TREN versus Me6‐TREN as ligands in SET‐LRP of methyl acrylate

The commercially available tris(2‐aminoethyl)amine (TREN) was used as ligand to mediate the single‐electron transfer‐living radical polymerization (SET‐LRP) of methyl acrylate in dimethyl sulfoxide initiated with the bifunctional initiator bis(2‐bromopropionyl)ethane and catalyzed by both nonactivated and activated Cu(0) wire. A comparative study between TREN and tris(2‐dimethylaminoethyl)amine (Me₆‐TREN) ligand, that is more commonly used in SET‐LRP, demonstrated that TREN provided a slower polymerization but the chain‐ends functionality of the resulting bifunctional poly(methyl acrylate) was near quantitative and comparable to that obtained when Me₆‐TREN was used as a ligand. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012.     

无水FeCl_3存在下丙烯酸甲酯的单电子转移活性自由基聚合动力学

单电子转移活性自由基聚合(SET-LRP)是一种可以对聚合物进行有效分子设计,合成不同拓扑结构并且能够有效调节其相对分子质量和相对分子质量分布的新型聚合方法,具有潜在的应用前景。以2-溴丙酸甲酯作为引发剂,Cu(0)/三(N,N-二甲基氨基乙基)胺(Me6-TREN)为复合催化体系,通过在二甲基亚砜中添加不同摩尔浓度的无水FeCl_3来研究其对丙烯酸甲酯的SET-LRP聚合动力学的影响。结果表明,随着三价铁离子量的增加,其链增长速率常数下降并且出现诱导期延长现象,说明三价铁离子参与了SET-LRP的聚合动力学过程,它和在同样实验条件下二价铜所起的作用截然不同,这可能是由于三价铁离子的氧化导致反应体系中一价铜的浓度降低引起的。此项工作从另外一个角度解释了零价铜催化下SET-LRP聚合诱导期产生的原因。     

Atom transfer radical addition (ATRA) catalyzed by copper complexes with tris[2-(dimethylamino)ethyl]amine (Me6TREN) ligand in the presence of free-radical diazo initiator AIBN

In this article, we focus on the evaluation of tris[2-(dimethylamino)ethyl]amine (Me(6)TREN) ligand in copper catalyzed ATRA in the presence of free-radical diazo initiator AIBN (2,2'-azobis(2-methylpropionitrile)). The addition of carbon tetrachloride to 1-hexene, 1-octene and cis-cyclooctene proceeded efficiently to yield 89, 85 and 85% of monoadduct, respectively, using the catalyst to alkene ratio of 1 : 2500. For alkenes that readily undergo free radical polymerization, such as methyl acrylate, catalyst loadings as high as 0.4 mol-% were required. Furthermore, modest yields of the monoadduct were obtained with less active alkyl halides (chloroform and bromoform) using 250 : 1 and 500 : 1 ratios of alkene to copper(II). Interestingly, the addition of carbon tetrachloride to cis-cyclooctene produced only 1-chloro-4-(trichloromethyl)-cyclooctene, while carbon tetrabromide yielded 1,2 and 1,4-regioisomers in 75 : 25 ratio. The activity of [Cu(II)(Me(6)TREN)X][X] (X = Br(-) and Cl(-)) complexes in ATRA in the presence of AIBN was additionally probed by adding excess free ligand, source of halide anions and triphenylphosphine. The results indicated that disproportionation is a likely cause for lower activity of Me(6)TREN as compared to TPMA (tris(2-pyridylmethyl)amine).     

Synthesis of double hydrophilic poly(ethylene oxide)‐b‐poly(2‐hydroxyethyl acrylate) by single‐electron transfer–living radical polymerization

In this study, the polymerization of (2‐hydroxyethyl) acrylate (HEA), in polar media, using Cu(0)‐mediated radical polymerization also called single‐electron transfer–living radical polymerization (SET‐LRP) is reported. The kinetics aspects of both the homopolymerization and the copolymerization from a poly(ethylene oxide) (PEO) macroinitiator were analyzed by ¹H NMR. The effects of both the ligand and the solvent were studied. The polymerization was shown to reach very high monomer conversions and to proceed in a well‐controlled fashion in the presence of tris[2‐(dimethylamino)ethyl]amine Me6‐TREN and N, N,N′, N″, N″‐pentamethyldiethylenetriamine (PMDETA) in dimethylsulfoxide (DMSO). SET‐LRP of HEA was also led in water, and it was shown to be faster than in DMSO. In pure water, Me₆‐TREN allowed a better control over the molar masses and polydispersity indices than PMDETA and TREN. Double hydrophilic PEO‐b‐PHEA block copolymers, exhibiting various PHEA block lengths up to 100 HEA units, were synthesized, in the same manner, from a bromide‐terminated PEO macroinitiator. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Tetramethylguanidino‐tris(2‐aminoethyl)amine: A novel ligand for copper‐based atom transfer radical polymerization

