Chain Extension Reaction Research Articles

Sticky swinging arm dynamics: studies of an acyl carrier protein domain from the mycolactone polyketide synthase.

Type I modular polyketide synthases (PKSs) produce polyketide natural products by passing a growing acyl substrate chain between a series of enzyme domains housed within a gigantic multifunctional polypeptide assembly. Throughout each round of chain extension and modification reactions, the substrate stays covalently linked to an acyl carrier protein (ACP) domain. In the present study we report on the solution structure and dynamics of an ACP domain excised from MLSA2, module 9 of the PKS system that constructs the macrolactone ring of the toxin mycolactone, cause of the tropical disease Buruli ulcer. After modification of apo ACP with 4'-phosphopantetheine (Ppant) to create the holo form, (15)N nuclear spin relaxation and paramagnetic relaxation enhancement (PRE) experiments suggest that the prosthetic group swings freely. The minimal chemical shift perturbations displayed by Ppant-attached C3 and C4 acyl chains imply that these substrate-mimics remain exposed to solvent at the end of a flexible Ppant arm. By contrast, hexanoyl and octanoyl chains yield much larger chemical shift perturbations, indicating that they interact with the surface of the domain. The solution structure of octanoyl-ACP shows the Ppant arm bending to allow the acyl chain to nestle into a nonpolar pocket, whereas the prosthetic group itself remains largely solvent exposed. Although the highly reduced octanoyl group is not a natural substrate for the ACP from MLSA2, similar presentation modes would permit partner enzyme domains to recognize an acyl group while it is bound to the surface of its carrier protein, allowing simultaneous interactions with both the substrate and the ACP.

A novel biodegradable polyurethane based on hydroxylated polylactic acid and tung oil mixtures. I. Synthesis, physicochemical and biodegradability characterization

A novel biodegradable polylactic acid-based polyurethane (PU) was synthesized via a chain extension reaction between hydroxylated polylactic acid (PLA-OH) and hydroxylated tung oil (HTO) using 1,6-hexamethylene diisocyanate (HDI) to link the two polyols and dibutyltin dilaurate (DBTDL) as a catalyst. Both PLA-OH and HTO, as polyols, were separately synthesized in our laboratory. Three different molecular weights of PLA-OH prepolymers were used, and the molar ratio of PLA-OH to HTO was also changed to investigate the effect of these two parameters on the structure and properties of the final PUs. Chemical structures of PLA-OH, HTO, and final PUs were investigated by Fourier transform infrared (FTIR) and Hydrogen-1 nuclear magnetic resonance (1HNMR) spectroscopies. Thermal transitions and thermal stability of the final PUs were, respectively, studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The FTIR and 1HNMR results showed that the chain-extension reaction of the two polyols with HDI was sufficiently achieved. The TGA results showed that the polyurethanes based on the lower molecular weight PLA segments were more thermally stable; it was not degraded up to 270 °C. DSC results showed that incorporating HTO in the PU chains led to formation of more flexible PU chains, while the glass transition temperatures of the PUs of higher PLA-OH molecular weights were higher than those of lower ones.

4-Vinylphenyl Glycidyl Ether: Synthesis, RAFT Polymerization, and Postpolymerization Modifications with Alcohols

4-Vinylphenyl glycidyl ether (4VPGE), an epoxide-containing styrenic monomer, was synthesized and then polymerized in a controlled fashion under reversible addition–fragmentation chain-transfer (RAFT) polymerization conditions using butyl 1-phenylethyl trithiocarbonate as the chain-transfer agent. The high degree of chain-end functionalization of the produced polymers was confirmed by chain extension reactions with styrene that afforded well-defined block copolymers. Phenyl glycidyl ether was utilized as a model compound to identify the optimal reaction conditions for alcoholysis of the glycidyl moiety using BF3 as a Lewis acid catalyst, and postpolymerization modifications were subsequently carried out on the epoxide groups of poly4VPGE with a library of structurally diverse alcohols to yield a number of β-hydroxy ether-functionalized polymers.

