adsorbents attached by sintering to glass. XI. influence of pH of glass binders on formation of sintered thin layers. Okumura, T., J. Pharm. SOC.Jpn., 1974,94, 1045-1053. (T18) Sintered thin-layer chromatography with flame-ionization-detector scanning. Okumura, T., Kadono, T., Iso’o, A,, J. Chromatogr., 1975, 108. (T19) Impregnation of sulfuric acid on Silica gel G to quantitate spots on thin-layer chromatograms. Peterson, F. J., Duthie, A. H., Lab. Pract., 1974, 23, 245-246. (T20) Variations In the manufacture of commercial silica gel plates. Turano, P.,Turner, W. J., J. Chromatogr., 1974, 90, 388-389. (T21) Applications of the Nichrome-wire ring chamber in paper chromatography. Shahid, M. A,, Chughtai, N. A,, Afzal, A. U., Pak. J. Sci. lnd. Res., 1973,16, 199-201. (T22) Bibliography of electrophoresis, 1968 to 1972, and survey of applications. J. Chromatogr., Suppl. Vol. No. 4, 1975, 861 pp.
2223-2224. (T24) Improved penicillin-selective enzyme electrode. Cullen, L. F., Rusling, J. F., Schleifer, A., Papariello, G. J., Anal. Chem., 1974, 46, 19551961. (T25) Use of precipitate-based silicone-rubber ion-selective electrodes and silicone-rubber-based graphite voltammetric electrodes in continuous analysis. A review. Feher, Z., Nagy, G., Toth, K.. Pungor, E., Analyst (London), 1974,99,699-708. (T26) Methylephedrine- and ephedrine-selective electrodes. Fukarnachi. K., Nakagawa. R., Morimoto, M., Ishibashi, N., Jpn. Anal., 1975, 24, 428-432. (T27) Liquid membrane electrodes responsive to such organic anions as antiseptics and artificial sweetenings. Shigematsu, T., Ota, A., Matsui, M., Bull. lnst. Chem. Res. Kyoto Univ., 1973, 51, 268-272.
Electrochemlstry (T23) Potassium-ion-responsive coated-wire electrode based on valinomycin. Cattrall, R. W., Tribuzio, S.,Freiser, H., Anal. Chem., 1974, 46,
Mass Spectrometry (T28) Fieid-ionization mass spectrometry: a tool for the analycal chemist. Anbar, M., Aberth, W. H., Anal. Chem., 1974, 44, 59A-62A, 64A. (T29) Field-desorption mass spectrometry. Beckey, H. D., Schulten, H. R., Angew. Chem., lnt. Ed. Engl., 1975, 14, 403-415. (T30) Application of quadrupole mass filters in
fielddesorption mass spectrometry. Gierlich, H. H., Heinen, H. J., Beckey, H. D., Biomed. Mass Spectrom., 1975, 2, 31-35. (T31) Modern ionization techniques in mass spectrometry. Milne, G. W. A,, Lacey, M. J., CRC Crit. Rev. Anal. Chem., 1974, 4, 45-104. (T32) A high-precision fluorimeter for biochemical measurements. Peterson, J. I., Friauf, W. S., Leighton, S. B., Anal. Biochem., 1974, 56, 255271. Mlscellaneous (T33) New type of continuous counter-current extraction: extractor with two continuous phases. Pan, S.C., Sep. Sci., 1974, 9, 227-248. (T34) Problem in liquid scintillation counting: adsorption of ( 14C)polyoxyethylene giycoi in dilute solutions. Crouthamel, W. G., Van Dyke, K., Anal. Biochern., 1975,66,234-242. (T35) New method for determination of purity by means of calorimetric differential thermal analysis. Staub, H., Perron, W., Anal. Chem., 1974, 46, 128--130. (T36) Automated, stepping differential calorimeter for the analysis of purity. fynger, J., Anal. Chem., 1975,47, 1380-1384.
Rubber Coe W. Wadelin” and Marion C. Morris Research Division. The Goodyear Tire and Rubber Co., Akron, Ohio 443 16
This review covers chemical analysis of rubber and characterization of rubber by physical, chemical, and spectroscopic methods. Methods for the identification, characterization, and determination of rubber and materials in rubber are included, but the analysis of rubber additives when they are not contained in rubber is not included. Polymers other than rubber are covered in another review in this issue (130). The literature which became available to the authors between September 1974, the end of the period covered by the last review in the series (202), and September 1976, is covered. Abbreviations recommended in ASTM Designation D1418-76 have been used ( 5 ) .They are listed in Table I.
GENERAL INFORMATION Review articles have been written describing selection of known methods to give the most information when a limited amount of sample is available (119)or when speed is desired (82, 124). Ultraviolet, visible, NMR, and ESR spectroscopy were reviewed (204). Infrared spectroscopy was not included as it has been covered recently (79). Fourier transform carbon-13 NMR (31)and infrared (103) spectroscopy as applied to rubber were also reviewed.
