Synthesis and photodegradation of poly[1,4-bis(dimethylsilyl)naphthalene]

Summary Poly[1,4-bis(dimethylsilyl)naphthalene](I), a copolymer with alternating 1,4-naphthalene and disilyl units, has been prepared by the Wurtz coupling of 1,4-bis(dimethylchlorosilyl) naphthalene (II) or 1,4-bis(dimethylfluorosilyl)naphthalene (III) with sodium metal dispersion in toluene. The molecular weight distribution of I prepared from III is significantly higher than when I is prepared from II. I has been characterized by ¹H, ¹³C and ²⁹Si NMR, IR, UV, GPC, TGA and elemental analysis. Photolysis of I in benzene/methanol solution results in rapid degradation of I.     

Synthesis of high molecular weight copolymer of styrene and butadiene bearing high 1,4‐cis butadiene unit from copolymerization with CpTiCl3/methylaluminoxane catalyst

Copolymerization of styrene (St) and butadiene (Bd) with CpTiCl₃/methylaluminoxane (MAO) catalyst in the presence or absence of chloranil (CA) was investigated. The CpTiCl₃/MAO catalyst showed a high activity for the copolymerization of St with Bd. The 1,4‐cis contents in the Bd units for the copolymerization of St and Bd with the CpTiCl₃/MAO catalyst was observed, and the 1,4‐cis content was optimum at a MAO/Ti mole ratio of around 225. The effect of the polymerization temperature on the copolymerization was noted, as was the effect of the 1,4‐cis microstructure in the Bd units for the copolymerization of St and Bd. The addition of CA to the CpTiCl₃/MAO catalyst was found to influence the molecular weight of the copolymer. The high weight‐average molecular weight copolymer (M_w = ca. 50 × 10⁴) consisting of mainly a 1,4‐cis microstructure of Bd units (1,4‐cis = 80.0%) was obtained from the copolymerization with the CpTiCl₃/MAO catalyst in the presence of CA (CA/Ti mole ratio = 1) at 0°C. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2942–2946, 2003     

Synthesis and properties of poly(dioxynaphthyleneisophthaloyl)s with various isomeric naphthylene links

Summary By condensation of 1,4-, 1,5-, 1,6-, 2,3-, 2,6-, and 2,7-naphthalenediol (ND) isomers with a isophthaloyl chloride six aromatic polyesters were prepared, and after removal of low molecular weight materials by extraction with acetone their properties were investigated. Effects of the isomerism of the naphthylene units on the properties of the polyesters were discussed. All the polyesters except one derived from 2,7-ND were soluble in a mixed solvent of phenol/p-chlorophenol/1,1,2,2-tetrachloroethane (TCE). Weight-average molecular weight of the polymer derived from 2,3-ND having the lowest inherent viscosity of 0.10 dL/g was measured to be 12,200 g/mol in TCE by means of a laser light scattering spectrometer. Polydispersity of this sample was determined to be 1.59 by a gel permeation chromatography with o-chlorophenol at 100°C. Glass transition temperatures of the polymers ranged from 144 to 195°C, depending on their molecular weight and chain structure. The polyesters derived from 1,6- and 2,3-NDs were amorphous and all the others were crystalline. Melting temperatures (T_m) of the polymers range from 341°C to 417°C and the polymer derived from 2,6-ND showed the highest T_m. All the polymers had initial decomposition temperature higher than 400°C and showed residue more than 50 wt% at 600°C.     

Microstructure‐thermal property relationship of high trans‐1,4‐poly(butadiene) produced by anionic polymerization of 1,3‐butadiene using an initiator composed of alkyl aluminum,n‐butyl lithium,and barium alkoxide

This article deals with the characterization of high trans‐1,4‐poly(butadiene) (TPBD) prepared by means of an anionic polymerization using an initiator composed of alkyl aluminum, n‐butyl lithium, and barium alkoxide. By controlling both initiator composition and polymerization temperature, a set of TPBD was prepared with well‐known number of 1,4‐trans units, molecular weight distribution, and average molecular weight. Analyses by differential scanning calorimetry and diffraction of wide‐angle X‐rays showed a direct relationship between the microstructure of the polymer and its thermal properties. By increasing the number of 1,4‐trans units (70–90%), the crystallinity of the polymer was increased (10–30%); polymers with less than 65% of 1,4‐trans units were amorphous, whereas TPBD with a number of 1,4‐trans units greater than 80% were polymorphous and presented two endothermic transitions. Summing up, the results presented in this article indicate that cyclohexane solutions of alkyl aluminum, n‐butyl lithium, and barium alkoxide allow produce polybutadienes with enough amount of 1,4‐trans units to display a regular microstructure that makes them susceptible to experience‐induced crystallization, likewise at a reaction rate similar to that observed for the commercial production of poly(butadiene) with n‐butyl lithium. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers     

