Dynamic light-scattering characterization of the molecular weight distribution of a broadly distributed phenolphthalein poly(aryl ether ketone)

Using a recently developed laser light-scattering (LLS) procedure, we accomplished the characterization of a broadly distributed unfractionated phenolphthalein poly(aryl ether ketone) (PEK-C) in CHCl₃ at 25°C. The laplace inversion of precisely measured intensityintensity time correlation function from dynamic LLS leads us first to an estimate of the characteristic line-width distribution G(T) and then to the translational diffusion coefficient distribution G(D). By using a previously established calibration of D (cm²/s) = 2.37 ×10⁻⁴M^−0.57, we were able to convert G(D) into a differential weight distribution f_w(M). The weight-average molecular weight M_w calculated from f_w(M) agrees well with that directly measured in static LLS. Our results indicate that both the calibration and LLS procedure used in this study are ready to be applied as a routine method for the characterization of the molecular weight distribution of PEK-C. © 1996 John Wiley & Sons, Inc.     

High-temperature dynamic laser light-scattering characterization of polyethylene in trichlorobenzene

Polyethylene samples were characterized in trichlorobenzene at 135°C by high-temperature dynamic laser light scattering (LLS). Precise measurements of the intensity-intensity time correlation function permit us to make a Laplace inversion to obtain an estimate of the normalized translational diffusion coefficient distribution [G(D)]. After establishing a calibration between the translational diffusion coefficient (D) and molar mass, by using six moderately dispersed polyethylene samples, we were able to transform G(D) to molecular weight distribution (MWD), and to calculate the weight average molecular weight (M_w), which weights were comparable with the ones obtained by using static LLS and size exclusion chromatograph (SEC). The advantages and limitations of using dynamic LLS as a routine method to characterize of polyethylene are discussed. © 1993 John Wiley & Sons, Inc.     

Dynamic light‐scattering characterization of the molecular weight distribution of unfractionated polyimide

Using a developed laser light‐scattering (LLS) procedure, we accomplished the characterization of an unfractionated polyimide (UPI) in CHCl₃ at 25°C. The Laplace inversion of precisely measured intensity–intensity time correlation function from dynamic LLS leads us first to an estimate of the characteristic line‐width distribution G(Γ), and then to the translational diffusion coefficient distribution G(D). By using a previously established calibration of D (cm²/s) = 3.53 × 10^?4 M^?0.579, we were able to convert G(D) into a molecular weight distribution. The weight‐average molecular weight M_w, calculated from the molecular weight distribution, agrees well with that directly measured in static LLS. Our results indicate that both the calibration and LLS procedure used in this study are ready to be applied as a routine method for the characterization of the molecular weight distribution of polyimide. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1670–1674, 2001     

Determination of the absolute molecular weight of a styrene–butyl acrylate emulsion copolymer by low-angle laser light scattering (LALLS) and GPC/LALLS

The application of low-angle laser light scattering (LALLS) and combined GPC/LALLS for the measurement of absolute molecular weight distribution of a styrene–butylacrylate (30/70) emulsion copolymer is discussed. From the static light scattering measurements in four different solvents, i.e., toluene, tetrahydrofuran (THF), methyl ethyl ketone (MEK), and dimethylformamide (DMF), the true weight average molecular weight (M _w) and heterogeneity parameters are determined. The apparent M _w obtained from the static measurement in THF was in good agreement with the M _w determined from the multiple solvent analysis, suggesting the validity of using THF as the mobile phase in the combined GPC/LALLS analysis.     

Characterization of novel thermoplastic polymers with phenolphthalein in their backbone chains

Different molecular weight phenolphthalein poly(ether ketone) (PEK-C) and phenolphthalein poly(ether sulfone) (PES-C) fractions in chloroform (CHCl₃) were studied by static and dynamic laser light scattering (LLS). The dynamic LLS revealed that both the PEK-C and PES-C samples contain some large polymer clusters formed in the process of polymerization. These large clusters can be removed by filtering the solution with a 0.1-μm filter. The positive second virial coefficient (A₂) shows that CHCl₃ is a good solvent for these polymers at room temperature. The persistence length and the Flory characteristic ratio of these polymers in CHCl₃ at 25°C are ～2 nm and ～3, respectively, which indicate that these polymer chains are flexible. A combination of static and dynamic LLS results, namely the weight-average molecular weight from static LLS and the line-width distribution from dynamic LLS, lead to two calibrations between the translational diffusion coefficient (D) and molecular weight (M): D = 2.20 × 10^?4 M^?0.56 for PEK-C and D = 2.45 × 10^?4 M^?0.55 for PES-C in CHCl₃. Using these calibrations, we are able to estimate not only the molecular weight distributions of these fractionated polymers, but also unfractionated PEK-C and PES-C samples.     