POLYMER IDENTIFICATION The term “total thermal analysis” was introduced to include T G (thermogravimetry), DTG (derivative thermogravimetry), DSC (differential scanning calorimetry), and T,(glass transition temperature). The measurements, except for T , are done in both nitrogen atmosphere and in oxygen (17j). In tread and black sidewall stocks SBR, BR, and polyisoprene can be distinguished. The polyisoprenes, NR and IR, can be distinguished from each other in sulfur cured, carbon black filled stocks, but not in peroxide cured, unfilled stocks. The ability to make this distinction was also observed by others (25).The effect of sulfur level (171), carbon black level (171), and carbon black type (25) was studied. I t was also observed that NR and IR can be distinguished by pyrolysis a t 350 “ C .followed by infrared or GC (gas chromatographic) examination of the pyrolyzate. As in total thermal analysis, the difference occurs only in sulfur cured,
carbon black filled samdes. The Dvrolvsis Droduct whose concentration is observed is dipentene (52). White sidewall blends of EPDM/NR/SBR/CIIR (173), CR/NR. or CR/NR/CSM (174) and innerliners of IIR. halogenated’IIR, or NR/CIIR (175) were also identified by total thermal analysis. Preparation of vulcanizates for infrared examination was reviewed. Degradation with 1,2-dichlorobenzene was preferred over pyrolysis or decomposition a t 200 “C. Any polymer present to the extent of 20% or more will be recognized (73). The method of combining 1,2-dichlorobenzene with a peptizer (39),which is very effective, was not mentioned. Polyurethanes were degraded by acid (137), amines (106, 137), alkali (102), or methanol to form compounds which could be examined by spectroscopy or chromatography. Polyethers intended for use in EU were degraded with a mixed anhydride of acetic and p-toluene-sulfonic acids. T h e acetates of ethylene glycol, propylene glycol, and many polyfunctional initiators were identified. The oxyethylene and oxypropylene group contents were determined by gas chromatography (193). Infrared spectra and thermal analysis were used to generally classify polyurethanes as to type (120). The diisocyanate component was identified by pyrolysis-GC (71). Polypentenamers present to the extent of 10%or more in vulcanizates with SBR, BR, IR, or NR can be identified by the GC detection of glutaraldehyde in the ozonolysis products (115).
Table I. Abbreviations Recommended by ASTM ( 5 ) CSM EPDM BR CllR CR IIR IR NBR NR SBR EU
Chlorosulfonyl-polyethylene Terpolymer of ethylene, propylene, and a diene with the residual unsaturated portion of the diene in the side chain. Butadiene rubber Chloroisobutene-isoprene rubber Chloroprene rubber Isobutene-isoprene rubber Isoprene synthetic rubber Nitrile-butadiene rubber Natural rubber Styrene-butadiene rubber Polyester urethane
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MOLECULAR WEIGHTS A N D D I S T R I B U T I O N S OF HOMOPOLYMERS GPC (gel permeation chromatography) is still the most widely used method for MW (molecular weight) characterization. Recently, however, there has been a resurgence of LS (light scattering) techniques both for solution and for work in the bulk state. This is primarily due to the advent of laser technology which has provided intense coherent light. It is often advantageous to couple GPC with viscometry or LS techniques (81,82). Extensive reviews are available for literature on MW characterization prior to December 1974 (129, 202).
