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Poly(vinyl alcohol) grafted with poly(d,l-lactide) or poly(d,l-lactide-co-glycolide) oligomers, were synthesized in our laboratory and investigated with respect to their potential for tissue engineering applications. In order to understand their structure–properties relationships the effect of length and composition as well as number of polyester grafts on PVA backbone chain on water uptake capability and hydrophilicity/hydrophobicity balance and on mechanical properties of hydrogels was evaluated. The E moduli of hydrogels display values between 0.01 and 100 MPa. The results indicate the route for the development of polymers with a very broad range of properties similar to those of natural cartilage tissue. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3682–3688, 2013

The swellability and mass loss of poly(vinyl alcohol)-graft-[poly(rac-lactide)/poly(rac-lactide-co-glycolide)] hydrogels upon hydrolysis are strongly affected by the composition of the hydrogels. Hydrophobic hydrogels remain at a relatively constant mass for a couple of weeks, and the mass decreases dramatically thereafter, whereas more hydrophilic hydrogels lose mass right from the beginning. All hydrogels display water uptake values between 90 and 280% within 8 weeks. For longer periods of degradation, the water uptake increases up to a maximum of about 900%. Studies of the thermal properties of samples upon degradation and their IR measurements have shown that the degradation rate is related to the physical and chemical structure of the hydrogels and hence to the hydrophobic/hydrophilic balance; that is, the degradation increases with the increasing hydrophilicity of the material. As a result, degradation can be engineered through the variation of the composition and structure of the material. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

The bis(ethylene carbonate) monomers 3,4-O-isopropylidene-D-mannitol-1,2:5,6-dicarbonate (2) and D-mannitol-1,2:5,6-dicarbonate (1) were prepared fromD-mannitol in yields of 81 and 74%, respectively. These AA-type monomers were reacted with α, ω-diamines (H2N—(CH2) x –NH2; x = 2–10 and 12) as BB-type monomers in the sense of a polycondensation reaction. The molecular weights of the polyurethanes with pendant hydroxy groups obtained were determined by means of gel permeation chromatography in dimethylacetamide/LiCl and are in the range of 20 × 103 to 87 × 103 with polydispersity indices of ca. 1.6. The polyurethanes show primary and secondary hydroxy groups with a ratio of ca. 15:85. This is a consequence of the different direction of opening of the substituted ethylene carbonate ring which results in structurally isomeric repeating units. The polyurethanes obtained from 2 and diamines with two free hydroxy groups and two protected hydroxy groups in the repeating unit are semicrystalline materials with mel...

Mono- and bifunctional poly(phenylene oxide) (PPO) macroinitiators for atom transfer radical polymerization (ATRP) were prepared by esterification of mono- and bishydroxy telechelic PPO with 2-bromoisobutyryl bromide. The macroinitiators were used for ATRP of styrene to give block copolymers with PPO and polystyrene (PS) segments, namely PPO-block-PS and PS-block-PPO-block-PS. Various ligands were studied in combination with CuBr as ATRP catalysts. Kinetic investigations revealed controlled polymerization processes for certain ligands and temperature ranges. Thermal analysis of the block copolymers by means of DSC revealed only one glass transition temperature as a result of the compatibility of the PS and PPO chain segments and the formation of a single phase; this glass transition temperature can be adjusted over a wide temperature range (ca 100–199 °C), depending on the composition of the block copolymer. Copyright © 2005 Society of Chemical Industry

Lipase-catalyzed ring-opening bulk polymerizations of 6(S)-methyl-morpholine-2,5-dione (MMD) were investigated. Selected commercial lipases were screened as catalysts for MMD polymerization at 100 C. Polymerizations catalyzed with 10 wt % porcine pancreatic lipase type II crude (PPL), lipase from Pseudomonas cepacia, and lipase type VII from Candida rugosa resulted in MMD conversions of about 75% in 3 days and in molecular weights ranging from 8200 to 12,100. Poly(6-methyl-morpholine-2,5-dione) [poly(MMD)] had a carboxylic acid group at one end and a hydroxyl group at the other end. However, lipase from Mucor javanicus showed lower catalytic activity for the polymerization. During the polymerization, racemization of the lactate residue took place. PPL was selected for further studies. The rate of polymerization increased with increasing PPL concentration under otherwise identical conditions. When the PPL concentration was 5 or 10 wt % with respect to MMD, a conversion of about 70% was reached after 6 days or 1 day, respectively, whereas for a PPL concentration of 1 wt %, the conversion was less than 20% even after 6 days. High concentrations of PPL (10 wt %) resulted in high number-average molecular weights (

Summary: Random copolymers of methyl methacrylate (MMA), butyl methacrylate (BMA) and allyl methacrylate (AMA) were prepared via atom transfer radical polymerization (ATRP). AMA is a bifunctional monomer with two double bonds of different reactivity: a highly reactive methacrylate double bond and an allyl ester double bond of lower reactivity. In order to obtain linear polymers with pendant allyl ester groups, the copolymerization conditions have to be optimized with respect to the concentration of AMA, the catalyst system applied – especially the ligand – and the temperature. By means of kinetic studies the reaction parameters for a controlled polymerization were determined. The results obtained show that the higher the temperature and the amount of AMA is the higher is the probability of irregular chain growth and side reactions induced by the pendant allyl ester groups such as hydrogen abstraction from the allyl position or radical addition to the allyl ester double bond. The random copolymers were photochemically crosslinked by using 2,2-dimethoxy-2-phenylacetophenone as photoinitiator. The thermal properties of linear and crosslinked polymers were determined. The glass transition temperatures of both show no significant difference at low AMA content and thus low crosslinking densities. GPC eluograms of MMA/BMA (70:30) copolymers with 5 mol-% AMA at different conversions.