Chopping high‐molecular weight poly(1,4‐butylene carbonate‐co‐aromatic ester)s for macropolyol synthesis

The condensation of a mixture of dimethyl carbonate and phthalate derivatives with 1,4‐butanediol (BD), catalyzed by sodium alkoxide, generated high‐molecular weight poly(1,4‐butylene carbonate‐co‐aromatic ester)s with molecular weights (M_n) of 50–120 kDa. The subsequent addition of polyols [BD, glycerol propoxylate, 1,1,1‐tris(hydroxymethyl)ethane, or pentaerythritol] chopped these high‐molecular weight polymers to afford macrodiols or macropolyols with facile control of their molecular weights (M_n, 2000–3000 Da) and unique chain topological compositions. Macropolyols prepared by chopping poly(1,4‐butylene carbonate‐co‐terephthalate) were waxy in nature, whereas those containing isophthalate and phthalate units were oily. The macropolyols synthesized by this chopping method may have potential applications in the polyurethane industry. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43754.     

Synthesis and chain extension of poly(L‐lactic acid‐co‐succinic acid‐co‐1,4‐butene diol)

L ‐Lactic acid (LA) was copolymerized with succinic acid (SA) and 1,4‐butenediol (1,4‐BED) in bulk state with titanium(IV) butoxide as a catalyst to produce poly(LA‐co‐SA‐co‐1,4‐BED) (PLASBED). Poly(L ‐lactic acid) (PLLA) homopolymer obtained from a direct condensation polymerization of LA had weight average molecular weight (M_w) less than 4.1 × 10⁴ and was too brittle to prepare specimens for the tensile test. Addition of SA and 1,4‐BED to LA produced PLASB with M_w as high as 1.4 × 10⁵ and exhibited tensile properties comparable to a commercially available high‐molecular‐weight PLLA. Chain extension by intermolecular linking reaction through the unsaturated 1,4‐BED units in PLASBED with benzoyl peroxide further increased the molecular weight and made PLASBED more ductile and flexible to show elongation at break as high as 450%. Biodegradability of PLASBED measured by the modified Sturm test was nearly independent of the 1,4‐BED content. Gel formation during the chain extension did not exert any significant influence on the biodegradability either. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1116–1121, 2005     

Alternating copolymers of butadiene and propylene: Properties and characterization

Alternating copolymers of butadiene and propylene (BPR) made by a solution polymerization technique with a modified catalyst of the Furukawa type have highly regular structures. The constitutional repeating unit consists of one propylene and one 1,4-trans-butadiene unit. No chain imperfections were detected, except for ≦2% 1,4-cis-butadiene units. The configurations of the chiral tertiary carbon atoms in the propylene units could not be directly determined by spectroscopic methods. The intrinsic viscosities of the samples studied lie between 1.1 and 1.8 dL/g. The high molecular weight fractions (M > 2 × 10⁵) show long-chain branching. Crystallization effects, namely, a decrease in specific volume with time, and melting are observed after annealing unoriented samples at temperatures between ?30 and ?50°C. X-ray diffraction shows that the structure of the ordered phase depends on polymerization conditions, varying between a liquid crystal-like close packing of parallel chain segments and imperfect crystalline, three-dimensionally periodic arrangements of chains. Both in the noncrystalline and crystalline ordered phases, the molecules are arranged in layers with a spacing of 0.47 nm. The crystalline chains have nonplanar and not fully extended conformations with a repeat distance of 0.72 nm. The rate of crystallization and the relative decrease in volume (≦1.3%) are small compared to stereoregular polymers like natural rubber and high-cis polybutadiene. In crosslinked specimens, stretched 1:6 to 1:10, the crystalline or liquid crystal-like structure persists up to +60°C. The imperfect nature of the crystallization of BPR is caused by stereoisomerism of the chiral carbon atoms. The chains are probably composed of short tactic sequences separated by tactic arrangements.     

