Narrow Molar Mass Distribution Research Articles

Thermoresponsive (star) block copolymers from one-pot sequential RAFT polymerizations and their self-assembly in aqueous solution

A series of hydrophobically end-capped linear triblock copolymers as well as of three-arm and four-arm star block copolymers was synthesized in a one-pot procedure from N,N-dimethylacrylamide (DMA) and N,N-diethylacrylamide (DEA). The sequential reversible addition-fragmentation chain transfer (RAFT) polymerization of these monomers via the R-approach using bi-, tri- and tetrafunctional chain transfer agents (CTAs) bearing hydrophobic dodecyl moieties proceeded in a well-controlled manner up to almost quantitative conversion. Polymers with molar masses up to 150 kDa, narrow molar mass distribution (PDI ≤ 1.3) and high end group functionality were obtained, which are thermoresponsive in aqueous solution showing a LCST (lower critical solution temperature) transition. The temperature-dependent associative behavior of the polymers was examined using turbidimetry, static and dynamic light scattering (SLS, DLS), and small angle neutron scattering (SANS) for structural analysis. At 25 °C, the polymers form weak transient networks, and rather small hydrophobic domains are already present for polymer concentrations of 5 wt%. However, when heating above the LCST transition (35–40 °C) of the PDEA blocks, the enhanced formation of hydrophobic domains is observed by means of light and neutron scattering. These domains have a size of about 12–15 nm and must be effectively physically cross-linked as they induce high viscosity for the more concentrated samples. SANS shows that these domains are ordered as evidenced by the appearance of a correlation peak. The copolymer architecture affects in particular the extent of ordering as the four-arm star block copolymer shows much more repulsive interactions compared to the analogous copolymers with a lower number of arms.

Synthesis and Solution Self‐Assembly of Polyisoprene‐block‐poly(ferrocenylmethylsilane): A Diblock Copolymer with an Atactic but Semicrystalline Core‐Forming Metalloblock

Polyisoprene‐block‐poly(ferrocenylmethylsilane) (PI‐b‐PFMS) copolymers, containing the atactic but semicrystalline PFMS block, have been prepared by sequential anionic polymerization of isoprene and methyl[1]silaferrocenophane. The reaction to form the metalloblock is not living in nature, but still enabled three block copolymers to be prepared (PI35‐b‐PFMS5, PI200‐b‐PFMS10, and PI247‐b‐PFMS23) with relative narrow molar mass distributions (polydispersity < 1.3). The self‐assembly of all three materials was studied in PI selective n‐alkanes and found to afford lenticular platelets, tapered cylindrical micelles, and regular cylinders, as the length of the PFMS block increased. PI200‐b‐PFMS10 micelles could be increased in length by self‐seeding a sample of short micelles at temperatures of 90 °C and above; however, this process also resulted in an increase in width. Addition of a solution of PI247‐b‐PFMS23 copolymer to preformed seed micelles also resulted in an increase in length, although growth is not linearly related to the amount of copolymer added beyond ≈600 nm. image

Lithium naphthalenides in non-polar or in low-polarity media: some insights regarding their use as initiators in anionic polymerizations

The synthesis of bidirectional anionic initiators by the reaction between metallic lithium (Li) and naphthalene (Naph), under mild conditions, in non-polar (benzene) or low-polarity media (benzene/THF mixtures) is reported. The efficiency of these initiators to provide macromolecules with well-defined structures was demonstrated. Model linear homopolymers from styrene (S) or hexamethyl(ciclotrisiloxane) (D3) monomers were synthesized using classical anionic polymerization (high-vacuum techniques). The model polymers obtained were analyzed using the conventional analytical techniques, and showed narrow molar mass distributions, a broad range of molar masses (from 3000 to 1,000,000 g/mol) and polydispersity indexes (Mw/Mn) lower than 1.1. High molar mass polymers were obtained using pure benzene as solvent, whereas lower molar masses were obtained in benzene/THF mixtures in which the concentration of THF was lower than 10 % v/v. The ratio [Li]/[Naph] and the nature of the reaction medium are the experimental parameters to be controlled to obtain the desired lithium naphthalenides.