Poly(allyl methacrylate) (PAMA) and random copolymers of styrene (St) with allyl methacrylate (AMA) were prepared via atom transfer radical polymerization. For the homopolymerization of AMA, the maximum conversion depends on the reaction conditions and on the monomer/initiator ratio. For the copolymerization, AMA conversions of up to 90% were obtained while no cross-linking occurred. Kinetic studies of the homopolymerization revealed a controlled polymerization up to a certain conversion whereas at higher conversions, multimodal molecular weight distributions caused by branching reactions and cross-linking were observed. The copolymerization of AMA with St allowed a controlled reaction up to conversions higher than 90%. The copolymers obtained were soluble in standard organic solvents. In a subsequent reaction, these copolymers were cross-linked both thermally and photochemically using suitable initiators. Moreover, pendant double bonds were brominated quantitatively.

Tetramethylene urea (TeU) is successfully copolymerized with γ-butyrolactone (γBL), leading to an alternating poly(amide urethane) with alternating carbonyl-amino-tetramethylene-amino and carbonyl-trimethylene-oxy repeating units (Mn = 12 600; Mw = 21 100; Mn = 1.67) and with a Tm of 196.5 °C and a Tg of 36.4 °C. Small defects in the microstructure of the alternating poly(amide urethane) arise from the formation of TeU−TeU diads. Furthermore, TeU is successfully copolymerized with mixtures of γBL and ethylene carbonate (EC) or 1,2-propylene carbonate (PC). From NMR spectroscopic data of the terpolymers obtained, it is concluded that the reactivity of the five-membered cycles used increases in the following order: EC ≫ PC ≈ γBL. It is possible to increase the content of γBL repeating units in the poly[(TeU−γBL)-stat-(TeU−EC)] or poly[(TeU−γBL)-stat-(TeU−PC)] by increasing the fraction of γBL in the feed. 13C NMR spectroscopy reveals that TeU−EC or TeU−PC and TeU−γBL units are randomly distributed in th...

The ring-opening polymerization (ROP) of the cyclic ester amide (cEA) 5 (systematic name, l-oxa-8-aza-cyclotetradecane-9,14-dione)- prepared from adipic anhydride and 1-amino-6-hexanol - in the melt at 165 °C and in solution at 100 °C and 120 °C with Bu 2 Sn(OMe) 2 or Ti(OBu) 4 as initiator yields the alternating poly(ester amide) (PEA) 4 (systematic name, poly(5-(6-oxyhexylcarbamoyl)-pentanoate) with regular microstructure. Kinetic studies for different monomer-to-initiator ratios, different reaction media, initiators and temperatures reveal that the ROP is a first-order reaction with respect to the monomer. Under suitable polymerization conditions termination and transfer reactions are suppressed. The elementary chain growth reaction proceeds by a coordination insertion mechanism in analogy to the polymerization of lactones. By using monohydroxy- and bishydroxy-functional telechelic poly(ethylene oxide) and Sn(octoate) 2 as the initiating system poly(ethylene oxide)-block-poly(ester amide)s and poly(ester amide)-block-poly(ethylene oxide)-block-poly(ester amide)s are obtained. The poly(ester amide) 4 is a semicrystalline material with a melting point of 140 °C, the block copolymers are phase separated systems showing two melting points characteristic for the respective homopolymers.

Poly(amide urethane)s were prepared from e-caprolactam, amino alcohols, and diphenyl carbonate or ethylene carbonate in three steps. Polycondensation was performed either with α-hydroxy-ω-O-phenyl urethanes or with α-hydroxy-ω-O-hydroxyethyl urethanes; it was found that the reactivity at 90 °C of the first is much higher than that of the latter. For nearly equal reactivity, the temperature for the polycondensation of α-hydroxy-ω-O-hydroxyethyl urethanes had to be increased from 90 °C to 150 °C. The microstructure of the resulting poly(amide urethane)s differs by the content of urea groups in the polymer chains, which is 5% for poly(amide urethane)s prepared from α-hydroxy-ω-O-phenyl urethanes and 15% for poly(amide urethane)s prepared from α-hydroxy-ω-O-hydroxyethyl urethanes. As a consequence, the thermal properties of the poly(amide urethane)s differ slightly.

Alternating poly(amide urethane)s from e-caprolactam, amino alcohols H2N–(CH2)x–OH (x=2–6), and diphenyl carbonate were prepared by polycondensation of α-hydroxy-ω-O-phenylurethanes 4a-e. The degree of oligomerization was adjusted by the conversion. Oligomers with two or three O-phenylurethane end groups and predetermined molecular weight were prepared by polycondensation of the α-hydroxy-ω-O-phenylurethanes 4a-e in the presence of comonomers with O-phenylurethane end groups in a given concentration. In order to prepare oligomers with hydroxyl and carboxyl groups at both chain ends suitable for coupling reactions, chain analogous reactions were performed with amino acids and amino alcohols. The microstructure of the polymers and the nature of end groups was determined by means of 1H NMR spectroscopy and the molecular weights were determined by means of gel permeation chromatography. The poly(amide urethane)s 5a-e prepared are semicrystalline materials with melting points between 150 and 200 °C.

Tetramethylene urea (TeU, 1) is successfully copolymerized with 1,2-propylene carbonate (PC, 2), leading to a polyurethane (M n = 12 200; M w 18 400; M w /M n = 1.50) with T m of 145.7°C and a T g of 53.7°C. Mechanistic studies with a blocked isocyanate model compound revealed that, at no stage of the reaction is the TeU ring opened to form an isocyanate. Hence, a well-underlined mechanims for the copolymerized is proposed. Furthermore, TeU, is successfully copolymerized with mixtures of PC and ethylene carbonate (EC, 3). From NMR spectroscopic data of the polyurethanes obtained, it is concluded that PC is less reactive than EC. However, it is possible to increase the PC content in poly(TeU-EC-stat-TeU-PC) by increasing the PC/EC ratio in the feed. 13 C NMR spectroscopy reveals that a random copolymer is obtained. This conclusion is supported by differential scanning calorimetry (DSC) data, which show a continuous decrease in T m with increasing PC content.

