Triblock copolymers of 2-methyl-2-oxazoline and poly(ethyleneglycoladipate)

Summary 2-methyl-2-oxazoline was polymerized by using poly(ethyleneglycoladipate) having tosylate end groups as an initiator. Polymerization was carried in bulk, and ABA type block copolymers were obtained containing poly(N-acetylethylenimine) as A block (hard part) and poly(ethyleneglycoladlpate) as B block (soft part).     

Temperature responsive bio-compatible polymers based on poly(ethylene oxide) and poly(2-oxazoline)s

This review covers the LCST behavior of two important polymer classes in aqueous solution, namely poly(2-oxazoline)s and systems whose thermo-responsiveness is based on their structural similarity to poly(ethylene oxide) (PEO). In order to elucidate the progress that has been made in the design of new thermo-responsive copolymers, experimental data that were obtained by different research groups are compared in detail. Copolymerization with hydrophilic or hydrophobic comonomers represents a suitable method to tune the coil to globule transition temperature of several homopolymers, and incorporation of other monomers provided further interesting features, such as pH responsiveness or sensing properties. In addition, living and controlled polymerization techniques enabled access to defined end groups and more advanced polymer architectures, such as graft copolymers or double responsive block copolymers. The effect of such structural variations on the temperature responsive behavior of the (co)polymers is discussed in detail.     

Graft copolymers with poly(ethylene oxide) segments

Graft copolymers containing poly(ethylene oxide) as side chains attached to the backbone have attracted significant interest because of their unique properties. They have expanded a class of materials important for science and biomedicine. This review article describes a variety of synthetic procedures, i.e. directly by the macromonomer method or by the ‘grafting from’ technique as well as indirect routes via a polymeric precursor. The uses of these graft copolymers in numerous applications are presented to show their versatile nature and their potential. Copyright © 2007 Society of Chemical Industry     

Organization of poly(2-ethyl-2-oxazoline)-block-poly(2-phenyl-2-oxazoline) copolymers in water solution

Diblock copolymers were prepared from 2-ethyl-2-oxazoline and 2-phenyl-2-oxazoline via living cationic polymerization using sequential addition of the monomers. Copolymer assemblies in aqueous solutions and on surface were studied with respect to changes in the hydrophilic-hydrophobic balance induced by increasing the length of the hydrophobic poly(2-phenyl-2-oxazoline) segment while the hydrophilic poly(2-ethyl-2-oxazoline) chain was kept constant with an average of 60 monomer units. The copolymer with a short segment of four 2-phenyl-2-oxazoline units assembled into highly hydrated aggregates that decreased twice in size after drying. Their structure was destroyed and network morphologies were formed upon spin-coating. The increase of the length of the hydrophobic segment resulted in aggregates that dissociated to micelle-sized particles when subjected to mechanical shear by spin-coating or filtering. These observations imply that the aggregates are multi-core structures originating from the assembly of primarily formed micelles. The copolymer self-assembly was evidenced by a combination of techniques: DLS, SLS, AFM and SEM.     

Phase behavior of aqueous systems containing block copolymers of poly(ethylene oxide) and poly(propylene oxide)

Phase behavior of aqueous systems containing block copolymers of poly(ethylene oxide (PEO) and poly(propylene oxide) (PPO) was evaluated by building up temperature-concentration phase diagrams. We have studied bifunctional triblock copolymers (HO-PEO-PPO-PEO-OH) and monofunctional diblock copolymers (R-PEO-PPO-OH and R-PPO-PEO-OH, where R length is linear C₄ and C_12–14). The cloud points of the polymer solutions depended on EO/PO ratio, polarity, R length and position of the hydrophilic and hydrophobic segments along the molecule. Such factors influence on the solutions behavior was also analyzed in terms of critical micelle concentration (CMC), which was obtained from surface tension vs. concentration plots. Salts (NaCl and KCl) added into the polymer solutions change the solvent polarity decreasing the cloud points. On the other hand, the cloud points of the polymer solutions increased as a hydrotrope (sodium p-toluenesulfonate) was added. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1767–1772, 1997     

Synthesis and bulk properties of poly(tetrahydrofuran)-poly(2-methyl-2-oxazoline) ABA triblock copolymers

