Synthesis and characterization of (star polystyrene)-block-(polyisoprene)-block-(star polystyrene) copolymers

A (star polystyrene)-block-(linear polyisoprene)-block-(star polystyrene) copolymer, (S)_nI(S)_n, was prepared. The star polystyrene was produced via anionic polymerization of polystyrene macromonomers each containing an unsaturated double bond (vinyl) at the chain end. This vinyl-terminated polystyrene macromonomer (SSTM) was obtained beforehand via the synthesis of a living polystyrene using alkyllithium and the termination with p-chloromethylstyrene (PCMS). The living site in the core of the star polystyrene enabled the construction of the succeeding polyisoprene block resulting in the living (star polystyrene)-block-(linear polyisoprene) copolymer, (S)_nI. This living diblock copolymer was then coupled with 1,2-dibromoethane (DBE) to form the well-defined (S)_nI(S)_n. Compared to a linear polystyrene-block-polyisoprene-block-polystyrene, SIS, with the same molecular weight, (S)_nI(S)_n had a higher T_g and exhibited a lamellae-forming phase separation in conjunction with many dislocation defects. The thermal stability appeared independent of the molecular structure, and the radius of gyration and viscosity of (S)_nI(S)_n were much smaller than SIS.     

Synthesis of poly(ɛ-caprolactone-b-isobutylene) diblock copolymer and poly(ɛ-caprolactone-b-isobutylene-b-ɛ-caprolactone) triblock copolymer

Summary Poly(isobutylene-b-ɛ-caprolactone) diblock and poly(ɛ-caprolactone-b-isobutylene-b-ɛ-caprolactone) triblock copolymers have been prepared and characterized. The synthesis involved the living cationic polymerization of IB, followed by capping with 1,1-diphenylethylene or 1,1-p-ditolylethylene and end-quenching with 1-methoxy-1-trimethylsiloxy-2-methyl-propene to yield methoxycarbonyl functional PIB. Hydroxyl end-functional PIB polymers were quantitatively obtained by the subsequent reduction of methoxycarbonyl end-functional PIB with LiAlH₄. The structure of hydroxyl end-functional PIBs was confirmed by ¹H NMR and IR spectroscopy. Poly(ɛ-caprolactone-b-isobutylene) diblock copolymers and poly(ɛ-caprolactone-b-isobutylene-b-ɛ-caprolactone) triblock copolymers were synthesized by the living cationic ring-opening polymerization of ɛ-caprolactone with hydroxyl end-functional PIB as macroinitiator in the presence of HCl•Et₂O via the “activated monomer mechanism”. The block copolymers exhibited close to theoretical M_ns and narrow molecular weight distributions. Received: 30 January 2002/Revised version: 19 February 2002/ Accepted: 19 February 2002     

Poly(methyl methacrylate)-block-polysulfide-block-poly(methyl methacrylate) copolymers obtained by free-radical polymerization combined with oxidative coupling

Summary Poly(methyl methacrylate)-block-polysulfide-block-poly(methyl methacrylate) copolymers were synthesized for the first time through a new method involving the free radical polymerization of MMA in the presence of a thiocol oligomer as a chain transfer agent, followed by chemical oxidation of the remaining SH end-groups. The chain transfer constant of the SH end-groups of the thiocol was estimated from the rate of consumption of the thiol groups versus the rate of consumption of the monomer (C_T=0.67). The triblock copolymers synthesized were characterized by SEC and ¹H NMR measurements.     

Triblock and star-block copolymers of N-(2-hydroxypropyl)methacrylamide or N-vinyl-2-pyrrolidone and D,L-lactide: synthesis and self-assembling properties in water

Novel A-B-A triblock and star-block amphiphilic copolymers, i.e. poly(N-(2-hydroxypropyl)methacrylamide)-block-poly(D,L-lactide)-block-poly(N-(2-hydroxypropyl)metha-crylamide), poly(N-vinyl-2-pyrrolidone)-block-poly(D,L-lactide)-block-poly(N-vinyl-2-pyrrolidone), star-poly(D,L-lactide)-block-poly(N-(2-hydroxypropyl)methacrylamide) and star-poly(D,L-lactide)-block-poly(N-vinylpyrrolidone), were synthesized and characterized. These polymers were prepared by free radical polymerization of N-(2-hydroxypropyl)methacrylamide and N-vinyl-2-pyrrolidone in the presence of either poly(D,L-lactide) dithiol or star-poly(D,L-lactide) tetrakis-thiol, both biodegradable macromolecular chain-transferring agents. All copolymers self-assembled in aqueous solution to form supramolecular aggregates of 20–180 nm in size. The critical aggregation concentration of the copolymers ranged from 5 to 24 mg/L, depending on their hydrophobicity. The partition equilibrium constant of pyrene in the hydrophobic core of micelles was between 0.71×10⁵ and 1.63×10⁵. The triblock copolymer micelles were loaded with two model poorly water-soluble drugs, namely, indomethacin (1.5–16.4% w/w) and paclitaxel (0.4–1.5% w/w), by a dialysis procedure. These triblock and star-block copolymers could prove useful as nanocarriers for the solubilization and delivery of hydrophobic drugs.     