Polyurea microcapsules from isocyanatoethyl methacrylate copolymers

ABSTRACTThe synthesis of two types of isocyanate side chain containing copolymers, poly(methyl methacrylate‐co‐isocyanatoethyl methacrylate) (P(MMA‐co‐IEM)) and poly(benzyl methacrylate‐co‐isocyanatoethyl methacrylate) (P(BnMA‐co‐IEM)), which were synthesized by Cu(0)‐mediated radical polymerization, is reported. Polymerization proceeded to high conversion giving polymers of relatively narrow molar mass distributions. The incorporation of the bulky aromatic groups in the latter copolymer rendered it sufficiently stable toward hydrolysis and enabled the isolation of the product and its characterization by 1H and 13C NMR, and FTIR spectroscopy and SEC. Both P(MMA‐co‐IEM) and P(BnMA‐co‐IEM) were functionalized with dibutylamine, octylamine, and (R)‐(+)‐α‐methylbenzyl‐amine, which further proved the successful incorporation of the isocyanate groups. Furthermore, P(BnMA‐co‐IEM) was used for the fabrication of liquid core microcapsules via oil‐in‐water interfacial polymerization with diethylenetriamine as crosslinker. The particles obtained were in the size range of 10–90 µm in diameter independent of the composition of copolymer. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 2698–2705

Stress relaxation following uniaxial extension of polystyrene melt and oligomer dilutions

The filament stretching rheometer has been used to measure the stress relaxation following the startup of uniaxial extensional flow, on a narrow molar mass distribution (NMMD) polystyrene melt and styrene oligomer dilutions thereof. All samples used here were characterized in molecular weight, mechanical spectroscopy, and constant strain rate uniaxial extension in the work of Huang et al. [Macromolecules 46, 5026–5035 (2013); ACS Macro Lett. 2, 741–744 (2013)]. The stress relaxation following the steady extensional stress was measured on a 285 kg/mole NMMD polystyrene and two 1.92 kg/mole styrene oligomer dilutions thereof {PS-285k, PS-285k/2k-72, and PS-285k/2k-44 in the work of Huang et al. [Macromolecules 46, 5026–5035 (2013)]}. The two dilutions contained 28 and 56 wt. % oligomer, respectively. Further, the stress relaxation on a 545 kg/mole NMMD polystyrene diluted with 48 wt. % 0.972 kg/mole styrene oligomer {PS-545k/1k-52 in the work of Huang et al. [ACS Macro Lett. 2, 741–744 (2013)]} was measured as well. All the terminal relaxations could be predicted by a Doi and Edwards, e.g., pure configurational, type of model. At smaller time scales, agreement with a molecular stress function type of constitutive representation was observed for all measured relaxations.

Molar mass fractionation in aqueous two-phase polymer solutions of dextran and poly(ethylene glycol)

Dextran and poly(ethylene glycol) (PEG) in phase separated aqueous two-phase systems (ATPSs) of these two polymers, with a broad molar mass distribution for dextran and a narrow molar mass distribution for PEG, were separated and quantified by gel permeation chromatography (GPC). Tie lines constructed by GPC method are in excellent agreement with those established by the previously reported approach based on density measurements of the phases. The fractionation of dextran during phase separation of ATPS leads to the redistribution of dextran of different chain lengths between the two phases. The degree of fractionation for dextran decays exponentially as a function of chain length. The average separation parameters, for both dextran and PEG, show a crossover from mean field behavior to Ising model behavior, as the critical point is approached.

Phosphazene-Promoted Metal-Free Ring-Opening Polymerization of 1,2-Epoxybutane Initiated by Secondary Amides

The in situ generation of an anionic initiator X– obtained by the deprotonation of various secondary amides with tBuP4 phosphazene base was tested as possible way to initiate the polymerization of 1,2-epoxybutane. The initiation efficiency of different amide-containing molecules was investigated. Particular attention was given to the detection of eventual transfer or side reactions, especially due to nucleophilic attacks on the initiator moiety at the α-chain end. In all cases, the initiation of the polymerization by the amidate anion was effective. And in most cases, the polymerization proceeded in a controlled manner to afford amide end-capped poly(butylene oxide) with narrow molar mass distribution and expected molar masses.

