Determination of polymer branching with gel-permeation chromatography. II. Experimental results for polyethylene

The recently developed methods of characterizing branching in polymers from gelpermeation chromatography and intrinsic viscosity data are verified experimentally. An iterative computer program was written to calculate the degree of branching in whole polymers. Long-chain branching in several low-density polyethylene samples was determined by both the fraction and whole polymer methods. The two methods gave consistent ranking of the branching in the samples although absolute branching indices differed. Effects of various experimental errors and the particular model used for branching were investigated. For polyethylene, the data show that the effect of branching on intrinsic viscosity is best described by the relation 〈g₃〉_W^1/2 = [η]_br/[η]₁ where 〈g₃〉_w is the weight-average ratio of mean-square molecular radii of gyration of linear and trifunctionally branched polymers of the same weight-average molecular weight.     

Evaluation and Application of a Commercial Single Capillary Viscometer System for The Characterization of Molecular Weight Distribution and Polymer Chain Branching

Abstract

The objective of this paper is to critically evaluate the performance of the newly introduced Millipore Waters GPC-viscometer system. In particular, the capabilities of the data analysis methodology are evaluated and limitations are identified. Potential modifications to improve the data analysis methodology and to make it more user friendly are suggested. The characterization of molecular weight, molecular weight distribution and polymer branching for polymer standards and polymers of commercial interest are reported.     

A Method of Self Calibration for Molecular Weight Distribution Determinations for Liquid Crystalline Polymers

Abstract

A method of molecular weight calibration was devised for various substituted liquid crystalline polymers with substantial molecular weight repeat units. With the use of gel permeation chromatography, oligomer peak separation was achieved offering a method for self calibration for molecular weight distribution determinations. Employing an overlay of a low molecular weight polystyrene standard, a retention time marker was utilized as a source from which to mark an oligomer peak. The calibration plot produced using this technique showed much better correlation coefficients than that of the polystyrene calibration plot. In addition, molecular weight determinations made from the two techniques yielded two distinct molecular weight averages and distributions, indicating polystyrene to be a poor relative calibration method for the liquid crystalline polymers tested. The technique illustrates the utility of alternative calibration methods when samples show certain physical characteristics.     

Characterization of Branched Poly (vinyl Acetate) by GPC and Low Angle Laser Light Scattering Photometry

Abstract

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 M_w 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 M_w). M_w 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.

Most importantly it was unambiguously shown that the commonly used universal calibration parameter (UCP) with GPC, [n]M_w, is incorrect for polymers with molecules having the same hydrodynamic volume but different molecular weights, i. e., those with only chain branching (LCB), copolymers with compositional drift, and polymer blends. The correct UCP was found to     

Evaluation of a Commercial Differential Viscometer as a GPC Detector and Its Application to Polymer Characterization

Abstract

When used as a GPC detector, Viscotek's differential viscometer (DV) measures specific viscosities at each elution volume across the chromatogram. With the addition of a concentration detector, intrinsic viscosities may be calculated. As a result, true molecular weights can be calculated via the universal calibration method.

It was found that true molecular weights and branching analysis obtained using DV for acrylate polymers initiated by VAZO and benzoyl peroxide show excellent agreement with those from low angle laser light scattering (LALLS) measurement. Moreover, comparison of intrinsic viscosities for different polymers at the same molecular weights can be made from the DV technique. In general, linear polymers will have a higher IV than branches ones and the concept has been verified for acrylate polymers in this work.

A comparison between DV and LALLS in terms of capabilities, ease of use, and maintenance is also included.     

