Copolymers pyrolysis techniques

This pyrolysis technique was used in the analysis of copolymers of acrylonitrile with styrene in a broad range of monomer ratio variations [34]. An ampoule containing a weighed amount (5—10 mg) of the polymer was pre-evacuated down to a residual pressure of 10" mmHg. The pyrolysis was conducted for 20—30 min at 500°C. The composition of the copolymers can be determined from the peaks of hydrocyanic acid and toluene, which are present in the pyrolysis products in amounts proportional to those of acrylonitrile and toluene, respectively, initially present in the copolymer. 

Pyrolysis techniques are particularly suited for the more difficult polymer/additive analysis problems on account of intricate architecture and morphological features, e.g. in case of (i) polymer-bound additive functionalities (AOs, FRs) (ii) impact modifiers such as terpolymers (e.g. styrene-hydrogenated butadiene-styrene), graft polymers (e.g. EPM-g-PBT) and an internal rubbery phase in core/shell polymers (e.g. acrylate-based cross-linked polymer) [527] and (Hi) interfacial agents (e.g. graft copolymers, sizings). 

Smith [841] has discussed applications of pyrolysis techniques for polymeric systems with emphasis on the qualitative identification of components in a copolymer or polymer blend, identification of low-level polymer contaminants, characterisation of copolymer sequencing, differentiation between copolymers and physical blends of homopolymers, determination of monomer ratios in copolymers, and the study of polymer kinetics and degradation mechanisms. Pyrolysis destroys the stereostructure of the polymers. Gaseous components generated from pyrolysis of a wide variety of polymers have been analysed both off-line and on-line by IR spectroscopy to determine (quantitatively) the major components of the parent resin, e.g. rubbers... 

A method is discussed below for the determination of the composition of an ethylene-butene-1 copolymer containing up to about 10% butene. This technique has been applied to the pyrolysis gas chromatography of ethylene-butene copolymers. Pyrolysis were carried out at 410°C in an evacuated gas vial and the products swept into the gas chromatograph. Under these pyrolysis conditions, it is possible to analyse the pyrolysis gas components and obtain data within a range of about 10% relative. The peaks observed on the chromatogram were methane, ethylene, ethane, combined propylene and propane, isobutane, 1-butene, trans-2-butene, cis-2-butene, 2-methyl-butane and n-pentane. 

Pyrolysis technique hyphenated to GC/MS (Py-GC/MS) has extended the range of possible tools for characterisation of synthetic polymers/copolymers. Under controlled conditions at elevated temperature (500-1400 C) in the presence of an inert gas, reproducible decomposition products characteristic of the original polymer sample are... 

Combination techniques such as microscopy—ftir and pyrolysis—ir have helped solve some particularly difficult separations and complex identifications. Microscopy—ftir has been used to determine the composition of copolymer fibers (22) polyacrylonitrile, methyl acrylate, and a dye-receptive organic sulfonate trimer have been identified in acryHc fiber. Both normal and grazing angle modes can be used to identify components (23). Pyrolysis—ir has been used to study polymer decomposition (24) and to determine the degree of cross-linking of sulfonated divinylbenzene—styrene copolymer (25) and ethylene or propylene levels and ratios in ethylene—propylene copolymers (26). 

Pyrolysis-MS, together with TGA analysis, was chosen recently as the technique with which to investigate the thermal behaviour of two polythiophene copolymers, since insolubility in common solvents of conducting polymers limits... 

Catalytic processes, in advanced cracking techniques, 20 778-779 Catalytic pyrolysis, 10 619 Catalytic random copolymers, 7 635-638 Catalytic reaction process, 10 83-84 rate of, 10 84-85... 

A wide variety of polymers have been analyzed by gel-permeation, or size-exclusion, chromatography (sec) to determine molecular weight distribution of the polymer and additives (86—92). Some work has been completed on expanding this technique to determine branching in certain polymers (93). Combinations of sec with pyrolysis—gc systems have been used to show that the relative composition of polystyrene or acrylonitrile—polystyrene copolymer is independent of molecule size (94). Improvements in gpc include smaller cross-linked polystyrene beads having narrow particle size distributions, which allow higher column efficiency and new families of porous hydrophilic gels to be used for aqueous gpc (95). 

