Reactions of polymers having β-alkoxyenoate moieties in the main chain

The hydrolysis and the substitution reaction of the main chain of the polymer having β-alkoxyenoate moieties in the main chain are described. The hydrolysis of the polymer prepared from 2,2-dimetylpropylene-1,3-bis(propiolate) and p-xylene glycol under acidic conditions proceeded smoothly to obtain diols in quantitative yield by the cleavage of both ester and vinyl ether moieties. On the other hand, carboxylic acids were obtained by the hydrolysis of the polymer under alkaline conditions. The aminolysis with pyrrolidine gave the β-aminoenoate by the selective fission of vinyl ether moieties in quantitative yield. Furthermore, a polymer having β-aminoenoate moieties in the main chain was obtained by the reaction with piperazine via the displacement of the main chain. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 787–793, 1997     

Characterization of an Isozyme of β-Glucosidase from Sweet Almond

A sweet almond β-glucosidase (EC 3.2.1.21) isozyme was purified from commercial crude product. The process of purification consisted of a Protein-Pak Q anion exchange chromatography following by a Superdex 75 HR gel filtration separation. The purified enzyme is a monomeric glycoprotein with molecular weight of 58 kDa and pI=4.55 which is distinguished from reported isozymes. The enzyme has apH optimum in the range of 5.2-5.6 when p-nitrophenyl-β-D-glycopyranosides are used as substrate and is stable up to 50 °C at that pH range. The purified protein also exhibits profound β-galactosidase and σ-L-arabinosidase activity. The study of substrate specificity revealed that lacking of hydroxymethyl group at C-5 of glycosides resulted in higher affinity for substrate binding to enzyme, whereas the chemical step of hydrolysis (k_cst) was prevented significantly. The pH activity profile displayed a bell-shaped curve for all measured p-nitrophenyl-β-D-glycopyranosides with apparent pK₁ and pK₂ values of 4.4-4.7 and 6.2-6.4, respectively. This isozyme was strongly inhibited by δ-gluconolactone (K_i = 160 μM) and 4-phenylimidazole (K_i = 17.8 μM) reversibly at pH 6.2. Among the tested glycoses, the binding affinity of N-acetyl-β-D-glucosamine to the enzyme (K_l = 52 mM) was 6 times stronger than that of glucose and its epimers.     

Preparation,characterization and properties of β-chitin and N-acetylated β-chitin

Free amino groups in β-chitin from squid pen were acetylated to obtain N-acetylated β-chitin. After careful control of degree of acetylation, thermal and mechanical properties of β-chitin and N-acetylated β-chitin were compared. The structural differences of β-chitin and N-acetylated β-chitin were characterized by Fourier transform infrared (FTIR) and wide-angle x-ray diffraction (WAXD) analysis. The results indicated that the crystallinity of N-acetylated β-chitin was higher than that of β-chitin and N-acetylated β-chitin exhibited characteristics similar to α-chitin. Equilibrium water content (EWC) of β-chitin reached to about 50% and this hydrophilic nature was assumed to be caused by a relatively weak hydrogen bonding force of β-chitin with parallel main chains. On the other hand, EWC of N-acetylated β-chitin was 40% due to the introduction of ordered structure. β-chitin and N-acetylated β-chitin have the tensile strength of 0.4 and 0.7 Mpa in the swollen state, respectively. Viscoelastic properties and thermal relaxation behaviors were investigated by dynamic mechanical thermal analysis (DMTA). DMTA spectra of these samples showed that α-transition peaks of β-chitin and N-acetylated β-chitin were observed at 170 and 190°C, respectively. These relaxation peak maxima were assigned to be their glass transition temperature. In addition, a second relaxation peak of β-chitin resulting from acetamide groups was found at 112°C and a broad relaxation peak of N-acetylated β-chitin at around 81–100°C. As a result of thermogravimetric analysis, 10% weight loss temperatures of β-chitin and N-acetylated β-chitin were 270 and 285°C, respectively. © 1996 John Wiley & Sons, Inc.     