G P C T h e o r y and Reviews. Investigations into the mechanism of GPC indicate that there is more than one process contributing to separation and dispersion. However, these processes do not have the same relative importance for all types of column packings (139).These are the molecular sieve and the occlusion mechanisms. The latter is dependent upon the thermodynamic compatibility of the polymer molecules with the absorbent matrix and depend upon solvent power as well as the nature of the packing (16,48,198). One can independently estimate the sizes of dissolved polymer molecules from hydrodynamic volume theory and by using small angle x-ray scattering. The results are in line with the effects of solvent and concentration on GPC elution volumes (162). Columns composed of long glass frits having capillary dimensions just above the polymer coil size were constructed as a model to test the concept of separation by flow. The experimental results were in reasonable agreement with theory (132). Other investigations along this line relate to the column temperature in relation to theta conditions (46,47). Reviews are available dealing with the role of polymer chain structure in GPC separation (78, 156). Calibration of GPC. The universal calibration technique based upon hydrodynamic volume remains the basis for most calibration procedures (74).It has been under careful scrutiny (33). It is clear that the product, intrinsic viscosity times MW, is a valid calibration parameter for many polymeric materials (49). Other investigators have found that the parameter was universal only when the molecular geometries of all the Samples involved were similar (4). The applicability of the universal calibration technique to low MW polymers was in doubt because of the known deficiency of the Mark Houwink relationship for predicting viscosities for low MW materials. It has now been shown that the universal calibration curve can be applied to oligomers (2). In practice there are several experimental problems that must be taken into account in calculating MW averages. The most serious of these are the nonlinearity of the calibration curve and the skewing of the peak due to imperfect resolution. A technique to correct for nonlinear calibration has been published (30). Skewing corrections have been dealt with by several investigators (19, 135). One technique that corrects for imperfect resolution is said to allow the use of equipment with inherently poor resolution. A computer program is given (192). A review on practical calibration considerations is available (63).A detailed investigation of axial dispersion has been made with radioactive polystyrene. It provides a valuable basis for testing of theories (18, 20). G P C Column Packings. Polystyrene gel packings, Styragel, remain the most used packing material. Small particle size gels have been found to increase the efficiency of separation (44,45,97).Packings having diameters of the order of 10 ym make it possible to determine the MWD (molecular weight distribution) of a polymer mixture in less than 20 minutes with the same accuracy as by conventional GPC. Controlled porosity glass was compared to Styragel packings in one investigation. The dependence of retention volume of polystyrene on flow rate and on sample size was similar in both systems. Corrections for axial dispersion were equivalent (181).Highly porous trimethylsilylated silica beads are said to be capable of high performance in GPC. The number of theoretical plates was between 400 and 4000 plates per foot for these columns (197).Porous alumina (50)and porous silica ( 5 1 ) were found capable of giving good column efficiencies when suitable particle sizes were used. GPC separations were performed with several commercially available column packing materials and the results were analyzed to obtain the ratio of weight to number average MW. This parameter for 134R
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narrow MM‘D materials is suggested as a convenient parameter for comparing column efficiencies (41).Various methods are used to determine the separation efficiencies of columns. The reason that they do not agree in ranking a series of columns has been investigated (37). CHARACTERIZATION BY COMPOSITION A N D BRANCHING GPC is not inherently well suited to analysis for composition or branching. However, when coupled with suitable detectors these parameters may be determined. il’here a onewave length detector is not sufficient, operation in a stop and go fashion allows use of the complete spectrum (126).Such techniques require only 252 hours as compared to 20 hours for preparative fractionation (128). In the case of hydroxy terminated polybutadienes, a UV absorbing derivative was prepared to investigate the functionality distribution ( 7 ) . A study has been made of the experimental variables in preparative scale GPC ( 4 2 ) .Up to 20 grams per day were fractionated by preparative GPC maintaining polydispersities of 1.1 or less (144). Characterization of Branching. A mixture of star shaped and linear poljmers both nearly monodisperse was used to test the efficiency of GPC for characterization of star shaped polymers. It was shown that the peak for star shaped polymers having three branches of equal MW is very close to that of a polymer comprising two of the same branches. Very high efficiency columns are required for separation (95).Equations were derived for the determination of branchin of polymers from GPC and intrinsic viscosity data. T h e app icability was shown by using published data on polystyrene ( 3 ) . Comb shaped branched polystyrenes were examined by GPC and LS (96). G r a f t a n d Block Copolymers. The GPC elution volume of PVC (poly(vinylchloride1) was only slightly changed by grafting of styrene (113).PYC was also grafted with butadiene. The polystyryl carbanion was found to be more efficient at grafting than the polybutadienyl carbanion (114).Yiscosity, GPC, and LS data for two- and three-block isoprene-styrene block copolymers showed that the dimensions of the copolymers were only slightly larger than the sum ofthe unperturbed dimensions of the individual sequences (136).Using an indirect approach, rhe polystyrene fraction of a butadiene stjrene block rubber was accurately characterized by degradation of the rubber and subsequent GPC of the fragments (112).Block copolymers of polystyrene polydimethylsiloxane and polyisoprene/polydimethylsiloxanewere studied by GPC. LS. and osmometry (122).
