Terminal Unsaturation Research Articles

Synthesis of Epoxy Methacrylate Resin and Coatings Preparation by Cationic and Radical Photocrosslinking.

This work involves the synthesis of hybrid oligomers based on the epoxy methacrylate resin. The EA resin was obtained by the modification of industrial-grade bisphenol A-based epoxy resin and methacrylic acid has been synthesized in order to develop multifunctional resins comprising both epoxide group and reactive, terminal unsaturation. Owing to the presence of both epoxy and double carbon–carbon pendant groups, the reaction product exhibits photocrosslinking via two distinct mechanisms: (i) cationic ring-opening polymerization and (ii) free radical polymerization. Monitoring of EA synthesis reactions over time using PAVs, MAAC and NV parameters, and the FT-IR method reveals that esterification reactions proceed faster at the start, exhibiting over 40% of conversion within the initial 60 min, which can be associated with a relatively high concentration of reactive sites and low viscosity of the reaction mixture at the initial reaction stage. With the further increase in the reaction time, the reaction rate tends to decrease. The control of the EA synthesis process can guide how to adjust reactions to obtain EAs with desired characteristics. Based on obtained values, one can state that the optimum synthesis time of about 4–5 h should be adopted to prepare EAs having both epoxy groups and unsaturated double bonds. The structure of the obtained EA was confirmed by FT-IR and NMR methods, as well as the determination of partial acid value and epoxy equivalent. Samples at various stages of synthesis were cured with UV radiation in order to study the kinetics of the process according to cationic and radical polymerization determined via photo-differential scanning calorimetry (photo-DSC) and real-time infrared spectroscopy (RT-IR) and then the properties of the cured coatings were tested. It turned out that the cationic polymerization was slower with a lower conversion of the photoreactive groups, as compared to the radical polymerization. All the obtained EA coatings were characterized by good properties of cured coatings and can be successfully used in the coating-forming sector.

Photocurable Epoxy Acrylate Coatings Preparation by Dual Cationic and Radical Photocrosslinking

In this work, epoxy acrylate resin (EA) based on the industrial-grade bisphenol A-based epoxy resin (Ep6) and acrylic acid (AA) has been synthesized in order to develop hybrid resin comprising both epoxide group and reactive, terminal unsaturation. Obtained epoxy acrylate prepolymer was employed to formulate photocurable coating compositions containing, besides the EA binder, also cationic or radical photoinitiators. Hence, when cationic photoinitiators were applied, polyether-type polymer chains with pending acrylate groups were formed. In the case of free radical polymerization, epoxy acrylates certainly formed a polyacrylate backbone with pending epoxy groups. Owing to the presence of both epoxy and double carbon–carbon pendant groups, the reaction product exhibits photocrosslinking via two distinct mechanisms: (i) cationic ring-opening polymerization and (ii) free radical polymerization. Therefore, photopolymerization behavior of synthetized hybrid resin with various photoinitiators was determined via photo-differential scanning calorimetry (photo-DSC) and real-time infrared spectroscopy (RT-IR) methods, and properties of cured coatings were investigated. The performance of the following type of photoinitiators was tested in the cationic photopolymerization: diaryliodonium cations or triarylsulfonium cations, and the following type of photoinitiators were used to induce free radical photopolymerization: α-hydroxyketones, acylphosphine oxides, and their mixtures. Lastly, the basic physicomechanical properties of cured coatings, such as tack-free time, hardness, adhesion, gloss, and yellowness index, were evaluated. Some structural factors and parameters of cationic and radical photoinitiators and photopolymerization mechanisms affecting the epoxy acrylate hybrid coatings performance are discussed.

Amphiphilic Triblock Copolymers Containing Polypropylene as the Middle Block.

The synthesis of stereoregular telechelic polypropylene (PP) and their use to access triblock amphiphilic copolymers with the PP block located in the center is described. The strategy consists of selectively copolymerizing propylene and a di-functional co-monomer (1,3-diisopropenylbenzene) to yield a α,ω-substituted polypropylene. Initiation of the copolymerization favors insertion of DIB over propylene; propagation steps favor insertion of propylene. Termination via a chain-transfer reaction yields the terminal unsaturation of the polymer. The telechelic polypropylene is then converted into α,ω-hydroxyl-terminated polypropylene and used as a macroinitiator for the synthesis of triblock copolymers. Water-soluble amphiphilic triblock polymers are also synthesized. The use of catalytic reactions simultaneously provides the stereocontrol of the polypropylene and high productivity (multiple chains of block copolymer per metal center).

