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Three methods of predicting dynamic viscosity of branched polyethylenes from size exclusion chromatography (SEC), refractive index/light-scattering detection data were examined: relating parameters in the Cross viscosity equation to molecular weight averages, use of a mixing rule, and a method based on the similarity of the cumulative molecular property distributions to a dimensionless viscosity versus frequency plot. The use of accurate SEC data was emphasized. The third “curve similarity” method provided the most promising results. The use of cumulative g′ (the molecular contraction factor based on intrinsic viscosity) distributions, in addition to cumulative molecular weight distributions, enable very useful sample comparisons.

Equations are presented for calculating molar mass averages and molar mass distributions from matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) data and from size exclusion chromatography (SEC) data. The utility of polydispersity is examined as an indicator of the expectation of MALDI-TOF MS mass discrimination effects. Cumulative distributions are found to be rich in information for comparing the two techniques and are easily obtained from both SEC and MALDI-TOF MS data. Analyses of a series of narrow molar mass distribution poly(methyl methacrylate) (PMMA) standards and one polydisperse sample have been performed with both methods. MALDI-TOF MS did not detect dimer and trimer in the PMMA samples, and it often indicated lower amounts of high-molar-mass polymers than did SEC. The results showed that the distribution breadth, as evidenced by the standard deviation of the distribution (calculated from the polydispersity and number-average molar mass), correlated well with the molar mass range observed in the MALDI-TOF MS spectra, whereas the polydispersity alone did not. Ratioing the extremes in the molar mass concentrations measured with the SEC differential refractometer, which were necessary to adequately define molar mass distributions, showed that detector dynamic range values as high as approximately 370,000 were required for the polydisperse samples. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 627–639, 2005

A fiber-optic-assisted, charge-coupled device spectrometer was used to monitor the color of molten polymer concentrates during extrusion. Color coordinates L*, a* and b* were calculated from each of the reflectance spectra as polyethylene color concentrate was replaced by a purge material and as the purge material was replaced by another color concentrate. A method of calculating replacing component residence time distributions and component washout residence time distributions from the spectra was developed and applied. Results with a red and a blue concentrate showed that dimensionless time (time/average residence time) superimposed both residence time distributions and color coordinate variations during changeover from two different extruder screw speeds.

The objective of this work was to examine the application of various multivariate methods to determine the composition of a flowing, molten, immiscible, polyethylene–polypropylene blend from near-infrared spectra. These spectra were acquired during processing by monitoring the melt with a fiber-optic-assisted in-line spectrometer. Undesired differences in spectra obtained from identical compositions were attributed to additive and multiplicative light scattering effects. Duplicate blend composition data were obtained over a range of 0 to 100% polyethylene. On the basis of previously published approaches, three data preprocessing methods were investigated: second derivative of absorbance with respect to wavelength (d2), multiplicative scatter correction (MSC), and a combination consisting of MSC followed by d2. The latter method was shown to substantially improve superposition of spectra and principal component analysis (PCA) scores. Also, fewer latent variables were required. The continuum regression (CR) approach, a method that encompasses ordinary least squares (OLS), partial least squares (PLS), and principle component regression (PCR) models, was then implemented and provided the best prediction model as one based on characteristics between those of PLS and OLS models.

The object of this study is to develop multidetector size-exclusion chromatography (SEC) methods to determine the number of arms per molecule across the molecular size distribution of star-branched polymers. An empirical fit between the intrinsic viscosity molecular contraction factor g‘ and the number of arms f is used as an alternative to converting g‘ values to root mean square radii ratios used by random walk models. The quantitative analysis of star polymer distributions by SEC is then reduced to understanding factors unique to the accurate measurement of g‘ across the molecular size distribution. Two methods of analyzing SEC data are then tested: (1) the “conventional method” utilizing values of weight-average molecular weight and intrinsic viscosity at each retention volume and (2) the method of component chromatograms. The latter is a new method useful when only a few different types of branching are present. It depends on fitting each detector's chromatograms as the sum of component chromatograms. Plotting the intrinsic viscosity of the branched polymer versus that of the linear polymer at the same molecular weight was useful for diagnosing problems. The conventional method was defeated by axial dispersion in the narrow chromatograms and the homogeneity of branching in the samples. The component chromatogram method avoids the axial dispersion problem but its value depends on how accurately the component peaks reflected the true situation. In this study, the method provided the most reasonable values when component peaks were grouped together. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 552–570, 2002