Phenoxycarbonyloxymethyl ethylene carbonate 4 was synthesized from glycerol carbonate and phenyl chloroformate Polyurethanes with pendant hydroxyl greups were obtained from polycondensation reactions of this AA* monomer with diamines. These polymers contan primary as well as secondary hydroxyl groups The obtained polyurethanes are amorphous materials. The glass transition temperature decreases with increasing number of methylene groups between the urethane groups.

Bis(hydroxy)telechic bisphenol A polycarbonate (PC) was prepared via melt polycondensation of bisphenol A (BPA) and diphenyl carbonate (DPC) using lanthanum(m) acetylacetonate as a catalyst for transesterification. Subsequently, the polycarbonate was converted to a bifunctional macroinitiator for atom transfer radical polymerization (ATRP) with the reagent, α-chlorophenylacetyl chloride. The macroinitiator was used for the polymerization of styrene (S) and methyl methacrylate (MMA) to give PS-block-PS and PMMA-block-PC-block-PMMA triblock copolymers. These block copolymers were characterized by NMR and GPC. When styrene and methyl methacrylate were used in large excess, significant shifts toward high molecular weights were observed with quantitative consumption of the macroinitiator. Several ligands were studied in combination with CuCl as the ATRP catalyst. Kinetic studies reveal the controlled nature of the polymerization reaction for all the ligands used.

Alternating poly(ester amide)s 6a-e from succinic anhydride and α,ω-amino alcohols H 2 N-(CH 2 ) x -OH (x = 2-6) 2a-e were obtained in two steps: α-carboxyl-ω-hydroxy amides 3a-e were prepared from the starting materials in a highly selective reaction, followed by a polycondensation reaction. 1 H and 13 C NMR analyses of the poly(ester amide) s clearly reveal the alternating microstructure. The poly(ester amide)s with homologous α,ω-amino alcohols H 2 N-(CH 2 ) x -OH (x = 2-6) are semicrystalline materials, their melting points show the odd/even effect observed for [n]-polyamides and [n]-polyurethanes. Heating the poly(ester amide)s 6a-e yields the corresponding N-(hydroxyalkyl) imides 4a-e with no trace of cyclic ester amides. Theoretical calculations revealed that the cyclic ester amides 5a-e are clearly richer in energy than the isomeric N-(hydroxyalkyl) imides. These results show that cyclic ester amides can not be prepared from N-(hydroxyalkyl) imides by ring-enlargement reactions.

The ring-opening polymerization of the cyclic ester amide (cEA, 2) (systematic name, 1-oxa-7-aza-cyclotridecane-8,13-dione)prepared from adipic anhydride and 1-amino-5-pentanolin the melt at temperatures above 145 °C with Bu2Sn(OMe)2, Ti(OBu)4, Al(O-sec-Bu)3, or Sn(octoate)2 as initiator yields the poly(ester amide) (PEA, 3) (systematic name, poly(5-(5-oxypentylcarbamoyl)pentanoate) with regular microstructure. This poly(ester amide) is a semicrystalline material with a melting point of 108 °C. The elementary chain growth reaction proceeds by a coordination insertion mechanism in analogy to the polymerization of lactones. The monomer-to-initiator ratio and the conversion determine the number-average molecular weight. By using hydroxy telechelic poly(ethylene oxide) with Sn(octoate)2 as initiator poly(ester amide)-block-poly(ethylene oxide) and poly(ester amide)-block-poly(ethylene oxide)-block-poly(ester amide) were obtained. Kinetic studies for different monomer-to-initiator ratios, different temperature...

Poly(esters amide)s from adipic anhydride and α, ω-amino alcohols were obtained by polycondensation of α-carboxyl-ω-hydroxyl amides under mild conditions in solution or by bulk polycondensation at elevated temperatures. For the polycondensation in bulk the influence of catalyst and of temperature on the number-average molecular weight was studied. At a temperature of 170 °C the poly-condensation process is followed by a ring-closing depolymerisation and the formation of cyclic ester amides. Ten- to fourteen-membered cyclic ester amides were obtained and characterized. The ring-opening polymerisation of these cyclic ester amides leads, in a controlled mode, to poly(ester amide)s. The interconversion of poly(ester amide)s and cyclic ester amides by ring-closing depolymerisation and ring-opening polymerisation is possible. The poly(ester amide)s from adipic anhydride and homologous α, ω-amino alcohols H 2 N-(CH 2 ) x -OH (x = 2-6) are semicrystalline materials, their melting points show the odd/even effect observed for [n]-polyamides and [n]-polyurethanes.