Kinetics of Amine–Bis(phenolate) Iron-Mediated ATRP Up to High Pressure

Atom-transfer radical polymerization (ATRP) of styrene catalyzed by chloro-substituted amine–bis(phenolate)iron complexes was investigated via online vis/NIR spectroscopy up to 6000 bar. Pressure significantly increases the rate of ATRP by enhancing both the equilibrium constant, KATRP, and the propagation rate coefficient, kp. The observed negative reaction volume, ΔrV(KATRP), is due to a stronger contraction of the ligand sphere for the Lewis-acidic FeIII complex compared to the FeII complex. Despite the enormous rate enhancement of ATRP, narrow molar mass distributions may be obtained even at very high pressure and thus very high rates.

Zinc complexes bearing tridentate O,N,O-type half-Salen ligands for ring-opening polymerization of lactide

A number of unreported zinc complexes based on tridentate O,N,O-type half-Salen ligands were prepared. All the complexes were characterized by 1H, 13C NMR and elemental analysis. These complexes were used as catalysts with 2-propanol for the ring-opening polymerization of l-lactide and rac-lactide. They were effective in lactide polymerization with good conversions. And polymerizations were living with the narrow molar mass distributions. The bulky substituents with relatively larger steric hindrance of the ligands coordinated to the central metal centers had relatively low polymerizing activity.

Visible-Light-Controlled Living Radical Polymerization from a Trithiocarbonate Iniferter Mediated by an Organic Photoredox Catalyst

Living radical polymerization of acrylates and acrylamides from trithiocarbonate iniferters using a compact fluorescent lamp (CFL) bulb and 10-phenylphenothiazine as an organic photoredox catalyst is reported. With this system, chain growth can be efficiently switched between "on" and "off" in response to visible light. Polymer molar masses increase linearly with conversion, and narrow molar mass distributions are obtained. The excellent fidelity of the trithiocarbonate-iniferter enables the preparation of triblock copolymers from macro-iniferters under the same visible-light mediated protocol, using UV light without a photoredox catalyst or under traditional thermally induced RAFT conditions. We expect that the simplicity and efficiency of this metal-free, visible-light-mediated polymerization will enable the synthesis and modification of a range of materials under mild conditions.

Fluorescent dye-labeled TIPNO type regulator for nitroxide mediated reversible-deactivation radical polymerization

Abstract The TIPNO-type mediator containing fluorescent probe was used to initiate nitroxide mediated reversible-deactivation radical polymerization of styrene. Benzothioxanthene and pyrene were the fluorescent markers. One probe, benzothioxanthene, was attached to the initiating fragment of the polymer chain and the second probe, pyrene, was part of the propagating end of the polymer chain. Mainly UV absorption as well as partly fluorescence spectroscopy was applied to quantify the marked initiating chain ends and marked active alkoxyamine-terminated chain ends. Calculated theoretical molar masses are based on the assumption that all the initiating and propagating chain ends of the polymers bear fluorescent probes. Comparison of these data with the molar masses from GPC gave us the fraction of the marked active polymer chain ends and the fraction of polymers that were formed by thermal initiation. This represents a unique method for evaluation of the extent of livingness of polymerization process. At lower mediator concentration, the extent of marked initiating chain ends and the extent of marked propagating chain ends decreased with rising conversion and at 40% conversion only 50% of the polymer initiating and propagating chain ends contained labels. For the higher mediator concentration, marked initiating fragments of polymer chains were 95% and marked propagating chain ends were 93% at 40% conversion. The prepared polymers are characterized by a narrow distribution of molar masses for all conversion scales.

Alternating ring-opening copolymerization of cyclohexene oxide with phthalic anhydride catalyzed by iron(III) salen complexes

A series of three iron(III) salen complexes was synthesized and successfully used for copolymerization of cyclohexene oxide and phthalic anhydride. Catalytic systems based on an iron(III) salen complex in combination with 4-(dimethylamino)pyridine (DMAP) or bis(triphenylphosphine)iminium chloride (PPNCl) cocatalysts produced purely alternating copolymer with narrow molar mass distributions. [N,N′-Bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexylenediamine] iron(III) chloride was the most active complex and afforded the copolymer even in the absence of the cocatalysts. Other iron complexes were completely inactive in absence of a cocatalyst. Both DMAP and PPNCl alone were able to catalyze the copolymerization, affording purely alternating copolymers in good yields.