It has been reported that pyrolysis gas chromatographic techniques could be used to differentiate between block and random copolymers (18). However, it was not possible to distinguish between the block copolymers and mixtures of polystyrene and the alternating copolymers of styrene and maleic anhydride by the PGC technique used in this investigation. However, differences were noted in the DTA thermograms of the alternating copolymer, the block copolymer, and the mixture of polystyrene and the alternating copolymer. 

Pyrolysis gas chromatography has been widely used for copolymer analysis. This technique may offer many advantages over other detection techniques for copolymer analysis by SEC. One obvious advantage is the small sample size required. Another is the capability of application to copolymers which cannot utilize UV or IR detectors [3]. 

When the sequences in the copolymer are longer than 6-8 carbons, techniques other than NMR are needed to directly determine their length. The use of pyrolysis followed by GC-MS analysis has been proposed to And the long sequences as fragments in the pyrolyzate, but the data produced are complicated and difficult to interpret (Tosi, 1968 Yamada et al., 1990 Tulisalo et al., 1985 Hu, 1981). 

This study combines a thermal analysis technique -thermogravimetry with atmospheric pressure chemical ionization mass spectrometry and applies the combined technique to the third question. The literature contains references relating to the analysis of styrene butadiene copolymers using thermal analysis techniques (1-5). Pyrolysis - mass spectrometry (5) and vacuum thermogravimetry - mass spectrometry (7) have also been used to investigate polymers such as polystrene and styrene butadiene rubber. 

Nakagawa and co-workers [18] used techniques based on high resolution Py-GC and Py-GC and TGA to measure thermal degradation of chloromethyl substituted polystyrene. A typical TGA weight loss curve is shown in Figure 4.1. Degradation starts at 200 "C and peaks at 400 °C. Typical pyrolysis products of chloromethylated styrene-divinyl benzene (St-DVB) copolymers are the monomers, dimers and trimers of styrene, p-methyl styrene, and divinyl and ethyl styrene. For styrene chloromethyl St-DVB copolymers, in addition to the above, /-methyl styrene monomer and m- and p-chloromethyl styrene monomers are also present in pyrolysates. 

Van Schooten and Evenhuis [86, 87] applied their pyrolysis (500 °C)-hydrogenation-gas chromatography technique to unsaturated ethylene-propylene copolymers, i.e., ethylene-propylene-dicyclopentadiene and ethylene-propylene-norbornene terpolymers. The pyrograms show that very large cyclic peaks are obtained from unsaturated rings methylcyclopentane is found when methylnorbornadiene is incorporated cyclopentane when dicyclopentadiene is incorporated methylcyclohexane and 1,2-dimethylcyclohexane when the addition compounds of norbornadiene with isoprene and... 

An effective understanding of copolymerization chemistry can only be realized through the analysis of the products of the reactions. There have been many accounts of the applications of n.m.r. spectroscopy to polymers and the evaluation of sequence distributions in copolymers figures highly in some of the reviews. " A computer simulation of the C n.m.r. spectrum has been described. Other techniques which have received recent attention are excimer fluorescence spectroscopy for alternating copolymers, mass spectroscopy for ethylene-propylene oxide copolymers, and pyrolysis g.l.c. > A review of analytical techniques has been made by Fujiwara, Mori, Nishioka, and Takeuchi. In a complementary series of articles infi red and Raman spectroscopy have been reviewed by Tanaka C n.m.r. of branched copolyma by Fujiwara and the particular problems of solid and liquid polymer aiuilysis by Tsuge and Mukoyama, respectively. 

Various experimental techniques have come to the fore in copolymer composition studies. The two major techniques employed are infrared (IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. Controlled pyrolysis linked to gas chromatography (Py-GC) and IR spectroscopy is being employed in a growing number of applications. 

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