Synthesis and characterization of block poly(ester‐ether‐urethane)s from bacterial poly(3‐hydroxybutyrate) oligomers

Telechelic hydroxylated poly(3‐hydroxybutyrate) (PHB‐diol) oligomers have been successfully synthesized in 90–95% yield from high molar mass PHB by tin‐catalyzed alcoholysis with different diols (mainly 1,4‐butanediol) in diglyme. The PHB‐diol oligomers structure was studied by nuclear magnetic resonance, Fourier transformed infrared spectroscopy MALDI‐ToF MS, and size exclusion chromatography, whereas their crystalline structures, thermal properties and thermal stability were analyzed by wide angle X‐ray scattering, DSC, and thermogravimetric analyses. The kinetic of the alcoholysis was studied and the influence of (i) the catalyst amount, (ii) the diol amount, (iii) the reaction temperature, and (iv) the diol chain length on the molar mass was discussed. The influence of the PHB‐diol molar mass on the thermal stability, the thermal properties and optical properties was investigated. Then, tin‐catalyzed poly(ester‐ether‐urethane)s (PEEU) of M_n = 15,000–20,000 g/mol were synthesized in 1,2‐dichloroethane from PHB‐diol oligomers (P_ester) with modified 4,4'‐MDI and different polyether‐diols (P_ether) (PEG‐2000, PEG‐4000, and PPG‐PEG‐PPG). The influence of the PHB‐diol chain length, the P_ether/P_ester ratio, the polyether segment nature and the PEG chain length on the thermal properties and crystalline structures of PEEUs was particularly discussed. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1949–1961     

Synthesis of block copolymers by oligomer-coupling reactions in the bulk: Bisimidazoline/cooh and bisoxazolinone/nh2 reactions

The polyaddition reaction of bisimidazolines with α, ω-dicarboxy polyamide-12 in the bulk at 200–240°C (oligomer coupling reaction) produces high MW polymers, while degradation reactions were observed with aliphatic polyesters. The chain extension of a α, ω-dicarboxy polyamide-polyoxytetramethylene-polyamide oligomer with 2, 2'-tetramethylene-bis(imidazoline) yielded a poly(poly-ether-block-polyamide). 4-substituted and 4, 4-disubstituted bis(5(4H)oxazolinones) are efficient coupling agents for amino-terminated oligomers, allowing the rapid synthesis of copolymers containing polyether and polyamide blocks. The chemistry of these chain-coupling reactions has been studied by NMR. DSC shows the phase separation between the hard (polyamide) and the soft (polyether) blocks.     

Synthesis and characterization of phenolic‐type beads by dispersion polymerization of 2‐phenoxyethanol with formaldehyde using gum acacia powder as stabilizer

In this study, we report the preparation of phenolic beads (PB) via a novel dispersion polymerization of 2‐phenoxyethanol (PE) and formaldehyde, in which gum acacia powder (GAP), formic acid, and sulfuric acid are employed as the steric stabilizer, the reaction medium and the catalyst, respectively. The effects of a variety of reaction parameters, including the stabilizer concentration, the agitation rate, the polymerization temperature, the molar ratio of formaldehyde to 2‐phenoxyethanol (F/P) and the amount of sulfuric acid, on the particle size and size distribution (PDI) as well as particle morphology have been investigated. Particularly, phenolic beads of a size 565 µm as well as a narrow particle size distribution (PDI = 1.153) have been prepared under the following conditions: the stabilizer concentration 2.5%, the agitation rate 700 rpm, the polymerization temperature 60°C, the molar F/P ratio 3:1, and the amount of catalyst 8 ml. In addition, a mechanism for the particle formation in dispersion polymerization of PE and formaldehyde has also been proposed. Copyright © 2009 John Wiley & Sons, Ltd.     

Formation and Structure of Hydrolytic Methylaluminoxane Activators

Methylaluminoxane (MAO) activators have sheet structures which form ion-pairs on reaction of neutral donors such as octamethyltrisiloxane (OMTS). The ion-pairs can be detected by electrospray ionization mass spectrometry (ESI-MS) in polar media. The growth of these reactive precursors during hydrolysis of Me₃Al can be monitored using ESI-MS. Density functional theory, combined with numerical simulation of growth, indicates that this process involves rapid formation of low MW oligomers, followed by assembly of these species into low MW sheets. These can grow through further addition of low MW oligomers or by fusion into larger sheets. The mechanism of these growth processes leads to the prediction that even-numbered sheets should be favored, and this surprising result is confirmed by ESI-MS monitoring experiments of both activator growth and MAO aging.     

