High Gel Fraction Research Articles

Hydrogenation of acrylonitrile–butadiene copolymer latex using water-soluble rhodium catalysts

Hydrogenated acrylonitrile butadiene rubber (HNBR) is a high-performance elastomer which has found important applications in the automobile and petroleum industries. Compared to current NBR solution hydrogenation technology, direct hydrogenation of NBR in its aqueous form (i.e. NBR latex) is a “green” strategy as it is energetically favorable and environmentally friendly. Two water-soluble rhodium based catalysts, RhCl(TPPMS)3 (TPPMS = monosulfonated triphenylphosphane) and RhCl(TPPTS)3 (TPPTS = trisulfonated triphenylphosphane), were investigated for NBR latex hydrogenation. The NBR in aqueous latex could be hydrogenated using the RhCl(TPPMS)3 catalyst, attaining HNBR with as much as 95 mol% CC bond removal. A limited fraction of CC bond reduction was observed when RhCl(TPPTS)3 was used as the catalyst. Using the RhCl(TPPMS)3 catalyst, the hydrogenation reaction could be conducted at mild temperature with no addition of organic co-solvent. The presence of Rh metal in the resultant HNBR confirmed the phase transfer of the RhCl(TPPMS)3 catalyst and was considered as a crucial factor for achieving a successful reaction. The observed influence of process conditions on the activity of hydrogenation has led to an extrapolation of a mild reaction condition mechanism for the RhCl(TPPMS)3 system. Additionally, in-house NBR latices with different gel content were synthesized and investigated in the hydrogenation experiment for comparison. One of the major observations is that the high gel fraction in NBR could greatly limit the hydrogenation reaction which could be a reasonable explanation for the low conversion of CC bonds reported previously.

Molecularly imprinted composite cryogel for albumin depletion from human serum

A new composite protein-imprinted macroporous cryogel was prepared for depletion of albumin from human serum prior to use in proteom applications. Polyhydroxyethyl-methacylate-based molecularly imprinted polymer (MIP) composite cryogel was prepared with high gel fraction yields up to 83%, and its morphology and porosity were characterized by Fourier transform infrared, scanning electron microscopy, swelling studies, flow dynamics, and surface area measurements. Selective binding experiments were performed in the presence of competitive proteins human transferrin (HTR) and myoglobin (MYB). MIP composite cryogel exhibited a high binding capacity and selectivity for human serum albumin (HSA) in the presence of HTR and MYB. The competitive adsorption amount for HSA in MIP composite cryogel is 722.1 mg/dL in the presence of competitive proteins (HTR and MYB). MIP composite cryogel column was successfully applied in the fast protein liquid chromatography system for selective depletion of albumin in human serum. The depletion ratio was highly increased by embedding beads into cryogel (85%). Finally, MIP composite cryogel can be reused many times with no apparent decrease in HSA adsorption capacity.

SYNTHESIS OF POLY(ACRYLAMIDE-CO-ACRYLIC ACID)-STARCH BASED SUPERABSORBENT HYDROGELS BY GAMMA RADIATION: STUDY ITS SWELLING BEHAVIOR

Modification of poly (acrylamide-co-acrylic acid) superabsorbent hydrogels with varying starch concentration (1-3%) via simultaneous gamma radiation have been carried out. The structure and morphology of copolymers were characterization by Fourier transform infra red spectroscopy and scanning electron microscopy. The gel fraction, swelling kinetics and the equilibrium degree of swelling (EDS) of the hydrogels were studied. It was found that the an increase in the starch content present in the hydrogels (1-3%) and with increase irradiation dose from 10 kGy up to 30 kGy, the swelling ratio decreased from 250-100 g/g. Incorporation of 1% starch increases the EDS of the hydrogels up 350 g/g. Under maximum conditions, poly(AAm-co-AA)-starch hydrogels with high gel fraction (~93%) was prepared from aqueous solution containing 5% AAm, 15% acrylic acid and 0-3% starch. The hydrogels were sensitive against salts solution.