Nitroxide‐terminated poly(styrene‐co‐diethyl fumarates) and derived block copolymers

Copolymerization of styrene (S) and diethyl fumarate (DEF) at 125°C in the presence of 2,2,6,6‐ tetramethylpiperidin‐1‐yloxyl radical (TEMPO) and initiated with a thermal initiator, 2,2′‐azobisisobutyronitrile (AIBN), was studied. The molar fraction of DEF in the feed, F_DEF, varied within 0.1–0.9. An azeotropic composition, (F_DEF)_A = 0.38, was found for the copolymerization under study. At F_DEF = 0.1–0.4, a quasi‐living process was observed, transforming to a retarded conventional radical copolymerization at a higher content of DEF in the initial mixtures. The obtained TEMPO‐terminated S‐DEF copolymers were used to initiate polymerization of styrene. Poly(styrene‐ co‐diethyl fumarate)‐block‐polystyrene copolymers were prepared with molecular weight distributions depending on the amount of inactive polymer chains in macroinitiators, as indicated by size‐exclusion chromatography. A limited miscibility of the blocks in the synthesized block copolymers was revealed by using differential scanning calorimetry. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2432–2439, 2002     

Synthesis of poly(ethylene oxide)-block-poly(methyl methacrylate)-block-polystyrene triblock copolymers by two-step atom transfer radical polymerization

The synthesis of ABC triblock copolymer poly(ethylene oxide)-block-poly(methyl methacrylate)-block-polystyrene (PEO-b-PMMA-b-PS) via atom transfer radical polymerization (ATRP) is reported. First, a PEO-Br macroinitiator was synthesized by esterification of PEO with 2-bromoisobutyryl bromide, which was subsequently used in the preparation of halo-terminated poly(ethylene oxide)-block-poly(methyl methacrylate) (PEO-b-PMMA) diblock copolymers under ATRP conditions. Then PEO-b-PMMA-b-PS triblock copolymer was synthesized by ATRP of styrene using PEO-b-PMMA as a macroinitiator. The structures and molecular characteristics of the PEO-b-PMMA-b-PS triblock copolymers were studied by FT-IR, GPC and ¹H NMR.     

Synthesis of poly(fluorinated styrene)‐block‐poly(ethylene oxide) amphiphilic copolymers via atom transfer radical polymerization: potential application as paper coating materials

BACKGROUND: The surface of a substrate which comprises a fibrous material is brought into contact with a type of amphiphilic block copolymer which comprises hydrophilic/hydrophobic polymeric blocks. These amphiphilic copolymers have been synthesized by atom transfer radical polymerization (ATRP) technique. The atom transfer radical polymerization of poly(2,3,4,5,6‐pentafluorostyrene)‐block‐poly(ethylene oxide) (PFS‐b‐PEO) copolymers (di‐ and triblock structures) with various ranges of PEO molecular weights was initiated by a PEO chloro‐telechelic macroinitiator. The polymerization, carried out in bulk and catalysed by copper(I) chloride in the presence of 2,2′‐bipyridine ligand, led to A–B–A amphiphilic triblock and A–B amphiphilic diblock structures. RESULTS: With most of the macroinitiators, the living nature of the polymerizations led to block copolymers with narrow molecular weight distributions (1.09 < M_w/M_n < 1.33) and well‐controlled molecular structures. These block copolymers turned out to be water‐soluble through adjustment of the PEO block content (>90 wt%). Of all the block copolymers synthesized, PFS‐b‐PEO(10k)‐b‐PFS containing 10 wt% PFS was found to retard water absorption considerably. CONCLUSION: The printability of paper treated with the copolymers was evaluated with contact angle measurements and felt pen tests. The adsorption of such copolymers at the solid/liquid interface is relevant to the wetting and spreading of liquids on hydrophobic/hydrophilic surfaces. Copyright © 2009 Society of Chemical Industry     