Amphiphilic Triblock Copolymers Containing Polypropylene as the Middle Block

AbstractThe synthesis of stereoregular telechelic polypropylene (PP) and their use to access triblock amphiphilic copolymers with the PP block located in the center is described. The strategy consists of selectively copolymerizing propylene and a di‐functional co‐monomer (1,3‐diisopropenylbenzene) to yield a α,ω‐substituted polypropylene. Initiation of the copolymerization favors insertion of DIB over propylene; propagation steps favor insertion of propylene. Termination via a chain‐transfer reaction yields the terminal unsaturation of the polymer. The telechelic polypropylene is then converted into α,ω‐hydroxyl‐terminated polypropylene and used as a macroinitiator for the synthesis of triblock copolymers. Water‐soluble amphiphilic triblock polymers are also synthesized. The use of catalytic reactions simultaneously provides the stereocontrol of the polypropylene and high productivity (multiple chains of block copolymer per metal center).

Evaluation of new coinitiators of camphorquinone useful in the radical photopolymerization of dental monomers

This work reports the design and synthesis of two new monomers with tertiary amines and four methacrylic (MBTTM) or acrylic (MBTTA) terminal unsaturations, and their evaluation as coinitiators in the photopolymerization of monomers useful in dentistry. Both monomers were characterized by FT-IR, 1H NMR, and UV–vis spectroscopies. Experimental Bis-GMA/TEGDMA or UDMA/TEGDMA resins were formulated using camphorquinone as the photoinitiator and the MBTTM or MBTTA compounds as coinitiators. As control, resins using EDAB as coinitiator were formulated. The photopolymerizable resins formulated using the new coinitiators achieved double bond conversion values close to 40% in 30 s. Regarding polymerization rate, experimental resins formulated with MBTTM or MBTTA had lower values. The flexural strength of the experimental BisGMA/TEGDMA resins did not have statistically significant differences with the control group (p > 0.05). On the other hand, the experimental resins formulated with UDMA/TEGDMA presented higher flexural strength and elastic modulus. Finally, the cell viability test showed that none of the resins formulated with MBTTM or MBTTA as coinitiators were cytotoxic. Due to their characteristics, MBTTM and MBTTA monomers are potentially useful as coinitiators in the formulation of photopolymerizable materials for dental use.

Microwave-assisted hydrosilylation of polypropylene and its application to in-situ grafted polypropylene/SiO2 nanocomposites

Grafting end-functionalized polypropylene (PP) to the surfaces of nanoparticles is a promising approach in boosting physical properties of PP-based nanocomposites. In this study, a practical pathway is presented for the fabrication of PP-grafted nanocomposites: Reactive silicon alkoxy groups were introduced through microwave-assisted hydrosilylation of terminal unsaturation of vis-breaking PP. Thus obtained hydrosilylated PP was added as a reactive additive in melt compounding of PP with SiO2 nanoparticles to implement in-situ grafting. Significant improvements were attained in the dispersion of SiO2 nanoparticles, the crystallization rate and the tensile strength.

Design, synthesis, and cytotoxicity evaluation of threonine-based galactoceramide with aromatic groups and various fatty-acyl side chains

