End-group Analysis Research Articles

Chain Transfer to Solvent in Propene Polymerization with Ti Cp-phosphinimide Catalysts: Evidence for Chain Termination via Ti–C Bond Homolysis

Propene polymerization using Ti Cp-phosphinimide catalysts in toluene and related aromatic solvents leads to the formation of benzyl-terminated polymer chains. End-group analysis suggests that these are formed after a 2,1-insertion event; density functional theory (DFT) studies support a mechanism involving homolysis of a Ti-sec-alkyl bond. This reaction could enable the catalytic formation of chain-end functionalized polyolefins. More importantly, it demonstrates that Ti–C homolysis might limit activity but does not necessarily constitute an irreversible deactivation mechanism.

Synthesis of polyfluorene containing simple functional end group with aryl palladium(II) complexes as initiators

A series of aryl Pd(II) complexes of the formula PdL2(Ar)Br (L = PPh3, 1–8; L = PCy3, 9–11; L = PEt3, 12) and [Pd(P(o-tol)3)(Ar)(μ-Br)]2 (13–18; Ar = substituted phenyl with simple functional group, Cy = cyclohexyl, o-tol = o-tolyl) has been synthesized by direct oxidative addition of Pd(0) precursor and excess aryl bromide. In contrast, the corresponding Pd(II) bromide coordinated with partly aryl-aryl exchanged phosphine was isolated for the bidentate 1,2-bis(diphenylphosphino)ethane (dppe) or 1,3-bis(diphenylphosphino)propane (dppp) ligand, indicating that the aryl-aryl exchange occurs more easily probably because of the chelate effect of the bidentate ligand and the intramolecular π-π interaction between neighboring phenyl rings. Suzuki-Miyaura coupling polymerization of AB-type fluorene monomer with these Pd(II) complexes as initiators was carried out. The aryl Pd(II) complexes with P(o-tol)3 exhibit the catalyst-transfer polymerization at room temperature. Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) characterization and end group analysis reveal that the functional group is anchored at the end of polymer backbone. Furthermore, the groups can be transferred to other more useful active groups via simple organic reaction.

Preparation of poly(glycolide-co-lactide)s through a green process: Analysis of structural, thermal, and barrier properties

We have successfully synthesized poly(lactide), poly(glycolide), and poly(lactide-co-glycolide) copolymers in bulk by ring-opening homo- and copolymerization of glycolide and l-lactide, using sodium hydride as the environmentally friendly and nontoxic initiator. Random copolymers were obtained, and the microstructure was characterized by nuclear magnetic resonance (1H and 13C NMR) and matrix-assisted laser desorption ionization mass spectrometry (MALDI MS). The mechanism of reaction was elucidated by analysis of the polymer end groups. Homopolymer and copolymers films and their blends were obtained, and structure and physical properties analyzed. Thermal degradation analysis showed superior characteristics of copolymers with respect to the blends. Transport properties of water vapor were also evaluated and correlated to the copolymer composition.

Structural Analysis of the End Groups and Substructures of Commercial Poly(ethylene terephthalate) by Multiple-WET 1H/13C NMR

Structural Analysis of the End Groups and Substructures of Commercial Poly(ethylene terephthalate) by Multiple-WET ¹H/¹³C NMR

Living ROMP Syntheses and Redox Properties of Triblock Metallocopolymer Redox Cascades

A number of reports have described the synthesis by ring-opening metathesis polymerization (ROMP) of diblock metallopolymers containing ferrocene and organocobalt complexes using the very efficient Grubb’s third-generation metathesis catalyst. Here the first triblock metallocopolymers are reported using this catalyst with ferrocenyl, pentamethylferrocenyl, and cobalticenyl groups in the side chains of a polynorbornene backbone. Among the six possible synthetic schemes for the successive ROMP reactions of the blocks, two of them have been successfully conducted with adequate characterization using the end-group analysis, MALDI-TOF mass spectroscopy, and Bard–Anson’s electrochemical method. The cyclic voltammetry studies showed that the integrity of reversible redox systems was preserved in cascades of heterogeneous electron transfers in both metallocopolymers with significant adsorption and electrostatic effects. This research paves the way for the design and synthesis of multiblock metallocopolymers offer...

