Poly(triacontamethylene triacontanedioate) as polyethylene analogue: Properties and enzymatic degradation

Diethyl triacontanedioate (CH₃CH₂O₂C(CH₂)₂₈CO₂CH₂CH₃) and triacontane- 1,30-diol (HO(CH₂)₃₀OH) were prepared and condensed to synthesize poly(triacontamethylene triacontanedioate) (PTRM). The properties of (PTRM) were compared with those of commercial low density polyethylene (LDPE), and enzymatic degradation of the PTRM was investigated. PTRM showed not only high melting point of 113°C and a thermal stability comparable to LDPE. The elongation at break is low (about 5%) and the tensile strength is around 12.5 MPa, higher than that of LDPE. The small contact angles indicate that PTRM has good wettability compared with LDPE. The increase of total organic carbon by Rhizopus arrhizus lipase and the resulting change of surface morphology confirmed that PTRM is biodegradable.     

Critical epitaxial layers of different kinds of polyethylene on highly oriented isotactic poly(propylene) substrates

Epitaxial crystallization of high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE) and low-density polyethylene (LDPE) in the epitaxial system with highly oriented isotactic poly(propylene) (iPP) has been investigated by electron microscopy. The results obtained by bright field electron microscopy and electron diffraction confirmed that all of the three kinds of PE (HDPE, LLDPE and LDPE) have the ability of epitaxy on iPP surfaces. There exists a critical thickness of the PE layer in which the PE can grow epitaxially on iPP substrates. When the PE/iPP layered films are heat-treated at a temperature above the melting temperature (T_m) of PE and below T_m of iPP for 10 min and then quenched to room temperature, the critical layer thickness of epitaxial HDPE, LLDPE and LDPE is about 250, 120 and 30 nm, respectively. For PE further apart from the interface, the epitaxial orientation becomes disturbed due to simultaneous spherulitic nucleation or lamellar twisting of the epitaxially grown lamellae.     

Modified affine law for the elastic and optical properties of low density polyethylene

A unified study of the anomalous mechanical properties and birefringence of low density polyethylene (LDPE) is attempted within the frame work of the rotating element model. The present paper investigates the validity of the affine transformation rule used in the Ward model and suggests a modified affine law which is based on the consideration that the units are only reoriented and, unlike the affine law, are not deformed due to the uniaxial stretching. The relationship between the angles made by the C-axis of the unit with the drawing direction in the undrawn state (θ) and the drawn state (θ), is deduced as sin θ = f(n) sin θ′. From the birefringence data of different polymers a two parameter relation of the form f (n) = exp [–(n – 1)^α/β] is suggested. Using this new orientation function, the agreement of the predicted values of E₀ and E₉₀ for LDPE for the entire draw ratio range between temperatures of 60°C to ?125°C, is quite satisfactory. An interesting feature is that the abrupt change in the values of the parameters α and β at two different temperatures may be associated with a phase transition of LDPE at an intermediate temperature.     

Long chain branching and solution properties of low density polyethylene

The intrinsic viscosity, osmotic pressure and light scattering of solutions of fractionated samples of low density polyethylene (LDPE) were measured to study its long chain branching. The following relation was obtained between the two branching indices: g_η is the ratio of the intrinsic viscosities of the branched and linear polymers with the same molecular weight, and g_s is the corresponding ratio of the radii of gyration. The average number of long branches per molecule, n_w, was calculated according to the theory of ZIMM and STOCKMAYER derived for random branching, and it was found that the dependence of n_w on the molecular weight is expressed by with α = 0.85. This relation indicates that the long branching frequency or density decreases gradually with molecular weight for LDPE.     

