Narrow MWDs Research Articles

Tannic Acid‐Inspired Star‐Like Macromolecules via Temporally Controlled Multi‐Step Potential Electrolysis

AbstractInspired by tea stains, a plant polyphenolic‐based macroinitiator is prepared for the first time by partial modification of tannic acid (TA) with 2‐bromoisobutyryl bromide. In accordance with the “grafting from” methodology, a naturally occurring star‐like polymer with a polar gallotannin core and a hydrophobic poly(n‐butyl acrylate) side arms is synthesized via a simplified electrochemically mediated ATRP (seATRP), utilizing multiple‐step potential electrolysis. To investigate the kinetics of the electrochemical catalytic process triggered by reduction of Cu(II) or Fe(III) catalytic complex in the presence of the multifunctional initiator, cyclic voltammetry measurements are conducted. The naturally derived tannin macromolecule shows narrow MWDs (Đ = 1.57). Moreover, solvolysis of the star polymer to cleave the side arms and characterize them indicates that all chains grow to the same length (homopolymers with Mw/Mn <1.17), which confirms the well‐controlled seATRP. The structure of the obtained TA‐based systems is characterized microscopically (AFM) and spectroscopically (1H NMR, FT‐IR). Atomic force microscopy measurements precisely determine the diameters of the obtained star polymers (19.7 ± 3.3 nm). These new star polymers may find biomedical applications as drug delivery systems and antifouling or antimicrobial coatings.

A controlled synthesis method of alkyl methacrylate block copolymers via living anionic polymerization at ambient temperature.

A controlled synthesis method of alkyl methacrylate block copolymers such as poly(methyl methacrylate)-b-poly(ethyl methacrylate) (PMMA-b-PEMA), poly(methyl methacrylate)-b-poly(butyl methacrylate) (PMMA-b-PBMA) and poly(ethyl methacrylate)-b-poly(butyl methacrylate) (PEMA-b-PBMA) via living anionic polymerization was innovated with potassium tert-butoxide (t-BuOK) as initiator in tetrahydrofuran(THF) solvent. The sequential anionic copolymerization could be smoothly conducted at 0 °C and the conversion of all monomers reached up to almost 100%. The copolymers were characterized by gel permeation chromatography (GPC), proton nuclear magnetic resonance (1H-NMR), fourier transform infrared spectroscopy (FTIR) and dynamic mechanical analysis (DMA). It was found that all block copolymers were in a narrow MWD while Mw and weight ratio of each block were coincided with the theoretical values and feed ratio. DMA measurement indicated that all the block copolymers have two glass transition temperatures which have proved the certain microphase separation and the partial compatibility of the blocks. The similar results were achieved after changing feed order or addition amount. Furthermore, the reactivity ratio was also studied and confirmed that reactivity ratio of MMA was the largest among alkyl methacrylate. Based on these results, the anionic block copolymerization containing polar alkyl methacrylate monomers at a commercial scale starts to become possible.

Precise Synthesis of Bottlebrush Block Copolymers from ω-End-Norbornyl Polystyrene and Poly(4-tert-butoxystyrene) via Living Anionic Polymerization and Ring-Opening Metathesis Polymerization

A facile and efficient synthetic grafting-through strategy for preparing well-defined bottlebrush block copolymers (BBCPs) was developed through a combination of living anionic polymerization (LAP) and ring-opening metathesis polymerization (ROMP). ω-End-norbornyl polystyrene (NPSt) and poly(4-tert-butoxystyrene) (NPtBOS) were synthesized by LAP using terminator of chlorine moiety containing silane-protecting amine and coupled with a subsequent amidation using norbornyl activated ester. Bottlebrush homopolymers of NPSt were obtained by ROMP with ultrahigh molecular weights (MWs, Mw = 2928 kDa) and narrow molecular weight distributions (MWDs, Đ = 1.07) at high degree of polymerizations (DPw = 1084). Well-defined BBCPs with ultrahigh MWs (Mw ∼ 3055 kDa) and narrow MWDs (Đ ∼ 1.13) were synthesized through sequential ROMP of NPSt with NPtBOS. The effect of ultrahigh MWs was investigated by self-assembly of the BBCPs in which the phase-separated BBCPs presented periodic lamellar structures and exhibited structural colors from blue to pink.

