We describe the preparation of amphiphilic diblock copolymers made of poly(ethylene oxide) (PEO) and poly(hexyl methacrylate) (PHMA) synthesized by anionic polymerization of ethylene oxide and subsequent atom transfer radical polymerization (ATRP) of hexyl methacrylate (HMA). The first block, PEO, is prepared by anionic polymerization of ethylene oxide in tetrahydrofuran. End capping is achieved by treatment of living PEO chain ends with 2‐bromoisobutyryl bromide to yield a macroinitiator for ATRP. The second block is added by polymerization of HMA, using the PEO macroinitiator in the presence of dibromobis(triphenylphosphine) nickel(II), NiBr2(PPh3)2, as the catalyst. Kinetics studies reveal absence of termination consistent with controlled polymerization of HMA. GPC data show low polydispersities of the corresponding diblock copolymers. The microdomain structure of selected PEO‐block‐PHMA block copolymers is investigated by small angle X‐ray scattering experiments, revealing behavior expected from known diblock copolymer phase diagrams.
SAXS diffractograms of PEO‐block‐PHMA diblock copolymers with 16, 44, 68 wt.‐% PEO showing spherical (A), cylindrical (B), and lamellae (C) morphologies, respectively. 相似文献
Novel biodegradable thermosensitive triblock copolymers of poly(D ,L ‐3‐methylglycolide)‐block‐poly(ethylene glycol)‐block‐poly(D ,L ‐3‐methylglycolide) (PMG‐PEG‐PMG) have been synthesized. Ring‐opening polymerization of D ,L ‐3‐methyl‐glycolide (MG) initiated with poly(ethylene glycol) (PEG) and Ca[N(SiMe3)2]2(THF)2 provided triblock copolymers with alternating lactyl/glycolyl sequences of controlled molecular weight, low polydispersity index and uniform chain structure. At relatively low temperatures (≈ 10 °C) these copolymers formed clear solutions in water up to high concentrations (50 wt.‐%). Depending on molecular mass ratios of PMG and PEG blocks, a sol‐gel transition or an increase in viscosity without gel formation was observed upon increasing the temperature of the aqueous solutions. The temperature‐induced gelation was ascertained by rheology and dynamic differential scanning calorimetry (DDSC).
Phase diagram of PMG‐PEG‐PMG 1 400‐1 450‐1 400 in an aqueous solution. 相似文献
Summary: Poly(ethylene oxide)‐block‐poly(methylidene malonate 2.1.2) block copolymer (PEO‐b‐PMM 2.1.2) bearing an allyl moiety at the poly(ethylene oxide) chain end was synthesized by sequential anionic polymerization of ethylene oxide (EO) and methylidene malonate 2.1.2 (MM 2.1.2). This allyl functional group was subsequently modified by reaction with thiol‐bearing functional groups to generate carboxyl and amino functionalized biodegradable block copolymers. These end‐group reactions, performed in good yields both in organic media and in aqueous micellar solutions, lead to functionalized PEO‐b‐PMM 2.1.2 copolymers which are of interest for cell targeting purposes.
Synthetic route to α‐allyl functionalized PEO‐b‐PMM 2.1.2 copolymers. 相似文献
Poly(3‐hexylthiophene)‐block‐poly(2‐ethyl‐2‐oxazoline) amphiphilic rod–coil diblock copolymers have been synthesized by a combination of Grignard metathesis (GRIM) and ring‐opening cationic polymerization. Diblock copolymers containing 5, 15, and 30 mol‐% poly(2‐ethyl‐2‐oxazoline) have been synthesized and characterized. The synthesized rod–coil block copolymers display nanofibrillar morphology where the density of the nanofibrills is dependent on the concentration of the poly(2‐ethyl‐2‐oxazoline) coil segment. The conductivity of the diblock copolymers was lowered from 200 to 35 S · cm?1 with an increase in the content of the insulating poly(2‐ethyl‐2‐oxazoline) block. By contrast, the field‐effect mobility decreased by 2–3 orders of magnitude upon the incorporation of the poly(2‐ethyl‐2‐oxazoline) insulating segment.
A new series of poly(perfluorohexylethyl methacrylate)‐block‐poly(ethylene oxide)‐block‐poly(perfluorohexylethyl methacrylate), PFMA‐b‐PEO‐b‐PFMA triblock copolymers has been synthesized by atom transfer radical polymerization using bifunctional PEO macroinitiators. The molecular structure of the block copolymers was confirmed by 1H NMR spectroscopy and SEC. X‐ray scattering studies have been carried out to investigate their bulk properties. SAXS has shown cubic arrangement of spheres (bcc), hexagonally packed cylinders (hpc) and lamellar microdomain formation in the melt of triblock copolymers investigated, depending on composition. Crystallization was, however, found to destroy the ordered melt morphology and imposes a lamellar crystalline structure. WAXS, DSC and polarized light microscopy measurements confirmed the crystallization of PEO segments in block copolymers. Long PFMA blocks were found to have significant effect on PEO crystallization.