A series of linear triblock-copolymers of the ABA type in which the central B-block is poly(tetrahydrofuran) (polyTHF) and the A-segments are poly(2-methyl-2-oxazoline) (polyMeOX) were synthesized by a one-pot sequential monomer addition copolymerization, utilizing the living nature of the cationic ring-opening polymerization of both monomers. Films of the copolymers, casted from chloroform solutions, exhibit excellent mechanical properties in comparison with the homopolymers with comparable molecular weights, which was ascribed to the phase separation occurring between the two copolymer segments. Materials, in which the polyTHF B-segment have a molecular weight 13 000 g/mol or higher and each polyMeOX A-block a molecular weight 1500 g/mol, kept elastomeric properties up to 130 °C notwithstanding the fact that this temperature is considerably higher than the melting point of polyTHF and the glass transition temperature of polyMeOX. It was found that these triblock-copolymer materials show a shape memory effect. These observations are attributed to the high degree of phase separation between the two blocks and the strong polar interactions between the polyMeOX segments. Received: 20 March 1997/Revised: 5 September 1997/Accepted: 8 September 1997     

Self-association of double-hydrophilic copolymers of acrylic acid and poly(ethylene oxide) macromonomer

Poly(ethylene oxide) (PEO) end-capped by a methacrylate unsaturation was copolymerized with acrylic acid by RAFT with dibenzyltrithiocarbonate as a chain transfer agent. Tapered triblock copolymers consisting of a poly(acrylic acid) (PAA) inner block and comb-like outer blocks of PEO macromomers were formed as result of the comonomers reactivity ratios. Composition of these copolymers and length of the PEO branches were varied. Dynamic light scattering (DLS) was used to characterize the aggregates formed in water and to investigate their response to stimuli, such as pH, temperature and ionic strength. In parallel, the morphology of the aggregates was directly observed by transmission electron microscopy (TEM). Well-defined aggregates were formed in the 5<pH<8 range, with a morphology strongly depending on the copolymer composition. At pH<5, the copolymers were poorly soluble and no well-defined structure was observed, whereas free chains were formed at pH>8 as consequence of the complete ionization of the PAA block.     

Synthesis and characterization of anionic graft copolymers containing poly(ethylene oxide) grafts

Graft copolymers containing poly(ethylene oxide) side chain attached to maleic anhydride‐alt‐vinyl methyl ether (MA‐VME) copolymer were prepared by coupling MA‐VME and poly(ethylene glycol) monomethyl ether (MPEG) by esterification in DMF at 90°C. MPEG and dodecyl alcohol (DA) were grafted onto MA‐VME copolymer in o‐xylene at 140°C in the presence of p‐toluene sulfonic acid as catalyst. The molecular weights of MPEG were found to influence the rate of the grafting reaction and the final degree of conversion. The graft copolymers were characterized by IR, GPC, and ¹H‐NMR. DSC was used to examine thermal properties of the graft copolymers. The analysis indicates that grafts have phase‐separated morphology with the backbone and the MPEG grafts forming separate phases. The properties in aqueous solutions of these grafts were studied with respect to aggregation behavior and viscometric properties. In aqueous solution, the polymers exhibited polyelectrolyte behavior (i.e., a dramatic increase of the viscosity upon neutralization). Graft copolymers with DA have lower viscosities. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1138–1148, 2002     

Block copolymers comprising poly(ethylene oxide) and poly(hydroxyethyl methacrylate) blocks: synthesis and characterization

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.     

Synthesis and properties of amphiphilic poly(ethylene oxide)-grafted cardo poly(aryl ether sulfone) copolymers

A series of comb-type amphiphilic copolymers (PES-g-PEO) with a stiff poly(aryl ether sulfone) backbone and flexible PEO side chains was synthesized via a “grafting onto” technique. By controlling the monomer feed ratios, high molecular weight copolymers with a range of PEO side chain content were prepared and used to form tough and flexible membranes. The PES-g-PEO membranes displayed high thermal stability (T_d > 230 °C) and good mechanical properties. The water contact angles of the PES-g-PEO membranes ranged from 60.5° to 66.7°, 20° lower than those of poly(aryl ether sulfone) membranes (82-86°), indicating that the PEO side chains improved the hydrophilicity of the membranes. Wide-angle X-ray diffraction results indicated that the PES-g-PEO membranes possessed an amorphous structure, that is, crystallization of the PEO side chains did not occur. The Li-ion conductivity reached 2.26 × 10⁻⁴ S/cm at room temperature, much higher than that of the pure PEO-based system (10⁻⁶ S/cm), due to the presence of the amorphous PEO side chains between the PES backbones, which provided an effective Li-ion transport pathway.     

