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A detector system for GPC has been built consisting of a pressure cell and capillary viscometer, a constant flow rate pumping system, a concentration detector, and a computer interfacing system. This detector system provides two chromatograms; pressure drop (ΔP) vs retention volume and concentration (C) vs retention volume. Since at constant flow rate ΔP is proportional to the effluent viscosity η, the intrinsic viscosity of any effluent fraction can be computed from the equation, where subscripts 1 and 0 refer to the solution and solvent, respectively. The precision and accuracy of the above technique were evaluated using well characterized broad and narrow molecular weight distribution polymers. Both the precision and accuracy were found to be comparable to light scattering and other classical molecular weight measurement techniques. In its present form, the molecular weight detector system was found to be very sensitive to polymers with very high molecular weights, as expected, and also useful for molecular weights less than 50,000.

A semiquantitative bubble formation mechanism is presented for the baking of polymer films, utilizing poly(methyl methacrylate) (PMMA)-ethyl acetate (EA) solutions as the model system. It is shown that bubble growth phenomena can he accounted for in terms of the competition between vapor pressure buildup and the rate of vapor dissolution. According to the proposed mechanism, the local pressure buildup of solvent in the polymer film is controlled by the solvent partial pressure above a solution having a planar interface at the corresponding temperature and solvent concentration. This pressure can he estimated by Raoult's law. The vapor dissolution rate, on the other hand, is dominated by the liquid-phase diffusion of the solvent. A method of obtaining the diffusion coefficient as a function of temperature and solvent concentration from isothermal thermogravimetric analysis (TGA) is also given.

Poly (vinyl acetate), PVAC, synthesized by bulk polymerization over a range of initiator concentrations ([AIBN] = 10−5 to 4 × 10−3 g-mole/1), temperatures (50°C, 60°C, 70°C, and 80°C) and conversion levels (3 to > 90%) were characterized using low angle laser light scattering (LALLS) photometry to measure Mw of the whole polymers. A number of these samples were characterized using GPC with a differential refractive index (DRI) and LALLS detector to measure the molecular weight distribution (weight fraction versus Mw). Mw for PVAC samples synthesized at suitably low initiator levels at various conversions were found to agree with classical light scattering measurements after Graessley. An electronic device and a technique which optimizes the sensitivity and the signal-to-noise ratio of the LALLS photometer throughout the molecular weight distribution (MWD) of the GPC chromatogram were devised. These considerably simplify the operation of the LALLS for both offline and online operation with GPC. Mo...

A critical angle illumination microscopy technique was used to study the in situ dissolution dynamics of polystyrene, poly (α-methylstyrene) and the two tactic forms of poly (methyl methacrylate), (PMMA), in several solvents. The dissolution characteristics; of polymers were found to be greatly influenced by several factors: type of polymer, processing condition of the sample, type of solvent, and tacticity, Polystyrene was found to exhibit extensive swelling in several solvents while atactic PMMA exhibited extensive cracking on dissolution. Isotactic PMMA, which has a glass temperature of about 70°C lower than the atactic PMMA, showed swelling behavior similar to atactic polystyrene, while the α-methylstyrene showed the cracking phenomena exhibited by atactic PMMA.

An automated gel permeation chromatograph-low-angle laser light-scattering system capable of measuring the molecular-weight distribution of soluble polymers without the necessity of calibration is described. The automation system eliminates most of the tediousness associated with molecular-weight distribution measurement. The molecular-weight distributions and molecular-weight averages of a broad range of polystyrene standards were determined using this technique. The results obtained are shown to agree closely with literature data.

Reorientation d'une serie homologue de p-chlorobenzoates de n-alkyle dans un liquide homogene ou en solutions dans CCl 4

The G values of poly(methyl methacrylates) (PMMA), polycarbonates, and a polylactone for γ-radiation were determined by using a computer-assisted GPC as the primary tool for the measurement of the number-average molecular weights Mn. The accuracy and precision of the automated GPC were found to have a normalized standard deviation (σ/Mn) of less than 7%. The G value of PMMA was determined to be essentially independent of molecular weight. For low molecular weight polymers, some nonlinearity in the I/Mn versus dosage plot was observed at low dosage, i.e., about 1 Mrad.

