Monomodal Molecular Weight Distribution Research Articles

Green Synthesis of Soluble Polysilsesquioxane with Phthalimide Groups.

Soluble polysilsesquioxane containing side-chain phthalimide groups (PSQ-PhI) was synthesized via a solvent- and catalyst-free hydrolytic polycondensation reaction using 2-[3-(triethoxysilyl)propyl]-1H-isoindole-1,3(2H)-dione. The composition and structure of polysilsesquioxane was confirmed via 1H, 13C, and 29Si NMR spectroscopy, Fourier transform infrared spectroscopy, gel permeation chromatography, thermogravimetric analysis, dynamic light scattering, X-ray diffraction analysis, and elemental analysis. The synthesized silsesquioxane showed a monomodal molecular weight distribution. The average molecular weight of polysilsesquioxane is 11,200 Da, and the polydispersity index is 1.10. 29Si NMR analysis showed a half-peak width w1/2 3.1 ppm at δ -68.3, which corresponds to the PhI(CH2)3SiO3/2 unit and indicates an ordered structure in the polymer, with some defects caused by the presence of uncondensed silanol groups. PSQ-PhI showed good thermal stability (Td5% decomposition at 345 °C). The polysilsesquioxane-based coating was transparent in the visible region.

Polymerization of Terminal Acetylenes by a Bulky Monophosphine-Palladium Catalyst

A well-defined palladium complex [(tBuXPhos)Pd(Me)(BArf)] bearing a bulky monophosphine ligand was synthesized and fully characterized. X-ray diffraction analysis shows that the 1,3,5-triisopropylaryl group of the dialkylbiaryl phosphine ligand exhibits a weak η6-interaction with the Pd(II) center. This catalyst exhibits excellent functional group tolerance and polymerizes propargyl esters containing benzoyl and acetyl groups, propargyl methyl ether, propargyl alcohol, benzyl acetylene, and phenyl acetylene to yield polymers with Mn values in the range of 5–15 kDa with monomodal molecular weight distributions between ca. 1.4 and 2.1.

Macrochain Transfer Agents for Catalytic Ring-Opening Metathesis Polymerization.

A monosubstituted 1,3-diene derivative attached to a polymer is demonstrated to act as a macrochain transfer agent in catalytic ring-opening metathesis polymerization. PEG- and PLA-based macrochain transfer agents were synthesized in a few steps and were characterized using NMR spectroscopy, size exclusion chromatography (SEC) and matrix-assisted laser desorption/ionization-time-of-flight (MALDI-ToF) mass spectrometry. Poly(l-lactide) based diblock copolymer, poly(ethylene glycol)-based diblock, and triblock (ABA type) copolymers of varied chain lengths were prepared catalytically in a one-pot approach via metathesis polymerization. Block copolymers were characterized by SEC and showed monomodal molecular weight distributions. Moreover, DOSY NMR spectroscopy further proved the block microstructures of the synthesized polymers.

ARGET ATRP of ethylene glycol dicyclopentenyl ether methacrylate with vegetable oil and terpene‐derived methacrylic monomers

AbstractHomo and statistical copolymerization reactions of ethylene glycol dicyclopentenyl ether methacrylate (EGDEMA) and a vegetable‐oil based methacrylic ester C13MA (average alkyl chain length = 13) are studied via activator regenerated electron transfer polymerization (ARGET ATRP) using only trace amounts of copper catalyst. Poly(EGDEMA) and poly(C13MA) homopolymers and statistical poly(EGDEMA‐stat‐C13MA) copolymers are cleanly synthesized with monomodal molecular weight distribution and dispersities Đ = Mw/Mn = 1.39–1.76 and Mn ~ 12 kg/mol. Chain end fidelity is confirmed by chain extension from poly(C13MA) macroinitiator with EGDEMA to make poly(C13MA‐b‐EGDEMA) diblock copolymers, which exhibit two distinct glass transition temperatures (Tgs), one for the poly(C13MA) block (−39°C) and the other for the poly(EGDEMA) block (23.9°C), suggesting microphase separation. Due to the relatively low Tg of poly(EGDEMA‐stat‐C13MA), terpene‐derived isobornyl methacrylate (IBOMA) is copolymerized with EGDEMA forming poly(EGDEMA‐stat‐IBOMA) statistical copolymers with Tgs ranging from 22.9–113°C. Additionally, crosslinking of the poly(EGDEMA) homopolymer and poly(EGDEMA‐stat‐C13MA) and poly(EGDEMA‐stat‐IBOMA) copolymers is achieved by UV thiol‐ene clicking of the pendent double bonds of EGDEMA units with suitable dithiols at 365 nm. For poly(EGDEMA), conversion of the thiol‐ene click reaction reaches 70%; where as the conversion of the clicking reactions is higher in the copolymers with a conversion up to 92% for poly(EGDEMA‐stat‐C13MA) and 97% for poly(EGDEMA‐stat‐IBOMA).