Sandwich Oil-absorptive Materials by a Semi-interpenetrating Resin Based on Poly(Butyl Methacrylate)-inter-Poly(Hydroxyethyl Methacrylate) in Poly(Ethylene Terephthalate) Nonwoven Cloth

A linear polymer was synthesized by suspension polymerization using butyl methacrylate (BMA) monomer and benzoyl peroxide (BPO) initiator. The resulting PBMA was interpenetrated into PHEMA crosslinking networks in N, N-dimethylacetamide (DMAc), using HEMA (hydroxyethyl methacrylate) as monomer, divinylbenzene (DVB) as crosslinking agent. After the reaction terminated, the mixed solution was made into sandwich oil-absorptive materials. The influence of the crosslinking agent and the mass ratio of PBMA and HEMA on the semi-interpenetrating (semi-IPN) structure and properties were analyzed by scanning electron microscopy (SEM), attenuated total reflection Fourier transform infrared spectroscopy (FTIR-ATR) and dynamic mechanical thermal analyzer (DMA), while swelling behaviour and gel fraction were also researched. Crosslinking density measurements were also carried out and calculated by Flory-Rehner theory. The results showed that with an increase of DVB, the semi-IPN exhibited a higher gel fraction. The glass temperature (Tg) was evaluated by DMA. Oil-absorptive properties were tested according to ASTM (F726-81). The highest oil absorptivity of sandwich oil-absorptive materials was 15.5 g/g to 10% crude oil diluted with toluene when the DVB content was 2%wt. (based on HEMA monomer weight) with PBMA/HEMA (70/30 by weight).

SYNTHESIS OF POLYETHYLENE OXIDE (PEO)–CHITOSAN HYDROGEL PREPARED BY GAMMA RADIATION TECHNIQUE

Crosslinked PEO hydrogel containing chitosan for wound dressing has been prepared by gamma radiation technique. Chitosan solutions with different concentration (0.5-2% w/v) have been blended with 5% aqueous solution of PEO and irradiated at the doses 20-40 kGy by gamma rays. The copolymers were characterized by Fourier transform infra red spectroscopy and their physico-chemical properties of hydrogels were evaluated in terms of gel fraction, swelling ratio, elongation at break and antimicrobial activities. It was found that under maximum condition of incorporation 1% chitosan with irradiation dose of 20 kGy, PEO-chitosan hydrogels with high gel fraction (85%), swelling ratio (10 g/g) and elongation at break (145%) were obtained. The examination of the microbe penetration shows that the prepared hydrogels can be considered as a good barrier against microbes. Thus, PEO-chitosan hydrogel showed satisfactory properties for use as a wound dressing.

Accelerated artificial ageing of new dimer fatty acid-based polyamides

Replacing petroleum-based raw materials with renewable resources is now a major challenge in terms of economical and environmental viewpoints. Vegetable oils are expected to be an interesting alternative to produce a new generation of bio-based polymers. Due to the possible outdoor exposure in diverse applications, knowledge of the resistance to weather of these new materials is an important issue, not only for aesthetic aspects as in rapid yellowing, but also for changes in their properties. New innovative dimer acid-based bio-polyamides (DAPA) were exposed to an artificial ageing environment produced by a UV/condensation weathering device for different times. To follow and to evaluate this material ageing, several techniques were employed to correlate the chemical modifications, with the morphology and the mechanical properties. The formation of peroxide was found to be very rapid and accompanied by high gel fraction formation and chain breaking. Infrared spectroscopy showed a build-up of carbonyl absorption in the range 1700–1780 cm −1, due to primary and secondary photo-oxidation products. In correlation with these morphological evolutions and in agreement with the high decrease of fusion enthalpy by differential scanning calorimetry, X-Ray diffraction showed an amorphous solid state after ageing. Strain–stress measurements revealed a change in DAPA behaviour, varying from a ductile to an elastomeric material, before and after ageing, respectively.