Biodegradable ABA triblock copolymers with poly(ethylene oxide) and poly(glycolic acid-valine) blocks were synthesized via ring-opening polymerization of cyclo(glycolic acid-valine) using Ca-alcoholates of hydroxytelechelic PEO as the initiator. The L-valine residue racemized during copolymerization of cyclo(glycolic acid-valine). The crystallization of the block copolymers decreases with decreasing PEO content in the triblock copolymers and with increasing length of the poly(glycolic acid-valine) block. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2916–2919, 2002

Density functional (DFT) calculations were carried out on the B3LYP level of theory on bridged and unbridged cationic zirconocene complexes to clarify why unbridged [Zr(Cp)2(Me)(thf)][BPh4] is not active in the polymerization of methyl methacrylate (MMA), whereas [Zr{(Cp)2CMe2}(Me)(thf)][BPh4] polymerizes MMA readily, as we showed experimentally. It is shown, that the initial step of the polymerizationthe transfer of the metallocene bound methyl group to the first MMA moleculeis endothermic for [Zr(Cp)2(Me)(MMA)]+ but exothermic for [Zr{(Cp)2CMe2}(Me)(MMA)]+. Furthermoreand more importantthe activation energy is higher for the reaction of the unbridged compound compared to the activation energy of the bridged compound. From these results and an estimation of the rate constants it follows that in the temperature range investigated experimentally (−30 to +30 °C) either the endothermic product is not formed at all and/or the reversed reaction to the reactant is much faster than the reaction with the next MMA...

Monofunctional poly(ethylene oxide) macroinitiators with a molecular weight of 2000, 5000, 10 000, 20 000 and bifunctional poly(ethylene oxide) macroinitiators with a molecular weight of 20 000 were used for the atom transfer radical polymerisation (ATRP) of hydroxyethyl methacrylate (HEMA) in ethylene glycol as a solvent. The polymerisation proceeds in a controlled way up to high conversions. The molecular weight of the obtained copolymers increases linearly with conversion. A high rate of polymerisation was observed for the ATRP of HEMA. The effect of the poly(ethylene oxide) moiety on the course of the reaction is limited to solvating effects. The surface analysis of poly(ethylene oxide)/poly(hydroxyethyl methacrylate) block copolymers by means of atomic force microscopy in tapping mode using phase imaging shows phase separated domains with characteristic features related to the volume fraction of the respective blocks.

Full Paper: Chemical modification of recombinant hirudin (r-hirudin) is necessary whenever surface-confinement to a biomaterial or biotinylation for subsequent conjugation with carriers is intended. Here, we report a modification strategy that permits chemical discrimination between r-hirudin's amino groups and preserves its thrombin inhibitor activity. By reaction with Msc-ONSu, protective groups were successively introduced in r-hirudin yielding four derivatives (Msc) x -hirudin (1 ≤ x ≤ 4) and pure fractions were isolated by ion exchange chromatography. Structure-function relationships were studied for all derivatives and revealed a decrease in activity of more than 90% as compared to unprotected r-hirduin. MALDI-TOF MS was used to determine the locations of the Msc groups. Furthermore, evidence was provided that r-hirudin's N-terminal amino group is highly important for its anti-thrombin activity. Selective modification of the lysine residues which maintained the free N-terminal amino group preserved the anti-thrombin activity of r-hirudin even after biotinylation and subsequent linkage to streptavidin or confinement to a polymer surface. Anti-thrombin activity of r-hirudin derivatives and r-hirudin as determined by amidolytic assay. Low extinction expresses high anti-thrombin activity of the r-hirudin derivatives.

Monofunctional PEO-macroinitiators (mPEO-F) were prepared from monohydroxyfunctional poly(ethylene oxide)s and 2-chloro-2-phenylacetylchloride. In order to synthesise poly(ethylene oxide)-block-poly(styrene) (PEO-b-PS) the macroinitiators were applied to the atom transfer radical polymerisation (ATRP) of styrene in the bulk. Well-defined block copolymers were obtained with predetermined molecular weight and narrow molecular weight distribution. Kinetic aspects of ATRP of styrene depending on the molecular weight of the macroinitiator are discussed. Surface analysis by means of atomic force microscopy in tapping mode using phase imaging reveals characteristic morphologies as a function of the volume fraction of PEO. The higher the PEO content the more PEO is found at the polymer/air interface. The preparation of the samples has a main impact on the observed morphology. The polymer films are hygroscopic and alter their morphology being exposed to air.

The polymerization of 1-hexene with the catalyst systems Cp 2 ZrCl 2 /MAO and Me 2 SiInd 2 ZrCl 2 /MAO is investigated in order to elucidate the nature of the active species in zieconocene/MAO catalyzed polymerizations. Varying monomer concentration and monomer conversion does not result in any unexpected behavior. However, changing catalyst and cocatalyst concentration leads to broadened, or even bimodal, molecular weight distributions under certain reaction conditions. These results may be interpreted in terms of a coexistence of two active species with different rates of propagation and of termination.

Ring-opening polymerisation is a mean to transform stepwise polymerisation reactions into chain reactions, the cyclic monomers being prepared by intramolecular condensation of open chain bifunctional monomers [1,2]. The ring-opening polymerisation is initiated most conveniently with ionic initiators which may be of macromolecular structure. Thus, block- -and graft copolymers are obtained. To synthesize well-defined architectures the elementary reactions of the ring-opening polymerisation have to be known in detail since there are various unusual features. Six-membered cyclic carbonates, in particular 2,2-dimethyltrimethylene carbonate (DTC), are polymerised anionically and the copolymerisation of different cyclic carbonates results in random copolymers [3-14]. The copolymerisation of cyclic carbonates with e-caprolactone (ECL) yields block copolymers with a tapered structure between the two blocks showing a compositional gradient from DTC-rich to ECL-rich segments [6,10,15,16]. While in both cases the active species is an alcoholate, the active species in the anionic ring-opening polymerisation of pivalolactone (PVL) is a carboxylate; thus, copolymerisation with DTC yields block copolymers since the carboxylate once formed is unable to attack the cyclic carbonate [16,17].

The copolymerization of 5-[(4-fluorophenyl)sulfonyl]-2-fluorobenzoic acid with bis(4-hydroxyphenyl)sulfone in 1,1-dioxothiolane with sodium carbonate as a base results in carboxylated poly(ether sulfone)s. The polycondensation polymerization, however, is associated with partial decarboxylation. Conversely, the copolymerization of 2,5-dihydroxybenzoic acid (hydroquinone carboxylic acid) with bis(4-fluorophenyl)sulfone under identical conditions results in a poly(ether ether sulfone) with quantitative decarboxylation.