Synthesis of poly [(methylsi1oxane)-co-(dimethylsilazane)] copolymers as precursors of ceramic materials

Summary A series of new crosslinked poly[(methylsiloxane)-co-(dimethylsilazane)] copolymers were synthesized by cationic ring opening polymerization of the cyclic monomers 1,3,5,7 – tetramethylcyclotetrasiloxane and 2,2,4,4,6,6 – hexamethylcyclotrisilazane. These copolymers contain different concentrations of methylsiloxane and silazane co-monomer units. The thermal stability is strongly related to the concentration of methylsiloxane co-units in the copolymers. The weight loss curve of the copolymers lies in a temperature range between its two homopolymers. FT-IR studies are in good agreement with the proposed structure, either for the copolymers or for the residual powder ceramic obtained by pyrolysis. Two cured processes (thermal and UV) were used. The pyrolysis of the copolymers were carried out under argon atmosphere at 1200°C and in air at 1000 °C. Kinetic decomposition parameters of the copolymers such as a pre-exponential factor, the decomposition reaction orders and the activation energies were determined. The molecular weights were determined by osmometry. Received: 21 August 2002/Revised version: 20 February 2003/ Accepted: 21 February 2003 Correspondence to Mario Rodríguez-Baeza     

Synthesis and properties of conjugated copolymers having a tricarbonyl(arene)chromium and thiophene units in the main chain

Summary Palladium-catalyzed polymerization of η ⁶-(1,4-diethynylbenzene)tricarbonyl chromium (1) with 3-alkyl-2,5-dibromothiophene (2a-c) was carried out to give the corresponding alternating conjugated copolymers (5a-c) in good yields. The structures of the polymers were supported by ¹H NMR and IR spectra. The polymers obtained were soluble in common solvents such as THF, CH₂Cl₂, CHCl₃ and toluene. The molecular weights of the polymers were determined by GPC. Their thermal, optical and electrical properties were investigated in detail. Received: 18 March 2002 /Accepted: 1 April 2002     

Polyisobutylene based thermoplastic elastomers: VI. Poly(α-methylstyrene-b-isobutylene-b-α-methylstyrene) triblock copolymers by coupling of living poly (α-methylstyrene-b-isobutylene) diblock copolymers

Summary Poly(α-methylstyrene-b-isobutylene-b-α-methylstyrene) (PαMeSt-PIB-PαMePSt) triblock copolymers have been prepared via coupling of living diblock copolymers in a one pot procedure. The PαMeSt-PIB diblock copolymers were synthesized by living sequential cationic polymerization in methylcyclohexane (MeChx)/methylchloride (MeCl) solvent mixtures at −80 °C using BCl₃ for αMeSt polymerization and TiCl₄ for IB polymerization as coinitiators. The crossover efficiency, however, was only ∼57 %, due to intermolecular alkylation (indanyl ring formation) after the addition of TiCl₄. By modifying the PαMeSt end with a short segment of p-chloro-α-methylstyrene before IB addition the crossover efficiency was increased to 90 %. Coupling of the living block copolymers with 2,2-bis[4-(1-phenylethenyl)phenyl]propane (BDPEP) was rapid and gave ∼ 90 % efficiency. Received: 13 July 2000/Accepted: 3 August 2000     

Synthesis of poly(lactic acid-b-p-dioxanone) block copolymers from ring opening polymerization of p-dioxanone by poly(L-lactic acid) macroinitiators

Poly(lactic acid-b-p-dioxanone) block copolymers (P(LA-b-PDO)) were synthesized by ring-opening polymerization of p-dioxanone using poly(lactic acid) (PLA) with different molecular weights as macroinitiators in N₂ atmosphere. The copolymers were characterized by ¹H-NMR spectra. The thermal and crystalline behaviors and thermal stability of these copolymers were investigated by DSC, TGA and WAXD. The results indicated that the contents of each segment and the intrinsic viscosities affected the properties of copolymers obviously.     

