Detection of low levels of long‐chain branching in polydisperse polyethylene materials

Creep experiments have been applied to probe the zero‐shear viscosity, η₀, of polyethylene chains directly and precisely in a constant‐stress rheometer at 190°C. Such experiments, when combined with precise measurements of the weight‐average molecular weight, M_w, calibrated relative to linear chains of high‐density polyethylene, are shown to provide a very sensitive approach to detect low levels (0.005 branches per 1000 carbons) of long‐chain branching (LCB). This detection limit is shown to be insensitive to whether the molecular weight distribution (MWD) breadth, M_w/M_n, rises from about two to ten. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Light‐scattering study of poly(hydroxy ester ether) in N,N‐dimethylacetamide solution

Static and dynamic light‐scattering techniques were used to study biodegradable thermoplastic poly(hydroxy ester ether) in N,N‐dimethylacetamide (DMAc). A weight‐average molecular weight M_W = 6.4 × 10⁴ g/mol, radius of gyration R_G = 9.4 nm, second‐virial coefficient A₂ = 1.05 × 10^?3 mol mL/g², translational diffusion coefficient D = 1.34 × 10^?7 cm²/s, and hydrodynamic radius R_H = 8.3 nm are reported. In addition, the effect of H₂O on the polymer chain's conformation and architecture in a DMAc/H₂O solution is evaluated. Results suggest that H₂O makes the mixed solvent poorer as well as promotes polymer chain branching via intramolecular transesterification. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1737–1745, 2001     

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.     

New fluorine‐containing bissalicylidenimine–titanium complexes for olefin polymerization

Three new titanium complexes bearing salicylidenimine ligands—bis[(salicylidene)‐2,3,5,6‐tetrafluoroanilinato]titanium(IV) dichloride ( 1 ), bis[(3,5‐di‐tert‐butylsalicylidene)‐2,3,5,6‐tetrafluoroanilinato]titanium(IV) dichloride ( 2 ), and bis[(3,5‐di‐tert‐butylsalicylidene)‐4‐trifluoromethyl‐2,3,5,6‐tetrafluoroanilinato]titanium(IV) dichloride ( 3 )—were synthesized. The catalytic activities of 1 – 3 for ethylene polymerization were studied with poly(methylaluminoxane) (MAO) as a cocatalyst. Complex 1 was inactive in ethylene polymerization. Complex 2 at a molar ratio of cocatalyst to pre catalyst of Al_MAO/Ti = 400–1600 showed very high activity in ethylene polymerization comparable to that of the most efficient metallocene complexes and titanium compounds with phenoxy imine and indolide imine chelating ligands. It gave linear high‐molecular‐weight polyethylene [weight‐average molecular weight (M_w) ≥ 1,700,000. weight‐average molecular weight/number‐average molecular weight (M_w/M_n) = 4–5] with a melting point of 142°C. The ability of the 2 /MAO system to copolymerize ethylene with hexene‐1 in toluene was analyzed. No measurable incorporation of the comonomer was observed at 1:1 and 2:1 hexene‐1/ethylene molar ratios. However, the addition of hexene‐1 had a considerable stabilizing effect on the ethylene consumption rate and lowered the melting point of the resultant polymer to 132°C. The 2 /MAO system exhibited low activity for propylene polymerization in a medium of the liquid monomer. The polymer that formed was high‐molecular‐weight atactic polypropylene (M_w ～ 870,000, M_w/M_n = 9–10) showing elastomeric behavior. The activity of 3 /MAO in ethylene polymerization was approximately 70 times lower than that of the 2 /MAO system. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1040–1049, 2005     

Polymer Network Mobility and Environmental Stress Cracking Resistance of High Density Polyethylene

Zero shear viscosity and molecular weight between entanglements (M _e ) are determined from dynamic oscillatory shear experiments. Lower M _e value means higher number of entanglements in the system and is associated with increasing strain hardening stiffness. With the understanding that strain hardening is related to environmental stress cracking resistance (ESCR) of high density polyethylene (HDPE), M _e is then related to the ESCR of several resins in this study. The inversely proportional relationship between M _e and ESCR indicates that low network mobility due to an increasing number of chain entanglements increases the ESCR of HDPE.     