Optimizing Activators Regenerated by Electron Transfer for Atom Transfer Radical Polymerization of Methyl Methacrylate Initiated by Ethyl 2-bromopropionate

In this study, we used ethyl 2-bromopropionate (EBrP) as an initiator of activators regenerated by electron transfer for atom transfer radical polymerization (ARGET ATRP) of methyl methacrylate (MMA). We investigated in detail the effect on polymerization of different kinds of reducing agents and ligands, the amounts of the reducing agent and catalyst, and reaction temperature. We determined the molecular weight and dispersity of the polymers by gel permeation chromatography (GPC). The results reveal glucose to be the best reducing agent for this system. The monomer conversion increased with increases in the reaction temperature and in the feeding amounts of the reducing agent and catalyst. The optimum amount of the reducing agent and minimal amount of catalyst required depend on the particular system. For example, we polymerized MMA with 200 ppm of catalyst and 15-fold of glucose/CuCl2 resulting in a PMMA with high Mn (Mn,GPC = 48 700, Mn,theo = 48 500) and low dispersity (1.27). The first-order kinetics show that the molecular weights increased linearly with the monomer conversion and are consistent with the theoretical values, the chain extension reaction and end group analysis results also demonstrate that the characteristics of polymerization process belong to a typical “living”/controlled radical polymerization. Moreover, 1H-NMR analysis results indicate the stereoregularity of the polymer is given priority over syndiotactic architecture and the effect of the type of ligand on the stereoregularity is very slight.

Ultrasonically enhanced bulk ATRP of methyl methacrylate at high conversion with good livingness and control

A great challenge in controlled radical polymerization such as atom transfer radical polymerization (ATRP) has been related to keep the livingness and molecular weight control of the reaction at high conversion, especially in bulk polymerization. The objective of this work is to investigate the effects of ultrasound power on the polymerization at high conversion. The initiator for continuous activator regeneration ATRP is used for bulk polymerization of methyl methacrylate (MMA) as the model system. Good livingness and control up to high conversion are obtained through employing ultrasonic waves. By this method, MMA is polymerized in bulk up to “glass state” (88%) at 70°C with polydispersity about 1.2 under an operating frequency of 40 kHz and output power of 100 W. Chain extension reaction proves the livingness of the synthesized polymers at glassy state. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1683–1687, 2016

Investigation of the synthesis of poly-D,L-lactide-co-poly(ethylene glycol) flexible thermoplastic

ABSTRACTA series of biodegradable poly(D,L-lactide)-poly(ethylene glycol) multiblock poly(ether-ester-urethane)s with various lactide-to-poly(ethylene glycol) (LA/PEG) mole ratios has been successfully synthesized by ring-opening polymerization (ROP) followed by chain extension reaction through formation of urethane linkage. Resulting FT-IR spectra indicate complete polymerization of lactide monomers, while NMR analysis quantitatively marks the chain length of polymer blocks. The molecular weight and dispersion index of copolymers were investigated by GPC analysis. DSC thermogram and XRD diffractogram of the prepared copolymers were studied as well for revealing the thermal and crystallinity behavior of the copolymer as LA/PEG mole ratios varied.

Novel graft copolymers with aliphatic polyether and polyester main chains

A series of new graft copolymers was synthesized by a “grafting to” approach, in the course of which the polymer backbone was build up first by a chain extension reaction of polyether or polycaprolactone diols with bis-N-acyl lactams. During the first reaction step, benzoxazinone groups were introduced into the backbone which served as grafting sites for monoamino-terminated polyamide 12 or polystyrene. Chain extension and grafting could be performed successively and with high selectivity in the melt at 180–220 °C.The morphology and the thermo-mechanical behavior of the graft copolymers were strongly influenced by the type of the grafted side chains. Polymers with polyamide grafts exhibited a two phase morphology with a spherulitic superstructure in the micrometer scale. The tensile behavior of these polymers was characterized by a certain elastic component.In contrast, the phase morphology of a polystyrene grafted polymer was much finer. A strong influence on the glass transitions revealed improved compatibility between the components. Pronounced strain hardening was observed during the tensile test of polystyrene grafted samples.

Polyurethane/polyhydroxyurethane hybrid polymers and their applications as adhesive bonding agents

A polyurethane/polyhydroxyurethane (PU/PHU) hybrid polymer was synthesized by reaction of a cyclic-carbonate-terminated prepolymer with triethylenetetramine without employing isocyanates in the final curing step. This cured elastomer contains traditional urethane linkages from the initial prepolymer reaction as well as hydroxyurethane linkages from the final chain extension reaction. The PU/PHU hybrid exhibits microphase separation as made apparent by the presence of two glass transitions and elastomeric properties with Young's modulus of 37MPa and strain at break of 350%. Most importantly, the PU/PHU hybrid polymer exhibits adhesion to polyimide, poly(vinyl chloride) (PVC), and aluminum substrates that is similar to or enhanced relative to those of polyurethane controls and literature values for typical polyurethane adhesives. In particular, the PU/PHU hybrid has T-peel forces of 7.8, 10.5, and 3.4N/mm on polyimide, PVC, and aluminum, respectively, and undergoes predominantly cohesive failure rather than adhesive failure. The application of this material as a model consumer-applied adhesive for potential replacement of isocyanate-based polyurethanes is also briefly discussed.