With CuBr/tetramethylguanidino‐tris(2‐aminoethyl)amine (TMG₃‐TREN) as the catalyst, the atom transfer radical polymerization (ATRP) of methyl methacrylate, n‐butyl acrylate, styrene, and acrylonitrile was conducted. The catalyst concentration of 0.5 equiv with respect to the initiator was enough to prepare well‐defined poly(methyl methacrylate) in bulk from methyl methacrylate monomer. For ATRP of n‐butyl acrylate, the catalyst behaved in a manner similar to that reported for CuBr/tris[2‐(dimethylamino)ethyl]amine. A minimum of 0.05 equiv of the catalyst with respect to the initiator was required to synthesize the homopolymer of the desired molecular weight and low polydispersity at the ambient temperature. In the case of styrene, ATRP with this catalyst occurred only when a 1:1 catalyst/initiator ratio was used in the presence of Cu(0) in ethylene carbonate. The polymerization of acrylonitrile with CuBr/TMG₃‐TREN was conducted successfully with a catalyst concentration of 50% with respect to the initiator in ethylene carbonate. End‐group analysis for the determination of the high degree of functionality of the homopolymers synthesized by the new catalyst was determined by NMR spectroscopy. The isotactic parameter calculated for each system indicated that the homopolymers were predominantly syndiotactic, signifying that the tacticity remained the same, as already reported for ATRP. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5906–5922, 2005     

离子液体中单电子转移活性自由基聚合法制备星形聚丙烯酰胺

以季戊四醇为原料,合成了2,2-二溴甲基-1,3-二溴丙烷(PEBr4),并以此为四官能度引发剂,Cu0粉/三-(2-二甲氨基乙基)胺(Me6-TREN)为催化体系,在离子液体中实现了丙烯酰胺(AM)的单电子转移活性自由基聚合(SET-LRP),得到了窄分子量分布的星形聚丙烯酰胺(PAM),Mw/Mn约为1.26(MGPCn=14.1×103,转化率为43.4%)。 采用1H NMR对PAM结构进行表征确认,并采用GPC测定了PAM的分子量及分子量分布;考察了水、单体/催化剂(引发剂)配比对聚合反应的影响。 结果表明,少量水的加入能够加快聚合反应,使链增长速率常数由kappp=0.042 4 h-1增加至kappp=0.148 6 h-1;催化剂、引发剂用量越大,AM的SET-LRP的聚合反应速率越快,聚合反应的可控性越好,Mn随催化剂用量的增大及引发剂用量的减小而增大,且与理论分子量相近,分子量分布均呈下降趋势。     

单电子转移活性自由基聚合制备支化聚丙烯酸甲酯的研究

以丙烯酸2-(2-溴异丁酰氧基)乙酯(BIEA)为引发剂单体(inimer),丙烯酸甲酯(MA)为单体,Cu0/CuBr2和N,N,N',N″,N″-五甲基二亚乙基三胺(PMDETA)为催化体系,二甲亚砜(DMSO)为溶剂,在常温(25℃)下通过单电子转移活性自由基聚合(SET-LRP)合成支化聚丙烯酸甲酯.聚合反应过程中,采用气相色谱(GC)、核磁共振(1H-NMR)和三检测体积排除色谱(TD-SEC)等测试手段跟踪分析和表征支化聚合物的结构.研究结果表明,采用SET-LRP方法,铜粉作为催化剂,常温下聚合反应就能快速进行,130 min之内MA的转化率已达99%以上,制备出高分子量支化聚合物.随着反应的不断进行,聚合物支化程度不断提高,相比较同分子量下的线型聚合物其黏度不断下降,Mark-Houwink特征常数α最小可达0.290.此外,低分子量聚合物组分随着反应不断减少,在高单体转化率下,聚合体系中以高支化度的聚丙烯酸甲酯为主.     

