Characterization of the functionalization reaction product of poly(styryl)lithium with ethylene oxide

The functionalization reaction of poly(styryl)lithiums (M_n = 1.3–9.9 × 10³) with ethylene oxide in benzene proceeds quantitatively ( > 99%) to produce the corresponding hydroxyethylated polymer as determined by vapor phase osmometry, size exclusion chromatography, end-group titration, thin layer chromatography, and ¹H- and ¹³C-NMR spectroscopy. ¹³C-NMR spectral analysis of the functionalized polystyrene with M_n = 1.3 × 10³ was consistent with addition of only one ethylene oxide unit to poly(styryl)lithium, i.e., no evidence for ethylene oxide oligomerization was observed.     

Synthesis of amphiphilic copolymer brushes: Poly(ethylene oxide)‐graft‐polystyrene

A well‐defined amphiphilic copolymer brush with poly(ethylene oxide) as the main chain and polystyrene as the side chain was successfully prepared by a combination of anionic polymerization and atom transfer radical polymerization (ATRP). The glycidol was first protected by ethyl vinyl ether to form 2,3‐epoxypropyl‐1‐ethoxyethyl ether and then copolymerized with ethylene oxide by the initiation of a mixture of diphenylmethylpotassium and triethylene glycol to give the well‐defined polymer poly(ethylene oxide‐co‐2,3‐epoxypropyl‐1‐ethoxyethyl ether); the latter was hydrolyzed under acidic conditions, and then the recovered copolymer of ethylene oxide and glycidol {poly(ethylene oxide‐co‐glycidol) [poly(EO‐co‐Gly)]} with multiple pending hydroxymethyl groups was esterified with 2‐bromoisobutyryl bromide to produce the macro‐ATRP initiator [poly(EO‐co‐Gly)_(ATRP). The latter was used to initiate the polymerization of styrene to form the amphiphilic copolymer brushes. The object products and intermediates were characterized with ¹H NMR, matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry, Fourier transform infrared, and size exclusion chromatography in detail. In all cases, the molecular weight distribution of the copolymer brushes was rather narrow (weight‐average molecular weight/number‐average molecular weight < 1.2), and the linear dependence of ln[M₀]/[M] (where [M₀] is the initial monomer concentration and [M] is the monomer concentration at a certain time) on time demonstrated that the styrene polymerization was well controlled. This method has universal significance for the preparation of copolymer brushes with hydrophilic poly(ethylene oxide) as the main chain. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4361–4371, 2006     

ATNRC and SET‐NRC synthesis of PtBA‐g‐PEO well‐defined amphiphilic graft copolymers

A series of new well‐defined amphiphilic graft copolymers containing hydrophobic poly(tert‐butyl acrylate) backbone and hydrophilic poly(ethylene oxide) side chains were reported. Reversible addition‐fragmentation chain transfer homopolymerization of tert‐butyl 2‐((2‐bromopropanoyloxy)methyl)acrylate was first performed to afford a well‐defined backbone with a narrow molecular weight distribution (M_w/M_n = 1.07). The target poly(tert‐butyl acrylate)‐g‐poly(ethylene oxide) (PtBA‐g‐PEO) graft copolymers with low polydispersities (M_w/M_n = 1.18–1.26) were then synthesized by atom transfer nitroxide radical coupling or single electron transfer‐nitroxide radical coupling reaction using CuBr(Cu)/PMDETA as catalytic system. Fluorescence probe technique was employed to determine the critical micelle concentrations (cmc) of the obtained amphiphilic graft copolymers in aqueous media. Furthermore, PAA‐g‐PEO graft copolymers were obtained by selective acidic hydrolysis of hydrophobic PtBA backbone while PEO side chains kept inert. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Configurational properties of aromatic polyesters: Dipole moments of poly(diethylene terephthalate) chains

Dielectric constants have been determined for a fraction of poly(diethylene terephthalate) in benzene at several temperatures. The data indicate that the dipole moment ratio 〈μ²〉/Nm² is somewhat higher than that of poly(ethylene oxide), and its temperature coefficient is in the vicinity of zero. Both the dipole ratio and its temperature coefficient are in very good agreement with those predicted by the rotational isomeric state theory. Using this theory, the unperturbed dimensions of poly(diethylene terephthalate) were calculated and it was found that (〈r²〉/M)_∞ = 0.80 Ų (g mol wt)^?1, a value intermediate between those of poly(ethylene oxide) (0.57) and poly(ethylene terephthalate) (1.05).     