Tuning Ligand Concentration in Cu(0)-RDRP: A Simple Approach to Control Polymer Dispersity.

Cu(0)-reversible deactivation radical polymerization (RDRP) is a versatile polymerization tool, providing rapid access to well-defined polymers while utilizing mild reaction conditions and low catalyst loadings. However, thus far, this method has not been applied to tailor dispersity, a key parameter that determines the physical properties and applications of polymeric materials. Here, we report a simple to perform method, whereby Cu(0)-RDRP can systematically control polymer dispersity (Đ = 1.07–1.72), while maintaining monomodal molecular weight distributions. By varying the ligand concentration, we could effectively regulate the rates of initiation and deactivation, resulting in polymers of various dispersities. Importantly, both low and high dispersity PMA possess high end-group fidelity, as evidenced by MALDI-ToF-MS, allowing for a range of block copolymers to be prepared with different dispersity configurations. The scope of our method can also be extended to include inexpensive ligands (i.e., PMDETA), which also facilitated the polymerization of lower propagation rate constant monomers (i.e., styrene) and the in situ synthesis of block copolymers. This work significantly expands the toolbox of RDRP methods for tailoring dispersity in polymeric materials.

Precise Control of Both Dispersity and Molecular Weight Distribution Shape by Polymer Blending

AbstractThe breadth and the shape of molecular weight distributions can significantly influence fundamental polymer properties that are critical for various applications. However, current approaches require the extensive synthesis of multiple polymers, are limited in dispersity precision and are typically incapable of simultaneously controlling both the dispersity and the shape of molecular weight distributions. Here we report a simplified approach, whereby on mixing two polymers (one of high Đ and one of low Đ), any intermediate dispersity value can be obtained (e.g. from 1.08 to 1.84). Unrivalled precision is achieved, with dispersity values obtained to even the nearest 0.01 (e.g. 1.37→1.38→1.39→1.40→1.41→1.42→1.43→1.44→1.45), while maintaining fairly monomodal molecular weight distributions. This approach was also employed to control the shape of molecular weight distributions and to obtain diblock copolymers with high dispersity accuracy. The straightforward nature of our methodology alongside its compatibility with a wide range of polymerisation protocols (e.g. ATRP, RAFT), significantly expands the toolbox of tailored polymeric materials and makes them accessible to all researchers.

Precise Control of Both Dispersity and Molecular Weight Distribution Shape by Polymer Blending.

The breadth and the shape of molecular weight distributions can significantly influence fundamental polymer properties that are critical for various applications. However, current approaches require the extensive synthesis of multiple polymers, are limited in dispersity precision and are typically incapable of simultaneously controlling both the dispersity and the shape of molecular weight distributions. Here we report a simplified approach, whereby on mixing two polymers (one of high Đ and one of low Đ), any intermediate dispersity value can be obtained (e.g. from 1.08 to 1.84). Unrivalled precision is achieved, with dispersity values obtained to even the nearest 0.01 (e.g. 1.37→1.38→1.39→1.40→1.41→1.42→1.43→1.44→1.45), while maintaining fairly monomodal molecular weight distributions. This approach was also employed to control the shape of molecular weight distributions and to obtain diblock copolymers with high dispersity accuracy. The straightforward nature of our methodology alongside its compatibility with a wide range of polymerisation protocols (e.g. ATRP, RAFT), significantly expands the toolbox of tailored polymeric materials and makes them accessible to all researchers.

