Surface studies of ultra‐high molecular weight polyethylene irradiated with high‐energy pulsed electron beams in air

Ultra‐high molecular weight polyethylene (UHMWPE) was irradiated in air with high‐energy (9 MeV), pulsed electron beams to doses ranging from 2.5 to 100 Mrad and subsequently heat treated at 120°C for a time period of 120 min. Surface characterization of the target side of irradiated UHMWPE samples was carried out both before and after the heat treatment by means of attenuated total reflection Fourier‐transform infrared (FTIR/ATR) spectroscopy and microhardness measurement. The obtained results provided further evidence supporting our earlier observation (Tretinnikov, O. N.; Ogata, S.; Ikada, Y. Polymer 1998, 39, 6115) that thermal decomposition of hydroperoxides formed upon irradiation of UHMWPE with high‐energy, pulsed electron beams in air leads to surface crosslinking, and the subsequent surface hardening of the irradiated polymer. Importantly, we found that this phenomenon has the highest contribution to the surface hardness enhancement of the polymer when the radiation dose is in the range of 10–30 Mrad. In addition, we found that this irradiation and subsequent heat treatment of UHMWPE in air does not lead to formation of carbonyl‐containing products unless the radiation dose exceeds 20 Mrad. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1503–1512, 1999     

Parameters influencing the molecular weight of 3,6‐carbazole‐based D‐π‐A‐type copolymers

Condensation copolymerization reactions of carbazole 3,6‐diboronate with 4,7‐bis(5‐bromo‐2‐thienyl)‐2,1,3‐benzothiadiazole (DTBT) only produce low‐molecular‐weight donor (D)‐π‐acceptor (A) copolymers. High‐molecular‐weight copolymers for use in optoelectronic devices are necessary for achieving extended π‐conjugation and for controlling the copolymer processibility. To elucidate the cause of the persistently low molecular weight, we synthesized three 3,6‐carbazole‐based D‐A copolymers using copolymerizations of N‐9′‐heptadecanyl‐3,6‐carbazole with DTBT, N‐9′{2‐[2‐(2‐methoxy‐ethoxy)‐ethoxy]‐ethyl}‐3,‐6‐carbazole with DTBT, and N‐9′‐heptadecanyl‐3,6‐carbazole with alkyl‐substituted DTBT. We investigated several parameters for their influence on molecular copolymer weight, including the conformation of the chain during growth, the solubility of the monomers, and the dihedral angles between the donor and acceptor units. Size exclusion chromatography, UV–vis absorption spectroscopy, and computational studies revealed that the low molecular weights of 3,6‐carbazole‐based D‐A copolymers resulted from conjugation breaks and the resulting high coplanarity, which led to strong interactions between polymer chains. These interactions limited formation of high‐molecular‐weight‐copolymers during copolymerization. The strong intermolecular interactions of the 3,6‐carbazole moiety were exploited by incorporating 3,6‐carbazole units into poly[9′,9′‐dioctyl‐2,7‐flourene‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)] prepared from 9′,9′‐dioctyl‐2,7‐flourene and DTBT. Interestingly, the number average molecular weight increased gradually with increasing 2,7‐fluorene monomer content but the number of conjugation breaks was a range of 6–7. The hole mobilities of the copolymers were studied for comparison purposes. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Studies on grafting of tris(2‐methoxyethoxy)vinylsilane onto ethylene‐propylene‐diene terpolymer

New graft copolymer was prepared by incorporating tris(2‐methoxyethoxy)vinylsilane (TMEVS) on ethylene‐propylene‐diene terpolymer (EPDM) by using dicumyl peroxide (DCP) as initiator, in Haake Rheocord 90 torque rheometer. The effect of EPDM concentration, TMEVS concentration, reaction time, reaction temperature and initiator concentration on the graft co polymerization was studied. The grafting efficiency of TMEVS on EPDM was confirmed by Fourier Transform infrared (FT‐IR) spectroscopy. The grafting efficiency increased with increase in the silane concentration upto 6% by weight. The grafting efficiency decreased beyond 6% by weight due to homopolymerization of TMEVS and non‐availability of carbon–carbon double bond in the EPDM terpolymer. The thermal properties of peroxide cured EPDM and hot water cured EPDM‐g‐TMEVS were studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) analysis. The results show thermal properties like degradation tempertature and glass transition temperature of the EPDM‐g‐TMEVS were increased due to introduction of TMEVS on to EPDM terpolymer as well as the formation of thermally stable three‐dimensional network. Copyright © 2004 John Wiley & Sons, Ltd.     