Guanidine-based polycarbonate hydrogels: from metal-free ring-opening polymerization to reversible self-assembling properties

Bio-inspired stabilization of aliphatic polycarbonate-based hydrogels has been carried out by the metal-free ring-opening co-polymerization (ROP) of 6-membered cyclic carbonates containing, respectively, protected guanidine and carboxylic acid functions. Polyethylene glycol (PEG) bound to methylcarboxy trimethylene carbonate at each extremity was used as the cross-linker, and the copolymerizations were performed in CH2Cl2 for 24 h in the presence of 1,8-diazabicyclo[5.4.0]-undec-7-ene (DBU) and N-(3,5-trifluoromethyl)phenyl-N′-cyclohexylthiourea (TU), the catalyst and co-catalyst, respectively. Well-defined hydrogels of various compositions and presenting a high gel fraction were obtained. HR-MAS NMR has been successfully employed to validate our purification technique as well as to assess the selective de-protection of the guanidine and carboxylic acid functions. Evidence of self-assembling properties has been attested by differential scanning calorimetry (DSC), HR-MAS NMR analysis and swelling test experiments in aqueous buffered solutions at pH 4 and 8.

Nano- and bulk-tack adhesive properties of stimuli-responsive, fullerene–polymer blends, containing polystyrene-block-polybutadiene-block-polystyrene and polystyrene-block-polyisoprene-block-polystyrene rubber-based adhesives

Nano-tack (measured using AFM) and bulk-tack adhesive forces of blends of C60 and either polystyrene-block-polybutadiene-block-polystyrene (SBS) or polystyrene-block-polyisoprene-block-polystyrene (SIS) triblock copolymer pressure sensitive adhesives were measured after exposure to white light irradiation. The nano-tack adhesive forces in C60–SIS/SBS were found to decrease with increasing C60 concentration and exposure time, approaching the value for 100% polystyrene, providing an indication that significant surface hardening and crosslinking of the soft isoprene and butadiene phases occurs in the presence of C60. Films produced during the study were smooth, having low RMS surface roughness, and showed nanoscale phase separation between the soft (diene) and hard (styrene) segments. This phase separation disappeared after addition of C60 sensitizer and white light irradiation. Bulk adhesive measurements (tack and peel strength) showed a similar trend with C60 concentration and exposure time, and in irradiated systems containing as little as 0.2wt% C60, a significant decrease in adhesion was observed. Estimated Tg (measured using DMA, shear mode) of the soft-block shifts to higher temperatures (increasing by 30–40°C), and high gel fractions were obtained, indicating the presence of chemically crosslinked networks.

Novel michael addition networks containing urethane hydrogen bonding

AbstractCovalently crosslinked networks based on poly(propylene glycol) bis(acetoacetate) with either neopentyl glycol diacrylate or hydroxyethyl acrylate derivatized bis(4‐isocyanatocyclohexyl)methane (HMDI) were prepared utilizing the Michael addition reaction in the presence of catalytic quantities of diazabicyclo[5.4.0]undec‐7‐ene (DBU). These networks were prepared in the absence of solvent at 23 °C without the formation of byproducts. Mechanical and thermal analyses of the networks were performed utilizing DMA, tensile testing, and TGA. Tensile analysis revealed that the introduction of hydrogen‐bonding urethane linkages in the diacrylate segment resulted in higher tensile strengths and elongation to break compared with nonhydrogen‐bonding analogs. All crosslinked products exhibited high gel fractions and excellent thermomechanical properties. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4118–4128, 2007