The ring-opening polymerization of dimethylene urethane (3) (systematic name: 2-oxo-1,3-oxazolidine) with methyl trifluoromethane sulfonate as the initiator is inefficient. It was shown that equimolar amounts of dimethylene urethane and trifluoromethane sulfonate result in the expected active species - 2-methoxy-4,5-dihydro-1,3-oxazolium trifluoromethane sulfonate (5a) -: propagation, however, does not occur. Poly(dimethylene urethane) (4), was obtained by means of polycondensation of a linear monomer, i.e., 2-(2-phenoxycarbonylimino-1-ethoxycarbonylimino)-ethanol (9). This [3]-polyurethane is a semicrystalline material with a melting point of 200.7 °C. Heating above its melting point leads to dimethylene urethane by ring-closing depolymerization. The thermodynamical data support the experimental results with respect to the polymerization / depolymerization equilibrium.

In an adiabatic vacuum calorimeter thetemperature dependence of the heat capacity C p 0 of crystalline 2-methyltrimethylene urethane (MTU; systematic name: 5-methylperhydro-1,3-oxazin-2-one) and of amorphous poly(2-methyltrimethylene urethane) 5PMTU; systematic name: poly(5-methyl-2-oxo-1-oxa-3-azahexamethylene)] was studied between 6 and 335 K with an uncertainty of about 0.2%. In a calorimeter with a static bomb and an isothermal shiled the energies of combustion ΔU comb of the monomer and of the polymer were measured. From the experimental data the thermodynamic functions C p 0 (T), H 0 (T)-H 0 (0), S 0 (T), G 0 (T)-H°(0) were calculated in the range of 0 to 340 K, and enthalpies of combustion ΔH 0 comb and thermodynamic parameters of formation ΔH t 0 , ΔS t 0 , ΔG t 0 of the substances studied were estimated at T = 298.15 K and standard pressure. The configurational entropy S 0 conf of the polymer was estimated. The results were used to calculate the thermodynamic characteristics of MTU polymerization in bulk (ΔH 0 pol , ΔS 0 pol , ΔG 0 pol ) with ring-opening and formation of linear PMTU in the range of 0 to 340 K.

Full Paper: Four different types of polydepsipeptide-polyether block copolymers were synthesized via ring-opening polymerization of 3(S)-sec-butylmorpholine-2,5-dione (BMD) in the presence of hydroxytelechelic poly-(ethylene oxide) (PEO) with stannous octoate as a catalyst. The polymers were an AB block copolymer, an ABA block copolymer, an (A) 2 B star shaped copolymer and an (A) 2 B(A) 2 copolymer, where A is a poly[3(S)-sec-butyl-morpholine-2,5-dione] (PBMD) and B a poly(ethylene oxide) block. The molar ratio of BMD to PEO was varied to obtain copolymers with different weight fractions of PBMD blocks ranging from 59.8 to 96.7 wt.-%, The crystallinity of the PEO phase in the copolymers decreases in the following order: AB > (A) 2 B > ABA > (A) 2 B(A) 2 . The static contact angle θ decreases with increasing PEO content in the block copolymers.

The cationic ring-opening polymerization of tetramethylene urethane (TeU; systematic name, hexahydro-1,3-oxazepin-2-one, (1)) in the melt at 67 °C with methyl trifluoromethanesulfonate (TfOMe) as the initiator yields poly(tetramethylene urethane) (poly(TeU), (6)) with a regular microstructure. This [5]-polyurethane is a semicrystalline material with a Tg of 47 °C and a Tm of 209.5 °C. The reaction proceeds via an active chain end mechanism with a protonated cyclic endo iminocarbonate as the active species. The propagation step involves nucleophilic attack of the carbonyl oxygen of the monomer at the endocyclic methylene group adjacent to the oxygen atom of the active species. The propagation rate constant was 4.2 × 10-4 L·mol-1·s-1. The polymerization of tetramethylene urethane is accompanied by termination reactions; however, transfer reactions and backbiting reactions were not observed. Thermodynamic data support the ring-opening mechanism and the thermal stability (lack of ring-closing depolymerization...

We report the stereospecific polymerization of methyl methacrylate (MMA) with single-component cationic zirconocene catalysts. The complexes Me2CCpIndZrMe(thf)+BPh4- (1) and Me2CCp2ZrMe(thf)+BPh4- (2) are active catalysts for the polymerization of MMA, in remarkable contrast to other cationic zirconocenes. While 1 yields highly isotactic poly(methyl methacrylate) (PMMA), 2 is syndiospecific at low temperatures. This is the first example for a rational control of PMMA microstructure via catalyst symmetry. Polymerization kinetics and stereospecificity control in MMA polymerization with 1 and 2 are discussed. On the basis of the experimental data, a possible polymerization mechanism is proposed.

Aliphatic [n]-polyurethanes were obtained by catalytic polycondensation of suitable α-hydroxy-ω-O-phenyl urethanes (III). 1H and 13C NMR analyses of the resulting [n]-polyurethanes (3 a–g) show a uniform microstructure consisting of urethane groups only, and with carbonate and urea groups being absent. The [n]-polyurethanes with linear alkylidene moieties (3 a–e) are highly crystalline materials, their melting points show the same odd-even effect as was observed for [n]-polyamides. The [n]-polyurethanes with branched alkylidene groups (3 f, g) show lower crystallinity (3 g) or are amorphous (3 f) materials. Upon heating, the [3]- and all the [4]-polyurethanes (3 a and 3 b, f, g) result in the corresponding cyclic urethanes by ring-closing depolymerization.

