Polyamide-silica gel hybrids containing metal salts: Preparation via the sol-gel reaction

The hydrolysis and condensation of tetramethoxysilane in a DMF solution of polyamides containing LiCl, CaCl₂ or ZnCl₂, both in presence and absence of polyoxazoline, resulted in the facile formation of polyamide-silica gel hybrids. Films were cast from the resulting mixtures and evaporation of the solvent resulted in the formation of clear, transparent hybrids with the salts dispersed at the molecular level. Pyrolysis of hybrids at 600 °C gave porous silica. Pore size and surface characteristics of these silica gel samples indicated a porous nature with a pore radius of 1.1 nm for silica gels obtained from hybrids HPA-6 (containing no salt) and HPA-9 (containing ZnCl₂) and a surface area of 213 m² g⁻¹ and 310 m² g⁻¹, respectively. Silica gel from hybrid HPA-7 (containing LiCl) had a pore radius of 1.9 nm and a surface area of 15 m² g⁻¹. The silica gel samples obtained from hybrids HPA-6, HPA-7 and HPA-9 exhibited narrow slit-like pores with a pore volume of 0.68 cm³ g⁻¹. Received: 7 January 1997/Accepted: 6 March 1997     

Exploring the effect of alkyl end group on poly(L-lactide) oligo-esters. Synthesis and characterization

Poly(L-lactide) (PLLA) oligo-esters with α-hydroxyl-ω-alkyl (alkyl = −CH₂−[CH₂−CH₂]_m−CH₃, where m = 1, 2, 4, 5, 6, 7, 8, 9, and 10) end groups were synthesized by ring-opening polymerization of L-lactide (L-LA) catalyzed by tin(II) 2-ethylhexanoate Sn(Oct)₂ in the presence of aliphatic alcohols as initiators (HO−CH₂−[CH₂−CH₂]_m−CH₃, where m = 1, 2, 4, 5, 6, 7, 8, 9, and 10). High yields (~ 62 to 71%) and M _n(NMR) in the range of 2120–2450 Da (PLLA) were obtained. Effects of alkyl end groups on thermal properties of the oligo-esters were analyzed by DSC, TGA and SAXS. Glass transition temperature (T _g) gradually decreases with increase in the percent of−CH₂−[CH₂−CH₂]_m−CH₃ end group, as results alkyl end group provides most flexibility to PLLA. An important effect of alkyl end group on a double cold crystallization (T _c1 and T _c2) was observed, and is directly related with the segregation phase between alkyl end group and PLLA. TGA analysis revealed that PLLA oligo-esters are more thermally stable with docosyl (−C₂₂H₄₅) respect to the butyl (−C₄H₉) end group, probably is due to steric hindrance of the end group (docosyl respect to butyl) toward intermolecular and intramolecular transesterification. SAXS analysis showed that alkyl end group as docosyl restricted the growth of lamellae thickness (D) due to steric hindrance. Characterization of hydroxyl and alkyl end groups in the PLLA oligo-esters was determined by MALDI-TOF, GPC, FT-IR and ¹ H and ¹³ C NMR.     

Effects of phenyl-based pendent groups on helical conformation of poly(<Emphasis Type="Italic">N</Emphasis>-propargylamides)

Five achiral N-propargylamide monomers with various phenyl-based substitutents, [HC ≡ CCH₂NHCOR, R for M1: C₆H₄CH₃; M2: C₆H₄CH₂CH₃; M3: C₆H₄(CH₂)₂CH₃; M4: C₆H₄(CH₂)₃CH₃; M5: C₆H₄C(CH₃)₃], were synthesized and polymerized with a rhodium catalyst, (nbd)Rh⁺B^-(C₆H₅)₄ (nbd = 2,5-norbornadiene). The corresponding five homopolymers were obtained in high yields of 90–95% and with moderate molecular weights (M _n ≥ 10 000). All the polymers possessed high cis contents (≥95%). Poly(1)–poly(3) exhibited UV-vis absorption peaks at approx. 350 nm, which indicates that the three polymers formed helical conformations, while no UV-vis absorption peaks could be observed in poly(4) and poly(5) in the wavelength range of 320–500 nm, demonstrating that these two polymers could not adopt helical structures under the examined conditions. To confirm the helical structures formed in poly(1)–poly(3), a chiral monomer, M6, was utilized to copolymerize with M2, which was used as the representative for M1−M3. M6 was utilized since its polymer could form stable helices under suited conditions. The resulting copolymers exhibited remarkable CD effects, however, the maximum wavelength in the copolymers varied remarkably, mainly depending on the composition of the copolymers. It is concluded that in the formation of ordered helical conformations, the substitutents of varied bulk led to different steric repulsion and varied synergic effects among the neighboring pendent groups.     