Study on biodegradable polymer materials based on poly(lactic acid). I. Chain extending of low molecular weight poly(lactic acid) with methylenediphenyl diisocyanate

Methylenediphenyl diisocyanate (MDI) was used as the chain extender for low molecular weight poly(lactic acid) (PLA) to produce high molecular weight biodegradable polymer material with a better heat resistance. PLA prepolymer with a number‐average molecular weight (M_n) of 5800 and a weight‐average molecular weight (M_w) of 9800 was produced by direct polycondensation using stannous octoate as the catalyst. After 40 min of chain extension at 175°C, the resulting polymer had a M_n of 15,000 and a M_w of 57,000. The glass transition temperature (T_g) of the low molecular weight PLA prepolymer was 48.6°C. After chain extension, the T_g of the resulting polymer was raised to 67.9°C, as determined by DSC. DMA results also indicate that the heat resistance was improved by the chain extension. The DSC spectrum and X‐ray diffraction pattern of annealed samples showed that both the crystallinity and rate of crystallization of PLA were lowered by chain‐extension reaction due to the formation of branched molecular structure. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2546–2551, 1999     

Effect of network morphology on adhesive performance in emulsion blends of acrylic pressure sensitive adhesives

High-gel containing latices and gel-free latex were blended at various weight ratios. The high-gel containing latices was made of poly(2-ethyl hexylacrylate-stat-acrylic acid) and the gel-free latex was made of poly(2-ethyl hexylacrylate-stat-acrylic acid-stat-isobutoxymethyl acrylamide) using semicontinuous emulsion polymerization. Films were cast at room temperature and dried at 121°C for 10 min. Adhesive performance was evaluated in terms of loop tack, peel, and shear holding power. It was found that interlinking the microgels by the linear polymer due to the isobutoxymethyl acrylamide-acrylic acid reaction in the film when heated gave synergistic effects in increasing shear. This interlinking could take place only if the molecular weight between crosslinks (M_c) of the microgels was greater than the entanglement molecular weight of the linear polymer (M_e), and if the weight average molecular weight of the linear polymer (M_w) was greater than 2 × M_e. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2109–2117, 2001     

PLGA based drug delivery systems (DDS) for the sustained release of insulin: insight into the protein/polyester interactions and the insulin release behavior

BACKGROUND: Drug delivery systems (DDS) were designed using insulin as model drug and poly (lactic–co‐glycolic) copolymers (PLGA) as polymeric matrix. The carriers were synthesized by direct self‐assembly of the insulin and the polyester under mild conditions. RESULTS: The kind and level of association between the protein and the polymer were studied using computational methods (combined MM2/PM3) and spectroscopic tools (Fourier transform infrared (FTIR), energy dispersive X‐ray (EDX) and X‐ray fluorescence spectroscopy (XFS)). The effect of the number average molecular weight (M_n) of the copolymer on the association efficiency (AE) drug–polymer as well as on the release profile has been explored. Mathematical models were used to predict the insulin release kinetic and mechanism. CONCLUSIONS: Satisfactory protein/PLGA association efficiencies (between 77 and 99%) were registered depending on the M_n of the PLGA. Hydrophobic and hydrophilic interactions were detected between the protein and the polymeric network by computational analysis. In vitro release studies demonstrated that copolyesters of about 8600 and 1500 Da were suitable for the gradual release of insulin while PLGA oligomers of average molecular weight between 700 and 800 Da were unsuitable as DDS. The insulin release kinetics fits well with the Korsmeyer model, following the anomalous transport mechanism. Copyright © 2010 Society of Chemical Industry     

Water‐soluble polymers. LXXXIII. Correlation of experimentally determined drag reduction efficiency and extensional viscosity of high molecular weight polymers in dilute aqueous solution

The extensional viscosity for aqueous solutions of high molecular weight poly(acrylamide) copolymers and poly(ethylene oxide) homopolymers was measured using a laboratory‐designed screen extensional rheometer. A Bingham model was developed to estimate the average local polymer coil extensional viscosity (η_coil). A strong correlation was found between the measured η_coil values and the polymer extensional viscosity predicted by a bead‐spring model. The dilute aqueous solution drag reduction was measured with a rotating disk instrument under conditions minimizing the effects of shear degradation. Extensional viscosity and drag reduction measurements were performed in deionized water and in 0.514M sodium chloride. The relative drag reduction efficiency values (Δ) in both solvents were found to strongly correlate with measured η_coil values. This is the first report of the accurate prediction of drag reduction behavior for a wide range of polymer types in various solvents from the independently measured molecular parameters η_coil and [η]C. The often‐used relative drag reduction efficiency expressed as the product of [η]C and Δ can now be replaced by the absolute drag reduction efficiency [η]Cη_coil. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1222–1231, 2001     

Solvent diffusion in silica/poly[styrene‐co‐(acrylic acid)] core‐shell microspheres by pulsed field gradient NMR techniques

