Copolymer chromatograms

Figure 12.8 Mia ocolumn size exclusion chromatogram of a styrene-aaylonitrile copolymer sample fractions ti ansfeired to the pyrolysis system are indicated 1-6. Conditions fused-silica column (50 cm X 250 p.m i.d.) packed with Zorbax PSM-1000 (7p.m 4f) eluent, THF flow rate, 2.0 p.L/min detector, Jasco Uvidec V at 220 nm injection size, 20 nL. Reprinted from Analytical Chemistry, 61, H. J. Cortes et al, Multidimensional chromatography using on-line microcolumn liquid chromatography and pyrolysis gas chromatography for polymer characterization , pp. 961 -965, copyright 1989, with peimission from the American Chemical Society.

Figure 12.9 Typical pyrolysis chromatogram of fraction from a styrene-acTylonitiile copolymer sample obtained from a miciocolumn SEC system 1, acrylonitrile 2, styrene. Conditions 5 % Phenylmetliylsilicone (0.33 p.m df) column (50 m X 0.2 mm i.d.) oven temperature, 50 to 240 °C at 10 °C/min carrier, gas, helium at 60 cm/s flame-ionization detection at 320 °C make-up gas, nitrogen at a rate of 20 mL/min. P indicates tlie point at which pyrolysis was made. Reprinted from Analytical Chemistry, 61, H. J. Cortes et ai, Multidimensional cliromatography using on-line microcolumn liquid cliromatography and pyrolysis gas cliromatography for polymer characterization , pp. 961-965, copyright 1989, with permission from tlie American Chemical Society.

The gel permeation chromatogram shown in Fig. 6 illustrates the purity of a block copolymer obtained by ion coupling. It is seen that about 5% of uncoupled block copolymer contaminates a triblock copolymer of narrow molecular weight distribution. The synthesis of star block polymers owes its recent development to the use of new coupling agents412. ... 

Fig. 6. Gel permeation chromatogram of the MS-PS-MS block copolymers obtained by coupling...

Figure 7. Chromatograms of AN/S copolymers ((a) 2 hr polymerization, 13% total solids (b) 4 hr polymerization, 24% total solids (c) 6-hr polymerization,...

Gel Permeation Chromatography (CPC) is often the source of molecular wei t averages used in polymerization kinetic modelling Q.,2). Kinetic models also r uire measurement of molecular weight distribution, conversion to polymer, composition of monomers in a copolymerization rea tion mixture, copolymer composition distribution, and sequence length distribution. The GPC chromatogram often reflects these properties (3,. ... 

In analysis of homopolymers the critical interpretation problems are calibration of retention time for molecular weight and allowance for the imperfect re >lution of the GPC. In copolymer analysis these interpretation problems remain but are ven added dimensions by the simultaneous presence of molecular weight distribution, copolymer composition distribution and monomer sequence length distribution. Since, the GPC usu y separates on the basis of "molecular size" in solution and not on the basB of any one of these particular properties, this means that at any retention time there can be distributions of all three. The usual GPC chromatogram then represents a r onse to the concentration of some avera of e h of these properties at each retention time. 

B. Measurement of Property Distributions for Copolymers. Figure 12 shows chromatograms of typical products in the copolymerization study (Column Code B2). Since the detector is responding to concentration, composition, and periiaps sequence length, the direct single detector interpretation as described for PMMA is not immediately applicable here. Tacticity variation is yet another consideration but ]s assumed of sa ond order importance for th samples (22). 

Interpretation of copolymer chromatograms in the literature does not include axial dispersion correction (3, 6) and little is known regarding it (5). The usual approach( is to utilize dual detectors and to assume that both detectors respond to at mos both composition and concentration. The two chromatograms then provide two equations in these two unknowns at each retention time. 

B. Development of the Method. Figure 16 shows normalized chromatograms for various copolymers from GPC 2 with 57% n-heptane in THF as its mobile phase. In beginning the development of this technique, two major aspects are important (i) Variation in Molecular Properties Expected Within a Chromatogram Slice and (ii) Sources of Error in Analyzing for These Properties. These are discussed in turn below. 

Figure 16. GPC 2 chromatograms obtained by sampling copolymer chromatograms on GPC 1 (letters correspond to samples in Table V—(%) A (0) B ...