A Comparative Study on Dinuclear and Mononuclear Aluminum Methyl Complexes Bearing Piperidyl-Phenolato Ligands in ROP of Epoxides.

Dinuclear aluminum methyl complexes stabilized by piperidyl-phenolato ligands were prepared and characterized. The ring-opening polymerizations of cyclohexene oxide (CHO) and propylene oxide (PO) initiated by dinuclear complexes and mononuclear analogues were investigated and compared. Enhanced activity of dinuclear complexes compared to that of mononuclear analogues in both the ring-opening polymerization of CHO and PO proves the synergistic interaction of two Al centers in the former. End-group analysis of oligomers by MALDI-TOF mass spectrometry confirms the role of methyl groups as initiating groups. A bimetallic mechanism is proposed, in which the cooperation of two Al centers are involved in polymerization processes.

Influence of the Processing Parameters on the Dispersion and Coloration Behavior of a Halogenated Copper Phthalocyanine‐Based Masterbatch

AbstractA monodispersed green masterbatch was produced through an industrial extrusion process, by mixing a commercial Polyamide 6 matrix (PA6) with a halogenated copper phthalocyanine green pigment. The production process was investigated and optimized in order to improve the pigment dispersion, reducing the clogging power and increasing the color strength of the resulting products. The compounding process based on three extrusions without filtration led to a filter pressure value (FPV) reduction of about 84% and a relative color strength (RCS) increase of about 50% with respect to the standard production process (i.e single extrusion). The thermal stability of the prepared compounds was evaluated by rheological test, viscosity measurements, and end group analysis, and it was found that a triple extrusion without filtration promoted thermo‐oxidative matrix degradation. However, the same processing conditions led to a significant reduction of the production waste, increasing the productivity and the quality of the final product.

End of Frustration: Catalytic Precision Polymerization with Highly Interacting Lewis Pairs.

Herein we report on the catalytic polymerization of diverse Michael-type monomers with high precision by using simple but highly active combinations of phosphorus-containing Lewis bases and organoaluminum compounds. The interacting Lewis pair catalysts enable the control of molecular weight and microstructure of the produced polymers. The reactions show a linear Mn vs consumption plot thus proving a living type polymerization. The initiation has been investigated by end-group analysis with ESI mass spectrometric analysis. With these main-group element Lewis acid base pairs, it is not only possible to polymerize sterically demanding, functionalized as well as heteroatom containing monomers but also, for the first time, to catalytically polymerize extended Michael systems, like 4-vinylpyridine.

Sizing and Thermal Stability of Prepared Tetraaminophthalocyaninatocopper(II) Derivatives-grafted Polymers

Different polymers were prepared by condensation polymerization of sebacic anhydride and adipic anhydride with ethylene glycol and poly(ethylene glycol). Their number average molecular weights were determined by end group analysis. Then, they were grafted on the prepared phthalocyaninatocopper(II) compounds with the general formula (NH2)4PcCu(II) having amino groups of 3,3',3'',3'''- or 4,4',4'',4'''- positions. All prepared polymers, compounds, and phthalocyaninatocopper(II)-grafted polymers were characterized by FTIR. The sizing measurements were carried out in 3,3',3'',3'''- (NH2)4PcCu(II) and 4,4',4'',4'''- (NH2)4PcCu(II) compounds with and without grafting polymers. The results showed that the grafting process led to decreasing in particle size and increasing in surface area. The grafting process was reflected positively on the thermal degradation of 3,3',3'',3'''- (NH2)4PcCu(II) and 4,4',4'',4'''- (NH2)4PcCu(II) grafted polymers. They had higher thermal stability accompanied with higher char residue and T50% weight loss with 3,3',3'',3'''-(NH2)4PcCu(II) and their grafted polymers being the best.