Synthesis of naturally-derived macromolecules through simplified electrochemically mediated ATRP.

The flavonoid-based macroinitiator was received for the first time by the transesterification reaction of quercetin with 2-bromoisobutyryl bromide. In accordance with the “grafting from” strategy, a naturally-occurring star-like polymer with a polar 3,3',4',5,6-pentahydroxyflavone core and hydrophobic poly(tert-butyl acrylate) (PtBA) side arms was synthesized via a simplified electrochemically mediated ATRP (seATRP), utilizing only 78 ppm by weight (wt) of a catalytic CuII complex. To demonstrate the possibility of temporal control, seATRP was carried out utilizing a multiple-step potential electrolysis. The rate of the polymerizations was well-controlled by applying optimal potential values during preparative electrolysis to prevent the possibility of intermolecular coupling of the growing polymer arms. This appears to be the first report using on-demand seATRP for the synthesis of QC-(PtBA-Br)5 pseudo-star polymers. The naturally-derived macromolecules showed narrow MWDs (Đ = 1.08–1.11). 1H NMR spectral results confirm the formation of quercetin-based polymers. These new flavonoid-based polymer materials may find applications as antifouling coatings and drug delivery systems.

A convergent approach to ring polymers with narrow molecular weight distributions through post dilution in ring expansion cationic polymerization

In this paper, we demonstrate a convergent approach to convert “fused” ring chains obtained via ring expansion cationic polymerization of vinyl ether with a hemiacetal ester (HAE)-based ring initiator (1) into “sing” ring ones of narrow MWDs.

Narrow molecular weight and particle size distributions of polystyrene 4-arm stars synthesized by RAFT-mediated miniemulsions

There are no reports of star polymers synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization in aqueous dispersions (e.g. emulsion, miniemulsions). In this work, we used two RAFT agents to produce linear and 4-arm star polymers in a well-controlled miniemulsion system using conventional surfactants (sodium dodecyl sulfate and hexadecane) and initiators (ammonium persulfate). The miniemulsions were formed through ultrasonication of the polymerization mixture to produce very small droplet sizes. Polymerization of styrene in these miniemulsions resulted in the formation of polymer nanoparticles of approximately 60 and 75 nm with narrow particle size distributions regardless of the targeted molecular weight. The rate of polymerization in these miniemulsions (100% conversion after 3.3 h) was significantly faster than in solution (60% conversion after 20 h). The reason for this fast rate was due to compartmentalization of the radicals within the growing particles. In addition, narrow MWDs were produced with polydispersity (PDIMWD) values below 1.22 for the linear and below 1.09 for the 4-arm star polymers. The particle size distributions were found to be narrow, less than 0.055 for the linear and less than 0.113 for the 4-arm star polymers. This is the first successful miniemulsion, to our knowledge, of 4-arm stars by RAFT to create both narrow molecular weight and narrow particle size distributions. The properties of such polymer latex particles are yet to be explored but they should have vastly different properties compared to latex particles with linear polymers. Our work opens a synthetic route to this class of latex particles previously unobtainable using conventional reagents, and providing exciting opportunities for various applications.

Kinetic study on the living/controlled cationic polymerization of p‐methoxystyrene coinitiated by tris(pentafluorophenyl)borane

AbstractA kinetic study of the living cationic polymerization of p‐methoxystyrene using 1‐(4‐methoxyphenyl)ethanol (1)/B(C6F5)3 initiating system in a mixture of CH3CN with CH2Cl2 1:1 (v/v) at room temperature was carried out utilizing a wide variety of conditions. The polymerization proceeded in a living fashion even in the presence of a large amount of water ([H2O]/[B(C6F5)3] ratio up to 20) to afford polymers whose Mn increased in direct proportion to monomer conversion with fairly narrow MWDs (Mw/Mn ≤ 1.3). The investigation revealed that the rate of polymerization was first‐order in B(C6F5)3 concentration, while a negative order in H2O concentration close to −2 was obtained. It was also found that the rate of polymerization decreased with lowering temperature, which could be attributed to a decreased concentration in free Lewis acid, the true coinitiator of polymerization. A mechanistic scheme to explain the kinetic behavior of living p‐methoxystyrene polymerization is proposed, which has been validated by PREDICI simulation on multiple‐data curves obtained by 1H NMR in situ polymerization experiment. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6928–6939, 2008