Dispersion Behavior of TiO2 Nanoparticles in LLDPE/LDPE/TiO2 Nanocomposites

Summary: TiO₂ nanoparticles were introduced into linear low‐density polyethylene (LLDPE)/low‐density polyethylene (LDPE) composite films in the form of master batch where TiO₂ was pre‐dispersed in LDPE by melt compounding. The dispersion behavior of TiO₂ nanoparticles was investigated by field‐emission scanning electron microscopy (FE‐SEM). The rheology results show that the viscosity of LDPE/TiO₂ master batch is lower than that of LLDPE/LDPE composites. Energy dispersive X‐ray spectrometer (EDS) composition distribution map indicates that TiO₂ nanoparticles were dispersed randomly in the master batch. Scanning electron microscopy (SEM) images show that LDPE/TiO₂ master batch is crushed into micron scale dispersed phases due to the shear stress during the blow‐forming process. Subsequently, TiO₂ nanoparticles in the dispersed phases are released into the ambient matrix and form a wide ring composed of monodispersed particles. The sizes of spherical crystals decrease due to the presence of TiO₂ nanoparticles in LLDPE/LDPE/TiO₂ nanocomposites. The transparency of LLDPE/LDPE/TiO₂ composite films decreases little compared to that of LLDPE/LDPE composite films.

SEM image of TiO₂ nanoparticles dispersed randomly in LLDPE/LDPE/TiO₂ composite films.     

Synthesis of a polyethylene-graft-polystyrene copolymer and its compatibilization for linear low density polyethylene/poly(phenylene oxide) blends

Based on unsteady diffusionkinetics, polyethylene(PE)-graft-polystyrene (PS) copolymers were designed and synthesized with a heterogeneous high yield titanium-based catalyst by copolymerization of ethylene with a PS-macromonomer using 1-hexene as a short main agent to promote the incorporation of the PS-macromonomer. The presence of 1-hexene facilitated the diffusion of the PS-macromonomer, giving rise to the significantly increased incorporation of the PS-macromonomer. Compatibilization of blends of linear low density polyethylene (LLDPE)/poly(phenylene oxide) (PPO) with the PE-g-PS copolymer were investigated using scanning electron microscopy (SEM) and dynamic mechanical analysis (DMA).     

Nonradiative energy transfer study on the interface of compatibilized linear low density polyethylene/poly(methyl methacrylate) blends

Blends of chromophore-labeled LLDPE and chromophore-labeled PMMA compatibilized by block copolymer of hydrogenated polybutadiene and methyl methacrylate (PHB-b-PMMA) were studied by nonradiative energy transfer (NRET) technique. The ratio of fluorescence intensity of the donor at 336 nm and the acceptor at 408 nm (I_D/I_A) decreased with an increase in block copolymer content. At about 8 wt.-% block copolymer content I_D/I_A reached a minimum value, indicating the interdiffusion of LLDPE chains and PMMA chains in the interface is strongest. The influence of temperature on the interdiffusion of polymer chains in the interface was also examined. Samples quenched in liquid nitrogen from 140°C showed lower energy transfer efficiencies than those annealed from 150°C to room temperature.     

DSC studies of linear low density polyethylene. Insights into the disrupting effect of different comonomers and the minimum fold chain length of the polyethylene lamallae

This paper reports a DSC examination of a series of linear low density polyethylenes (LLDPE) prepared variously with propylene, 1-butene or 4-methyl-1-pentene comonomers. The enthalpy of fusion of the crystalline regions of the LLDPE decreases progressively with increasing comonomer content and is effectively independent of the comonomer type. Disruption of polymer crystallinity is thus determined principally by the number and distribution of the chain irregularities. A sequence length of n = 14 was calculated as the critical chain dimension below which polyethylene segments cannot be readily packed into a stable crystal lattice.     

Photosulfonation of Low‐Density Polyethylene Films

Summary: Photosulfonation of low‐density polyethylene (LDPE) films by UV irradiation in the presence of gaseous sulfur dioxide (SO₂) and oxygen (O₂) was studied by attenuated total reflectance (ATR) infrared spectroscopy and X‐ray photoelectron spectroscopy (XPS). The ATR and XPS analysis and chemical modification of UV‐irradiated LDPE films demonstrated the generation of C?C double bonds and sultones in the reaction. These results indicated the possibility that sulfur trioxide (SO₃) was produced during the photosulfonation. New pathways for the SO₃ reaction with LDPE films, resulting in the formation of sulfonic acid groups, were proposed.

Overview of the mechanism proposed for the photosulfonation of low‐density polyethylene by SO₃ (produced upon UV‐irradiation of gaseous SO₂ and O₂).     