Some emerging techniques in polymer mwd characterization

Routine MW analysis of polymers is generally performed in solution by Gel Permeation Chromatography. The technique, however, presents increasing difficulties in the ultra-high and ultra-low MW range. Moreover, GPC is not applicable to most fluorinated and»high performance«thermoplastics which require dissolution temperatures close to the polymer melting point. In response to these challenges, polymer scientists have developed new methods of MWD determination. Although these methods have not yet reached the versatility of GPC, they present potential for further development and are interesting as complementary techniques to GPC. For sparingly soluble polymers, melt viscoelastic properties have been used to obtain information on polymer MWD. Flow birefringence, based on the orientation and extension of long flexible molecular chains in a shear field, has been applied to the characterization of ultra-high MW polymers. For low MW polymers and oligomers, the MALDI mass spectrometry technique, with its unique capabilities to resolve individual oligomers within a MWD, proves to be an interesting alternative to conventional GPC characterization.     

Bulk polymerization of lactides initiated by aluminum isopropoxide. I. Mechanism and kinetics

Commercially available Al isopropoxide (Al(OiPr)₃) has proved to be an efficient initiator for the bulk polymerization of lactide. The ring-opening polymerization proceeds through a “coordination-insertion” mechanism and the selective rupture of the acyl-oxygen bond of the monomer. Polyester chains are selectively end-capped with an aluminum alkoxide and an isopropoxy group. Therefore, substitution of Al tris(4-penten-1-olate) for Al(OiPr)₃ leads to the formation of macromonomers. In the temperature range from 110 to 150°C, polymerization is “living”, i.e. the molecular weight can be predicted by the initial monomer-to-Al molar ratio and the monomer conversion. The narrower polydispersity of poly(L,L-lactide) compared to the amorphous poly(D,L-lactide) (M̄w / M̄n 1.3 compared to 1.9, respectively), both prepared in the bulk, is thought to result from the restricted mobility of the crystallized isotactic polyester chains. When the temperature is increased up to 180°C, inter- and intramolecular transesterification reactions interfere with chain propagation.     

Effect of added zinc on the properties of cobalt-containing ceramic pigments prepared from layered double hydroxides

Layered double hydroxides (LDHs) with the hydrotalcite-type structure containing Co and Al, or Zn, Co and Al in the brucite-like layers and carbonate in the interlayer have been prepared by coprecipitation. The Zn/Co molar ratio was kept to 1 in all samples, while the divalent/trivalent molar ratio was varied from 2/1 to 1/2. The samples have been characterised by element chemical analysis, powder X-ray diffraction, differential thermal and thermogravimetric analysis, temperature-programmed reduction and FT-IR spectroscopy. A single hydrotalcite-like phase is formed for samples with molar ratio 2/1, which crystallinity decreases as the Al content is increased, developing small amounts of diaspore and dawsonite and probably an additional amorphous phase. Calcination at 1200 °C in air led to formation of spinels; a small amount of NaAlO₂ was observed in the Al-rich samples, which was removed by washing. The nature of the spinels formed (containing Co^II, Co^III, Al^III and Zn^II) strongly depends on the cations molar ratio in the starting materials and the calcination treatment, leading to a partial oxidation of Co^II species to Co^III ones. Colour properties (L*a*b*) of the original and calcined solids have been measured. While the original samples show a pink colour (lighter for the series containing Zn), the calcined Co,Al samples show a dark blue colour and the Zn,Co,Al ones a green colour. Changes due to the different molar ratios within a given calcined series are less evident than between samples with the same composition in different series. These calcined materials could be usable as ceramic pigments.     

Synthesis,Characterization and Ethylene Oligomerization Behavior of Neutral Nickel Complexes Bearing N‐Fluorinated Phenyl Salicylaldiminato Chelate Ligands

A series of neutral nickel complexes featuring N‐fluorinated phenyl salicylaldiminato chelate ligands was synthesized, and the novel molecular structure of complex C14 was further confirmed by X‐ray crystallographic analysis. The neutral nickel complexes showed high activity up to 9.96×10⁵ g oligomers/(mol Ni·h) and high selectivity of C₆ in catalyzing ethylene oligomerization using methylaluminoxane (MAO) as cocatalyst. It was observed that the strong electron‐withdrawing effect of the fluorinated salicylaldiminato ligand was able to significantly increase the catalytic activity for oligomerization of ethylene. In addition, the influence of reaction parameters such as Al/Ni molar ratio, reaction temperature, a variety of cocatalyst and ethylene pressure on catalytic activity was investigated.     

