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Molecular characteristics of room‐temperature soluble fractions of low‐density polyethylene film resins
Author(s) -
Yu Youlu,
Tso Chung C.,
DesLauriers Paul J.
Publication year - 2006
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.23811
Subject(s) - comonomer , polymer , branching (polymer chemistry) , molar mass distribution , polymer chemistry , polyethylene , methylene , size exclusion chromatography , chemistry , fourier transform infrared spectroscopy , side chain , molecular mass , low density polyethylene , gel permeation chromatography , materials science , organic chemistry , chemical engineering , polymerization , engineering , enzyme
The molecular characteristics of the room‐temperature soluble fractions (RT solubles) of three low‐density polyethylene film resins were characterized by size‐exclusion chromatography (SEC), SEC combined with FTIR (SEC–FTIR), and nuclear magnetic resonance spectroscopy (NMR). The high‐molecular‐weight components of the RT solubles were found to be highly branched components with uniform short‐chain branching (SCB) profiles. For the low‐molecular‐weight components, however, SCB content was a function of molecular weight (MW), increasing with an increase in MW. When the chain ends were considered as SCB equivalents, the distribution of the sum of SCB and chain ends across the molecular weight distribution was practically flat, suggesting that the driving force for polymer chains remaining in solution at RT was the length of the undisrupted methylene sequence in the backbone, or methylene run length, which was too short to form crystal lamellae with a melting temperature above RT, regardless of the molecular weight of the polymer. Moreover, the NMR results revealed that the polymer components of the RT solubles had “superrandom” SCB distributions, that is, the fraction of comonomer clusters in the polymer chains of the RT solubles was lower than that predicted by Bernoullian statistical analysis, indicating that the probability of adding a comonomer to a comonomer‐ended propagating chain was lower than that of adding a comonomer to an ethylene‐ended one, presumably because of an unfavorable steric effect. Furthermore, contrary to the common belief that RT solubles are mainly low‐molecular‐weight polymers, high‐molecular‐weight components were found in high concentrations in the RT solubles, with a cutoff MW as high as 1,000,000 g/mol. The proportion of RT solubles in the film resins was found to depend on the type of resin. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4992–5006, 2006