Imparting antifouling properties of poly(2-hydroxyethyl methacrylate) hydrogels by grafting poly(oligoethylene glycol methyl ether acrylate)

The antifouling properties of poly(2-hydroxyethyl methacrylate- co-methyl methacrylate) hydrogels were improved by the surface grafting of a brush of poly(oligoethylene glycol methyl ether acrylate) [poly(OEGA)]. The atom-transfer radical polymerization (ATRP) of OEGA (degree of polymerization = 8) was initiated from the preactivated surface of the hydrogel under mild conditions, thus in water at 25 degrees C. The catalytic system was optimized on the basis of two ligands [1,1,4,7,10,10-hexamethyl-triethylenetetramine (HMTETA) or tris[2-(dimethylamino)ethyl]amine (Me6TREN)] and two copper salts (CuIBr or CuICl). Faster polymerization was observed for the Me 6TREN/CuIBr combination. The chemical composition and morphology of the coated surface were analyzed by X-ray photoelectron spectroscopy, attenuated total reflectance Fourier transform infrared spectroscopy, contact angle measurements by the water droplet and captive bubble methods, scanning electron microscopy, and environmental scanning electron microscopy. The hydrophilicity of the surface increased with the molar mass of the grafted poly(OEGA) chains, and the surface modifications were reported in parallel. The antifouling properties of the coatings were tested by in vitro protein adsorption and cell adhesion tests, with green fluorescent protein, beta-lactamase, and lens epithelial cells, as model proteins and model cells, respectively. The grafted poly(OEGA) brush decreased the nonspecific protein adsorption and imparted high cell repellency to the hydrogel surface.     

苯乙烯的单电子转移活性自由基聚合

以2,2-二溴甲基-1,3-二溴丙烷（PEBr4）为引发剂,Cu0粉/三（2-二甲氨基乙基）胺（Me6-TREN）为催化体系,在二甲亚砜（DMSO）和H2O的混合溶剂中实现了苯乙烯（St）的单电子转移活性自由基聚合（SET-LRP）。 通过1H NMR和GPC分析表明,所得聚合物为星形结构并具有较窄的分子量分布Mw/Mn=1.20（MGPCn=25.3×103,转化率为42.6%）,且聚合物的链端保留了-Br端基。 考察了溶剂、反应温度及相转移催化剂对聚合的影响,结果表明,混合溶剂中H2O的体积分数由10%增加至20%导致了聚合速率的降低,表观聚合速率常数（kappp）由0.026 4 h-1减小至0.019 7 h-1;升高反应温度、增加催化剂用量以及相转移催化剂的加入分别导致聚合体系的kappp增加,同时,催化剂用量的增加和相转移催化剂的加入使聚合物的分子量分布系数降低。     

聚丙烯酸-b-聚(N-异丙基丙烯酰胺)嵌段共聚物的合成及其温度和pH值敏感性自组装研究

通过原子转移自由基聚合方法, 在丁酮/异丙醇混合溶剂中合成了分子量可控和分布较窄的聚丙烯酸叔丁酯-b-聚N-异丙基丙烯酰胺(PtBA-b-PNIPAM)嵌段共聚物, 用GPC和 1 H NMR对其结构进行了表征. PtBA-b-PNIPAM在甲苯中水解得到聚丙烯酸-b-聚N-异丙基丙烯酰胺(PAA-b-PNIPAM). 用动态光散射技术对PAA-b-PNIPAM在水溶液中的自组装行为随pH值和温度变化的响应进行了初步研究.     

Catalytic effect of dimethyl sulfoxide in the Cu(0)/tris(2‐dimethylaminoethyl)amine‐catalyzed living radical polymerization of methyl methacrylate at 0–90 °C initiated with CH3CHClI as a model compound for α,ω‐di(iodo)poly(vinyl chloride) chain ends

