Synthesis and characterization of phenolic hydroxyl terminated phenylquinoxaline oligomers

The synthesis of phenylquinoxaline oligomers of predictable molecular weight and with phenolic hydroxyl functional end groups is reported. The synthetic procedure utilizes 4-hydroxybenzil as a substituted monofunctional monomer in a conventional PPQ synthesis to both control molecular weight and introduce the functional end groups. The molecular weights of the oligomers were determined by derivatization of the hydroxyl end groups with 3-(trimethylsilyl)propionyl chloride, followed by ¹H-NMR analysis. Comparison of the integration of the trimethylsilyl resonance to the aromatic resonances allowed calculation of the number average molecular weight. A plot of log(η) vs. log(M_n) correlated well with that reported for high molecular weight PPQ. The end groups influenced the solubility behavior of the oligomers in chlorinated solvents, possibly due to hydrogen bonding. The oligomers were chain-extendable to high molecular weight, confirming their suitability for utilization in copolymerizations to prepare phenylquinoxaline-based block copolymers.     

Michael addition for crosslinking of poly(caprolactone)s

Poly(caprolactone) (PCL) networks have received significant attention in the literature because of many emerging potential applications as biodegradable materials. In this study, the Michael addition reaction was used for the first time to synthesize biodegradable networks using crosslinking of acetoacetate‐functionalized PCL (PCL bisAcAc) oligomers with neopentyl glycol diacrylate. Hydroxyl‐terminated PCL telechelic oligomers with number‐average molecular weights ranging from 1000 to 4000 g/mol were quantitatively functionalized with acetoacetate groups using transacetoacetylation. In addition to difunctional PCL oligomers, hydroxyl‐terminated trifunctional star‐shaped PCL oligomers were functionalized with acetoacetate groups. Derivatization of the terminal hydroxyl groups with acetoacetate groups was confirmed using FTIR spectroscopy, ¹H NMR spectroscopy, mass spectrometry, and base titration of hydroxyl end groups. PCL bisAcAc precursors were reacted with neopentyl glycol diacrylate in the presence of an organic base at room temperature. The crosslinking reactions yielded networks with high gel contents (>85%). The thermomechanical properties of the networks were analyzed to investigate the influence of molecular weight between crosslink points. The glass transition and the extent of crystallinity of the PCL networks were dependent on the molecular weight of the PCL segment. Dynamic mechanical analysis indicated that the plateau modulus of the networks was dependent on the molecular weight of PCL, which was related to the crosslink density of the networks. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5437–5447, 2009     

Novel self-assembled molecular aggregates formed by fluoroalkyl end-capped oligomers and their application

A variety of fluoroalkyl end-capped oligomers were prepared under mild conditions by the use of fluoroalkanoyl peroxide as a key intermediate. These oligomers can form the self-assembled molecular aggregates with the aggregations of end-capped fluoroalkyl groups in aqueous and organic media. Fluorinated self-assembled molecular aggregates containing carboxyl and sulfo groups were suggested to interact with positively charged HIV-1 to exhibit a potent anti-HIV-1 activity in vitro. In contrast, fluoroalkyl end-capped oligomers containing cationic segments exhibited not only the unique surface active properties imparted by fluorine as well as the usual low-molecular fluorinated surfactants, but also high surface antibacterial activity. Fluoroalkyl end-capped oligomers containing betaine-type segments were found to cause a gelation where the strong aggregation of the end-capped fluoroalkyl groups is involved in establishing the physical gel network in water and polar organic solvents under non-crosslinked conditions. Similarly, fluoroalkyl end-capped oligomers containing hydroxyl groups could cause a gelation, where the aggregation of fluoroalkyl groups and hydrogen-bonding interaction is involved in establishing a physical gel network in water and polar organic solvents under non-crosslinked conditions. Fluoroalkanoyl peroxide is also a convenient tool for the preparation of new fluoroalkyl end-capped oligomers containing recognition moieties such as diacetone segments. These fluorinated oligomers containing recognition moieties could form the self-assembled molecular aggregates to recognize selectively the hydrophilic amino and N,N-dimethylamino compounds as guest molecules.     