Synthesis of triblock copolymers of EO and FMA by ATRP. 相似文献
pH‐sensitive micelles formed by interchain hydrogen bonding of poly(methacrylic acid)‐block‐poly(ethylene oxide) copolymers were prepared and investigated at pH < 5. Both and Rh of the micelles increase with decreasing pH of the solution, displaying an asymptotic tendency at low pH values. The observed micelles are well‐defined nanoparticles with narrow size distributions (polydispersity ΔRh/Rh ≤ 0.05) comparable with regular diblock copolymer micelles. The CMCs occur slightly below c = 1 × 10?4 g · mL?1. The micelles are negatively charged and their time stability is lower than that of regular copolymer micelles based purely on hydrophobic interactions.
The physical properties of well‐defined poly(butyl methacrylate)‐block‐poly(butyl acrylate)‐block‐poly(butyl methacrylate) (PBMA‐b‐PBA‐b‐PBMA) triblock copolymers synthesized by atom transfer radical polymerization (ATRP) are reported. The glass transition and the degradation temperature of copolymers were determined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). DSC measurements showed phase separation for all of the copolymers with the exception of the one with the shortest length of either inner or outer blocks. TGA demonstrated that the thermal stability of triblock copolymers increased with decreasing BMA content. Dynamic mechanical analysis was used for a preceding evaluation of adhesive properties. In these block copolymers, the deformation process under tension can take place either homogeneously or by a neck formation depending on the molecular weight of the outer BMA blocks and on the length of the inner soft BA segments. Microindentation measurements were also performed for determining the superficial mechanical response and its correlation with the bulk behavior.
Stress‐strain curves for the different PBMA‐b‐PBA‐b‐PBMA specimens at room temperature and at 10 mm/min. 相似文献
Summary: A series of telechelic OH polysulfones (PSU) were converted to atom transfer radical polymerization (ATRP) macroinitiators by reaction with 2‐bromoisobutyryl bromide. Three macroinitiators with different chain lengths were extended with poly(butyl acrylate) (PBA) to form ABA triblock copolymers. The structure and dynamics of the ABA triblock copolymers with PSU central segments and various molecular weight PBA side chains were investigated by small‐angle X‐ray scattering and rheology. The block copolymers form micelles with a PSU core and PBA corona. The length of each block has an important effect on the structure and resulting dynamics of the copolymers. Dynamic mechanical measurements indicate three relaxation modes: (i) PBA segmental relaxation at high frequency; (ii) PBA relaxation of the corona block at intermediate frequency; (iii) an additional relaxation process related to structural rearrangement of the micelles at low frequency. The shear modulus plateau corresponding to a soft rubbery state extends over a very broad time or temperature range because of this slow additional relaxation.
Schematic illustration of the structural elements and the bulk supramolecular structure for a symmetric triblock copolymer with a stiff central segment strongly incompatible with the other constituent. 相似文献
Poly(3‐hexylthiophene)‐block‐poly(tetrahydrofuran) was synthesized by cationic ring‐opening polymerization of tetrahydrofuran (THF) using a poly(3‐hexylthiophene) macroinitiator. Poly(3‐hexylthiophene) macroinitiator used for the ring‐opening polymerization of THF was synthesized by reacting the hydroxypropyl end‐group with trifluoromethanesulfonic anhydride in the presence of 2,6‐di‐tert‐butylpyridine. 1H NMR spectroscopy and SEC data confirmed the formation of the di‐block copolymers. Field‐effect mobility of poly(3‐hexylthiophene)‐block‐poly(tetrahydrofuran) was measured in a thin‐film transistor configuration and was found to be 0.009 cm2 · V?1 · s?1.
The effect of sonication on the size and structure of polymeric aggregates formed by amphiphilic block copolymers was studied by the combination of dynamic and static light scattering. Poly(ethylene oxide)‐block‐polyisoprene, poly(ethylene oxide)‐block‐polystyrene diblock copolymers, and poly(ethylene oxide)‐block‐polyisoprene‐block‐poly(ethylene oxide) triblock copolymer were used as typical polymeric amphiphiles. Sonication was found to be an effective method to break up inter‐micellar associations and split large polymeric aggregates, present initially in the aqueous solutions, into monodisperse micelles. The content and type of hydrophobic block, copolymer solution‐preparation protocol, and copolymer concentration were also investigated as co‐factors in conjunction to the effect of sonication time.
