Polycondensation of activated L‐valine and L‐leucine esters with various lewis acids

To develop a novel polycondensation method for the preparation of poly (amino acid)s, we screened a transition metal or a rare‐earth triflate as a Lewis acid for the polycondensation of activated amino acid esters in N,N‐dimethylformamide solutions at room temperature. The polymerizations of 4‐nitrophenyl L ‐leucinate ( 1a ) and 4‐nitrophenyl L ‐valinate ( 1b ) scarcely proceeded without any Lewis acid at room temperature. In the presence of 5 mol % metal triflates, especially scandium(III) trifluoromethanesulfonate, the polymerizations of both monomers were promoted effectively. The products, which were collected by the reaction mixture being poured into water, were recognized as poly(L ‐valine)s by Fourier transform infrared spectroscopy, gel permeation chromatography analysis, and ¹H NMR spectroscopy. These results showed that a metal triflate as a Lewis acid could coordinate to a carbonyl oxygen of activated L ‐valinate and L ‐leucinate even in a highly polar solvent, such as N,N‐dimethylformamide; therefore, the polymerizations of activated L ‐valinate and L ‐leucinate were promoted. Because steric hindrance derived from the isobutyl group in 1b was less than that of the isopropyl unit in 1a , the effect of the metals was not as sensitive for the polymerization of 1b . © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 543–547, 2007     

Chemical synthesis of poly‐γ‐glutamic acid by polycondensation of γ‐glutamic acid dimer: Synthesis and reaction of poly‐γ‐glutamic acid methyl ester

α‐Methyl glutamic acid (L ‐L )‐, (L ‐D )‐, (D ‐L )‐, and (D ‐D )‐γ‐dimers were synthesized from L ‐ and D ‐glutamic acids, and the obtained dimers were subjected to polycondensation with 1‐(3‐dimethylaminopropyl)‐3‐ethylcarbodiimide hydrochloride and 1‐hydroxybenzotriazole hydrate as condensation reagents. Poly‐γ‐glutamic acid (γ‐PGA) methyl ester with the number‐average molecular weights of 5000∼20,000 were obtained by polycondensation in N,N‐dimethylformamide in 44∼91% yields. The polycondensation of (L ‐L )‐ and (D ‐D )‐dimers afforded the polymers with much larger |[α]_D | compared with the corresponding dimers. The polymer could be transformed into γ‐PGA by alkaline hydrolysis or transesterification into α‐benzyl ester followed by hydrogenation. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 732–741, 2001     

Bidentate coordination effect on polycondensation of amino acid esters between metal triflates and methoxy groups

To study the bidentate coordination effect on the polycondensation of L ‐valinates between metal triflates as a Lewis acid and methoxy groups, we carried out the polycondensation of 2‐methoxy‐4‐nitrophenyl L ‐valinate ( 1a ) and 2‐methoxyphenyl L ‐valinate ( 1b ) in the presence of the various kinds of rare‐earth triflates in DMF solution at room temperature. The polymerizations of 1a did not proceed without any metal triflates. In the presence of 5 mol% triflates, especially Sc(OTf)₃, the polymerization proceeded effectively. After the reaction mixture was poured into water, the product was collected, which was recognized as poly(L ‐valine)s by FTIR spectrum and GPC measurement. The yield of the product from the polymerization of 1a with Sc(OTf)₃ was higher than that from the polymerization of 4‐nitrophenyl L ‐valinate ( 1c ) with Sc(OTf)₃. This result indicates that the polymerization of 1a was promoted to introduce the methoxy group on the o‐position of the phenyl ring at the ester group with the aim of the bidentate coordination effect between metal triflates and L ‐valinate. As a control experiment, we carried out the polycondensation of 1b in the presence of 5 mol% metal triflates; however, any polymerization did not proceeded. That reason is from the lower activity of activated L ‐valinate ( 1b ). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2864–2868, 2008     

Polymerization of α‐amino acid N‐carboxyanhydrides catalyzed by rare earth tris(borohydride) complexes: Mechanism and hydroxy‐endcapped polypeptides