Organochromiumoxane yttriumoxane alumoxane oligomers: synthesis,properties, pyrolysis

Russian Chemical Bulletin - Ceramic-forming organochromiumoxane yttriumoxane alumoxane oligomers with a given molar ratio of Al: Cr and Al: Y, hydrolytically stable in air, have been synthesized....     

The iterative synthesis of discrete dimethylsiloxane oligomers: A practical guide

Discrete dimethylsiloxane oligomers are interesting building blocks for the synthesis of high χ–low N block co-oligomers (BCOs) forming highly organized nanostructures. Here, a practical guide to the synthesis of molecularly defined oligodimethylsiloxanes (oDMS) from 7-mer to 40-mer via a linear growth strategy is described. The iteration of a hydroxylation reaction and the condensation of mono- or bifunctional hydroxysiloxanes with chloro-octamethyltetrasiloxane results in asymmetric and symmetric siloxanes, respectively. The synthesis contains critical washing and purification steps to remove minor amounts of low and high-molecular weight byproducts, which are detected using Fourier transform infrared spectrometry, gas chromatography–mass spectrometry, and size-exclusion chromatography. The oligomers are obtained on a multigram scale in yields of 94–50% and in high purity with only one molar mass detected. The formation of the chloride, hydroxide or hydride functional groups is adequately analyzed using ²⁹Si NMR spectroscopy. The hydride terminated siloxane oligomers are used in Karstedt catalyzed hydrosilylation reactions with alkene-functional substrates to obtain oDMS-based oligomers and BCOs. Byproduct formation as a result of isomerization and reduction are followed by ¹H NMR spectroscopy and minimized using dry conditions and low-catalyst loadings.     

Kinetically controlled phase transitions in liquid‐crystalline polymers. III. Influence of the molecular weight and annealing temperature on two‐dimensional K phase formation in a side‐chain polyacrylate

Narrow fractions of a side‐chain acrylate oligomer/polymer with phenyl benzoate side chains are separated in a broad range of the degree of polymerization (7 ≤ P_w ≤ 149). An examination of the phase behavior of the obtained fractions has shown that only the longer macromolecules can form the two‐dimensional K (TDK) mesophase, whereas oligomers of a shorter main chain form the conventional nematic phase only. A critical P_w value has been observed to be necessary for the TDK mesophase formation. The temperatures and enthalpies of liquid‐crystalline phase transitions have been studied as a function of the molar mass, and the phase‐growth kinetics for the TDK phase have been studied with an Avrami treatment. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2352–2360, 2005     

Block Copolymers by high temperature oligomer-coupling reactions: Bis(5-oxazolinone)/OH reaction

High temperature chain-coupling reactions in the bulk between amino-, hydroxy- or carboxy-terminated polymers and various coupling agents have been studied and applied to the synthesis of copolymers with aliphatic polyester, polyether or polyamide blocks. Thus, carboxy-terminated oligomers can be coupled by bisoxazolines or bisimidazolines, while 4-substituted and 4, 4-disubstituted bis(5-oxazolinones) are efficient coupling agents for amino- or hydroxy-terminated oligomers. In the latter case, the use of a catalyst is necessary. The reaction has been optimized using a series of bisoxazolinones deriving from α-amino-acids and 1-dodecanol and α, ω-dihydroxy-poly(ϵ-caprolactone) as model compounds. High molar mass poly-ϵ-caprolactone containing α-aminoacid moieties has been obtained in the presence of tetrabutoxytitanium as a catalyst.     

