Control of polymerization processes of 10,12-pentacosadiynoic acid LB films

Studies have been carried out on KrF excimer laser light (EX), X-ray or electron beam (EB) induced polymerization of 10,12-pentacosadiynoic acid (PDA) Langmuir-Blodgett (LB) films in relation to molecular density or molecular arrangement of the films using X-ray diffraction analysis, infrared (IR) spectroscopy and Raman spectroscopy. The molecular arrangement or density of the PDA LB films was controlled by subphase conditions when the films were built up, such as pH, temperature of a subphase or salt concentration in the subphase. Polymerization sensitivity of the PDA LB film was affected by the arrangement or molecular density. On low density (A type) films the polymerization occurred by irradiation with EX, X-ray or EB, but on high density (B type) films the polymerization occurred only when the irradiation was carried out by high energy beams such as X-ray or EB. Decomposition of polymerized films was observed further by excessive irradiation of EX or X-ray, but not on the B type films. It was revealed by X-ray diffraction analysis that in the A type film, the PDA molecules bent to a larger extent than those in the B type film and the polymerization proceeded topochemically, that is, the thickness decreased little after EB irradiation in a helium atmosphere. On the other hand, in the B type film, the thickness decreased by about 10% as a result of EB irradiation. By IR reflection-absorption (RA) and Raman measurements, it was confirmed that conjugated diacetylenic bonds disappeared and conjugated double and new conjugated triple bonds appeared after high energy beam irradiations. These results support the supposition that 1,4-polymerization, i.e. polydiacetylene type polymerization, occurs easily in the A type film and 1,2- or 3,4-polymerization, i.e. polyacetylene type polymerization, occurs in the B type film, and that the polymerized A type film was decomposed at the polydiacetylenic bond when the irradiation continued further. It was also shown that the polyacetylene type polymer was obtained only when the B type film was irradiated with the high energy beam.     

Solid-state polymerization of derivatives of 2,4,6-octatriyne: 9. Topochemical reactions of monomers with conjugated triple bonds

The solid-state polymerization of monomers with three conjugated triple bonds gives rise to polymer single crystals. The lattice parameters of the polymers from 2,4,6-octatriyne-1,8-diol and 2,4,6-octatriyne-1,8-diol-bis(phenyl urethane) were determined. Based on these data and considering the mechanical properties and dichroism of the polymer crystals, it is concluded that polymerization proceeds according to a 1,4-addition to the triple bond system of the monomers. Only two of the three triple bonds of the monomers are affected by polymerization to form the polymer backbone of regularly alternating double, single and triple bonds. The residual triple bond is regularly arranged in the all-trans position as part of the substituents. The kinetics of the thermal and photopolymerization of these monomers are quite similar to those of the corresponding diynes. The activation energy of thermal polymerization was found to be 23 kcal/mol as compared to 19 kcal/mol for comparable diynes. The long wavelength limit of photosensitivity was found to be at about 380 nm as compared to 330 nm for diynes.     

Molar absorptivity of poly(methyl methacrylate) in the near-ultraviolet region

The molar absorptivities of methyl methacrylate monomer and of thermally polymerized, monomer-free poly(methyl methacrylate) have been measured in the range 2200–3000 Å, and smoothed values are presented at wavelength intervals of 20 Å over much of this range. Typical amounts of monomer present in a thermally polymerized bulk polymer and in films cast from CH₂Cl₂ solutions of the bulk polymer have been ascertained. The use of such absorptivity values to determine the amount of monomer present in polymer samples is evaluated.     

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.     

Electrochemical preparation of poly(2,5-dimethoxy-1,4-phenylene)

Summary p-Dimethoxybenzene was electro-oxidatively polymerized to give poly(2,5-dimethoxy-1,4-phenylene) with high yield. 1,4-Structure of polyphenylene was confirmed by ¹³C-NMR and IR spectrum. The polymer was deposited on electrode, and electrolysis solvent affected the polymer yield and morphology of the polymer. In a strongly basic solvent the polymerization was inhibited, which suggests that cation radical of p-dimethoxybenzene is an active species of this polymerization.     