Optimization of Process Parameters for Controlled Ring-Opening Polymerization of Lactide to Produce Poly(L-Lactide) Diols as Precursor for Polyurethanes

ABSTRACTSeries of poly(L-Lactide) diols with molecular weights (Mn) in 2,069–4,811 g mol−1 were synthesized from L-Lactide using stannous octoate catalyst and 1,4-butanediol chain extender. Operating conditions, i.e., temperature, catalyst concentration, chain extender concentration, and reaction time, were optimized. Maximum monomer conversion and Mn were observed at 0.5 mol% SnOct2 and 1.0 mol% 1,4 butanediol (BDO) at 145°C. Poly(L-Lactide) diols were analyzed by Fourier transform infrared, proton nuclear magnetic resonance, end-group analysis, and X-ray diffraction techniques. Fourier transform infrared confirmed the formation of poly(L-Lactide) diols. Poly(L-Lactide) diols’ % degree of crystallinity was determined by X-ray diffraction. Mn was calculated by proton nuclear magnetic resonance and end-group analysis.

Acid-Induced Room Temperature RAFT Polymerization: Synthesis and Mechanistic Insights

An acid-induced cyclohexanone/tert-butylhydroperoxide initiation system for ambient temperature reversible addition–fragmentation transfer (RAFT) polymerization of vinyl monomers is presented. The reaction system is optimized for the synthesis of poly(n-butyl acrylate) of various chain length. The polymerization shows typical living characteristics and polymers with dispersities close to 1.1 are obtained. Analysis of the polymer end groups by means of soft ionization mass spectrometry reveals the typical distribution of polymer containing both R and Z RAFT end groups and a minor distribution of a RAFT polymer carrying a cyclohexanone end group in α position. This observation demonstrates that the polymerization is initiated solely by ketone radicals despite a relatively complex initiation mechanism that involves several intermediates. The room temperature-derived homopolymers are successfully chain extended with tert-butyl acrylate resulting in well-defined block copolymer structures. To demonstrate the v...

Atom Transfer Radical Polymerization of Functionalized Vinyl Monomers Using Perylene as a Visible Light Photocatalyst.

A standardized technique for atom transfer radical polymerization of vinyl monomers using perylene as a visible-light photocatalyst is presented. The procedure is performed under an inert atmosphere using air- and water-exclusion techniques. The outcome of the polymerization is affected by the ratios of monomer, initiator, and catalyst used as well as the reaction concentration, solvent, and nature of the light source. Temporal control over the polymerization can be exercised by turning the visible light source off and on. Low dispersities of the resultant polymers as well as the ability to chain-extend to form block copolymers suggest control over the polymerization, while chain end-group analysis provides evidence supporting an atom-transfer radical polymerization mechanism.

Organic-acid mediated bulk polymerization of ε-caprolactam and its copolymerization with ε-caprolactone

Polyamides (PA) constitute one of the most important classes of polymeric materials and have gained strong position in different areas, such as textiles, fibers, and construction materials. Whereas most PA are synthesized by step-growth polycondensation, PA 6 is synthesized by ring opening polymerization (ROP) of e-caprolactam (e-CLa). The most popular ROP methods involve the use of alkaline metal catalyst difficult to handle at large scale. In this article, we propose the use of organic acids for the ROP of e-CLa in bulk at 180 °C (below the polymer's melting point). Among evaluated organic acids, sulfonic acids were found to be the most effective for the polymerization of e-CLa , being the Bronsted acid ionic liquid: 1-(4-sulfobutyl)−3-methylimidazolium hydrogen sulfate the most suitable due to its higher thermal stability. End-group analysis by 1H nuclear magnetic resonance and model reactions provided mechanistic insights and suggested that the catalytic activity of sulfonic acids was a function of not only the acid strength, but of the nucleophilic character of conjugate base as well. Finally, the ability of sulfonic acid to promote the copolymerization of e-CLa and e-caprolactone is demonstrated. As a result, poly(e-caprolactam-co-e-caprolactone) copolymers with considerably randomness are obtained. This benign route allows the synthesis of poly(ester amide)s with different thermal and mechanical properties. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 2394–2402

Synthesis, characterization and l-lactide polymerization behavior of rare-earth metal bis(silylamide) complexes supported by arylamido ligand

