Characterization of poly(3-octylthiophene). I: Molecular characterization in dilute solution

The poly(3-alkylthiophenes) are a class of electrically conducting polymers which are of particular scientific and commercial interest due to their solubility and meltability. A series of poly(3-octylthiophene) (P3OT) fractions having molecular weights in the range M_w=30,000 to 400,000 were generated by preparative gel permeation chromatography (GPC). Although the polymer remained weakly aggregated when dissolved in pure THF, the addition of an organic salt (1 wt.% tetrabutylammonium p-toluenesulfonate) resulted in complete molecular dissolution. We were thus able to completely and consistently describe the polymer's single-chain properties using three dilute solution characterization methods: viscometry, GPC, and integrated light scattering. The molecular weight dependence of the intrinsic viscosity and the radius-of-gyration were established, and were characteristic of solutions near the theta condition, indicating poor solvent quality. Calculation of the persistence length from our data revealed that the polymer backbone is only 2 to 3 times more rigid than common flexible polymers, despite its conjugated ring structure.     

An analytical solution to Tung's axial dispersion equation. Applications in gel permeation chromatography

Equations developed for correcting M_n, M_w, and [μ] for imperfect resolution are generally satisfactory. Choosing the appropriate instrumental spreading function is however a very difcult task. There is need for further research on this problem, in particular with polymer standards for which the DMWD or even M_z is known (in addition to M_n and M_w). A criterion for resolution in GPC which is based on a solution of Tung's axial dispersion equation has been proposed. The operation of GPC in recycle mode appears very promising. Equations have been developed to interpret data obtained in this operational mode. It is probable that a great deal of work will be done in this area in the very near future.     

A gel permeation chromatography calibration method for a broad molecular weight distribution polymer

A novel, precise, and simple method is described for developing a GPC calibration curve for a polymer where only broad molecular weight distribution samples are available. The method demands a GPC calibration curve for another polymer (e.g., polystyrene) and measurement of the intrinsic viscosity and an average molecular weight for each of several samples of the broad molecular weight distribution polymer in addition to GPC measurements on those samples. Results of applying the procedure to poly(n-lauryl methacrylate) are presented.     

Structural differences exhibited by networks prepared by chemical and photochemical reactions. III. Characterization by inverse GPC

The use of a new method, inverse GPC, as a tool for the characterization of elastomeric networks, allowed the obtaining of the distribution curves of the network strands. In agreement with previous studies it was shown that photocrosslinked materials exhibit a more homogeneous distribution of the crosslink points than do peroxide cured samples. From the GPC distribution curves, it was possible to calculate M _c, the average molecular weight of a network strand.     

Randomly branched styrene/divinylbenzene copolymers. I. Preparation,molecular weight characterization,and GPC analysis

A series of randomly branched copolymers of styrene and divinylbenzene were prepared using a benzoyl peroxide-initiated free-radical bulk polymerization at 78°C. DVB contents were varied from 0.01% to 2%. Two samples were polymerized with 0.4% DVB to different conversions: series 9A at 6% conversion and series 9B at 15% conversion (just short of the gelation point). Both samples were fractionated and the fractions characterized by ultracentrifugation, light scattering, osmometry, viscometry, and gel permeation chromatography. The data indicated that the fractions were not of narrow MWD and that the breadth of the MWD of the fractions from series 9B were greater than those of 9A. GPC calibration curves of M, [η], and M [η] were generated for both 9A and 9B fractions by employing curve-fitting techniques to the GPC data. For all of the fractions 9B, the molecular weight calibration provided accurate values of M?_z, M?_w, and M?_n, suggesting that no serious peak spreading had occurred in the GPC experiments. The universal calibration parameter M[η] for the 9A fractions agreed with that of linear polystyrene, while that of the high-conversion series 9B did not. It will be shown in a later paper that series 9B is highly branched, while 9A is lightly branched. Consequently, it is recommended that any GPC analysis of branching units make an allowance for the deviation of highly branched polymers from the linear M[η] calibration curve.     

Addition polyimides. II. Synthesis and characterization of bisitaconimide prepolymers

N,N′-bis(3,3′-itaconimidophenyl) sulfone has been synthesized by reacting itaconic anhydride with 3,3′-diamino diphenyl sulfone. The bisitaconimides and the intermediates were characterized by chemical analysis, IR, NMR, TG, and GPC. The degree of polymerization (DP) of the prepolymers of the bisitaconimide was followed by GPC and from the NMR data on vinylidene and aromatic proton ratios. The correlation between DP and intrinsic viscosity of the prepolymers was made use of to determine the Mark–Houwink constants (K and α). The thermal stability and the decomposition kinetics of the prepolymers were evaluated from TG data. The kinetic parameters, viz. energy of activation, E, and preexponential factor A, were computed using four nonisothermal integral equations, and their values are not appreciably affected by the degree of polymerization, within the range studied.     