Shape memory polymers based on uniform aliphatic urethane networks

AbstractAliphatic urethane polymers have been synthesized and characterized, using monomers with high molecular symmetry, to form amorphous networks with very uniform supermolecular structures, which can be used as photo‐thermally actuable shape memory polymers (SMPs). The monomers used include hexamethylene diisocyanate (HDI), trimethylhexamethylenediamine (TMHDI), N,N,N′,N′‐tetrakis(hydroxypropyl)ethylenediamine (HPED), triethanolamine (TEA), and 1,3‐butanediol (BD). The new polymers were characterized by solvent extraction, NMR, XPS, UV/VIS, DSC, DMTA, and tensile testing. The resulting polymers were found to be single phase amorphous networks with very high gel fraction, excellent optical clarity, and extremely sharp single glass transitions in the range of 34–153°C. Thermomechanical testing of these materials confirms their excellent shape memory behavior, high recovery force, and low mechanical hysteresis (especially on multiple cycles), effectively behaving as ideal elastomers above Tg. We believe these materials represent a new and potentially important class of SMPs, and should be especially useful in applications such as biomedical microdevices. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Synthesis of biodegradable hydroxyethylcellulose cryogels by UV irradiation

Biodegradable macroporous hydroxyethylcellulose (HEC) cryogels of good quality and high gel fraction yield (95%) were synthesized via a facile method. The latter involved a relatively fast preparation of homogeneous semidilute solution of polymer and photoinitiator, (4-benzoylbenzyl)trimethylammonium chloride, followed by freezing at a defined negative temperature, an extremely short UV irradiation and subsequent thawing. HEC cryogels were successfully prepared also by using H2O2 as a photoinitiator. The effects of the temperature of freezing, the HEC molecular weight and the concentration of HEC solution on the cross-linking efficiency, the swelling ratio and the enzymatic degradation of HEC cryogels were investigated. Due to the cryoconcentration phenomenon, cryogels are formed at substantially low initial concentrations of the studied polymers. The highest values of gel fraction yield are achieved in the 1–2wt.% concentration range at −20°C. As a rule, the higher the molecular weight, the greater the gel fraction yield of the resulting cryogels. Scanning electron microscopy (SEM) analysis reveals that the interior structure of HEC cryogels is completely different from the conventional HEC hydrogels. HEC cryogels undergo decomposition by the action of cellulase enzyme, however, due to their specific morphology, the rate of degradation is slower compared to the conventional HEC hydrogel of similar gel fraction yield.

Preparation of Polyglycidol/SiO2 Hybrid Films with Triethoxysilyl-Capped Poly(ethylene glycol)

The preparation and properties of polyglycidol (PGLD)/silica hybrid gels were investigated. The gels were synthesized by the reaction of hyperbranched PGLD and triethoxysilyl-capped poly(ethylene oxide) in the presence of colloidal silica 80 nm in size or tetraethyl orthosilicate (TEOS) under acidic circumstances. The crosslinking reaction gave hybrid gels with a relatively high gel fraction over 98%. The degree of gel swelling obtained by the reaction using colloidal silica and TEOS decreased with SiO2 content, while the stiffness of the gels increased with SiO2 content. Gels prepared from TEOS exhibited a swelling ratio ranging from 25% to 40%, which was relatively higher than those from colloidal silica. They also demonstrated a higher stiffness in comparison to those from colloidal silica, probably due to high crosslinking.

Radiation-chemical synthesis of crown-containing poly(ethylene oxide) hydrogels. Swelling behavior and crown ether retention

Poly(ethylene oxide) hydrogels containing physically immobilized dicyclohexano-18-crown-6 (DCH18C6) were synthesized by radiation-chemical cross-linking. DCH18C6 concentration in initial polymer solution has insignificant effect on the gelation dose at the weight ratio of crown ether to polymer lower than 0.2. The higher molecular weight of PEO results in lower gelation dose and higher gel fraction. An increase in absorbed dose leads to a noticeable decrease in the swelling ratio corresponding to a denser hydrogel network. At the same time the absorbed dose in the range of 5–100 kGy has no pronounced effect on the DCH18C6 retention.