Steady flow and dynamic viscosity of branched butadiene–styrene block copolymers

Steady flow and dynamic viscosities were determined for symmetrical linear and starbranched block copolymers of butadiene and styrene above their upper (polystyrene) glass transition. Block structures examined were B-S-B, (B-S-)₃, S-B-S, (S-B-)₃ and (S-B-)₄. At constant molecular weight and total styrene content viscosities were greater for polymers terminating in styrene blocks, irrespective of branching. Branching decreased the viscosity of either polybutadiene-terminated or polystyrene-terminated block polymers, compared at equal M _w. However, comparisons at equal block lengths showed that the length of the terminal blocks, not the total molecular weight, governs the viscoelastic behavior of these polymers to a surprisingly good approximation. This unusual result is rationalized in terms of the two-phase domain structure of these polymers, which persists to a significant degree in the melt. Below the glass transition of the polystyrene blocks the effects of branching were masked by differences in the morphology of the domain structure unrelated to branching.     

Gel Permeation Chromatography of Unsaturated Polyester Resins. Possibilities and Limitations

Abstract

The use of gel permeation chromatography (GPC) for the characterization of unsaturated polyester resins is demonstrated on several examples. Number-average molecular weights determined by this method are compared to data obtained by means of vapor pressure osmometry (VPO) and by end group analysis (EG). The determination of the polyester resin composition as a function of molecular weight by stop-and-go UV scanning procedure is described. A comparison of theoretical and experimental molecular distribution is applied to the estimation of branching extent.     

Rotational viscosity of ferroelectric liquid-crystalline polysiloxanes

Abstract

Some physical parameters of comb-shaped ferroelectric liquid-crystalline polymers were measured. Their rotational viscosities are two or three orders of magnitude larger than that of low molecular weight ferroelectric liquid crystals. Furthermore, they are found generally to be proportional to the second power of the weight-average molecular weight. Spontaneous polarization of the ferroelectric liquid-crystalline polymers has little dependence on molecular weight.     

Polyphenyl-as-triazines from Perfluoroalkyleneamidrazones

Abstract

High molecular weight polyphenyl-as-triazines were prepared at ambient temperature by the cyclopolycondensation of perfluoroglutaramidrazone and perfluoroadipamidrazone with various bis(1,2-dicarbonyl) monomers. The effect which the perfluoroalkylene group had upon certain chemical and physical properties of the polymers was determined. Thermal evaluation involved TGA, DSC, TMA, and isothermal weight loss studies of films at 232 °C in air. The polymers exhibited excellent hydrolytic stability as evidenced by retention of n _inh after boiling in water (24 hr) and 10% sodium hydroxide solution (8 hr). A stable uncyclized intermediate was isolated from the reaction of perfluoroadipamidrazone and benzil which was cyclized to the phenyl-as-triazine model compound [3,3′ -perfluorotetramethylenedi (5,6-diphenyl-as-triazine)].     

Long-Chain Branching under Conditions of Nonuniform Branching Probability

Abstract

Long-chain branching can occur during free radical polymerization and is especially important for polyethylene. An improved method of calculating the effect of long-chain branching on molecular weight distribution was presented in an earlier paper in which the assumption was made that the probability of branching at each monomer unit was constant throughout the polymerization. A method of including a nonuniform probability of branching in the calculations is presented. Calculation results show that the predictions of the two mathematical models are similar and both models fit published data on polyethylene equally well.     

A Comparison of Polymer Separation Efficiency and Resolution by Gradient LC,GPC and TLC

Abstract

The specific resolution of gradient LC and reversed phase TLC methods for the separation of different molecular weight standards of poly(isoprene), poly(ethylene glycol), poly(ethylene oxide), poly(styrene) and poly(α-methylstyrene) were determined. It was found that gradient LC has an order of magnitude greater resolving power (for high polymers) than gel permeation chromatography (GPC) while TLC had from two to five times the resolving power of GPC in the molecular weight range investigated. This is a direct result of the greater selectivity of gradient LC and TLC techniques. The specific resolution is also dependent on the type of gradient used to achieve fractionation for the LC technique.     