A variety of conditions, including catalysts [CuCl, CuI, Cu₂O, and Cu(0)], ligands [2,2′‐bipyridine (bpy), tris(2‐dimethylaminoethyl)amine (Me₆‐TREN), polyethyleneimine, and hexamethyl triethylenetetramine], initiators [CH₃CHClI, CH₂I₂, CHI₃, and F(CF₂)₈I], solvents [diphenyl ether, toluene, tetrahydrofuran, dimethyl sulfoxide (DMSO), dimethylformamide, ethylene carbonate, dimethylacetamide, and cyclohexanone], and temperatures [90, 25, and 0 °C] were studied to assess previous methods for poly(methyl methacrylate)‐b‐poly(vinyl chloride)‐b‐poly(methyl methacrylate) (PMMA‐b‐PVC‐b‐PMMA) synthesis by the living radical block copolymerization of methyl methacrylate (MMA) initiated with α,ω‐di(iodo)poly(vinyl chloride). CH₃CHClI was used as a model for α,ω‐di(iodo)poly(vinyl chloride) employed as a macroinitiator in the living radical block copolymerization of MMA. Two groups of methods evolved. The first involved CuCl/bpy or Me₆‐TREN at 90 °C, whereas the second involved Cu(0)/Me₆‐TREN in DMSO at 25 or 0 °C. Related ligands were used in both methods. The highest initiator efficiency and rate of polymerization were obtained with Cu(0)/Me₆‐TREN in DMSO at 25 °C. This demonstrated that the ultrafast block copolymerization reported previously is the most efficient with respect to the rate of polymerization and precision of the PMMA‐b‐PVC‐b‐PMMA architecture. Moreover, Cu(0)/Me₆‐TREN‐catalyzed polymerization exhibits an external first order of reaction in DMSO, and so this solvent has a catalytic effect in this living radical polymerization (LRP). This polymerization can be performed between 90 and 0 °C and provides access to controlled poly(methyl methacrylate) tacticity by LRP and block copolymerization. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1935–1947, 2005     

Copper(0)‐mediated living radical polymerization of acrylonitrile: SET‐LRP or AGET‐ATRP

Cu(0)‐mediated living radical polymerization was first extended to acrylonitrile (AN) to synthesize polyacrylonitrile with a high molecular weight and a low polydispersity index. This was achieved by using Cu(0)/hexamethylated tris(2‐aminoethyl)amine (Me₆‐TREN) as the catalyst, 2‐bromopropionitrile as the initiator, and dimethyl sulfoxide (DMSO) as the solvent. The reaction was performed under mild reaction conditions at ambient temperature and thus biradical termination reaction was low. The rapid and extensive disproportionation of Cu(I)Br/Me₆‐TREN in DMSO/AN supports a mechanism consistent with a single electron transfer‐living radical polymerization (SET‐LRP) rather than activators generated by electron transfer atom transfer radical polymerization (AGET ATRP). ¹H NMR analysis and chain extension experiment confirm the high chain‐end functionality of the resultant polymer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Poly(acrylate‐b‐styrene‐b‐isobutylene‐b‐styrene‐b‐acrylate) Block Copolymers via Carbocationic and Atom Transfer Radical Polymerizations

A series of polyacrylate‐polystyrene‐polyisobutylene‐polystyrene‐polyacrylate (X‐PS‐PIB‐PS‐X) pentablock terpolymers (X=poly(methyl acrylate) (PMA), poly(butyl acrylate) (PBA), or poly(methyl methacrylate) (PMMA)) was prepared from poly (styrene‐b‐isobutylene‐b‐styrene) (PS‐PIB‐PS) block copolymers (BCPs) using either a Cu(I)Cl/1,1,4,7,7‐pentamethyldiethylenetriamine (PMDETA) or Cu(I)Cl/tris[2‐(dimethylamino)ethyl]amine (Me₆TREN) catalyst system. The PS‐PIB‐PS BCPs were prepared by quasiliving carbocationic polymerization of isobutylene using a difunctional initiator, followed by the sequential addition of styrene, and were used as macroinitiators for the atom transfer radical polymerization (ATRP) of methyl acrylate (MA), n‐butyl acrylate (BA), or methyl methacrylate (MMA). The ATRP of MA and BA proceeded in a controlled fashion using either a Cu(I)Cl/PMDETA or Cu(I)Cl/Me₆TREN catalyst system, as evidenced by a linear increase in molecular weight with conversion and low PDIs. The polymerization of MMA was less controlled. ¹H‐NMR spectroscopy was used to elucidate pentablock copolymer structure and composition. The thermal stabilities of the pentablock copolymers were slightly less than the PS‐PIB‐PS macroinitiators due to the presence of polyacrylate or polymethacrylate outer block segments. DSC analysis of the pentablock copolymers showed a plurality of glass transition temperatures, indicating a phase separated material.     