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     

Sulfur-containing optically active polymers. V. Synthesis and chiroptical properties of optically active poly(γ-ketosulfide)s prepared by polyaddition of 1,3-dimercaptobenzene to 4,4-dimethyl-2,5-cyclohexadien-1-one or to trans,trans-2,5-heptadien-3-one in the presence of chiral amines

Optically active poly(γ-ketosulfide)s having the asymmetric centers disposed along the main chain have been prepared by step polyaddition of 1,3-dimercaptobenzene to 4,4-dimethyl-2,5-cyclohexadiene-1-one, or to trans, trans-2,5-heptadiene-3-one, in the presence of catalytic amounts of chiral amines. The extent of asymmetric induction on the resulting polymeric product is found to be higher when the alicyclic ketone reagent is employed and is enhanced by lowering the catalyst concentration. The comparison of stereochemical features and chiroptical properties of appropriate low molecular weight analogues with those of the polymeric derivatives indicates that a comparable asymmetric induction occurs in polymers and model compounds, and that the former systems do not display appreciable evidence of ordered secondary structures, in agreement with a low stereoregularity degree along the macromolecular backbone. © 1996 John Wiley & Sons, Inc.     

On the exotherm of polyacrylonitrile. II. Examination of deuterated polymers

A series of α-, β,β-, and α,β,β-deuterium-labelled acrylonitrile monomers were prepared and polymerized. Secondary deuterium isotope effects on the polymerization and on the pyrolysis reactions that precede carbon fiber formation were observed. When deuterium is in the α-position, the polymerization rate is greater and the molecular weight is higher. It is proposed that either the propagation rate constant or both that constant and the termination rate constant are increased on deuterium substitution. In differential scanning calorimetry, the polyacrylonitrile exotherm occurs at higher temperatures and is narrower when deuterium is substituted at the α-position. On the other hand, the thermal gravimetric analysis activation energy for weight loss of polymer at temperatures below the acrylic exotherm is lower when deuterium is in the α-position, relative to the α-hydrogen polymers. As there is no correlation between the weight loss energy of activation and the various exotherm parameters, the weight loss energy of activation and the various exotherm parameters, the weight loss and exotherm are considered to be independent events. Examination of the distribution of deuterium substituted ammonia species evolved during 100–240°C thermal treatment of the α-and β, β-deuterated polyacrylonitriles provides a clear indication that both the α- and β-positions are directly involved in hydrogen migration to nitrogen, but the mechanism of ammonia generation remains unclear. © 1995 John Wiley & Sons, Inc.     

Biochemistry and Molecular Biology of Snake Neurotoxin

A review of research on snake neurotoxin is presented, with emphasis on the chemical modification studies and molecular cloning of postsynaptic and presynaptic neurotoxins from Naja naja atra (Taiwan cobra) (Fig. 1a) and Bungarus multicinctus (Taiwan banded krait) (Fig. 1b). Cobrotoxin and α-bungarotoxin are the primary postsynaptic neurotoxins isolated from the venom of N. naja atra and B. multicinctus, respectively. Although they share a common three-dimensional structure, the functional elements essential for the manifestation of their toxicity are different. Selective and stepwise chemical modification of cobrotoxin indicate that at least two cationic groups, an ?-amino group of Lys-47 and a guanidino group of Arg-33 common to all known postsynaptic neurotoxins, are functionally important for its neuromuscular blocking activity. However, for α-bungarotoxin, the side chains of several basic amino acid residues are involved in the multipoint contact between the toxin and acetylcholine receptor. Moreover, the conserved Trp residue is essential for the neurotoxicity of cobrotoxin, but not for α-bungarotoxin. The cDNAs encoding cobrotoxin and α-bungarotoxin was constructed from the cellular RNA isolated from the venom glands of N. naja atra and B. multicinctus by polymerase chain reaction. The sequence of their 3′-untranslational region, signal peptide and 5′-untranslational region share a high degree of homology, suggesting that they are evolutionarily related. Expression of both neurotoxic protein in E. coli generated polypeptide chains for reactions with the antisera against the native neurotoxins. Presynaptic neurotoxins constitute a different group of neurotoxic proteins in snake venom proteins. These presynaptic neurotoxins are either basic phospholipase A₂ (PLA₂) per se or contain basic PLA₂ as an indispensible part of their structures. Thus, the presynaptic neurotoxins usually show both PLA₂ activity and presynaptic neurotoxicity. β-Bungarotoxin (β-Bgt), the main presynaptic PLA₂ neurotoxin isolated from the venom of B. multicinctus (Taiwan banded krait), consists of two dissimilar polypeptide chains, a PLA₂ subunit (A chain) and potassium channel recognition subunit (B chain). Chemical modification studies show that the toxin might possess two functional sites, one responsible for the catalytic activity and the other for its pharmacological properties. Molecular cloning and expression of the A chain and B chain of β-Bgt reveal that the A chain of β-Bgt is an active subunit with PLA₂ activity, and that the B chain is involved in voltage-gated potassium channel blocking action observed with β-Bgt.     