Potassium enolates of N,N‐dialkylamides as initiators of anionic polymerization

AbstractStable potassium enolates of N,N‐diethylacetamide [α‐potassio‐N,N‐diethylacetamide (1)], N,N‐diethylpropionamide [α‐potassio‐N,N‐diethylpropionamide (2)], and N,N‐diethylisobutyramide [α‐potassio‐N,N‐diethylisobutyramide (3)] were prepared by the proton abstraction of the corresponding N,N‐diethylamides with diphenylmethylpotassium (Ph2CHK) or potassium naphthalenide in THF. The relative nucleophilicity of 1–3 was estimated to be in the order of 1 < 3 < 2 from the results of the alkylation reaction with methyl iodide. N,N‐diethylacetamide transferred its α‐proton to 2 quantitatively in THF at 0 °C, whereas no reaction occurred between N,N‐diethylisobutyramide and 2; this indicated the relative basicity to be 1 < 2 ∼ 3. Anionic polymerizations of N,N‐diethylacrylamide (DEA) and methyl methacrylate were quantitatively initiated with 2 in THF at −78 °C, whereas the initiation efficiencies of 2 for styrene and 2‐vinylpyridine were about 2 and 67%, respectively. The initiation of DEA with 1–3 at −78 or 0 °C in THF gave poly (DEA)s having broad molecular weight distributions (MWDs; Mw/Mn = 2) and ill‐controlled molecular weights. In contrast, poly(DEA)s of narrow MWDs (Mw/Mn < 1.2) and predicted Mn's were obtained with 2 in the presence of diethylzinc (Et2Zn) at −78 °C, whereas the initiations with 1/Et2Zn and 3/Et2Zn at −78 °C resulted in poor control of the molecular weights. At the higher temperature of 0 °C, all the binary initiator systems (1–3/Et2Zn) induced controlled polymerizations of DEA in terms of the conversion, molecular weight, and MWD. The poly(DEA)s produced with 1–3/Et2Zn at 0 °C showed mr‐rich configurations (mr = 76–89%), as observed for the poly(DEA) generated with Ph2CHK/Et2Zn. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1260–1271, 2007

Synthesis of Polymer Brushes Composed of Poly(phenylacetylene) Main Chain and Either Polystyrene or Poly(methyl methacrylate) Side Chains

Novel cylindrical polymer brushes consisting of a highly cis-transoidal poly(phenylacetylene) main chain and either polystyrene (PS) or poly(methyl methacrylate) (PMMA) side chains were synthesized by the macromonomer method. Two phenylacetylene-terminated macromonomers, namely, M−PS (Mn = 1830) and M−PMMA (Mn = 1860), were prepared by atom transfer radical polymerization (ATRP) of styrene and methyl methacrylate, respectively, using acetylene-functionalized initiators. M−PS and M−PMMA were polymerized successfully with the [(nbd)RhCl]2/Et3N (2,5-norbornadiene) catalyst [Rh-1] to give high molecular weight polymer brushes, poly(M−PS) (e.g., Mw 1660 × 103) and poly(M−PMMA) (e.g., Mw 1480 × 103), respectively, according to GPC−RALLS. Further, well-defined poly(M−PS) (e.g., Mn 47 × 103, Mw/Mn 1.12) and poly(M−PMMA) (e.g., Mn 30 × 103, Mw/Mn 1.16) with narrow MWDs were obtained with an Rh-based living polymerization catalyst [Rh-2]. The present polymer brushes were yellow to orange due to the conjugated main ...

Photosensitive copolymers with various types of azobenzene side groups synthesized by living cationic polymerization

Well-defined photoresponsive polymers of vinyl ethers with various azo side groups were synthesized via living cationic copolymerization using Et1.5AlCl1.5 in the presence of an ester as an added base. Despite the apparently undesirable structures, too basic or bulky, of azo-containing monomers for cationic polymerization, all copolymerizations with an alkyl vinyl ether proceeded with livingness to yield the product polymers with extremely narrow MWDs (Mw/Mn = 1.06−1.13). It should be noted that living polymers were produced even from a monomer with the dimethylamino group. The different azo groups in the product copolymers permitted reversible photo-responsive isomerization at a specific wavelength related to the structure of the azo group.