Polymer‐coated SiO₂ particles are prepared by precipitation of poly[styrene‐co‐(acrylic acid)] on SiO₂ microspheres through an improved phase inversion method. The diffusion resistance of the polymer membrane was considered to be the critical reason for producing tailor‐made polyethylene by catalysts supported on these polymer‐coated particles. This paper employs pulsed field gradient NMR (PFG‐NMR) to distinguish diffusion of n‐hexane in different regimes, i.e., in the space between each particle, the pores in SiO₂ and the polymer shell, by their respective diffusion coefficients. By varying the observation time, the time scale of the molecular exchange is discussed. A three‐region ansatz was used to interpret the exchange and diffusion in polymer‐coated SiO₂ system, and was compared with results acquired with noncoated particles. At long diffusion times, the mean‐squared displacement, and thus the averaged self‐diffusion coefficient, of hexane in the system of polymer‐coated SiO₂ particles is significantly reduced. The PSA membrane is identified as an efficient barrier against molecular exchange between the pores in SiO₂ and the intraparticle space. Consistently, the relaxation measurements indicated that the mobility of n‐hexane molecules, especially the rotation of n‐hexane, was limited by the PSA membrane. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40160.     

Relationship between the structure and mechanical properties of polypropylene: Effects of the molecular weight and shear‐induced structure

A series of homopolymer polypropylenes (PPs), within a weight‐average molecular weight (M_w) range of 100–1600 kg/mol, were manufactured as dumbbell microspecimens. The effects of the molecular weight and shear‐induced crystallization on the mechanical properties and morphology were studied to gain a better understanding of the structure–property relationship. The results showed that the crystallinity decreased from 50 to 41% and the lamellar thickness increased as M_w increased. Tensile tests demonstrated that the stiffness and especially the tensile strength rose to extremely high values (Young's modulus = 2400 N/mm², stress at 30% strain = 120 N/mm²). Furthermore, the strain hardening effect was strongly affected by the lamellar thickness and highly oriented superstructures. Dynamic mechanical analysis demonstrated that the mobility of the molecular chains depended on M_w and on the lamellar thickness. In addition, the viscoelastic properties of unannealed and annealed samples indicated further the existence of shish‐kebab structures caused by shear‐induced crystallization during injection molding. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 519–533, 2007     

Effects of the cosurfactant 1‐butanol and feed composition on nanoparticle properties produced by microemulsion copolymerization of styrene and methyl methacrylate

The concentration of the cosurfactant 1‐butanol (BuOH) determined the polymer weight and size for a series of poly(styrene‐co‐methyl methacrylate)s (P(St‐co‐MMA)) synthesized by the free‐radical (o/w) microemulsion technique. A factorial design established the levels of the experimental conditions for the polymerization i.e., concentration of the surfactant, sodium dodecyl sulfate (SDS); concentration of the cosurfactant, BuOH; temperature and ratio of the styrene (St) to methyl methacrylate (MMA). An increase in the weight‐average molecular weight (M_w) and number‐average molecular weight (M_n) was observed in the P(St‐co‐MMA) series with an increase in BuOH concentration from 1 to 5 wt %. These effects could arise from the micellar aggregation induced by interfacial BuOH. The unique micellar conditions could be exploited to synthesize copolymers of varying molecular weight and size. Additionally, the composition of the copolymers was virtually templates of the feed composition. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Ionic conductivity of solid polymer electrolytes for dye‐sensitized solar cells

We developed an ionic conductivity model of solid polymer electrolytes for dye‐sensitized solar cells (DSSCs) based on the Nernst–Einstein equation in which the diffusion coefficient is derived from the molecular thermodynamic model. We introduced concentration‐dependence of the diffusion coefficient into the model, and the diffusion coefficient was expressed by differentiating the chemical potential by concentration. The ionic conductivities of polymer electrolytes (PEO/LiI/I₂ system) were investigated at various temperatures and compositions. We prepared a set of PEO in which an EO : LiI mole ratio of 10 : 1 was kept constant for PEO·LiI·(I₂)_n compositions with n = 0.02, 0.05, 0.1, 0.15, 0.2, and 0.3 (mole ratio of LiI : I₂). The ionic conductivities of the electrolytes were measured using a stainless steel/polymer‐electrolyte/stainless steel sandwich‐type electrode structure using alternating current impedance analysis. The values calculated using the proposed model agree well with experimental data. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Experimental investigation of flow induced molecular weight fractionation during extrusion of HDPE polymer melts

In this work, two different HDPEs with virtually identical number, M_n, and weight, M_w, average molecular weights were investigated from rheological as well as die drool phenomenon point of view. It has been revealed that long-chain branching, low polymer melt elasticity and shear viscosity significantly reduce die drool phenomenon at the die exit region. It has been concluded that die drool phenomenon of HDPE polymer melts can be explained by the flow induced molecular weight fractionation.     