Chain extension and mechanical properties of unsaturated aliphatic copolyesters based on poly(L‐lactic acid)

Chain extension of poly(L ‐lactic acid) (PLLA) with unsaturated groups (PLBM) was attempted using benzoyl peroxide (BPO) and the resulting variation in molecular weight and mechanical properties was explored. Bulk copolymerization of L ‐lactic acid (LA)/1,4‐butanediol (BD)/maleic acid (MA) (100/1/1) isomerized some of the cis‐structured maleate units into trans‐structured fumarate units. The optically active LA promoted isomerization during the condensation polymerization. Chain extension of PLBM with BPO did not bring about a discernible increase in the molecular weight when the chain extension was carried out in various solvents with different radical abstraction abilities. In contrast, the hot pressing of PLBM containing BPO increased the molecular weight and sometimes produced chloroform‐insoluble gels depending on the BPO concentration and temperature. The chain extension at low temperatures increased the flexibility of PLBM considerably. However, PLBM lost the flexibility precipitously as the chain‐extension temperature increased above 120°C. The biodegradation rate of PLBM was much slower than that of PLLA. The biodegradation rate was further lowered by the chain extension. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1802–1807, 2003     

Chromatographic investigations of macromolecules in the critical range of liquid chromatography,XIII. Separation of blends of styrene-butadiene rubber and butyl rubber

The separation of blends of styrene-butadiene rubber and butyl rubber is accomplished by liquid chromatography at the critical point of adsorption. Using a non-polar stationary phase and methyl ethyl ketone-cyclohexane as the eluent, the critical point of adsorption of polybutadiene is established. Under these chromatographic conditions, the blends are separated regardless of the molar masses of the components. The exact chemical structure of the blend components can be analysed by coupling the chromatographic separation to FTIR detection. The FTIR spectra of the components reveal information on the styrene and butadiene content and the conformation of the butadiene units (1,2-, 1,4-cis, 1,4-trans units). Poorly soluble high molar mass samples are separated by combining critical separation with a gradient elution technique.     

1,3‐butadiene polymerization using Co/Nd‐based Ziegler/Natta catalyst: Microstructures and properties of butadiene rubber

Among Ziegler‐Natta catalysts used for 1,3‐butadiene (1,3‐BD) polymerization, the advantage of a neodymium (Nd)‐based catalyst is that it provides butadiene rubber (BR) with a high content of cis?1,4 configuration and a low amount of vinyl?1,2 units. Whereas, a cobalt (Co)‐based catalyst can produce BR with a low content of trans?1,4 configuration. Thus, this research was aimed to prepare BR containing a high content of cis?1,4 configuration with low amounts of both trans?1,4 and vinyl?1,2 units using a combination of Nd‐ and Co‐based Ziegler/Natta catalysts with triethyl aluminum (TEAL) and diethyl aluminum chloride (DEAC) acting as a co‐catalyst and a chlorinating agent, respectively. The effects of the molar Co/Nd ratio, TEAL concentration, DEAC loading, 1,3‐BD content, solvent type, and reaction temperature on % conversion, microstructures, molecular weight, and molecular weight distribution of the obtained BR (Co/Nd‐BR) were evaluated. The Co/Nd‐BR having >97% of cis?1,4 configuration, <2% of trans?1,4 structure, and <1% of vinyl?1,2 unit with >80% conversion was achieved when 3.01 M of 1,3‐BD concentration was treated in a toluene/cyclohexane mixture (7/3 [w/w]). The Co/Nd‐BR exhibited no gel formation with high mechanical performance, which was equivalent to commercial BR produced from a Nd‐based catalyst system. POLYM. ENG. SCI., 55:14–21, 2015. © 2014 Society of Plastics Engineers     

On the synthesis and properties of some saturated and unsaturated esters of 2-cyano-2, 4-pentadienoic acid

The preparation and properties of some new saturated and unsaturated esters of 2-cyano-2,4-pentadienoic acid (CPDA) are described. A comparison is also made with the known CPDA monomers synthesized under identical conditions. It was found that the monomer yields are dependent on the structure of the corresponding CPDA esters. This fact was explained with solvatation effects, occurring during the isolation procedures. The base-catalyzed anionic bulk polymerization of CPDA esters was studied by means of spectral methods. The data indicated that during the homopolymerization 1,4-addition of monomer molecules takes place to give a steric copolymer consisting of 1,4-cis and 1,4-trans structural units. The ability of poly-CPDA esters was also followed to form crosslinks at room and higher temperatures.     

