Synthesis and characterization of biodegradable-cum-crosslinkable well-defined polyesters via chain-growth polycondensation in solid-liquid phase

Well-defined aliphatic polyesters, polyglycolide (PGA), polylactide (PLA) and their copolymers (PLGA) were prepared by chain-growth polycondensation of potassium 2-bromocarboxylates in solid-liquid phase. The polymerization proceeded in a living fashion without any side reactions. The degrees of polymerization (D_p) of polyesters was in agreement with the feed ratio of monomer to initiator. The polymer, which was only composed of heptamer, octamer and nonamer, possessed a narrow molecular weight distribution. Furthermore, the end groups of polymers, such as allyl and phenyl units, were directly yielded during the polymerization for the further modifying and crosslinking. The synthesized polyesters with allyl end groups were successfully crosslinked, and the products possessed biodegradability in phosphate buffer solution at 37 °C.     

Chain-growth polycondensation of potassium 3-cyano-4-fluorophenolate derivatives for well-defined poly(arylene ether)s

Polycondensation normally proceeds in a step-growth reaction manner to give polymers with a wide range of molecular weights. However, the polycondensation of potassium 2-alkyl-5-cyano-4-fluorophenolate ( 1 ) proceeded at 150°C in a chain polymerization manner from initiator, 4-fluoro-4′-trifluoromethyl benzophenone ( 2 ), to give aromatic polyethers having controlled molecular weights and low polydispersities (M_w/M_n ⩽ 1.2). The resulting polycondensation of 1 had all of the characteristics of living polymerization and displayed a linear correlation between molecular weight and monomer conversion, maintaining low polydispersities. Sulfolane was a better solvent for chain-growth polycondensation of 1 than other aprotic solvents. The polyether from 1 with a low polydispersity showed higher crystallinity than that with a broad molecular weight distribution, obtained by the conventional polycondensation of 1 without 2 .     

Kumada chain-growth polycondensation as a universal method for synthesis of well-defined conjugated polymers

Kumada chain-growth polycondensation (KCGP) is a novel method for the synthesis of well-defined conjugated polymers. Because the Ni-catalyst can transfer in an intramolecular process to the propagating chain end, the polymerization follows chain-growth mechanism. With this newly developed method, various conjugated polymers, such as polythiophenes, poly(p-phenylene) (PPP), polypyrrole (PPy), and polyfluorene with controlled molecular weights and relatively narrow polydispersities (PDIs), have been prepared. Especially, the polymerizations for poly(3-alkylthiophene)s (P3ATs), PPP, and PPy exhibited quasi-living characteristics, which allows preparing polymer brushes, fully-conjugated block copolymers, and macroinitiators and macro-reactants for the synthesis of rod-coil block copolymers. In the current review, the progress in this new area is summarized.     

Inductive effect-assisted chain-growth polycondensation. synthetic development from para- to meta-substituted aromatic polyamides with low polydispersities

The polycondensation of m-(octylamino)benzoic acid esters (1) with base was investigated in order to extend the synthesis of well-defined condensation polymers from para-substituted polymers to meta-substituted ones. We expected that the aminyl anion of 2 would deactivate the ester moiety at the meta position of 2 owing to the strong inductive effect of the anion, resulting in, not self-polycondensation, but chain-growth polycondensation. The methyl ester monomer 1a polymerized with lithium hexamethyldisilazide (LiHMDS) in the presence of phenyl benzoate (3a) as an initiator at 0 degrees C to afford a polymer with a low polydispersity, but the product contained a small amount of self-condensation polymer. On the other hand, the polymerization of the ethyl ester monomer (1b) with phenyl 4-methylbenzoate (3b) proceeded through chain polymerization without self-polycondensation. The Mn values of the polymers increased linearly in proportion to the [1b]0/[3b]0 ratio, and the Mw/Mn ratios remained narrow over the entire [1b]0/[3b]0 range. Furthermore, a block copolymer of N-alkylated poly(m-benzamide) and poly(p-benzamide) with a low polydispersity was synthesized by the monomer addition method under this polymerization condition.     