In this work, rare earth tris(borohydride) complexes, Ln(BH₄)₃(THF)₃ (Ln = Sc, Y, La, and Dy), have been used to catalyze the ring‐opening polymerization of γ‐benzyl‐L ‐glutamate N‐carboxyanhydride (BLG NCA). All the catalysts show high activities and the resulting poly(γ‐benzyl‐L ‐glutamate)s (PBLGs) are recovered with high yields (≥90%). The molecular weights (MWs) of PBLG can be controlled by the molar ratios of monomer to catalyst, and the MW distributions (MWDs) are relatively narrow (as low as 1.16) depending on the rare earth metals and reaction temperatures. Block copolypeptides can be easily synthesized by the sequential addition of two monomers. The obtained P(γ‐benzyl‐L ‐glutamate‐b‐ε‐carbobenzoxy‐L ‐lysine) [P(BLG‐b‐BLL)] and P(γ‐benzyl‐L ‐glutamate‐b‐alanine) [P(BLG‐b‐ALA)] have been well characterized by NMR, gel permeation chromatography, and differential scanning calorimetry measurements. A random copolymer P(BLG‐co‐BLL) with a narrow MWD of 1.07 has also been synthesized. The polymerization mechanisms have been investigated in detail. The results show that both nucleophilic attack at the 5‐CO of NCA and deprotonation of 3‐NH of NCA in the initiation process take place simultaneously, resulting in two active centers, that is, an yttrium ALA carbamate derivative [H₂BOCH₂(CH)NHC(O)OLn? ] and a N‐yttriumlated ALA NCA. Propagation then proceeds on these centers via both normal monomer insertion and polycondensation. After termination, two kinds of telechelic polypeptide chains, that is, α‐hydroxyl‐ω‐aminotelechelic chains and α‐carboxylic‐ω‐aminotelechelic ones, are formed as characterized by MALDI‐TOF MS, ¹H NMR, ¹³C NMR, ¹H–¹H COSY, and ¹H–¹³C HMQC measurements. By decreasing the reaction temperature, the normal monomer insertion pathway can be exclusively selected, forming an unprecedented α‐hydroxyl‐ω‐aminotelechelic polypeptide. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Amino acid‐based bioanalogous polymers. Synthesis,and study of regular poly(ester amide)s based on bis(α‐amino acid) α,ω‐alkylene diesters,and aliphatic dicarboxylic acids

The purpose of this research was to synthesize new regular poly(ester amide)s (PEAs) consisting of nontoxic building blocks like hydrophobic α‐amino acids, α,ω‐diols, and aliphatic dicarboxylic acids, and to examine the effects of the structure of these building block components on some physico‐chemical and biochemical properties of the polymers. PEAs were prepared by solution polycondensation of di‐p‐toluenesulfonic acid salts of bis‐(α‐amino acid) α,ω‐alkylene diesters and di‐p‐nitrophenyl esters of diacids. Optimal conditions of this reaction have been studied. High molecular weight PEAs (M_w = 24,000–167,000) with narrow polydispersity (M_w/M_n = 1.20–1.81) were prepared under the optimal reaction conditions and exhibited excellent film‐forming properties. PEAs obtained are mostly amorphous materials with T_g from 11 to 59°C. α‐Chymotrypsin catalyzed in vitro hydrolysis of these new PEA substrates was studied to assess the effect of the building blocks of these new polymers on their biodegradation properties. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 391–407, 1999     

Cyclic polypeptides by thermal polymerization of α‐amino acid N‐carboxyanhydrides

The NCAs of the following five amino acids were polymerized in bulk at 120 °C without addition of a catalyst or initiator: sarcosine (Sar), L ‐alanine (L ‐Ala), D ,L ‐phenylalanine (D ,L ‐Phe), D ,L ‐leucine (D ,L ‐Leu) and D ,L ‐valine (D,L ‐Val). The virgin reaction products were characterized by viscosity measurements ¹³C NMR spectroscopy and MALDI‐TOF mass spectrometry. In addition to numerous low molar mass byproducts cyclic polypeptides were formed as the main reaction products in the mass range above 800 Da. Two types of cyclic oligo‐ and polypeptides were detected in all cases with exception of sarcosine NCA, which only yielded one class of cyclic polypeptides. The efficient formation of cyclic oligo‐ and polypeptides explains why high molar mass polymers cannot be obtained by thermal polymerizations of α‐amino acid NCAs. Various polymerization mechanisms were discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4012–4020, 2008     

Imidazole‐initiated polymerizations of α‐amino acid N‐carboxyanhydrides – simultaneous chain‐growth and step‐growth polymerization