Coulombic screening in polydiacetylene crystals

The strong colour of polydiacetylene polymer crystals is due to the backbone exciton. The energy of the exciton is strongly affected by Coulombic interactions with the surrounding crystalline environment. X-ray diffraction and optical absorption measurements of the blue phase polymer crystals of 4BCMU show that a change in the energy of the polydiacetylene backbone exciton can be related to a change in the inter-backbone spacing within the crystals. Over the range of inter-backbone spacings measured, this variation is in very good agreement with Coulombic screening theory. It is calculated from these results that inter-backbone Coulombic screening lowers the value of the exciton energy in the blue phase polymer crystals of 4BCMU by −0.362eV, which is 15.4% of the total exciton energy. Coulombic screening is shown to have an important effect on the optical absorption properties of other polydiacetylene derivatives. Calculations and resonant Raman spectroscopy measurements show that a combination of a low level of Coulombic screening and strain in the crystal lattice accounts for the red colour of the polymer crystals of PTS-12 and TCDU.     

In Situ polymerization in binary polymer/monomer mixtures: A novel route to polymeric composites

The formation of a polymer/polymer composite by solid-state polymerization of trioxane (TOX) crystals grown within binary trioxane/polycaprolactone or trioxane/poly(oxythylene) mixtures is reported. At present, such composites have been formed with trioxane-rich (hypoeutectic) mixtures. It is observed that in this composition range, much higher yields are obtained through thermal orientation of the TOX crystals which result in very highly ordered systems as revealed by optical and electron microscopy. These POM-rich composites were not, however, amenable to mechanical testing.     

负载TiCl3(OC4H9)催化剂引发异戊二烯聚合研究

以负载TiCl3(OC4H9)催化剂引发异戊二烯聚合,研究n(Al):n(Ti)、n(Ti):n(IP)、聚合温度及聚合工艺对聚合活性的影响,以FT-IR表征了聚合物结构。结果表明:在n(Al):n(Ti)=80时催化剂具有最高的催化活性,随着n(Ti):n(IP)升高聚合转化率升高,低温预聚有利于催化效率增加。聚合所得产物为β晶型的反1,4-聚异戊二烯结晶聚合物。     

The solid-state polymerization and physical properties of bis(ethyl urethane) of 2,4-hexadiyne-1,6-diol: 3. Mechanical properties

The mechanical properties of partly and fully polymerized single-crystal fibres of a substituted polydiacetylene have been investigated. In particular the Young's moduli, fracture stresses and creep properties have been measured. The Young's modulus was found to increase with conversion from monomer to polymer up to a maximum value of 62 GPa. The fracture stress was found to vary with both the degree of conversion and fibre diameter. Strengths of up to 1.4 GPa have been determined for fully polymerized, 20 μm diameter fibres. It has not been possible to detect any creep or time-dependent deformation for the fibres. The variation of the mechanical behaviour with conversion from monomer to polymer has been explained in terms of the Voigt and Reuss models and related to the structure of the crystals. The dependence of the fracture stress upon fibre diameter has been accounted for in terms of the presence of defects upon the surface of the crystals.     

Morphological effects on the bulk polymerization of trioxane in the solid state by γ-radiation

The solid-state polymerization by γ-radiation and postpolymerization of bulk samples of trioxane has been investigated. Different thermal treatment results in radically different initial morphologies of the melt-crystallized trioxane which in turn have a profound influence on the yield and morphology of the resulting poly(oxymethylene) (POM). The polymerization yield increases in the following series: melt-crystallized trioxane with an “opaque” (small grains) morphology, as-grown needles, trioxane with a “quasi-transparent” morphology, and finally thermally oriented crystals. Furthermore, little additional POM is formed during repeated polymerization cycles. The observation of an extensive nodulation of the polymer fibrils when the yield is high is consistent with a multiple-stage growth model for the solid-state polymerization of trioxane.     