Development of catalyst‐transfer condensation polymerization. Synthesis of π‐conjugated polymers with controlled molecular weight and low polydispersity

We describe the development of chain‐growth condensation polymerization for the synthesis of well‐defined π‐conjugated polymers via a new polymerization mechanism, catalyst‐transfer polymerization. We first studied the condensation polymerization of Grignard‐type hexylthiophene monomer with a Ni catalyst as a part of our research on chain‐growth condensation polymerization, and found that this polymerization also proceeded in a chain‐growth polymerization manner. However, the polymerization mechanism involving the Ni catalyst was different from that of previous chain‐growth condensation polymerizations based on substituent effects; the Ni catalyst catalyzed the coupling reaction of the monomer with the polymer, followed by the transfer of Ni(0) to the terminal C? Br bond of the elongated molecule. This catalyst‐transfer condensation polymerization is generally applicable for the synthesis of polythiophene with an etheric side chain and poly(p‐pheneylene), as well as for the synthesis of polyfluorene via the Pd‐catalyzed Suzuki–Miyaura coupling reaction. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 753–765, 2008     

Synthesis of well-defined poly(p-benzamide) from chain-growth polycondensation and its application to block copolymers

Poly(p-benzamide) with a defined molecular weight and a low polydispersity and block copolymers containing this well-defined aramide was synthesized. Phenyl 4-(4-octyloxybenzylamino)benzoate ( 1b ) polymerized at room temperature in the presence of base and phenyl 4-nitrobenzoate ( 2a ) as an initiator in a chain-growth polycondensation manner to give well-defined aromatic polyamides having the 4-octyloxybenzyl groups as a protecting group on nitrogen in an amide. It was confirmed by a model reaction that deprotection of this protecting group proceeded completely with trifluoroacetic acid (TFA) without breaking the amide linkage. The utility of this approach to poly(p-benzamide) with a low polydispersity was demonstrated by the synthesis of block copolymers of poly(p-benzamide) and poly(N-octyl-p-benzamide) or poly(ethylene glycol). The SEM images of the supramolecular assemblies of the former block copolymer showed μm-sized bundles and aggregates of flake structures.     

Catalyst-transfer polycondensation for the synthesis of poly(p-phenylene) with controlled molecular weight and low polydispersity

To examine whether catalyst-transfer polycondensation, which affords well-defined polythiophenes, has generality for other conjugated polymers, the synthesis of poly(p-phenylene) (PPP) with various Ni catalysts was investigated. Monomer 1, 1-bromo-4-chloromagnesio-2,5-dihexyloxybenzene, was polymerized with Ni(dppe)Cl2 in the presence of equimolar LiCl to give PPP with a narrow polydispersity. The number-average molecular weight (Mn) of PPP thus obtained increased in proportion to the conversion of 1, indicating that this polymerization also proceeded in a chain-growth polymerization manner. Furthermore, the molecular weight of PPP was controlled by the feed ratio of 1 to the Ni catalyst up to at least Mn = 30000.     

Two‐dimensional liquid chromatography with active solvent modulation for studying monomer incorporation in copolymer dispersants

A pseudo‐comprehensive two‐dimensional liquid chromatography approach with size exclusion chromatography in the first dimension and gradient reversed‐phase liquid chromatography in the second dimension was successfully developed for the characterization of vinyl acetate/acrylic acid copolymers and vinyl acetate/itaconic acid/acrylic acid terpolymers. Active solvent modulation was exploited to prevent the polymer breakthrough in the second dimension separation caused by the strong solvent used in the first dimension. The conditions of the active solvent modulation valve were optimized to achieve sufficient on‐line dilution and to completely prevent polymer breakthrough without adding excessive time to the modulation cycle. Using this approach, copolymers made with different monomer ratios and processes were studied. Heterogeneous composition distribution due to insufficient monomer incorporation was detected in some of the copolymer samples. We demonstrated that with active solvent modulation, the two‐dimensional liquid chromatography approach is no longer limited to water‐soluble polymers and can be used for a broader range of polymers and copolymers.     