Effect of electron radiation and triallyl isocyanurate on the average molecular weight and crosslinking of poly(ε‐caprolactone)

Investigation of the effect of electron radiation on the flow rate and average molecular weight of poly(ε‐caprolactone) (PCL) as well as on formation of the gel fraction of this polymer being irradiated in the presence of triallyl isocyanurate (TAIC) was the aim of the present paper. It was found that PCL macromolecules upon the electron radiation underwent both degradation and linking, because of which the polymer molecular weight increased. The processes associated with elongation of the polymer chains prevailed over the degradation ones. It was also found that PCL irradiated in the presence of TAIC underwent crosslinking resulting in formation of a significant amount of the gel fraction. The largest amount of this fraction was created upon the radiation with the dose of 60 kGy, which was confirmed by the results of determination of the swelling index. Changes in properties of PCL, occurring because of the electron radiation, are important for controlling viscosity of polymeric materials during processing of these materials. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis of poly(m‐phenylene) and poly(m‐phenylene)‐block‐ poly(3‐hexylthiophene) with low polydispersities

Well‐defined poly(m‐phenylene) (PMP), which is poly(1,3‐dibutoxy‐m‐phenylene), was successfully synthesized via Grignard metathesis polymerization. PMP with a reasonably high number‐average molecular weight (M_n) of 25,900 and a very low polydispersity index of 1.07 was obtained. The polymerization of a Grignard reagent monomer, 1‐bromo‐2,4‐dibutoxy‐5‐chloromagnesiobenzene, proceeded in a chain‐growth manner, probably due to the meta‐substituted design producing a short distance between the MgCl and Br groups and thereby making a smooth nickel species (? C? Ni? C? ) transfer to the intramolecular chain end (? C? Ni? Br) over a benzene ring. PMP showed a good solubility in the common organic solvents, such as tetrahydrofuran, CH₂Cl₂, and CHCl₃. Furthermore, a new block copolymer comprised of PMP and poly(3‐hexylthiophene) was also prepared. The tapping mode atomic force microscopy image of the surface of the block copolymer thin film on a mica substrate showed a nanofibril morphology with a clear contrast. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Thermo‐stable 2‐(arylimino)benzylidene‐9‐arylimino‐5,6,7,8‐tetrahydro cyclohepta[b]pyridyliron(II) precatalysts toward ethylene polymerization and highly linear polyethylenes

A series of 2‐(arylimino)benzylidene‐9‐arylimino‐5,6,7,8‐tetrahydrocyclohepta[b] pyridyliron(II) chlorides was synthesized and characterized using FT‐IR and elemental analysis, and the molecular structures of complexes Fe3 and Fe4 have been confirmed by the single‐crystal X‐ray diffraction as a pseudo‐square‐pyramidal or distorted trigonal‐bipyramidal geometry around the iron core. On activation with methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), all iron precatalysts exhibited high activities toward ethylene polymerization with a marvelous thermo‐stability and long lifetime. The Fe4 /MAO system showed highest activity of 1.56 × 10⁷ gPE·mol^?1(Fe)·h^?1 at 70 °C, which is one of the highest activities toward ethylene polymerization by iron precatalysts. Even up to 80 °C, Fe3 /MAO system still persist high activity as 6.87 × 10⁶ g(PE)·mol^?1(Fe)·h^?1, demonstrating remarkable thermal stability for industrial polymerizations (80–100 °C). This was mainly attributing to the phenyl modification of the framework of the iron precatalysts. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 830–842     