Relaxation patterns of endlinking polydimethylsiloxane near the gel point

While the rheological behavior at the gel point (GP) itself is well known, many questions remain about the approach to the gel point (from either side). For studying this phenomenon, rheological experiments were performed on crosslinked polydimethylsiloxanes (PDMS) and characteristic patterns in the relaxation behavior were abstracted into a phenomenological model for the relaxation time spectrum. The well known power law with slope-n and cutoff at the longest relaxation time λ _max governs the relaxation near the gel point. Beyond the gel point, an additional box-like contribution appears in the spectrum. The relaxation exponent n decreases with increasing extent of crosslinking. The longest relaxation time λ _max and equilibrium modulus G_e show power-law scaling with the distance from the gel point, |p − p_c|. For samples with imbalanced stoichiometric ratios r ≥ 1, the function n (p − p_c) is independent of r. Samples with strong crosslinker deficiency (r = 0.5) exhibit a different functional form for n (p − p_c) from those with r ≥ 1. The power law relaxation with decreasing n in the terminal zone was found previously for a different crosslinking system. It seems to be a common pattern for partially crosslinked materials from polymeric precursors. Received: 11 December 1997/Revised version: 18 December 1997/Accepted: 18 December 1997     

An investigation into the synthesis of polycarbazole squaraine derivatives

The polycondensation of squaric acid with 1,2-(9-Ethylcarbazol-3-yl)ethene and N-ethyliminostilbene in polyphosphoric acid yielded insoluble polymers which included substituted phosphate groups on the phenyl rings. The presence of phosphorus in these polymers was identified using solid-state ³¹P NMR and EDAX techniques. Furthermore the phosphate groups were not ionic, hence no charge-balancing anions were present. Both polymers did not electrically conduct but exhibited dielectric breakdown values of 0.1 and 0.06 MV cm⁻¹ respectively. Received: 16 December 1996/Revised: 10 March 1997/Accepted: 10 March 1997     

Synthesis of side chain liquid crystalline poly(vinyl ether)s containing 2,2′-dimethyl-4-methoxy-4′-[undecanyloxy-4-benzoyl]ester biphenyl side group

The synthesis and characterization of 2,2′-dimethyl-4-methoxy-[(11-vinyloxy)undecanyloxy-4-benzoyl]ester biphenyl (7), its cationic polymerization to side chain liquid crystalline polymers with relative number average degrees of polymerization (DP) of 2, 8 and 19 are presented. The mesogenic vinyl ether monomer displays an inverse monotropic nematic phase. The oligomers with DP = 2 and DP = 8 display an enantiotropic nematic, while the polymer with DP = 19 exhibits an inverse monotropic smectic A and an enantiotropic nematic phase. All the liquid crystalline polymers display only liquid crystalline phases and do not undergo side chain crystallization even though eleven methylenic units are used as the flexible spacer. Received: 28 February 1997/Accepted: 23 May 1997     

Multi-arm star-branched polyisobutylene ionomers

A series of multi-arm star-branched polyisobutylenes was synthesized via living carbocationic polymerization. Arms with molecular weights ranging from 10,000 to 30,000 g/mol were prepared using the cumyl chloride/TiCl₄/pyridine initiation system in 60/40 (v/v) hexane/methyl chloride at − 80 °C and linked by sequential addition of divinylbenzene. The weight average number of arms per star polymer, N _w, scaled inversely with arm molecular weight and ranged from 32 to 5. Star-telechelic ionomers were produced by sulfonation of the aromatic initiator residue at the end of each arm, followed by neutralization. Sulfonation was quantitative as indicated by acid-base titration. Potassium ionomers were elastic solids which were marginally soluble in THF; the precursors were tacky and freely soluble in THF. Ionic modification did not alter the glass transition temperature (− 66 °C), but the thermal decomposition temperature in N₂ was increased from 375 to 400 °C. Received: 25 July 1997/Accepted: 27 August 1997     

Asymmetric polymerization of N-substituted maleimides with organolithium — bisoxazolines complex

