Long-chain branching polymer contents

Research on the modelling, optimization and control of emulsion polymerization (latex) reactors and processes has been expanding rapidly as the chemistry and physics of these systems become better understood, and as the demand for new and improved latex products increases. The objectives are usually to optimize production rates and/or to control product quality variables such as polymer particle size distribution (PSD), particle morphology, copolymer composition, molecular weights (MW s), long chain branching (LCB), crosslinking frequency and gel content. 

NMR remains a very useful technique to estimate branch content in hydrocarbon polymers and constitutes a direct quantitative approach. However, using NMR in quantifying branch content has a drawback in that the results for the branch content obtained will always overestimate long-chain branching, i.e., branches longer than about six carbons. Hence, the sensitivity of NMR to determine branch content is limited to high levels of short-chain branching. But... 

For high density polyethylene the MWD represents one of the basic parameters which, together with average molecular weight, density, short and long chain branching content, determines the physical, mechanical and rheological properties of the polymer and therefore its end uses (Table 1). 

These polysaccharides are one of the renewable resources that are most widely found in nature. These polymers present in plants together with cellulose and lignin. Hemicellulose is different from other celluloses in terms of the monomer composition, and has a long chain and molecular chain branching. The content of these compounds differ from species to species [9,10]. 

The zero-shear viscosity t]o of linear polymers scales exponentially with molecular weight [102] above the critical chain length Me, but LCB polymers repeatedly deviate from this dependency. In comparison to linear polymers of similar M, polymers with low levels of LCB exhibit enhanced zero-shear viscosity values and, in a qualitative sense, C-NMR-based LCB content often [85, 92, 93], but not always [100], correlates well with the viscosity increase. For long-chain branched LDPE, the t]q in comparison to linear polyethylene of similar is lower [103, 104]. A zero-shear viscosity t]o value higher than that of the corresponding linear polymers of similar M , is reported to occur at an LCB content of 0.2 LCB/10,000 C but the increase becomes more pronounced as the LCB content grows [85, 91, 92, 105,106]. This feature of low amounts of LCB has also been utilized to explore the extent of metallocene LCB [13, 85, 106, 107]. 

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