Hyperbranched polymers from divinylbenzene and 1,3-diisopropenylbenzene through anionic self-condensing vinyl polymerization

Hyperbranched polymers were synthesized using anionic self-condensing vinyl polymerization (ASCVP) by forming ‘inimer’ (initiator within a monomer) in situ from divinylbenzene (DVB) and 1,3-diisopropenylbenzene (DIPB) using anionic initiators in THF at −40 °C. The reaction of equimolar amounts of DVB and nBuLi results in the formation of hyperbranched poly(divinylbenzene) through self-condensing vinyl polymerization (SCVP). The hyperbranched polymers were invariably contaminated with small amount of gel (<15%). No gelation was observed when using DIBP with anionic initiators. The presence of monomer-polymer equilibrium in the SCVP of DIPB restricts the growth of hyperbranched poly(DIPB). The inimer synthesized from DIPB at 35 °C undergoes intermolecular self-condensation to different extent depending on the nature of anionic initiator at −40 °C. The molecular weight of the hyperbranched polymers was higher when DPHLi was used as initiator. A small amount of styrene ([styrene]/[Li⁺]=1) was used to promote the chain growth by inducing cross-over reaction with styrene, and subsequent reaction of styryl anion with isopropenyl groups of inimer/hyperbranched oligomer. The hyperbranched polymers were soluble in organic solvents and exhibited broad molecular weight distribution (2<M_w/M_n<17).     

Synthesis and radical polymerization of end-allenoxy polyoxyethylene macromonomer

Poly(ethylene glycol) allenyl methyl ether (2) was prepared by the reaction of poly(ethylene glycol) monomethyl ether (the number average molecular weight (M_{n) = 550}) with propargyl bromide, followed by the base-catalyzed isomerization reaction. Functionality of end-allenyl groups in the obtained macromonomer was determined as 92% (from ¹H-NMR). The radical polymerization of 2 was carried out in bulk and in benzene at 60 or 120°C to yield a polymer with poly(ethylene glycol) side chains. For instance, a polymer (3, M_n = 3900) was obtained in 39% yield by the polymerization of 2 in bulk at 60°C for 48 h using 6 mol% of α,α′-azobisisobutyronitrile (AIBN). The obtained polymer was soluble in organic solvents as well as water.     

Biodegradable multiblock PEO/PLA thermoplastic elastomers: molecular design and properties

Given the need for highly flexible biodegradable polymers, a series of poly(ethylene oxide)/poly(l-lactic acid) (PEO/PLA) (PELA) multiblock poly(ether-ester-urethane)s, were synthesized and characterized. The first step of the synthesis consisted of the ring-opening polymerization of l-lactide, initiated by the hydroxyl terminal groups of the PEO chain, followed by the chain extension of these PLA-PEO-PLA triblocks, using hexamethylene diisocyanate (HDI). The trimers comprised PEO segments in the 1000-10,000 molecular weight range, with the length of each PLA block covering the 200-10,000 interval. DSC and X-ray analyses revealed that, depending on their composition, amorphous matrices, monophasic crystalline materials and copolymers comprising two crystalline phases, were generated. The multiblock copolymers synthesized exhibited superior mechanical properties, with ultimate tensile strength values around 30 MPa, Young's moduli as low as 14 MPa and elongation at break values well above 1000%. Because of their phase segregated morphology, most of these multiblock copolymers displayed remarkable mechanical properties also when fully hydrated, with typical UTS values around 9 MPa.     

Formation of dendrite crystals in poly(ethylene oxide) interacting with bioresourceful tannin

A dendritic morphology, induced by miscibility with strong intermolecular interaction between poly(ethylene oxide) (PEO) and bioresourceful tannin [tannic acid (TA)]. Mechanism was investigated by differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy, wide-angle X-ray diffraction, and polarized optical microscopy. The cell crystallography preference in correlation to the intermolecular interaction in the dendrites in PEO/TA (70/30) blend was analyzed. Dendritic morphology was more distinct at PEO/TA = 70/30 composition, where the spherulitic growth rate showed a highly nonlinear relationship with respect to crystallization time (R α t ^1/2). Diffusion limitation mechanism caused by the crystallography preference attributed to the strong intermolecular interaction between PEO and TA was at work.     