Salt metathesis of LnCl3, [2,6-iPr2C6H3N(SiMe3)]Li and LiN(SiHMe2)2 in 1:1:2 molar ratio in THF produced the mono-arylamido-ligated rare-earth metal bis(silylamide) complexes [2,6-iPr2C6H3N(SiMe3)]Ln[N(SiHMe2)2]2(THF) (Ln = Y (1), Lu (2), La (3)) in good isolated yields. All these complexes were characterized by elemental analysis, NMR spectroscopy and FT-IR spectroscopy. 1 was further structurally authenticated by single crystal X-ray diffraction. These complexes alone could serve as highly active initiators for l-lactide polymerization in toluene at 50 °C. Employing 1 as the initiator, l-lactide polymerization proceeded in a controllable fashion via the coordination-insertion mechanism verified by end group analysis of the oligomer.

Generic applications of (13) C-detected NMR diffusion to formulated systems with suppression of thermal convection induced by proton decoupling.

Fast and effective structural/compositional analysis on formulated systems represents one of the major challenges encountered in analytical science. (13) C-detected diffusion represents a promising tool to tackle the aforementioned challenges, particularly in industry. Toward exploring the generic applications of (13) C-detected diffusion, thermal convection induced by (1) H decoupling has been identified as a key factor that resulted in significantly reduced resolution in the diffusion dimension. Optimization of experimental parameters and utilization of double-stimulated echo-based pulse sequence both can effectively suppress the thermal convection caused by the (1) H decoupling, the success of which allows robust and generic applications of (13) C-detected diffusion to systems from mixtures of small molecules, polymer blends, and copolymers to actual complex formulated systems. The method is particularly powerful in differentiating small molecules from polymers, polymer blends from copolymers, and end-group analysis. Copyright © 2016 John Wiley & Sons, Ltd.

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.

Sizing and Thermal Stability of Prepared Tetraaminophthalocyaninatocopper(II) Derivatives-grafted Polymers

Different polymers were prepared by condensation polymerization of sebacic anhydride and adipic anhydride with ethylene glycol and poly(ethylene glycol). Their number average molecular weights were determined by end group analysis. Then, they were grafted on the prepared phthalocyaninatocopper(II) compounds with the general formula (NH2)4PcCu(II) having amino groups of 3,3',3'',3'''- or 4,4',4'',4'''- positions. All prepared polymers, compounds, and phthalocyaninatocopper(II)-grafted polymers were characterized by FTIR. The sizing measurements were carried out in 3,3',3'',3'''- (NH2)4PcCu(II) and 4,4',4'',4'''- (NH2)4PcCu(II) compounds with and without grafting polymers. The results showed that the grafting process led to decreasing in particle size and increasing in surface area. The grafting process was reflected positively on the thermal degradation of 3,3',3'',3'''- (NH2)4PcCu(II) and 4,4',4'',4'''- (NH2)4PcCu(II) grafted polymers. They had higher thermal stability accompanied with higher char residue and T50% weight loss with 3,3',3'',3'''-(NH2)4PcCu(II) and their grafted polymers being the best.