Emploi de l'interferometrie de Fabry Perot pour observer la diffusion dynamique de la lumiere depolarisee de p-dichlorophenylmethane et de ses melanges avec le PMMA, entre −4 et +98°C

The contribution of parameters such as molecular weight, molecular weight distribution and stereochemistry to electron beam sensitivity of poly(methyl methacrylate), PMMA, has been investigated. The sensitivity is interpreted here as the minimum radiation dose required to obtain a predetermined solubility rate ratio, S/So = SR, of the exposed, S, and unexposed, So, material. The G-value was foam be independent of molecular weight, molecular weight distribution, and stereochemistry. Data indicate that the weight average molecular weight ratio correlates better with SR than the number average molecular weight ratio. The tacticity of the resist and the developer solvent molecular weight or size have a large effect on solubility rate. Although the solubility rate pf isotactic PMMA is much greater than the syndiotactic and heterotactic stereoforms, the sensitivity appears to be independent of tacticity. In a homologous series of n-alkyl acetate developer solvents, the molecular size of the solvent has a greater effect on the solubility rate than the molecular weight of the resist. A developer solvent has been selected from the n-alkyl acetates which enhanced the sensitivity of PMMA.

Poly(methyl methacrylate), PMMA, is used as a model polymer to determine quantitatively the effect of molecular weight, molecular weight distribution, and tacticity on electron beam sensitivity. The heterotactic, syndiotactic, and isotactic stereoforms of PMMA were synthesized with molecular weights ranging from 104 to 107 and dispersivities from 1.2 to about 10. The G-values as determined by gamma radiation are about 1.3 and are independent of the three parameters. However, the solubility rate of PMMA is very dependent on the tacticity, and the relative solubility rates are in the order syndiotactic < heterotactic ≪ isotactic. The weight-average molecular weight ratio was found to give a better correlation with solubility rate ratio than the number-average molecular weight ratio. The molecular size of the developer solvent was shown to have a much greater effect on the solubility rate than the molecular weight of the resist. An optimal developer solvent for PMMA can be systematically selected from a homologous series of n- alkyl acetates which enhance the resist sensitivity.

Poly(olefin sulfones) are readily degraded by an electron beam and thus could be used as electron beam resists. However, films greater than 3000 A thick crack during formation and especially during solvent development following exposure to an electron beam. As crystallinity accentuates cracking owing to swelling stresses at the crystalline–amorphous interface, the morphology of various poly(olefin sulfones) was studies by light scattering. Materials investigated were solvent-cast and hot-pressed films of poly(butene-1 sulfone) (PBS), poly(cyclopentene sulfone) (PCPS), poly(bicycloheptene sulfone) (PBCHS), and two terpolymers of poly(cyclopentene sulfone–co–butene-1 sulfone), in which the molar ratios of cyclopentene to butene-1 were 50/50 (TP1) and 70/30 (TP2). All hot-pressed samples showed scattering patterns characteristic of randomly oriented rod-like superstructures 8–10 μm in length. Among the solvent-cast films, however, only PBS and TP2 samples scattered light indicative of crystallinity. Scattering from these samples were analyzed in terms of “random orientation fluctuation” light scattering theory. Correlation distances of 1.7 and 1.5 μm for the PBS and TP2, respectively, were obtained. The solvent-cast crystalline films (PBS and TP2) had a tendency to crack during dissolution as did the amorphous films of PCPS and PBCHS, indicating that cracking depends on the glass temperature as well as crystallinity. Only the amorphous terpolymer TP1 did not crack, presumably owing to its relatively low glass temperature effected by the butene-1 moiety.

The dissolution of glassy polymers is described by a phenomenological model of the motion of two boundaries: the liquid-gel boundary and the gel-glass boundary. The motion of these boundaries, as well as the concentration profile in the layers of a dissolving polymer, was obtained by numerical solution of the Stefan boundary value problem. Confirmation of the experimental program written to simulate the problem is established by its good agreement with direct observation of the dissolution dynamics of polystyrene in methyl ethyl ketone. A potential application of this model to the study of the dissolution dynamics of other polymer-solvent systems is done by simulating the dissolution of three types of polymer-solvent pairs: 1) swelling of rubber, 2) high glass transition concentration, and 3) low glass transition concentration. Contrasting dissolution characteristics are shown for the effect of different types of polymer-solvent pairs as well as for the effect of different molecular weights for the same type of polymer-solvent pair.

