortunately, the effect... 

Figure 4.4 High field C-NMR spectra of low-density polyethylene. (A) Ethyl branched copolymer (B) hexyl branched copolymer (C) LDPE.

Fig. 17. In an ethyl-branched linear low-density polyethylene (7-5 QHs/ 1000 C atoms) crystallized alongside the sample of Fig. 16, there are no very thick lamellae. This is a consequence of exclusion of ethyl branches from the crystal lattice, in contrast to methyl branches which are included. Replica of an...

Fig. 4. Melt-crystallized polyethylene lamellae (a) linear polymer crystallized at 130°C as a planar crystal in which successive layers spiraling around the central (etched-out) giant screw dislocation are not in contact (b) ridging along 6 in a 17,000 mass fraction of linear poljrmer crystallized at 129°C (c) an ethyl-branched copolymer crystallized at 123°C showing a central S-profile, asymmetrically placed screw dislocations and new layers diverging therefrom. From Ref. 66.

Wignal and co-workers (207) investigated phase separation of linear (high density) and short-chain branched (linear low density) polyethylenes (HDPE/LLDPE) by of combination of SAXS, SANS, DSC, and TEM. According to SANS, this blend is homogeneous in the melt when the ethyl branch content in LLDPE is low, but due to the structural and melting point differences between HDPE and LLDPE, the components may phase-separate in the solid state. 

Once it is confirmed that the sample is a LLDPE, it is necessary to identify the ot-olefin used as the comonomer. The following comonomers are commonly utilized in the polyethylene industry butene-1, hexene-1, 4-methyl-pentene-1, and octene-1. The cost of LLDPE increases with the order of the comonomers as listed, and LLDPE formed from butene-1 as comonomer is the most common form. Butene-1 will produce ethyl branching, —CH2 —CH2 —CH2—CH(CH2CH3)CH2—CH2—, which produces an... 

Modeling polyethylene containing methyl and ethyl branches... 

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