Synthesis of poly(N‐isopropylacrylamide) with a low molecular weight and a low polydispersity index by single‐electron transfer living radical polymerization

The single‐electron transfer living radical polymerization (SET‐LRP) method in the presence of chain transfer agent was used to synthesize poly(N‐isopropylacrylamide) [poly(NIPAM)] with a low molecular weight and a low polydispersity index. This was achieved using Cu(I)/2,2′‐bipyridine as the catalyst, 2‐bromopropionyl bromide as the initiator, 2‐mercaptoethanol as the chain transfer agent (TH), and N,N‐dimethylformamide (DMF) as the solvent at 90 °C. The copper nanoparticles with diameters of 16 ± 3 nm were obtained in situ by the disproportionation of Cu(I) to Cu(0) and Cu(II) species in DMF at 22 °C for 24 h. The molecular weights of poly(NIPAM) produced were significantly higher than the theoretical values, and the polydispersities were less than 1.18. The chain transfer constant (C_tr) was found to be 0.051. Although the kinetic analysis of SET‐LRP in the presence of TH corroborated the characteristics of controlled/living polymerization with pseudo‐first‐order kinetic behavior, the polymerization also exhibited a retardation period (k > k_tr). The influence of molecular weight on lower critical solution temperature (LCST) was investigated by refractometry. Our experimental results explicitly elucidate that the LCST values increase slightly with decreasing molecular weight. Reversibility of solubility and collapse in response to temperature well correlated with increased molecular weight of poly(NIPAM). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Effect of Structure of Functionalizing Molecules on the Inter‐Macromolecular Reactions and Blending of Poly(ethylene‐co‐propylene) (EPM) with Poly(6‐aminohexanoic Acid) (PA6)

Two different functionalizing systems, i.e., monohexadecyl maleate (= hexadecyl hydrogen (2Z)‐but‐2‐enedioate) in the presence of dicumyl peroxide (= bis(1‐methyl‐1‐phenylethyl) peroxide) or 4‐carboxybenzenesulfonazide (= 4‐(azidosulfonyl)benzoic acid), were used in distinct experiments to perform in a one‐step procedure the formation of a EPM–PA6 graft copolymer, necessary to obtain a compatibilized blend, from a molten mixture of ethylene–propylene copolymer (EPM) and polyamide 6 (PA6). The characterization of the graft polymer by selective solvent extraction of the blends and the subsequent IR and NMR analysis of the various fractions established the occurrence of functionalization reactions preferentially onto the polyolefin with both reagents. Also the formation in good yield of graft copolymers at the phases interface was observed. Moreover, the morphology and thermal characterizations of the blends by means of SEM and DSC analyses were used to evaluate the compatibilization extent in comparison with blends obtained by the conventional two‐step procedure or by the one‐step procedure with commercial maleic acid derivatives.     

Sorption and diffusion of normal alkanes through poly(ethylene‐co‐vinyl acetate) membranes

The transport behavior of uncrosslinked and crosslinked poly(ethylene‐co‐vinyl acetate) membranes has been investigated using normal alkanes as probe molecules, in the temperature range of 30–60 °C. Benzoyl peroxide was used for crosslinking the matrix. It has been observed that, a critical concentration of crosslinker is necessary for maximum solvent uptake, followed by a decrease at higher concentration. The effect of free volume on liquid transport was investigated by positron annihilation lifetime spectroscopy. The mechanism of transport has been found to deviate from the regular Fickian behavior. The dependence of the transport coefficients on crosslink density, nature of penetrants, and temperature was studied. The polymer–solvent interaction parameter, enthalpy, and entropy of sorption have also been estimated from the transport data. The affine and phantom models for chemical crosslinks were used to predict the nature of crosslinks. Finally, the experimental sorption data were compared with theoretical predictions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2470–2480, 2007     