Preparation of nanoparticles of double‐hydrophilic PEO‐PHEMA block copolymers by AGET ATRP in inverse miniemulsion

Atom transfer radical polymerization with activators generated by electron transfer initiating/catalytic system (AGET ATRP) of 2‐hydroxyethyl methacrylate (HEMA) was carried out in inverse miniemulsion. Water‐soluble ascorbic acid as a reducing agent and mono‐ and difunctional poly(ethylene oxide)‐based bromoisobutyrate (PEO‐Br) as a macroinitiator were used in the presence of CuBr₂/tris[(2‐pyridyl)methyl]amine (TPMA) and CuCl₂/TPMA complexes. The use of poly(ethylene‐co‐butylene)‐block‐poly(ethylene oxide) as a polymer surfactant resulted in the formation of stable HEMA cyclohexane inverse dispersion and PHEMA colloidal particles. All polymerizations were well‐controlled, allowing for the preparation of well‐defined PEO‐PHEMA and PHEMA‐PEO‐PHEMA block copolymers with relatively high molecular weight (DP > 200) and narrow molecular weight distribution (M_w/M_n < 1.3). These block copolymers self‐assembled to form micellar nanoparticles being 10–20 nm in diameter with uniform size distribution, and aggregation number of ～10 confirmed by atomic force microscopy and transmission electron microscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4764–4772, 2007     

Bioengineering functional copolymers. III. Synthesis of biocompatible poly[(N‐isopropylacrylamide‐co‐maleic anhydride)‐g‐poly(ethylene oxide)]/poly(ethylene imine) macrocomplexes and their thermostabilization effect on the activity of the enzyme penicillin G acylase

Stimuli‐responsive poly[(N‐isopropylacrylamide‐co‐maleic anhydride)‐g‐poly(ethylene oxide)]/poly(ethylene imine) macrobranched macrocomplexes were synthesized by (1) the radical copolymerization of N‐isopropylacrylamide and maleic anhydride with α,α′‐azobisisobutyronitrile as an initiator in 1,4‐dioxane at 65 °C under a nitrogen atmosphere, (2) the polyesterification (grafting) of prepared poly(N‐isopropylacrylamide‐co‐maleic anhydride) containing less than 20 mol % anhydride units with α‐hydroxy‐ω‐methoxy‐poly(ethylene oxide)s having different number‐average molecular weights (M_n = 4000, 10,000, or 20,000), and (3) the incorporation of macrobranched copolymers with poly(ethylene imine) (M_n = 60,000). The composition and structure of the synthesized copolymer systems were determined by Fourier transform infrared, ¹H and ¹³C NMR spectroscopy, and chemical and elemental analyses. The important properties of the copolymer systems (e.g., the viscosity, thermal and pH sensitivities, and lower critical solution temperature behavior) changed with increases in the molecular weight, composition, and length of the macrobranched hydrophobic domains. These copolymers with reactive anhydride and carboxylic groups were used for the stabilization of penicillin G acylase (PGA). The conjugation of the enzyme with the copolymers significantly increased the thermal stability of PGA (three times at 45 °C and two times at 65 °C). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1580–1593, 2003     

Compatibility studies of styrene and hydroxyl containing styrene copolymers with poly(ethylene oxide)