Living cationic isomerization polymerization of β-pinene. III. Synthesis of end-functionalized polymers and graft copolymers

α-End-functionalized polymers and macromonomers of β-pinene were synthesized by living cationic isomerization polymerization in CH₂Cl₂ at −40°C initiated with the HCl adducts [ 1; CH₃CH(OCH₂CH₂X)Cl; X = chloride ( 1a ), acetate ( 1b ), and methacrylate ( 1c )] of vinyl ethers carrying pendant substituents X that serve as terminal functionalities. In conjunction with TiCl₃(OiPr) and nBu₄NCl, these functionalized initiators led to living β-pinene polymerization where the carbon–chlorine bond of 1 was activated by TiCl₃(OiPr). Similarly, end-functionalized poly(p-methylstyrene)-block-poly(β-pinene) were also obtained. ¹H-NMR analysis showed that the polymers possess controlled molecular weights (DP _n = [M]₀/[ 1 ]₀) and number-average end functionalities close to unity. The end-functionalized methacrylate-capped macromonomers form 1c were radically copolymerized with methyl methacrylate (MMA) to give graft copolymers carrying poly(β-pinene) or poly(p-methylstyrene)-block-poly(β-pinene) as graft chains attached to a PMMA backbone. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1423–1430, 1997     

A Mild Isomerization Reaction for β,γ‐Unsaturated Ketone to α,β‐Unsaturated Ketone

A series of β,γ‐unsaturated ketones were isomerized to their corresponding α,β‐unsaturated ketones by the introduction of DABCO in iPrOH at room temperature. The endo‐cyclic double bond (β,γ‐position) on ketone was rearranged to exo‐cyclic double bond (α,β‐position) under the reaction conditions.     

Novel copolymer networks via the combination of polyaddition and anionic polymerization

A two‐step synthetic route to novel copolymer networks, consisting of polymethacrylate and polyacetal components, was developed by combining the polyaddition and anionic polymerization techniques. The functional polymethacrylates containing hydroxyl or vinyloxyl side groups were used as crosslinkers. They were anionically synthesized as follows: the copolymer of 2‐hydroxyethyl methacrylate (HEMA) and methyl methacrylate (MMA) was prepared by the anionic copolymerization of 2‐(trimethylsiloxy)ethyl methacrylate and MMA, followed by hydrolysis. The copolymer poly(HEMA‐co‐MMA) thus obtained possessed a hydroxyl group in each of its HEMA units. Another kind of vinyloxyl‐containing (co)polymer was prepared by the anionic homopolymerization of 2‐(vinyloxy)ethyl methacrylate (VEMA) or its copolymerization with MMA. The resulting (co)polymer possessed reactive vinyloxyl side groups. The copolymer networks were obtained by reacting each of the above‐mentioned (co)polymers with a polyacetal prepared via the polyaddition between a divinyl ether and a diol. Three divinyl ethers (ethylene glycol divinyl ether, 1,4‐butanediol divinyl ether, and 1,6‐hexanediol divinyl ether) and three diols (ethylene glycol, 1,4‐butanediol, and 1,6‐hexanediol) were employed as monomers in the polyaddition step, and their combinations generated nine kinds of polyacetals. When a polyaddition reaction was terminated with a divinyl ether monomer, a polyacetal with two vinyloxyl end groups was obtained, which could further react with the hydroxyl groups of poly(HEMA‐co‐MMA) to generate a copolymer network. On the other hand, when a diol was used as terminator in the polyaddition, the resulting polyacetal possessed two hydroxyl end groups, which could react with the vinyloxyl groups of poly(VEMA) or poly(VEMA‐co‐MMA), to generate a copolymer network. All the copolymer networks exhibited degradation in the presence of acids. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 117–126, 2001     