The curing performance of UV-curable semi-interpenetrating polymer network structured acrylic pressure-sensitive adhesives

This article reports on the curing performance of UV-curable acrylic binders prepared with trifunctional monomers and a photoinitiator. The curing reaction was achieved by direct excitation of pressure-sensitive adhesives (PSAs) by irradiation with a 100-W high-pressure mercury lamp with different UV doses. The curing performance of PSAs was studied by photo-differential scanning calorimetry (photo-DSC), gel-fraction determination and Fourier transform infrared–attenuated total reflection (FTIR–ATR) spectroscopy. The reaction rate and extent of UV curing were found to be strongly dependent on the curing rates of the trifunctional monomers, trimethylolpropane triacrylate (TMPTA) and trimethylolpropane ethoxylated (6) triacrylate (TMPEOTA), which have different molecular weights. Exothermic areas increased with increasing acrylic acid concentration. Moreover, gel fractions sharply increased after UV irradiation and then remained constant with prolonged UV exposure. TMPTA blends had higher gel fractions than TMPEOTA blends because of TMPTA's fast curing rate. Also, the gel fractions of TMPTA blends showed no variation with acrylic acid concentration. However, the FTIR–ATR absorption peak areas representing the relative concentration of C=C bonds showed more conspicuous trends for the curing reaction. Although the gel fractions of TMPTA blends showed no differences, the relative concentrations of C=C bonds increased with increasing acrylic acid concentration. In addition, TMPTA blends showed higher relative concentrations of C=C bonds because of the faster curing rate of TMPTA.

Biocomposites synthesized from chemically modified soy oil and biofibers

AbstractComposites with good mechanical properties were prepared from chemically modified soy oils and biofibers without additional petroleum‐based polymers. These composites were prepared from maleic anhydride and epoxide functionalized soybean oils that were cured in the presence of various biofibers (e.g., kenaf, kayocell, protein grits, and solka‐floc) by a flexible amine catalyst. Rigid thermosets characterized by a high‐crosslink‐density network and a high gel fraction were obtained. Fourier transform infrared was used to follow the cure reaction via the disappearance of the characteristic anhydride adsorptions. Composites with high tensile strength and low elongation were obtained when kenaf fibers were treated with (2‐aminoethyl)‐3‐aminopropyl‐trimethoxysilane and then added to the epoxidized/maleated soy matrix and cured with hexamethylenediamine. These biobased composites could provide inexpensive epoxy resin alternatives for a wide variety of industrial applications. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 69–75, 2006

Synthesis and characterization of triglyceride‐based polyols and tack‐free coatings via the air oxidation of soy oil

AbstractThe effect of time and temperature on the air oxidation of soybean oil in the absence of catalysts or added initiators was investigated. It was possible to divide the air oxidation of soybean oil into three regimes. The first regime of air oxidation resulted in insignificant change in the hydroxyl number. During this regime, it was proposed that natural antioxidants, which are present in raw soybean oil, were consumed and peroxide formation occurred. A drastic increase in hydroxyl number due to the formation and subsequent decomposition of peroxides marked the second regime of air oxidation. In the third regime of air oxidation, free radical crosslinking of the soybean oil occurred, and an insoluble gel was formed. The three regimes of air oxidation were used as a guide for the preparation of soy‐based polyols and crosslinked polymers. Crosslinked, tack‐free coatings were prepared from a metal catalyzed oxidation of soybean oil, where soybean oil and ambient oxygen were the only reactants. Higher temperatures (125°C) were more efficient than lower (50°C) for obtaining high gel fractions and tack‐free coatings. Cure of the coatings was expedited with exposure of the coating to UV irradiation after initial heating. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 690–697, 2006

Development of a fast drying hybrid lacquer in a low‐relative‐humidity environment based on kurome lacquer sap