With the increasing popularity of evaporative interfaces, detection using Fourier Transform Infrared (FTIR) spectrometry in the mid-infrared region is becoming more important in size-exclusion chromatography (SEC). FTIR spectrometry is a powerful, and potentially very widely applicable, method for obtaining chemical functional group information for each molecular size fraction. Quantitative evaluation of polymer composition across the SEC chromatogram can provide more accurate characterization of heterogeneous polymer samples for problem solving and for material specification. The evaporative interface removes the SEC mobile phase at the exit of the column and deposits the eluting polymer as a continuous film stripe or as a series of discrete films on infrared transparent substrates. Initially this detection approach was used only for qualitative analysis. More recently, it is being used quantitatively. Previously we demonstrated that the quality of the film generated by the evaporative interface was critical to determining the suitability of the resulting FTIR spectra for quantitative analysis. In a continuation of this work, the objective of this paper is to develop a procedure for obtaining valid quantitative results for polymer blends with the interface. Experimental topics include improving the quality of polymer films by post-SEC treatments, off-line FTIR calibrating using other means to obtain high quality polymer films, and utilizing in-line SEC detectors in calibration. Interpretation aspects focus upon peak fitting of FTIR spectra, linear regression, partial least squares, and data pre-processing. PLS prediction with internal calibration using the second derivative of solvent-annealed film spectra was found to provide the best compromise between processing time, accuracy and precision.

Local polydispersity is the term describing the variety of molecules present at the same retention volume in size exclusion chromatography (SEC) analysis. In the analysis of a linear homopolymer, local polydispersity is generally attributed to the effect of axial dispersion: it can cause molecular size variety (i.e., imperfect resolution) at each retention volume and thus local polydispersity in the molecular weight. In the analysis of polymer blends (copolymers and branched polymers), it is possible to have local polydispersity, even when the resolution is perfect, because molecules of different compositions (or degrees of branching) can have the same molecular size in solution. Conventional SEC interpretation assumes no local polydispersity if the axial dispersion effects are negligible. Three methods are currently available for detecting local polydispersity by using a combination of differential refractive index, light scattering, and viscometer detectors: the chromatogram comparison method, the conventional calibration curve comparison method, and the universal calibration comparison method. Here we experimentally assess these three methods using polymer blends and emphasize the chromatogram comparison method. All three are shown to be useful for assessing triple detector systems, but they are capable of detecting local polydispersity due to molecular heterogeneity only for very large differences in specific refractive index increments in the blend components. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 370–383, 2001

Traditional methods of evaluating fractionation in size exclusion chromatography (SEC) include number of theoretical plates, resolution indices and calculation of molecular weight averages. Most recently, fractionation evaluation has become evaluation of local polydispersity where “local polydispersity” is molecular variety at a particular retention volume. The three published methods for determining local polydispersity using triple-detector SEC are examined. All have two major uncertainties: the degree to which the observed local polydispersity affect the whole polymer molecular weight averages and the origin of the local polydispersity. New methods of answering these questions are examined using the SEC analysis of polymer blends. One method utilizes a plot where the area under the curve is the total number of moles of polymer. Calculation of this curve with equations containing different assumptions provides the needed significance test over the range where all three detectors have sufficient...

This work is an investigation of morphology and de-mixing of polymer blends during melt flow through a tube. Morphology is the relative size, shape and location of each distinguishable phase present in a polymer blend. De-mixing is the shear-induced migration of different types of polymers away from each other during the flow. The ability to tailor de-mixing during extrusion can potentially result in a new family of plastics waste recycling processes with mixed waste entering an extruder and separate streams of different polymer types leaving it. Also, control of morphology development can lead to the formation of layered structures without the need for two or more extruders and co-extrusion. This work is directed at elucidating morphology development and de-mixing of polymer blends in the most simple process design: melt flow through a tube. Shear-induced migration was quantitatively shown in various polyethylene-polypropylene, polypropylene-nylon 6 and polyethylene-nylon 6 blends. The migration observed was in accord with the hypothesis that the system tends to minimize its rate of energy dissipation for a fixed flow rate. The ratio of the viscosity of the dispersed phased to that of the continuous phase greatly influenced the morphology of polypropylene-nylon 6 and polyethylene-nylon 6 blends: a droplet-dispersed phase structure occurred at a high viscosity ratio, whereas a multi-layer structure resulted at viscosity ratios near unity. Shear-induced deformation and coalescence contributed to formation of the multi-layer structure.