In galactoceramides, presence of fatty-acyl group on amide moiety or phytosphingosine group is some of the important features that influence the cytotoxicity. Continuous efforts are in progress to modify the fatty-acid moiety and phytosphingosine group present on the galactoceramides to enhance the cytotoxic potential of these compounds. Hence, in the present study, threonine-based β-galactoceramide and its derivatives were prepared by modifying the fatty-acyl group on amide moiety with different fatty-acyl moieties and aromatic acids employing trichloroacetimidate methodology. The structurally related threonine-based ceramide part was synthesized in multi-step process using different reagents. The ceramide part was glycosylated with galactose using trichloroacetimidate as donor. Further, all the synthesized compounds were evaluated for in vitro cytotoxicity against three cancer cell lines and one normal cell line and all the compounds exhibited good to moderate cytotoxicity against all the tested cancer cell lines. In aromatic derivatives, the compound 8i exhibited promising activity against MCF7, A549 and HeLa cancer cell lines with IC50 values of 14.08, 14.78, and 16.70 µM, respectively. In fatty-acid derivatives, two compounds exhibited promising activity, i.e., compound 8m against HeLa with IC50 value 16.34 µM and compound 8n against MCF7 with IC50 value 18.05 µM. Based on structure–activity relationship, aromatic acid derivatives exhibited potential activity as compared to fatty-acid derivatives. Further, the influence of some of the key factors such as spacer chain length between aromatic residue and amide functional group, methoxy substituents on aryl group, terminal unsaturation of fatty acid and branching chain effect on the cytotoxicity are discussed.

Pt@ZIF-8 composite for the regioselective hydrogenation of terminal unsaturations in 1,3-dienes and alkynes

Size and regioselective catalysis in a Pt@ZIF-8 composite.

Stereoselective total synthesis of rubrenolide and rubrynolide

The stereoselective total synthesis of rubrenolide and rubrynolide has been accomplished successfully. The synthetic strategy involves Evans alkylation and asymmetric CBS reduction to establish the required stereogenic centers. Other key steps involve Horner–Wadsworth–Emmons (HWE) olefination to construct the side chain, alkynylation to introduce terminal unsaturation in the side chain, and TEMPO-BAIB-mediated lactonization.

Unsaturated phosphazenes as co-solvents for lithium-ion battery electrolytes

This paper covers the synthesis and use of a related family of cyclic phosphazene solvents containing terminal unsaturations that are being considered as electrolyte additives in lithium-ion cells. A brief synopsis on the synthesis and purification of these compounds is given. Data will be presented that covers physical and chemical properties of the phosphazenes as well as the properties when blended at various levels with representative organic carbonate baseline solvents. Electrochemical cycling data will be presented using commercially available electrode couples as well as studies focusing on cell performance at early lifetime as well as after repeated cycles. Conclusions regarding the effect of the unsaturated phosphazene compounds and their interaction with various alkyl carbonates, and their effect on cell performance will be presented.

Copolymerization of Ethylene and Methyl Acrylate by Cationic Palladium Catalysts That Contain Phosphine-Diethyl Phosphonate Ancillary Ligands

A series of benzo-linked phosphine-diethyl phosphonate (P-PO) and phosphine-bis(diethyl phosphonate) (P-(PO)2) ligands and the corresponding (P-PO)PdMe(2,6-lutidine)+ and (P-(PO)2)PdMe(2,6-lutidine)+ complexes were synthesized. Cationic (P-PO)PdMe(2,6-lutidine)+ complexes are active for ethylene oligomerization/polymerization, with activities of 2 kg mol–1 h–1 for {κ2-1-PiPr2-2-P(O)(OEt)2-5-Me-Ph}PdMe(2,6-lutidine)+ (3c), 125 kg mol–1 h–1 for {κ2-1-PPh2-2-P(O)(OEt)2-5-Me-Ph}PdMe(2,6-lutidine)+ (3a), and 1470 kg mol–1 h–1 for {κ2-1-P(2-OMe-Ph)2-2-P(O)(OEt)2-Ph}PdMe(2,6-lutidine)+ (3b). The polyethylene is highly linear, with over 80% terminal unsaturation and low (230–1890 Da) molecular weight in all cases. 3b copolymerizes ethylene with methyl acrylate, exhibiting highly selective (95%) in-chain (rather than chain-end) acrylate incorporation. The P-(PO)2 catalyst {κ2-1-P(4-tBu-Ph)(2-P(O)(OEt)2-5-Me-Ph)-2-P(O)(OEt)2-5-Me-Ph}PdMe(2,6-lutidine)+ (3d) is more active for ethylene homopolymerization (2640 kg mol–1 h–1), yielding linear, low-molecular-weight polymer (1280–1430 Da) with predominantly internal olefin placement. In ethylene/methyl acrylate copolymerization, 3d incorporates 2.6 mol % methyl acrylate, 60% of which is in-chain. Both 3b and 3d catalyze ethylene/acrylic acid copolymerization, albeit with low (<10 kg mol–1 h–1) activities and acrylic acid incorporation up to 1.1 mol %.