镍催化转移缩聚合成全氟环丁基芳基醚聚合物

研究了通过镍催化转移缩聚的方法来合成全氟环丁基芳基醚聚合物.首先,我们以对溴苯酚和1,2-二溴四氟乙烷为起始原料,通过两步反应得到对溴三氟乙烯基芳基醚,进一步加热环化二聚得到单体1,2-二(4-溴苯氧基)六氟环丁烷.该二聚物再与异丙基格氏试剂发生镁交换反应,生成格氏试剂中间体,在催化剂Ni(dppe)Cl2的存在下发生镍催化转移缩聚生成聚合物.研究了反应时间、温度和单体投料比对催化缩聚反应的影响.     

s‐Triazine‐based hyperbranched polyethers: Synthesis,characterization, and properties

A series of s‐triazine‐based hyperbranched polyethers (HBPE) have been synthesized to obtain thermostability but flexible polymers by an interfacial polycondensation of different diols as A₂ and cyanuric chloride as B₃ monomers using A₂ + B₃ approach in the presence of a phase transfer catalyst. The polymerization reaction parameters are optimized, and the results indicate that the optimum conditions for the interfacial polycondensation are a 2:3 mole ratio of cyanuric chloride to diol using butanediol, benzyldimethylhexadecyl ammonium chloride as the catalyst, dichloromethane as the organic solvent, and a three‐step procedure with keeping the reaction mixture at different low temperatures for 2h/2h/5h. Other techniques such as high‐temperature solution, one‐step polycondensation, and transesterification were also carried out to synthesize the HBPE but proved to be not suitable due to large number of side reactions. The synthesized polymers were characterized by FTIR, ¹H NMR, and ¹³C NMR spectroscopy, hydroxyl number determination, solution viscosity measurements, and GPC analysis. The thermal behavior of the hyperbranched polymer was investigated by thermogravimetric analysis and differential scanning calorimetry. All the results were compared with those from an analogous linear polyether, obtained from 2‐methoxy‐4,6‐dichloro‐s‐triazine and butanediol by using the same polymerization technique. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3994–4004, 2010     

Chain-growth polymerization of azide–alkyne difunctional monomer: Synthesis of star polymer with linear polytriazole arms from a core

This article reports a chain-growth coupling polymerization of AB difunctional monomer via copper-catalyzed azide–alkyne cycloaddition (CuAAC) reaction for synthesis of star polymers. Unlike our previously reported CuAAC polymerization of AB _n (n ≥ 2) monomers that spontaneously demonstrated a chain-growth mechanism in synthesis of hyperbranched polymer, the homopolymerization of AB monomer showed a common but less desired step-growth mechanism as the triazole groups aligned in a linear chain could not effectively confine the Cu catalyst in the polymer species. In contrast, the use of polytriazole-based core molecules that contained multiple azido groups successfully switched the polymerization of AB monomers into chain-growth mechanism and produced 3-arm star polymers and multi-arm hyperstar polymers with linear increase of polymer molecular weight with conversion and narrow molecular weight distribution, for example, M_w/M_n ~ 1.05. When acid-degradable hyperbranched polymeric core was used, the obtained hyperstar polymers could be easily degraded under acidic environment, producing linear degraded arms with defined polydispersity. © 2019 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 84–90     

Catalyst-transfer polycondensation. mechanism of Ni-catalyzed chain-growth polymerization leading to well-defined poly(3-hexylthiophene)

We studied the mechanism of the chain-growth polymerization of 2-bromo-5-chloromagnesio-3-hexylthiophene (1) with Ni(dppp)Cl2 [dppp = 1,3-bis(diphenylphosphino)propane], in which head-to-tail poly(3-hexylthiophene) (HT-P3HT) with a low polydispersity is obtained and the M(n) is controlled by the feed ratio of the monomer to the Ni catalyst. Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectra showed that the HT-P3HT uniformly had a hydrogen atom at one end of each molecule and a bromine atom at the other. The reaction of the polymer with aryl Grignard reagent gave HT-P3HT with aryl groups at both ends, which indicates that the H-end was derived from the propagating Ni complex. The degree of polymerization and the absolute molecular weight of the polymer could be evaluated from the 1H NMR spectra of the Ar/Ar-ended HT-P3HT, and it was found that one Ni catalyst molecule forms one polymer chain. Furthermore, by reaction of 1 with 50 mol % Ni(dppp)Cl2, the chain initiator was found to be a bithiophene-Ni complex, formed by a coupling reaction of 1 followed by insertion of the Ni(0) catalyst into the C-Br bond of the dimer. On the basis of these results, we propose that this chain-growth polymerization involves the coupling reaction of 1 with the polymer via the Ni catalyst, which is transferred intramolecularly to the terminal C-Br bond of the elongated molecule. We call this mechanism "catalyst-transfer polycondensation".     