In an adiabatic vacuum calorimeter, the temperature dependence of the heat capacity C O p of dimethylene urethane (DMU) and poly(dimethylene urethane) (PDMU) was studied between 6 and 335 K with an uncertainty of about 0.2%. In a calorimeter with a static bomb and an isothermal shield, the energies of ΔU comb of the monomer and of the polymer were measured. From the experimental data, the thermodynamic functions C o p (T), H 0 (T) - H 0 (0), S 0 (T), G 0 (T) - H 0 (0) were calculated in the range from to 335 K, and enthalpies of combustion ΔH 0 comb and thermochemical parameters of formation ΔH 0 f , ΔS 0 f , ΔG 0 f of the substances studied were estimated at T = 298.15 K and standard pressure. The results were used to calculate the thermodynamic characteristics of the ring-opening polymerization of DMU in bulk (ΔH 0 pol , ΔS o pol , ΔG 0 pol ) with formation of linear poly(dimethylene urethane) in the range from 0 to 330 K. In addition, the ceiling temperature T 0 ceil was determined.

The cationic bridged zirconocene complex, [iPr(Cp)(InD)Zr(Me)(THF)][BPh 4 ] (1-BPh 4 ) was synthesized. Polymerization of methyl methacrylate with 1-BPh 4 in CH 2 Cl 2 at temperatures between -20 and 20°C led to the formation of isotactic poly(mehtyl methacrylate). The low polydispersity index of the polymer obtained and a successfull two step polymerization of methyl methacrylate with 1-BPh 4 are hints towards a living polymerization mechanism. 1 H and 13 C NMR analysis revealed an enantiomorphic site-controlled mechanism for the formation of isotactic poly(methyl methacrylate).

Hydroxy-telechelic poly(methyl methacrylate)s of molecular weights below 5000 were obtained by atom transfer radical polymerization (ATRP) of methyl methacrylate followed by end-capping with allyl alcohol via atom transfer radical addition (ATRA). As initiators for the ATRP, monofunctional initiators with an additional hydroxy group in the molecule or bifunctional initiators were employed. The successful synthesis of the hydroxy-telechelic PMMA was proved by determination of their molecular weight using MALDI-TOF-MS. The efficiency of the end-capping reaction was determined by 1H NMR spectroscopy using the allyl N-(4-tolyl)carbamate as end-capping agent. Block copolymers comprising a poly(ethylene oxide) (PEO) block and a poly(methyl methacrylate) (PMMA) block were prepared by ATRP using a macroinitiator on the PEO basis. The dormant species of the macroinitiator consists of the phenyl chloroacetate moiety which shows a high rate of initiation. The successful synthesis of the poly(ethylene oxide)-block-poly(methyl methacrylate) was proved by 1H NMR spectroscopy; the ratios of EO/MMA repeating units in the feed and the copolymer were nearly equal.

This review covers most of the authors' work on ring-opening polymerization and copolymerization of heterocyclic monomers during the time of their cooperation since 1985. The mechanistic aspects of anionic ring opening polymerization of cyclic carbonates with a variety of functional groups are described first. By sequential polymerization of first styrene, methyl methacrylate or suitable heterocyclic monomers and then secondly a cyclic carbonate, the site transformation is highlighted. The influence of the chemical nature of macroinitiators with identical active sites on the course of polymerization of cyclic carbonates was studied for poly(ethylene oxide), poly(tetrahydrofuran), and poly(dimethylsiloxane) macroinitiators. For the copolymerization of cyclic carbonates with lactones and lactide the dependence of the polymer microstructure on the polymerization conditions is discussed on the basis of the copolymerization mechanism. The copolymerization of cyclic carbonates with e-caprolactam and with tetramethylene urea results in an alternating copolymer, i. e. a poly(ester urethane) and an [m, n]-polyurethane, respectively, the key step being the insertion of the lactam or the cyclic urea into the carbonate chain. The cationic ring opening polymerization of cyclic six and seven membered carbamates leading to [4]- and [5]-polyurethane with uniform microstructure is reported with respect to kinetic, mechanistic, and thermodynamic aspects. This new access to [n]-polyurethanes by a chain growth reaction allows the synthesis of well defined polymer architectures with polyurethane sequences. Sequential polymerization of tetrahydrofuran and the cyclic carbamate with mono- and bifunctional initiators leads to the respective A–B and B–A–B block copolymers. Site transformation from the oxonium to the immonium active species is the key step in the polymerization mechanism. Finally, mechanistic aspects of the ring-opening polymerization of cyclic ester-amides are presented.

The atom transfer radical polymerization (ATRP) of styrene and methyl methacrylate with α,α-dichlorotoluence (DCT) as initiator results in the respective chlorotelechelic polymers. From a kinetic point of view, however, the polymerization of styrene and methyl methacrylate show a different behavior: for the polymerization of styrene DCT is a bifunctional, for the polymerization of methyl methacrylate it is a monofunctional initiator.

ABA type block copolymers with poly[3(S)-isobutylmorpholine-2,5-dione] (PIBMD, A) and poly(ethylene oxide) (M n = 6000, PEO, B) blocks, PIBMD-b-PEO-b-PIBMD, were synthesized via ring-opening polymerization of 3(S)-isobutylmorpholine-2,5-dione in the presence of hydroxytelechelic poly(ethylene oxide) with stannous octoate as a catalyst. M n of the resulting copolymers increases with increasing 3(S)-isobutylmorpholine-2,5-dione content in the feed at constant mole ratio of monomer (M) to catalyst (C) (M/C = 125). No racemization of the leucine residue takes place during both homopolymerization of IBMD and polymerization of IBMD in the presence of PEO and Sn(Oct) 2 . The melting temperature of the PIBMD segments in the block copolymers depends on the length of the PIBMD blocks. The melting temperature of the PEO blocks is lower than that of the homopolymer, and the crystallinity of the PEO block decreases with increasing length of the PIBMD blocks. The PIBMD block crystallizes first upon cooling from the melt. This leads to only imperfect crystallization or no crystallization of the PEO blocks.