Biodegradable block copolymers with poly(ethylene oxide) and poly(glycolic acid‐valine) blocks

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     

Structure of insoluble complex formed by a block copolymer of 2-ethyl-2-oxazoline and ethylene oxide and poly(methacrylic acid)

Complexes that were insoluble in water were formed by mixing aqueous solutions of a block copolymer of 2-ethtyl-2-oxazoline (EOX) and ethylene oxide (EO) and those of poly(methacrylic acid) (PMAA). The structures of these complexes were investigated by the results obtained mainly by infrared spectroscopy, X-ray diffraction, and differential scanning calorimetry. The molar ratio of MAA in the complexes was also estimated by analyzing the infrared spectra. Whereas homopolymers of EOX and EO formed nearly equimolar complexes with PMAA irrespective of the feed molar ratio, the molar ratio of MAA in the complexes formed by the block copolymer and PMAA depended on the feed molar ratio. Although the infrared spectra indicated structural differences between the homopolymer of EOX and EOX in the block copolymer before forming complexes, the spectra obtained for the complexes formed by the homopolymer and the block copolymer were similar to each other.     

Biodegradability of poly(ethylene terephthalate) copolymers with poly(ethylene glycol)s and poly(tetramethylene glycol)

Poly(ethylene terephthalate) copolymers were prepared by melt polycondensation of dimethyl terephthalate and excess ethylene glycol with 10–40mol% (in feed) of poly(ethylene glycol) (E) and poly(tetramethylene glycol) (B), with molecular weight (MW) of E and B 200–7500 and 1000, respectively. The reduced specific viscosity of copolymers increased with increasing MW and content of polyglycol comonomer. The temperature of melting (T_m), cold crystallization and glass transition (T_g) decreased with the copolymerization. T_m depression of copolymers suggested that the E series copolymers are the block type at higher content of the comonomer. T_g was decreased below room temperature by the copolymerization, which affected the crystallinity and the density of copolymer films. Water absorption increased with increasing content of comonomer, and the increase was much higher for E1000 series films than B1000 series films. The biodegradability was estimated by weight loss of copolymer films in buffer solution with and without a lipase at 37°C. The weight loss was enhanced a little by the presence of a lipase, and increased abruptly at higher comonomer content, which was correlated to the water absorption and the concentration of ester linkages between PET and PEG segments. The weight loss of B series films was much lower than that of E series films. The abrupt increase of the weight loss by alkaline hydrolysis is almost consistent with that by biodegradation.     

Heterobifunctional poly(ethylene oxide)

Summary Well-defined poly(ethylene oxide)s with a primary amino group at one end and a hydroxyl group at the other terminus were synthesized with new sila-protected amino functionality initiator, potassium N-[2-(2,2,5,5-tetramethyl-1-aza-2,5-disilacyclopentyl)-ethyl]methyl amide [1b]. 1b initiated an anionic polymerization of ethylene oxide (EO) to form a polymer (PEO) without any side reactions such as a cleavage reaction of protective group and a chain transfer reaction. The molecular weights of the PEO determined from GPC and MALDI TOF-MS spectrometry agreed well with those from end group analysis using ¹H and ¹³C NMR and TLC and also with the expected value from EO/initiator ratio. From these results, it was concluded that the polymers thus obtained had a primary amino group at one end and a hydroxy group at the other end and can be regarded as hetrobifunctional PEO.     

Synthesis and characterization of amphipathic poly(methyl methacrylate)-b-poly(ethylene oxide) diblock copolymers

Summary This paper describes the synthesis and characterization of amphipathic diblock copolymers of poly(methyl methacrylate) (PMMA) and poly(ethylene oxide) (PEO). The synthesis involved the coupling of acyl chloride-terminated PMMA block with methoxy poly(ethylene oxide) (MPEO). Carboxylic acid chloride-terminated PMMA was generated by treating with thionyl chloride the parent carboxylic PMMA, which was prepared by free radical polymerization of methyl methacrylate (MMA) using benzoyl peroxide (BPO) as the initiator and -mercaptopropionic acid (MPA) as the chain transfer agent. The proposed mechanism of MMA polymerization is in good agreement with the experimental results which indicate that as a side reaction nonfunctional (aromatic) counterpart is produced in a small quantity. The coupling of the acyl chloride-terminated PMMA with MPEO was quantitative.     