Atom transfer radical polymerization of methyl acrylate,methyl methacrylate and styrene in the presence of trolamine as a highly effective promoter

Transition metal-mediated atom transfer radical polymerization(ATRP) is a ‘‘living'/controlled radical polymerization. Recently, there has been widely increasing interest in reducing the high costs of catalyst separation and post-polymerization purification in ATRP. In this work, trolamine was found to significantly enhance the catalytical performance of Cu Br/N,N,N0,N0-tetrakis(2-pyridylmethyl) ethylenediamine(Cu Br/TPEN) and Cu Br/tris[2-(dimethylamino) ethylamine](Cu Br/Me6TREN). With the addition of 25-fold molar amount of trolamine relative to Cu Br, the catalyst loadings of Cu Br/TPEN and Cu Br/Me6 TREN were dramatically reduced from a catalyst-to-initiator ratio of 1 to 0.01 and 0.05,respectively. The polymerizations of methyl acrylate, methyl methacrylate and styrene still showed first-order kinetics in the presence of trolamine and produced poly(methyl acrylate), poly(methyl methacrylate) and polystyrene with molecular weights close to theoretical values and low polydispersities. These results indicate that trolamine is a highly effective and versatile promoter for ATRP and is promising for potential industrial application.     

Alkyl halide/tertiary amine as novel initiators for free radical polymerizations of methyl methacrylate,methyl acrylate and styrene

A series of combinations of alkyl halide with tertiary amine such as ethyl α-bromophenylacetate/tris[2-(dimethylamino)ethyl)]amine (αEBP/Me₆TREN), ethyl 2-bromoisobutyrate/triethylamine (EBiB/TEA), and ethyl 2-chloropropionate/N,N,N′,N′,N′′-pentamethyldiethylenetriamine (ECP/PMDETA) have been developed as novel free radical initiators and used for the polymerizations of methyl acrylate (MA), methyl methacrylate (MMA) and styrene (St). The effects of the structure of alkyl halide and tertiary amine on the polymerization of MA were investigated. Gel permeation chromatograph (GPC) and proton nuclear magnetic resonance (¹H NMR) have been utilized to analyze the end group of the obtained poly(methyl acrylate). Electron spin resonance (ESR) spectroscopy was employed to identify the structure of the radicals produced by αEBP/Me₆TREN, and the results indicated that αEBP reacted with Me₆TREN via a single electron transfer (SET) nucleophilic mechanism to produce corresponding ethyl α-phenylacetate radicals which subsequently initiated the polymerization of MA. As both alkyl halide and tertiary amine are commercially available at low cost, non-explosive, and ease of use and storage in comparison with conventional azo, peroxide or persulfate initiators, the combination of alkyl halide and tertiary amine as a free radical initiator is promising for large-scale practical applications.     

Atom transfer radical polymerization from cellulose fibers at ambient temperature

Cellulose fibers have been successfully grafted with poly(methyl acrylate) using atom transfer radical polymerization, mediated by Me6-TREN and Cu(I)Br at ambient temperature. The initially hydrophilic cellulose was first modified by reacting the hydrozyl groups with 2-bromoisobutyryl bromide whereupon methyl acrylate was grafted from the surface. The resulting polymer-grafted papers were extremely hydrophobic, thetaa = 133 degrees . FT-IR analysis indicates that the amount of grafted polymer can be controlled by adding sacrificial initiator to the polymerizing system. Size exclusion chromatography of the bulk polymer revealed narrow polydispersities and a molecular weight corresponding to the ratio [M]:[I].     

Synthesis and characterization of poly(vinylidene fluoride‐co‐chlorotrifluoroethylene)‐grafted‐poly(acrylonitrile) via single electron transfer–living radical polymerization process

Preparation of functional fluoromaterials through chemical modification of traditional fluoropolymers has been recognized as an economic and convenient strategy to expand the application areas of fluoropolymers. Poly(vinylidene fluoride‐co‐chlorotrifluoroethylene)‐grafted‐polyacrylonitrile (P(VDF‐co‐CTFE)‐g‐PAN) has been successfully synthesized via single electron transfer–living radical polymerization (SET–LRP) process initiated with macroinitiator P(VDF‐co‐CTFE) in the presence of trace amount of Cu(0)/tris(2(dimethylamino)ethyl)amine (Me₆‐TREN) in dimethyl sulfoxide (DMSO) at ambient temperature. The typical side reactions happened on P(VDF‐co‐CTFE) induced by the nitrogen‐containing solvents and high reaction temperature in atom transfer radical polymerization process could be avoided in SET–LRP process by using the mild reaction conditions. Well‐controlled polymerization features were observed under varied reaction conditions including the different reaction temperature, catalyst concentration, as well as monomer amount in feed. An induction period of 0.5–1.0 h in the polymerization procedure was observed at low temperature, which may be attributed to the Cu₂O from the surface of the Cu(0) powder. When Cu(0) catalyst is activated, the introduction period is eliminated. The polymerization rates were decelerated by adding excessive Me₆‐TREN for the formation of more stable CuCl₂/(Me₆‐TREN)₂. The structure of P(VDF‐co‐CTFE)‐g‐PAN was demonstrated by FTIR, NMR, DSC, and TGA. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Mimicking “nascent” Cu(0) mediated SET‐LRP of methyl acrylate in DMSO leads to complete conversion in several minutes