Study of segmented ethylene terephthalate–caprolactone copolymer by differential refractometry and light scattering

A segmented ethylene terephthalate (ET)–caprolactone (CL) copolymer was characterized by light scattering in chloroform tetrahydrofuran and butanone. The flexibility of the copolymer chain is comparable with that of typical flexible chains, such as polystyrene. In the process of applying the Bushuk–Benoit light scattering theory to the segmented PET–PCL copolymer, we encountered not only the problem of finding three solvents with different refractive index but also the problem of determining the specific refractive index increments for the PET and PCL segments in the copolymer, i.e., ν_PET and ν_PCL . In principle, the approximate values of ν_PET and ν_PCL can be obtained from the PET and PCL homopolymers, respectively. In reality, it involves many practical problems, e.g., to find three solvents not only for copolymer but also for the PET and PCL homopolymers. In this study, a different method was used to find both ν_PET and ν_PCL , wherein the ν values of at least two segmented PET–PCL copolymers with different PET compositions were used. With ν_PET , ν_PCL , and ν, we characterized the absolute molecular weight. Further, we show that the composition of an unknown segmented PET–PCL copolymer can be estimated from ν_PET , ν_PCL , and ν. © 1994 John Wiley & Sons, Inc.     

Molecular weight influence on shape memory effect of shape memory polymer blend (poly(caprolactone)/styrene-butadiene-styrene)

The shape memory effect (SME) does not only concern the macroscopic structure. It concerns also the polymer structure at morphological, macromolecular, and molecular scales. This effect may depend on different physicochemical properties like morphology heterogeneity, chain rigidity, steric hindrance, chain polarity, free volume, cross-linking or entanglement density, molecular shape and weight, and so on. Hence, finding the relationship between the SME and these properties is very important. This can help to obtain the knowledge about the phenomenon origin and mechanism. One of the basic polymer properties, which can have direct SME, may be the molecular weight (M_w ). The question here is: If the M_w of a shape memory polymer (SMP) changes, for different reasons like degradation, what will be the effect of this change on its SME. In order to answer to this question, the investigation is focused on an SMP blend of 40% poly(ɛ-caprolactone) (PCL) and 60% styrene-butadiene-styrene (SBS). Then, enzymatic hydrolysis is performed on this blend to change its M_w . It is shown that this change is only related to the variation in the M_w of PCL. After that, different samples with a distinct average M_w are prepared and characterized by various experimental methods. Shape memory tests are performed on these blends, and the recovery rate (R_r ) for each of them is determined. It is found that when M_w of PCL decreases, its degree of crystallinity, its glass transition, and its melting temperatures, corresponding to the PCL phase, increase. However, the elongation at break of the blend declines with the reduction in M_w . The tests show that the alteration in the blend's M_w influences its SME. Indeed, R_r of the (PCL/SBS) mixture drops with the decrease in M_w of PCL.     

Light scattering characterization of poly(tetrafluoroethylene‐co‐perfluoromethyl vinyl ether) copolymer

Static and dynamic light scattering experiments were performed to characterize the copolymer of tetrafluoroethylene (TFE) and perfluoromethyl vinyl ether (PMVE). Solvents of perfluoro‐2‐butyltetrahydrofuran (FC‐75) and Flutec PP11 (PP11) were used to dissolve the TFE‐PMVE copolymer. By taking advantage of the solvent properties of FC‐75 and PP11, homogeneous TFE‐PMVE copolymer solutions were specially prepared in a FC‐75/PP11 mixed solvent. Such prepared solutions could provide a strong enough scattered intensity for light scattering studies. The molecular weight, molecular weight distribution, chain dimensions, and conformation were determined for the TFE‐PMVE copolymer in the FC‐75/PP11 mixed solvent. A combination of viscosity and molecular weight measurements enabled the calculation of the k value in the relation of η₀ = k (M_w)^3.4 and thus the prediction of the molecular weight of a given TFE‐PMVE copolymer with the same composition by using only the simpler and more readily available rheological measurements. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 733–739, 2000     