ATRP of (meth)acrylates initiated with a bifunctional initiator bearing trichloromethyl functional groups and structural analysis of the formed polymer

ATRP of methyl methacrylate (MMA), initiated with 1,3-bis{1-methyl-1-[(2,2,2-trichloroethoxy)carbonylamino]ethyl}benzene as a bifunctional initiator (BI) under CuCl catalysis was studied in the presence of 2,2′-bipyridine (bpy) or hexamethyltriethylenetetramine (HMTETA) ligands, in bulk or in toluene. With the bpy, the polymerization reaches only limited monomer conversions and products have broad MWDs. In contrast, polymerization in the presence of HMTETA is a well-controlled process, affords virtually quantitative conversion, giving PMMAs with narrow MWDs and predictable molecular weights within a range of more than one order of magnitude. NMR analysis of the prepared PMMA proved formation of linear polymers with im-measurable extent of chain branching or β-scission as undesired side reactions. The prepared α,ω-dichloro-PMMAs were used as macroinitiators for ATRP of tert-butyl acrylate ( t-BuA), giving the corresponding triblock copolymers with narrow MWDs and molecular weights controllable in a wide range. Block copolymerizations were performed in dimethyl formamide (DMF) or acetone in the presence of pentamethyldiethylenetriamine (PMDETA) as ligand and could be accelerated by addition of metallic copper.

Amine Additives for Fast Living Radical Polymerization of Methyl Methacrylate with RuCl2(PPh3)3

A series of amines were effective as additives for the control and rate enhancement of the living radical polymerization of methyl methacrylate (MMA) with RuCl2(PPh3)3. On addition of n-Bu3N and n-Bu2NH, the polymerization with R−Cl/RuCl2(PPh3)3 in toluene at 80 °C reached 90% conversion in 50 h and 94% in 20 h, respectively, while only 46% in 120 h without additives. The polymers obtained with n-Bu3N and n-Bu2NH had controlled molecular weights that increased in direct proportion to monomer conversion and narrow MWDs (Mw/Mn = 1.1−1.2). This is in sharp contrast to the uncontrolled molecular weights and broad MWDs (Mw/Mn = 1.7−2.0) obtained in the additive-free systems. Primary amines like n-BuNH2 and cyclic secondary amines like piperidine induced much faster polymerizations to result in broad MWDs (Mw/Mn = 1.7−1.8). Other additives such as pyridines, amides, alcohols, phenols, esters, and dimanies were not effective as additives for the ruthenium-catalyzed polymerizations. Interactions between the added amines and RuCl2(PPh3)3 were observed by 1H NMR analysis of the mixtures, where the amines coordinate to the ruthenium center and form highly active mononuclear ruthenium complexes.

Anionic polymerization of acrylates. XII. Polymerization of methyl methacrylate and tert-butyl acrylate initiated with alkyllithiums or methyl 2-lithioisobutyrate in the presence of lithium tert-butoxide

Ligated anionic polymerization of methyl methacrylate (MMA) and tert-butyl acrylate ( t-BuA) initiated either with 1,1-diphenyl-3-methylpentyllithium (DPMPLi) or α-methyl styryllithium (α-MStLi) or methyl 2-lithioisobutyrate (MIB-Li) stabilized with lithium tert-butoxide ( t-BuOLi) was studied at −60 °C. In combination with DPMPLi, or α-MStLi, stabilizing efficiency of the alkoxide is negligible; MMA polymerizes with high reaction rate, but the chains self-terminate after all the monomer has been consumed, which was tested in two-dose experiments. Ageing of mixed DPMPLi/ t-BuOLi solutions as well as an excess of the alkoxide over the initiator have no effect on the stability of the growing chain-ends. In the presence of ten-fold excess of t-BuOLi, MIB-Li initiates slow polymerization of MMA with high stability of active centers. Three MMA doses were successively polymerized producing polymers with narrow MWDs in all steps, so that the active centers remained living for more than 4 h. t-BuA also polymerized in a living manner with the same system.