Asymmetric anionic polymerizations of achiral N-substituted maleimide (RMI) (N-cyclohexyl (CHMI), N-phenyl (PhMI), N-tert-butyl (TBMI)) by n-butyllithium (n-BuLi) or fluorenyllithium (FlLi) complexes of chiral bisoxazoline derivatives in toluene gave optically active polymers ([α]²⁵ ₄₃₅− 2.9° to − 8.2°). The polymers prerared with initiator of n-BuLi – 2,2′-bis(4,4′-isopropyl-,3-oxazoline) showed negative specific rotations (poly(RMI), [α]²⁵ ₄₃₅− 5.8° to − 8.2°) which were greater than those ([α]²⁵ ₄₃₅− 2.9° to − 5.9°) with other chiral 2,2′-bis(4,4′-alkyl-1,3-oxazoline) (alkyl group = iso-butyl and benzyl). Received: 29 July 1997/Revised: 27 August 1997/Accepted: 1 September 1997     

A new method for determination of fibril volume fraction in polymer crazes by small-angle X-ray scattering

A new method for the determination of the volume fraction ν _f of fibrils formed inside the crazes in polymers before their brittle fracture has been proposed. The method utilizes small-angle X-ray scattering measured on an absolute scale in combination with the precise measurement of the sample deformation. The method has been applied to the crazes in polystyrene for which the data on ν _f are abundant. The result ν _f = 0.26 is in good agreement with those obtained by other methods ranging ν _f = 0.21 – 0.30, which confirms the validity of the proposed method. Received: 3 April 1997/Accepted: 2 June 1997     

Copper adsorption and enzyme immobilization on organosilane-glutaraldehyde hybrids as support

Summary New hybrids SiglutX (X=l to 3) were synthesized from silylant agents: (CH₃O)₃Si-R-NH₂ [R = −(CH₂)₂₋, −(CH₂)₂NH(CH₂)₂₋ and −(CH₂)₂NH(CH₂NH(CH₂)₂₋]. The primary amine groups crosslinked with linear glutaraldehyde in two stages: crosslinking and sol-gel processes. The resulting polymers are amorphous, insoluble in organic as well as in acidic or alkaline aqueous media. The hybrids have a large capacity for copper adsorption with very similar kinetic behaviors, defining a plateau after 1 h. The adsorption increases with the increase of nitrogen atoms attached to the organic chain length of the precursor silylant, being 0.25±0.01, 0.37±0.01 and 0.50±0.01 mmol g⁻¹ for X = 1 to 3, respectively. These hybrids also presented a good ability for immobilizing enzymes with distinguishable affinities. The amount of catalase and urease immobilization increased significantly from Sight1 to Siglut2, while the amount of glucose oxidase and invertase anchored decreased from Siglutl to Siglut2. Undefined amounts of enzyme immobilized for Sight3 could be related to possible difficulties arising from its degradation during the interactive process. Received: 30 October 2002/Revised version: 26 February 2003/ Accepted: 26 February 2003 Correspondence to Claudio Airoldi     

Electrical conductivity in iodine-doped nonconjugated polyanilinefurfural

Polyanilinefurfural (PAF) has been prepared. Its chain contains aromatic and furan rings, but the backbone is nonconjugated. However, when treatment with iodine, the color of PAF turns metallic black, and PAF becomes electrically conductive. The electrical conductivity of I₂-doped PAF can reach 10⁻³ S ⋅ cm⁻¹ which is more than 10 orders of magnitude higher than what was observed at the pristine state. The effects of iodine content on the conductivity of PAF and the conductivity stability were investigated. FTIR spectra, U.v./vis absorption spectra, E.s.r. measurement and X.p.s. measurement of the undoped and doped PAF were studied. This paper will demonstrate that: if given appropriate substituents and dopants, significant charge transfer may be expected even for nonconjugated polymers and it may display electronic conductivity to a certain level. Received: 20 November 1996/Revised: 7 February 1997/Accepted: 10 February 1997     

Synthesis and characterization of polyamides based on cubane-1,4-dicarboxylic acid

The direct polycondensations of cubane-1,4-dicarboxylic acid with 1,4-phenylenediamine (2 a), 4,4′-oxydianiline (2 b), 4,4′-sulfonyldianiline (2 c), and 9,9′-bis(4-aminophenyl)florene (2 d) were carried out in N-methyl-2-pyrrolidone/pyridine containing triphenylphosphite and lithium chloride at 110 °C for 9 h. Polyamide 3 a obtained from 2 a was scarcely soluble in organic solvent even during heating, and was soluble only in conc-H₂SO₄, whereas 3 c and 3 d derived from 2 c and 2 d, respectively, were readily soluble in N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, and dimethylsulfoxide. After treating polyamide 3 d with the rhodium complex catalyst in NMP, cubane units were quantitatively converted into cyclooctatetraenes. Received: 3 March 1997/Accepted: 1 April 1997     