Features of reaction amino-cyclocarbonate for production of new type nonisocyanate polyurethane coatings

We have studied different ways of preparing UV resistant oligomers with terminated cyclocarbonates, epoxy and amino groups. We have studied possibility of preparing HNIPU UV stable coatings. Linear and branched amino containing oligomers based on di- and tricyclocarbonates and primary diamines were investigated. It was found that oligomers should be used for curing epoxy-saturated resins, but since the residual quantity of amines this system can't be used for UV resistant coatings. The same problem was in system on the base of nonisocyanate epoxy-urethane oligomers cured by tertiary amines. Coating on the base of acrylic cyclocarbonates and oligomers with primary amines are similar to conventional polyurethane coatings on the base of acrylic hydroxyl containing oligomers and isocyanates, but mechanical properties and chemical resistance are better.     

Side chain crosslinking of aromatic polyethers for high temperature polymer electrolyte membrane fuel cell applications

Novel aromatic polymers bearing polar pyridine units in the main chain and side chain crosslinkable hydroxyl and propargyl groups have been successfully synthesized. The polymers have been investigated in terms of their critical properties related to their application in high temperature polymer electrolyte membrane fuel cells, such as doping ability, mechanical properties, and thermal stability. Crosslinked membranes were prepared by direct crosslinking of hydroxyl side chain groups with decafluorobiphenyl used for the first time as a crosslinking agent. However, further functionalization of hydroxyl groups to the propargyl derivative has also led to crosslinked polymers after thermal curing. Both types of crosslinked membranes exhibited higher glass transition temperatures as well as lower doping levels when doped in phosphoric acid compared with the non crosslinked analogs, confirming the formation of a successfully crosslinked network. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Highly Soluble Phenylethynyl-terminated Imide Oligomers and Thermosetting Polyimides Based on 2,2′3,3′-Biphenyltetracarboxylic Dianhydride

The properties of a series of imide oligomers were characterized according to their molecular weights, solubility, and thermal and rheological properties. This series of imide oligomers was synthesized via a two-step method using 2,2′,3,3′-biphenyltetracarboxylic dianhydride(3,3′-BPDA) and aromatic diamines as the monomers, and 4-phenylethynyl phtlialic anhydride(PEPA) as the end-capping agent. The imide oligomers based on 3,3′-BPDA showed excellent solubility in low boiling point solvents and low melt viscosity, which were attributed to their unique bent architectures. High-performance thermosetting polyimides were produced from these oligomers via thermal crosslinking of the phenylethynyl groups. The mechanical and thermal properties of the thermosets were studied using tensile testing, dynamic mechanical thermal analysis(DMTA), and thermogravimetric analysis(TGA). The 3,3′EPDA-based thermosets exhibited excellent thermal properties, with glass transition temperatures of up to 455℃, and 5% mass loss temperatures of up to 569℃ in air. The thermosets based on 3,3-BPDA showed superior thermal properties compared to those derived from TriA-X series oligomers.     

Comparison of Thiophene–Pyrrole Oligomers with Oligothiophenes: A Joint Experimental and Theoretical Investigation of Their Structural and Spectroscopic Properties

We have prepared a new series of mixed thiophene–pyrrole oligomers to investigate the electronic benefits arising from the combination of these two heterocycles. The oligomers are functionalized with several hexyl and aryl groups to improve both processability and chemical robustness. An analysis of their spectroscopic (absorption and emission), photophysical, electrochemical, solid state, and vibrational properties is performed in combination with quantum‐chemical calculations. This analysis provides relevant information regarding the use of these materials as organic semiconductors. The balance between the high aromatic character of pyrrole and the moderate aromaticity of thiophene allows us to address the impact of the coupling of these heterocycles in conjugated systems. The data are interpreted on the basis of the aromaticity, molecular conformations, ground and excited electronic state structures, frontier orbital topologies and energies, oxidative states, and quinoidal versus aromatic competition.     

