Polyolefins, analysis fractionation

B. Monrabal, Crystallization analysis fractionation a new technique for the analysis of branching distribution in polyolefins. J. Appl. Polym. Sci. 52(4), 491-499 (1994)... 

Fig.l Cumulative and differential crystallization analysis fractionation (Crystaf) profiles of a blend of two polyolefins... 

Abstract The synthesis and characterization of polyolefins continues to be one of the most important areas for academic and industrial research. One consequence of the development of new tailor-made polyolefins is the need for new and improved analytical techniques for the analysis of polyolefins with respect to molar mass, molecular topology and chemical composition distribution. This review presents different new and relevant techniques for polyolefin analysis. The analysis of copolymers by combining high-temperature SEC and FTIR spectroscopy yields information on chemical composition and molecular topology as a function of molar mass. Crystallization based fractionation techniques are powerful methods for the analysis of short-chain branching in LLDPE and the analysis of polyolefin blends. These methods include temperature-rising elution fractionation, crystallization analysis fractionation and the recently developed crystaUization-elution fractionation. 

Keywords Crystallization analysis fractionation Field Flow Fractionation High performance liquid chromatography Hyphenated techniques Liquid chromatography Polyolefin analysis SEC-NMR coupling Size exclusion chromatography Temperature rising elution fractionation Two-dimensional liquid chromatography... 

As described in the previous sections, there are a number of fractionation techniques that are used very successfully in polyolefin analysis, including HT-SEC, CRYSTAF and TREE. For copolymers, CRYSTAF and TREF provide information about the chemical composition distribution. The drawbacks of these methods are that (1) they are very time-consuming and (2) they work only for crystallizable polyolefins. The latest development in this field, CEF, is able to obtain similar results to TREF in less than 1 h and is, therefore, a significant improvement. Still, CEF is based on crystallization and can only address the crystallizable part of a polyolefin sample. 

The chemical composition distribution of polyolefins is measured (indirectly) by either temperature rising elution fractionation (Tref) or crystallization analysis fractionation (Crystaf). These two techniques provide similar information on the chemical composition distribution of polyolefins and can be used interchangeably in the vast majority of cases. Both methods are based on the fact that the crys-tallizability of HOPE and LLDPE depends strongly on the fraction of a-olefin comonomer incorporated into the polymer chains, that is, chains with an increased a-olefin fraction have a decreased ciystallizability. A similar statement can be made for polypropylene and other polyolefin resins that are made with prochiral monomers resins with high stereoregularity and regioregularity have higher crystalliz-abilities than atactic resins. 

B. Monrabal, Analysis of Metallocene Type Polyolefins by CRYSTAF (Crystallization Analysis Fractionation), International GPC Symposium, San Diego, 1996. 

Although PFE lacks a proven total concept for in-polymer analysis, as in the case of closed-vessel MAE (though limited to polyolefins), a framework for method development and optimisation is now available which is expected to be an excellent guide for a wide variety of applications, including non-polyolefinic matrices. Already, reported results refer to HDPE, LDPE, LLDPE, PP, PA6, PA6.6, PET, PBT, PMMA, PS, PVC, ABS, styrene-butadiene rubbers, while others may be added, such as the determination of oil in EPDM, the quantification of the water-insoluble fraction in nylon, as well as the determination of the isotacticity of polypropylene and of heptane insolubles. Thus PFE seems to cover a much broader polymer matrix range than MAE and appears to be quite suitable for R D samples. 

Applications Multidimensional SEC techniques can profitably be applied to soluble polymer/additive systems, e.g. PPO, PS, PC - thus excluding polyolefins. A fully automated on-line sample cleanup system based on SEC-HRGC for the analysis of additives in polymers has been described, as illustrated for PS/(200-400ppm Tin-uvin 120/327/770, Irgafos 168, Cyasorb UV531) [982], In this process, the high-MW fractions are separated from the low molecular masses. SEC is often used as a sample cleanup for on-line analysis of additives in food extracts these analyses are usually carried out as on-line LVI-SEC-GC-FPD. 

Polyolefins, other synthetic polymers, and water-soluble macromolecules have been investigated in highspeed SEC systems. High-speed SEC can be a major time saver in two-dimensional chromatography applications, which require about 10 hr analysis time for cross-fractionation. This can be reduced by a factor of 10, to about 1 hr, which makes it much more interesting for many laboratories. Details on these and additional highspeed applications can be found in Ref. [4]. 

Cross fractionation, which refers to the sequential fractionation in terms of composition and molecular weight offers the promise of the most complete structural analysis for polyolefins. This is particularly true in the case of LLDPE because, as indicated above, these resins exhibit both broad distributions of molecular weight and of comonomer. Also, since molecular weight and comonomer content are not strongly inter-related one might expect to find significant differences in the structural distributions of resins made by differing processes. 

As indicated in the introduction there is a distinct correlation between the commercial growth of linear low density polyethylene and the resurgence of interest in the temperature rising elution fractionation technique. It is clear, however, from the wide variety of examples noted in this review that the scope of TREF extends well beyond the LLDPE area. Since the TREF technique is becoming available to many more research workers it is anticipated that there will be continued growth and development which will lead to greater sophistication in the way the technique is utilized, particularly in the polyolefin area. The power of TREF for blend analysis and cross-fractionation is certain to be exploited in the coming years. 

The classical techniques for chemical composition analysis of polyolefins are based on crystallization behaviour of different components of these materials. These techniques are only apphcable for the crystalline part of the sample and the amorphous part is obtained as a bulk fraction. Nevertheless, these techniques are stiU the analytical workhorse in most polyolefin research laboratories. The reason behind this is that most of the commercially important polyolefin materials are semi-crystalline. There has been a number of recent advances in these techniques that have enabled a reduction in analysis time, better resolution and mathematical modelling etc. The most fascinating innovation in this regard is the development of CEF. CEF combines the separation powers of both TREF and CRYSTAF, resulting in better separation of fractions along with considerable reduction in analysis time. CEF has the promise and potential to be the major technique in crystallization analysis in future. 

These effects, supported by a marked increase of melt viscosity, were related to the occurrence of chemical interactions between the polyamides and functionalized polyolefins at the interface. DSC analysis showed that incompatible Ny6/PP and Ny6/LDPE blends exhibit at all compositions separated crystallization peaks of the two components, whereas the compatibilized blends displayed fractionated and/or coincident crystallization phenomena. For Ny6/PP-AA blends where Ny6 is the matrix, the crystallization of the polyamide phase takes place in a narrow range, close to 190 C, as observed for pure Ny6 (Hg. 10.26a). When Ny6 is the dispersed phase. 

This book covers all aspects of the analysis of plastics by chemical and physical methods. It is divided into eight chapters which each deal with a particular polymer or group of polymers - polyolefins, polypropylene, higher alkene polymers, styrene polymers, chlorine-containing polymers, methacrylates, polybutadienes, polyesters and polyethers. The techniques discussed include spectroscopy, chromatography, fractionation,. X-ray diffraction, autoradiography, DTA, TGA and DSC. 

---