Near-infrared in-line monitoring of polymer processing means using a fiber-optic-assisted spectrometer to obtain spectra of the polymer melt flowing through commonly used processing equipment (an extruder). Conditions in the extruder are typically 200 °C and 20 MPa. This paper shows the design of interfaces between the spectrometer and the molten polymer. Three designs are shown, each permitting monitoring at a different location in the process: a melt-at-die interface, a melt-in-barrel interface, and a strand interface. These designs are for monitoring just before the extruder exit, in the main barrel of the extruder, and after the product exits from the extruder as a strand, respectively. All these interfaces protect the inserted fiber-optic probe from the harsh environment within the extruder while permitting easy replacement of a probe without interrupting the process. This latter characteristic is very important because it permits easy probe repair as well as the use of other types of probes (for monitoring color or particles, for example) to be used during a run. Examples of near-infrared spectra obtained with each of the interfaces used with an immiscible blend of polyethylene and polypropylene are shown. Large differences in the spectra demonstrate that the design of the interface will affect multivariate analysis directed at composition prediction. Subsequent papers are directed at using the melt-at-die interface for composition prediction and accounting for nonlinear relationships between absorbance and concentration.

Size exclusion chromatography (SEC) is now a common polymer analysis method employed in polymer reaction engineering studies. However, this once simple technique is no longer very simple. In this overview we selectively review the literature relevant to the practical use of SEC to obtain quantitative results. Fractionation, detection, calibration, resolution correction and system development are examined in turn. It becomes evident that, at this stage in SEC development, each of these areas is advancing very rapidly. This means that valuable additional quantitative information on polymer molecular properties is now obtainable.However, this additional information is accompanied by significant additional sources of error and uncertainty. The original SEC with only a differential refractive index detector is currently the most reliable and precise system, as well as being the most limited in what information it provides. New methods of linking results from such simple systems with multi-detector “res...

Local polydispersity refers to variety in the types of molecules present at the same retention volume in an analysis by size exclusion chromatography (SEC). Such variety is undesired because it can be a major source of inaccuracy in SEC interpretation. A rapid, practical, method for detecting the presence of local polydispersity is presented. In this method, data from a differential viscometer (DV) and light scattering (LS) detector are used together with a universal calibration curve to generate a differential refractive index (DRI) chromatogram for the sample, while assuming that it does not exhibit local polydispersity. This reconstructed DRI chromatogram is compared to the actual DRI chromatogram. It is shown that any significant difference between the two indicates the presence of local polydispersity. Plots of residuals (the difference between the heights of the two DRI chromatograms vs. retention volume) allow the significance of the local polydispersity to be assessed and the retention volume range encompassing the local polydispersity to be defined.

The objective of this work is to obtain a simple method for detecting local polydispersity. Local polydispersity is the presence of a variety of different types of molecules at the same retention volume in SEC. One source of local polydispersity is axial dispersion. However, the topic of this paper is the detection of local polydispersity which is independent of axial dispersion effects This “perfect resolution” local polydispersity can occur because SEC separates on the basis of molecular size in solution and thus for complex polymer molecules, such as copolymers or branched polymers, a variety of combinations of molecular weight and composition can produce the same molecular size. In conventional SEC interpretation, it is assumed that with high resolution columns local polydispersity is absent. Highly misleading analyses can result if this assumption is invalid. Two very simple methods were developed in this work. The first method enabled polystyrene-poly(dimethyl siloxane) blends to be examine...

Size-exclusion chromatography using halogenated aromatic solvents such as trichlorobenzene at 145°C is widely used for industrial polyolefins. Such high temperature operation requires special instrument design and causes many operational problems. In this work, a new eluting solvent, methyl cyclohexane, has been successfully used at 90°C for the size-exclusion chromatography of industrial (high-molecular-mass) grades of polypropylene and polyethylene. Sample preparation involves dissolution in decalin at temperatures as high as 140°C, followed by dilution in methyl cyclohexane at 90°C previous to injection into the SEC column running with methyl cyclohexane as the mobile phase. In addition to permitting operation at 90°C, methyl cyclohexane is less toxic than the usual solvents and has a differential refractive index sensitivity advantage as well. It also provides new opportunities for ultraviolet, fluorescence, and infrared detection for functionalized polyolefins. However, one disadvantage is that polystyrene adsorbs from this solvent on styrene-based packings. Thus, narrow fractions of polyisobutylene (PIB) were used in place of polystyrene for universal calibration. Another disadvantage is that methyl cyclohexane is more flammable than halogenated aromatic solvents. A quantitative assessment of the new solvent system is in progress. Initial results are promising and are presented in this paper.