Aliphatic poly(ester amide)s from sebacic acid and aminoalcohols of different chain length: Synthesis, characterization and soil burial degradation

High molar mass aliphatic poly(ester amide)s were prepared from sebacic acid and aminoalcohols of different chain length by melt polycondensation and chain extension reactions. Low molecular weight aliphatic poly(ester amide)s were synthesized by melt polycondensation starting from sebacic acid and linear aminoalcohols of different chain lengths, ranging from 2 to 6 methylene groups. Then, chain extension reaction was carried out by using 1,6-hexamethylene diisocyanate (HMDI). The poly(ester amide)s obtained were characterized by viscometry, DSC, MALDI mass spectrometry, and NMR. The poly(ester amide)s with a reduced viscosity ranging from 0.5 to 1.5 dL g−1 showed a good film-ability.The degradability in soil of poly(ester amide) film samples was investigated. The weight loss of commercial poly(3-hydroxy butyrate) (PHB), poly(3-hydroxy butyrate-co-3-hydroxy valerate) 76/24 (P(HB-co-HV) 76/24), poly(caprolactone) (PCL), and two poly(butylene succinate) based samples (Bionolle), was also studied under controlled soil burial conditions. The rates of soil burial degradation of synthetic poly(ester amide)s and commercial biodegradable polyesters having different structures were compared. Interestingly, the poly(ester amide)s synthesized show higher weight loss values than polyester films after 5 and 10 days of soil burial degradation test.

Thioether-Mediated Degenerative Chain-Transfer Cationic Polymerization: A Simple Metal-Free System for Living Cationic Polymerization

Cationic degenerative chain-transfer polymerization of vinyl ethers and p-alkoxystyrenes was investigated using a series of thioethers as a reversible chain-transfer agent via the equilibrium between a growing carbocationic species and the resulting sulfonium intermediate in the presence of a small amount of triflic acid (TfOH) as a cationogen. The stable thioether, which was easily prepared from isobutyl vinyl ether (IBVE) and n-butanethiol, efficiently controls the molecular weight of the resulting poly(IBVE) up to Mn ∼ 1 × 105 with narrow molecular weight distributions (MWDs) (Mw/Mn ∼ 1.2). Upon increasing the bulkiness of the alkyl substituents in the thiols (R–SH; R: n-Bu < s-Bu < t-Bu) or those in the monomers (CH2═CHOR′, R′: ethyl < isobutyl < cyclohexyl), the MWDs became broader due to the slower formation of the sulfonium intermediate for the degenerative chain-transfer reaction. For p-methoxystyrene, thioethers derived from bulkier alkylthiols or more electron-rich thiophenols are more effective. A silyl-protected difunctional dithioether produced telechelic polymers possessing hydroxyl groups at both chain ends and stable thiol linkers in the middle of the polymer chains. These polymers were subsequently used in chain-extension reactions in conjunction with diisocyanates and diols as chain extenders to be converted into high molecular weight polymers linked via urethane linkages.

Reactive extrusion effects on rheological and mechanical properties of poly(lactic acid)/poly[(butylene succinate)‐co‐adipate]/epoxy chain extender blends and clay nanocomposites

ABSTRACTPoly(lactic acid) (PLA), a biosource, biodegradable polymer, is not suitable for some important polymer processing operations, such as film blowing and blow molding, due to its low melt strength. Moreover, while it has high tensile modulus and strength in the solid state, it exhibits low ductility. The present work is an extension of our earlier effort to improve the processability and mechanical properties of PLA by blending with poly[(butylene succinate)‐co‐adipate)] (PBSA), a biodegradable polymer with lower glass transition temperature. We evaluate the influences of incorporation of an epoxy chain extender and nanoclay on the properties of the blend. Since earlier work was conducted in a batch mixer, the influence of melt processing in the twin screw extruder and the differences between products obtained in the extruder and the batch mixer are evaluated and explained. Based on earlier work, the following PLA/PBSA blend ratios of 90:10, 80:20 and 70:30 were selected. All the samples were prepared in the twin‐screw extruder at two different screw speeds (50 and 150 rpm), to evaluate the effects of residence time and shear rates. The morphology and structure of the blends were examined using field emission scanning electron microscopy. Transmission electron microscopy (TEM) and X‐ray diffraction (XRD) were used to evaluate the levels of intercalation and exfoliation in the nanocomposites. The chain extension reaction was evaluated using nuclear magnetic resonance (NMR) spectroscopy and other techniques. Rheological properties (dynamic oscillatory shear and elongational viscosity measurements) and mechanical characteristics of the pure components, blends, and nanocomposites were studied and discussed in light of the composition and morphology of the blends and the nanocomposites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42664.