Tailoring Polymer Dispersity by RAFT Polymerization: A Versatile Approach

Summary Dispersity (Ɖ) can significantly affect polymer properties and is a key parameter in materials design. Here, we report a straightforward and versatile batch method based on reversible addition-fragmentation chain transfer (RAFT) polymerization to tailor the molecular weight distributions for a wide range of monomer classes, including acrylates, acrylamides, methacrylates, and styrene. In addition, our methodology is compatible with more challenging monomers, such as methacrylic acid, methyl vinyl ketone, and vinyl acetate. Control over Ɖ is achieved by mixing two RAFT agents with sufficiently different chain-transfer activities in various ratios, affording polymers with monomodal molecular weight distributions over a broad dispersity range (Ɖ ∼ 1.09–2.10). Our experimental findings were supported by simulations through the use of deterministic kinetic modeling, and our method was further demonstrated for the preparation of well-defined block co-polymers, regardless of the initial homopolymer dispersity.

Tailoring Polymer Dispersity in Photoinduced Iron-Catalyzed ATRP.

Although dispersity (Đ) plays an important role in controlling polymer properties, there are very few chemical methods that can sufficiently tune it. Here we report a simple, batch, and environmentally benign photoinduced iron-catalyzed ATRP methodology that enables the efficient control of Đ for both homopolymers and block copolymers. We show that by judiciously varying the concentration of the FeBr3/TBABr catalyst, a range of dispersities can be obtained (1.18 < Đ < 1.80) while maintaining monomodal molecular weight distributions. High end-group fidelity was confirmed by MALDI-ToF-MS and was further supported by the efficient synthesis of in situ block copolymers where the dispersity of the second block could be controlled upon demand. Importantly, through the use of low ppm amounts of the catalyst, perfect temporal control could be attained during intermittent "on/off" cycles. This work considerably expands the chemical toolbox for tuning Đ of homo- and block copolymers.

Tuning Dispersity by Photoinduced Atom Transfer Radical Polymerisation: Monomodal Distributions with ppm Copper Concentration

AbstractDispersity significantly affects the properties of polymers. However, current methods for controlling the polymer dispersity are limited to bimodal molecular weight distributions, adulterated polymer chains, or low end‐group fidelity and rely on feeding reagents, flow‐based, or multicomponent systems. To overcome these limitations, we report a simple batch system whereby photoinduced atom transfer radical polymerisation is exploited as a convenient and versatile technique to control dispersity of both homopolymers and block copolymers. By varying the concentration of the copper complex, a wide range of monomodal molecular weight distributions can be obtained (Đ=1.05–1.75). In all cases, high end‐group fidelity was confirmed by MALDI‐ToF‐MS and exemplified by efficient block copolymer formation (monomodal, Đ=1.1–1.5). Importantly, our approach utilises ppm levels of copper (as low as 4 ppm), can be tolerant to oxygen and exhibits perfect temporal control, representing a major step forward in tuning polymer dispersity for various applications.

Tuning Dispersity by Photoinduced Atom Transfer Radical Polymerisation: Monomodal Distributions with ppm Copper Concentration.

Dispersity significantly affects the properties of polymers. However, current methods for controlling the polymer dispersity are limited to bimodal molecular weight distributions, adulterated polymer chains, or low end-group fidelity and rely on feeding reagents, flow-based, or multicomponent systems. To overcome these limitations, we report a simple batch system whereby photoinduced atom transfer radical polymerisation is exploited as a convenient and versatile technique to control dispersity of both homopolymers and block copolymers. By varying the concentration of the copper complex, a wide range of monomodal molecular weight distributions can be obtained (Đ=1.05-1.75). In all cases, high end-group fidelity was confirmed by MALDI-ToF-MS and exemplified by efficient block copolymer formation (monomodal, Đ=1.1-1.5). Importantly, our approach utilises ppm levels of copper (as low as 4 ppm), can be tolerant to oxygen and exhibits perfect temporal control, representing a major step forward in tuning polymer dispersity for various applications.