Effects of tetrahydrofuran as a structure modifier in preparation of SBS thermoplastic block copolymers in cyclohexane

Linear styrene-butadiene block copolymers of polyA-block-polyB-block-polyA type (SBS) were synthesized in the presence of varying amounts of THF functioning as the polar structure modifier. The efficiency of this modifier was studied by analyzing the microstructure of synthesized polymers using ¹³C-NMR, and the effect of THF on polymerization kinetics was determined by progressive buildup of the molecular weight measured by GPC. Polymerization at 4000 ppm THF concentration resulted in the highest styrene polymerization rate while a 1 wt % concentration gave the highest butadiene polymerization rate. The vinyl content increased from 20 to 64% with an increase in the amount of THF from 200 ppm to 1 wt % while the content of trans-1,4 and cis-1,4 units decreased. For SBS polymer synthesized via a sequential process, the use of THF as the structure modifier enhanced the crossover efficiency that would otherwise result in a skewed molecular weight distribution with a higher polydispersity. For SBS polymer made via a coupling process, the coupling efficiency decreased when the amount of THF exceeded a certain limit. The temperature dependence of the coupling efficiency was also investigated. © 1996 John Wiley & Sons, Inc.     

A study of miscibility of blends of polybutadienes of varying microstructure

The miscibility of various amorphous polybutadienes with mixed microstructures of 1,4 addition units (cis, 1,4 and trans 1,4) and 1,2 addition units have been investigated. The studies here involved optical transparency, differential scanning calorimetry, and small angle light scattering. It was found that a 90 percent (cis) 1, 4 addition polybutadiene was immiscible with high (91 percent) 1,2 addition polybutadiene. Reduction of the 1,2 content to 71 percent induced an upper critical solution temperature (UCST) with the cis 1,4 polymer. Polybutadienes with 50 percent and 10 percent 1,2 contents were miscible above the crystalline melting temperature of the cis 1,4 polybutadiene. Immiscibility of the 91 percent 1,2 addition polymer was also found with a 10 percent 1,2 polybutadiene. The latter polymer also exhibits an UCST with the 71 percent 1,2 polymer. The results are used to interpret the characteristics of blends of polybutadienes of varying microstructure.     

Polymerization and polymer properties of (2-methyl-5-tert-butylphenyl)acetylene: steric effects of the ring substituents

Summary (2-Methyl-5-tert-butylphenyl)acetylene (2Me5tBuPA) polymerized in the presence of MoCl₅-n-Bu₄Sn catalyst in 1,4-dioxane to give a high molecular weight polymer . Not only MoCl₅- but also WCl₆-based catalysts were effective. The polymer obtained was a dark brown solid, soluble in organic solvents such as toluene and CHCl₃, and formed a freestanding film by solution casting. The onset temperature of weight loss of the polymer in air was 260 °C. Its oxygen permeability coefficient was 43 barrers, which is twice that of natural rubber. Differences from the results (usually lower molecular weight, not film-forming, and thermally less stable) of both poly(phenylacetylene) and poly[o-methylphenyl)acetylene] are attributable to the synergistic steric effect of the o-methyl and m-tert-butyl groups.     

Styryl Group,a Friend or Foe in Medicinal Chemistry

The styryl (Ph-CH=CH-R) group is widely represented in medicinally important compounds, including drugs, clinical candidates, and molecular probes as it positively impacts the lipophilicity, oral absorption, and biological activity. The analysis of matched molecular pairs (styryl vs. phenethyl, phenyl, methyl, H) for the biological activity indicates the superiority aspect of styryl compounds. However, the Michael acceptor site in the styryl group makes it amenable to the nucleophilic attack by biological nucleophiles and transformation to the toxic metabolites. One of the downsides of styryl compounds is isomerization that impacts the molecular conformation and directly affects biological activity. The impact of cis-trans isomerism and isosteric replacements on biological activity is exemplified. We also discuss the styryl group-bearing drugs, clinical candidates, and fluorescent probes. Overall, the present review reveals the utility of the styryl group in medicinal chemistry and drug discovery.     

New Blue Light Emissive Polyazomethine(S) Containing Bromo-Triphenyl Units: Synthesis and Photophysics

A series of bromo-substituted triphenylamine based poly(azomethine)s (P1-P3) were synthesized from the N¹-(4-aminophenyl)-N¹-(4-bromophenyl)benzene-1,4-diamine (DA) and aromatic dialdehydes. The viscosity of P1-P3 solutions (0.97 to 1.12 g dL^?1) and molecular weight distribution analysis by Gel Permeation Chromatography (GPC) discloses the attainment of appreciable molecular weight. The optical transparency and fluorescence properties of the P1-P3 were explored by UV-vis and photoluminescence spectral analysis. From which it was concluded that the presence of 4-bromotriphenylamine and azomethine (CH = N) linkage in our synthesized materials are possibly responsible for the fluorescence with quantum efficiencies of 0.9–2.1 %.     