Polycarbonate-modified epoxies. I. Studies on the reactions of epoxy resin/polycarbonate blends prior to cure

An epoxy resin based upon the diglycidyl ether of bisphenol-A was modified with poly(bisphenol A carbonate) (PC). Prior to aromatic amine cure, the possible reactions in the epoxy resin/PC blend were investigated using GPC and FTIR techniques. It was shown that at 150°C, the epoxy resin acted as a plasticizer and promoted the crystallization of PC. In addition, a transesterification between the secondary hydroxyl groups in the epoxy resin with the carbonate groups in PC occurred. This reaction resulted in degraded PC chains with phenolic hydroxyl end groups. There was no evidence of reaction of epoxide groups at 150°C in this blend. At 200°C, the secondary hydroxyl groups acted as a catalyst converting most of the aromatic–aromatic carbonates to the aromaticndash;liphatic and aliphaticndash;aliphatic carbonates through transesterification. At this elevated temperature, the secondary hydroxyl groups were regenerated by the addition reaction between the epoxide groups and the phenolic hydroxyl end groups, either from the transesterification or the hydrolysis of PC. This addition reaction combining the PC chains and epoxy chains eventually resulted in a crosslinked polymer if the extent of reaction was high. Thus, by using a melt blending process at high temperature, e.g., 200°C, a copolymer network structure of PC-modified epoxy could be formed. The fracture toughness should be increased by increasing the capability for plastic deformation due to the incorporation of PC chains into the network; results will be reported in a future study. © 1996 John Wiley & Sons, Inc.     

L-乳酸齐聚物的制备及其三羰基铼衍生物的合成

以L-丙交酯为原料, 通过正交保护基对其羧基、羟基进行修饰, 合成并表征了乳酸3个系列的12个化合物. 同时以合成得到的乳酸六聚体为原料, 合成并表征了羟基封端的聚乳酸-聚乙二醇-三齿螯合剂系列化合物, 并将其与[Et₄N]₂[Re(CO)₃Br₃]配位合成了其冷标记三羰基铼配合物. 产物通过IR, ¹H NMR, ¹³C NMR, ESI-HRMS, MALDI-HRMS或元素分析进行了表征. 该方法为扩展聚乳酸化学修饰法在材料科学中的应用奠定了基础. 此外分子量可控的乳酸-乙二醇结构铼配合物的设计合成扩展了其在分子影像科学的应用.     

BN-Embedded Polycyclic Aromatic Hydrocarbon Oligomers: Synthesis,Aromaticity, and Reactivity

BN-embedded oligomers with different pairs of BN units were synthesized by electrophilic borylation. Up to four pairs of BN units were incorporated in the large polycyclic aromatic hydrocarbons (PAHs). Their geometric, photophysical, electrochemical, and Lewis acidic properties were investigated by X-ray crystallography, optical spectroscopy, and cyclic voltammetry. The B−N bonds show delocalized double-bond characteristics and the conjugation can be extended through the trans-orientated aromatic azaborine units. Calculations reveal the relatively lower aromaticity for the inner azaborine rings in the BN-embedded PAH oligomers. The frontier orbitals of the longer oligomers are delocalized over the inner aromatic rings. Consequently, the inner moieties of the BN-embedded PAH oligomers are more active than the outer parts. This is confirmed by a simple oxidation reaction, which has significant effects on the aromaticity and the intramolecular charge-transfer interactions.     

Matrix-assisted laser desorption/ionization time-of-flight/time-of-flight tandem mass spectra of poly(butylene adipate)

Matrix-assisted laser desorption/ionization time-of-flight/time-of-flight tandem mass spectrometry (MALDI-TOF/TOF-MS/MS) was employed to analyze four poly(butylene adipate) (PBAd) oligomers and to investigate their fragmentation pathways as a continuation of our work on the MALDI-TOF/TOF-MS/MS study of synthetic polymers. MALDI-TOF/TOF-MS/MS analysis was performed on oligomers terminated by carboxyl and hydroxyl groups, methyl adipate and hydroxyl groups, dihydroxyl groups, and dicarboxyl groups. The sodium adducts of these oligomers were selected as precursor ions. Different end groups do not influence the fragmentation of sodiated polyester oligomers and similar series of product ions were observed in all the MALDI-TOF/TOF-MS/MS spectra. According to the structures of the most abundant product ions identified in the present work, three fragmentation pathways have been proposed to occur most frequently in PBAd: beta-hydrogen-transfer rearrangement, leading to the selective cleavage of the --O--CH(2)-- bonds; --CH(2)--CH(2)-- (beta--beta) bond cleavage in the adipate moiety; and ester bond scission.     

