On the determination of methyl content in polyethylenes

Abstract

A method for the quantitative determination of the degree of branching (methyl content) in ethylene polymers is described. This method involves the use of a calibration curve prepared from hydrocarbons of known methyl content. Because of the importance to the calibration of having hydrocarbon with a methyl content roughly that of the polymers to be measured, the hydrocarbon, n‐C58H118, was prepared and its synthesis is given. The methyl contents of a series of polyethylenes, both commercial and experimental, were determined, and the results correlated with some physical properties of the polymers. A quantitative relationship was shown between the crystallinity of a polymer, as measured by the density, and the degree of branching. Qualitative relationships between molecular weight and branching and between mechanical properties and branching were also shown.

Temperatures and enthalpies of (solid + solid) and (solid + liquid) transitions of n-alkanes

“…Muller (65) and Nyburg et al (63,66) who denoted it "C 18 -P1"; C 28 to C 36 ; monoclinic key structure described by Shearer and Vand (67) and denoted "C 36 -P2 1 /a" by Nyburg et al; (63) C 38 , C 40 and C 44 ; orthorhombic key structure determined by Boistelle et al (68) and called "C 38 -Pbca" by Nyburg et al; (63) C 46 , C 50 and C 60 ; orthorhombic key structure determined by Shearer and Vand (67) and Teare (69) and denoted "C 36 -Pca2 1 " by Nyburg et al (63) According to Boistelle et al (68) and Craig et al, (62) the orthorhombic structure, whose crystallographic space group is Pbca, corresponds to a stacking of alternate monoclinic layers, related to each other by a two-fold axis perpendicular to the (00 ) planes.…”

“…Takamizawa et al (75) have carried out thermal and structural analyses on pure C 48 , C 60 , C 61 , C 65 and C 69 , and found by synthesis at room temperature that their structure was orthorhombic and had the space group Pca2 1 in the Hermann-Mauguin notation (80) for the even-numbered C 48 and C 60 and Pbcm for the odd-numbered C 61, C 65 and C 69 . They observed in these alkanes a (solid + solid) transition which leads to the appearance of a monoclinic phase C(A2), also denoted M 101 in Sullivan and Weeks notation, (76) with the space group denoted A2 (80) …”

Experimental Enthalpy Increments from the Solid Phases to the Liquid Phase of Homologous n-Alkane Series (C18 to C38 and C41, C44, C46, C50, C54, and C60)

“…Because of the importance of the n -alkanes (hereafter denoted by C n ), numerous studies − have been carried out to determine their thermodynamic properties and their structural behavior. Although numerous values of the temperatures and enthalpies of solid−solid and solid−liquid transitions of C n 's are available ...…”

The effect of short-chain branching on the thermolysis/reactive distillation of polyethylene

“…In this region, however, it is not possible to easily differentiate absorption associated with shortchain branching from end groups. 15,16 Methylene groups have a characteristic infrared absorption at approximately 1470 cm Ϫ1 . The variation in the ratios of the peak area at 1470 cm Ϫ1 (CH 2 ) to 1378 cm Ϫ1 (CH 3 ) of the nonvolatile residue with time for reactions of HDPE and LLDPE as determined by FTIR are presented in Figures 6 and 7, respectively.…”