AbstractHybrid lacquers that dry quickly in a low‐relative‐humidity environment were synthesized with the repeated kurome lacquer process and an organic silicone compound. An investigation by gel permeation chromatography showed that fractions with different molecular weights showed a lower monomer concentration than the pure kurome lacquer. Fourier transform infrared spectra of the hybrid lacquers revealed that absorption due to the ether of the quinone olefin and/or dibenzofuran appeared around 1470 and 1080 cm−1 and increased with the number of drying days. The gel fractions in the lacquer films increased according to the number of drying days, and this showed that the hybrid lacquers had higher gel fractions than the pure kurome lacquer in the initial stage of dryness. In addition, the drying mechanism of the hybrid lacquers was analyzed with an automatic drying time recorder and rigid‐body pendulum physical property testing measurements. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1055–1061, 2005

Thermal crosslinking of ethene copolymers containing 1,2-cyclopropane units

The possibility to obtain crosslinked polyethene (XLPE) from new ethene copolymers containing cyclopropane rings (C3), synthesized by ethene/1,3-butadiene copolymerizations with a hindered metallocene catalyst, has been explored. In particular, the thermal crosslinking of these copolymers, for C3 molar content in the range 0.3–2.7%, has been studied for annealing temperatures up to 200 °C and compared with the thermal behavior of other ethene–butadiene copolymers. Only for the ethene–C3 copolymers, the annealing procedures in the temperature range 160–200 °C lead to high gel fractions. These crosslinking processes occur in reasonable times and leave nearly unaltered the polymer crystallinity. Moreover, annealing procedures up to 140 °C do not produce appreciable crosslinking. All these features suggest that these new copolymers could be suitable for possible industrial fabrication processes of XLPE.

Branching and gelation in atom transfer radical polymerization of methyl methacrylate and ethylene glycol dimethacrylate

Bulk copolymerization of methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDMA) was initiated by methyl α-bromophenylacetate (MBPA) and mediated by copper bromide (CuBr) ligated with 1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA). The atom transfer radical polymerization (ATRP) of pure MMA yielded polymers with well controlled molecular weights and the homopolymerization was taken as a reference for the copolymerization analysis. The copolymerization experienced autoacceleration in rate due to a diffusion-controlled radical deactivation. The onset of autoacceleration came earlier with an increase in the EGDMA fraction. At low EGDMA fractions, the molecular weight versus conversion data deviated from linearity due to branching. The ratio of the copolymer molecular weight over homo-poly(methyl methacrylate) gave an estimate for the branching density, which increased initially and leveled off at high conversion. At high EGDMA fractions, the ATRP system experienced gelation. The pregel branching density increased with conversion, and at the gel point, it agreed with Flory's gelation theory assuming cross-linking free of cyclization. The branching densities at the high gel fractions were very close to the maximum values possibly achieved with the added EGDMA fractions. These results suggested that the ATRP system was very effective in preparing homogeneous polymer networks with a high cross-linking efficiency. POLYM. ENG. SCI., 45:720–727, 2005. © 2005 Society of Plastics Engineers

Radiation-induced grafting polymerization of MMA onto polybutadiene rubber latex

The grafting of methyl methacrylate (MMA) onto polybutadiene rubber latex by the direct radiation method was carried out. The effects of monomer concentration, absorbed dose and dose rate of gamma rays on the grafting yield were investigated. The graft copolymers were characterized by transmission electron microscopy (TEM), FTIR spectroscopy, and differential scanning calorimetry. TEM photographs revealed that the core–shell structures of latex particles are formed at low MMA content, and with the increasing of MMA content, the semi-IPN-like structure with core–shell could be developed due to the high gel fraction of polybutadiene (PBD) seed particles. In addition, infrared analysis confirmed that MMA could be grafted onto PBD molecular chains effectively under appropriate irradiation conditions. The interfacial adhesion between PBD rubber (core) and PMMA (shell) phases could be enhanced with the increase of MMA concentration.