The N‐carboxyanhydrides (NCAs) of sarcosine (Sar), D ,L ‐leucine (D ,L ‐Leu), D ,L ‐phenylalanine (D ,L ‐Phe), and L ‐alanine (L ‐Ala) were polymerized in dioxane. Imidazole served as initiator and the NCA/initiator ratio was varied from 1/1 to 40/1. The isolated polypeptides were characterized by ¹H NMR spectroscopy, by MALDI‐TOF mass spectrometry, by viscosity measurements, and by SEC measurements in the case of poly(sarcosine). Cyclic oligopeptides were found in all reaction products and in the case of polySar, poly(D ,L ‐Leu), and poly(D ,L ‐Phe) the cycles were the main products. In the case of poly(L ‐Ala), rapid precipitation of β‐sheet lamellaes prevented efficient cyclizations and stabilized imidazolide endgroups. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5690–5698, 2005     

Investigation on thermoresponsive behavior of biodegradable poly(γ‐glutamic acid)‐graft‐L‐phenylalanine ethyl ester

The thermosensitivity of biodegradable and non‐toxic amphiphilic polymer derived from a naturally occurring polypeptide and a derivative of amino acid was first reported. The amphiphilic polymer consisted of poly(γ‐glutamic acid) (γ‐PGA) as a hydrophilic backbone, and L ‐phenylalanine ethyl ester (L ‐PAE) as a hydrophobic branch. Poly(γ‐glutamic acid)‐graft‐L ‐phenylalanine (γ‐PGA‐graft‐L ‐PAE) with grafting degrees of 7–49% were prepared by varying the content of a water‐soluble carbodiimide (WSC). γ‐PGA‐graft‐L ‐PAE with a grafting degree of 49% exhibited thermoresponsive phase transition behavior in an aqueous solution at around 80°C. The copolymers with grafting degrees in the range of 30–49% showed thermoresponsive properties in NaCl solution. A clouding temperature (T_cloud) could be adjusted by changing the polymer concentration and/or NaCl concentration. The thermoresponsive behavior was reversible. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Deprotonation reaction of α‐amino acid N‐carboxyanhydride at 4‐CH position by yttrium tris[bis(trimethylsilyl)amide]

Reaction of yttrium tris[bis(trimethylsilyl)amide] [(TMSN)₃Y] with equivalent L ‐alanine N‐carboxyanhydride (ALA NCA) yields yttrium α‐isocyanato carboxylate ( II ), yttrium ketenyl carbamate ( III ), and hexamethyldisilazane ( V ). The products indicate that 4‐CH group of ALA NCA monomer is deprotonated in addition to 3‐NH group, which has been neglected in NCA chemistry for decades. This result proves the acidity of 4‐CH in NCA and provides the first direct evidence for racemization phenomenon of NCA in strong base in microscopic aspect. Rare earth tris[bis(trimethylsilyl)amide] (TMSN)₃Ln (Ln = Sc, Y, La, Dy, and Lu) compounds are high efficient catalysts for ring‐opening polymerizations of NCAs. Polypeptides can be produced in quantitative yields with narrow molecular weight distributions below 1.3, and block copolypeptides can be facilely prepared by sequential addition method. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Molecular Bottlebrushes with Polypeptide Backbone Prepared via Ring‐Opening Polymerization of NCA and ATRP

A new type of molecular bottlebrush with poly‐L ‐lysine (PLL) as backbone was synthesized via ROP followed by ATRP. A Nϵ‐bromoisobutyryl functionalized Nα‐CBZ‐L ‐lysine was firstly synthesized and converted in polymerizable α‐amino acid N‐carboxyanhydride (NCA), which was then polymerized using Ni(0) transition metal complex to give well‐defined bromo‐functionalized homopolypeptide (PBrLL), from which we prepared two types of polypeptide bottlebrushes with polystyrene and poly(oligoethylene glycol methacrylate) as side‐chains. PBrLL macroinitiator was demonstrated to have high initiation efficiency for ATRP, which allowed good control over side‐chain length. CD and FTIR characterization revealed that both PBrLL macroinitiator and PLL backbone of bottlebrushes adopted α‐helical conformation in appropriate solvents.     