SEC OF SIMPLE POLYMERS WITH MOLAR MASS DETECTION IN PRESENCE OF INSTRUMENTAL BROADENING. COMPUTER SIMULATION STUDY ON THE CALCULATION OF UNBIASED MOLECULAR WEIGHT DISTRIBUTIONS

This theoretical work presents a correction procedure for calculating an unbiased MWD when analyzing a linear homopolymer by size exclusion chromatography with molar mass detection. The fractionation and the measurements are ideal, but the chromatograms are distorted by a nonuniform and skewed instrumental broadening (IB), and are contaminated with a zero-mean random noise. The main assumption is that the molecular weight calibration is linear in the chromatogram range. The following phenomenological procedure was proposed: (i) independently correct the mass- and molar mass chromatograms for IB through a robust inverse filtering technique; (ii) estimate the unbiased calibration from the ratio of the corrected chromatograms; (iii) adjust a straight line to the mid-values of that calibration; and (iv) estimate the unbiased MWD from the linear calibration and the corrected mass chromatogram. For the chromatogram inversions, a minimum sized broadening matrix was selected and a singular value decomposition technique was applied. The following effects were evaluated: of an increased measurement noise, of uncertainties in the range of the measured chromatograms, and of systematic errors in the IB function. The method fails for very narrow MWDs.

Polymerization of aliphatic disubstituted acetylenes by MoOCl4–n‐Bu4Sn–EtOH catalyst: Formation of polymers with narrow MWDs and confirmation of the living character

Polymerization of aliphatic disubstituted acetylenes by MoOCl4–n‐Bu4Sn–EtOH catalyst: Formation of polymers with narrow MWDs and confirmation of the living character

Direct Living Cationic Polymerization of p-Hydroxystyrene with Boron Trifluoride Etherate in the Presence of Water

Direct living cationic polymerization of p-hydroxystyrene (pHS) has been developed in the presence of a fairly large amount of water using BF3OEt2 as a Lewis acid catalyst and the adducts (1−4) of p-methoxystyrene (pMOS) and a series of protonic compounds as initiators. In contrast to most living cationic polymerizations, the water and the alcohol adducts (3 and 4, respectively) produced polymers with number-average molecular weights (Mn) close to the calculated values from the monomer/initiator mole ratios. With 4/BF3OEt2, the Mn increased with monomer conversion, and the living nature of the chains was confirmed by sequential monomer addition experiments. The polymerization proceeded even in the presence of a large amount water to afford polymers whose Mn increased in direct proportion to monomer conversion with fairly narrow MWDs (Mw/Mn < 1.4). This initiating system was also effective at or above ambient temperature (from −15 to +60 °C). The success of this controlled cationic polymerization of unprotected pHS is due to the stability of BF3OEt2 and to its tolerance of the hydroxy groups in the monomer and water and the proper selection of the initiator. This initiator contains a covalent C−O bond that is preferentially dissociated by an oxophilic Lewis acid, BF3. This is the first example of a direct living polymerization of pHS, by any mechanism, without protecting the hydroxy groups.

A Novel Successive Route to Well-Defined Water-Soluble Poly(2,3-dihydroxypropyl methacrylate) and Amphiphilic Block Copolymers Based on an Osmylation Reaction