Dehydrochlorinated poly(vinyl chloride)-g-polystyrene. II. Characterization and physical properties

Dehydrochlorinated poly(vinyl chloride)-g-polystyrene (DHPVC-g-PSt) prepared by free radical grafting was characterized, and some of its physical properties were evaluated. The presence of graft was established by the appearance of new absorption peaks in the IR spectra of the graft copolymer. GPC analysis showed increase in the average molecular weights of the graft copolymer upon increase in the PSt content. Besides, GPC revealed the uniform PSt distribution of DHPVC-g-PSt. A marked improvement in the thermal stability of DHPVC-g-PSt over that of DHPVC and DHPVC/PSt blends was observed. Graft copolymers with high percent grafting were thermally more stable than even the original PVC. Stress–strain data indicated decrease in yield stress, breaking stress and elongation, along with an increase in the initial modulus, upon increase in PSt content of the graft copolymer.     

Measurement of the absolute molecular weight and molecular weight distribution of polyolefins using low-angle laser light scattering

By connecting a low-angle laser light scattering photometer (LALLSP) on line with a high-temperature gel permeation chromatograph (GPC), molecular weight distributions were determined for three polyethylene standards (two high density and one low density) without resorting to column calibration procedures. In addition, the absolute weight-average molecular weight and second virial coefficients of four polyethylene standards (three high density and one low density) were obtained using low-angle laser light scattering. The molecular weights measured were in excellent agreement with those specified by the National Bureau of Standards. For the low density material, a microgel fraction was detected by the on-line LALLSP but not by the conventional GPC detector. This resulted in a z-average molecular weight of over 3 × 10⁶ daltons, an order of magnitude greater than that determined by conventional GPC techniques.     

Salt effect on gel permeation chromatography of partially charged polymers

The effect of the addition of 0.1M LiBr to dimethylformamide (DMF) solutions of charged and uncharged polymers has been studied by GPC and [η] measurements. LiBr has a salting-out effect on polyacrylonitrile (with (PAN-S) and without (PAN) sulfonate sulfur), polystyrene (PS), and poly(vinyl acetate) (PVAc), which is seen by a decrease in [η] and an increase in the GPC retention time. The increase in retention time is, however, abnormally high for charged polymers. Association in PAN and PAN-S solutions in DMF can explain the experimental observations.     

High-speed gel permeation chromatography. A study of operational variables

Systematic studies of operational variables affecting GPC separation using μ-Styragel of nominal porosity 10⁶, 10⁵, 10⁴, and 10³ Å are reported. The dependences of (1) flow rate, (2) injection volume, and (3) concentration on elution volume (V_e), the theoretical plate number (N), and peak width at half-height were examined. The values of V_e changed with changing (1), (2), and (3). The values of N were inversely proportional to the root of flow rate. The relation between sample load and N showed that lower concentration and larger injection volume were desirable for N than the opposite. The concentration dependence for high-speed GPC was significantly higher than classical low-speed GPC. The methods of minimizing the effects produced by the individual variables and the optimum operational conditions are discussed. Recommended operational conditions are as follows: flow rate, 1 to 2 ml/min; injection volume, 0.1 ml; sample concentration, below 0.4% (or if injection volume 0.5 ml, sample concentration below 0.1%).     

Synthesis and characterization of phenoxy resins prepared from diglycidyl ether of bisphenol a and various aromatic dihydroxyl monomers

This work describes the synthesis of various phenoxy resins by in situ fusion reaction of aromatic dihydroxyl and low molecular weight liquid diglycidyl ether of bisphenol A (DGEBA) with an aryl phosphonium salt catalyst. FTIR and ¹H-NMR spectra and GPC analyses were performed to characterize the resins. Analyses results indicated that resins have an adequate high molecular weight and physical properties when the reaction occurred after 5–10 min at 225–230°C. In addition, DSC and TGA analyses were performed to investigate the thermal properties of these phenoxy resins. According to these results, the lack of steric hindrance of the molecular structure in these phenoxy resins depressed the changes of T_g and weight loss. A series of phenoxy modified epoxy networks containing narrower polydisperity and higher M_n will exhibit the most significant effect on impact toughness. Moreover, the FTIR spectrum of the phenoxy resin as a function of temperature correlates well with the glass transition temperature. Furthermore, results presented herein demonstrate effective miscibility with thermoplastic polyurethane elastomer (TPU). © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2369–2376, 1999     