The grafting of acrylamide onto poly(ε‐caprolactone) and poly(1,5‐dioxepan‐2‐one) using electron beam preirradiation. III. The grafting and in vitro degradation of chemically crosslinked poly(1,5‐dioxepan‐2‐one)

Acrylamide was graft polymerized onto the surface of a chemically crosslinked and amorphous biodegradable polyester, poly(1,5‐dioxepan‐2‐one). Electron beam irradiation at a dose of 5 Mrad was used to generate the initiating species in the polyester. The degradation behavior in vitro at pH 7.4 and 37°C in a phosphate buffer solution was studied for untreated, irradiated, and acrylamide‐grafted polymer. Differences in weight loss performance were observed between virgin and treated polymers. The acrylamide‐grafted poly(1,5‐dioxepan‐2‐one) was totally degraded after 43 weeks as compared to 48 weeks for the irradiated and 55 weeks for the virgin polymer. On the other hand, the treated polymers showed a higher resistance to degradation in terms of weight loss during the intermediate part of the degradation, i.e., between about 5 and 35 weeks. After this period, the irradiated and particularly the acrylamide grafted poly(1,5‐dioxepan‐2‐one) degraded much more rapidly than the virgin polymer. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1659–1663, 1999     

Dicyclohexylammonium bromoacetate: a low molecular mass organogelator with a one‐dimensional secondary ammonium monocarboxylate (SAM) synthon

The asymmetric unit of the title salt, C₁₂H₂₄N⁺·C₂H₂BrO₂⁻, contains a dicyclohexylammonium cation connected to a bromoacetate anion by means of an N—H...O hydrogen bond. In the crystal, the ion pairs assemble via N—H...O interactions, forming zigzag infinite chains parallel to the c axis with the (...H—N—H...O—C—O...)_n motif that is considered to be a prerequisite for ensuring gelation properties of secondary ammonium monocarboxylate salts. The title salt was characterized by FT–IR, X‐ray powder diffraction (XRPD), TG–DTA and ¹H NMR spectroscopy in solution. Gelation experiments revealed that dicyclohexylammonium bromoacetate forms molecular gels with dimethylformamide and dimethyl sulfoxide. Scanning electron microscopy (SEM) was used to reveal morphological features of dried gels.     

The grafting of acrylamide onto poly(ε‐caprolactone) and poly(1,5‐dioxepan‐2‐one) using electron beam preirradiation. I. Influence of dose and Mohr's salt for the grafting onto poly(ε‐caprolactone)

Poly(ε‐caprolactone) films (TONE® 787) were irradiated by electron beam in air prior to grafting in aqueous solutions of acrylamide. The grafting kinetics and molecular weight of the grafted poly(acrylamide) chains were studied with irradiation doses between 2.5 and 20 Mrad and in the Mohr's salt concentration range of 0.0025–1 wt %. The grafting rate and yield were strongly dependent on the Mohr's salt concentration. By molecular weight analysis of grafted poly(acrylamide) chains, it was shown that the molecular weight is approximately proportional to the mass of the grafted PAAm. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1643–1649, 1999     

Preparation of water‐soluble,syndiotacticity‐rich,low molecular weight poly(vinyl alcohol) microfibrils in high yields with the low‐temperature polymerization of vinyl pivalate in tetrahydrofuran and saponification

To prepare water‐soluble, syndiotacticity‐rich poly(vinyl alcohol) (PVA) microfibrils for various industrial applications, we synthesized syndiotacticity‐rich, low molecular weight PVA by the solution polymerization of vinyl pivalate (VPi) in tetrahydrofuran (THF) at low temperatures with 2,2′‐azobis(2,4‐dimethylvaleronitrile) (ADMVN) as an initiator and successive saponification of poly(vinyl pivalate) (PVPi). Effects of the initiator and monomer concentrations and the polymerization temperature were investigated in terms of the polymerization behaviors and molecular structures of PVPi and the corresponding syndiotacticity‐rich PVA. The polymerization rate of VPi in THF was proportional to the 0.91 power of the ADMVN concentration, indicating the heterogeneous nature of THF polymerization. The low‐temperature solution polymerization of VPi in THF with ADMVN proved to be successful in obtaining water‐soluble PVA with a number‐average degree of polymerization (P_n) of 300–900, a syndiotactic dyad content of 60–63%, and an ultimate conversion of VPi into PVPi of over 75%. Despite the low molecular weight of PVA with P_n = 800, water‐soluble PVA microfibrillar fibers were prepared because of the high level of syndiotacticity. In contrast, for PVA with P_n = 330, shapeless and globular morphologies were observed, indicating that molecular weight has an important role in the in situ fibrillation of syndiotacticity‐rich PVA. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1103–1111, 2002     