Continuous Flow Aminolysis of RAFT Polymers Using Multistep Processing and Inline Analysis

The reversible addition–fragmentation chain transfer (RAFT) method enables the synthesis of polymers with well-defined architecture and narrow molar mass distribution. Simple postpolymerization reactions using amines and Michael acceptors make it possible to conjugate RAFT polymers to a variety of active small molecules and macromolecules. Herein we demonstrate an efficient continuous flow process for aminolysis of RAFT polymers and subsequent Michael addition reactions, using continuous flow reactors, resulting in either thiol- or thioether-terminated polymer chains. After initial reaction optimization we managed to achieve the following: (1) establishment of an integrated flow process, which is capable of producing free thiol containing polymer without the formation of disulfide byproduct; this was achieved by means of an inline, amine scavenging process post-aminolysis using a polymer supported column; (2) the application of UV spectroscopy for inline monitoring of the continuous flow aminolysis reacti...

Highly stereoselective bimetallic complexes for lactide and ε-caprolactone polymerization

A series of Schiff-base compounds containing bimetallic ligands and two aluminum centers have been synthesized and characterized by 1H, 13C NMR and elemental analysis. These compounds could be successfully used as catalysts for the polymerization of rac-lactide and e-caprolactone. The polylactides (PLAs) prepared with these compounds were highly isotactic enriched (Pm = 0.97). The nature and steric hindrance of the ligands coordinated to the central metal ions remarkably influenced the polymer properties. Kinetic studies revealed that the polymerization was first order with respect to each of these compounds and lactide/caprolactone monomers. All the polymerizations were living, with good molecular weight control and relatively narrow molar mass distributions.

Synthesis and characterization of half-salen complexes and their application in the polymerization of lactide and ε-caprolactone

A series of half-salen ligands and their aluminum Al(III) complexes that contained different substituents were designed and synthesized. All the ligands and their complexes were characterized by 1H, 13C NMR and elemental analysis. The complexes can be used as catalysts to produce polylactide and poly-ε-caprolactone. All polymerizations were living with narrow molar mass distributions. The Mn(obsd) values of the isolated polymers were in good agreement with Mn(calcd). The polymerization rate of the electrophilic substituted complex was higher than the non-electrophilic substituted analogues. The more bulky substituents with more steric hindrance of the complexes showed relatively low polymerizing activity. The aluminum complexes showed a moderate stereo-selectivity to the ring opening polymerization of rac-lactide to give isotactic enriched polylactide.

Controlled Radical Polymerization Using a Novel Symmetrical Selenium RAFT Agent

A novel symmetrical selenium-based reversible addition-fragmentation chain transfer (RAFT) agent, Se,Se’-dibenzyl carbonodiselenothioate (Se-RAFT), is synthesized and used in the RAFT polymerization of styrene. The results obtained show that the Se-RAFT agent is involved in the polymerization of styrene, as evidenced by narrow molar-mass distributions (M¯w/M¯n < 1.6) and the incorporation of the Se-RAFT moiety into the resultant polymer. The latter is confirmed by aminolysis, NMR spectroscopy, size-exclusion chromatography (SEC) and UV spectroscopy. This work provides detailed insight into the Se-RAFT polymerization mechanism. The Se-RAFT agent is unique in that the stabilizing and leaving groups are identical.

Dynamic scaling and kinetic roughening of poly(ethylene) islands grown by vapor phase deposition

Vapor phase deposition of poly(ethylene) is shown to produce uncross-linked thin films consisting of linear (CH2)100 oligomers with narrow molar mass distribution of dispersity DM=1.10. Early stages of the film formation are characterized by the growth of two-dimensional compact islands of constant 7–8nm thickness. The transversal evolution of islands is studied in the context of the Dynamic Scaling Theory. The aggregation regime is found to be valid in a narrow range of coverage 0.1<θ<0.3. The critical island size is estimated to be i=1. Kinetic roughening of the growing front gives a set of the scaling exponents αloc=0.67, αs=0.85, β=0.33 (β=0.2 for the late stages of growth) and z=2.2 that does not fit into any of the known universality classes. Macromolecular relaxation at the island edges is suggested to explain the observed inconsistence.