Biobased Thermoplastic Poly(ester urethane) Elastomers Consisting of Poly(butylene succinate) and Poly(propylene succinate)

In this study, a series of biobased and biodegradable thermoplastic poly(ester urethane)s (PEUs) with different compositions were synthesized via chain extension reaction of dihydroxyl terminated poly(propylene succinate) (HO-PPS-OH) and poly(butylene succinate) (HO-PBS-OH) with 4,4′-methylenediphenyl diisocyanate (MDI) as a chain extender. The thermal behaviors of PEUs were characterized by differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). All the PEUs showed a single glass transition temperature shifting with compositions; only one melting peak was observed when the feeding weight ratio of PPS to PBS was less than 8:2, and the crystallization ability of the PEUs decreased gradually with the increase in PPS content. The tensile and tensile hysteresis tests suggest that the PEUs showed the tensile behaviors of elastomers when the weight ratios of PPS/PBS were 7/3, 6/4, and 5/5, and the tensile hysteresis value and Young’s modulus increased with increase in PBS content. The tens...

Synthesis, characterization and isothermal crystallization behavior of poly(butylene succinate)-b-poly(diethylene glycol succinate) multiblock copolymers

In order to modify the properties of poly(butylene succinate), poly(diethylene glycol succinate) (PDGS) segment was incorporated by chain-extension reaction of dihydroxyl-terminated PBS and PDGS precursors using hexamethylene diisocyanate as a chain extender to form PBS-b-PDGS multiblock copolymers. The chemical structure and basic physical properties of the multiblock copolyesters were characterized by nuclear magnetic resonance spectroscopy, differential scanning calorimeter (DSC), wide angle X-ray diffraction, and tensile testing. The results suggested that the incorporation of PDGS segments would increase the elongation at break of PBS significantly while decrease its melting temperature and crystallization temperature slightly. The isothermal crystallization kinetics studied by DSC and polarized optical microscopy indicated that the crystallization rate of the multiblock polymers decreased gradually with increasing PDGS segment content while the crystallization mechanism kept unchanged and the spherulitic growth rate of the multiblock copolymers decreased gradually with increase in PDGS content due to its diluent effect to the crystallization of PBS segments. Copyright © 2015 John Wiley & Sons, Ltd.

The Preparation and Characterization of Branching Poly(ethylene terephthalate) and its Foaming Behavior

Chain extension was an effective method for increasing the molecular weight, the melt strength and the foaming property of linear polymer. In this paper, pyromellitic dianhydride (PMDA) was used as chain extender to improve these properties of linear poly (ethylene terephthalate) (PET). The intrinsic viscosity, rheological and thermal characterizations of various PET samples was investigated. The results demonstrated that the increasement of the viscoelasticity at low frequencies was correlated to the raise of the intrinsic viscosity and the formation of long chain branching. These structural changes resulted in the decreasement of the crystallization temperature and melt temperature as well as the increase in the cold crystallization values with the increasing content of PMDA. The cellular morphology and expansion ratio of CEPET foams were also obviously improved by the introduction of PMDA. The expansion ratio of CEPET foam with the PMDA content of 1.0 phr would reach 31.78. In addition, the effect of the chain extension reaction time on the intrinsic viscosity, the rheological behavior, and foaming properties of PET were also studied. The results showed that the intrinsic viscosity, the rheological behavior, and the foamability of CEPET also decreased gradually with increasing chain extension reaction time, which should be attributed to the occurrence of more and more intense thermal degradation.