BN‐Embedded Polycyclic Aromatic Hydrocarbon Oligomers: Synthesis,Aromaticity, and Reactivity

BN‐embedded oligomers with different pairs of BN units were synthesized by electrophilic borylation. Up to four pairs of BN units were incorporated in the large polycyclic aromatic hydrocarbons (PAHs). Their geometric, photophysical, electrochemical, and Lewis acidic properties were investigated by X‐ray crystallography, optical spectroscopy, and cyclic voltammetry. The B?N bonds show delocalized double‐bond characteristics and the conjugation can be extended through the trans‐orientated aromatic azaborine units. Calculations reveal the relatively lower aromaticity for the inner azaborine rings in the BN‐embedded PAH oligomers. The frontier orbitals of the longer oligomers are delocalized over the inner aromatic rings. Consequently, the inner moieties of the BN‐embedded PAH oligomers are more active than the outer parts. This is confirmed by a simple oxidation reaction, which has significant effects on the aromaticity and the intramolecular charge‐transfer interactions.     

聚四氢呋喃/聚苯乙烯交联嵌段及接枝共聚物的合成与阻尼性能

合成接枝共聚物和嵌段共聚物是研究阻尼材料的重要途径,这是由于可以在较广的范围内,调整共聚物的结构,使之具有良好的阻尼性能。这里我们选择了端羟基聚四氢呋喃与顺丁烯二酸酐反应,制成端乙烯基大分子单体及端乙烯基遥爪低聚物。然后与苯乙烯共聚,制成接枝共聚物和嵌段共聚物。从两者的比较中探讨各种因素对共聚物阻尼性能的影响规律。认为研究结果将有益于阻尼材料的分子设计,在反应体系及合成方法上,都比较简便,适于工业生产,便于推广应用。     

聚四氢呋喃/聚苯乙烯交联嵌段及接枝共聚物的合成与阻尼性能

Carboxyl vinyl terminated polytetrahydrofuran macromers and telechelic oligomers were synthesized from hydroxyl terminated polytetrahydrofuran by end group conversion. From these macromers or telechelic oligomers and styrene polytetrahydrofuran/polystyrene segmented and graft copolymers were synthesized and the effects of molecular structure on the damping properties of those copolymers were also studied.     

Direct mass spectrometry of polymers. VIII. Primary thermal fragmentation processes in polyurethanes

The primary fragmentation mechanisms in the thermal decomposition of several polyurethanes were studied by direct pyrolysis into the mass spectrometer. Ester exchange reactions predominate in the primary thermal fragmentation process, causing the formation of cyclic oligomers, which are subsequently cleaved to open-chain oligomers containing hydroxyl end groups.     

Synthesis of cyclic methacrylic acid oligomers by atom transfer radical polymerization

Poly(methacrylic acid) (PMAA) oligomers were synthesized by combining template polymerization and copper‐mediated atom transfer polymerization with multivinyl monomer of β‐cyclodextrin (CD) having 20.4 methacryloyl groups on both primary and secondary hydroxyl group sides of CD scaffold, with 1,3‐dibromobutane as an initiator. The initiation and propagation sites of polymerized sequence of β‐CD were connected by postpolymerization of polymerized products with CuBr and tris[(2‐dimethylamino)ethyl]amine (Me₆TREN) in a methanol/water mixture of 10 wt % of water. Polymerized and cyclized sequences, PMAA oligomers formed on the primary and the secondary hydroxyl group sides, were detached from β‐CD scaffold by hydrolysis. Molecular weights of PMAA oligomers were measured by GPC and matrix assisted laser desorption ionization time‐of‐flight mass measurement. By ¹H NMR measurements, it was found that three types of cyclic PMAA were obtained by postpolymerization. The cyclization preferentially occurred on the secondary hydroxyl group side than on the primary hydroxyl group side. From the structures of cyclic PMAA, two reaction positions were proposed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6262–6271, 2005     

Isolation and identification of the linear and cyclic oligomers of poly(ethylene terephthalate) and the mechanism of cyclic oligomer formation