Synthesis and physicochemical characterization of a well-defined poly(butadiene 1,3)-block-poly(dimethylsiloxane) copolymer

For the first time, order-order and order-disorder transitions were detected and characterized in a model diblock copolymer of poly(butadiene-1,3) and poly(dimethylsiloxane) (PB-b-PDMS). This model PB-b-PDMS copolymer was synthesized by the sequential anionic polymerization (high vacuum techniques) of butadiene 1,3 (B) and hexamethylciclotrisiloxane (D₃), and subsequently characterized by nuclear magnetic resonance (¹H and ¹³C NMR), size exclusion chromatography (SEC), Fourier Transform infrared spectroscopy (FTIR), Small-Angle X-ray scattering (SAXS) and rheology. SAXS combined with rheological experiments shows that the order-order and order-disorder transitions are thermoreversible. This fact indicates that the copolymer has sufficient mobility at the timescale and at the temperatures of interest to reach their equilibrium morphologies.     

Miscibility of C60-end-capped poly(ethylene oxide) with poly(vinyl chloride)

The miscibility of blends of single [60]fullerene (C₆₀)-end-capped poly(ethylene oxide) (FPEO) or double C₆₀-end-capped poly(ethylene oxide) (FPEOF) with poly(vinyl chloride) (PVC) has been studied. Similar to poly(ethylene oxide) (PEO), both FPEO and FPEOF are also miscible with PVC over the entire composition range. X-ray photoelectron spectroscopy showed the development of a new low-binding-energy Cl2p doublet and a new high-binding-energy O1s peak in FPEO/PVC blends. The results show that the miscibility between FPEO and PVC arises from hydrogen bonding interaction between the α-hydrogen of PVC and the ether oxygen of FPEO. From the melting point depression of PEO, FPEO or FPEOF in the blends, the Flory-Huggins interaction parameters were found to be −0.169, −0.142, −0.093 for PVC/PEO, PVC/FPEO and PVC/FPEOF, respectively, demonstrating that all the three blend systems are miscible in the melt. However, the incorporation of C₆₀ slightly impairs the interaction between PEO and PVC.     

Poly(hydroxyether sulfone) and its blends with poly(ethylene oxide): miscibility, phase behavior and hydrogen bonding interactions

Poly(hydroxyether sulfone) (PHES) was synthesized through polycondensation of bisphenol S with epichlorohydrin. It was characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy and differential scanning calorimetry (DSC). The miscibility in the blends of PHES with poly(ethylene oxide) (PEO) was established on the basis of the thermal analysis results. DSC showed that the PHES/PEO blends prepared by casting from N,N-dimethylformamide (DMF) possessed single, composition-dependent glass transition temperatures (T_gs), indicating that the blends are miscible in amorphous state. At elevated temperatures, the PHES/PEO blends underwent phase separation. The phase behavior was investigated by optical microscope and the cloud point curve was determined. A typical lower critical solution temperature behavior was observed in the moderate temperature range for this blend system. FTIR studies indicate that there are the competitive hydrogen bonding interactions upon adding PEO to the system, which was involved with the intramolecular and intermolecular hydrogen bonding interactions, i.e. -OH?OS, -OH?-OH and -OH versus ether oxygen atoms of PEO between PHES and PEO. In terms of the infrared spectroscopic investigation, it is judged that from weak to strong the strength of the hydrogen bonding interactions is in the following order: -OH?OS, -OH?-OH and -OH versus ether oxygen atoms of PEO.     