Initiation system effects in the cationic copolymerization of tetrahydrofuran (THF)

Summary Macromonomeric peroxy initiator, poly tetrahydrofuran (poly-THF=inimer) were synthesized via cationic polymerization of THF by the mono- (t-BuBP) and tetra-bromo methyl benzoyl peroxides (BDBP)/ZnCl₂ initiating system. The macromonomers were characterized by ¹H-NMR, IR, and GPC techniques. Methyl methacrylate (MMA) polymerization initiated by poly-THF inimers at 80°C and different times in bulk gave crosslinked poly-THF-b-polymethyl methacrylate block copolymers. Swelling ratios of the crosslinked block copolymers obtained by taking in same amounts of poly-THF inimer and MMA monomer in CHCl₃ were decreased versus time. It was compared the results obtained from t-BuBP-, BDBP-ZnCl₂ initiating systems with t-BuBP-, BDBP-AgSbF₆ initiating systems for THF monomer. Poly(THF-b-MMA) crosslinked block copolymers containing undecomposed peroxide groups initiated the thermal polymerization of styrene, S, were used to obtain poly(THF-b-MM_A-b-S) crosslinked multicomponent copolymers at 90°C. The crosslinked multi component copolymers were investigated sol-gel analysis and swelling ratios in CHCl₃. "Active" poly(THF-b-MM_A) having peroxygen group were used in the free radical coupling reaction of poly butadien (Poly Bd). Poly(THF-b-MM_A)-polybutadien crosslinked blend soluble graft copolymers were obtained. Received: 31 July 2001/Revised version: 16 June 2002/ Accepted: 5 July 2002     

Synthesis of biodegradable poly(trans-4-hydroxy-N-benzyloxycarbonyl-l-proline)-block-poly(ε-caprolactone) copolymers and micellar characterizations

A series of novel types of diblock poly(trans-4-hydroxy-N-benzyloxycarbonyl-l-proline)-block-poly(ε-caprolactone) (PHpr10-b-PCL) copolymers were synthesized by ring-opening polymerization from macroinitiator poly(trans-4-hydroxy-N-benzyloxycarbonyl-l-proline) (PHpr10) and ε-caprolactone (ε-CL) in the presence of organocatalyst dl-lactic acid (dl-LA). The M_n of the copolymers increased from 3370 to 19,040 g mol⁻¹ with the molar ratio (10-100) of ε-CL to PHpr10. These products were characterized by differential scanning calorimetry (DSC), ¹H NMR, and gel permeation chromatography. According to DSC, the glass-transition temperature (T_g) of the diblock copolymers depend on the molar ratio of monomer/initiator that were added. The hydrolytic degradation behavior of PHpr-b-PCLs was evaluated from weight-loss measurements and the change of M_n and M_w/M_n. With higher PCL contents resulted in a slower weight loss, while having a higher molecular weight loss percentage. Their micellar characteristics in an aqueous phase were investigated by fluorescence spectroscopy, transmission electron microscopy (TEM), and dynamic light scattering (DLS). The block copolymers formed micelles in the aqueous phase with critical micelle concentrations (CMCs) in the range of 1.33-4.22 mg L⁻¹. The micelles exhibited a spindly shape and showed a narrow monodisperse size distribution. The obtained micelles have a relatively high drug-loading of about 26% when the feed weight ratio of amitriptyline hydrochloride (AM) to polymer was 1/1. An increase of molecular weight and hydrophobic components in copolymers produced a higher CMC value and greater loading efficiencies were observed.     

Preparation and properties of poly(ethylene oxide) star polymers

Poly(ethylene oxide) (PEO) star polymers were prepared by anionic polymerization of methacryloyl chloride and glyceryl trimethacrylate with sec‐butyllithium in cyclohexane. The ensuing polymers were grafted with poly(ethylene glycol) of molecular weight 400. The final product was washed with methylene chloride and analyzed with infrared spectroscopy, differential scanning calorimetry, and thermogravimetry. Star polymers of PEO were also prepared by anionic polymerization of glycidol with sec‐butyllithium in cyclohexane. The initiator was chosen so as to yield a polymer of 10,000 molecular weight. The resulting polymers were analyzed by nuclear magnetic resonance, infrared spectroscopy, and thermogravimetry. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 322–327, 2003     

Synthesis of block copolymers of poly(p-dioxanone) block poly(tetrahydrofuran)

Summary The triblock copolymers of poly(p-dioxanone)-b-poly(tetrahydrofuran)-b-poly(p-dioxanone) were synthesized by ring-opening polymerization of p-dioxanone in the presence of dihydroxyl poly(tetrahydrofuran)(PTHF) using stannous octoate (SnOct₂) as a catalyst. The effects of feed ratio, reaction time and reaction temperature on the copolymerization were investigated. It was found that the optimal reaction temperature and time were 80 °C and 42 hours, respectively, and the molar ratio of p-dioxanone/SnOct₂ (PDO/cat.) had little influence on the inherent viscosity of the copolymers. The triblock copolymers were characterized by various analytical techniques such as ¹H-NMR and DSC.     

