Copolymer analysis chemical composition distribution

SEC-ESIMS is a valuable tool for polymer characterization. Compounds are separated based on their hydrodynamic size in solution, but upon detection, an absolute molecular weight is also furnished. Only 1% of the SEC effluent is required for ESIMS analysis, thereby accommodating the popular SEC detectors. SEC-ESIMS provides an attractive solution to the calibration of SEC without the use of external calibrants. Chemical composition distribution information on copolymers is easily afforded provided the individual monomers differ in molecular weight. The successively acquired mass spectra contain narrow fractions of the overall distribution that simplifies the analysis of complex formulations. Unfortunately, we have not been able to provide structured details on materials beyond 5000 Da due to the low resolution of the quadrupole mass spectrometer. Nevertheless, SEC-ESIMS is an exciting hyphenated techniques for polymer characterization. 

The company Polymer Char (Valencia, Spain) was created for developing fully automated PO characterization instruments. The first device, commerciahzed and patented in 1994, was the CRYSTAF, crystallization analysis fractionation, for the fast measurement of the chemical composition distribution (CCD) in PE, PP, copolymers, and blends. Next came the SEC (with a quadruple detector system) and then SEC/a-TREF and p-TREF instruments. The first commercial, fully automated cross-fractionating SEC/TREF apparatus for microstructure characterization of POs was described by Ortin et al. (2007). The instrument yields a bivariate distribution CCD by TREE fractionation and then SEC fraction analysis in a single run. A schematic diagram of this new cross-fractionation instrument is shown in Fig. 18.7. 

Zimm-Schulz distribution (88,89). Using an analysis method similar to that used previously on the poly(Q -MeSty)-6Zoc -poly(4-vinyl pyridine) system, the MMD of both parts of the copolymer were determined. The data analysis method was claimed to verify the random coupling hypotheses. The hypothesis (90) that the polydispersity of individual blocks is higher than the polydispersity of the whole polymer was confirmed (85). That is, block copolymers with narrow MMD have broad complex chemical composition distribution. 

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. 

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. 

Coupled HPLC-NMR measurements performed at slow flow rates in fully deuterated solvents and at room temperature have been made in several studies to determine polymer MWD, to analyze the end-groups and the copolymer chemical composition distribution, and to assess the chemical structure and the degree of polymerization of all oligomer species [176-178]. Gradient HPLC-NMR was used in the analysis of the chemical composition distribution of random poly (styrene-co-ethyl acrylate) copolymers [179]. A major drawback in most of these studies is that the measurements could only be conducted at ambient or slightly elevated temperatures, which limits the method applicability, since many polymers, such as polyethylene, polypropylene, and polyolefin copolymers are soluble at high temperatures. 

Mean-square unperturbed dimensions a and their temperature coefficient, d tin 0) I d T, are calculated for ethylene-propylene copolymers by means of the RIS theory. Conformational energies required in the analysis are shown to be readily obtained from previous analyses of PE and PP, without additional approximations. Results thus calculated are reported as a function of chemical composition, chemical sequence distribution, and stereochemical composition of the PP sequences. Calculations of 0 / nP- are earned out using ( ) r r2 = 0.01, 1.0, 10.0, and 100.0, (ii) p, = 0.95, 0.50, and 0.05, liii) bond length of 153 pm and bond angles of 112°for all skeletal bonds, iv) = 0 and 10°, and (v) statistical weight factors appropriate for temperatures of 248, 298, and 348 K. Matrices used are ... 

The term cross-fractionation (CF) refers to analyses of distributions in differing directions by means of separation processes. Cross-fractionation is a significant tool for the evaluation of the complex distribution which copolymers normally have with respect to molar mass (MMD) and chemical composition (CCD). The idea of CF implies separation by one parameter and subsequent analysis of the fractions obtained for the distribution of the other parameter through another separating process. 

In a relatively short period of time the Lab Connections Transform system found its way into a large number of laboratories. Applications of the technique have been discussed in various fields. Willis and Wheeler demonstrated the determination of the vinyl acetate distribution in ethylene-vinyl acetate copolymers, the analysis of branching in high-density polyethylene, and the analysis of the chemical composition of a jet oil lubricant [143].Provder et al. [144] showed... 

Beckett described inductively coupled plasma mass spectrometry (ICP-MS) as an off-line detector for FFF which could be applied to collected fractions [ 149]. This detector is so sensitive that even trace elements can be detected making it very useful for the analysis of environmental samples where the particle size distribution can be determined together with the amount of different ele-ments/pollutants, etc. in the various fractions. In case of copolymers, ICP-MS detection coupled to Th-FFF was suggested to yield the ratio of the different monomers as a function of the molar mass. In several works, the ICP-MS detector was coupled on-line to FFF [150,151]. This on-line coupling proved very useful for detecting changes in the chemical composition of mixtures, in the described case of the clay minerals kaolinite and illite as natural suspended colloidal matter. 

Heterogeneous or complex polymers are distributed in more than one molecular parameter. For functional homopolymers one has to deal Avith the overlapping effects of molar mass distribution and functionality type distribution, whereas copolymers are distributed at least in molar mass and chemical composition. For many years, detector development and the use of several detectors attached to SEC have been the major thrusts in chromatographic analysis of complex macromolecules. In particular, the combination of a refractive index and an ultraviolet detector has been used extensively, although only a limited number of polymers is UV active. Therefore the application of this technique is certainly not universal. On the other hand, SEC has its merits in the daily routine because it is simple, fast, and very reproducible. 

Potential compositional analysis. While the strong dependence of retention on the chemical composition of the polymer has only recently been firmly established, this dependence opens the way for the characterization of chemical composition by thermal FFF. It is likely that thermal FFF can be combined with another method sensitive only to molecular size (such as SEC or flow FFF), to provide simultaneous information on molecular mass and compositional distributions, which might be particularly useful for copolymers [28]. 

Analysis of plastics is a complex task and involves preliminary tests, determination of nonmetallic and metallic elements, analysis of functional groups and double bonds, molecular weight determinations, chemical compositional analysis, sequence length distribution in copolymers, determination of tacti-city and branching in polymers, and analysis of additives. Because of the great variety in structures in commercially produced plastics, the number of methods that can be applied for their analysis is considerable. 

---