Synthesis of polypeptides from activated urethane derivatives of α‐amino acids

A series of activated urethane‐type derivatives of α‐amino acids were synthesized and applied to polypeptide synthesis. The urethane used herein, N‐(4‐nitrophenoxycarbonyl)‐α‐amino acids 1 , were synthesized by N‐carbamoylation of γ‐benzyl‐L ‐glutamate, β‐benzyl‐L ‐aspartate, L ‐leucine, L ‐phenylalanine, and L ‐proline, with 4‐nitrophenyl chloroformate. When 1 was dissolved in N,N‐dimethylacetamide (DMAc) and heated at 60 °C, it was smoothly converted into the corresponding polypeptides with releasing 4‐nitrophenol and carbon dioxide. Spectroscopic analyses of the obtained polypeptides revealed that they were comparable with the authentic polypeptides synthesized by the ring‐opening polymerizations of amino acid N‐carboxyanhydrides (NCAs). Besides the successful polycondensations of a series of 1 , their polycondensations of 1a and other 1 were also successfully carried out to obtain the corresponding statistic copolypeptides. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2525–2535, 2008     

Convenient synthesis of poly(γ‐benzyl‐L‐glutamate) from activated urethane derivatives of γ‐benzyl‐L‐glutamate

A series of activated urethane‐type derivatives of γ‐benzyl‐L ‐glutamate were synthesized, and their potential as monomers for polypeptide synthesis was investigated. The derivatives of the focus of this work were a series of N‐aryloxycarbonyl‐γ‐benzyl‐L ‐glutamate 1 , of which aryl groups were phenyl, 4‐chlorophenyl, and 4‐nitrophenyl. These urethanes 1 were reactive in polar solvents such as dimethylsulfoxide, N,N‐dimethylformamide (DMF), and N,N‐dimethylacetamide (DMAc), and were efficiently converted into poly(γ‐benzyl‐L ‐glutamate) (poly(BLG)) under mild conditions; at 60 °C without addition of any catalyst. Among the three urethanes, that having 4‐nitrophenoxycarbonyl group 1c was the most reactive to give poly(BLG) efficiently, as was expected from the highly electron deficient nature of the nitrophenoxycarbonyl group. On the other hand, the urethane 1a having phenoxycarbonyl group was also efficiently converted into poly(BLG), in spite of the intrinsically less electrophilicity of the phenoxycarbonyl group. In addition, the successful formation of poly(BLG) by the reaction of 1a favored its diluted concentration (0.1 M) much more than 2.0 M, the optimum initial concentration for 1c . ¹H NMR spectroscopic analyses of the reactions in situ revealed that the predominant pathway from 1 to poly(BLG) involved the intramolecular cyclization of 1 into the corresponding N‐carboxyanhydride, with release of phenol and its successive ring‐opening polymerization with release of carbon dioxide. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2649–2657, 2008     

Preparation of novel poly(ethylene oxide‐co‐glycidol)‐graft‐poly(ε‐caprolactone) copolymers and inclusion complexation of the grafted chains with α‐cyclodextrin

A well‐defined comblike copolymer of poly(ethylene oxide‐co‐glycidol) [(poly(EO‐co‐Gly)] as the main chain and poly(ε‐caprolactone) (PCL) as the side chain was successfully prepared by the combination of anionic polymerization and ring‐opening polymerization. The glycidol was protected by ethyl vinyl ether to form 2,3‐epoxypropyl‐1‐ethoxyethyl ether (EPEE) first, and then ethylene oxide was copolymerized with EPEE by an anionic mechanism. The EPEE segments of the copolymer were deprotected by formic acid, and the glycidol segments of the copolymers were recovered after saponification. Poly(EO‐co‐Gly) with multihydroxyls was used further to initiate the ring‐opening polymerization of ε‐caprolactone in the presence of stannous octoate. When the grafted copolymer was mixed with α‐cyclodextrin, crystalline inclusion complexes (ICs) were formed, and the intermediate and final products, poly(ethylene oxide‐co‐glycidol)‐graft‐poly(ε‐caprolactone) and ICs, were characterized with gel permeation chromatography, NMR, differential scanning calorimetry, X‐ray diffraction, and thermogravimetric analysis in detail. The obtained ICs had a channel‐type crystalline structure, and the ratio of ε‐caprolactone units to α‐cyclodextrin for the ICs was higher than 1:1. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3684–3691, 2006     

A convenient synthesis of α,α′‐ homo‐ and α,α′‐hetero‐bifunctionalized poly(ε‐caprolactone)s by ring opening polymerization: The potentially valuable precursors for miktoarm star copolymers