Cu(0) was prepared via disproportionation of Cu(I)Br in the presence of Me₆‐TREN in various solvents in a glove box. The resulting nanopowders were used as mimics of “nascent” Cu(0) catalyst in the single‐electron transfer living radical polymerization (SET‐LRP) of methyl acrylate (MA), providing faster polymerization than any commercial Cu(0) powder, Cu(0) wire, or Cu(I)Br and achieving 80% conversion in only 5 min reaction time. Despite the high rate, a living polymerization was observed with linear evolution of molecular weight, narrow polydispersity, no induction period, and high retention of chain‐end functionality. In addition to providing an unprecedentedly fast, yet controlled LRP of MA, these studies suggest that the very small “nascent” Cu(0) species formed via disproportionation in SET‐LRP are the most active catalysts. Thus, when bulk Cu(0) powder or wire may be the most abundant catalyst and dictates the overall kinetics, any Cu(0) produced via disproportionation will be rapidly consumed and contributes to the overall catalytic cycle. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 403–409, 2010     

SET‐LRP of methyl acrylate to complete conversion with zero termination

The single electron transfer‐living radical polymerization of methyl acrylate (MA) initiated by bis(2‐bromopropionyl)ethane (BPE) in dimethyl sulfoxide was carried out to 100% monomer conversion and complete absence of bimolecular termination under the following reaction conditions: [MA]/[BPE]/[Me₆‐TREN]/[CuBr₂] = 60/1/0.21/0.01 and [MA]/[BPE]/[TREN]/[CuBr₂] = 60/1/0.25/0.05. These polymerizations were mediated by 0.5 cm of hydrazine‐activated Cu(0) wire of 20 gauge (0.812 cm in diameter), corresponding to a surface area of 0.14 cm² of Cu(0) per 3 mL reaction volume (2/1 v/v monomer/solvent). A higher extent of bimolecular termination (5–13%) was observed at complete conversion when longer lengths of Cu(0) wire were used. In the absence of CuBr₂ the activated Cu(0) wire/Me₆‐TREN catalyst in dimethyl sulfoxide also allowed the synthesis of perfectly bifunctional and monofunctional PMAs at complete conversion. This was also demonstrated by the quantitative reinitiation experiments from the chain(s) end(s) of these macroinitiators. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Polyamine-stabilized sodium aryloxides: simple initiators for the ring-opening polymerization of rac-lactide

Metalation of 2,4,6-tri(methyl)phenol ((Me)ArOH) and 2,6-di(tert-butyl)-4-methylphenol ((Bu)ArOH) with NaN(SiMe(3))(2) in toluene and in the presence of stoichiometric amounts of the polydentate amines N,N,N',N'-tetramethylethylenediamine (TMEDA) and N,N,N',N',N'-pentamethyldiethylenetriamine (PMDETA) affords three new sodium aryloxide complexes [Na(μ-OAr(Bu))(TMEDA)](2) (3), [Na(μ-OAr(Me))(PMDETA)](2) (4), and [Na(OAr(Bu))(PMDETA)] (5). Complexes 3 to 5 have been isolated as crystalline materials in reasonable yields and characterized in the solid state by X-ray crystallography and in solution by NMR spectroscopy. Complexes 3 to 5 and the related [tris(2-dimethylaminoethyl)amine] (Me(6)TREN) derivatives [Na(OAr(Me))(HOAr(Me))(Me(6)TREN)] (1) and [Na(OAr(Bu))(Me(6)TREN)] (2), recently prepared in our group, are shown to be active as initiators for the ring-opening polymerization (ROP) of rac-lactide with benzyl alcohol as a co-initiator. However, during the course of the polymerization reactions intrachain and stereorandom transesterification side-reactions were observed under some of the experimental conditions tested.