Multiarm star poly(glycidol)-block-poly(styrene) as modifier of anionically cured diglycidylether of bisphenol A thermosetting coatings

Well-defined multiarm star copolymer poly(glycidol)-b-poly(styrene) (PGOH-b-PS) with an average number of PS arms per molecule of 85 has been prepared. The core first approach has been selected as the methodology using atom transfer radical polymerization (ATRP) of styrene to grow the arms from an activated hyperbranched poly(glycidol) as core. This activated hyperbranched macroinitiator was prepared by esterification of hyperbranched poly(glycidol) (PGOH) with 2-bromoisobutyryl bromide.PGOH-b-PS was used to modify diglycidylether of bisphenol A coatings cured by anionic ring-opening mechanism using 1-methyl imidazole as the initiator. The kinetics of the curing process, studied by dynamic scanning calorimetry (DSC), was not much affected when PGOH-b-PS was added to the formulation. By rheometry the effect of this new polymer topology on the complex viscosity (η^*) of the reactive mixture was analyzed. The phase-separation of the modified coatings was proved by dynamic thermomechanical analysis (DMTA) and electronic microscopy (SEM and TEM) showing nano- or microphase separation as a function of the modifier content. The addition of this star polymer led to increase in the rigidity in terms of Young's modulus and in the microhardness in comparison to neat DGEBA.     

Polyimides with main-chain ethylene oxide units: synthesis and properties

This paper describes the synthesis of a new series of well-defined bis(ether anhydride)s based on ethylene oxide sequences of known length (up to six ethylene oxide units) with phthalic acid anhydride end-caps, and extends the synthesis of bisphenoxyamines based on ethylene oxide sequences to six ethylene oxide units. The dianhydrides and diamines were used in combination to synthesize a series of segmented polyimides of well-defined structures having defined sequences of from zero up to six ethylene oxide units separated by N-phenylphthalimide units. The polymers are characterized in terms of solubility, thermal stability, thermal transition behaviour, including crystal melting behaviour; glass-transition temperatures vary systematically with structure and composition. One polymer exhibits liquid crystallinity. The water absorption characteristics of the polymers, which vary from a hydrophobic aromatic polyimide to polymers containing up to 52.7 wt% ethylene oxide, were determined. The crystal melting behaviour is discussed in conjunction with data from other segmented polyimides containing similar structural units.     

Solution and bulk rheological behavior of poly(ethylenes) based on VERSIPOL™ catalysts

Palladium catalysts [(ArNC(Me)-C(Me)NAr)Pd(CH₂)₃(COOMe)]⁺ (VERSIPOL™) or [(ArNC(Me)-C(Me)NAr)Pd(CH₂)₃(COOMe)]⁺ (Ar=2,6-i-Pr₂-C₆H₃, 2,6-Me₂-C₆H₃ or C₆H₅ and Ar′=3,5-(CF₃)₂-C₆H₃) were synthesized and tested, in dichloromethane, for the polymerization of ethylene. The influence of the substituent present on the diimine ligand on the molar mass of the resulting polymers was examined first. Poly(ethylene)s obtained in the presence of catalysts containing the bulky 2,6-i-Pr₂ group, prepared at different ethylene pressures, exhibited almost identical weight average molar mass values, but were characterized by great differences in hydrodynamic volume, radius of gyration and intrinsic viscosity values. These differences were attributed to the evolution of the topology going from hyperbranched to almost linear. Similar observations were made earlier. The major part of the work dealt with new results on the behavior of these PE samples examined in terms of particle scattering function q^5/3I(q) (Kratky-Porod) plot based on small angle neutron scattering experiments and on the semi-dilute solution behavior. Some results on the bulk rheological properties of these polymers were presented in the last section and corroborated the results obtained in dilute or semi-dilute solution. The data were compared also to PE obtained with other catalysts.     