Characterization of spherical microlatex particles made of linear uncrosslinked polystyrene chains

Laser light scattering (LLS), including both angular dependence of the absolute scattering intensity (static LLS) and of the line-width distribution G(Γ) (dynamic LLS), were used to characterize two kinds of pauci-chain polystyrene (PCPS) microlatices (latex-1 and latex-2). Each PCPS particle contains only a few linear uncrosslinked polystyrene chains. In static LLS, the weight-average particle molar mass (M_w) was measured; and simulataneously in dynamic LLS, the diffusion coefficient distribution was obtained from Laplace inversion of precisely measured intensity-intensity time correlation function. Our results reveal that, on average, latex-1 and latex-2 contain ∼13 and ∼7 linear polystyrene chains, resp. A combination of both static and dynamic LLS results enables us to calculate the average density of PCPS. Our results have also shown that the particle density of latex-1 and latex-2 are 0.90 and 0.80 g/cm³, respectively, which are lower than the density of conventional polystyrene latex particles or bulk polystyrene. Our results imply that the particle density decreases as the average number of polystyrene chains inside the particles decreases.     

Solid‐state polymerization of poly(ethylene terephthalate): Effect of organoclay concentration

Poly(ethylene terephthalate) (PET)/Cloisite 30B (C30B) nanocomposites of different organoclay concentrations were prepared using a water‐assisted extrusion process. The reduction of the molecular weight (M_w) of the PET matrix, caused by hydrolysis during water‐assisted extrusion, was compensated by subsequent solid‐state polymerization (SSP). Viscometry, titration, rheological, and dynamic scanning calorimetry measurements were used to analyze the samples from SSP. The weight‐average molecular weight (M_w) of PET increased significantly through SSP. PET nanocomposites exhibited solid‐like rheological behavior, and the complex viscosity at high frequencies was scaled with the M_w of PET. The Maron–Pierce model was used to evaluate the M_w of PET in the nanocomposites before and after SSP. It was found that the extent and the rate of the SSP reaction in nanocomposites were lower than those for the neat PETs, due to the barrier effect of clay platelets. Consequently, the SSP rate of PET increased with decreasing particle size for the neat PET and PET nanocomposites. The effect of the M_w of PET on the crystallization temperature, crystallinity, and the half‐time, t_½, of nonisothermal crystallization was also investigated. With increasing M_w of PET, t_½ increased, whereas T_c and X_c decreased. POLYM. ENG. SCI., 54:2925–2937, 2014. © 2014 Society of Plastics Engineers     

The phase behavior and the Flory-Huggins interaction parameter of blends containing amorphous poly(resorcinol phthalate-block-carbonate), poly(bisphenol-A carbonate) and poly(ethylene terephthalate)

The phase behavior of the blends of poly(ethylene terephthalate) (PET) and poly(Resorcinol Phthalate-block-Carbonate) (RPC) and the blends of PET and poly(Bisphenol-A Carbonate) (PC) was investigated by dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). Blends of high molecular weight PET and RPC copolymer with 20 mol% resorcinol phthalate (RPC20) showed two glass transition temperatures in DMA and DSC but the cold crystallization rate of PET phase was substantially lowered as compared to neat PET, indicating partial miscibility at all compositions. The RPC20 with M_w = 31,500 g/mol formed miscible blends with PET when PET has weight-average molecular weight <9500 g/mol. The Flory-Huggins interaction parameter between PET and RPC20 was calculated to be 0.029 ± 0.003 by using the Flory-Huggins equation at critical composition and molecular weight. PC with M_w = 30,000 g/mol formed miscible blends with PET only when PET had molecular weight <2800 g/mol, indicating PC/PET blends were much less miscible than RPC20/PET blends. Group contribution methods agreed well with the experimental results obtained both in the present study and a previous study [1], predicting that the addition of a resorcinol phthalate block to a PC backbone should increase the miscibility of PC and PET.     