Monoaryloxo ytterbium(III) chlorides supported by β‐diketiminato ligands as novel initiators for the living ring‐opening polymerization of ε‐caprolactone

Ring‐opening polymerization of ε‐caprolactone (ε‐CL) was carried out using β‐diketiminato‐supported monoaryloxo ytterbium chlorides L¹Yb(OAr)Cl(THF) (1) [L¹ = N,N′‐bis(2,6‐dimethylphenyl)‐2,4‐pentanediiminato, OAr = 2,6‐di‐tert‐butylphenoxo‐], and L²Yb(OAr′)Cl(THF) (2) [L² = N,N′‐bis(2,6‐diisopropylphenyl)‐2,4‐pentanediiminato, OAr′ = 2,6‐di‐tert‐butyl‐4‐methylphenoxo‐], respectively, as single‐component initiator. The influence of reaction conditions, such as polymerization temperature, polymerization time, initiator, and initiator concentration, on the monomer conversion, molecular weight, and molecular weight distribution of the resulting polymers was investigated. Complex 1 was well characterized and its crystal structure was determined. Some features and kinetic behaviors of the CL polymerization initiated by these two complexes were studied. The polymerization rate is first order with respect to monomer. The M_n of the polymer increases linearly with the increase of the polymer yield, while polydispersity remained narrow and unchanged throughout the polymerization in a broad range of temperatures from 0 to 50 °C. The results indicated that the present system has a “living character”. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1147–1152, 2006     

Synthesis of new optically active α,α′,β‐trisubstituted‐β‐lactones as monomers for stereoregular biopolyesters

Various optically active (4R)‐alkyloxycarbonyl‐3,3‐dialkyl‐2‐oxetanones as monomers were synthesized from L‐(S)‐malic acid in six steps to prepare a new family of stereopolyesters for biomedical applications. The synthesis began with an esterification followed of a dialkylation in the aim to introduce hydrophobic groups as methyl or reactive group as allyl. Then, a saponification has permitted to obtain the corresponding diacids that reacted with appropriate alcohols to furnish different monoesters. The last and most important step was activation of hydroxyl group of monoesters with the asymmetric carbon configuration inversion according to the Mitsunobu reaction. Thus, this reaction has provided lactones from monoesters with 100% enantiomeric excess which was confirmed by ¹H NMR and by the synthesis of corresponding isotactic and semicrystalline homopolyesters. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2586–2597     

Theoretical Study Of β2,3‐Peptide Models

Conformational features of α,β‐disubstituted β^2,3‐dipeptide models have been studied with quantum mechanics method. Geometries were optimized with the HF/6‐31G** method, and energies were evaluated with the B3LYP/6‐31G** method. Solvent effect was evaluated with the SCIPCM method. For (2S,3S)‐β^2,3‐dipeptide model 1 , a six‐membered‐ring hydrogen bonded structure is most stable. However, the conformation corresponding to the formation of the 14‐helix is only about 1.7 kcal/mol less stable in methanol solution, indicating that the 14‐helix is favored if a (2S,3S)‐β^2,3‐polypeptide contains more than 5 residues. On the other hand, the conformation corresponding to the formation of β‐sheet is most stable for (2R,3S)‐β^2,3‐dipeptide model 2 , suggesting that this type of β‐peptides is intrinsically favored for the formation of β‐sheet secondary structure.     