Copolymers of styrene with vinylphenyl trifluoromethyl carbinol, p-vinylphenyl trifluoromethyl carbinol, vinylphenyl hexafluorodimethyl carbinol, and p-vinylphenol are conditionally compatible with poly(ethylene oxide), depending on their composition and blending ratios, whereas copolymers of styrene and vinylphenyl methyl carbinol are much less compatible with poly(ethylene oxide), as determined by T_g criteria and differential scanning calorimetry. The crystallinity of poly(ethylene oxide) is changed in the copolymer/poly(ethylene oxide) blends, as indicated by depressions of the poly(ethylene oxide) melting point. Hydrogen-bond formation has been studied in two selected blends by infrared (IR) spectroscopy. Hydrogen bonding dissociation and reassociation as a function of temperature are reported. The conformation changes of poly(ethylene oxide) in the blends, the interaction between copolymer and poly(ethylene oxide) as well as in the reference blend, polystyrene/poly(ethylene oxide), are also investigated.     

Synthesis of new amphiphilic diblock copolymers containing poly(ethylene oxide) and poly(α‐olefin)

This article discusses an effective route to prepare amphiphilic diblock copolymers containing a poly(ethylene oxide) block and a polyolefin block that includes semicrystalline thermoplastics, such as polyethylene and syndiotactic polystyrene (s‐PS), and elastomers, such as poly(ethylene‐co‐1‐octene) and poly(ethylene‐co‐styrene) random copolymers. The broad choice of polyolefin blocks provides the amphiphilic copolymers with a wide range of thermal properties from high melting temperature ～270 °C to low glass‐transition temperature ～?60 °C. The chemistry involves two reaction steps, including the preparation of a borane group‐terminated polyolefin by the combination of a metallocene catalyst and a borane chain‐transfer agent as well as the interconversion of a borane terminal group to an anionic (? O^?K⁺) terminal group for the subsequent ring‐opening polymerization of ethylene oxide. The overall reaction process resembles a transformation from the metallocene polymerization of α‐olefins to the ring‐opening polymerization of ethylene oxide. The well‐defined reaction mechanisms in both steps provide the diblock copolymer with controlled molecular structure in terms of composition, molecular weight, moderate molecular weight distribution (M_w/M_n < 2.5), and absence of homopolymer. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3416–3425, 2002     

Effect of molecular weight on the refractive index increments of polystyrene,poly(ethylene glycol), poly(propylene glycol), and poly(dichlorophenylene oxide) in solution

The variation of refractive index increments with molecular weight has been studied using solutions of polystyrene (2.2 × 10³ < M_w < 1.8 × 10⁶), poly(ethylene glycol) (1.0 × 10³ < M_w < 2.0 × 10⁴), and poly(dichlorophenylene oxide) (3.3 × 10³ < M_w < 4.8 × 10⁵) in toluene and poly(propylene glycol) (1.2 × 10³ < M_w < 4.0 × 10³) in benzene. The refractive index increments of polyglycols containing aliphatic ether moieties are negative in these solvents. However, poly(dichlorophenylene oxide) polymers, which contain aromatic ether moieties, give positive values. Linear and branched halogenated poly(phenylene oxide)s show an asymptotic approach of the refractive index increment to the same limiting value, but the approach is more rapid for the branched polymer.     

Multibranched star-shaped polyethers

Synthesis of multibranched star-shaped polyethers having poly(ethylene oxide)s (PEO) arms is described. The novel method of preparing these multibranched macromolecules consists in reaction of the -OH ended oligomers with dicyclic compounds; e.g. monoalkyl ethers of poly(ethylene oxide) with diepoxides in the presence of a basic catalyst, converting a part of the ∼OH groups into ∼OC^σ end groups (alkoxide anions). Analysis of the structure of these macromolecules was mostly based on ¹H NMR, MALDI-TOF, and SEC with triple detection. The absolute values of M_w (LS), M_w/M_n, and [η] are given, indicating formation of macromolecules of high molar mass and highly branched. The number of branches was estimated by several methods, including comparison of the Mark-Houwink (M-H) dependencies of the obtained products with the M-H dependence for PEO stars with exactly known number of arms. The final stars were phosphorylated at the −OH ended branches. Almost exclusively monoesters of phosphoric acid were found in ³¹P (¹H) NMR.     