Measurement of molecular weight of poly(vinyl chloride)

Molecular weights of six bulk-process and five suspension-process PVC samples have been measured as part of a study aimed at developing a technique for gel permeation-chromatographic analysis of this polymer in tetrahydrofuran at room temperature. Osmometric M?_n values measured in cyclohexanone appear to be valid; the results are insensitive to thermal history or ultrasonic irradiation of the solution. Corresponding measurements in tetrahydrofuran changed with measurement temperature and indicated the presence of stable supermolecular PVC aggregates in this solvent. Such aggregates can be dispersed by ultrasonic treatment of the solution for brief periods. Simultaneous degradation of PVC molecules appears to be prevented by addition of small concentrations of nonionic surfactant to the tetrahydrofuran solutions. Treated solutions are suitable for GPC analyses at ambient temperatures. The results of osmometry, light scattering, and GPC agreed well.     

Polymeric reaction of acrylic polymer–monomer system irradiated by low-energy electron beam. II. Effect of ester structure of acrylic polymer

Polymeric reactions of polyacrylate–benzyl acrylate (BzA) systems induced by a low-energy electron beam were investigated by changing the species of polyacrylates added to the system. The gel fraction, the proportion of BzA units incorporated into gel by infrared (IR) analysis, and the molecular weight and its distribution curves by gel permeation chromatography (GPC) were examined to elucidate the reaction mechanism for the polymer–monomer system. The GPC curves were detected by both ultraviolet (UV) and refractive index (RI). As the UV-detected GPC curves represent the benzyl groups of graft polymers and homo polymers, the polymerization reactions can be followed by GPC. Ester structures of acrylic polymers were varied in order to examine how much the ester group affects such individual reactions as crosslinking, graft polymerizations, and homopolymerizations. In the case of both polyisobutylacrylate–BzA and poly(isoamyl acrylate)–BzA systems, the crosslinking and graft reactions predominated, while in the case of poly(t-butyl acrylate)–BzA systems, homopolymerization was the main reaction. These results can be explained by the structure and reactivity of polymer radicals and viscosity of the system.     

Cyclic fatty acid monomer formation in frying fats. I. Determination and structural study

The formation of monomeric cyclic fatty acids was studied in a model system in which partially hydrogenated soybean oil (PHSO) was heated intermittently for 80 hr of simulated deep fat frying. Oil samples (fresh and heated) and their methyl esters were fractionated according to their molecular size using gel permeation chromatography (GPC). Oils and GPC fractions were analyzed for cyclic monomers by the following steps: (i) preparation of fatty acid methyl esters (FAME); (ii) microhydrogenation of FAME; (iii) urea fractionation of hydrogenated FAME; (iv) analysis by capillary gas liquid chromatography (GLC), and (v) structural characterization of cyclic monomer peaks by mass spectrometry (GC-MS). Under simulated frying conditions the concentration of cyclic monomers increased from 736 ppm (0.07%) in fresh oil to 1803 ppm (0.18%) in heated oil. GC-MS with capillary columns allowed the identification of several C₁₈ α-disubstituted cyclohexane and cyclopentane isomers as hydrogenated methyl esters. Other noncyclic and contaminant compounds eluting within the expected GLC retention range of cyclic monomers also were identified in all the samples and GPC fractions.     

Epoxy resins based on aromatic glycidylamines. IV. Preparation of N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenylmethane from aniline and analysis of the product by GPC and HPLC

Epoxy resins containing N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenylmethane (TGDDM) were prepared from aniline and epichlorohydrin and analyzed by GPC and HPLC. The product composition was compared with that of resins prepared from 4,4′-diaminodiphenylmethane (DDM) and epichlorohydrin, which had been analyzed in our previous work. A new byproduct designated Y4 was isolated by semipreparative HPLC and identified by NMR and mass spectroscopy. The course of formaldehyde condensation with N,N-dichlorohydrin of aniline (DCHA) was followed by GPC and HPLC and the mechanism of formation of Y4 was proposed on the basis of obtained results. Attention was also paid to the differences in reactivity of DCHA diastereoisomers.     