Y
S P E C I F I C G P C APPLICATIONS GPC is useful for studying polymerization and degradation kinetics of polymers. The role of ion pairs in anionic polymerization kinetics has been determined (1661. The importance of disproportionation and combination as termination mechanisms in radical polymerization was in1,estigated (21, 22). Dilute solutions of polystyrene in several aromatic solvents were irradiated using high energy electrons. The results indicated that main chain scission in polystyrene occurred at random locations (81). Accelerated heat aging studies on fluorosilicone rubber by GPC indicated the amount of degradation in the presence of air and inert atmosphere (911 . Basic raw materials for polyurethanes may be characterized by GPC ( 1 7 , 180).Rapid identification of solid polyurethane elastomer components was made by pyrolysis gel chromatography (26). The processing properties of rubbers are affected by the MN’D (34).The variable processability of emulsion SBR was related to MII’D. A rapid method of GPC suitable for process control was developed (177) making use of an unusual detector. For Polystyrene, the effects of extrusion on molecular and rheological properties were examined (183,. In extensional tests of polystyrene, samples with narrow MU‘D necked in the final stages and showed viscous failure (190).The importance of the use of GPC in determining MR’Din process control has been discussed ( 5 7 ) .GPC applications in processing are given including monitoring of resin uniformity and accurate polymer blendin (125). The 8 P C intrinsic viscosity method was used to determine the long chain branching of CR (40). Solvent dependences and
Coe W. Wadelin is a graduate of Mt. Union College (B.S., 1950) and Purdue University (M.S., 1951; Ph.D., 1953). Since 1953 he has been with the Research Division of the Goodyear Tire and Rubber Co. in Akron. Ohio, where he is a section head in spectroscopy. He is a member of the American Chemical Society and its Analytical Division. He was a Fellow at MIT's Center for Advanced Engineering Study in 1968-69.
Marion C. Morrls, Research Scientist, Physical Chemistry, Basic Polymer Research Department, the Goodyear Tire and Rubber Co., Akron, Ohio, joined the staff in 1962. Dr. Morris earned his B.S. degree at the University of Akron in 1954, his M.S. in physical chemistry in 1961, and his Ph.D. at the University of Akron Institute of Polymer Science in 1963. His interests are in the physical characterization of high polymers, particularly in methods relating molecular characteristics to bulk behavior. These have included studies in rubber-like elasticity, viscoelastic response, crystallization and glass temperature in rubber blends, and gel-permeation chromatography. He served on the committee for the Akron-Summit Polymer Conference in 1971 through 1975. Dr. Morris is a member of the American Chemical Society.
concentration effects in GPC were also determined for CR (94).
MWD has been determined for guayule rubber and compared to NR. The MW's are found to be of the same order of magnitude but there are large differences in gel content (28). The cyclic structure of oligomers in polymers formed in the metathesis reaction of cyclooctene was confirmed by separation using GPC (85).Using infrared with GPC it was learned that the microstructure of BR remained essentially constant across the MWD (127). LIGHT SCATTERING TECHNIQUES G P C Coupled Light Scattering. The effluent from GPC was simultaneously and continuously monitored with a refractometer detector and a low angle laser LS photometer. This provided a direct determination of MWD without the conventional calibration. Measuring the intensity of scattered light a t very low angles greatly simplified the procedure for determining MW. The ability to work at very low concentrations also simplifies calculations (142). A LS photometer coupled with a GPC was interfaced with a computer to obtain on-line MWD data for polymers. MW data thus obtained for a number of polystyrene standards were in agreement with literature data (140).A LS detector for GPC thus shows more promise than did the capillary viscometer detector (141,196). Because of the very narrow beam, interference by dust particles is obvious and is easily corrected. A low angle laser L S device is commercially available (36). The role of LS in industrial polymer characterization has been given (208). An extensive review is available for inelastic laser light scattering from synthetic and biological polymers (169).LS in studying multicomponent polymer systems has been reviewed (108). Several computer programs are available to treat LS data. Some of these programs provide nonlinear least squares analysis to find optimum fit of the observed data to scattering functions (90, 165, 170). Accurate characterization of styrene-butadiene copolymers required the use of solvents such that the differences between the specific refractive indices of the appropriate homopolymer solutions do not depend strongly on polymer molecular weight (35). LS and viscometric analysis of cyclized polyisoprene showed an increase in the steric hindrance factor with progressing cyclization (199).The development of quasi-elastic LS permits the precise determination of translational diffusion coefficients of macromolecules. This technique is also called intensity fluctuation spectroscopy. The theory and use of this technique to measure diffusion coefficients of polydisperse systems has been reviewed (154). The technique was used to study two
monodisperse polystyrene samples and one having a broad MWD (155).An autocorrelation function has been proposed for relating polydispersity and quasi-elastic LS (194). The results on atactic polystyrene indicate that the measured relaxation times were much closer to the free draining mode than the nondraining Zimm prediction (123). Branching. Series of linear four and six branched regular star polyisoprenes were synthesized and characterized by LS (77). Star polymers from styrene in divinylbenzene were investigated (62).Model comb shaped polymers of polystyrene were studied by LS, osmometry, viscometry, and diffusion (541.