A detailed study of the factors affecting the dissolution rate of poly(methyl methacrylate), PMMA, showed that the magnitude of the increase in the dissolution rate of irradiated PMMA could not be entirely attributed to the reduction in the molecular weight, MW. The formation of non-polymeric volatile fragments by radiation exposure, i.e., CO, CO2H2, CH3OH and CH4 causes a large increase in the solvent flux into the polymer matrix, thereby causing a large increase in the dissolution rate of exposed PMMA. The volatilization of these low molecular weight fragments cause an increase in the “excess free volume” (microporosity) of the glassy PMMA. The relative magnitudes of the contribution of the MW reduction and the formation of volatile matter on the increase in the solubility rate of the irradiated polymer were found to depend on the molecular size of the solvent, and also on the enthalpy of mixing.

In this report we show by experimental and theoretical investigations that the commonly used GPC universal calibration parameter, the intrinsic viscosity multiplied by the weight average molecular weight ([η] Mw) is incorrect. The error which can arise by using [η] M to calculate the molecular weight across the GPC chromatogram for nonuniformly branched polymers [poly(vinyl acetate) and low density polyethylene] and copolymers with compositional drift, could be very large. We also show conclusively that the number average molecular weight Mn is the correct average to use for the universal calibration parameter. We therefore recommend that our general universal Calibration parameter [η] Mn be used for calculating the molecular weight across the chromatogram for all polymer systems (linear and branched homopolymers, copolymers with or without compositional drift and for polymer blends).

The detailed design and computer interfacing of a GPC molecular weight detector based on a real time viscometer are described. The working drawings presented will permit one to fabricate and duplicate the viscometer and the complete GPC molecular weight detector system. The uses and advantages of a laboratory automation system in analyzing GPC results are also described.

Gel permeation chromatography (GPC), sometimes referred to as size-exclusion chromatography (SEC), has progressed at an almost explosive rate since its introduction less than two decades ago. One has only to refer to the open literature or thumb through the list of Chromatographic equipment manufacturers anxious to sell their latest innovation to be fully convinced of this fact. Because of the extensive progress in GPC technique and instrumentation, the author had a very difficult time in deciding the scope of this review. Mindful that he may be criticized of being myopic in his presentation of the most significant and recent contributions and guilty of gross omission of important references, the author has nevertheless decided to narrow the scope to three major areas and a few key references. The three major areas to be covered are: (1) data acquisition and processing, (2) high-pressure chromatography and (3) detectors. Extensive progress has been made in the computerization of both data acquisition and data reduction, the latter allowing molecular weight distribution (MWD) and molecular weight averages to be obtained on the sample in a matter of minutes rather than hours or days. The main beneficiaries of the computerization of data acquisition and processing have been those concerned with polymer quality control, for it has liberated them from the drudgery of the manual digitization, integration, and normalization of the chromatograms required to reduce them to a useful format. The hours of monotonous eye-straining work to obtain MWD and molecular weight averages has been reduced to a few seconds of punching a few keys of the data system console. The development of the high-pressure Chromatograph has added a new dimension to GPC, for, when it is combined with a computerized data system, the MWD can be obtained almost in real time in relation, for example, to a characteristic time of a polymerization reactor. In high-speed Chromatograph y under nearly ideal conditions (low-viscosity mobile phase and molecular weight of no more than a few hundred thousand), the MWD can be obtained in a few minutes. This capability allows the use of GPC as on-line process-control equipment. The Chromatograph can be used as part of a “feed-back” loop to control the polymerization conditions to obtain a product of consistent MWD.

The Gel Permeation Chromatograph has been used for obtaining values of weight-average and number-average molecular sizes Aw and An and the heterogeneity indices Aw/An for a series of polypropylenes. Absolute values of Mw and Mn, the weight-average and number-average molecular weights, have also been obtained from the same samples with light-scattering and osmotic pressure methods. Comparisons of the data from the gel permeation chromatograph with the data from the absolute measurements have been used for calculating Q, the constant used for converting Aw and An to the corresponding Mw and Mn values. Other correlations of interest, such as intrinsic viscosity versus weight-average molecular weight and melt flow, and Newtonian viscosity versus weight-average molecular weight, are also given.

In the last decade, since the introduction of cross-linked divinyl benzene/polystyrene copolymer gel [1] as stationary phase for GPC (gel permeation chromatography), over 400 publications dealing in various subjects of GPC have appeared. Included are more than ten general reviews by Determann [2], Altgelt and Moore [3], Lambert [4], Tung [5], Boyer [6], Brezezinski [7], Cantow et al. [8], Heitz and Kern [9], Pederson and Proceda [10], and Nakamura [11]. The most extensive, perhaps, is that by Lambert [4] which gives 280 references. Since the above serve as more than adequate references on the general aspects of GPC, it is felt that a review on a specific subject of GPC will be more appropriate at this time.