Crystallization of poly(ethylene oxide) in i-polypropylene–poly(ethylene oxide) blends

A two-stage stable system of isotactic polypropylene–poly(ethylene oxide) blend, in which poly(ethylene oxide) can be permanent either in molten or in crystallized states in the temperature range from 280 to 327 K, was described. The behavior of that blend was explained in terms of fractionated crystallization. A fine dispersion of poly(ethylene oxide) inclusions is required for efficient suppression of crystallization initiated by heterogeneous nuclei. The application of a thin film of polypropylene-poly(ethylene oxide) 9 : 1 blend obtained by quenching for multiuse erasable and rewritable carriers for visible information has been demonstrated. The same sample exhibits different dynamic mechanical properties when poly(ethylene oxide) inclusions are molten or crystallized. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2047–2057, 1997     

Miscibility of polystyrene with poly(ethylene oxide) and poly(ethylene glycol)

The intrinsic viscosity of polystyrene–poly(ethylene oxide) (PS–PEO) and PS–poly(ethylene glycol) (PEG) blends have been measured in benzene as a function of blend composition for various molecular weights of PEO and PEG at 303.15 K. The compatibility of polymer pairs in solution were determined on the basis of the interaction parameter term, Δb, and the difference between the experimental and theoretical weight-average intrinsic viscosities of the two polymers, Δ[η]. The theoretical weight-average intrinsic viscosities were calculated by interpolation of the individual intrinsic viscosities of the blend components. The compatibility data based on [η] determined by a single specific viscosity measurement, as a quick method for the determination of the intrinsic viscosity, were compared with that obtained from [η] determined via the Huggins equation. The effect of molecular weights of the blend components and the polymer structure on the extent of compatibility was studied. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1471–1482, 1998     

Crystallization behavior and morphology of double crystalline poly(trimethylene terephthalate)/poly(ethylene oxide terephthalate) copolymers

Double crystalline poly(trimethylene terephthalate)/poly(ethylene oxide terephthalate) copolymers (PTT/PEOT), with PTT content ranging from 16.5 to 65.5 wt%, were synthesized by melt copolycondensation. The morphological transformation of samples from microphase separation to macrophase separation was investigated by gel permeation chromatography and transmission electron microscopy. Differential scanning calorimetry and in situ wide‐angle X‐ray diffraction suggested that all copolycondensation samples displayed double crystalline behavior. The melt‐crystallization peak temperatures (T_{m, c} values) of PTT chains monotonously increased with increasing PTT content and were higher than that of homo‐PTT when the content of PTT was above 30.6 wt%. Interestingly, T_{m, c} values of PEOT chains were also increased with increasing PTT content. Polarized optical microscopy revealed that all copolycondensation samples studied could form ring‐banded spherulites and band spacing increased with increasing T_c values. In addition, band spacing decreased with increasing PTT content at a given T_c. Strangely, although PEOT was the main component in all copolycondensation samples, spherulitic morphology formed by the advance crystallization of PTT did not change after PEOT crystallization. Only a subtle change of quadrant tones was detected. © 2012 Society of Chemical Industry     

Crystallization, and morphology of poly(trimethylene terephthalate)/poly(ethylene oxide terephthalate) segmented block copolymers

A new type of poly(ether-ester) based on poly(trimethylene terephthalate) as rigid segments and poly(ethylene oxide terephthalate) as soft segments was synthesized and its crystallization behavior and morphology were investigated. Differential Scanning Calorimetry revealed that the copolymer containing 57 wt% soft segments presented a low glass transition temperature (−46.4 °C) and a high melting temperature (201.8 °C), suggesting that it had the typical characteristic of thermoplastic elastomer. With increasing soft segment content from 35 to 57 wt%, the crystallization morphology transformed from banded spherulites to compact seaweed morphology at a certain film thickness, which was due to the change of surface tension and diffusivity caused by increasing the soft segment content. Moreover, with the decrease of film thickness from 15 to 2 μm, the crystallization morphology of the copolymer (57 wt% soft segment) changed from wheatear-like, compact seaweed to dendritic. Scanning Electron Microscopy revealed that some flower-like crystals presenting in the bulk, which had been surprisingly found in the poly(ether-ester) segmented block copolymers for the first time. Possible mechanism was discussed in the text.     

Nanostructures from photo-cross-linked amphiphilic poly(ethylene oxide)-b-alkyl diblock copolymers

Poly(ethylene oxide) monomethylether was functionalized by alkyl chains of various lengths (l=10-19 methylene groups) bearing a polymerizable methacrylate moiety. Each synthesis step on the polymer gives quantitative functionalization rates. The self-assembly of the amphiphilic polymers in water was studied by light scattering for various end-groups. Sterical and polar effects were shown to influence the micellization step. The cores of the micelles formed by PEO-C_l-methacrylate were irreversibly cross-linked by UV irradiation. Star polymers that are stable under dilution in good solvent are obtained after 1-min irradiation. The hydrodynamic radius and the molar mass of the nanoparticles depend on the amount of photoinitiator introduced in the cores.