The peak shape changes in differential viscometer (DV) chromatograms, shown in Part I of this series, were investigated. Chromatograms were obtained with narrow-molecular-weight distribution standards of increasing molecular weight. Peak shape changes were not observed when the DV detector was operated in series with the differential refractive index (DRI) detector rather than in parallel. Flowrate variations during elution of each sample in the parallel detector configuration appear to be the reason for the changes. At high molecular weights (≥460,000), polydispersity of the standards also contributed. Molecular weight averages of broad-molecular-weight distribution polymers were not affected by the detector configuration used. With a series configuration, a new method of determining interdetector volume and interpreting narrow-molecular-weight distribution polymers is presented.

Interdetector volume accounts for the time delay between detectors when more than one detector is used in size exclusion chromatography (SEC). In this work, interdetector volumes are determined from chromatograms for concentration detectors in series and in parallel, as well as for a parallel differential viscometer (DV)—differential refractometer (DRI) combination. The three methods examined for accomplishing this determination (peak apex, multipoint, and centroid methods) all provided equivalent results for truly monodisperse, low-molecular-weight compounds in all cases. For the DV-DRI combination, the interdetector volume obtained for the latter two methods increased with increasing molecular weight. This result was attributed to increasing peak skewness observed for DV chromatograms of narrow-molecular-weight standards as molecular weight increased. This occurred despite the fact that their normalized DRI chromatograms were all superimposable. In addition to helping to explain current widespr...

A blend of 10 vol % poly(methyl methacrylate) (PMMA) in a polystyrene (PS) matrix was prepared by mixing the polymers in the form of 1.0 μm diameter latex particles, followed by melt pressing the powder at 110 °C into void-free films. These were annealed for various periods of time at 180 °C, and the aggregation and coalescence of the PMMA microspheres were followed by laser confocal fluorescence microscopy. Contrast was provided by a fluorescent dye attached to the PMMA polymer. Brownian motion as a contributor to aggregation could be ruled out. The major factor leading to particle aggregation was identified as flow within the sample, likely due to inhomogeneities on heating, leading to convective fluxes in the sample. At early stages of annealing, Ostwald ripening contributed to the coarsening process.

A stepwise peroxide initiated degradation of a PRO-FAX reactor grade polypropylene by reactive extrusion was compared with a single step degradation process. Measured properties of the polypropylene and the degraded products included shear and intrinsic viscosity, melt flow index, melting and crystallization temperatures, flexural modulus, tensile modulus and yield stress. It was found that there is a trend to achieve higher MFI values if a stepwise degradation is carried out. It was also verified that a stepwise process results in a stronger reduction in the overall viscosity of the polypropylene and in the slope of the viscosity curves. The change in the slope of the viscosity-shear rate relationship is especially evident at lower shear rates. This effect appears to be more pronounced as the peroxide concentration increases.

A simple method is proposed for using a size-exclusion chromatograph equipped with both concentration and light-scattering detectors to calibrate other chromatographs having only concentration detectors. The method is developed and demonstrated for poly(ethylene terephthalate) in methylene chloride/dichloroacetic acid. It is shown that, in addition to circumventing the need for a light-scattering instrument on other chromatographs to be used for the analysis of PET, precision and accuracy of results are improved over those obtainable with light-scattering detection. The method uses averaging of the light-scattering detector data to establish a correlation between the molecular weight of the polymer of interest and the molecular weight of polystyrene at each retention volume. This correlation can then be used for other instruments employing the same mobile phase and only a concentration detector. Although the method assumes the validity of the universal calibration curve, the actual curve is not required, nor are Mark–Houwink constants or intrinsic viscosities. © 1994 John Wiley & Sons, Inc.