Poly(ethylene oxide) and its blends with sodium alginate

A series of blends based on poly(ethylene oxide) (PEO) and sodium alginate (NaAlg) were prepared by solution casting method. The blends thus obtained were characterized by using Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), tensile strength test, contact angle measurements and atomic force microscopy (AFM). FT-IR studies indicate that there are the hydrogen bonding interactions due to the ether oxygen of PEO and the hydroxyl groups of NaAlg. The thermal stability of the blends was slightly affected with increasing NaAlg content. DSC results showed that both melting point and crystallinity depend on the composition of the blends. Mechanical properties of the blend films were improved compared to those of homopolymers. Surface free energy components of the blend films were calculated from contact angle data of various liquids by using Van Oss-Good methodology. It was found that the surfaces both of the blends are enriched in low surface free energy component, i.e. NaAlg. This conclusion was further confirmed by the AFM images observation of the surface morphology of these blends.     

Solvent assisted post-polymerization of PET

We have examined the influence of the solvent mixture diphenyl ether-biphenyl (DPE-BP) on the post-polymerization of poly(ethylene terephthalate) (PET) of intrinsic viscosity (IV=0.42 dL/g) in the swollen state and in solution, by following the IV increase and the end-group depletion. During the swollen state polymerization (SwSP) of thin disks (180 μm) at 195 °C, the initially rapid step growth polymerization slows dramatically beyond IV=1.2 dL/g in 5 h, and is unable to proceed beyond 1.4 dL/g. This appears to be related to the temporarily restricted mobility of the end groups due to the observed solvent induced crystallization, because sufficient reactive end groups can be directly detected, and further post-polymerization in melt state is possible. When limitations due to crystallization are eliminated by carrying out post-polymerization in solution at 250 °C, it proceeds to IV=1.8 dL/g in a single step. Since solution polymerization eliminates the requirement of handling fine PET particles, it offers an attractive route to high molecular weight PET, particularly when the solution can be directly used for further processing, e.g. into fibers.     

Formation of banded and non-banded poly(l-lactic acid) spherulites during crystallization of films of poly(l-lactic acid)/poly(ethylene oxide) blends

In this study, a series of poly(l-lactic acid) (PLLA)/poly(ethylene oxide) (PEO) blends with different PLLA concentrations was prepared. Films of these blends crystallized with and without a coverslip were characterized by the presence and absence of banded structures, respectively. This difference in morphology was observed because the PEO component of the blends was oxidized at a high temperature (125 °C) in air without the protection of a coverslip. X-ray photoelectron spectroscopy (XPS) results showed that the surface of the blends crystallized in nitrogen without a coverslip contained mostly PLLA while the surfaces of the same blends crystallized under a coverslip contained only a moderately higher concentration of PLLA than their bulks. The migration of PLLA to the surface of the blends during crystallization in nitrogen when no coverslip was used was due to its low surface tension. Phase images obtained using atomic force microscopy (AFM) indicated that the banded structures consisted of valleys and ridges, which were in fact flat-on and edge-on lamellae, respectively. A detailed time-of-flight secondary ion mass spectrometry (ToF-SIMS) examination suggested that PLLA and PEO were located mainly on the surfaces of the ridges and valleys, respectively.     

High yield preparation of all-organic raspberry-like particles by heterocoagulation via hydrogen bonding interaction

We describe here a straightforward strategy towards the high yield preparation of raspberry-like all-organic particles. Poly(acrylic acid)-b-poly(butyl acrylate) core–shell nanoparticles (D ∼ 80 nm) and larger poly(ethylene oxide)-b-poly(butyl acrylate) core–shell (D ∼ 230 nm), synthesized by RAFT emulsion polymerization, were mixed at high solids content (23 wt%) at room temperature without any particular precaution (no dropwise addition, no pH adjustment). Raspberry-like particles constituted of one central PEO-b-PBA particle surrounded by about thirty PAA-b-PBA particles were successfully obtained, with no coagulum formation. The heteroaggregation process is probably driven by the hydrogen-bond interactions between the PAA and the PEO shells of the particles. The raspberry-like particles were characterized using electron microscopy (TEM and cryo-TEM), dynamic light scattering (DLS), chromatography (HDC) and calorimetry (ITC), demonstrating the selectivity of the process.     