In the determination of molecular weight distributions by GPC, the traditional column arrangement is such that the fractionation process proceeds from a high-permeability limit to a low-permeability limit column. We report computer comparisons of data obtained from columns in their normal ordering (high- to low-permeability limit), reverse ordering, and random ordering. The columns had a permeability limit range from 1 × 106 A down to 1 × 103 A, and the polymers had a molecular weight range of 1.8 × 106 down to 2.1 × 103. The concentrations used varied from 0.05% up to 0.5%. The data show significantly different results, with the random arrangement the preferred ordering. A qualitative model for the separation mechanism is presented to account for the improvement in resolution. Additional data are presented which show that serious errors (as high as 45%, depending on concentration) will be encountered in GPC studies, unless the calibration curve is obtained at the same relative concentration as the samples, with definite overloading effects occurring at the higher concentrations. A new method of curve fitting was used in the higher molecular weight region to give meaningful calibration curves.

This work is concerned with the dispersion of high-molecular-weight solutes in dilute solutions flowing through empty capillary tubing, such as that which is found between chromatographic columns and detectors, etc., in gel permeation or liquid chromatographs. Residence time distributions of solvent as well as solutes were measured simultaneously. This was done for both pulse and step solution inputs using a two-cell detection system. The solutes, o-nitrotoluene and narrow-distribution polystyrene (gel permeation chromatographic standards), were monitored with an ultraviolet detector while hexane (hexane-chloroform (20:80) was used to dissolve the polymer solutes) was monitored with a refractometer in a chloroform mobile phase. Polystyrene concentrations were 0.20 percent and 0.15 percent. Three tubing lengths and two flow rates were studied. The results indicate that polymer molecules have residence time distributions which are different from those of small molecules. This lends support to our belief that molecular entanglements occur among the polymer molecules which causes radial concentration non-uniformities and virtual two-phase flow.

A phenomenological model based on a set of partial differential equations and boundary conditions is proposed for chromatography and, in particular, for gel permeation chromatography. The intractable boundary value problem, which does not have a closed form solution, was handled through the use of numerical methods employing a very large and very fast computer (IBM 360/195). The chromatograms generated by the computer simulator were compared with experimental chromatograms of various molecular weight polymers. The computer generated overlay plots of the simulated and experimental chromatograms showed good agreement (the two plots almost superimposed). The effect of other parameters on the chromatogram, i.e., flow rate, stationary phase bead size, solute diffusion coefficient in the stationary and mobile phases, and the partition coefficient were also investigated.

Poly(vinylbutyral) samples of two different degrees of butyralization and varying molecular weights were studied in several solvents using the techniques of low-angle light scattering, exclusion chromatography and viscometry. The polymers showed evidence of aggregation in certain solvents. The aggregation could be broken up by heating to moderate temperature (~70°C), but would reform at room temperature in a period of time dependent on concentration. No dependence of apparent Mw on solvent was detected apart from that caused by aggregation. Chain dimensions calculated from intrinsic viscosities and molecular weights measured in non-aggregated solutions were compared with literature values of freely rotating dimensions calculated for a given degree of butyralization and tacticity.

The viscoelastic and dielectric properties of two A-B-A type block copolymers were determined. One contains styrene-butadiene- styrene (SBS) blocks and the other styrene-isoprene-styrene (SIS) blocks. Samples were prepared by casting from solutions of these polymers in benzene/heptane, carbon tetrachloride and methylethyl- ketone/tetrahydrofuran. The viscoelastic behavior of SIS block copolymers is apparently unaffected by the casting solvent, while that of the SBS block copolymers is similar from the former two solvents but drastically modified for the MEK/THF-cast sample. Shift factors utilized in constructing the viscoelastic master curves were found to obey the WLF equation as modified by Shen and Kaelble, except for the MEK/THF-cast SBS block copolymer. Dielectric loss curves were obtained over an extended frequency range. For comparison, the mechanical loss curve for a CCl4-cast SBS block copolymer was computed from master curve by linear programming. In both cases the only observed loss peaks were those resulting from the primary glass transitions of the respective blocks. No peak was found in the intermediate temperature range that may be attributable to the “mixed” regions.