Synthesis of tetrakis bromine terminated phthalocyanine and its methylmethacrylate polymers via ATRP

A phthalocyanine (Pc) initiator, tetrakis(2-bromopropyloxyester)ethylthiophthalocyaninatozinc(II) (ZnPc-Br), was prepared and successfully applied to atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) for the first time. Bromine end groups of the synthesized Pc took part in the initiation of the MMA chain growth. Polymerization was demonstrated by monomodal molecular weight distribution of the synthesized polymers and their increasing molecular weight behavior with reaction time. UV-Vis absorption, fluorescence, and transmittance properties of the polymers were also examined. The results indicate that the ZnPc-Br-based initiator is potentially applicable in ATRP applied to MMA in order to obtain and develop functional acrylic materials.

Synthesis and characterization of di-nuclear bis(benzotriazole iminophenolate) cobalt complexes: catalysis for the copolymerization of carbon dioxide with epoxides.

A family of di-nuclear bis(benzotriazole iminophenolate) (BiIBTP) cobalt complexes containing diverse ancillary carboxylate derivatives have been synthesized and structurally characterized. The one-pot synthesis of the BiIBTP ligand precursor with cobalt perchlorate salt (2.0 equiv.) and carboxylic acid derivatives (2.0 or 5.0 equiv.) in the presence of triethylamine (5.0 equiv.) under refluxing methanolic solution generated bimetallic di-carboxylate Co(ii)/Co(ii) complexes [(C83CBiIBTP)Co2(O2CR)2] (R = C6H5 (1), C6F5 (2), 4-CF3-C6H4 (3), 4-OMe-C6H4 (4), CF3 (5)) in ≧65% yields. Interestingly, the Co(ii)/Co(iii) mixed-valence complex 6 resulted from the treatment of 1 with silver perchlorate (1.0 equiv.) as the oxidizing agent under an O2-atmosphere in 50% yield. The crystal structure of 6 reveals an ionic and di-nuclear benzoate species composed of a cationic moiety formulated as [(C83CBiIBTP)Co2(O2CC6H5)2]+ and a counterbalanced perchlorate anion, and both metal atoms are attributed to hexa-coordinated cobalt ions with varied coordination environments. Catalysis results of CO2/epoxide copolymerization indicated that complex 1 was more efficient than 2-6 where compound 6 was shown to be the least active. Co complex 1 incorporating benzoate coligands was demonstrated to effectively catalyze the CO2-copolymerization of cyclohexene oxide (CHO), 4-vinyl-1,2-cyclohexene oxide or cyclopentene oxide, producing the associated CO2-based polycarbonates with >99% carbonate repeated units under optimal conditions. Not only the controllable character of complex 1 for CO2/CHO copolymerization is enabled, but also 1 has been shown to catalyze such a copolymerization in the "immortal" manner. Using the same di-cobalt catalyst in combination with excess ratios of neopentyl glycol (up to 150 equiv.) as the chain transfer agent could give low molecular weight poly(cyclohexene carbonate) polyols with monomodal molecular weight distributions. This work offers the facilely prepared di-nuclear cobalt complexes as catalysts for the efficient catalysis of CO2-copolymerization.

Amphiphilic tadpole-shaped POSS-poly(glycerol methacrylate) hybrid polymers: synthesis and self-assembly

A new series of well-defined amphiphilic hybrid polymers of tadpole-shaped architecture with polyhedral oligomeric silsesquioxane (POSS) nanocage as the hydrophobic head and poly(glycerol methacrylate) (PGMA) as the hydrophilic tail (POSS-PGMA) has been synthesized via atom transfer radical polymerization (ATRP). The aminopropylIsobutyl POSS, a monofunctional POSS nanocage, was transformed into ATRP initiator by treating with 2-bromoisobutyrylbromide. The POSS-PGMA was achieved in two steps. First, solketal methacrylate (SMA) (the precursor monomer for GMA), synthesized by reacting solketal with methacryloyl chloride, was polymerized under typical ATRP conditions with THF as the solvent at 40 °C, employing the synthesized POSS based initiator, and CuCl/N,N,N,N,N-pentamethyldiethylenetriamine as the catalyst system. The size exclusion chromatography (SEC) chromatograms reveal monomodal molecular weight distributions and narrow polydispersity indices; suggesting that well-defined tadpole-shaped hybrid polymers have been achieved. This further confirms that the monofunctional POSS initiator is able to affectively polymerize SMA in a controlled fashion under ATRP conditions. In the second step, the obtained POSS-PSMA was transformed into amphiphilic POSS-PGMA by acid hydrolysis. The successful transformation could be verified by 1H NMR and FTIR spectroscopy. Finally, because of the amphiphilic nature, the obtained POSS-PGMA could self-assemble when dispersed in water as confirmed by measuring the critical aggregation concentration (CAC) by fluorescence spectroscopy, using pyrene as the fluorescence probe. The CAC was found to increase with increasing the PGMA chain length. The large hydrodynamic size of the self-assembled structures, as determined by the laser light scattering data, however, suggests that the aggregates are not of typical core-shell type micelles.