Matrix-assisted laser desorption/ionisation time-of-flight characterisation of biodegradable aliphatic copolyesters

Matrix-assisted laser desorption/ionisation time-of-flight (MALDI-TOF) and the off-line size exclusion chromatography matrix-assisted laser desorption/ionisation (SEC/MALDI) method has been applied to the structural characterisation and the molar mass (MM) determination of a series of biodegradable copolyesters synthesised by high temperature melt polycondensation reaction, and of two commercial copolyesters with the trade name Bionolle. The MALDI-TOF spectra of these copolymers showed the presence of cyclic oligomers in the lower mass region, in accord with expectations from polycondensation kinetics, and the presence of all linear species expected from their method of synthesis. The presence of unexpected linear species with olefin and carboxyl as end groups suggested the occurrence of undesirable thermal degradation processes during the melt polycondensation reaction. The absolute average molar masses obtained by the SEC-MALDI method turned out to be lower, by a factor of about two for succinate/adipate copolymers, and by a factor of three for succinate/sebacate copolymers, with respect to those computed by using polystyrene standards in SEC. Furthermore, the MALDI-TOF spectra of SEC fractions allowed not only the detection of linear and cyclic oligomers contained in these samples, but also the simultaneous determination of the average molar mass of both cyclic and linear oligomers. Due to the smaller hydrodynamic volume of cyclic chains with respect to linear ones, the ratio (M( cycle)/M( linear))( Ve) at a fixed elution volume was found to be 1.25, in good agreement with the theoretical value of 1.24. Copyright 2000 John Wiley & Sons, Ltd.     

Synthesis and enzymatic degradation of end-functionalized biodegradable polyesters

End-functionalization of biodegradable polymers/oligomers based on L-lactide and glycolide by cholesteryl moiety was investigated. We established the feasibility of preparing the functionalized polymers/oligomers, Chol-(LG)_m+n, through ring-opening copolymerization initiated by cholesterol bearing a hydroxyl group, without adding any catalyst. The functionalized polymers/oligomers of different molecular weights were obtained by controlling the feed ratio of the initiator cholesterol to the monomers. The chemical structure of end-functionalized polymers/oligomers was confirmed by FTIR and ¹H NMR. Incorporation of cholesteryl moiety into the polymer chains induces liquid crystallinity in the resultant oligomers when the molecular chains are not very long. The enzymatic degradation studies, for all the samples, were carried out using enzyme, proteinase K. Interestingly, the enzymatic degradation of cholesteryl end-functionalized polymers/oligomers resulted in a lamella-like porous structure on the sample surface, which is altogether different from the commonly reported spherical-pore structure formed during the degradation of conventional polyesters.     

一种吡啶二亚胺类铁催化剂的合成及乙烯低聚研究

设计并合成了一种新型吡啶二亚胺类铁配合物 ,该配合物配体中将氟取代基和甲基取代基结合在一起 ,用于乙烯齐聚活性可以达到 10 7g molFe·h ,产物中 90 %以上是 1 丁烯 ,1 己烯和 1 辛烯等低碳数α 烯烃 .低聚反应温度对低聚活性和低聚物分布有很大影响 ,随着反应温度的提高 ,齐聚活性降低 ,低聚物明显向低碳数分布移动 .随着Al Fe的增加 ,低聚活性先迅速增加 ,在Al Fe为 10 0 0时达到最大 ,然后又迅速降低 ;低聚物的分布基本不受Al Fe的影响 .比较了几种具有相似结构的化合物及其低聚性能与新合成的催化剂 ,讨论了配合物结构与低聚活性和低聚物性能之间的关系 .合适的邻位取代基位阻和取代基电子效应是决定催化剂活性和低聚物分布的主要因素 .     

Preparation of linear low‐density polyethylene by the in situ copolymerization of ethylene with an iron oligomerization catalyst and rac‐ethylene bis(indenyl) zirconium (IV) dichloride

An iron oligomerization catalyst, [(2‐ArN?C(Me))₂C₅H₃N]FeCl₂ [Ar = 2,6‐C₆H₃(F)₂], was combined with rac‐ethylene bis(indenyl)zirconium (IV) dichloride [rac‐Et(Ind)₂ZrCl₂] to prepare linear low‐density polyethylene (LLDPE) by the in situ copolymerization of ethylene. A series of LLDPEs with different properties were prepared by the alteration of the reaction temperature, Fe/Zr molar ratio, Al/(Fe + Zr) molar ratio, and reaction time. The structures of the polymers were characterized with differential scanning calorimetry, ¹³C NMR, gel permeation chromatography (GPC), and so forth. The melting points, crystallizations, and densities of the resulting products increased, and the average branching degree decreased, as the reaction temperature, Al/(Fe + Zr) ratio, and reaction time increased. The melting points, crystallizations, and densities of the polymers decreased, and the average branching degree increased, when the Fe/Zr ratio increased. The ¹³C NMR and GPC results showed that there were no unreacted α‐olefins remaining in the resulting polymers because the percentage of low‐molar‐mass sections (C₄–C₁₀) of the oligomers obtained with this catalyst was very high (>70%). In addition, the formation of polymers with two melting points under different reaction conditions was examined in detail, and the results indicated that the two melting points of the polymers could be attributed to polyethylene with different branches. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 984–993, 2005     