Novel precursors for production of 3-hydroxyvalerate-containing poly[(R)-hydroxyalkanoate

Polyhydroxyalkanoates (PHAs) with tailored properties are needed to meet consumer demands regarding the use of eco-compatible biobased polymeric materials and relevant plastic items. Inserting 3-hydroxvalerate (3HV) monomeric units in PHA biopolyesters results in poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyvalerate] (PHBHV) copolyesters aimed at their conversion into production of biodegradable eco-friendly plastic items. As inexpensive novel precursor substrate structurally related to 3HV, a mixture of odd-numbered carboxylic acids with 9–17 carbon atoms was produced by oxidative ozonolysis of alkenes. This mixture was successfully applied for biomediated PHBHV production by Cupriavidus necator. Applying this mixture as carbon substrate, a molar 3HV fraction exceeding 0.12 was obtained. The isolated copolyesters featured a low degree of crystallinity, narrow molar mass distribution, and low melting temperatures. These properties should make application of the novel 3HV-precursors interesting for large-scale production of easily processable copolyesters.

Bis(β‐diketiminato) lanthanide amides: synthesis, structure and catalysis for the polymerization of l‐lactide and ε‐caprolactone

Treatment of the chlorides (L2,6‐iPr2Ph)2LnCl (L2,6‐iPr2Ph = [(2,6‐iPr2C6H3)NC(Me)CHC(Me)N(C6H5)]−) with 1 equiv. of NaNH(2,6‐iPr2C6H3) afforded the monoamides (L2,6‐iPr2Ph)2LnNH(2,6‐iPr2C6H3) (Ln = Y (1), Yb (2)) in good yields. Anhydrous LnCl3 reacted with 2 equiv. of NaL2,6‐iPr2Ph in THF, followed by treatment with 1 equiv. of NaNH(2,6‐iPr2C6H3), giving the analogues (L2,6‐iPr2Ph)2LnNH(2,6‐iPr2C6H3) (Ln = Sm (3), Nd (4)). Two monoamido complexes stabilized by two L2‐Me ligands, (L2‐Me)2LnNH(2,6‐iPr2C6H3) (L2‐Me = [N(2‐MeC6H4)C(Me)]2CH)−; Ln = Y (5), Yb (6)), were also synthesized by the latter route. Complexes 1, 2, 3, 4, 5, 6 were fully characterized, including X‐ray crystal structure analyses. Complexes 1, 2, 3, 4, 5, 6 are isostructural. The central metal in each complex is ligated by two β‐diketiminato ligands and one amido group in a distorted trigonal bipyramid. All the complexes were found to be highly active in the ring‐opening polymerization of L‐lactide (L‐LA) and ε‐caprolactone (ε‐CL) to give polymers with relatively narrow molar mass distributions. The activity depends on both the central metal and the ligand (Yb &lt; Y &lt; Sm ≈ Nd and L2‐Me &lt; L2,6‐iPr2Ph). Remarkably, the binary 3/benzyl alcohol (BnOH) system exhibited a striking ‘immortal’ nature and proved able to quantitatively convert 5000 equiv. of L‐LA with up to 100 equiv. of BnOH per metal initiator. All the resulting PLAs showed monomodal, narrow distributions (Mw/Mn = 1.06 − 1.08), with molar mass (Mn) decreasing proportionally with an increasing amount of BnOH. The binary 4/BnOH system also exhibited an ‘immortal’ nature in the polymerization of ε‐CL in toluene. Copyright © 2014 John Wiley &amp; Sons, Ltd.

ChemInform Abstract: A Guide to the Synthesis of Block Copolymers Using Reversible‐Addition Fragmentation Chain Transfer (RAFT) Polymerization

AbstractReview: 50 refs.