A novel polymerization approach via thiol‐yne addition

AbstractThe ability of thiyl radicals to add to terminal unsaturations in an efficient way made them considered being one of the click reactions. Recently, thiol‐yne addition reactions have been used extensively for the synthesis of crosslinked networks and dendrimers and postpolymerization functionalization protocols. Herein, we report a novel step‐growth type reaction for highly functional linear polymers using a monoalkyne and dithiol compound. First, we investigated the model reaction between 1‐octyne and 1‐octanethiol as well as 1,4‐butanedithiol compounds, which were initiated via self‐, thermal‐, and UV‐initiation; the UV‐initiation was found to be the most efficient method and completed within 2‐h reaction time. The same conditions were applied for the polymerization of four different functional alkynes bearing different functional groups with two dithiol compounds. All polymerizations resulted in highly functional linear polymers with number averaged molecular weights ranging from 5 to 30 kDa, except for propargylic acid and its methyl ester, where only oligomers formed. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Thermal Oxidation and Structural Changes of Degraded Polyethylene in an Oxygen Atmosphere

High-temperature bulk thermolysis of high density polyethylene was performed to obtain degraded polyethylene, which was then left in an oxygen atmosphere for oxidation reaction at 160°C at different oxidation times, yielding a series of polyethylene degradation–oxidation products. Using infrared spectroscopy, chemical titration, gel chromatography, and differential scanning calorimetry, the structural changes of the polyethylene degradation–oxidation products were investigated. Hydroxyl, carboxyl, ester, and other functional groups were introduced into the molecular chains of oxidation products, and the number of carboxyl groups sharply increased with increasing oxidation time. The breaking of molecular chains as well as combination reactions, such as esterfication, during the oxidation process lead to decrease of number-average molecular weight () and increase of both weight-average molecular weight () and molecular weight distribution, and an initial increase and leveling off of the carboxyl number per molecular chain. It is noteworthy that oxidation occurred primarily near weak bonds, mainly terminal vinyl unsaturations. Thus, compared with degraded polyethylene, the oxidation products showed little changes in the melting and crystallization behaviors; even when the oxidation time was up to 4 hr, the drop in the melting and crystallization temperature was less than 3°C. These results might lay a foundation for exploring tailored low molecular weight polymers to be used just as they are or after chemical modifications of olefinic functions.

Effect of the vinyl concentration on the structural and rheological characteristics of peroxide-modified high-density polyethylenes

The effect of the hydrogenation of the terminal vinyl groups on the peroxide modification and rheological properties of high-density polyethylene (HDPE) was investigated. The aim of the study was to determine exclusively the effect of the terminal vinyl groups on the peroxide crosslinking and rheological properties of HDPE with one polymer type. This was achieved by hydrogenation of the terminal vinyl groups of a commercial HDPE to obtain an identical material from a structural point of view, which differed only in the nature of the terminal unsaturations, and the comparison of its level of peroxide crosslinking with that of the original polymer. Hydrogenated and unhydrogenated polymer samples were modified at 170°C with different amounts of organic peroxide ranging from 125 to 5000 ppm. Changes in the molecular structure were determined by Fourier transform infrared spectroscopy, size exclusion chromatography, and rheological measurements. Hydrogenation of the terminal groups of the original polymer significantly reduced the rate of modification or crosslinking. The dynamic viscosity and elasticity increased with the level of peroxide modification. Unhydrogenated samples exhibited rapid increases in viscosity and elastic modulus, whereas their hydrogenated counterparts required about 500% of the amount of peroxide needed for the unhydrogenated sample to attain similar structural changes. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

A Joined Theoretical−Experimental Investigation on the 1H and 13C NMR Signatures of Defects in Poly(vinyl chloride)