Four poly(N,N‐dimethylacrylamide)‐block‐poly(L ‐lysine) (PDMAM‐block‐PLL) hybrid diblock copolymers and two PLL homo‐polypeptides are prepared via ROP of ε‐trifluoroacetyl‐L ‐lysine N‐carboxyanhydride initiated by primary amino‐terminated PDMAM and n‐hexylamine respectively. The PLL blocks render the copolymers a multi‐responsive behavior in aqueous solution due to their conformational transitions from random coil to α‐helix with increasing pH, and from α‐helix to β‐sheet upon heating. The random coil‐to‐α‐helix transition is found to depend on the PLL length: the longer the peptide segment, the more readily the transition occurred. The same trend was observed for the α‐helix‐to‐β‐sheet transition, which was found to be inhibited for short polypeptides unless conjugated with the PDMAM block.
Furan‐terminated poly(oxyethylene)‐block‐poly(L‐lactide) (MePEG‐PLLA‐F) and poly(oxyethylene)‐block‐poly(D‐lactide) (MePEG‐PDLA‐F) are synthesized by ring‐opening polymerization of L‐ and D‐lactides, respectively, in the presence of poly(ethylene glycol) monomethyl ether (MePEG) and the following terminal reaction with furfuryl isocyanate. Their mixed micelle solution turns to gel quickly with stereocomplexation of the enantiomeric PLLA and PDLA. When 1,8‐bis(maleimido)diethylene glycol (BMG) is added to the mixed micelle solution, the gelation is promoted by the terminal coupling of the copolymers driven by the Diels–Alder reaction of the furanyl groups and BMG giving a gel having higher strength.
Model poly[ethylene‐block‐(L ,L ‐lactide)] (PE‐block‐PLA) block copolymers were successfully synthesized by combining metallocene catalyzed ethylene oligomerization with ring‐opening polymerization (ROP) of L ,L ‐lactide (LA). Hydroxy‐terminated polyethylene (PE‐OH) macroinitiator was prepared by means of ethylene oligomerization on rac‐dimethyl‐silylen‐bis(2‐methyl‐benz[e]indenyl)‐zirconium(IV)‐dichloride/methylaluminoxane (rac‐MBI/MAO) in presence of diethyl zinc as a chain transfer agent, and subsequent in situ oxidation with synthetic air. Poly[ethylene‐block‐(L ,L ‐lactide)] block copolymers were obtained via ring‐opening polymerization of LA initiated by PE‐OH in toluene at 100 °C mediated by tin octoate. The formation of block copolymers was confirmed by 1H NMR spectroscopy, fractionation experiments, thermal behavior, and morphological characterization using AFM and light microscopy techniques.
Summary: The relationship between the architecture of block copolymers and their micellar properties was investigated. Diblock, 3‐arm star‐shaped and 4‐arm star‐shaped block copolymers based on poly(ethylene glycol) and poly(ε‐caprolactone) were synthesized. Micelles of star‐shaped block copolymer in an aqueous solution were then prepared by a solvent evaporation method. The critical micelle concentration and the size of the micelles were measured by the steady‐state pyrene fluorescence method and dynamic light scattering, respectively. The CMC decreased in the order di‐, 3‐arm star‐shaped and 4‐arm star‐shaped block copolymer. The size of the micelles increased in the same order as the CMC. Theory also predicts that the formation of micelles becomes easier for 4‐arm star‐shaped block copolymers than for di‐ and 3‐arm star‐shaped block copolymers, which qualitatively agrees with the experiments.
Summary: The crystallization behavior of crystalline‐crystalline diblock copolymer containing poly(ethylene oxide) (PEO) and poly(ε‐caprolactone) (PCL), in which the weight fraction of PCL is 0.815, has been studied via differential scanning calorimeter (DSC), wide‐angle X‐ray diffraction (WAXD), and polarized optical microscopy (POM). DSC and WAXD indicated that both PEO and PCL blocks crystallize in the block copolymer. POM revealed a ring‐banded spherulite morphology for the PEO‐b‐PCL diblock copolymer.