Mechanism-Guided Design of Chain-Growth Click Polymerization Based on a Thiol-Michael Reaction

The development of chain-growth click polymerization is challenging yet desirable in modern polymer chemistry. In this work, we reported a novel chain-growth click polymerization based on the thiol-Michael reaction. This polymerization could be performed efficiently under ambient conditions and spatiotemporally regulated by ultraviolet light, allowing the synthesis of sulfur-containing polymers in excellent yields and high molecular weights. Density functional theory calculations indicated that the thiolate addition to the Michael acceptor is the rate-determining step, and introducing the phenyl group could facilitate the chain-growth process. This polymerization is a new type of chain-growth click polymerization, which will provide a unique approach to creating functional polymers.     

酶促缩聚和原子转移自由基聚合法合成AB型两亲性嵌段共聚物

Novozyme-435催化10-羟基癸酸进行自缩聚反应得到线性聚酯, 端基分别是羟基(—OH)和羧基(—COOH), 在三乙胺催化下, 分别用α-溴代丙酰溴和三甲基氯硅烷(TMSCL)进行端基官能化生成一个单官能度的大分子引发剂, 在CuCl/2,2'-联吡啶(bpy)催化体系中, 引发甲基丙烯酸环氧丙酯(GMA)的原子转移自由基反应(ATRP), 得到聚(10-羟基癸酸酯)/聚甲基丙烯酸环氧丙酯(PHDA-b-PGMA) AB 型两亲性嵌段共聚物, 其结构及分子量(分布)通过核磁共振和凝胶渗透色谱(GPC)确证. 此AB型两亲性嵌段共聚物在水溶液中能自组装形成纳米粒子, 用原子力显微镜(AFM)观察粒子的形状和大小.     

Condensative chain polymerization. II. Preferential esterification of propagating end group in Pd-catalyzed CO-insertion polycondensation of 4-bromophenol derivatives

For a development of condensative chain polymerization where polycondensation proceeds from an initiator in a chain polymerization manner to yield polymer with a defined molecular weight and a narrow molecular weight distribution, the Pd-catalyzed polycondensation of 4-bromophenol derivatives with CO is studied. Model reactions showed that monomer reacted the polymer terminal Br preferentially compared to the monomer Br, but that the ester exchange reaction of polymer backbone with monomer phenoxide occurred in some extent. In the polymerization of 4-bromo-2-n-octylphenol with CO using 4-bromo-2,6-dimethylphenyl benzoate as an initiator, the molecular weight of polymer increased in proportion to time up to 30 min. The GPC elution curves showed that oligomers were produced from the initiator. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2607–2618, 1999     

1,3,5,5-tetraphenyl-Δ3-1,2,4-triazolin-2-yl radical–properties in the controlled radical polymerization of poly(methyl methacrylate) and polystyrene

The triazoline derivative 1 was used as an additive in the chain-growth controlled radical polymerization of vinylic monomers to afford narrowly distributed polymers. This new system is applicable to styrene as well as to methacrylates. The monomer consumption and the variation of the molar mass were monitored with time. Thermal properties of the obtained polymers were also studied. After isolation of the polymers, the growth of the chains was re-initiated in the presence of a second monomer and yielded block copolymers.     