1H and 13C chemical shifts of PVC chains have been evaluated using quantum chemistry methods in order to evidence and interpret the NMR signatures of chains bearing unsaturated and branched defects. The geometrical structures of the stable conformers have been determined using molecular mechanics and the OPLS force field and then density functional theory with the B3LYP functional and the 6-311G(d) basis set. The nuclear shielding tensor has been calculated at the coupled-perturbed Kohn-Sham level (B3LYP exchange-correlation functional) using the 6-311+G(2d,p) basis set. The computational scheme accounts for the large number of stable conformers of the PVC chains, and average chemical shifts are evaluated using the Maxwell-Boltzmann distribution. Moreover, the chemical shifts are corrected for the inherent and rather systematic errors of the method of calculation by employing linear regression equations, which have been deduced from comparing experimental and theoretical results on small alkane model compounds containing Cl atoms and/or unsaturations. For each type of defect, PVC segments presenting different tacticities have been considered because it is known from linear PVC chains that the racemic (meso) dyads are characterized by larger (smaller) chemical shifts. NMR signatures of unsaturations in PVC chains have been highlighted for the internal -CH=CH- and -CH=CCl- units as well as for terminal unsaturations like the chloroallylic -CH=CH-CH2Cl group. In particular, the 13C chemical shifts of the two sp2 C atoms are very close for the chloroallylic end group. The CH2 and CHCl units surrounding an unsaturation present also specific 13C chemical shifts, which allow distinguishing them from the others. In the case of the proton, the CH2 unit of the -CHCl-CH2-CCl=CH- segment presents a larger chemical shift (2.6-2.7 ppm), while some CHCl units close to the -CH=CH- unsaturations appear at rather small chemical shifts (3.7 ppm). The -CH2Cl and -CHCl-CH2Cl branches also display specific signatures, which result in large part from modifications of the equilibrium conformations and their reduced number owing to the increased steric interactions. These branches lead to the appearance of 13C peaks at lower field associated either to the CH unit linking the -CH2Cl and -CHCl-CH2Cl branches (50 ppm) or to the CHCl unit of the ethyl branches (60 ppm). The corresponding protons resonate also at specific frequencies: 3.5-4.0 ppm for the -CH2Cl branch or 3.8-4.2 ppm for the terminal unit of the -CHCl-CH2Cl branch. Several of these signatures have been detected in the experimental 1H and 13C NMR spectra and are consistent with the reaction mechanisms.

Pyrrolo-dC oligonucleotides bearing alkynyl side chains with terminal triple bonds: synthesis, base pairing and fluorescent dye conjugates prepared by the azide–alkyne “click” reaction

5-(Octa-1,7-diynyl)-2'-deoxyuridine was converted into the furano-dU derivative 7 by copper-catalyzed cyclization; the pyrolodC-derivative 3 was formed upon ammonolysis. The bicyclic nucleosides 3 and 7 as well as the corresponding non-cyclic precursors 4 and 6 all containing terminal C[triple bond]C bonds were conjugated with the non-fluorescent 3-azido-7-hydroxycoumarin 5 employing the copper(I)-catalyzed Huisgen-Sharpless-Meldal cycloaddition "click reaction". Strongly fluorescent 1H-1,2,3-triazole conjugates (30-33) are formed incorporating two fluorescent reporters-the pyrdC nucleoside and the coumarin moiety. Oligonucleotides incorporating 6-alkynyl and 6-alkyl 7H-pyrrolo[2,3-d]pyrimidin-2(3H)-one nucleosides (3 and 2f) have been prepared by solid-phase synthesis using the phosphoramidite building blocks 10 and 13 ; the pyrrolo-dC oligonucleotides are formed during ammonia treatment. The duplex stability of oligonucleotides containing 3 and related derivatives was studied. Oligonucleotides with terminal triple bonded nucleosides such as 3 are more stabilizing than those lacking a side chain with terminal unsaturation; open-chain derivatives (4) are even more efficient. The click reaction was also performed on oligonucleotides containing the pyrdC-derivative and the fluorescence properties of nucleosides, oligonucleotides and their coumarin conjugates were studied.