Synthesis and characterization of novel biocompatible palm oil‐based alkyds

Novel alkyds of short, medium, and long oil length were synthesized using a two‐stage alcoholysis‐polyesterification method from bio‐sourced starting materials. Alcoholysis reaction mixtures of palm kernel oil and glycerol underwent transesterification to convert triglycerides to monoglycerides within 3 h. Kinetic studies showed that the polyesterification reaction rates obeyed second order kinetics up to 15 min, followed by chain branching and crosslinking. The alkyd chemical structure was confirmed by nuclear magnetic resonance and Fourier Transform infrared spectroscopy. Gel permeation chromatography revealed that the average molecular weight of the alkyds was confined to <2,000 Da which is advantageous for the production of nanoscale drug carriers. Differential scanning calorimetry showed that the alkyds possess low glass transition temperatures within a very narrow range of −49.3°C–−52.7°C. Thermogravimetric analysis revealed good thermal stability with alkyd degradation occurring above 200°C. Cell viability assay confirmed that the alkyds were non‐toxic to 3T3 mouse fibroblasts following exposure of cell cultures for 24 h to solutions of concentration ranging from 3 to 100 μg/mL. These findings highly recommend consideration of the novel, bio‐sourced alkyds for pharmaceuticals manufacture and controlling drug delivery.Practical applications: A family of short, medium, and long oil length alkyds was synthesized as novel biomaterials from fully bio‐sourced and renewable starting materials. The alkyds are characterized by molecular weights below 2,000 Da, low Tg around −50°C and high thermal stability. The alkyds to exhibit favorable biocompatibility as demonstrated by non‐toxicity towards to 3T3 mouse fibroblasts in cell culture. Thus the novel bio‐sourced alkyds offer significant potential as excipients for pharmaceuticals manufacture and controlling drug delivery.Novel biocompatible palm oil‐based alkyds are investigated through synthesis reaction, kinetic study, and characterization tests. Alkyd synthesis involved two‐stage alcoholysis‐polyesterification reactions to produce short, medium, and long oil length alkyds. In the kinetic study of polyesterification reaction, water released was collected and acid value was determined with the results indicating high yield of alkyds with 97–98% of extent of polyesterification. The characterization of alkyds are carried out using spectroscopic, end group, thermal, and chromatographic analysis, plus biocompatible assay. The proposed chemical structure of the alkyd chain is determined from FTIR and NMR spectroscopy analysis. End group analysis indicated low acid groups but high hydroxyl numbers. Thermal analysis revealed the Tg ranged from −49.3°C to −52.7°C (DSC test) and thermal stability up to 200°C (TGA test). Average molecular weight is found to be less than 2,000 Da from GPC measurement or chromatographic analysis. All alkyds exhibited non‐toxic to 3T3 mouse fibroblast via biocompatible ‐ cell viability assay.

Elucidation of a side reaction occurring during nitroxide-mediated polymerization of cyclic ketene acetals by tandem mass spectrometric end-group analysis of aliphatic polyesters.

In order to prevent side reactions while developing new polymerization processes, their mechanism has to be understood and one first key insight is the structure of the end-groups in polymeric by-products. The synthetic method scrutinized here is the nitroxide-mediated polymerization (NMP) of a cyclic ketene acetal, a promising alternative process to the production of polyesters. Polymer end-group characterization was performed by mass spectrometry (MS), combining elemental composition information derived from accurate mass data in the MS mode with fragmentation features recorded in the MS/MS mode. Electrospray was used as the ionization method to ensure the integrity of original chain terminations and a quadrupole time-of-flight (QTOF) instrument was employed for high-resolution mass measurements in both MS and tandem mass spectrometry (MS/MS) modes. Occurrence of side reactions in the studied polymerization method, first evidenced by an unusual increase in dispersity with conversion, was confirmed in MS with the detection of two polymeric impurities in addition to the expected species. Fragmentation rules were first established for this new polyester family in order to derive useful structural information from MS/MS data. In addition to a usual NMP by-product, the initiating group of the second polymeric impurities revealed the degradation of the nitroxide moiety. Unambiguous MS/MS identification of end-groups in by-products sampled from the polymerization medium allowed an unusual side reaction to be identified during the NMP preparation of polyesters. On-going optimization of the polymerization method aims at preventing this undesired process.

Synthesis and Ring-Opening Polymerization of Cyclic Butylene 2,5-Furandicarboxylate

A new synthetic pathway for the polymerization of furan based polyesters is reported in this work. First, poly(butylene 2,5-furandicarboxylate) cyclic oligoesters (COEs) are chemically synthesized by semi-batch esterification. The structure of the COEs is confirmed by infrared spectroscopy, 1H, and 13C-NMR, while the molecular weight distribution of the COEs is determined by matrix-assisted laser desorption/ionization time of flight mass spectroscopy. The cyclic oligoesters are then successfully polymerized via ring-opening polymerization using tetrakis(2-ethylhexyl)-titanate as catalyst. Differential scanning calorimetry and 1H-NMR analysis unambiguously proves the formation of polymeric species. Both end-group analysis from 1H-NMR spectrum and calculation through Flory–Fox equation give comparable estimates of the number average molecular weight: 5.8 × 103 g mol−1 and 7.8 × 103 g mol−1, respectively.