载体型钛系催化剂的丙烯与乙烯共聚合研究

以载体型钛系齐格勒-纳塔催化剂进行了丙烯和乙烯无规共聚合的研究。对聚合温度、铝钛摩尔比、给电子体浓度和加氢等行为作了考察。共聚合速度和共聚物的比浓粘度呈规律性变化。用~(13)C-NMR和DSC测定了共聚物的组成、序列分布、熔点和结晶度.结果表明,在共聚合反应速度曲线上,在丙烯和乙烯分别为10mol％组成处,出现两个最大值。随共聚物中乙烯含量增加(2—10mol％),其熔点和结晶度降低,DSC峰变低、变宽,在乙烯含量达10mol％处出现双峰(128/116℃)反映出无规共聚链出现不同的序列分布。     

Mg-Al类水滑石层板结构中Al/Mg比与稳定性的关系

通过改变Mg和Al的数量构建不同Al/Mg比的类水滑石层板模型, 采用量子化学密度泛函理论(DFT), 优化并计算各种Al/Mg比的水滑石结构, 通过对键长、电荷、能量等分析, 得出Al/Mg比对水滑石稳定性的影响规律. 在实际的水滑石层板结构中, 当Al/Mg比为1:2和1:3时, 最适宜形成稳定水滑石相, 且1:3比1:2更具优势.     

One-Pot Synthesis and Formation Mechanism of Hollow ZSM-5

Coffin-shaped hollow ZSM-5 zeolite (HZZ) particles with shell thickness of about 200 nm and hollow diameter of approximately 1.5 μm were synthesized in one pot by using tetrapropylammonium bromide (TPABr), aluminum triisopropoxide Al[OCH(CH₃)₂]₃ and tetraethoxysilane (TEOS) as the structure-directing agent (SDA), aluminum and silica source, respectively. The appropriate molar ratios of TPABr/SiO₂ and Si/Al as well as suitable crystallization temperature are the key factors for the formation of HZZ. The formation of the HZZ can be attributed to the existence of intrinsic density variation inside the initial amorphous aggregates and the Al zoning in the outer surface of the ZSM-5 particles. Amorphous silica with low crystallinity formed at early stages and low Al concentration, which has been subsequently dissolved and recrystallized on the ZSM-5 particle surface through Ostwald ripening, leading to the formation of HZZ. This approach, which uses a high concentration of SDA, will provide new possibilities and insight into the prospective fabrication of hollow zeolites.     

Morphology of poly(p‐oxybenzoyl) crystal prepared by direct polycondensation of p‐hydroxybenzoic acid with p‐toluenesulfonyl chloride in pyridine

Poly(p‐oxybenzoyl) (POB) crystals were prepared with the reaction‐induced crystallization of oligomers during the direct polycondensation of p‐hydroxybenzoic acid (HBA) with p‐toluenesulfonyl chloride (TsCl) and N,N‐dimethylformamide in pyridine. Sheaflike lozenge‐shaped POB crystals were obtained, of which the longer diagonal was 7.0–8.0 μm. The influence of the polymerization condition on the morphology was examined to optimize the preparative condition for the crystals exhibiting the clearest habit, and the favorable condition was determined as the molar ratio of TsCl to HBA of 1.3 and polymerization concentration of 3.0%. The crystals possessed extremely high crystallinity and outstanding thermal stability. The formation mechanism of the crystal was proposed as follows. When the number‐average degree of polymerization of the oligomers exceeded a critical value of about 4, they were precipitated to form the hexagonal lamellae. The crystals were grown very quickly to lozenge‐shaped crystal through screw dislocation with the continuous precipitation of oligomers from the solution. Finally, the further polymerization occurred in the precipitated crystal with developing polymer‐chain packing. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3275–3282, 2003