ABA triblock copolymers from two mechanistic techniques: Polycondensation and atom transfer radical polymerization

ABA triblock copolymers were synthesized using two polymerization techniques, polycondensation, and atom transfer radical polymerization (ATRP). A telechelic polymer was synthesized via polycondensation, which was then functionalized into a difunctional ATRP initiator. Under ATRP conditions, outer blocks were polymerized to form the ABA triblock copolymer. Six types of samples were prepared based on a poly(ether ether ketone) or poly(arylene ether sulfone) center block with either poly(methyl methacrylate), poly(pentafluorostyrene), or poly(ionic liquid) outer blocks. As polycondensation results in polymers with broad molecular weight distribution (MWD), the center of these triblock copolymers are disperse, while the outside blocks have narrow MWD due to the control afforded from ATRP. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 228–238     

Chain-growth polycondensation for well-defined aramide. Synthesis of unprecedented block copolymer containing aramide with low polydispersity

Poly(p-benzamide) with a defined molecular weight and a low polydispersity and a block copolymer containing this well-defined aramide was synthesized. Phenyl 4-aminobenzoate, which would yield poly(p-benzamide), did not polymerize under the conditions of chain-growth polycondensation. However, phenyl 4-(4-octyloxybenzylamino)benzoate (1b) polymerized at room temperature in the presence of base and phenyl 4-nitrobenzoate (2) as an initiator in a chain-growth polycondensation manner to give well-defined aromatic polyamides having the 4-octyloxybenzyl groups as a protecting group on nitrogen in an amide. It was confirmed by a model reaction that deprotection of this protecting group proceeded completely with trifluoroacetic acid (TFA) without breaking the amide linkage. The utility of this approach to poly(p-benzamide) with a low polydispersity was demonstrated by the synthesis of block copolymers. Thus, phenyl 4-(octylamino)benzoate (1a) polymerized in the presence of 2 and base, followed by addition of 1b and base to the reaction mixture of the prepolymer to yield the block copolymer of 1a and 1b with a controlled molecular weight and a low polydispersity. The block copolymer was treated with TFA, resulting in a soluble block copolymer of poly(N-octyl-p-benzamide) and poly(p-benzamide). The SEM images of the supramolecular assemblies of the block copolymer showed mum-sized bundles and aggregates of flake structures.     

Synthesis of sequence‐controlled copolymers from extremely polar and apolar monomers by living radical polymerization and their phase‐separated structures

A series of copolymers composed of two monomer units having a polar phosphorylcholine group and an apolar fluorocarbon group with a controlled monomer unit sequence were synthesized by a reversible addition‐fragmentation chain transfer (RAFT) living radical polymerization method. 2‐Methacryloyloxyethyl phosphorylcholine (MPC) and 2,2,2‐trifluoroethyl methacrylate (TFEMA) were selected as the monomers, because they have disparate polarity. Furthermore, to investigate the influence of the monomer unit sequence in a polymer chain on the phase‐separated structure in the bulk and surface structure, copolymers having a continuous change in the monomer unit composition along the polymer chain (gradient copolymer) were synthesized, as well as random and block copolymers. The analysis of instantaneous composition revealed a continuous change in the monomer unit composition in the gradient copolymer and the statistical monomer unit sequence in the random copolymer. Thermal analysis assumed that the gradient sequence of the monomer unit would make the phase‐separated structure in the bulk ambiguous, while the well‐defined and monodispersive block sequence would undergo the distinct phase‐separation due to the extreme difference in the polarity of the component monomer units. The preliminary surface characterization of the synthesized polymers indicated the monomer unit sequence in the polymer chain would much influence on the surface structure. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6073–6083, 2005     

Synthesis of reactive aromatic polyesters having pendant chlorohydrin moieties

A monomer containing a chlorohydrin moiety, propyl chlorohydrin diphenolate (PCHDP), was synthesized. Reactive polyesters having these pendant chlorohydrin moieties were prepared by the interfacial polycondensation of isophthaloyl chloride with PCHDP or with PCHDP and diphenolic acid using phase transfer catalyst. The molar ratio of reactants and the phase ratio of water to organic solvent strongly affect the molecular weight of resulting polymers and polymers with high molecular weight are obtained at the molar ratio of 1.0–1.15 and the phase ratio of 2.0–3.5. Swelling of the growing polymers is dependent on the molar ratio of the reactants and the phase ratio because of the hydrophilic and hydrophobic nature of the pendant chlorhydrin moiety. The resulting polymers are not soluble in any solvent except water in which hydrolysis occurs. Thus so, the structure of polymers was confirmed by ¹³C CP/MAS NMR. © 1996 John Wiley & Sons, Inc.