Two new ring opening polymerization (ROP) initiators, namely, (3‐allyl‐2‐(allyloxy)phenyl)methanol and (3‐allyl‐2‐(prop‐2‐yn‐1‐yloxy)phenyl)methanol each containing two reactive functionalities viz. allyl, allyloxy and allyl, propargyloxy, respectively, were synthesized from 3‐allylsalicyaldehyde as a starting material. Well defined α‐allyl, α′‐allyloxy and α‐allyl, α′‐propargyloxy bifunctionalized poly(ε‐caprolactone)s with molecular weights in the range 4200–9500 and 3600–10,900 g/mol and molecular weight distributions in the range 1.16–1.18 and 1.15–1.16, respectively, were synthesized by ROP of ε‐caprolactone employing these initiators. The presence of α‐allyl, α′‐allyloxy and α‐allyl, α′‐propargyloxy functionalities on poly(ε‐caprolactone)s was confirmed by FT‐IR, ¹H, ¹³C NMR spectroscopy, and MALDI‐TOF analysis. The kinetic study of ROP of ε‐caprolactone with both the initiators revealed the pseudo first order kinetics with respect to ε‐caprolactone consumption and controlled behavior of polymerization reactions. The usefulness of α‐allyl, α′‐allyloxy functionalities on poly(ε‐caprolactone) was demonstrated by performing the thiol‐ene reaction with poly(ethylene glycol) thiol to obtain (mPEG)₂‐PCL miktoarm star copolymer. α‐Allyl, α′‐propargyloxy functionalities on poly(ε‐caprolactone) were utilized in orthogonal reactions i.e copper catalyzed alkyne‐azide click (CuAAC) with azido functionalized poly(N‐isopropylacrylamide) followed by thiol‐ene reaction with poly(ethylene glycol) thiol to synthesize PCL‐PNIPAAm‐mPEG miktoarm star terpolymer. The preliminary characterization of A₂B and ABC miktoarm star copolymers was carried out by ¹H NMR spectroscopy and gel permeation chromatography (GPC). © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 844–860     

Synthesis of Pyrrolidines and Pyrrolizidines with α‐Pseudoquaternary Centers by Copper‐Catalyzed Condensation of α‐Diazodicarbonyl Compounds and Aryl γ‐Lactams

N‐aryl γ‐lactams react intermolecularly with acceptor–acceptor diazo reagents, usually dicarbonyl compounds, in a copper‐catalyzed process to yield functionalized pyrrolidines with α‐pseudoquaternary centers. As 1,2‐acyl or ‐phosphoryl migration is preferred, single regioisomers are obtained. Furthermore, in the presence of a Lewis acid, subsequent Friedel–Crafts reactions yield tricyclic pyrrolizidines in excellent yields (90–96 %) and diastereoselectivities (up to >20:1).     

Catalytic Asymmetric 1,2‐Addition of α‐Isothiocyanato Phosphonates: Synthesis of Chiral β‐Hydroxy‐ or β‐Amino‐Substituted α‐Amino Phosphonic Acid Derivatives

α‐Amino phosphonic acid derivatives are considered to be the most important structural analogues of α‐amino acids and have a very wide range of applications. However, approaches for the catalytic asymmetric synthesis of such useful compounds are very limited. In this work, simple, efficient, and versatile organocatalytic asymmetric 1,2‐addition reactions of α‐isothiocyanato phosphonate were developed. Through these processes, derivatives of β‐hydroxy‐α‐amino phosphonic acid and α,β‐diamino phosphonic acid, as well as highly functionalized phosphonate‐substituted spirooxindole, can be efficiently constructed (up to 99 % yield, d.r. >20:1, and >99 % ee). This novel method provides a new route for the enantioselective functionalization of α‐phosphonic acid derivatives.     

α‐Amino acid: an effective ligand for asymmetric catalysis of transfer hydrogenation of ketones

Ruthenium complexes, prepared by mixing the potassium salt of α‐amino acids and [RuCl₂(arene)]₂, acted as catalysts for the asymmetric transfer hydrogenation of ketones from 2‐propanol in the presence of KOH. For example, the transfer hydrogenation of acetophenone from 2‐propanol was catalyzed effectively by the ruthenium complex prepared from potassium L ‐prolinate and [RuCl₂(p‐cymene)]₂ to give (R)‐1‐phenylethanol in 72% yield with 81% ee. The yields and enantioselectivities of the product were influenced strongly by the structure of the α‐amino acidate ligand, arene ligand, and substrate, by the amount of additional base, and by the concentration of the substrates. The best enantiomeric excesses of the products was 92%, when 1‐tetralone was subjected to this reaction using a prolinated ruthenium complex bearing p‐cymene. Furthermore, the potassium salts of dipeptides were tested as a ligand for this transfer hydrogenation. Copyright © 2001 John Wiley & Sons, Ltd.     