Microgel formation and thermo‐mechanical properties of UV‐curing unsaturated polyester acrylates

AbstractThe effect of internal and terminal unsaturation on the properties of the acrylated polyester films was investigated. Four types of acrylated polyester resin were prepared using adipic acid, maleic anhydride, neopentyl glycol, trimethylolpropane, and acrylic acid. Terminal and internal double bond content as well as branching was adjusted by the molar quantities of trimethylolpropane and maleic anhydride, respectively. A reactive diluent, trimethylolpropane triacrylate (TMPTA), was also used. A three‐factor, three‐level Box‐Behnken design was used to investigate complex nonlinear relationships. Dynamic mechanical, fracture toughness, and tensile properties were evaluated with respect to the amount of terminal and internal unsaturation, and reactive diluent concentration. It was found that microgel formation extensively affects the final UV‐cured film properties. Small quantities of microgels function as micro‐support units, whereas high extent of microgelation causes phase separation through cluster formation and hence, decreases the mechanical properties. It is essential to control the extent of microgelation and phase separation to optimize product performance. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Synthesis of macromonomers of acrylic acid by telomerization: Application to the synthesis of polystyrene‐g‐poly(acrylic acid) copolymers

AbstractThe synthesis of macromonomers of acrylic acid was performed by telomerization in a three‐step process. The first step was the telomerization of tert‐butyl acrylate in the presence of thioglycolic acid. Different molecular weights were obtained with different ratios of the monomer to the transfer agent. Good control of the molecular weights and architectures of the oligomers (e.g., the presence of an acid function on the chain end) was observed. The transfer constant of tert‐butyl acrylate with thioglycolic acid was assessed (chain‐transfer constant = 0.6). In the second step, the terminal unsaturation of the oligomers was obtained by the reaction of the terminal acid groups with 2‐isocyanatoethyl methacrylate to yield the macromonomers of tert‐butyl acrylate. In the last step, the tert‐butyl acrylate groups were hydrolyzed in the presence of trifluoroacetic acid at room temperature. The macromonomers were copolymerized with styrene to obtain graft copolymers, and the reactivity ratios were evaluated. Finally, the copolymers were characterized with surface electron microscopy and atom force microscopy. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 395–415, 2007

Evaluation of Philips and Ziegler–Natta high-density polyethylene degradation during processing in an internal mixer using the chain scission and branching distribution function analysis

The oxidative and thermo-mechanical degradation of HDPE was studied during processing in an internal mixer under two conditions: totally and partially filled chambers, which provides lower and higher concentrations of oxygen, respectively. Two types of HDPEs, Phillips and Ziegler–Natta, having different levels of terminal vinyl unsaturations were analyzed. Materials were processed at 160, 200, and 240 °C. Standard rheograms using a partially filled chamber showed that the torque is much more unstable in comparison to a totally filled chamber which provides an environment depleted of oxygen. Carbonyl and transvinylene group concentrations increased, whereas vinyl group concentration decreased with temperature and oxygen availability. Average number of chain scission and branching ( n s) was calculated from MWD curves and its plotting versus functional groups' concentration showed that chain scission or branching takes place depending upon oxygen content and vinyl groups' consumption. Chain scission and branching distribution function (CSBDF) values showed that longer chains undergo chain scission easier than shorter ones due to their higher probability of entanglements. This yields macroradicals that react with the vinyl terminal unsaturations of other chains producing chain branching. Shorter chains are more mobile, not suffering scission but instead are used for grafting the macroradicals, increasing the molecular weight. Increase in the oxygen concentration, temperature, and vinyl end groups' content facilitates the thermo-mechanical degradation reducing the amount of both, longer chains via chain scission and shorter chains via chain branching, narrowing the polydispersity. Phillips HDPE produces a higher level of chain branching than the Ziegler–Natta's type at the same processing condition.

Terminal Functionalization of Polypropylene by Radical-Mediated Thiol−Ene Addition

The radical-mediated addition of alkanethiols to the terminal unsaturation of polypropylene (PP) is used to prepare functional polyolefin derivatives without altering the molecular weight of the parent material. The sulfide product of thiol−ene addition, as well as the internal olefin resulting from a remarkable thiyl radical-mediated olefin migration, is characterized using a model hydrocarbon, 2,4-dimethylhept-1-ene. The yield of 3-mercaptopropyltrimethoxysilane (MPTMS) addition to atactic-PP is examined in detail, and the functionalization of high molecular weight isotactic-PP is used to produce moisture-curing resins that bind to siliceous fillers. The limited unsaturation content of PP, along with the high temperatures needed to modify the resin in its melt state, is shown to impact negatively on the reaction conversion due to the reversibility of thiyl radical attack on olefin.