Long-chain branching characterization

G. Fleury, G. Schlatter, and R. Muller. Non linear rheology for long chain branching characterization, comparison of two methodologies Fourier transform rheology and relaxation. Rheologica Acta, 44 (2004), 174-187. 

Another parameter coinranly used for characterizing long chain branching is the number of branch points (or frequency) per 1000 repeat units. The number average number of branch points can be calculated across the chromatogram from... 

The method outlined above for characterizing branched polymers will hereafter be referred to as the molecular weight and branching distribution (MWBD) method. In the following sections, its application to the long chain branching in polyvinyl acetate and high pressure low density polyethylene will be demonstrated. 

The MWBD method, when coupled with high speed SEC techni-gues, is more rapid for long chain branching measurements than NMR. In addition, the branching distribution information that it provides, once epsilon has been determined, can not be obtained by other branching characterization methods unless the polymer is fractionated. 

Parameter characterizing the effect of long-chain branches on the size of a branched molecule in solution and defined as the ratio of the mean-square radius of gyration of a branched molecule, si), to that of an otherwise identical linear molecule si), with the... 

A useful approach to detection in polymer HPLC presents the on-line hyphenation of different measurement principles. For example, an RI detector combined with a UV photometer produces valuable additional information on the composition of some copolymers. Further progress was brought with the triple detection RI plus LALS plus VISCO [313], which is especially suitable for branched macromolecules and the tetra detection UV plus RI plus LALS plus VISCO, which enables characterization of some complex polymer systems, exhibiting a distribution not only in their molar mass and architecture, but also in their chemical composition such as long chain branched copolymers. 

Linear low-density polyethylene (LLDPE)440-442 is a copolymer of ethylene and a terminal alkene with improved physical properties as compared to LDPE. The practically most important copolymer is made with propylene, but 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene are also employed.440 LLDPE is characterized by linear chains without long-chain branches. Short-chain branches result from the terminal alkene comonomer. Copolymer content and distribution as well as branch length introduced permit to control the properties of the copolymer formed. Improvement of certain physical properties (toughness, tensile strength, melt index, elongation characteristics) directly connected to the type of terminal alkene used can be achieved with copolymerization.442... 

Characterization of Long-Chain Branching in Polyethylenes Using High-Field Carbon-13 NMR... 

We study here the case of a branched polyethylene (LDPE FN 1010), characterized by long chain branching, whose rheological behaviour has been previously described in Chapter II-l. Compared to linear LLDPE, it exhibits strain-hardening in elongational situations and higher values of first normal stress difference. 

The characterization of star-branched polymers has been performed using triple detection because it was not obvious, in the beginning of this study, that universal calibration could be applied to star-branched polymers. In fact, the GPC software used handles experimental data as a double dual detection, GPC-viscometry and GPC-LALLS. Experimentally, it has been found that excellent agreement between results from these two sets of data can be obtained. GPC-viscometry uses a universal calibration curve and GPC-LALLS is free of any molecular weight calibration curve. Therefore, the universal calibration works well with very long chain branched polymers, even with a very particular... 

L. J. Rose and F. Beer, Characterization of long chain branching in LDPE s using SEC with on-line viscosity and light scattering detectors, MolMass International Conference Proceedings, 1999 (www.chem.leeds.ac.uk/molmass 99). 

Wang, W.-J. Kharchenkob, S. Miglerb, K. Zhu, S. Triple-detector GPC characterization and processing behavior of long-chain-branched polyethylene prepared by solution polymerization with constrained geometry catalyst. Polymer 2004, 45 (19), 6495-6505. 

Randall, J. C. Characterization of long-chain branching in polyethylenes using high-held. C-NMR. ACS Symp. Ser. 1980, 142, 93-118. 

Wood-Adams, P. Dealy, J.M. deGroot, A.W. Redwine, O.D. Effect of molecular structure on the linear viscoelastic behavior of polyethylene. Macromolecules 2000, 33 (20), 7489-7499. Trinkle, S. Friedrich, C. Van Gurp-Palmen plot a way to characterize polydispersity of linear polymers. Rheol. Acta 2001, 40 (4), 322-328. Trinkle, S. Walter, P. Friedrich, C. Van Gurp-Palmen plot. II. Classification of long chain branched polymers by their topology. Rheol. Acta 2002, 41 (1-2), 103-113. 

The development of single-site catalysts in the 1980s together with new multireactor processes and new comonomers opened the route for the design of new resins with improved performance for different applications. New polyolefin copolymers may have a complex microstructure and, besides molar mass and composition distribution, it is necessary to characterize the bivariate distribution (interdependence of molar mass and composition) and, on occasions, the level of long chain branching and stereoregularity. 

The characterization of the new polyolefins necessarily demands a separation step of the polymer by certain parameters and, in most cases, a cross-fractionation is required to obtain the full bivariate distribution. Other features like long chain branching and stereoregularity need to be characterized as well and eventually as a function of molar mass. 

Molar mass distribution is a dominant microstracture parameter that, in copolymers, needs to be measured with additional information to account for long chain branching, comonomer incorporation, or ethylene propylene combinations (in the case of EP copolymers). The combination of GPC and IR spectroscopy has been shown to be of great value in the characterization of copolymers. The importance of automation and sample care, especially in the case of polypropylene, has been discussed as well as the significant improvement in sensitivity by the use of IR MCT detectors. There are big expectations for the analysis of ultrahigh molar mass polyolefins by the new AF4 technology. 

Long-chain branching can be characterized by SEC-viscometry (in THF) of the starting PVAc used for the hydrolysis to PVA. The Mark-Houwink plot of log [t ] versus log molecular weight for fully hydrolyzed PVA supports a linear structure for the polymer. 

Because PVAc is a widely used thermoplastic, developments in its characterization have tracked advances in SEC technology as a whole. This chapter outlines procedures and conditions for characterizing the molecular weight and long-chain branching distributions in PVAc. Several studies were discussed, indicating that the principle of universal calibration applies to PVAc in THF. 

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