A novel two-step successive route to well-defined water-soluble poly(2,3-dihydroxypropyl methacrylate) [poly(DHPMA)] and the amphiphilic block copolymers of DHPMA with styrene (St) or methyl methacrylate (MMA) was developed by combining the living anionic polymerization method with an osmylation reaction. Homopolymers of allyl methacrylate (AMA) with various molecular weights (Mn = 5900−170 000) and narrow molecular weight distributions (MWD; Mw/Mn = 1.06−1.16) were first prepared by the anionic polymerization of AMA using 1,1-diphenylhexyllithium (DPHL) as the initiator, in THF, in the presence of LiCl ([LiCl]/[DPHL]0 = 3), at −70 °C. Under similar conditions, the anionic block copolymerization of AMA with MMA generated well-defined di- and triblock copolymers with controlled molecular weights and compositions as well as narrow MWDs (Mw/Mn = 1.05−1.16). Further, block copolymers of St and AMA with various compositions were prepared by performing the anionic block copolymerization of AMA from a 1,1-diphenylethylene-capped anionic living poly(St). In both the homopolymerization of AMA and its block copolymerization with MMA or St, its allyl side group remained unreacted. Without the (co)polymer separation from the (co)polymerization solution, the allyl groups of the (co)polymer were directly reacted with an excess of N-methylmorpholine N-oxide (NMO), in the presence of a small amount of osmium tetroxide as catalyst, at room temperature. This osmylation procedure changed the poly(AMA) component to poly(DHPMA). During this process, no cross-linking or polymer chain damage occurred, and well-defined water-soluble poly(DHPMA) and amphiphilic block copolymers were obtained. The molecular weight, molecular architecture, and the copolymer composition affect the hydrophilicities of the osmylated (co)polymers, and all these factors can be accurately controlled during the (co)polymerization step.

Polymerization of aliphatic disubstituted acetylenes by MoOCl4-n-Bu4Sn-EtOH catalyst: Formation of polymers with narrow MWDs and confirmation of the living character

The polymerization of aliphatic disubstituted acetylenes was examined with MoOCl 4 -n-Bu 4 Sn-EtOH (1/1/2) ternary catalyst in anisole at 0 °C. Various linear aliphatic disubstituted acetylenes such as 2-nonyne provided polymers with narrow molecular weight distributions (weight-average molecular weight/number-average molecular weight = 1.05-1.20). The living character of the polymerization was proven by both the time profile of the polymerization and the multistage polymerization of 2-nonyne. The initiation efficiency was about 3%, which is rather low. Although 5-dodecyne, which has a triple bond in a more inner part, polymerized more slowly than 2-nonyne, their living characters were hardly different. Diblock copolymers were synthesized by the sequential living polymerization of internal linear alkynes.

Effect of Lithium tert-Alkoxides on Anionic Polymerization of Butadiene Initiated with a Bifunctional Initiator

Polymerization of buta-1,3-diene initiated by bifunctional dilithium initiator in tert-butyl methyl ether, hexane and hexane-toluene mixtures was studied in the presence of Li tert-butoxide, 2-methylpentan-2-olate, 3-methylpentan-3-olate or 2,3-dimethylbutan-2-olate. The alkoxides lower the overall polymerization rate and affect, to a certain extent, microstructure of formed polymers. When applied in a concentration equal to that of the initiating centres, they lower the content of vinyl structures in polybutadiene by 10-12%. Increasing concentration of the alkoxide has no perceptible effect and, if used in 12-fold excess over the initiator, the content of 1,2-structures even increases. Polymers prepared in the presence of an alkoxide mostly have unimodal and narrow MWDs.

NiBr2(Pn-Bu3)2-Mediated Living Radical Polymerization of Methacrylates and Acrylates and Their Block or Random Copolymerizations

Nickel(II) bromide bis(tri-n-butylphosphine) [NiBr2(Pn-Bu3)2] induced living radical polymerization of methyl methacrylate (MMA), methyl acrylate (MA), and n-butyl acrylate (BA) in conjunction with an organic bromide initiator [R−Br: CCl3Br, (CH3)2CBrCO2C2H5, and (CH3)2CBrCOPh] in the presence of Al(Oi-Pr)3 additive. In addition, the initiating system with an MMA “dimer” model of the bromine-capped dormant polymer [(CH3)2C(CO2CH3)CH2(CH3)CBrCO2CH3] gave living polymers with very narrow MWDs (Mw/Mn ∼ 1.1). Similar living polymerizations were possible in the absence of Al(Oi-Pr)3. NiBr2(Pn-Bu3)2 led to faster living polymerizations at a high temperature (120 °C; ∼90% conversion in 2.5 h) or at its high concentration, because it is more thermally stable and more soluble in organic solvents than NiBr2(PPh3)2. This feature permitted the synthesis of living PMMA of higher molecular weight (Mn ∼ 4 × 105) with narrow molecular weight distributions (Mw/Mn = 1.2−1.4). The NiBr2(Pn-Bu3)2-based system was also ...