Formation of pore‐filled ion‐exchange membranes with in situ crosslinking: Poly(vinylbenzyl ammonium salt)‐filled membranes

Robust, polyelectrolyte‐filled, microporous membranes were prepared by the introduction and crosslinking of a preformed polymer within the pores of a poly(propylene) host membrane. Specifically, poly(vinylbenzyl chloride) (PVBCl) was reacted with piperazine or 1,4‐diaminobicyclo[2.2.2]octane in an N,N‐dimethylformamide (DMF) solution contained in the pores of the microporous base membrane. The remaining chloromethyl groups were reacted with an amine, such as trimethylamine, to form positively charged ammonium sites. This simple two‐step procedure gave dimensionally stable, anion‐exchange membranes in which the degree of crosslinking and the mass loading were determined by the concentration of PVBCl and crosslinker in the starting DMF solution. The incorporated polyelectrolyte gel was evenly distributed within the pores of the host membrane with no surface layers present. The membranes are fully characterized. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 807–820, 2001     

Stereospecific and molecular weight‐controlled polymerization of 1,3‐butadiene with Co(acac)3‐MAO catalyst

The polymerization of butadiene (Bd) with Co(acac)₃ in combination with methylaluminoxane (MAO) was investigated. The polymerization of Bd with Co(acac)₃‐MAO catalysts proceeded to give cis‐1,4 polymers (94 – 97%) bearing high molecular weights (40 × 10⁴) with relatively narrow molecular weight distributions (M_w's/M_n's). The molecular weight of the polymers increased linearly with the polymer yield, and the line passed through an original point. The polydispersities of the polymers kept almost constant during reaction time. This indicates that the microstructure and molecular weight of the polymers can be controlled in the polymerization of Bd with the Co(acac)₃‐MAO catalyst. The effects of reaction temperature, Bd concentration, and the MAO/Co molar ratio on the cis‐1,4 microstructure and high molecular weight polymer in the polymerization of Bd with Co(acac)₃‐MAO catalyst were observed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2793–2798, 2001     

Molecular‐Weight‐Dependence on Domain Formation of Grafted Poly(ethylene‐co‐propylene) in a Poly(propylene) Matrix

Several novel poly(propylene)‐graft‐poly(ethylene‐co‐propylene) copolymers with isotactic poly(propylene) (PP) backbones and ethylene/propylene rubber (EPR) branches were synthesized. The thermomechanical properties of these samples were investigated using a dynamic mechanical analyzer. There appeared to be a critical EPR molecular weight above which a two‐phase system developed with EPR domains dispersed in a PP matrix. This domain formation gave an enhanced loss modulus compared to a commercial high impact PP product below 40°C.     

Synthesis and characterization of new highly organosoluble poly(ether imide)s based on 3,3′,5,5′‐tetramethyl‐2,2‐bis[4‐(4‐dicarboxyphenoxy)phenyl]propane dianhydride