Blends of linear low density polyethylene (LLDPE) and polypropylene (PP) show diverse mechanical property behavior in the published literature. The main objectives of this work were: to investigate the effect of viscosity of the component phases on the mechanical properties of such blends and to use the results to obtain a method for compatibilizing diaper manufacturing waste. The significant result of the study was that although LLDPE/PP blends are often termed “incompatible,” when viscosity of the components was more closely matched to each other, increases of as much as 50% in tensile strength and modulus were observed over the “rule of mixtures” line. Also, scanning electron microscopy then showed a more diffuse interface between the component phases. Three dimensional views of plots of viscosity ratio of the blend components as a function of temperature and shear rate were used to demonstrate the closer matching of viscosities for the blend components of the higher performing blends. In processing diaper manufacturing waste, addition of a high molecular weight PP in a manufacturing scale single screw extruder, to provide a closer match of viscosities of the blend components, significantly improved mechanical properties.

This paper presents the development of a model for free radical initiated polypropylene degradation during reactive extrusion that combines a kinetic model of the polypropylene degradation reaction with a simplified model of the melting mechanism in the extruder. The free radical initiated degradation of polypropylene is characterized by a narrowing of the molecular weight distribution (MWD) and a decrease in the molecular weight averages. A high temperature SEC is used to determine MWD's for three different commercially available polypropylenes degraded at various initiator concentrations in a 1.5 inch single screw extruder (L/D = 24:1). The predictions of the kinetic model alone and the combined kinetic-melting model are compared with the experimentally determined MWD's and molecular weight averages for the degraded polypropylenes. The predictions of a modified kinetic model that includes the possibility of termination by combination are also examined. The kinetic-melting model is found to provide significantly improved predictions of the experimentally determined MWD's and molecular weight averages in comparison to the original kinetic model. A viscosity-molecular weight relationship is also developed, which is then used to determine the gain of the degradation process as a function of the initiator concentration from the molecular weight averages predicted by the kinetic-melting model. Earlier work has shown such prior knowledge of the process gain can be used to significantly improve the performance of process control schemes for the degradation process.

It is now theoretically possible to obtain absolute accurate values of number-average molecular weight of complex polymers (e.g., branched polymers or copolymers) using size exclusion chromatography (SEC) with only a detector that measures the difference between the eluting polymer solution viscosity and the viscosity of the pure mobile phase (a differential viscometer [DV] detector). However, both precision and accuracy of these “DV Mn” values are of concern. In this work, the precision of NBS 706 polystyrene was found to be two to three times worse for the DV Mn than for the conventionally calculated Mn. Also, regarding accuracy, the DV Mn values were affected by the location of the universal calibration curve along the retention volume axis (a problem intimately associated with the problem of specifying the correct interdetector volume), the sensitivity of the DV detector to low molecular weights present in the sample, and axial dispersion. Each of these sources of error are examined in turn and two methods of calculating Mn values are proposed. © 1994 John Wiley & Sons, Inc.

Factors that are important to the quantitative analysis of polymer composition distribution by high-performance liquid chromatography (HPLC)-Fourier transform infrared (FT-IR) using a solvent-evaporation interface are investigated. These factors include the effects of the location and distribution of the deposited polymer films, as well as the morphology of the deposit. Consideration is given to the influence of these factors on the chromatographic resolution and FT-IR spectral quality. Size-exclusion separations of polystyrene and poly(methyl methacrylate) in tetrahydrofuran are used to demonstrate the impact of these effects on the quantitative use of the resulting FT-IR spectra. Results indicate that all absorbance bands are not uniformly affected by spectral distortions, but that compositional information can be obtained on simple blends. The effectiveness of a post-sample-collection solvent-annealing procedure is also considered.

In Part I of this work, experimental data showed that the effect of low concentrations of free radical initiator injected into polyethylene during extrusion depended upon the degree of unsaturation and branching in the feed as well as the molecular weight. This paper shows attempts to quantitatively explain these reactive extrusion results through development of two kinetic models based upon the rate equations for reactions considered dominant. The first model developed incorporated unsaturation via consideration of simultaneous crosslinking-endlinking reactions. It contains two variable parameters: the overall initiator efficiency and a ratio of two rate constants reflecting the reactivity of the unsaturated bonds. The model was able to fit the changes in molecular weight distribution of both the low density and linear low density polyethylene but not the high density polyethylene samples. In addition to fitting the molecular weight distribution, this model also provided reasonable values of initiator efficiencies for crosslinking, endlinking, and chain extension reactions, as well as the number of terminal vinyls of the products. The second model is a special case of the first: it neglects the presence of unsaturation in the feed. This second model is actually the usual “crosslinking” model widely known from a derivation based upon statistical arguments. It was not able to fit most molecular weight distributions obtained. However, the model was shown to be useful for accounting for observed molecular weight distribution for a high density polyethylene sample of low initial unsaturation. Also, it was able to explain the amount of gel formed as a function of initiator concentration.