Novel Polyisobutylene Stars. XXVIII. A star block comprising three poly (isobutylene-b-acrylonitrile) arms radiating from an aromatic core: Synthesis and characterization*

Summary The synthesis and characterization of a novel three arm star-block comprising a cumyl core out of which radiate three poly(isobutylene-b-acrylonitrile) arms is presented. The synthesis strategy comprised three major steps (see Scheme 1): 1. The synthesis of ?(PIB-OH)₃, 2. Quantitative transformation of the -OH termini to -OCOC(CH₃)₂Br termini, and 3. Controlled ATRP of acrylonitrile mediated by the latter termini. The definition of a suitable solvent system, methylene chloride/cyclohexanone (CH₂Cl₂/CHO) was critical for the synthesis. The ?(PIB-b-PAN)₃, M_{n,PIB block}= 6000 g/mol and M_{n,PAN block}= 1,800 g/mol was characterized by solid state ¹³C NMR spectroscopy, thermal gravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis. Received: 8 January 2002/Revised version: 4 March 2002/ Accepted: 5 March 2002     

Synthesis of star‐shaped poly(ε‐caprolactone)‐b‐poly(L‐lactide) copolymers: From star architectures to crystalline morphologies

Hexa‐armed star‐shaped poly(ε‐caprolactone)‐block‐poly(L ‐lactide) (6sPCL‐b‐PLLA) with dipentaerythritol core were synthesized by a two‐step ring‐opening polymerization. GPC and ¹H NMR data demonstrate that the polymerization courses are under control. The molecular weight of 6sPCLs and 6sPCL‐b‐PLLAs increases with increasing molar ratio of monomer to initiator, and the molecular weight distribution is in the range of 1.03–1.10. The investigation of the melting and crystallization demonstrated that the values of crystallization temperature (T_c), melting temperature (T_m), and the degree of crystallinity (X_c) of PLLA blocks are increased with the chain length increase of PLLA in the 6sPCL‐b‐PLLA copolymers. On the contrary, the crystallization of PCL blocks dominates when the chain length of PLLA is too short. According to the results of polarized optical micrographs, both the spherulitic growth rate (G) and the spherulitic morphology are affected by the macromolecular architecture and the length of the block chains. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Poly(ethylene oxide)‐block‐polystyrene copolymers obtained by radical polymerization involving chain‐transfer processes

Poly(ethylene oxide)‐block‐polystyrene (PEO–PSt) block copolymers were prepared by radical polymerization of styrene in the presence of iodoacetate—terminated PEO (PEO‐I) as a macromolecular chain‐transfer agent. PEO‐I was synthesized by successively converting the OH end‐group of α‐methoxy ω‐hydroxy PEO to chloroacetate and then to the iodoacetate. The chain‐transfer constant of PEO‐I was estimated from the rate of consumption of the transfer agent versus the rate of consumption of the monomer (C_{tr, PEO‐I} = 0.23). Due to the involvement of degenerative transfer, styrene polymerization in the presence of PEO‐I displayed some of the characteristics of a controlled/‘living’ process, namely an increase in the molecular weight and decrease of polydispersity with monomer conversion. However, because of the slow consumption of PEO‐I due to its low chain‐transfer constant, this process was not a fully controlled one, as indicated by the polydispersity being higher than in a controlled polymerization process (1.65 versus < 1.5). The formation of PEO–PSt block copolymers was confirmed by the use of size‐exclusion chromatography and ¹H NMR spectroscopy. Copyright © 2004 Society of Chemical Industry     

Hydrolysis of poly(ester-ether-ester) block copolymers in the presence of endothelial cells: in vitro modulation of endothelin release

In previous papers, we studied the hydrolytic degradation of six poly(ester-ether-ester) block copolymers, i.e. three poly(ε-caprolactone)-block-poly(oxyethylene)-block-poly(ε-caprolactone) copolymers and three poly(l-lactide)-block-poly(oxyethylene)-block-poly(l-lactide) copolymers. Their degradation products, 6-hydroxyhexanoic acid and l-lactic acid, have now been found to modulate endothelin release by human umbilical vein endothelial cells, with no significant alteration of the vasoconstrictor-vasodilator balance previously determined. The influence of the same degradation products on the cell proliferation has also been determined and discussed. Received: 13 January 1997/Revised: 2 May 1997/Accepted: 3 May 1997