Morphology,crystallization, and thermal behaviour of isotactic polypropylene/low density polyethylene blends

The morphology, the crystallization and thermal behaviour of isotactic polypropylene (IPP) in its blends with two different samples of low density polyethylene (LDPE) was investigated at temperatures high enough to prevent any solidification of LDPE. It is found that pre-existing liquid LDPE domains are incorporated in intra-spherulitic regions during the isothermal crystallization of iPP. The radial growth rate of spherulites is almost unaffected by the LDPE content. The overall rate of crystallization of iPP, on the contrary, is strongly depressed by the addtion of LDPE. A depression of the equilibrium melting temperature of iPP, due to kinetic and morphological effects, is also observed. The depression of the overal kinetic rate constant is accounted for by the negative effect (decrease in the number of nuclei) that the addition of LDPE has on the primary nucleation process of iPP.     

Miscibility of linear and branched polyethylene in the liquid state

HDPE/LDPE blends and the pure components were crosslinked either by irradiation or by di-tert-butyl peroxide in the liquid state. The degree of crosslinkage was characterized by the reciprocal degree of swelling Q^?1 (xylene, 2 h, 140°C). Above a critical degree of crosslinkage corresponding to Q^?1 = 0,2 the DSC curves of HDPE/LDPE blends show only one single crystallization peak on cooling from the melt and only one single melting peak on subsequent heating. This is an unequivocal proof for the single phase structure of HDPE/LDPE blends in the liquid state. Crosslinking with Q^?1 ≥ 0,2 prohibits fractional crystallization and forces the unbranched CH₂ sequences of both components between the crosslinks into one crystal lattice.     

Long‐Chain Branching and Rheological Properties of Ethylene‐1‐Hexene Copolymers Synthesized from Ethylene Stock by Concurrent Tandem Catalysis

Summary: Concurrent tandem catalysis systems have shown a significant advantage in the convenient synthesis of linear low‐density polyethylene (LLDPE) from a sole ethylene monomer stock by uniquely coupling the tandem action between an ethylene oligomerization catalyst and an ethylene copolymerization catalyst in a single reactor. Recently, we have reported the successful synthesis of ethylene‐hexene derived LLDPE using an effective concurrent tandem catalysis system comprising (η⁵‐C₅H₄CMe₂C₆H₅)TiCl₃ ( 1 )/MMAO and a CGC copolymerization catalyst, [(η⁵‐C₅Me₄)SiMe₂(^tBuN)]TiCl₂ ( 2 )/MMAO. In this work, we report the results from an extensive study on the important rheological properties of LLDPE grades prepared with this tandem catalysis system. Two sets of LLDPE samples having different short‐chain branching density (SCBD) were prepared with the tandem catalysis system under various catalyst concentrations and at temperatures of 25 and 45 °C. The melt rheological properties of these polymers were evaluated using small‐amplitude dynamic oscillation measurements. These polymers have been found to possess typical rheological properties found in long‐chain branched (LCB) polymers, such as enhanced zero‐shear viscosity (η₀), improved shear‐thinning, elevated dynamic moduli, and thermorheological complexity, which indicate the presence of long‐chain branching in the polymers. The long‐chain branching density (LCBD) of the two respective sets of polymers were qualitatively compared and correlated to the polymerization conditions including catalyst ratio and temperature. This work represents the first study on the rheological properties of LLDPE synthesized with concurrent tandem catalysis, and it discloses another appealing feature of this unique approach—its ability to produce LCB LLDPE from a single ethylene monomer stock.

Synthesis of linear low‐density polyethylene (LLDPE) from ethylene using ethylene oligomerization catalyst and an ethylene copolymerization catalyst.     

Large scale fractionation of polyethylene by means of the continuous polymer fractionation (CPF) method

The countercurrent extraction method recently developed for the continuous polymer fractionation (CPF) was applied to linear polyethylene (M?_w = 55 kg/mol; M?_n = 16,7 kg/mol). At temperatures higher than 130°C, moderately concentrated solution of polyethylene were extracted to remove the low-molecular-weight components. Discontinuous fractionation experiments served to detect the best suited solvents. Diphenyl ether was chosen to demonstrate that the present extraction can be performed even with the same single solvent used to prepare the feed. For very high-molecular-weight polymers, mixed solvents are, however, normally better than single ones, since they allow an easier tailoring of thermodynamic conditions, and yield much less viscous solutions. Mixtures of tetralin and triethylene glycol turned out to be best suited for polyethylene. By means of four successive CPF runs with the single solvent, polyethylene fractions with non-uniformities U = (M?_w/M?_n) ? 1 of approx. 0,3 to 0,4 were obtained on a 100 g scale. The rule of thumb that U can be halved in each CPF step without extensive optimization of the method was corroborated.     