Copolymer Characterization. T h e LS technique was evaluated for determining compositional heterogeneity in copolymers. The agreement of heterogeneity parameters was poor suggesting that LS is not well suited for determining the amount of A or AB in ABA block polymers (182). The formation of micelles has been observed in butanone solutions of styrene-butadiene-styrene triblock copolymers. Some conjectures regarding the nature of such micelles are made on the basis of LS results (110).Sedimentation analysis and LS show this supermolecular micelle structure (195). Solubility a n d Incompatibility. LS measurements were made for the system polystyrene-cyclohexane. An estimation was made of the temperature dependence of the extrapolated zero angle scattering intensity. Similarities were found in the critical solution behavior of macromolecular solutions to other critical binary mixtures (104). Parameters were defined characterizing the interaction of non-identical polymer molecules in dilute solution by LS (109).The fluctuation theory of LS for moderately concentrated polymer solutions is extended in a phenomenological fashion to include angle dependent terms and apply to the incompatibility of two polymers in a single solvent (201). The incompatibility of graft copolymers has been determined by LS (111). L a t e x a n d Bulk Polymers. A photometer has been designed for rapid measurement of angular scattering patterns from individual particles. Computer comparison of actual to theoretical diagrams for various compositions and characteristics were made (121). The continuous distribution of particle sizes of polystyrene latex was measured by intensity correlation spectroscopy (11).The technique combining zonal ultracentrifugation and angular light scattering was developed for size distribution analysis of polydisperse and chemically mixed polymer latex systems (203). Low angle laser light scattering provides a measure for the degree of nonrandomness in cross-linking. The nonrandomness index for a series of polymer networks is found to vary systematically by a factor of over 100 depending upon the history of network formation. Intensity fluctuation spectroscopy at any given angle provides a probe for local viscoelasticity of a gel without applying an external driving force (207). A harmonically bound particle model was derived for interpretation of quasi-elastic LS by gels (206).Polarized LS measurements for polystyrene networks swollen by benzene show that optical mixing spectroscopy can provide detailed measurements of the interaction between the polymer network and the swelling liquid (134). Quasi-elastic LS was used to determine the internal motion of macromolecules (67). T h e scale and extent of density heterogeneity of cross-linked SBR and NR have been investigated by small angle LS (150). Optical studies have been made of the deformation of model filled rubbers. The strain pattern about a lass bead imbedded in a stretched rubber was calculated a n f u s e d t o predict the birefringence and LS (138).Small angle LS studies have been made of the stress-induced crystallization of uncured polyisobutylene (176). A small angle LS device has been constructed for studies of supermolecular structure in thin polymer films (143).A method has been found for taking into account the multiple scattering effect from thin polymer films (153). A set of general equations has been derived for representation of the angular dependence of LS from correlated polymer systems. Explicit expressions for thin oriented rods were obtained (23). THERMAL PROPERTIES A revised list of physical constants of rubbers has been published for NR, IR, SBR, IIR, and CR. These include T,, heat capacity, thermal conductivity, melting temperature and ANALYTICAL CHEMISTRY, VOL. 49, NO. 5, APRIL 1977
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heat of fusion for polymers which are unvulcanized, gum vulcanized, and vulcanized with 50 parts carbon black (205). It has often been observed both by dilatometry and calorimetry that glasses in the transition range exhibit behavior similar to a first-order thermodynamic transition. This has been explained in terms of volume or enthalpy retardation kinetics (87). T , values from DSC measurements are commonly seen to vary with heating rate. I t has been shown that, using an enthalpy method, a value for the T , independent of heating rate can be derived (160). The lowering of T , of polymers dispersed as micro phases in continuous phases of lower T , was attributed to partial mixing of the phases (10). NMR proton spin-lattice relaxation times were measured in NR, IR, and BR gum stocks under pressure of 1to 3 kbar over the temperature range -100 "C to f l O O "C. The observed pressure dependence of the T , for these elastomers indicates that the configurational entropy rather than volume primarily determined the glass transion (117). Total thermal analysis provided a rapid and reasonably accurate method for the identification of tire rubber (173),as presented above under the heading Polymer Identification. The effects of soft segment variations have been noted in thermoplastic urethane elastomers (167).T of thermoplastic urethane elastomers shifted progressively &o higher temperatures as the relative hard segment content was increased. The variation was accurately described by the Fox relation for amorphous copolymers (168). The calorimetric and NMR data obtained for a segmented polyurethane elastomer showed ordered structures (68).A systematic approach for identification of various urethane rubbers using infrared and thermal analysis techniques has been given (120). A technique based on a high pressure argon system was applied to NR for the experimental determination of lamellar growth rates and the concurrent observations of changes in crystalline morphology. Three apparently different modes of crystallization were observed (60). The electron diffraction patterns of IR crystallized a t high pressure and quenched to 0 "C. before the release of pressure showed that the molecular conformation typical of normal spherulitic lamellar crystals was retained. The high pressure phase was much less ordered (59). The rate of stress-induced crystallization of NR was measured. An Avrami exponent of 0.88 was observed in the kinetics of crystallization. This corresponds to one-dimensional growth from previously formed nuclei (72).Measurement of crystallization rates of oriented IR and NR have also been made by dynamic x-ray diffraction techniques. Differences in the change of rate with increasing temperature have been noted for NR and IR (100).A model for the crystallization of networks under stress leads to a relationship between melting temperature and degree of network orientation (178). A review has been written on birefringence and low angle LS in the stress-induced crystallization of polymers (185).A review has also been written on strain-induced crystallization for polymers and NR (209). High cis-1,4-polybutadiene made with uranium catalyst was found to have faster crystallization rates and higher melting temperatures than did other known BR (53).This elastomer also showed stress-induced crystallization which accounted for improved ultimate properties (70).