Fast Access to Amphiphilic Multiblock Architectures by the Anionic Copolymerization of Aziridines and Ethylene Oxide.

An ideal system for stimuli-responsive and amphiphilic (block) polymers would be the copolymerization of aziridines with epoxides. However, to date, no copolymerization of these two highly strained three-membered heterocycles had been achieved. Herein, we report the combination of the living oxy- and azaanionic ring-opening polymerization of ethylene oxide (EO) and sulfonamide-activated aziridines. In a single step, well-defined amphiphilic block copolymers are obtained by a one-pot copolymerization. Real-time 1H NMR spectroscopy revealed the highest difference in reactivity ratios ever reported for an anionic copolymerization (with r1 = 265 and r2 = 0.004 for 2-methyl- N-tosylaziridine/EO and r1 = 151 and r2 = 0.013 for 2-methyl- N-mesylaziridine/EO), leading to the formation of block copolymers with monomodal and moderate molecular weight distributions ( Mw/ Mn mostly ≤1.3). The amphiphilic diblock copolymers were used to stabilize emulsions and to prepare polymeric nanoparticles by miniemulsion polymerization, representing a novel class of nonionic and responsive surfactants. In addition, this unique comonomer reactivity of activated-Az/EO allows fast access to multiblock copolymers, and we prepared the first amphiphilic penta- or tetrablock copolymers containing aziridines in only one or two steps, respectively. These examples render the combination of epoxide and aziridine copolymerizations via a powerful strategy for producing sophisticated macromolecular architectures and nanostructures.

Isolation and characterization of galactomannans from Prosopis affinis as potential gum substitutes

Galactomannans from the endosperm of mature seeds of Prosopis affinis were isolated following different extraction procedures in yields of up to 64%. The polysaccharides were characterized by HPLC, GC-MS, and NMR spectroscopy, and their physicochemical properties were studied by SEC/MALLS-QUELS/RI and rheological methods. The monosaccharide composition of the extracted galactomannans showed only mannose and galactose in a ∼1.5 ratio, similar to galactomannans found in guar gum and obtained from other Prosopis species. The structural characterization showed that these polysaccharides are composed by a β-(1→4)-linked mannose backbone with galactopyranosyl residues attached through α-(1→6) linkages. The weight-average molecular weight (Mw) of the P. affinis galactomannans went from (1.6 ± 0.2) x 106 to (1.8 ± 0.1) x 106 g/mol, and the intrinsic viscosity, in the 9.9 to 10.7 dL/g range, was comparable to that reported for other extracts from the Prosopis genre. Although the molecular weight distribution and intrinsic viscosity were dependent on the extraction procedure, the mannose-to-galactose ratio was almost invariant. Conformation plots showed that the polymer extracted at higher temperatures is more cohesive, a characteristic that could be attributed to a greater number of polymer-polymer interactions. Our findings show that the P. affinis galactomannan has nearly monomodal molecular weight distribution, functional properties similar to those of guar gum, and can be isolated from an abundant and readily available non-traditional source. It therefore represents a promising new biomaterial for the food and pharmaceutical industries that can be produced from the regional native flora in a sustainable way.