DSC heating curve for the PEO‐b‐PCL block copolymer. 相似文献
Summary: Various poly(ε‐caprolactone‐block‐1,4‐dioxan‐2‐one) (P(CL‐block‐PDX)) block copolymers were prepared according to the living/controlled ring‐opening polymerization (ROP) of 1,4‐dioxan‐2‐one (PDX) as initiated by in situ generated ω‐aluminium alkoxides poly(ε‐caprolactone) (PCL) chains in toluene at 25 °C. 1 1H NMR, PCS and TEM measurements have attested for the formation of colloids attributed to a growing PPDX core surrounded by a solvating PCL shell during the polymerization of PDX promoted by ω‐Al alkoxide PCL chains in toluene. The thermal behavior of the P(CL‐block‐PDX) copolymers was studied by DSC; showing two distinct melting temperatures (as well as two glass transition temperatures) similar to those of the respective homopolyesters. Finally, the thermal degradation of the P(CL‐block‐PDX) block copolymers was investigated by TGA simultaneously coupled to a FT‐IR spectrometer and a mass spectrometer for evolved gas analysis (EGA). The degradation occurred in two consecutive steps involving a first unzipping depolymerization of the PPDX blocks followed by the degradation of the PCL blocks via both ester pyrolysis and unzipping reactions.
TEM observation of P(CL‐block‐PDX) block copolyesters ( = 11 600 and = 22 100) as formed by vaporization starting from a diluted suspension in toluene/TCE mixture solvent (50/50 v/v). 相似文献
Summary: The synthesis of polyacrylonitrile‐block‐polystyrene (PAN‐b‐PS) copolymers by atom transfer radical polymerization (ATRP) is reported. Chain extension of bromine terminated PAN macroinitiators with styrene was performed using a CuBr/N,N,N′,N″,N″‐pentamethyldiethylenetriamine catalyst system and 2‐cyanopyridine as a solvent. The first‐order kinetic plots of styrene consumption showed a significant curvature, indicating a progressive decrease in the concentration of active species during copolymerization. The loss of the bromide end group was mainly ascribed to the elimination of HBr, as shown by 1H NMR spectroscopy. By varying the molar ratio of either the catalyst or the monomer to the initiator, a series of PAN‐b‐PS copolymers were prepared, with polydispersities as low as 1.3, and molar compositions ranging from 8.6/91.4 to 35.5/64.5.
1H NMR spectra of PAN‐b‐PS in DMF‐d7 at 80 °C. 相似文献
Summary: Bis(hydroxy)telechelic bisphenol A polycarbonate (PC) was prepared via melt polycondensation of bisphenol A (BPA) and diphenyl carbonate (DPC) using lanthanum(III ) 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‐PC‐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.
Formation of a bifunctional ATRP macroinitiator by esterification of bis(hydroxy)telechelic PC with α‐chlorophenylacetyl chloride. 相似文献
Copolymerization of carbon dioxide (CO2) and propylene oxide (PO) is employed to generate amphiphilic polycarbonate block copolymers with a hydrophilic poly(ethylene glycol) (PEG) block and a nonpolar poly(propylene carbonate) (PPC) block. A series of poly(propylene carbonate) (PPC) di‐ and triblock copolymers, PPC‐b‐PEG and PPC‐b‐PEG‐b‐PPC, respectively, with narrow molecular weight distributions (PDIs in the range of 1.05–1.12) and tailored molecular weights (1500–4500 g mol?1) is synthesized via an alternating CO2/propylene oxide copolymerization, using PEG or mPEG as an initiator. Critical micelle concentrations (CMCs) are determined, ranging from 3 to 30 mg L?1. Non‐ionic poly(propylene carbonate)‐based surfactants represent an alternative to established surfactants based on polyether structures.
A series of poly(vinylcarbazole‐ran‐styrene) copolymers with terminal hydroxyl groups were synthesized using nitroxide mediated polymerization (NMP) with the hydroxyl‐functional initiator VA‐086 and TEMPO as the mediator at 130 °C. Polymerizations were studied as a function of vinylcarbazole feed content, target molecular weight, and VA‐086/TEMPO ratio. The characterization of the copolymers was done by GPC and NMR. For feed concentrations of 40 mol‐% vinylcarbazole, copolymers with vinylcarbazole concentration up to 33 mol‐% could be obtained with narrow molecular weight distributions (PDI = 1.35) and exhibit pseudo‐“living” character up to conversions of about 20% if the target molecular weight was >100 kg · mol?1. 1H NMR indicated that the hydroxyl group was retained sufficiently with a functionality typically of about 0.7 hydroxyl groups per chain. Copolymers synthesized with higher vinylcarbazole feed content exhibited slower kinetics and were less controlled, resulting in much broader molecular weight distributions. The absence of control could be attributed to the absence of thermal initiation by vinylcarbazole which is advantageous toward controlling the radical concentration during the polymerization.