Apparent and Real Distribution in GPC (Experiments with PMMA Samples)

Abstract

Molecular weight distribution curves obtained by GPC are broadened if concentration and flow rate are fixed in the usual range. Therefore, the apparent nonuniformity U _app of the samples is larger than the real non-uniformity U = (M_w/M_n) ?1. For a number of fractionated and unfractionated samples of polymethyl methacrylate we determined M _n and M _w by osmotic, light-scattering, and viscosity measurements. Thus, the real value of U can be compared to U _app obtained by GPC at different concentrations and flow rates, υ. The excess nonuniformity U _exc is evaluated as function of concentration c, polydispersity, molecular weight, and flow rate. For c = 0 and υ = 0, U _exc is not far from zero. For standard conditions one certain value of the excess standard deviation of the elution volume allow calculation of U _exc for narrow and broader distributions and the obtaining of nearly correct values for the real nonuniformity U.     

Synthesis and characterization of water-based poly(vinyl acetate-co-butyl acrylate) latexes containing oligomeric protective colloid

Poly(vinyl acetate-co-butyl acrylate) latexes having oligomeric N-methylol acrylamide were prepared by semi-continuous emulsion polymerization. The effects of new protective colloid and comonomer ratios on the physicochemical and colloidal properties of latexes were investigated. The changes in homopolymer and copolymer latexes were determined by measuring viscosity, particle size, molecular weight (MW), molecular weight distribution (MWD), and surface tension. [`(M)]<sub>n</sub> \bar{M}_{n} values of copolymer latexes were found to be lower than the MWs of the poly(vinyl acetate) and poly(butyl acrylate) homopolymers. In general, [`(M)]_n \bar{M}_{n} and [`(M)]_\textw \bar{M}_{\text{w}} values of copolymer latexes changed irregularly with increasing BuA ratio in the copolymer composition.     

Light-scattering and size-exclusion chromatographic characterization of hydroxyethyl cellulose acetate

A recently developed analytical method of combining off-line laser light scattering (LLS) and size exclusion chromatography (SEC) was used to investigate a set of moderately distributed hydroxyethyl cellulose acetate (HECA) samples in tetrahydrofuran (THF) at room temperature. Our results have shown that this new LLS + SEC method is suitable for the characterization of molecular weight distribution of HECA. By using this method, we have simultaneously determined two calibrations of V (cm³) = 45.3 ? 1.89 log (M) and D (cm²/s) = 2.45 × 10^?4 M^?0.60, where M is the molecular weight of HECA; V, the elution volume in SEC; and D, the translational diffusion coefficient in dynamic LLS. In addition, our results have also indicated that the chain conformation of HECA in THF at room temperature is a slightly extended linear coil. © 1995 John Wiley & Sons, Inc.     

Molecular weight distribution of commercial PVC

The molecular weight distribution (MWD) of commercial suspension grade poly(vinyl chloride) (PVC) resins with K values from 50 to 93 and mass grade PVC resins with K values from 58 to 68 has been determined by size exclusion chromatography (SEC), using literature Mark‐Houwink coefficients. The MWD is characterized by the number average molecular weight (M_n), the weight average molecular weight (M_w) and the polydispersity (M_w/M_n). Our results for M_w are consistent with recently published data, but we find different results for M_n and consequently for M_w/M_n. The polydispersity of PVC increases with increasing K value. This effect can be explained by two mechanisms. The first mechanism is a reduced terminating reaction rate between two growing polymer chains (disproportionation) at higher molecular weight owing to the reduced mobility of the polymer chains. The second mechanism is long‐chain branching of molecules with high molecular weight which lets the molecules grow at two ends. For two examples graphs of the measured MWD are compared with the theoretically expected MWD.     

Copolymer characterization by surface tension

The use of surface tension measurements is proposed as a simple method for the determination of copolymerization ratios. The procedure depends on the parachor of the copolymer in the liquid state (∏), which is defined by ∏ = ∏_s + ∏₀(w_p/w_s)(M_s/M₀) for solutions and ∏ = [DP]∏₀ for liquid or molten polymers, where ∏_s is the parachor of the solvent of molecular weight M_s; w_p and w_s are the weights of the polymer and solvent in solution; while ∏₀ and M₀ are the parachor and molecular weight of the repeating unit of the copolymer, respectively. The validity of this relationship is demonstrated by analysis of the surface tension properties of liquid silicone polymers, polystyrene–Decalin solutions, and molten polymers as well as by the calculation of the composition of some characterized tetrahydrofuran–propylene oxide copolymers. The application of surface tension measurement is also suggested as a means of estimating the degree of chain branching in a polymer.     