Cationic polymerization of γ-methyl- and α-methylphenylallene

The cationic polymerizations of γ-methylphenylallene ( 1 ) and α-methylphenylallene ( 2 ) were carried out with some Lewis acids at 25 and 0°C in dichloromethane to obtain the corresponding polymers through allyl cations, respectively. Tin (IV) chloride was found to be an effective catalyst for the cationic polymerization of both allenes 1 and 2 compared with other Lewis acids. Thus, in the polymerization of 1 , methanol-insoluble polymer was only obtained using Tin (IV) chloride, and M?_n of methanol-insoluble polymer obtained by Tin (IV) chloride was the highest in the polymerization of 2 . From the analysis of ¹H- and ¹³C-NMR spectra of the obtained polymers, the polymer from 1 consisted of two kinds of units polymerized by each double bonds of allene 1 , whereas the polymer from 2 consisted of only one unit polymerized by terminal double bond of allene 2 . Moreover, effect of solvent on the cationic polymerizations of 1 and 2 were discussed.     

Theoretical study of ester enolate–imine condensation route to β-lactams

The condensation reaction of the enolate of methyl acetate with formaldimine to afford a β-lactam was studied using the MP2-FC/6-31+G* level of theory taking into account the electrostatic effect of the solvent by means of a self-consistent reaction field continuum model. The reaction is a stepwise process with three main steps: the formation of the C3(SINGLE BOND)C4 bond, the closure of the β-lactam ring, and the elimination of the methoxide ion. The formation of the C3(SINGLE BOND)C4 bond is rate determining and according to our calculations is not a reversible step. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 1826–1833, 1998     

Preparation of poly(alkylenebenzimidazole) by ruthenium complex catalyzed polycondensation of 3,3′‐diaminobenzidine with α,ω‐diols

The reactions of 3,3′‐diaminobenzidine with 1,12‐dodecanediol in 1 : 1–1:3 molar ratios in the presence of RuCl₂(PPh₃)₃ catalyst give poly(alkylenebenzimidazole), [ (CH₂)₁₁ O (CH₂)₁₁ Im / (CH₂)₁₀ Im ]_n (Im: 5,5′‐dibenzimidazole‐2,2′‐diyl) (I_a‐I_d) in 71–92% yields. The relative ratio between the [(CH₂)₁₁ O (CH₂)₁₁ Im ] unit (A) and the [‐ (CH₂)₁₀ Im ] unit (B) in the polymer chain varies depending on the ratio of the substrates used. The polymer I_a obtained from the 1 : 3 reaction contains these structural units in a 98 : 2 ratio. The polymers are soluble in polar solvents such as DMF (N,N‐dimethylformamide), DMSO (dimethyl sulfoxide), and NMP (N‐methyl‐2‐pyrrolidone) and have molecular weights M_n (M_w) of 4,200–4,800 (4,800–6,500) by GPC (polystyrene standard). The polymerization of the diol and 3,3′‐diaminobenzidine in higher molar ratios leads to partial cross‐linking of the resulting polymers I_e and I_f via condensation of imidazole NH group with CH₂OH group. Similar reactions of 3,3′‐diaminobenzidine with α,ω‐diols, HO(CH₂)_mOH (m = 4–10), in a 1 : 3 molar ratio give the polymers containing [ (CH₂)_m−1 O (CH₂) _m−1 Im ] and [ (CH₂) _m−2 Im ] units with partial cross‐linked structures. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1383–1392, 1999     

A rare occurrence of a β‐turn in an amyloid βA4 peptide

The fragment β(25–35) of the amyloid β‐peptide, like its parent βA4, has shown neurotrophic and late neurotoxic activities in cultured cells. The 3D structure of this important peptide was examined by ¹H and ¹³C 2D‐NMR and MD simulations in DMSO‐d₆ and water. The NMR parameters of chemical shift, ³J(N,Hα) coupling constants, temperature coefficients of NH chemical shifts and the pattern of intra and inter‐residue NOEs were used to deduce the structures. In DMSO‐d₆, the peptide was found to take up a type I β‐turn around the C‐terminal residues Ile⁸–Gly⁹–Leu¹⁰–Met¹¹, whereas in water at pH 5.5, it adopts a random coil conformation. This is only the second report of a β‐turn in the β‐amyloid class of peptides. The solution structures generated using restrained molecular dynamics were refined by MARDIGRAS to an R factor of 0.33 in the case of DMSO‐d₆ and to 0.56 for water. Copyright © 2002 John Wiley & Sons, Ltd.     