Synthesis of hydroxyl-capped comb-like poly(ethylene glycol) to develop shell cross-linkable micelles

A novel hydroxyl-capped comb-like poly[poly(ethylene glycol) methacrylate] (PPEGMA) was prepared via atom transfer radical polymerization (ATRP) of α-methylacryloyl-ω-hydroxyl-poly(ethylene glycol) at ambient temperature. The polymerization kinetics of the block copolymer was studied by gel permeation chromatography (GPC) and ¹H NMR. It is of interest to find the well-defined comb-like PEG can associate into micelles, which have hydrophilic PEG shell end-capped by hydroxyl groups. The hydroxyl in the shell were further cross-linked by divinyl sulfone (DVS), which could couple with two capped-end hydroxyl groups. The XPS, TEM, AFM and laser scattering particle size distribution analyzer results revealed that reactive micelles could be cross-linked by DVS. The reactive, cross-linkable micelles with PEG shell may have great potential as new drug carrier and nanoreactor, etc.     

Synthesis and characterization of poly (ethylene oxide) containing copolyimides for hydrogen purification

Reverse selective membranes comprising poly(ethylene oxide) (PEO) containing copolyimides (PEO-PI) with variations of acid dianhydrides and diamines have been synthesized for hydrogen purification. The reverse selectivity of the membranes decimate the energy required for hydrogen recompression process. Factors including PEO content, PEO molecular weight, and fractional free volume (FFV) that would affect the gas transport performance have been investigated and elucidated in terms of degree of crystallinity, phase separation in the PEO domain as well as inter-penetration between the hard and soft segments. In mixed gas tests of CO₂ and H₂ mixtures, a highly condensable CO₂ out compete H₂ for the sorption sites in hard segment and diminishes H₂ permeability. Thus the CO₂/H₂ selectivity in the mixed gas tests is much higher than that in pure gas tests. Mixed gas permeation tests at 35 °C and 2atm show that the best reverse selective membranes have a CO₂ permeability of 179.3 Barrers and a CO₂/H₂ permselectivity of 22.7. The physical properties of PEO-PIs have also been characterized by FTIR, DSC, GPC, WAXS, AFM and tensile strain tests.     

High molecular weight poly( -lactide) and poly(ethylene oxide) blends: thermal characterization and physical properties

The miscibility of high molecular weight poly( -lactide) PLLA with high molecular weight poly(ethylene oxide) PEO was studied by differential scanning calorimetry. All blends containing up to 50 weight% PEO showed single glass transition temperatures. The PLLA and PEO melting temperatures were found to decrease on blending, the equilibrium melting points of PLLA in these blends decreased with increasing PEO fractions. These results suggest the miscibility of PLLA and PEO in the amorphous phase. Mechanical properties of blends with up to 20 weight% PEO were also studied. Changes in mechanical properties were small in blends with less than 10 weight% PEO. At higher PEO concentrations the materials became very flexible, an elongation at break of more than 500% was observed for a blend with 20 weight% PEO. Hydrolytic degradation up to 30 days of the blends showed only a small variation in tensile strength at PEO concentrations less than 15 weight%. As a result of the increased hydrophilicity, however, the blends swelled. Mass loss upon degradation was attributed to partial dissolution of the PEO fraction and to an increased rate of degradation of the PLLA fraction. Significant differences in degradation behaviour between PLLA/PEO blends and (PLLA/PEO/PLLA) triblock-copolymers were observed.     

Synthesis of hyperbranched polymers via a facile self-condensing vinyl polymerization system - Glycidyl methacrylate/Cp2TiCl2/Zn

A facile self-condensing vinyl polymerization (SCVP) system, the combination of glycidyl methacrylate, Cp₂TiCl₂ and Zn, has been firstly used to prepare novel hyperbranched polymers, consisting of vinyl polymers as the backbone, and cyclic ester polymers (poly(?-caprolactone) or poly(l-lactide)) as the side chains. The polymerizations are initiated by the epoxide radical ring-opening catalyzed by Cp₂Ti(III)Cl which is generated in situ via the reaction of Cp₂TiCl₂ with Zn. The key to success is that the polymerizations can proceed concurrently via two dissimilar chemistries possessing the opposite active initiating species, including ring-opening polymerization (ROP) and controlled/living radical polymerization (CRP). We have demonstrated that this facile one-step polymerization technique can be applied successfully to prepare highly branched polymers with a multiplicity of end reactive functionalities including Ti alkoxide, hydroxyl and vinyl functional groups.     