Viscoelastic properties of branched polyethylene melts

The dynamic mechanical properties of branched polyethylenes in the molten state were determined in the frequency range 10^?3–10 radians/sec. The materials tested have remarkably similar rheological properties even though they vary greatly in molecular weight and molecular weight distribution. The similarity in properties is attributed to the influence of long chain branching on the relaxation spectra. A mechanistic argument is proposed to relate the observed behavior to molecular entanglement coupling. The concept of entanglement coupling involving long-chain branching leads to the expectation that the quasi-Newtonian and non-Newtonian viscosities of branched polymers may be either greater or less than those of linear polymers of the same species, which have comparable molecular weights. This is borne out by experiment.     

Simultaneous Calibration of Molecular Weight Separation and Column Dispersion of GPC by Coupling with Lallis

Abstract

It is shown theoretically and experimentally that both the calibration of the molecular weight separation and column dispersion can be evaluated simultaneously by coupling gel chromatograph with low angle light scattering photometer. The experimentally determined variation of the spreading factor with retention volume is quite similar to that obtained by Tung using reverse flow technique. A correction method is given for the lowering of inhomogeneity index printed by the data processor of the on-line GPC-LALLS.     

Synthesis and Characterization of α,ω‐bi[2,4‐dinitrophenyl (DNP)] poly(2‐methoxystyrene) Functional Polymers. Initial Evaluation of the Interaction of the Functional Polymers with RBL Mast Cells

Two series of functional polymers, α,ω‐bi[2,4‐dinitrophenyl][poly(ethylene oxide)‐b‐poly(2‐methoxystyrene)‐b‐poly(ethylene oxide)] (DNP‐PEO‐P2MS‐PEO‐DNP) and α,ω‐bi[2,4‐dinitrophenyl caproic][poly(ethylene oxide)‐b‐poly(2‐methoxystyrene)‐b‐poly(ethylene oxide)] (CDNP‐PEO‐P2MS‐PEO‐CDNP), were synthesized by anionic living polymerization. The polymers were characterized by FT‐IR, ¹H‐NMR and Gel Permeation Chromatography (GPC). The molecular weight distributions for the lower molecular weight functional polymers were slightly broad (1.3–1.5). However, the molecular weight distributions for higher molecular weight polymers were narrower (1.1–1.2). Differential scanning calorimetry (DSC) studies showed thermal transitions indicative of the presence of microphases in the polymer solid state. The polymers were white powders and soluble in tetrahydrofuran. The binding affinity of DNP‐PEO‐P2MS‐PEO‐DNP ligands towards anti DNP IgE was determined by titrations with fluorescently labeled FITC‐IgE. A water soluble CDNP‐PEO‐P2MS‐PEO‐CDNP/DMEG (dimethoxyethylene glycol) complex binds and achieves steady state binding with solution IgE within a few seconds. This strongly suggests that CDNP functional polymers with improved water solubility have potential in therapeutics. Higher molecular weight (water insoluble) CDNP‐PEO‐P2MS‐PEO‐CDNP polymers were electrosprayed as fibers (500 nm) on silicon surface. Fluorescence spectroscopy clearly showed that RBL mast cells were interacting with the fibers suggesting that the cell‐surface receptors were clustered along the fiber surface. These observations suggest that the functional polymers hold promise for developing an antibody detection device.     

DETERMINATION OF BRANCHING DISTRIBUTION IN HIGH cis-1,4-POLYBUTADIENE BY GPC AND AUTOMATIC VISCOMETRY

Based on the methods reported by Ambler and Kraus, a method has been developed for the determination of long-chain branching distribution in polymers by the combined use of GPC and intrinsic viscosity data of polymer fractions. In this method, g_i, λ_i, G_i, m_i, the weight percentage of polymer that is branched, etc. can be used simultaneously to characterize the distribution, degree and content of branching in polymers. Some relations between molecular weight polydispersity and branching polydispersity in Nickel-based high cis-1,4-polybutadiene samples are discussed. It was found that the number of long branches λ. per unit molecular weight is a function of molecular weight and all of the samples are highly branched at a molecular weight of about 10~6.     