In this novel application of a multivariate method, partial least-squares (PLS) was used to generate mid-infrared (MIR) spectra (rather than selected concentrations) from near-infrared (NIR) spectra. The NIR spectra were obtained by in-line monitoring of a molten polymer blend of polyethylene with polypropylene during extrusion. Off-line MIR spectra of blends were used to calibrate the PLS method. Then PLS was used to generate the MIR absorbance spectrum of a 50:50-by-weight blend not included in the calibration set from its NIR spectrum. The synthesized MIR spectrum agreed very well with a directly measured one. The exception was absorbance peaks which were so strong that they apparently represented responses that were nonlinear with respect to concentration. Although more evaluation work has yet to be done, these results are encouraging, and they indicate that NIR interpretation may readily borrow the strengths of MIR interpretation both qualitatively and quantitatively.

A new multiangle laser light-scattering (MALLS) detector for size exclusion chromatography promises simultaneous measurement of both weight-average molecular weight (Mw) and radius of gyration (rg) at each retention volume across the chromatogram. However, there are a variety of ways of interpreting the raw data to provide these results. This study examines variations of three different rearrangements of the basic light-scattering equation. Data from a room temperature analysis of polystyrene and a high-temperature analysis of polyethylene were used. The degree of fit of each equation to the data and the precision of the Mw and rg values are evaluated. To define precision, joint confidence regions (JCRs) were calculated and compared to simple confidence intervals based upon standard deviations in order to see the effect of interdependence of Mw and rg. Results showed that the Debye equation was superior to the inverse Debye equation (similar to the Zimm plot) for the interpretation of MALLS data. The effect of the quantity of data included in the regression model was also assessed. Use of only the most precise four detector angles was compared to use of a full set of 15 angles. Precision of weight-average molecular weight values was found to be improved as the detector angle decreased because of the shortened extrapolation to zero angle. Precision at room temperature was much superior to that at high temperature. Use of simple confidence intervals was shown to provide only a fair approximation to the more accurate JCR. The “natural scatter” of data shown by the JCR generally shows the same trend as do plots in the literature of Mw vs. rg. Thus, it is concluded that JCRs should be more often calculated in light-scattering studies in order to distinguish random scatter from meaningful correlations of these values. © 1993 John Wiley & Sons, Inc.

A systematic evaluation of two types of light-scattering detectors for size exclusion chromatography (SEC) was completed. The two detectors were the low-angle laser light scattering photometer (LALLS) and the multiangle laser light-scattering photometer (MALLS). Instrument evaluations were performed at both room (30–40°C) and high (135–145°C) temperatures using the polystyrene standard, NBS 706, at room temperature and the polyethylene standard, SRM 1476, at high temperature. Results of the evaluation showed that when experimental uncertainties were taken into account LALLS and MALLS demonstrated equivalent precision and accuracy for molecular weight determination. The main source of inaccuracy found (particularly for SRM 1476) was the sensitivity difference between the light-scattering and the concentration (DRI) detectors; i.e., the DRI detector was unable to measure very low concentrations of very high molecular weight material present in SRM 1476, whereas the light-scattering detectors respond strongly. It was shown that for LALLS the overall weight-average molecular weight (Mw) for the whole polymer calculated using an equation that did not require the DRI detector output circumvented this sensitivity problem while assuming that the low angle used was sufficiently close to zero. Use of this equation for MALLS is possible by extrapolating data from all angles used to obtain a light-scattering chromatogram at zero angle. However, this possibility was not examined here. A particular advantage of MALLS over LALLS is that MALLS can provide the z-average root mean square radius (commonly referred to here and in other light-scattering literature as the “radius of gyration”) values from the same data as those used to obtain molecular weight values. Although the radius of gyration values at each retention volume were not as precise as the corresponding weight-average molecular weights, at room temperature, precision was better than 2% for a significant portion of the chromatogram. © 1993 John Wiley & Sons, Inc.