Preparation and electrochemical behaviors of polymeric composite electrolytes containing mesoporous silicate fillers

In the present study, poly(ethylene oxide) (PEO)-based polymeric composite electrolytes (PCEs) had been prepared by using a different content of mesoporous silicate MCM-41, in order to examine the filler addition effect on the microstructural and electrochemical properties. The interactions between MCM-41 and PEO matrix were studied by XRD, DSC, and SEM techniques. The electrochemical properties of the PCEs, such as ionic conductivity, its temperature dependence, and lithium transference number were investigated. MCM-41 could maintain the pore structure effectively, resulting in nanocomposites that were homogeneously complexed with the PEO chains. The PCEs with 8 wt.% MCM-41 showed the smallest crystallinity, 30.4%. Accordingly, those PCEs showed the highest ion conductivity, 1.2 × 10⁻⁴ S/cm, a two-order-of-magnitude higher value than that of the pristine PEO-LiClO₄. This might have reflected decreased crystallinity and improved ion transport. Furthermore, those PCEs showed an increased Li ion transference number of ∼0.5. In conclusion, the filler addition could enhance the ionic conductivity and increase the Li ion transference number at the same time.     

The influence of competitive interactions on multiple eutectic phase behavior in poly(ethylene oxide) molecular complexes

Binary mixtures of poly(ethylene oxide) and resorcinol exhibit two eutectic phase transitions at 40 and 80 °C, which are separated by a single-phase stoichiometric complex at ≈33 mol% resorcinol. These eutectic temperatures increase slightly at higher molecular weights of poly(ethylene oxide). The eutectics and the molecular complex are absent in ternary mixtures with either 25 or 40 wt% poly(2-vinylpyridine) because both polymers contain electron-pair donors which participate in hydrogen bonding interactions with the hydroxyl groups of the small-molecule aromatic. In contrast, 25 wt% polystyrene does not disrupt the bi-eutectic phase behavior of poly(ethylene oxide) and resorcinol because polystyrene is inert in these ternary mixtures. The lightest lanthanides with the largest ionic radii in the first-row of the f-block, like LaCl₃(H₂O)₆ and CeCl₃(H₂O)_x, are more effective than neodymium, terbium and ytterbium trichloride hexahydrates from the viewpoint of (i) competing with resorcinol, (ii) interacting with poly(ethylene oxide), (iii) eliminating eutectic melting, and (iv) disrupting the 2:1 stoichiometric complex between poly(ethylene oxide) and resorcinol. High-resolution ¹³C solid state NMR spectroscopy identifies resorcinol in several different molecular environments. Multiple resonances are observed for chemically equivalent, but morphologically and crystallographically inequivalent, ¹³C sites in the solid state. The isotropic chemical shift of the phenolic ¹³C site in this small-molecule aromatic is very sensitive to the strength of intermolecular interactions in various phases. For example, self-association of resorcinol in pure crystalline phase γ yields a phenolic carbon chemical shift at 155 ppm. The formation of a 2:1 stoichiometric complex between poly(ethylene oxide) and resorcinol in co-crystallized phase β is identified by a phenolic carbon chemical shift at 158 ppm. When resorcinol and poly(2-vinylpyridine) interact in a homogeneous amorphous phase, the phenolic carbon resonance appears at a chemical shift of 160 ppm. A resorcinol-rich disordered crystalline phase in ternary mixtures with poly(ethylene oxide) and poly(2-vinylpyridine) yields a phenolic carbon resonance at 159 ppm. Temperature-composition projections of the binary and ternary phase diagrams, constructed via differential scanning calorimetry, allow one to interpret ¹³C NMR spectra of these strongly interacting blends and complexes in the solid state.