Photo‐induced controlled radical polymerization of methyl methacrylate mediated by photosensitive nitroxides

AbstractPhotosensitive nitroxides bearing different chromophore groups (benzophenone, naphthalene and quinoline) were synthesized and characterized. The photochemical properties of the synthesized products were investigated by UV−visible and fluorescence measurements. The results indicated that an efficient energy transfer from the chromophore moiety to the nitroxide radical moiety could occur within the molecular distances. The photo‐induced nitroxide‐mediated polymerization of methyl methacrylate (MMA) was performed using the photosensitive nitroxide/2,2‐dimethoxy‐2‐phenyl acetophenone as a bimolecular mediated system. The controlled character of the polymerization was confirmed by the linear tendency of molecular weight evolution with narrow molecular weight distribution (1.3−1.4). The experimental conditions, such as type of chromophore, initiator concentration and molar ratio of initiator/nitroxide, are discussed for a better understanding of the mechanism of the controlled polymerization. Using the polymerization products as macroinitiator, the chain extension reaction of MMA turned out to be able to re‐initiate further polymerization of the monomer. © 2014 Society of Chemical Industry

Application of bis(glycidyloxy)phenylphosphine oxide as a chain extender for polyamide-6

Figure melt torque of PA6 mixed with different contents of chain extender BGPPO. The addition of small molecule diepoxide (BGPPO) greatly enhanced the melt torque, rheological and mechanical properties of polyamide-6 through chain extension reaction.

Screw sense alone can govern enantioselective extension of a helical peptide by kinetic resolution of a racemic amino acid.

Helical peptides built principally from the achiral quaternary amino acid Aib but with an induced preferred screw-sense exhibit enantioselectivity in their chain-extension reactions when presented with a racemic tertiary amino acid. This is the first demonstration that secondary structure alone, in the absence of local chiral residues, can direct the enantioselectivity of peptide coupling.

Performance improvement of flame-retarded poly(butylene terephthalate)/aluminum diethylphosphinate composites by epoxy-functional polysiloxane

An epoxy-functional polysiloxane (EPM) was employed for improving the performance of flame-retarded poly(butylene terephthalate)/aluminum diethylphosphinate (PBT/AlPi) composites. The effect was investigated by UL-94 test, limiting oxygen index, mechanical test, torque rheometer measurement, differential scanning calorimetry, dynamic mechanical analysis, and heat distortion temperature. An obvious increase in torque evolution of the PBT/AlPi composite during processing was associated with chain-extending, branching, and cross-linking reaction by the combination of EPM. The addition of 0.6 wt% EPM remarkably enhanced not only the mechanical properties but also the flame retardancy and heat resistance of the PBT/AlPi composite. A high-performance PBT/AlPi composite was developed by virtue of EPM.

Facile and highly efficient “living” radical polymerization of hydrophilic vinyl monomers in water

In this work, well-defined polymerization of water soluble poly(ethylene glycol) monomethyl ether methacrylate (PEGMA), 2-hydroxyethyl methacrylate (HEMA), 2-(dimethylamino)ethyl methacrylate (DMAEMA) and N,N-dimethyl-acrylamide (DMA) were successfully conducted in water by a facile and efficient polymerization system, only including oxidatively stable copper(II) acetate and 1-cyano-1-methylethyl diethyldithiocarbamate (MANDC). The effects of temperature, copper concentration, and monomer concentration on polymerization of PEGMA were systematically investigated to optimize the polymerization conditions. The polymerization of PEGMA can be conveniently carried out with ppm levels of the copper catalyst at 30–70 °C. The linearity of the kinetic plots, linear increase of molecular weight with conversion, and narrow molecular weight distribution (Mw/Mn < 1.3) of the polymer showed the typical character of “living” radical polymerization (LRP). Chain-extension reactions further verify the “living” features of this polymerization system.

Composition dependence of physical properties of biodegradable poly(ethylene succinate) urethane ionenes

To obtain an excellent comprehensive performance of poly(ethylene succinate) (PES), we have synthesized a series of poly(ethylene succinate) (PES) urethane ionenes (PESUIs) with various content of urethane ionic group by the chain extension reaction of dihydroxyl-terminated poly(ethylene succinate) and diethanolamine hydrochloride with hexamethylene diisocyanate as a chain extender, and we systematically investigated the composition dependence of the physico-chemical properties of PESUI through a series of characteristic techniques. The results of thermal and crystallization behaviors suggest that the incorporation of urethane ionic group slightly affects the glass transition temperature, melting temperature, and thermal stability, and significantly accelerates the crystallization rate of PES without changing the crystallization mechanism. The fastest crystallization rate was reached with the incorporation of 4 mol% urethane ionic groups. Spherulitic morphology observation indicates that nucleation density significantly increased, while spherulitic growth rate gradually decreased with increase in urethane ionic group content. Both complex viscosity and storage modulus initially increased and then decreased with increase in urethane ionic group content, and their maximum values were observed for the sample with 4 mol% of urethane ionic group. Mechanical properties slightly varied with urethane ionic group content.