Chromatographic techniques are described which can be used to isolate and identify the linear and the cyclic oligomers of poly(ethylene terephthalate). Extraction of the oligomers from high molecular weight polymer produces at least eight different cyclic species, some of which are isolated and identified. The cyclic dimer, the cyclic trimer, and the cyclic tetramer of poly(ethylene terephthalate) have also been prepared by acid chloride esterification and transesterification. Similar materials can be isolated from the ethylene glycol distillate obtained from the polymer melt. The mechanism of cyclic oligomer formation has been studied by determining the rate of formation of the cyclic oligomers during polymerization and during melt extrusion of polyesters which did not initially contain cyclic oligomers. The rate of formation depends upon the concentration of hydroxyl groups; hence, the cyclic oligomers are formed by transesterification from the chain ends or cyclodepolymerization. Therefore oligomers are inevitably produced during polymerization.     

The Effect of Pristine and Hydroxylated Oxide Surfaces on the Guaiacol HDO Process: A DFT Study

The acid-base character of oxide supports is crucial for catalytic reactions. In this work, the acid-base properties of five oxide surfaces common in heterogeneous catalysis were investigated and related to their interaction with monolignol compounds derived from lignin. We have used density functional theory simulations also to understand the role of the surfaces’ hydroxylation state. The results show that moderate hydroxyl coverage on the amphoteric γ-Al₂O₃ (110) slightly strengthens the oxy-compounds’ adsorption due to an increase in Lewis acidity. Similarly, low hydroxyl coverage on the reducible TiO₂ (101) enlarges its adsorption capacity by up to 42 % compared with its clean surface. The higher affinity is attributed to the more favourable interaction between the surface-OH groups and the aromatic rings. Overall, the results indicate that hydroxyl coverage enhances the amphoteric and reducible adsorption capacity towards aromatic species.     

Formation of fibril structures in polymerizable, rod-coil-oligomer-modified epoxy networks

This paper describes the in situ preparation of fibrils in epoxy networks in which the fibril-like structures are cured polymerizable rod-coil oligomers. The epoxy-terminated alpha,omega-modified PEO oligomers, which are ABA rod-coil-rod oligomers with a poly(ethylene oxide) coil unit and two aromatic azomethine liquid-crystalline rod units, were synthesized and then further blended with an epoxy precursor. Uniform nanoscale columnar structures were observed in the neat rod-coil oligomers as well as in the crosslinked liquid-crystalline state. During the curing of the blends, the supramolecular nanoscale columnar structures of the rod-coil oligomers are transformed into polymeric fibrils where the epoxy functional end groups have co-reacted with epoxy precursors to form a crosslinked network.     

Preparation and Evaluation of Visible Light-Cured Multi-Methacrylates for Dental Composites

Abstract

To explore new VLC oligomers exhibiting low shrinkage, low water sorption, and improved mechanical properties, a family of multi-methacrylates, based on poly(isopropylidenediphenol) resin (BPA), was synthesized, characterized, and evaluated. The BPA resin, having an average of eight phenolic hydroxyl groups per molecule, was treated with ethylene carbonate and the resultant product esterified at four different grafted levels, using methacryloyl chloride. Structures of these EEBPA oligomers, were confirmed by FT-IR and ¹³C NMR. The EEBPA oligomer/TEGDMA (50/50, w/w) blends were combined with 0.5 wt% camphoroquinone(CQ) and 1.0 wt% N,N-dimethylaminoethyl methacrylate (DMAEM). The control was BisGMA/TEGDMA (50/50, w/w) blends having the same levels of CQ/DMAEM. Differential photocalorimetry (DPC) and differential scanning calorimetry (DSC) showed the multi-methacrylate/TEGDMA (neat resin) blends have polymerization characteristics comparable to the BisGMA/TEGDMA control. These multi-functional oligomers have lower polymerization shrinkage and lower uptake of water and other liquids. In addition, two experimental oligomers EEBPA #2 and #3 have higher compressive strength than the BisGMA and comparable diametral tensile strength to the BisGMA control. These results suggest that the new type of multi-functional methacrylate oligomers (EEBPA) have potential application in formulating dental composites with improved properties.