Melting behavior of ethylene oxide–propylene oxide (sym-PEP) block copolymers

Melting points and lamellar thicknesses have been measured for ethylene oxide–propylene oxide block copolymers (sym-PEP) with central poly(ethylene oxide) block lengths of 70–100 chain units and end poly(propylene oxide) block lengths of 0–30 chain units. Melting points of the block copolymers are lower than those of the corresponding poly(ethylene oxide) homopolymer by an amount (up to 15°C) which increases as the poly(propylene oxide) block length increases. Most samples have more than one melting transition, which can be assigned to variously folded chain crystals. End interfacial free energies σ_e for the various crystals have been estimated by use of Flory's theory of melting of block copolymers. For a given crystal type (e.g., once-folded-chain) σ_e is higher the longer the chain length of the end poly(propylene oxide) blocks. For a given copolymer σ_e is lower, the more highly folded the poly(ethylene oxide) chain.     

Preparation of poly(ethylene oxide)‐block‐poly(isoprene) by nitroxide‐mediated free radical polymerization from PEO macroinitiators

Amphiphilic poly(ethylene oxide)‐block‐poly(isoprene) (PEO‐b‐PI) diblock copolymers were prepared by nitroxide‐mediated polymerization of isoprene from alkoxyamine‐terminal poly(ethylene oxide) (PEO). PEO monomethyl ether (M_n ≈ 5200 g/mol) was functionalized by esterification with 2‐bromopropionyl bromide with subsequent copper‐mediated replacement of the terminal bromine with 2,2,5‐trimethyl‐4‐phenyl‐3‐azahexane‐3‐nitroxide. The resulting PEO‐alkoxyamine macroinitiator was used to initiate polymerization of isoprene in bulk and in solution at 125 °C to yield PEO‐b‐PI block copolymers with narrow molecular weight distributions (M_w/M_n ≤ 1.1). Polymerizations were first order in isoprene through 35% conversion. Micellar aggregates of PEO‐b‐PI in aqueous solution were crosslinked by treatment with a water‐soluble redox initiating system, and persistent micellar structures were observed in the dry state by AFM. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2977–2984, 2005     

Intrinsic viscosity of polymers of low molecular weight

Experimental evidence concerning the dependence of the intrinsic viscosity [η] on molecular weight M in the low molecular weight range (from oligomers to M = 5 × 10⁴) has been collected in a variety of solvents for about ten polymers, i.e., polyethylene, poly(ethylene oxide), poly(propylene oxide), polydimethylsiloxane, polyisobutylene, poly(vinylacetate), poly(methyl methacrylate), polystyrene, poly-α-methylstyrene, and some cellulose derivatives. In theta solvents, the constancy of the ratio [η]Θ/M^0.5 extends down to values of M much lower than those predicted by current hydrodynamic theories. In good solvents, and on decreasing M, the polymers examined, with the exception of polyethylene and some cellulose derivatives, show a decrease in the exponent a of the Mark-Houwink equation [η] = KM^a. This upward curvature gives rise to the existence of a more or less extended linear region where the equation [η] = K₀M^0.5 is obeyed. Below the linear range, i.e., for even shorter chains, the exponent a can increase, i.e., polydimethylsiloxane, or decrease below 0.5, i.e., poly(ethylene oxide), depending on the particular chain properties. These different dependences have been discussed in terms of: (a) variations of thermodynamic interactions with molecular weight; (b) variations of conformational characteristics (as for instance the ratio) 〈r0²/nl²〉, where 〈r0²〉 is the unperturbed mean square end-to-end distance and n is the number of bonds each of length l; (c) hydrodynamic properties of short chains.     

