Characterization of Short-Chain Branching SCB in LDPE

Ihe tubular reactor provides LDPE with a broader SCB distribution than the LDPE produced in the autoclave reactor. However, the autoclave reactor has a significantly higher SCB content in the region, with 10-15 methyl branches/1000 carbons. Wild also provided data showing the significant differences in the SCB distribution of various LDPE samples prepared by each type of reactor xmder different polymerization conditions. 

It was reported by F. Mirabella, Jr., and E. Ford that the amount of long-chain branching in LDPE samples over a density range of 0.917-0.922 and Melt index values of 0.25-2.5 was about 2.9-3.4 LCB/1000 carbon atoms [18]. 

The free-radical, backbiting process illustrated above as one aspect of the free-radical polymerization mechanism was originally proposed by 

Roedel in 1953 [14] to account for the short-chain branching content in LDPE. More recent characterization of LDPE by C-NMR has resulted in a more detailed understanding of the SCB in EDPE, which has shown that LDPE is a complex mixture of various types of branching. Methyl, ethyl, propyl, n-butyl, n-amyl and 2-ethyl hexyl are each present along the polymer backbone. Additional references [19] on the characterization of the short-chain branching content in LDPE are recommended. 

It is important to understand that the introduction of linear low-density polyethylene (LLDPE) in the 1960s and late 1970s, manufactured by the solution process and the gas-phase process, both operating at relatively low pressure utilizing a transition metal-based catalyst, provided a new type of polyethylene with unique properties that did not result in the elimination of the high-pressure process from commercial use. It opened new markets and applications for the polyethylene industry and resulted in its continued rapid growth. 

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