Calibration in High Temperature Gel Permeation Chromatography of Linear Polyethylenes

Abstract

The mathematical relationship between the gel permeation chromatography calibration curves of polystyrene and linear polyethylene has been determined in 1,2,4-trichlorobenzene at 130, 135 and 140°C. The experimentally determined relationship is in good agreement with that predicted from application of the principles of the universal calibration technique and published Mark-Houwink coefficients. Definition of this relationship enables the use of polystyrene as a secondary standard for gel permeation chromatographic determination of linear polyethylene molecular weight determinations.     

Grafted Polymeric Microspheres: A Synthetic Approach to Structurally Well-Defined Brush Polymers

Abstract

A simple method for the surface grafting of crosslinked polystyrene latex particles of narrow size distribution as core is described. Amino groups were generated on the surface of these microspheres by a two-step process of nitration and subsequent reduction. Polyethylene glycol chain of desired molecular weight was covalently linked to the surface amino group using diiso-cyanate-coupling reaction. The method is appropriate for designing brush polymers.

     

Determination of Compositional Heterogeneity of Polyamide Copolymers

Abstract

A gel permeation chromatograph equipped with dual detectors provides very useful information on compositional and molecular weight distributions. One copolymer composed of nylon 12 and polytetramethylene ether glycol, and the other of nylon 6 and natural rubber were discussed in this study. By trifluoroacetylation of the amide group, these polymers became soluble in common solvents such as dichlcromethane and tetrachloroethane. Good chromatograms were obtained using these solvents for the above copolymers. At the same time, the compositional heterogeneity was determined from the chromatograms obtained with refractive index and ultraviolet detectors.     

Data Treatment in Aqueous GPC with On-Line Viscometer and Light Scattering Detectors

Abstract

Gel Permeation Chromatography (GPC) is becoming a very powerful tool for polymer characterization with the coupling of mass detectors using viscometry and light scattering techniques. The triple coupling seems to be the best way since the light scattering detector gives absolute molecular weights and viscometric detection provides intrinsic viscosity, leading to absolute molecular weights through universal calibration and information on long-chain branching. However, instrumentation becomes more sophisticated, expensive and, simultaneously, very sensitive to several parameters which are not critical in classical GPC. Moreover, an on-line computer is required for data acquisition and appropriate software for reliable interpretation of chromatograms.

Our experiments were performed with a Waters Associates room temperature instrument in which a home-made continuous viscometer, using pressure transducers, and a light scattering detector (LALLS Chromatix-CMX 100) were inserted on-line between the column set and the refractometer. Data were interpreted through personal software written on HP9836 and PC-AT computers.

We describe, here, the behavior of some polymers in aqueous solutions, mainly those that are commonly used as calibration standards (polyethylene oxides, pullulans). Experiments were run using two different sets of columns (‘Ultrahydrogel’ from Waters Associates and ‘Shodex OH-Pak’ from Showa Denko K.K.) in several aqueous solvents, pure water or water with various salts (LiNO₃, NaNO₃, LiCl, NaCl, Na₂SO₄) at different concentrations. Intrinsic viscosities were determined through viscometric detection and weight average molecular weights through the LALLS detector, leading to a plot of universal calibration curves Log([ηl.M) versus elution volumes.     

Rare Earth Metal-Initiated Polymerizations of Polar and Nonpolar Monomers

Abstract

Organolanthanide(III) initiated polymerization of methyl methacryate gave both syndiotactic and isotactic living polymers of high molecular weight. Organolanthanide(III) initiated polymerization of alkyl acrylates also gave high molecular weight poly(alkyl acrylate)s with very narrow molecular weight distribuion in high yield. Molecular weights of the resulting polymers increased linearly with the conversion. Random and block copolymerizations of alkyl acrylates with methyl methacrylate were realized successfully. For the sake of development of the olefin polymerization catalyst, bulky substituents were introduced into Me₂Si bridged Cp rings and they were used as ligands for the lanthanide complexes. Tri- and divalent lanthanide complexes with such ligands showed high activity for olefin polymerization and gave high molecular weight polyolefins.