Evaluation of GPC methods for estimation of Mark–Houwink–Sakurada constants

Constants for the Mark–Houwink–Sakurada relation can be established in principle from GPC measurements on broad distribution polymers. The method requires use of two samples with different intrinsic viscosities or a single polymer for which [η] and M ⁿ M ^w are known. The [η]–M ^w combination is not reliable because M ^v and M ^w are often very similar in magnitude. The [η]M _n method is likewise not recommended because of the influence of skewing and axial dispersion effects on the GPC measurement of M _n. The simplest and safest way to use GPC data to estimate the MHS constants involves the measurement of GPC chromatograms of two polymer samples with different intrinsic viscosities. The method is not confined to the solvent used as the GPC eluant. The MHS constants derived from GPC appear to reflect the molecular weight range of the calibration samples and may not be as widely applicable as those from the more tedious classical methods which employ a series of fractionated samples.     

Determination of Polymer Branching with Gel Permeation Chromatography. Abstract of a Review

Abstract

The effect of long- and short-chain branching in polymer molecules on GPC separation is reviewed (1–4). The calculation of branched GPC curves is developed from the uiiiversal calibration techniques, which is based on the concept of hydrodynamic volume (M [η]) and previously established relationships for the effect of branching on molecular dimensions. Typical calibration curves are shown for different branching models and degrees of branching. As the branching level increases, the curves arc shown to approach a limiting value. Methods of characterizing branching level3 and molecular-weight distributions of fractions and whole polymers from GPC and intrinsic viscosity data arc prcsentecl. An iterative computer program is described which was written to calculate the degree of branching in whole polymers. Long-chain branching in beveral low-density polyethylene samples was determined, using both the fraction and the whole polymer methods. Effects of various experimental errors and branching models were investigated. For polyethylene, the data show that the effect of branching in intrinsic viscosity is best described by the relationship (g ₃) _w = [η]_br/[η] whre (g _s is the Zimin-Stockmeyer expression for trifunctional branch points in a polydisperse sample.     

High-temperature coupling of high-speed GPC with continuous viscometry. I. Long-chain branching in polyethylene

The coupling of a high-temperature liquid chromatograph (Waters 150C) with a home-made continuous capillary viscometer is described. This detector is the only one suitable for high-speed GPC when the small volume of the mobile phase prohibits the coupling with a classical viscometer. The pressure drop of the GPC effluent through the capillary is continuously measured along with the refractive index change. This dual detection leads to the determination of the intrinsic viscosity as a function of the elution volume, thus allowing a precise use of Benoit's universal calibration. The accuracy of our system is demonstrated in the case of the characterization of linear and branched polyethylene samples. The results concerning the average molecular weights as well as the branching factors (structure parameter g′ and long-chain branching frequencyλ) are in close agreement with those obtained by the classical way (coupling traditional GPC and discontinuous viscometry). It is well known that an estimate of the λ coefficient is extremely dependent on several hypotheses. However, for a set of commercial low-density polyethylenes, we obtained λ values about 0.5 × 10_?4, with no marked change along the molecular weight range.     

Synthesis of 1,2 dilinoleoyl and 1,2 dipalmitoylsn-3-glycerophosphorylcholine

The synthesis of 1,2 dilinoleoylsn-3-glycerophosphorylcholine (1,2-18∶2-sn-3-GPC) and 1,2 dipalmitoylsn-3-glycerophosphorylcholine (1,2-16∶0-sn-3-SPC) is described. Synthesis was accomplished by acylating free glycerophosphorylcholine (GPC) with the anhydride and potassium salt of the desired acid. Purification of 1,2-16∶0-sn-3-GPC was accomplished by crystallization, while purification of 1,2-18∶2-sn-3-GPC required the use of alumina column chromatography and then crystallization from acetone at −7C. Scientific contribution N. 491, Agricultural Experiment Station, University of Connecticut, Storrs.     

A novel addition curable novolac bearing phthalonitrile groups: synthesis,characterization and thermal properties

Summary Novel phenolic novolac resins, bearing phthalonitrile groups anchored to benzene ring through phenyl azo linkage were realized by the coupling reaction between novolac and phthalonitrile diazonium salt. The diazo-coupling occurred to a maximun of about 61%. The apparent molecular weight, determined form GPC showed a downward drift with increase in degree of phthalonitrile substitution. Analysis using DSC technique indicated that the resin underwent curing in a temperature range form 290 to 320 °C . The curing occurred via addition polymerization of phthalonitrile groups. The thermal stability and anaerobic char yield of the polymers increased proportion to the crosslinking. The probable cure mechanics were discussed.