Diffusion behavior of poly(ethylene imine) into keratin fibers using microspectrophotometry

In order to investigate the diffusion behavior of poly(ethylene imine) (PEI) into keratin fibers, cross‐sectional samples of bleached white human hair treated with PEI were prepared. We were successful in developing a method for analyzing the diffusion behavior of PEI into human hair, which to our knowledge is a first. The diffusion pattern of PEI into human hair, which cannot be determined by optical microscopy, can be determined by our method. After the treatment, the cross‐sectioned hair samples were dyed with Orange II and the cross‐sectional intensity scans were measured at a wavelength of 487 nm (λ_max of Orange II) with a microspectrophotometer. In our method, the diffusion pattern of PEI at pH 11.1 showed Fickian type characteristics. This suggests that the diffusion coefficient of PEI is essentially independent of the PEI concentration. By calculating the diffusion coefficient from the PEI concentration profile, the diffusion coefficient of PEI [number‐average molecular weight (M_n) = 300 and 600] into the bleached human hair was found to be on the order of 10^?10 cm²/s. In addition, the diffusion coefficient of PEI (M_n = 600) with urea added increased twofold in comparison with that of PEI without urea added. This experiment demonstrated that urea acts as a penetration accelerator for PEI. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 65–71, 2005     

The effect of shear rate on the molecular weight determination of acrylamide polymers from intrinsic viscosity measurements

The rheological response of dilute solutions of high molecular weight polyacrylamides at low shear rates has been measured using a capillary viscometer that provided for a fivefold variation in shear rate at each concentration. The non-Newtonian effects were found to be significant for polyacrylamides with number-average molecular weights exceeding 10⁶. The molecular weight average–intrinsic viscosity relationship most widely used in the literature, [η] = 6.80 × 10^?4M , was found to be valid when [η] was measured at high shear rates where the polymer solutions approached Newtonian behavior. A new relationship was developed relating M _n to the intrinsic viscosity extrapolated to zero shear rate.     

Visible‐light‐induced controlled/living radical polymerization of styrene with a phenyl seleno group at one terminal chain end: 1‐(Phenylseleno)ethyl benzene as a photoiniferter

The photopolymerization of styrene with a well‐defined molecular architecture and a low polydispersity index and with methyl and phenylseleno (? SePh) groups at α‐ and ω‐chain ends, respectively, was performed via a controlled/living radical polymerization with a new initiating system, 1‐(phenylseleno)ethyl benzene/tert‐butyl diphenyl (phenylseleno) silane, through the absorption of visible light at room temperature. A novel initiating living radical polymerization was examined. The yield and number‐average molecular weight (M_n) of the resulting polymer increased with the reaction time. Furthermore, a linear relationship was found in a plot of M_n versus the polymer yield. These results indicated that this polymerization proceeded through a living radical mechanism. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 348–355, 2004     

Schiff base‐substituted polyphenol: synthesis,characterisation and non‐isothermal degradation kinetics

BACKGROUND: Polymers of phenols and aromatic amines have emerged as new materials in fields such as superconductors, coatings, laminates, photoresists and high‐temperature environments. The stability, kinetics and associated pollution of the thermal decomposition of oligophenols are of interest for the aforementioned fields. RESULTS: A new Schiff base polymer, derived from N,N′‐bis(2‐hydroxy‐3‐methoxyphenylmethylidene)‐2,6‐pyridinediamine, was prepared by oxidative polycondensation. Characterisations using Fourier transform infrared, UV‐visible, ¹H NMR and ¹³C NMR spectroscopy, thermogravimetric/differential thermal analysis, gel permeation chromatography, cyclic voltammetry and conductivity measurements were performed. The number‐average (M_n) and weight‐average molecular weight (M_w) and dispersity (D = M_w/M_n) of the polymer were found to be 61 000 and 94 200 g mol^?1 and 1.54, respectively. Apparent activation energies of the thermal decomposition of the polymer were determined using the Tang, Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose and Coats–Redfern methods. The most likely decomposition process was a D_n deceleration type in terms of the Coats–Redfern and master plot results. CONCLUSION: The mechanism of the degradation process can be understood through the use of kinetic parameters obtained from various non‐isothermal methods. Copyright © 2009 Society of Chemical Industry     

Propylene oligomers: extraction methods and characterization by FTIR,HPLC, and SEC

Propylene oligomers were isolated from polymer matrix by dissolution precipitation and Soxhlet methods and characterized by Fourier transform infrared spectrometry, ultraviolet, high‐performance liquid chromatography, and gel permeation chromatography. Both extracts showed that these hydrocarbon chemicals have a maximal absorption at 210 nm and are eluted from a C8 column with a strong mobile phase (tetrahydrofuran). However, their average molecular weights are different depending upon the quality of extraction: the fraction obtained by the dissolution‐precipitation method is homogeneous in molecular weight, whereas the one obtained by Soxhlet extraction has a higher polydispersity index (M_n /M_w ). The specific migration test of propylene oligomers in a food simulant (isooctane) shows total diffusion within 60 min. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 371–375, 1999