Fractionated crystallisation of polyethylene and ethylene/α-olefin copolymers dispersed in immiscible polystyrene matrices

In this work, several PS/HDPE (high density polyethylene), PS/LLDPE (linear low density polyethylene) and PS/ULDPE (ultra low density polyethylene) blends were prepared in a composition range were atactic polystyrene (PS) was always the matrix component. All the types of polyethylenes employed, when dispersed into droplets, exhibited fractionated crystallisation exotherms in the temperature range between 67 and 70°C. These low crystallisation temperatures are probably closer to the homogeneous nucleation temperature of linear polyethylene than any previously reported value, since they occur at higher supercoolings. The higher values of crystallisation temperatures previously reported could be explained by the crystallisation from heterogeneous nuclei of relatively low nucleation efficiency or by a weak nucleation capacity of the droplets interface. By applying a self-nucleation procedure we were able to corroborate that what causes the fractionated crystallisation is the lack of highly active heterogeneous nuclei (i. e., those normally active at low supercoolings in the bulk polymer) in every droplet. When polyethylene/α-olefin copolymers are finely dispersed in a PS matrix, a molecular segregation process can be induced during mixing facilitated by the heterogeneous distribution of short chain branches in the copolymers. The crystallisation of droplets that contained mostly these highly branched chains occurs at temperatures lower than 50°C, thereby producing another low temperature exotherm which may be the lowest present in the blend and could be mistaken by the crystallisation of homogeneously nucleated crystals. We have shown that the self-nucleation technique can help to distinguish these low temperature exotherms from those originated by differences in nucleation behaviour; therefore, a plausible interpretation of all the possible fractionated crystallisation exotherms of ethylene/α-olefin copolymer droplets was made possible.     

Mechanism of the short chain branching in low density polyethylene

In this paper the validity of the well-known Roedel's “back-biting” mechanism is questioned. It is shown that number and type of branches depend on the degree of order (entropy) of compressed ethylene molecules. A new mechanism for the short chain branching in low density polyethylene is proposed, based on the effect of the supermolecular species in compressed ethylene in this reaction. An equation for calculation of the number of branches for ethylene polymerization in a wide range of temperature (?5 to + 200°C) and pressure (40 to 7000 atm) is given.     

Effects of barium chloride adsorbed to polyethylene glycol (PEG) microspheres on co-culture of human blood mononuclear cell and breast cancer cell lines (MCF-7)

This study investigated the effects of BaCl₂ adsorbed to polyethylene glycol (PEG) microspheres on human blood mononuclear cells (MN) co-cultured with breast cancer cell lines (MCF-7). The MCF-7 cells were obtained from the American Type Culture Collection and the blood mononuclear (MN) cells from volunteer donors. MN cells, MCF-7 cells and their co-culture (MN and MCF-7 cells) were pre-incubated for 24?h with or without 25 and 1000?pg?L^?1 BaCl₂ (Ba₂₅ and Ba₁₀₀₀), PEG microspheres or 25 and 1000?pg?L^?1 BaCl₂ adsorbed to PEG microspheres (PEG-Ba₂₅ and PEG-Ba₁₀₀₀). Rheological parameters and apoptosis were determined. Fluorescence microscopy and flow cytometry analyses revealed that BaCl₂ was able to adsorb the PEG microspheres. The blood flow and viscosity curves were similar among the treatments. In general, apoptosis rates increased in co-cultured cells, co-cultured cells incubated with Ba₂₅ and with PEG-Ba₂₅, but the highest rates were observed in co-cultured cells incubated with PEG-Ba₁₀₀₀. In conclusion, BaCl₂ adsorbed to PEG microspheres exhibited dose-dependent antitumor effects against human MCF-7 breast cancer cells co-cultured with MN cells, thereby offering a possible therapeutic alternative for treating this disease provided they are administered at very low concentrations.     