Die Kristallstrukturen von Me3SiI · β-Picolin und Me3SiI · γ-Picolin Vergleich der Lewis-Basen Pyridin, β-Picolin und γ-Picolin

The Crystal Structure of Me₃SiI · β-Picoline and Me₃SiI · γ-Picoline A Comparison between the Lewis-Bases Pyridine, β-Picoline, and γ-Picoline The reaction of Iodinetrimethylsilane with β- und γ-Picoline (Pic) leads to solid 1 : 1 compounds Me₃SiI · β-Picoline 1 , Me₃SiI · γ-Picoline 2. The reaction was performed at room temperature. Yellow single crystals were obtained by sublimation. Single crystal X-ray investigations confirm that both compounds are ionic [Me₃SiPic]⁺I^?. The comparison of β-Picoline with γ-Picoline and Pyridine (Py) demonstrates that the presence of a methyl group and also its position has no significant influence on the Si? N bond length in compound 1, 2 and on the adduct Me₃SiI · Py.     

Synthesis of Phenanthrene Derivatives through the Reaction of an α,α‐Dicyanoolefin with α,β‐Unsaturated Carbonyl Compounds

Phenanthrene derivatives were prepared by reacting an α,α‐dicyanoolefin with different α,β‐unsaturated carbonyl compounds resulting from Wittig reaction of ninhydrin and phosphanylidene or condensation of barbituric acid and an aldehyde. The easy procedure, mild and metal‐catalyst free, reaction conditions, good yields, and no need for chromatographic purifications are important features of this protocol. The structures of the product of type 3 and 5 were corroborated spectroscopically (IR, ¹H‐ and ¹³C‐NMR, and EI‐MS). A plausible mechanism for this type of reaction is proposed (Scheme 1).     

Structure and molecular conformation of tussah silk fibroin films treated with water–methanol solutions: Dynamic mechanical and thermomechanical behavior

The thermal response of tussah (Antheraea pernyi) silk fibroin films treated with different water–methanol solutions at 20°C was studied by means of dynamic mechanical (DMA) and thermomechanical (TMA) analyses as a function of methanol concentration and treatment time. The DMA curves of α-helix films (treated with ≥80% v/v methanol for 2 min and 100% methanol for 30 min) showed the sharp fall of storage modulus at about 190°C, and the loss peak in the range 207–213°C. The TMA curves were characterized by a thermal shrinkage at 209–211°C, immediately followed by an abrupt extension leading to film failure. Both storage and loss modulus curves significantly shifted upwards for β-sheet films, obtained by treatment with ≤60% methanol for 30 min. The loss peak exhibited a maximum at 236°C. Accordingly, the TMA shrinkage at above 200°C disappeared. The films broke beyond 330°C, failure being preceded by a broad contraction step. Intermediate DMA and TMA patterns were observed for the other solvent-treated films. The loss peak shifted to higher temperature (219–220°C), and a minor loss modulus component appeared at about 230°C. This coincided with the onset of a plateau region in the storage modulus curve. The TMA extension–contraction events in the range 200–300°C weakened, and the samples displayed a final broad contraction (peak temperature 326–338°C) before breaking. The DMA and TMA response of these films was attributed to partial annealing by solvent treatment, which resulted in the formation of nuclei of β-sheet crystallization within the film matrix. The increased thermal stability was probably due to the small β-sheet crystals formed, which acted as high-strength junctions between adjacent random coil and α-helix domains. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2717–2724, 1998