POLYMER CHARACTERIZATION BY SPECTROMETRIC AND CHEMICAL METHODS In the past few years, carbon-13 NMR instruments have become available in many laboratories. This valuable tool has been put to work on polymers as evidenced by numerous publications. The field was reviewed (31).The application of high field (220 to 300 MHz) proton NMR to polymers was also reviewed (80, 161). Chemical shift assignments were made for the carbon-13 NMR spectrum of BR. Cis-1,4, trans-1,4, and 1,2 structures can be distinguished (61, 187). Sequences in BR were also studied (1).In two instances, hydrogenated polybutadiene was also studied to help confirm assignments and sequence distribution (38, 157). The carbon-13 NMR spectra of solid samples of cis-1,4polyisoprene, trans -1,4-polyisoprene, and carbon-filled cis 1,4-polyisoprene were reported. Carbon black broadens the lines by a factor of 5 to 10 (164). Cis-trans composition of polypentenamer was determined 136R
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by carbon-13 NMR but no information was obtained on sequence distribution (32). The carbon-13 NMR peaks of SBR were assigned in terms of the various diad arrangements (98,991. Proton NMR a t 300 MHz resolves cis-l,4 and trans-l,4 structures in BR. This cannot be done a t frequencies of 100 MHz or lower. The olefinic peaks are split into triplets which are assigned to triads (163). Proton NMR a t 300 MHz was also used to study polyisoprene. High temperature improves the resolution of the 3,4and trans-1,4-methyl protons (133). Guayule and hevea polyisoprenes were compared at 300 MHz (29). The infrared bands were assigned for an alternating copolymer of butadiene and acrylonitrile, contrasting i t with a random copolymer (69). Fourier transform infrared was used to confirm that oxygen attacks BR a t the alpha-methylene position (146).The reaction of oxygen with conjugated polyenes in polyisoprene was studied with the help of a method in which Prussian Blue is formed and measured colorimetrically (131). TLC (thin-layer chromatography) distinguishes styrenebutadiene random, tapered, diblock, and triblock copolymers (55,88). Gradient elution with CHC13 in CCld gives separation according to styrene content while elution mixtures of polar solvent and nonsolvent give separation according to molecular weight (107). The styrene blocks of styrene-butadiene block copolymers were determined by degradation of the butadiene blocks with tert- butyl-hydroperoxide and osmium tetroxide and recovery of the resulting polystyrene. The microstructure of the butadiene units was determined by infrared (112). BR, polyisoprene, and butadiene-propylene copolymer were degraded by ozonolysis. The products were interpreted in terms of the 1,2 and 1,4 structures in the polymers (76). Examination of the surface of ozonized NR by attenuated total reflectance of infrared radiation revealed the presence of ozonides and carbonyl groups (8). Instead of the usual determination of cross-link density by gravimetric measurement of swelling solvent, the solvent (xylene) was extracted by CHC13 and measured by GC. Results compared well with gravimetric measurements in which benzene was used (144).
DETERMINATION OF POLYMERS IN POLYMER MIXTURES A N D CONSTITUENTS I N COPOLYMERS The amount of polyethylene in peroxide cross-linked blends with BR was determined by metathesis with 2-octene and recovery pf the unreactive polyethylene (86). Bound styrene was determined in SBR by nitration to form p-nitrobenzoic acid with measurement by polarography (178). This is a modification of earlier work which used an ultraviolet absorption measurement (84). DETERMINATION OF RUBBER T G and DTG can be used to determine polymer in carbon filled vulcanizates. Oil and plasticizer are first volatilized under nitrogen followed by polymer a t higher temperatures (25,189).NBR tends to carbonize giving low values but DTG can overcome this error (189). UNSATURATION Efforts were concentrated on polymers such as EPDM and IIR which contain small amounts of unsaturation. The amount of m-chloroperbenzoic acid which reacts with the double bonds was measured by a n iodometric titration (56). Time averaged proton NMR was also used (191). 2,4-Dinitrobenzenesulfenyl chloride was added to double bonds as an ultraviolet-active marker (6). SULFUR A N D SULFIDES Sulfur was determined by LC (liquid chromatography) (180).