The objective of this work is to combine reaction, extrusion, and orientation together in a process so as to provide product in a form which is not limited to fiber or film. Three coupled problems form the focus of the work: (i) devising a practical, continuous extrusion-orientation method; (ii) generating low concentrations of free radicals in the polymer to tailor molecular weight distribution before orientation; (iii) generating high concentrations of free radicals in the polymer to form a network in the oriented polymer without destroying its superior properties after orientation. A continuous extrusion method for orienting polymer in forms other than fibers and films was devised based upon two melt pullers. Operation of a prototype of the equipment showed it capable of providing draw ratios of greater than ten. Injection of low initiator concentrations during extrusion (i.e., before orientation) directed at solving the second problem had an effect which depended upon the degree of branching, the molecular weight, and the degree of unsaturation of the polyethylene. Large increases in molecular weight could be obtained. However, in agreement with previous work, formation of branched molecules drastically limited draw ratios attainable by the extrusion-orientation process. To obtain high concentrations of free radicals, bench scale experiments demonstrated that a recently published method involving the use of a UV sensitizer and crosslinker followed by irradiation was directly adaptable to this process (with the irradiation applied after orientation) and provided significant improvements in creep resistance. Various attempts involving die design to obtain orientation and high initiator concentrations as well as gamma radiation to induce crosslinking after orientation were attempted and appear far less promising than the above methods.

The closely related topics of resolution correction and the determination of interdetector volume were examined. In determining the interdetector volume (δ) by searching to superimpose two types of intrinsic viscosity calibration curve (one from narrow standards and one from a broad standard), the underlying equation based upon symmetrical axial dispersion theory was derived. This equation combined with experimental results showed that the local intrinsic viscosity value is very similarly affected by interdetector volume and by band spreading. The result supported the idea of using an effective δ to effect an axial dispersion correction to local intrinsic viscosity data. However, it also increased the difficulty of finding both δ and standard deviation (δ) simultaneously by numerical search. Furthermore, attempts to apply the method to the chromatograms of narrow standards showed inadequate superposition. Following calculation of skewing factors, the superposition problems were attributed to skewing of the chromatograms of the monodisperse polymer standards used. © 1993 John Wiley & Sons, Inc.

Five different types of calibration curve currently used in size exclusion chromatography-differential viscometer (SEC–DV) systems were identified and their use summarized. A simple method of deriving weighting factors for fitting local intrinsic viscosity calibration curves was shown to greatly improve the precision of calculated molecular weight distributions. The problem of reliably extrapolating the fitted curves to allow for differences in sensitivity among detectors has yet to be examined. With regard to Mark—Houwink constants, a method of fitting data from the SEC–DV system to obtain more statistically sound values was derived. For the data used here, the new method involves fitting a plot of logarithm of the local intrinsic viscosity of the sample vs. logarithm of the universal calibration curve parameter, Ji. Results for the data obtained appeared only slightly more precise than those for the traditional method. However, the new method promises improved reliability. © 1993 John Wiley & Sons, Inc.

Ortho-chlorophenol (OCP) has previously been reported as one component in mixed solvent systems for the size exclusion chromatography of poly (ethyiene terephthalate) (PET)1,2, In order to avoid the problems involved in maintaining mixed solvents, a technique has been developed to analyze PET in OCP alone. The system has been calibrated using narrow polystyrene and broad PET standards. Problems addressed include the high viscosity and high refractive index of OCP, solvent purity, sample preparation, and sample degradation. The system has been used to investigate the hydrolysis and degradation of PET during extrusion processes.

The time required for polymer molecules to pass from one detector to another is a critical parameter for interpretation of multidetector size exclusion chromatography data. A method of utilizing numerical optimization to determine this quantity is presented. The chromatography system included a differential refractive index detector (DRI) in combination with a low-angle laser light scattering photometer (LALLS) and a differential viscometer (DV). The optimization method requires a conventional calibration curve (in terms of intrinsic viscosity rather than molecular weight if the DV detector is used) and the raw data from analysis of a broad molecular weight distribution linear homopolymer standard. A cubic polynomial and a least square cubic spline were used to fit the conventional calibration curve. In interpretation of the DV data, it was necessary to use a least square cubic spline to fit the conventional calibration curve. Results obtained are “effective” in that they intrinsically provide ag...