Poly(N‐vinylpyrrolidone)–polydimethylsiloxane amphiphilic ABA triblock copolymers

ABSTRACTTriblock copolymers of N‐vinylpyrrolidone (NVP) and polydimethylsiloxane (PDMS) were synthesized by reversible addition‐fragmentation chain transfer (RAFT) polymerization using two different types of difunctional telechelic PDMS‐based dixanthate macroinitiators. The incorporation of PDMS into the triblock copolymers was evidenced by 1H NMR spectroscopy and varied between 4 mol % and as high as 20 mol %, dependent on reaction time and monomer conversion. The copolymer homogeneity was characterized in terms of molecular weight distribution determined by GPC to estimate the level of control over the chain length. Monomodal molecular weight distributions were observed, and 1H NMR spectroscopy indicated the copolymers had number average molecular weights (Mn) ranging between 28,000 and 160,000 g/mol. In addition, thin film phase separation and critical micelle concentrations for these copolymers were analyzed via transmission electron microscopy and surface tension measurements, respectively. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3387–3394

"Living" Polymerization of Ethylene and 1-Hexene Using Novel Binuclear Pd⁻Diimine Catalysts.

We report the synthesis of two novel binuclear Pd–diimine catalysts and their unique behaviors in initiating “living” polymerization of ethylene and 1-hexene. These two binuclear catalysts, [(N^N)Pd(CH2)3C(O)O(CH2)mO(O)C(CH2)3Pd(N^N)](SbF6)2 (3a: m = 4, 3b: m = 6) (N^N≡ArN=C(Me)–(Me)C=NAr, Ar≡2,6–(iPr)2C6H3), were synthesized by simply reacting [(N^N)Pd(CH3)(N≡CMe)]SbF6 (1) with diacrylates, 1,4-butanediol diacrylate and 1,6-hexanediol diacrylate, respectively. Their unique binuclear structure with two identical Pd–diimine acrylate chelates covalently linked together through an ester linkage was confirmed by NMR and single crystal XRD measurements. Ethylene “living” polymerizations were carried out at 5 °C and under ethylene pressure of 400 and 100 psi, respectively, with the binuclear catalysts, along with a mononuclear chelate catalyst, [(N^N)Pd(CH2)3C(O)OMe]SbF6 (2), for comparison. All the polyethylenes produced with both binuclear catalysts show bimodal molecular weight distribution with the number-average molecular weight of the higher molecular weight portion being approximately twice that of the lower molecular weight portion. The results demonstrate the presence of monofunctional chain growing species resembling catalyst 2, in addition to the expected bifunctional species leading to bifunctional “living” polymerization, in the polymerization systems. Both types of chain growing species exhibit “living” characteristics under the studied conditions, leading to the simultaneous linear increase of molecular weight in both portions. However, when applied for the “living” polymerization of 1-hexene, the binuclear catalyst 3a leads to polymers with only monomodal molecular weight distribution, indicating the sole presence of monofunctional chain growing species. These two binuclear catalysts are the first Pd–diimine catalysts capable of initiating bifunctional ethylene “living” polymerization.

Syntheses of triblock bottlebrush polymers through sequential ROMPs: Expanding the functionalities of molecular brushes

Syntheses of triblock bottlebrush polymers through sequential ROMPs: Expanding the functionalities of molecular brushes

Synthesis of narrow molecular weight distribution polyvinyl acetate by gamma–rays initiated RAFT/MADIX miniemulsion polymerization

Abstract For the first time, conventional and controlled miniemulsion polymerization of vinyl acetate (VAc) was performed using gamma radiation as alternative source of initiation. Reversible addition-fragmentation chain transfer/macromolecular design via interchange of xanthates (RAFT/MADIX) technique was applied to control the polymerization process. For this purpose, S-2-cyano-2-propyl-O-ethyl xanthate ( C TA) was used as chain transfer agent. To illustrate the advantages of using gamma radiation instead of other initiation sources, we compared gamma radiation and the 2,2′-azobis(isobutyronitrile) (AIBN) as initiators in the polymerization mediated by RAFT/MADIX technique. Compared with conventional miniemulsion polymerization, the controlled polymerization process allowed obtaining monomodal molecular weight distribution s and a significant control over the molecular weight distribution. The miniemulsions showed colloidal stability during polymerization and stable latices were obtained in a short reaction time with high conversion. Gamma radiation demonstrated to be a better initiator than AIBN for the miniemulsion polymerization of VAc, mediated by RAFT/MADIX.