Fourier transform infrared (93) and laser Raman (92) spectroscopy were used to study the mechanism of crosslinking in BR. The evidence confirms that the active sulfurating agent is a polysulfide of an accelerator which attacks allylic hydrogens.
A dielectric method was used to analyze polyisoprene for the amount of sulfur outside of network centers. By measuring before and after reaction with triphenyl phosphine to transform disulfides and polysulfides to monosulfides, the number of polysulfide cross-links was determined ( 9 ) . For quality control purposes, sulfur content can be determined by DSC (24).
CURING AGENTS AND AGE RESISTERS Curing agents were differentiated by their reactivity with acids or bases or their solubility in various solvents. The separated materials were then subjected to TLC or GC for identification (116). LC (180)and TLC (152)were used to identify and determine curing agents and age resisters. The amine residues left in vulcanizates by sulfenamides were derivatized and identified by TLC (83). 2-Morpholinodithiobenzothiazole was assayed by reducing with NaBH4 and titrating the resulting 2-mercaptobenzothiazole with AgN03. Application of the method to rubber stocks is being studied (13). The amount of curing agent can be determined for quality control purposes by DSC (24). Tetraethylthiuram disulfide was determined in the presence of PBNA (N-phenyl-2-naphthylamine)and rosin in extracts of CR by making the extract alkaline and measuring its absorption at 259 nm. PBNA was then measured at 312 nm (105).
CARBON BLACK Determination of carbon black by TGA has been the subject of several studies (25,145,189).The sample is first heated in the absence of oxygen to volatilize oil, plasticizer, and polymer. Then oxygen is introduced and the carbon black is burned off. The weight loss in the second step is calculated as carbon black. This works well with hydrocarbon polymers. NBR and CR, however, carbonize during the first step and give high results. DTG can differentiate the original carbon black from the carbon residue left by the polymer and correct for the potential error (145, 189). In addition, the dependence of oxidation rate on particle size can be used to identify the type of carbon black in some cases (145). METALS The residue remaining after burning off carbon black in the process mentioned above is the traditional "ash" (25, 189). The same approach was used to determine fillers in silicone rubber except that the heating- was all done in the absence of oxygen (206). Selenium and tellurium were determined by atomic absorption spectrophotometry (188). LITERATURE CITED (1) Alaki, Y., Yoshimoto, T., Imanari, M., Takeuchi, M., Rubber Chem. Technol., 48, 350 (1973). (2) Ambler, M. R., J. Polym. Sci., Polym. Lett. Ed., 14, 683 (1976). (3) Ambler, M. R., Mate, R. D., Purdon, J. R., Jr., J. Polym. So., Polym. Chem. Ed., 12, 1759 (1974). (4) Ambler, M. R., Mclntyre, D., J. Poiym. Sci., Polym. Lett. Ed., 13, 589 (1975). (5) American Society for Testing Materials, "1976 Annual Book of ASTM Standards, Pt. 37," Philadelphia, Pa., 1976, p 357. (6) Anderson, J. N., J. Appl. Polym. Sci., 18, 2819 (1974). (7) Anderson, J. N., Baczek, S. K., Adams, H. E., Vescelius, L. E., ibid., 19,2255 (1975). (8) Andries, J. B., Ross, D. B., Diem, H. E., Rubber Chem. Technol., 48, 41 (1975). (9) Bakuie, R., Honskus, J., lnt. Polym. Sci. Techno/., 3(1), T86 (1976). (10) Bares, J., Macromolecules, 8,244 (1975). (11) Bargeron, C. E., J. Chem. Phys., 81,2134 ( 1974). (12) Barratt, A. J., Fraser, R. T. M., Healey. M. J., U.S.N.T.I.S., AD/A Rep., 1973, 005173/0 GA;
WATER Five methods for determination of water were compared (12).It was concluded that it is impossible to define water content in absolute terms. The best method was judged to be attainment of constant weight over PzOj but this might take several weeks. When results are needed quickly, an oven-GC method was recommended (58,89). The coefficient of pore formation has been found to be dependent on moisture content (66). The measurements are carried out on an instrument designed to measure the volume expansion of foam rubber mixes (65). ANALYSIS RELATED TO SAFETY AND HEALTH The volatile materials released during cure of rubber stocks were studied by GC/MS (158).Residual MOCA[4,4'-methylenebis(o -chloroaniline)] was determined with sensitivity of 0.03% (15). Sampling in highway tunnels, (149),on a car air intake filter (148),and directly behind a tire (43)reaffirms that tire wear debris is particulate matter too large to be respirable. The debris accounts for less than 4% of the total airborne particulate matter associated with cars and trucks. Residual butadiene, acrylonitrile, and styrene in polymers can be determined to levels of 1ppm or less by GC headspace analysis. Water added to polymer solutions displaces the higher boiling monomers into the headspace, thereby increasing sensitivity (280). Residual diphenylguanidine (101 ) and benzothiazole curing agents (75) were extracted from rubber and separated by TLC. Unreacted hexamethylene diisocyanate and 2,4-toluene diisocyanate were determined in polyurethane prepolymers by direct injection of benzene solutions into a GC (151). Traces of 2-naphthylamine down to 0.3 ppm were determined in PBNA by derivatizing with trifluoroacetic anhydride and measuring by GC (14). OTHER DETERMINATIONS Acetone extraction can be completed in one minute if a high speed disintegration stirrer is used to disperse the sample (82). Chlorine was determined at levels up to 1%by oxygen flask combustion followed by turbidimetric measurement of AgCl (641. Blowing agents such as hydrazides and azides were determined by polarography (159). The COS number of NR latex was determined by passing nitrogen through an acidified sample to sweep the COZ into soda asbestos in a weighing tube (27). Tire, footwear, and eraser residues of interest in forensic investigations can be detected by fluorescence emission spectroscopy. Oils and age resisters are responsible for the fluorescence (118).