Study of the structure of polyethylene and poly(tetrafluoroethylene) radiation grafted ion-exchange copolymers

Cation- and anion-exchange copolymers were synthesized by radiation induced copolymerization of acrylic acid and 4-vinylpyridine onto polyethylene and poly(tetrafluoroethylene) (PTFE) films. The grafting was carried out by the direct method of single or multiple (discrete) irradiation by γ-rays from a ⁶⁰Co source. The grafting degree was from 10 to 121% for polyethylene and from 2.5 to 50% for poly(tetrafluoroethylene), depending on the irradiation dose (1–50 kGy). The calorimetric curves of the copolymers synthesized showed a glass transition temperature (T_g) at 333 ± 10 K. The enthalpies of melting and crystallization decreased with increasing degree of grafting. The data from wide angle X-ray analysis indicated an increase of the amorphous part with degree of grafting. At lower grafting degrees of poly(acrylic acid) and poly(4-vinylpyridine) (up to 15%) onto PTFE matrix, the size of the crystallites was found to increase. The penetration of the grafted functional monomer leads to partial deorientation of the initial LDPE film.     

Synthesis and properties of branched polyethylene/high‐density polyethylene blends using a homogeneous binary catalyst system composed of early and late transition metal complexes

Branched polyethylene/high‐density polyethylene blends (BPE/HDPE) with a wide range of molecular weights, melt flow indexes (MFI), and intrinsic viscosity were prepared using the homogeneous binary catalyst system composed by Ni(α‐diimine)Cl₂ ( 1 ) (α‐diimine = 1,4‐bis(2,6‐diisopropylphenyl)‐acenaphthenediimine) and {Tp^Ms*}TiCl₃ ( 2 ) (Tp^Ms* = hydridobis(3‐mesitylpyrazol‐1‐yl)(5‐mesitylpyrazol‐1‐yl)) activated with MAO and/or TIBA in hexane at two different polymerization temperatures (30 and 55 °C) and by varying the nickel loading molar fraction (x_Ni). At all temperatures, a non‐linear correlation between the x_Ni and the productivity was observed, suggesting the occurrence of a synergistic effect between the nickel and the titanium catalyst precursors, which is more pronounced at 55 °C. The molecular weight of the BPE/HDPE blends considerably decreases with increasing Al/M molar ratio. The melt flow indexes (MFI) and intrinsic viscosities (η) are strongly affected by x_Ni, but the melting temperatures are nearly constant, 132 ± 3 °C. Dynamic mechanical thermal analysis (DMTA) shows the formation of different polymeric materials where the stiffness varies according to the x_Ni and temperature used in the polymerization reaction. The surface morphology of the BPE/HDPE blends studied by scanning electron microscopy (SEM) revealed a low miscibility between the PE phases resulting in the formation of a “sandwich structure” after etching with o‐xylene.

     

Application of the composite model for the mechanical properties of high density polyethylene

The existing models of high density polyethylene (HDPE) fail to tackle effectively the development of mechanical anisotropy on drawing at different temperatures. This paper is concerned with the theoretical interpretation of the anisotropic elastic properties of HDPE by applying the composite model proposed by the authors. The model takes into account the change in orientation and crystallinity on drawing. As far as the orientational changes on drawing are concerned, it is seen that the pseudo affine deformation law tan θ = ?(n) · tan θ′ with ?(n) = n^?3/2 is applicable at ?60°C only. It is further found that the two parameter analytical form of ?(n) reproduces the correct orientational changes on drawing for the entire temperature range from ?60 to 100°C. The agreement of the calculated values of E₀ and E₉₀ over the entire temperature range at all drawing ratios is quite satisfactory.     

Chlorination of polyethylene single crystals

Chlorination under mild conditions of suspensions of polyethylene single crystals demonstrated that a selective attack on the fold surface takes place. Two polyethylene molecular weight fractions (M_n = 47000 and M_n = 150 000) were used and single crystals were grown isothermally from p-xylene at 88°C. The chlorine content was changed from 4 wt.-% to 30 wt.-% and to this level no evidence for crystal attack and loss of crystallinity was found. The melting temperatures of chlorinated single crystals decrease with increasing chlorination up to about 15 wt.-% chlorine content and then stay constant for higher chlorine contents. Moreover, the heat of melting of the chlorinated single crystals is constant and is independent of the chlorine content up to 25 wt.-%. These results are compared with those of samples of chlorinated polyethylene recrystallized from solution and from the melt.