SEC-FTIR yields the average polymer structure as a function of molecular mass, but no information on the distribution of the chemical composition within a certain size fraction. SEC-FTIR is mainly used to provide information on MW, MWD, CCD, and functional groups for different applications and different materials, including polyolefins and polyolefin copolymers [703-705]. Quantitative methods have been developed [704]. Torabi et al. [705] have described a procedure for quantitative evaporative FUR detection for the evaluation of polymer composition across the SEC chromatogram, involving a post-SEC treatment, internal calibration and PLS prediction applied to the second derivative of the absorbance spectrum. 

The LCCC chromatograms in Fig. 17.13 show that PEO is well separated from the copolymer fractions that elute at elution volumes between 1.5 and 2.8 mL. 

Under these conditions, the polyethylene oxide blocks behave chromatographi-cally invisible and retention of the block copolymer is solely directed by the polypropylene oxide block, yielding fractions of different degrees of polymerization (m) with respect to PPO. The assignment of the peaks was based on comparison with the chromatogram of a polypropylene glycol. 

The chromatogram in Fig. 17.15 reflects the oligomer distribution of the PO inner block, but does not give any information on the chain lengths of the PEO outer blocks or the total molar mass. This lack of information can be compensated by 2D liquid chromatography. Fig. 17.16 represents the contour plot of the 2D separation of the block copolymer in the sequence LCCC versus SEC. The separation with respect to the PO block length is now obtained along the ordinate, while the abscissa reflects... 

Figure 14. Gel permeation chromatograms of polystyrene and polystyrene-polybutadiene diblock copolymer prepared with Ba-Mg-Al. Conditions solvent, cyclohexane 50° C.

Figure 2. Gel Permeation Chromatogram of the copolymer (a) before and (b) after removal of the t-BOC protecting groups...

An example for the synthesis of poly(2,6-dimethyl-l,4-phenylene oxide) - aromatic poly(ether-sulfone) - poly(2,6-dimethyl-1,4-pheny-lene oxide) ABA triblock copolymer is presented in Scheme 6. Quantitative etherification of the two polymer chain ends has been accomplished under mild reaction conditions detailed elsewhere(11). Figure 4 presents the 200 MHz Ir-NMR spectra of the co-(2,6-dimethyl-phenol) poly(2,6-dimethyl-l,4-phenylene oxide), of the 01, w-di(chloroally) aromatic polyether sulfone and of the obtained ABA triblock copolymers as convincing evidence for the quantitative reaction of the parent pol3rmers chain ends. Additional evidence for the very clean synthetic procedure comes from the gel permeation chromatograms of the two starting oligomers and of the obtained ABA triblock copolymer presented in Figure 5. 

The exclusive formation of the block copolymer has been confirmed by selective fractionation, NMR spectroscopy, and SEC analysis. For instance, the copolymerization of eCL and 6VL has been followed by SEC. Figure 2 compares the SEC chromatograms of the first PCL block and the final poly(eCL-h-6VL) diblock copolymer. The molecular weight of the macroinitiator is shifted towards higher values in close agreement with the theoretical value expected from the comonomer-to-Al(OzPr)3 molar ratio, and the MWD remains very narrow during the copolymerization process (PDI=1.10). 

The chromatogram of Kraton 1107 shows the other components of the sample besides the major coupled diene S-l-l-S small amounts of "kill" polystyrene, uncoupled S-1 block copolymer, and material with higher molecular weight than that of SlIS are indicated. As indicated in Figures 2a and 3a, the LB polymers all showed a small polystyrene "kill" component and a high molecular weight shoulder on the block copolymer peak with a molecular weight of about twice that of the block copolymer. 

The DVB-linked MA polymers showed evidence of "kill" polystyrene and block copolymer arm with peak elution volumes at the same position as in the LB chromatograms. Note that in Figure 2b, the LALLS chromatogram has a shoulder on the major peak which is not observable in the DRl chromatogram this corresponds to a sign change in the slope of the log M(v) vs. v relationship. 

Figure 2. Sephacryl S-400 Chromatogram of Acrylamide/N-isopropyl Acrylamide (10/90) Copolymer.

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