New alternating poly(amide-ester)s derived from β-hydroxy acids and α-amino acids 3a,b or e-aminocaproic acid 4a-c were prepared. Two approaches were considered: (i) polycondensation of N-(β-hydroxyacyl)-amino acids la,b and 2b,c and (ii) ring-opening polymerization of cyclic amide-esters 5a-c and 6a-c. For all the linear precursors polycondensation reactions result in oligomers with number average molecular weights lower than 5000. The ring-opening polymerization of the cyclic precursors is substrate specific and is sensitive to changes in the polymerization conditions. For N-(3-hydroxybutyroyl)-e-aminocaproic acid lactone [c(3HB-eAC); 5b] (IUPAC nomenclature: 2-methyl-5-aza-1-oxa-cycloundecan-4, 11-dione) bulk and solution polymerizations result in oligomers with an alternating ester amide microstructure. Polymerization of N-(3-hydroxypropionyl)-e-aminocaproic acid lactone [c(3HP-eAC); 5a] (IUPAC nomenclature: 5-aza-1-oxa-cycloundecan-4-11-dione) in dimethylformamide solution and with Bu 2 Sn(OMe) 2 as initiator high molecular weight linear, semicrystalline polymers were obtained (T m = 145.9°C). Polymerization of N-(hydroxypivaloyl)-e-aminocaproic acid lactone [c(HPv-eAC); 5c] (IUPAC nomenclature: 3,3-dimethyl-5-aza-1-oxa-cycloundecan-4-11-dione) in bulk results in amorphous alternating poly(amide-ester)s with cyclic structure (Tg = 6.8°C). The fourteen membered cyclo(diamide-diester)s 6a-c (IUPAC nomenclatures:: 4,11-diaza-1,8-dioxa-cyclotetradecan-2,5,9,12-tetraone (6a), 7,14 dimethyl-4,11-diaza-1,8-dioxa-cyclotetradecan-2,5,9,12-tetraone (6b), 3,10-dimethyl-4,11-diaza-1,8-dioxa-cyclotetradecan-2,5,9,12-tetraone (6c) based on β-hydroxy acids and α-aminoacids could not be polymerized.

The polymerization of N-(hydroxypivaloyl)-e-aminocaproic acid lactone [c(HPv-eAC), 1] a) in bulk at 170°C was found to result in a high molecular weight fraction with M n 20000 (GPC in DMAC, calibration with polystyrene) and an oligomeric fraction depending on the initiator employed. Separation of the polymeric fraction is unsuccessful by using fractional precipitation, however, by means of dialysis a polymeric fraction with a polydispersity index Q < 1.5 was isolated. NMR spectroscopic analysis of the polymer reveals a strictly alternating microstructure with hydroxypivaloyl and e-aminocaproyl repeating units. Regardless of the initiator used no endgroups were detected in both the polymeric and the oligomeric fraction. Even more, GPC analysis of the well resolved oligomeric series reveals the same elution volumes for a given oligomer, regardless of the initiator used. These results led us to conclude that poly(hydroxypivalate-alt-aminocaproate) has cyclic constitution. The glass transition temperature of the semicrystalline polymer is T g = 6,6°C, the melting point T m = 66,6°C. A kinetic study of the polymerization reveals that the monomer conversion does not follow a pseudo first order rate law even at very low conversions. A mechanism for the initiation and the polymerization is discussed.

In an adiabatic vacuum calorimeter the temperature dependence of the heat capacity C 0 p of tetramethylene urethane (TMU) (2-oxo-hexahydro-1,3-oxazepine) and poly(tetramethylene urethane) (PTMU) was studied between 4.3 and 300 K with an uncertainty of about 0.2%. In a calorimeter with a static bomb and an isothermal shield the energies of combustion ΔU comb of the monomer and the polymer were measured. From the experimental data the thermodynamic functions C 0 p , H 0 (T)-H 0 (0), S 0 (T), G 0 (T)-H 0 (0) were calculated in the range of 0 to 300 K, and enthalpies of combustion ΔH 0 comb and thermochemical parameters of formation ΔH 0 f , ΔS 0 f , ΔG 0 f of TMU and PTMU were estimated at T= 298.15 K and standard pressure. The results obtained were used to calculate the thermodynamic characteristics of TMU polymerization in bulk (ΔH 0 pol , ΔS 0 pol , ΔG 0 pol with opening of the seven-membered ring and formation of the linear polymer PTMU, in the range of 0 to 300 K. It was found that the values of the standard Gibbs function of the process (ΔG 0 pol = (-41)-(-42) kJ.mol -1 ) are always negative and do not substantially depend upon temperature in the whole temperature interval studied. This implies that the equilibrium TMU ⇄ PTMU is far on the side of the polymer. The upper (ceiling) limiting temperature of TMU polymerization is T 0 ceil > 1 000 K.

The atom transfer radical polymerization (ATRP) of styrene and methyl methacrylate with differently substituted model and macroinitiators was performed, in order to evaluate qualitatively the structural features which affect the efficiency of the initiation step. It was found that substituents which stabilize radicals enhance the dissociation of the halogen atom and lead to high initiation efficiencies of the model initiators and macroinitiators. The phenyl group and the oxycarbonyl group result in the efficient initiators 1a and 3a for the initiation of both styrene and methyl methacrylate. Further, it was shown that the poly(ethylene oxide) moiety in the initiator, because of its low solubility, e.g. in styrene/poly(styrene) mixtures, leads to phase separation that effects the reactivity of the initiating group.