Morphology and photophysical properties of luminescent electrospun fibers prepared from diblock and triblock polyfluorene-<Emphasis Type="Italic">block</Emphasis>-Poly(2-vinylpyridine)/PEO blends

We successfully prepared luminescent electrospun (ES) fibers from the polymer blends of diblock poly[2,7-(9,9-dihexylfluorene)]-block-poly(2-vinylpyridine)(di-PFPVP) or triblock P2VP-b-PF-b-P2VP (tri-PFPVP) with polyethylene oxide (PEO) using a single-capillary spinneret. The morphology and photophysical properties of ES fibers were explored via the molecular architecture, solvent selectivity, and different molecular weights of PEO. The ES fibers had diameters around 400–800 nm using solvent of methanol (MeOH)/H₂O while those using CHCl₃ were around 1–3 μm, which was probably due to the difference on the solvent dielectric constant. Furthermore, the PF aggregated size and emission peak maximum in the ES fibers increased with enhancing the block copolymer composition using CHCl₃. However, an insignificant variation was observed using MeOH/H₂O. The larger PF aggregated size of the di-PFPVP/PEO blend ES fibers resulted in the red-shifting and broader emission peak, in comparison with that of the tri-PFPVP/PEO blend ES fibers. The efficient interaction of the PEO with the PVP block in two different block copolymers accounted for the above results. In the ES fibers using the low molecular weight of PEO (Mn~100 K), it exhibited a red-shifting on the PL spectra in comparison with the spin-coated films due to the geometrical confinement. Nevertheless, such confinement was probably significantly reduced using the high molecular weight PEO (Mn~2000 K) and thus an insignificant variation was found on the PL spectra. The present study demonstrated that their aggregate morphology and photophysical properties of ES fibers prepared from conjugated rod-coil block copolymer blends could be significantly tuned through polymer architecture, solvent selectivity, and copolymer composition.     

Effects of molecular weight on dual light‐ and thermo‐responsive behaviors of homopolymers with azobenzene units and terminal oligo(ethylene glycol) units

A series of water‐soluble dual light‐ and thermo‐responsive homopolymers bearing azobenzene units and terminal oligo(ethylene glycol) units with well‐defined molecular weight (M _n = 0.69 × 10⁴ to 4.60 × 10⁴ g mol^?1) were synthesized via reversible addition–fragmentation chain transfer polymerization. All the homopolymers exhibited reversible photoisomerization and their lower critical solution temperatures showed an unusual increase with increasing molecular weight. Interestingly, by increasing the molecular weight, the aggregate morphology of these polymers was found to evolve from a spherical to a cylindrical shape. © 2017 Society of Chemical Industry     

Effect of electron donors on 1,3‐butadiene polymerization by a Ziegler–Natta catalyst based on neodymium

High‐cis polybutadiene produced by catalyst systems based on a rare earth is an elastomer used to produce green tires. This type of tire presents lower rolling resistance, which allows higher fuel economy, and thus fewer chemical compounds are discharged into the atmosphere. In this work, the influence of electron donors [tetrahydrofuran (THF) and tetramethylethylenediamine (TMEDA)] present in the polymerization solvent on the microstructure and molecular weight characteristics of the polybutadiene produced by neodymium catalysts was studied. The catalyst synthesis was carried out in glass bottles for 1 h at a temperature between 5 and 10°C. The catalyst components were diisobutylaluminum hydride, neodymium versatate, and tert‐butyl chloride. The polymerization reaction was carried out for 2 h. The reaction temperature was kept at 70± 3°C. The addition of TMEDA or THF above a determined concentration reduced the catalytic activity, molecular weight, and concentration of cis‐1,4 units (<96%), whereas the polydispersity increased. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2539–2543, 2005     

Synthesis and properties of amino acid-derived optically active photo-responsive polymers

Optically active azobenzenedicarboxylic acids were synthesized from l-alanine, and the polycondensation of the diacids with o-, m-, p-xylylenediols, 5-norbornene-2,3-endo,endo- and exo,exo-dimethanols, m-, p-xylylenediamines, and trans-1,4-cyclohexanediamine was carried in N,N-dimethylformamide. Polymers with weight-average molecular weights of 3,300–33,700 were obtained in 63%-quantitative yields. All the polymers reversibly isomerized the azobenzene units from trans to cis and vice versa upon UV- and visible-light irradiations. The polymers exhibited no evidence for the formation of a chiral secondary structure.