Rearrangement of the main chain of the organocobalt polymers

The polymers 3 having pyridine moieties in the main chain were synthesized by the reaction of the organocobalt polymers 1 having cobaltacyclopentadiene moieties in the main chain with various nitriles 2. When brown colored 1 and excess 2 were heated in tetrahydrofuran at 80 °C for 24 h and then at 150 °C for 12 h in a sealed tube, the polymers 3 were obtained by the precipitation with methanol in good yields. From the spectroscopic measurements, the resulting polymers 3 were found to contain 35 – 90% of the pyridine moieties depending on the structures of 1. Received: 7 July 1997/Revised: 14 August 1997/Accepted: 25 August 1997     

Phase behaviour of poly(benzophenoneimide)s having n-alkyloxymethyl side chains

A series of poly(benzophenoneimide)s (C_m-BP-PIs) having n-alkyloxymethyl side chains (−CH₂O-n-CmH_2m+1, m = 4, 6, 8) have been examined by X-ray diffraction, differential scanning calorimetry (DSC) and polarizing optical microscopy. The samples showed basically two phase transitions and both transition temperatures decreased with increasing side chain length. The first transitions were ascribed to glass transitions and the second ones were assigned to liquid crystal-to-isotropic transitions. Eicosane (n-C₂₀H₄₂) which is chemically very similar to the side chain was miscible with the side chains of C₈-BP-PI, which induced depression of the glass transition temperature. Received: 17 February 1997/Revised: 1 April 1997/Accepted: 4 April 1997     

Synthesis and characterization of biodegradable amphiphilic triblock copolymers methoxy-poly(ethylene glycol)-b-poly(L-lysine)-b-poly(L-lactic acid)

Starting from MPEG-NH₂, a series of amphiphilic triblock copolymers MPEG-b-PLL-b-PLA were synthesized through PEG-NH₂-initiated ring-open polymerization of N ^ε-benzyloxycarbonyl-L-lysine, followed by acylation coupling between the amino-terminated MPEG-b-PZLL-NH₂ and carboxyl-terminal PLA and the deprotection of amines. The block copolymers were characterized by FT-IR, ¹H NMR, GPC, DSC and TEM. The copolymer functional groups, molecular and block structures were verified by FT-IR, ¹H NMR and DSC, respectively. The GPC results indicate that the chain lengths of each block can be controlled by varying the feed ratios of the monomer and initiator, providing the polymer samples with a narrow molecular weight distribution (M _w /M _n = 1.10 ~ 1.25). The TEM analysis shows that the triblock polymers can self-assemble into polymeric micelles in aqueous solution with spherical morphology. The cell-cytotoxicity assay indicates that the triblock polymers show no obvious cytotoxicity against Bel7402 human hepatoma cells.     

Copolymerization of 1-butene and 1-hexene with supported titanium catalyst

With TiCl₄/MgCl₂ (Ti) and Al(i-Bu)₃ (Al) as catalysts, the thermoplastic copolymer of 1-butene(Bt) and 1-hexene(He) was synthesized successfully. The effects of Bt/He, Ti/(He+Bt), Al/Ti, temperature and reaction time on conversion, catalyst efficiency(CE), intrinsic viscosity([η]) and insoluble content were studied. The copolymer was analyzed with Fourier transform-infrared (FTIR) and nuclear magnetic resonance (¹H-NMR). Results showed that the optimal polymerization conditions were: He/Bt = 0.25, temperature 40°C−50°C, Al/Ti = 400−500, Ti/(Bt+He) = 3 × 10⁻⁵ − 4 × 10⁻⁵, time 4 h. Intrinsic viscosity was found to increase with increasing Ti/(Bt+He) and decreasing Al/Ti and polymerization temperature. When the molar content of He, Al/Ti and polymerization temperature increased, the insoluble content in CH₂Cl₂ of copolymers decreased. When Ti/(Bt+He) and reaction time increased, the insoluble content in CH₂Cl₂ of copolymers also increased. The crystallization and stereoregularity of poly(1-butene) decreased with the addition of He. Translated from China Synthetic Rubber Industry, 2006, 29(6): 429–434 [译自: 合成橡胶工业]     

Stereoselective 1-3-butadiene polymerization using new titanium chelates

Ternary titanium chelates Ti_x(RCOO^-)_y(C₁₆H₁₁O₆ ^-)_z (R = H, CH₃, CH₃CH₂) combined with AlEt₂Cl selectively polymerise 1,3-butadiene giving > 95% cis-1-4-polybutadiene. The stereoselectivity, activity and oligomer contents are dependent on reaction temperature and Al/Ti ratio. Received: 30 April 1997/Revised: 19 July 1997/Accepted: 1 August 1997     