Synthesis and self‐assembly morphologies of amphiphilic multiblock copolymers [poly(ethylene oxide)‐b‐polystyrene]n via trithiocarbonate‐embedded PEO macro‐RAFT agent

An amphiphilic multiblock copolymer [poly(ethylene oxide)‐b‐polystyrene]_n [(PEO‐b‐PS)_n] is synthesized by using trithiocarbonate‐embedded PEO as macro‐RAFT agent. PEO with four inserted trithiocarbonate (M_n = 9200 and M_w/M_n = 1.62) groups is prepared first by condensation of α, ω‐dihydroxyl poly(ethylene oxide) with S, S′‐Bis(α, α′‐dimethyl‐α″‐acetic acid)‐trithiocarbonate (BDATC) in the presence of pyridine, then a series of goal copolymers with different St units (varied from 25 to 218 per segment) are obtained by reversible addition‐fragmentation chain transfer (RAFT) polymerization. The synthesis process is monitored by size exclusion chromatography (SEC), ¹H NMR and FT‐IR. The self‐assembled morphologies of the copolymers are strongly dependent of the length of PS block chains when the chain length of PEO is fixed, some new morphologies as large leaf‐like aggregates (LLAs), large octopus‐like aggregates (LOAs), and coarse‐grain like micelles (CGMs) are observed besides some familiar aggregates as large compound vesicles (LCVs), lamellae and rods, and the effect of water content on the morphologies is also discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6071–6082, 2006     

Carbenoid polycondensation with telechelic polyethers having dichloroacetic acid ester groups

Poly(ethylene oxide) [poly(EO)], with number-average molecular weights (M_ns) of 1000 and 2000, and poly(tetrahydrofuran) [poly(THF)] with M_ns of 1000 and 2000, possessing dichloroacetic acid ester end groups ( 1 , and 2 , respectively) were prepared from precursor diols by esterification with dichloroacetyl chloride in the presence of pyridine. 1 and 2 were subjected to the reaction with copper metal in DMSO to produce the corresponding segmented polyethers containing fumarate/maleate groups within the main chain ( 3 and 4 , respectively), through a polycondensation of carbalkoxy carbenoid intermedlates generated via α, α-dichloro elimination from the end groups of 1 and 2 . The radical polymerization of styrene in the presence of 3 and 4 produced network copolymers consisting of poly (EO) or poly(THF) and polystyrene segments. © 1994 John Wiley & Sons, Inc.     

Study of molecular motion of block copolymers in solution by high-resolution proton magnetic resonance

Molecular motions of hydrophobic–hydrophilic water-soluble block copolymers in solution were investigated by high-resolution proton magnetic resonance (NMR). Samples studied include block copolymers of polystyrene–poly(ethylene oxide), polybutadiene–poly(ethylene oxide), and poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide). NMR measurements were carried out varying molecular weight, temperature, and solvent composition. For AB copolymers of polystyrene and poly(ethylene oxide), two peaks caused by the phenyl protons of low-molecular-weight (M?_n = 3,300) copolymer were clearly resolved in D₂O at 100°C, but the phenyl proton peaks of high-molecular-weight (M?_n = 13,500 and 36,000) copolymers were too broad to observe in the same solvent, even at 100°C. It is concluded that polystyrene blocks are more mobile in low-molecular-weight copolymer in water than in high-molecular-weight copolymer in the same solvent because the molecular weight of the polystyrene block of the low-molecular-weight copolymer is itself small. In the mixed solvent D₂O and deuterated tetrahydrofuran (THF-d₈), two peaks caused by the phenyl protons of the high-molecular-weight (M?_n = 36,000) copolymer were clearly resolved at 67°C. It is thought that the molecular motions of the polystyrene blocks are activated by the interaction between these blocks and THF in the mixed solvent.     