Phosphoryl group differentiating α‐amino acids from β‐ and γ‐amino acids in prebiotic peptide formation

In recent years β‐amino acids have increased their importance enormously in defining secondary structures of β‐peptides. Interest in β‐amino acids raises the question: Why and how did nature choose α‐amino acids for the central role in life? In this article we present experimental results of MS and ³¹P NMR methods on the chemical behavior of N‐phosphorylated α‐alanine, β‐alanine, and γ‐amino butyric acid in different solvents. N‐Phosphoryl α‐alanine can self‐assemble to N‐phosphopeptides either in water or in organic solvents, while no assembly was observed for β‐ or γ‐amino acids. An intramolecular carboxylic–phosphoric mixed anhydride (IMCPA) is the key structure responsible for their chemical behaviors. Relative energies and solvent effects of three isomers of IMCPA derived from α‐alanine (2a–c), with five‐membered ring, and five isomers of IMCPA derived from β‐alanine (4a–e), with six‐membered ring, were calculated with density functional theory at the B3LYP/6‐31G** level. The lower relative energy (3.2 kcal/mol in water) of 2b and lower energy barrier for its formation (16.7 kcal/mol in water) are responsible for the peptide formation from N‐phosphoryl α‐alanine. Both experimental and theoretical studies indicate that the structural difference among α‐, β‐, and γ‐amino acids can be recognized by formation of IMCPA after N‐phosphorylation. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 232–241, 2003     

Radical copolymerization of maleimide with ethyl α‐ethylacrylate and α‐ethylacrylic acid via RAFT

The copolymerization of maleimide (MI) with α‐ethylacrylic acid (EAA) and with ethyl α‐ethylacrylate (EEA) in the presence of 2‐phenylprop‐2‐yl dithiobenzoate (PPDB) was investigated. The copolymerization of MI and EAA was difficult to conduct with the reversible addition–fragmentation chain transfer (RAFT) mechanism because reinitiation of expelled radicals by fragmentation chain transfer was inhibited by the association of EAA in polar solvent and the strong interaction of the imino of MI with the carboxyl of EAA between the propagation chains. When the carboxylic group of EAA was esterified, then the copolymerization went well via RAFT, and alternating copolymers with controlled molecular weight were obtained. Combining by electron spin resonance showed a different result. It was found that before 30% of the comonomer conversion had occurred, the copolymer poly(EEA‐co‐MI) showed increasing molecular weight with the conversion and a rather narrow molecular weight distribution; then the molecular weight of the copolymer began to retard. This phenomenon of retardation was aggravated at high temperature. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3828–3835, 2004     

Supramolecular polyseudorotaxanes formation between star‐block copolymer and α‐cyclodextrin: From outer block to diblock inclusion complexation

A series of star‐block poly(L ‐lactide)‐b‐poly(ethylene oxide) (SPLLA‐b‐PEO) copolymers were synthesized by ring‐opening polymerization (ROP) and DCC chemistry. The inclusion complexes of SPLLA‐b‐PEO copolymers and α‐cyclodextrin (α‐CD) were prepared with two different methods. FTIR, ¹H NMR, WAXD, DSC, and TGA indicate that α‐CD only can be threaded onto PEO blocks in inclusion complexes of α‐CD‐SPLLA‐b‐PEO1.1K‐a, α‐CD‐SPLLA‐b‐PEO2K‐a, and α‐CD‐SPLLA‐b‐PEO5K‐a formed without heating and ultrasonication, and can be threaded onto both PLLA and PEO blocks in inclusion complexes of α‐CD‐SPLLA‐b‐PEO1.1K‐b, α‐CD‐SPLLA‐b‐PEO2K‐b, and α‐CD‐SPLLA‐b‐PEO5K‐b formed with heating and ultrasonication. Namely, α‐CDs can be threaded onto PEO blocks and the flanking bulky PLLA blocks of star‐block copolymers to form stable polyseudorotaxanes with heating method and ultrasonication to conquer the activation energy barrier of the inclusion complexation between bulky PLLA and α‐CD and the effect of the steric hindrance of star‐block copolymers. With the alteration of preparing methods, the inclusion complexes of α‐CD with the outer PEO block or PEO and PLLA blocks were obtained successfully. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2754–2762, 2009