In situ activation of rac-(SBI)Zr(NMe2)2 for the polymerization of propylene

Summary. Sequential NMR-scale reactions have been carried out in order to generate cationic methylzirconium complexes by the reaction of rac-(SBI)Zr(NMe₂)₂ (1, SBI = Me₂Si(indenyl)₂) with methylaluminoxane (MAO) or various noncoordinating anions such as [HNMePh₂][B(C₆F₅)₄], [HNEt₂Ph][B(C₆F₅)₄], and [Ph₃C][B(C₆F₅)₄]. Reaction of 40 equiv. of MAO with 1 at room temperature was leaded to the formation of stable cationic methylzirconium complexes which polymerize propylene to isotactic polypropylene (iPP). For the activation of 1 with noncoordinating anions 1 was firstly methylated with 4 equiv. of AlMe₃ to give rac-(SBI)ZrMe₂ 2, and then 1 equiv. of noncoordinating anions was added to the resulting solution mixture containing 2 and various aluminum complexes dissolved in CD₂Cl₂ solvent. Complex 2 was immediately converted to cationic methylzirconium complex [rac-(SBI)Zr(μ-Me)₂AlMe₂]⁺ (3), the adduct of the base-free rac-[(SBI)ZrMe]⁺ cation and AlMe₃. Addition of small amount of liquid propylene to the NMR tube containing 3 and other byproducts was leaded to the formation of iPP showing meso pentad value of over 85%. Received: 6 May 1997/Revised: 22 July 1997/Accepted: 28 July 1997     

2D Cationic Metal-Organic Frameworks of Ag+ with Mixed Ligands (Semi-Rigid Dipyridyl, 3-pmpmd, and Diphosphine, dppe)

Abstract  

With the complex 1 or 2 ([Ag(3-pmpmd)]_n·n(X) (X⁻ = BF₄ ⁻, 1; X = PF₆ ⁻, 2) from the semi-rigid 3-pmpmd (N,N′-bis(3-pyridylmethyl)-pyromellitic diimide) ligand and AgBF₄ or AgPF₆ as the precursor, two new coordination polymers [Ag₂(3-pmpmd)₂(dppe)(BF₄)₂]_n·4nDMF (3) and [Ag₂(3-pmpmd)₂(dppe)(PF₆)₂]_n·4nDMF (4) with the 2D cationic MOFs (metal-organic frameworks), have been obtained in the presence of the second dppe (Ph₂P(CH₂)₂PPh₂) ligand. In the 2D layer network, the 3-pmpmd ligands show the Z _T -mode and the Z _C -mode conformations, and the bridged dppe ligands have the same anti conformation. In the meantime, the functions of the two selected ligands, together with the supramolecular interactions from counter ions and solvates molecules within, should play a key role in the construction of the 2D noninterpenetrated network.     

Synthesis of sterically hindered ethyl vinyl ethers containing electron acceptors and their polymerization behaviors

3,5-Dimethoxy-4-(2′-vinyloxyethoxy)benzylidenemalononitrile (2) and methyl 3,5-dimethoxy-4-(2′-vinyloxyethoxy)benzylidenecyanoacetate (3) were prepared and polymerized by radical and cationic initiators. Bifunctional monomers 2 and 3 did not polymerize by radical initiators, but copolymerized readily with ethyl vinyl ether in γ-butyrolactone solution at 65 °C. The trisubstituted terminal double bond participated in the vinyl polymerization and radical polymerization of 2 and 3 with ethyl vinyl ether led to swelling polymers 8 and 9 that were not soluble in common solvents due to cross-linking. Under the same polymerization conditions ethyl vinyl ether polymerized well with model compounds of 3,4,5-trimethoxybenzylidenemalononitrile (10) and methyl 3,4,5-trimethoxybenzylidenecyanoacetate (11), respectively, to give 1 : 1 alternating copolymers 12 and 13 in high yields. Polymers 8 and 9 showed a thermal stability up to 300 °C without any characteristic T_g peaks in DSC thermograms. Alternating copolymers 12 and 13 were soluble in common solvents such as acetone and DMSO, and the inherent viscosities of the polymers were in the range of 0.33 – 0.55 dL/g. Films of polymers 12 and 13 cast from acetone solution were cloudy and tough and T_g values obtained from DSC thermograms were in the range of 163 – 168 °C. Received: 2 August 1996/Revised version: 17 September 1996/Accepted: 20 September 1996