Unperturbed dimensions of poly(ethylene oxide)

The intrinsic viscosities of fractions of poly(ethylene oxide) in the molecular weight range 1.5 × 10³ to 10⁶ have been measured at 25°C in benzene, carbon tetrachloride, and acetone; at 35°C in 0.45M aqueous potassium sulfate; and at 50°C in methyl isobutyl ketone and diethylene glycol diethyl ether. The latter three are practically theta solvents. The value of (r₀² /M)^1/2 for poly(ethylene oxide) is calculated to be 0.84 Å from the molecular weights of the high molecular weight fractions, and their intrinsic viscosities in the theta solvents and acetone. Erroneous values result if the usual methods of determination are applied to the data obtained for the low molecular weight (<10⁴) fractions or to the intrinsic viscosities in the very good solvents, benzene and carbon tetrachloride.     

Thermoresponsive star triblock copolymers by combination of ROP and ATRP: From micelles to hydrogels

Novel biocompatible, biodegradable, four‐arm star, triblock copolymers containing a hydrophobic poly(ε‐caprolactone) (PCL) segment, a hydrophilic poly(oligo(ethylene oxide)475 methacrylate) (POEOMA475) segment and a thermoresponsive poly(di(ethylene oxide) methyl ether methacrylate) (PMEO₂MA) segment were synthesized by a combination of controlled ring‐opening polymerization (ROP) and atom transfer radical polymerization (ATRP). First, a four‐arm PCL macroinitiator [(PCL‐Br)₄] for ATRP was synthesized by the ROP of ε‐caprolactone (CL) catalyzed by stannous octoate in the presence of pentaerythritol as the tetrafunctional initiator followed by esterification with 2‐bromoisobutyryl bromide. Then, sequential ATRP of oligo(ethylene oxide) methacrylate (OEOMA475, M_n = 475) and di(ethylene oxide) methyl ether methacrylate) (MEO₂MA) were carried out using the (PCL‐Br)₄ tetrafunctional macroinitiator, in different sequence, resulting in preparation of (PCL‐b‐POEOMA475‐b‐PMEO₂MA)₄ and (PCL‐b‐PMEO₂MA‐b‐POEOMA475)₄ star triblock copolymers. These amphiphilic copolymers can self‐assemble into spherical micelles in aqueous solution at room temperature. The thermal responses of the polymeric micelles were investigated by dynamic light scattering and ultraviolet spectrometer. The properties of the two series of copolymers are quite different and depend on the sequence distribution of each block along the arms of the star. The (PCL‐b‐POEOMA475‐b‐PMEO₂MA)₄ star copolymer, with the thermoresponsive PMEO₂MA segment on the periphery, can undergo reversible sol‐gel transitions between room temperature (22 °C) and human body temperature (37 °C). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

ESR spectroscopy to determine the molecular mobility of poly(ethylene oxide) grafts in amphiphilic graft copolymers

The ethylene oxide (EO) mobility in polystyrene-graft-[poly(ethylene oxide)] (PS-g-PEO) and polystyrene-graft-[stearyl poly(ethylene oxide)] (PS-g-SPEO) copolymers was evaluated by spin probe techniques. The ESR spectra indicate that 4-hydroxyl-TEMPO (TEMPO = 2,2,6,6-tetramethylpiperidine-N-oxyl) is strongly biased to the PEO phase of the PS-g-(S)PEO membranes. The rotational correlation time τ_c can also be employed to assess the PEO mobility in PS-g-(S)PEO membranes. Although τ_c of PS-g-(S)PEO usually decreases with increasing surface density of EO, it is of interest that τ_c is rather high when the surface within a depth of at least 5 nm is fully occupied by SPEO (sample PS-g-SPEO-72.6).     

The preparation and characterisation of novel polyether gels

Poly(ethylene oxide)s end-capped with n-alkane chains (C₁₆-C₂₁) have been found to form stable gels in aqueous media. The crosslinks are believed to occur through association of the n-alkane chains. The dependence of the degree of swelling of the gels on the lengths of the alkane and poly(ethylene oxide)(M_n= 10000, 20000 and 30000) chains were studied. Degrees of swelling have been compared with results predicted by simple network theory.