This paper presents the development of a novel in-line extrusion rheometer based on the flow of polymer through a wedge (vertically tapered slit). This rheometer is suitable for measuring changes in rheological properties on-line during reactive extrusion, because it can be used to estimate the viscosity for a range of shear rates without the need to change the polymer flow rate (i.e., extruder throughput). Equations have been developed to estimate the parameters of the power-law equation, used to describe the viscosity-shear rate relationship, from measurements of pressure drops along the wedge. An experimental in-line wedge rheometer has been built and used to measure the viscosity for a series of polypropylenes prepared via reactive extrusion. Viscosity measurements from the experimental in-line wedge rheometer are compared with measurements from a capillary rheometer. Good agreement is found between the capillary and wedge rheometer measurements.

The objective of this work was to investigate the compatibilization of a blend of linear low density polyethylene with polypropylene by Injection of a free radical initiator during extrusion. The reactive extrusion process utilized a single screw extruder equipped with two static mixers. The initiator was injected into the extruder feedport and temperature programming used to cause most reaction to occur within the static mixers. Although elongation at yield was increased by 37 percent, impact strength and yield strength decreased by 17 and 54 percent, respectively. Scanning electron microscopy showed that the maximum size of the dispersed phase decreased from a maximum size of four microns to less than two microns upon addition of initiator. Size exclusion chromatography (SEC), temperature rising elution chromatography (TREF), and differential scanning calorimetry showed that the polypropylene in the blend was degrading while the polyethylene was increasing in molecular size. The combination of SEC and TREF was particularly useful in elucidating this result. No copolymer was discerned by any of the methods used.

Methods of assessing new technology are achieving increased importance because rapid technological changes cause obsolescence of evaluations before they are completed. Users now must often evaluate the specific version of the new technology that they receive. Four major areas are used here to provide examples of assessment methods: high resolution columns, coupled concentration-molecular weight-differential viscometer detectors, flow rate monitoring using a thermal pulse flowmeter and determination of Mark-Houwink constants from polydisperse standards. Specific methods of assessment examined centre about error analysis and sensitivity analysis. Several of the methods use the conventional calibration curve. The idea of correction priority (i.e. thoroughly examining the most fundamental significant corrections first) is emphasized.

Nanogels are highly branched, swellable polymer structures with average diameters between 1 and 100nm. Size-exclusion chromatography (SEC) fractionates materials in this size range, and it is commonly used to measure nanogel molar mass distributions. For many nanogel applications, it may be more important to calculate the particle size distribution from the SEC data than it is to calculate the molar mass distribution. Other useful nanogel property distributions include particle shape, area, and volume, as well as polymer volume fraction per particle. All can be obtained from multi-detector SEC data with proper calibration and data analysis methods. This work develops the basic equations for calculating several of these differential and cumulative property distributions and applies them to SEC data from the analysis of polymeric nanogels. The methods are analogous to those used to calculate the more familiar SEC molar mass distributions. Calibration methods and characteristics of the distributions are discussed, and the effects of detector noise and mismatched concentration and molar mass sensitive detector signals are examined.

Quantitative evaluation of polymer composition across the SEC chromatogram can provide more accurate characterization of heterogeneous polymer samples for problem solving and for material specification. To this end Fourier-transform infrared spectroscopy (FTIR) with solvent–evaporation interfaces has become a very powerful detector for size-exclusion chromatography (SEC). The solvent–evaporation interface removes the mobile phase at the exit of the chromatograph and deposits the separated molecular sizes as polymer films on infrared transparent substrates. Quantitative interpretation of the FTIR spectra obtained from these films has recently been found to be best accomplished by using partial least squares. In this paper, polystyrene and poly(methylmethacrylate), alone, as blends, and a copolymer were analyzed in a SEC equipped with an evaporative interface. Molecular weight effects, wavelength selection, the effect of averaging spectra on results, and selection of the best data preprocessing method were investigated. General methods of evaluating these variables were developed to arrive at conditions for this particular “model” situation in order to provide a basis for the analysis of more complex polymers.

The color of pigmented polyolefin melts was measured in-line during processing by using a fiber optic equipped visible-near-infrared spectrophotometer. Pigment loadings varied from 3.6 to 56 wt.% with some formulations containing up to 33.1 wt% calcium carbonate filler. Results showed that within specification color could be distinguished from off specification color. Also, pigment degradation and temperature tolerance could be assessed. Predicting needed off-line measured color from these in-line results will be the subject of Part II of this series.