Molecular characterization and rheological properties of modified poly(ethylene terephthalate) obtained by reactive extrusion

The use of a tetrafunctional epoxy‐based additive to modify the molecular structure of poly(ethylene terephthalate) (PET) was investigated with the aim of producing PET foams by an extrusion process. The molecular structure analysis and shear and elongation rheological characterization showed that branched PET is obtained for 0.2, 0.3 and 0.4 wt% of a tetrafunctional epoxy additive. Gel permeation chromatography (GPC) analysis led to the conclusion that a randomly branched structure is obtained, the structure being independent of the modifier concentration. The evolution of shear and extensional behavior as a function of molecular weight (M_w), degree of branching, and molecular weight distribution (MWD) were studied, and it is shown that an increase in the degree of branching and M_w and the broadening of the MWD induce an increase in Newtonian viscosity, relaxation time, flow activation energy and transient extensional viscosity, while the shear thinning onset and the Hencky strain at the fiber break decrease markedly.     

Branched copolymers with biodegradable core and pendant oxirane groups

The reactive oxirane groups were incorporated into the macromolecule as substituents in the side chains of loosely‐grafted copolymer or in the arms of star‐shaped copolymer using glycidyl methacrylate (GMA) in the controlled atom transfer radical polymerization (ATRP). The branched GMA copolymers with various architectures were obtained by using hydrophobic copolymers containing six and seven units of caprolactone 2‐(methacryloyloxy)ethyl ester (CLMA) functionalized with bromoester groups, and trifunctional poly(ε‐caprolactone) (PCL), as well as hydrophilic tri‐, and six‐functional acetal derivatives of D ‐glucopyranosides as (macro)initiators with biodegradable and biocompatible properties. The well‐defined copolymers with core‐shell structures and polymerization degrees of GMA in the range of 20–100 per side chain/arm at 20–70% of monomer conversion within 1–6 h and narrow molecular weight distributions (M_w/M_n = 1.14–1.4) were obtained. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Calculation method of molecular weight averages in polymerization with chain-length-dependent termination

A systematic method for calculating the molecular weight distribution moments in free radical polymerization where termination rate depends on the size of the participating radicals, is presented. The central part of the method is the evaluation of the distribution of termination rates in the balance equations. From an adopted functional form of the termination rate constant, the moment equations are derived. For evaluating the moments of the termination rate distribution an approximate reconstruction of the radical chain length distribution using Laguerre polynomials is proposed. The calculation method can handle termination by disproportionation and combination simultaneously and allows easily to take into account diffusioncontrolled initiation, propagation and chain transfer reactions. The usefulness of the method is illustrated by simulating the bulk polymerization of methyl methacrylate and styrene. The calculated results of conversion, molecular weight averages (M _n,M _w,M _z and M _z+1) and polydispersity are in good agreement with the reported experimental data.     

Rheological properties of polypropylenes with different molecular weight distribution characteristics

Relationships between the rheological properties and the molecular weight distribution of two polypropylene series with different molecular weight distribution characteristics were studied. The end correction coefficient in capillary flow is determined by the molecular weight M_w and the molecular weight distribution M_w/M_n, and is higher as both characteristic values are larger. The die swell ratio at a constant shear rate depends on M_w, M_w/M_n, and M_z/M_w, and is higher as the three characteristic values are larger. The critical shear rate at which a melt fracture begins to occurs depends on the molecular weight M_w and the molecular weight distribution M_z/M_w, and is proportional to M_z/M_w² in a log–log plot. The critical shear stress does not depend on the molecular weight, and is higher as M_z/M_w is higher. The zero‐shear viscosity is determined by a molecular weight of slightly higher order than M_w, and the characteristic relaxation time is determined by M_z. The storage modulus at a constant loss modulus scarcely depends on the molecular weight, and is higher as the molecular weight distribution M_w/M_n is higher. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2128–2141, 2002