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Contribution No. 563 from The Goodyear Tire & Rubber Co., Research Laboratory, Akron, Ohio 44316.
Water Analysis M. J. Fishman" and D. E. Erdmann U.S. Geological Survey, Lake wood, Colo. 80225
This seventeenth review of the literature of analytical chemistry applied to water analysis covers the period from October 1974 through September 1976. The present review follows the plan of the previous reviews, the last of which appeared in Analytical Chemistry for April 1975 (9);however, the editors of Analytical Chemistry requested that the review authors cover their respective fields in a more selective manner and not attempt to provide an all-inclusive bibliography. The material used in preparing this review comes mainly from major analytical journals and United States Government publications. Conference proceedings, obscure foreign journals, and most trade journals are generally excluded. The summary of each article is shorter than in the past and the reader should refer to the publication cited for complete details. A review of the literature on water pollution control, which includes a section on analytical methods and instrumentation, is published annually by the Water Pollution Control Federation. The 1974 reviews by Brezonik ( 4 ) ,Suffet et al. ( l a ) , Minear et al. (12),and Olofsson and Ghosh ( 1 4 ) include 1295 references and cover such topics as major inorganics, trace inorganics, water characteristics, organics, continuous monitoring, automated analysis, and sampling procedures. The 1975 reviews by Brezonik and Carriker ( 3 ) ,Chlan and DeWalle ( 5 ) ,Ghosh and Olofsson ( I O ) , and Shuman and Fogleman (17) include 941 references and cover the same topics. Analytical techniques that have found widest application in the study of inorganic pollutants were compared by Coleman (6) on the basis of sensitivity, accuracy, precision, multielement capability, and range of application. Where possible, he discussed future trends in each technique. The techniques included microscopy, atomic spectroscopy, mass and x-ray spectrometry, neutron activation analysis, and electrochemical methods. Several analytical techniques for measuring and monitoring trace metals were reviewed by Minear (13).His review covered molecular absorption, molecular fluorescence, atomic absorption, and electrochemical techniques.
Phillips and Mack (15) reported on current commercial techniques and techniques being developed for measuring four major categories of water pollutants: metals, nutrients, pesticides, and oxygen demand. They limited their discussion to the most widely used techniques in water-quality monitoring: atomic absorption spectrometry, emission spectrometry, gas chromatography, gas membrane electrodes, and chemical oxidizers. Both manual and automated instruments for laboratory and field use are discussed. Birks and Gilfrich (2) in a general review of x-ray spectrometry devoted a section to its application to the field of water pollution. Elder, Perry, and Brady (8) reported that energy-dispersive x-ray fluorescence is a relatively recent development in the field of x-ray spectrometry that improves capability for rapid multielement analysis. Application of the technique to determine dissolved trace metals in water requires transfer of the dissolved elements to a uniform target suitable for analysis. This is accomplished by precipitating the elements with the nonspecific chelating agent, ammonium-1-pyrrolidine dithiocarbamate, and filtering through a membrane filter. DuCros and Salpeter (7) discussed automated methods for assessing water quality. Greater concern for water quality has caused significant increases in the analytical workloads of laboratories. The availability of automated wet-chemistry instrumentation and methodologies has provided these laboratories with the capability to analyze larger number of samples for more parameters more economically and more accurately than the use of manual methods permits. A review on the application of ion-selective electrodes in water analysis is given by Pungor and Toth (16).The types of electrodes and the theory of membrane electrodes are discussed, and determinations of various anions and cations are described. A spark source mass spectrometer that uses electronic detection and a dedicated data analysis system was applied by Taylor and Taylor (19) to multielement analysis of environANALYTICAL CHEMISTRY, VOL. 49, NO. 5, APRIL 1977
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