Lipase-catalyzed ring-opening bulk polymerizations of 3(S)-isopropylmorpholine-2,5-dione (IPMD) were investigated. Selected commercial lipases were screened as catalysts for IPMD polymerization at 100°C. Polymerizations catalyzed with lipases PPL, PS, and CR result in IPMD conversions of about 50%, and in molecular weights of the products ranging from 3500 to 17500. Poly(3-isopropylmorpholine-2,5-dione) has a carboxylic acid group at one end and a hydroxyl group at the other end. During the polymerization, racemization of the valine residue takes place. Lipase PPL was selected for further studies. The apparent rate of polymerization increases with PPL concentration and polymerization time. When the PPL concentration is 5 wt.-% and 10 wt.-% with respect to the monomer, a conversion of about 70% is reached after 5 d and 7 d, respectively, while for PPL concentrations of 1 wt.-% and 0.5 wt.-% the conversion is less than 15% even after 11 d. High concentrations of PPL (10 wt.-%) result in high M n values (

Departamento de Ingenieri´a Qui´mica, Universidad Polite´cnica de Catalun˜a,E. T. S. de Ingenieros Industriales, Diagonal 647, 08028 Barcelona, Spain(Received: October 2, 1998; revised: November 26, 1998)SUMMARY: Two heterotelechelic poly(ethylene glycol)s were synthezised by end group modification of a-hydro-x-hydroxy-poly(oxyethylene) (PEG). The first reaction route starts from heterobifunctionala-hydro-x-octadecanoyloxy-poly(oxyethylene) (400) and comprises the synthesis ofa-hydro-x-carboxymethoxy-poly(oxyethylene). The second pathway starts from homotelechelic PEG(400) and leads to a-(2-propenyl)-x-carboxymethylthio-poly(oxyethylene). Purification of the desired products was accomplished by means ofion exchange chromatography on DEAE Sephadex. PEG derivatives were characterized by means of NMR,IR, HPLC and GPC. MALDI-TOF-MS recorded in the reflectron mode served as a fine method that providesinformation on chemical composition as well as molecular weight.

The synthesis of cyclo(amide-ester)s based on α-amino acids and e-aminocaproic acid in combination with β-hydroxy acids was achieved by ring-expansion reactions. Three different approaches were followed: (i) According to Shemyakin, e-caprolactam or diketopiperazines were acylated with differently substituted β-benzyloxyacyl chlorides. Removal of the protecting group by hydrogenolysis over a palladium catalyst results in hydroxyacyl incorporation into the e-caprolactam or the diketopiperazine ring and formation of the eleven-membered cyclo(amide-ester)s 1 a–c or the fourteen-membered cyclo(diamide-diester)s 2 a–c. (ii) Alternatively, the cyclo(amide-ester)s 1 a–c were obtained via intramolecular nucleophilic substitution of the halogen atom in N-(3-halogenoacyl)-e-caprolactam by the oxygen atom of the lactam unit followed by reaction with water. (iii) Finally, results on the intramolecular Michael addition in N-(acryloyl)- and N-(crotonyl)-e-caprolactams are presented. The Michael addition was induced by the nucleophilic addition of the lactam oxygen atom to the CC double bond followed by a sequence of reactions, which leads to the cyclo(amide-ester)s 1 a, b.

N-(3-Hydroxypropionyl)-e-aminocaproic acid lactone [c(3HP-eAC), 1] was polymerized in dimethylformamide solution with dibutyldimethoxytin as initiator at 100°C. A strictly alternating poly(amide-ester), poly(3-hydroxypropionate-alt-e-aminocaproate), was obtained, a semicrystalline polymer with a melting point of 145.9°C. The polymerization was found to proceed via a tin alcoholate active species as was deduced from 'H NMR endgroup analysis of the polymer quenched with water. In addition, the active chain ends were quenched with diphenyl chlorophosphate and analyzed by means of 31 P NMR spectroscopy; a diphenylalkyl phosphate was identified, proving the alcoholate active site. The polymerization follows a pseudo-first order rate law only at low conversions. However, a linear dependence of the number-average molecular weight on conversion was found, proving that transfer reactions play a minor part throughout the polymerization process. A mechanism for the initiation and propagation is proposed.

Di- and triblock copolymers with tetramethyleneoxy and trimethylene urethane repeating units were prepared by sequential polymerization of tetrahydrofuran (THF) and trimethylene urethane (TU) with the monofunctional initiator methyl trifluoromethanesulfonate (TfOMe) and the bifunctional initiator trifluoromethanesulfonic acid anhydride (TfOTf), respectively. The block copolymers obtained after purification show a uniform A-B resp. A-B-A microstructure as was deduced from NMR and GPC analyses. The block copolymers are semicrystalline materials with distinct melting points of the poly(THF) and the poly(TU) domains.

A blend of polycaprolactone (PCL) and poly(2,2-dimethyltrimethylene carbonate) (PDTC) containing catalytic amounts of dibutyltin dimethoxide was prepared from solution. The blend was then subjected to melt-mixing at 200°C and samples were taken after different times. According to thermal analysis data, with the increase of reaction time a gradual loss of the crystallizability of the blend components is observed, and after 70 min at 200°C the system becomes completely amorphous. 13 C NMR data suggest that the loss of crystallizability of the blend is accompanied by an abrupt decrease in PCL and PDTC sequence lengths reaching after 70 min at 200°C an average length of about two repeating units each. These effects are explained by transesterification reactions between the lactone and carbonate units.