A new bis(ether anhydride), 3,3′,5,5′‐tetramethyl‐2,2‐bis[4‐(4‐dicarboxyphenoxy)phenyl]propane dianhydride ( 3 ), was prepared in three steps: the nitro displacement of 4‐nitrophthalonitrile with 2,2‐bis(4‐hydroxy‐3,5‐dimethylphenyl)propane, the alkaline hydrolysis of the intermediate bis(ether dinitrile), and the subsequent dehydration of the resulting bis(ether diacid). A series of new highly soluble poly(ether imide)s with tetramethyl and isopropylidene groups were prepared from the bis(ether anhydride) 3 with various diamines by a conventional two‐stage synthesis including polyaddition and chemical cyclodehydration. The resulting poly(ether imide)s had inherent viscosities of 0.54–0.73 dL g^?1. Gel permeation chromatography measurements revealed that the polymers had number‐average and weight‐average molecular weights of up to 54,000 and 124,000, respectively. All the polymers showed typical amorphous diffraction patterns. All of the poly(ether imide)s showed excellent solubility and were readily dissolved in various solvents such as N‐methyl‐2‐pyrrolidinone, N,N‐dimethylacetamide, N,N‐dimethylformamide, pyridine, cyclohexanone, tetrahydrofuran, and even chloroform. Most of the polymers could be dissolved with chloroform concentrations as high as 30 wt %. These polymers had glass‐transition temperatures of 244–282 °C. Thermogravimetric analysis showed that all polymers were stable, with 10% weight losses recorded above 463 °C in nitrogen. These transparent, tough, and flexible polymer films were obtained through solution casting from N,N‐dimethylacetamide solutions. These polymer films had tensile strengths of 81–102 MPa and tensile moduli of 1.8–2.0 GPa. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2556–2563, 2002     

Toughening of a propylene‐b‐(ethylene‐co‐propylene) copolymer by a plastomer

Several blends, covering the entire range of compositions, of a metallocenic ethylene‐1‐octene copolymer (CEO) with a multiphasic block copolymer, propylene‐b‐(ethylene‐co‐propylene) (CPE) [composed of semicrystalline isotactic polypropylene (iPP) and amorphous ethylene‐co‐propylene segments], have been prepared and analyzed by differential scanning calorimetry, X‐ray diffraction, optical microscopy, stress‐strain and microhardness measurements, and dynamic mechanical thermal analysis. The results show that for high CEO contents, the crystallization of the iPP component is inhibited and slowed down in such a way that it crystallizes at much lower temperatures, simultaneously with the crystallization of the CEO crystals. The mechanical results suggest very clearly the toughening effect of CEO as its content increases in the blends, although it is accompanied by a decrease in stiffness. The analysis of the viscoelastic relaxations displays, first, the glass transition of the amorphous blocks of CPE appearing at around 223 K, which is responsible for the initial toughening of the plain CPE copolymer in relation to iPP homopolymer. Moreover, the additional toughening due to the addition of CEO in the blends is explained by the presence of the β relaxation of CEO that appears at about 223 K. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1869–1880, 2002     

Synthesis of ultra‐high‐molecular‐weight ethylene‐propylene copolymer via quasi‐living copolymerization with N‐heterocyclic carbene ligated vanadium complexes

The quasi‐living copolymerization of ethylene with propylene was achieved by using N‐heterocyclic carbene (NHC) ligated vanadium complex ( V3 , VOCl₃[1,3‐(2,6‐ⁱPr₂C₆H₃)₂(NCH?)₂C:]) due to the stabilization of active center by the introduction of bulky and electron rich NHC ligand with bulky isopropyl substituents at the ortho positions of the phenyl rings. The weight‐average molecular weight (M_w) of the resulting copolymer increases linearly with its weight in 20 min. The ultra‐high‐molecular‐weight (UHMW) ethylene‐propylene copolymer (M_w = 1612 kg mol^?1) can be synthesized with V3 /Et₃Al₂Cl₃ catalytic system. The novel complex V4′ (VCl₃[1,3‐(2,4,6‐Me₃C₆H₂)₂(NCH?)₂C:]·2THF) was constructed by the introduction of two coordinated tetrahydrofuran molecules and decrease in steric hindrance at the ortho positions of phenyl rings. The UHMW ethylene‐propylene copolymer (M_w = 1167 kg mol^?1) can also be synthesized by using V4′ /Et₃Al₂Cl₃ catalytic system. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 553–561