Anionic polymerization initiated by the lamellar compounds of LiC12: 2. Thermodynamics and the propagation mechanisms in 1,4 Cis and 1.4 Trans of isoprene, -H-n.m.r. study

The polymerization of isoprene initated by LiC₁₂ in cyclohexane yields polymers whose microstructures are quite different from those obtained in homogeneous media. These microstructures change during the reaction. For the low yields, the polymer may contain up to 96% 1,4 cis. The evolution of the microstructure with the mass of the polymer formed per g of initiator is also temperature dependent. With certain types of ‘ternary’ lamellar compounds it is possible to obtain (at high yields) polymers with a high content of 1,4 cis. A mechanism of polymerization is proposed that takes into account the influence of one (or more) graphite layer over the interactions between the lithium cation of the growing living end and the monomer.     

Epoxy-functional thermoplastic copolymers and their incorporation into a thermosetting resin

The customization of polymer networks can be made possible via dual-functional monomers, molecules characterized by two different reactive substituents that allow for versatile methods of polymerization. The dual-functional, epoxy-methacrylate monomers, glycidyl methacrylate (GMA), and vanillyl alcohol epoxy-methacrylate (VAEM), were polymerized with methyl methacrylate (MMA) via reversible addition-fragmentation chain transfer (RAFT) polymerization to form low molecular weight (~10–20 kDa) epoxy-functional thermoplastic copolymers, poly(VAEM-co-MMA), and poly(GMA-co-MMA). The copolymers were blended at 5 wt% into an epoxy resin system containing EPON Resin 828 and EPIKURE W Curing Agent and cured thermally to create unique interpenetrating polymer networks (IPNs). The resulting IPNs were compared to the cured neat resin and evaluated for thermal and mechanical properties, where maintained thermal properties and enhancements of stiffness and toughness were demonstrated.     

Approaches to branched polystyrene using bulk free-radical polymerization

Preparation of branched polystyrene using continuous bulk styrene polymerization is extremely difficult due to gel formation and can even lead to reactor plugging. This investigation explores the concept of post-polymerizer branching by placing latent functional groups along the polymer backbone which couple during high-temperature devolatilization of the polymerized effluent. The latent functional monomer pair investigated is glycidyl methacrylate and acrylic acid. The key to producing a branched polystyrene that is thermally stable is to add one of the latent functional monomers in large excess, making the other monomer the limiting reagent. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 683–687, 1997     

Synthesis,Characterization and Material Application of Poly(Urea-Imide)s,Part 1

Poly(urea-imide)s (PUIs) were prepared by Diels-Alder (DA) intermolecular polymerization of hexamethylenebis(2-furanmethylurea) (BFU) (1) with various bismaleimides (2a-f). The DA reaction was carried out using 1,4-dioxane as solvent, as well as in bulk, followed by aromatization (dehydration) of poly(tetrahydro phthalimide) intermediates (3a-f) in the presence of acetic anhydride. All the PUIs (3a-f, 4a-f and 5a-f) were characterized by elemental analysis, IR spectral studies and thermogravimetrically. BFU (1) and bismaleimides (2a-f) were polymerized (at 145 ± 10°C) by in situ DA intermolecular reaction into moderately thermally stable PUIs (5a-f), glass fiber and carbon fiber composites without evolution of any byproducts. The prepared composites were characterized by chemical resistance and mechanical properties.     

本体法和溶液法合成反式-1,4-聚异戊二烯的结构对比分析

分析对比了通过溶液聚合法和本体沉淀聚合法所制得反式-1,4-聚异戊二烯(TPI)的反式结构含量、结晶度、熔点、相对分子质量及其分布以及催化剂体系,并对其相似和差异产生的原因进行了探讨。结果表明,用两种聚合方法获得的TPI具有相近的反式结构含量、结晶度和相对分子质量及其分布,溶液聚合TPI的熔点明显高于本体沉淀聚合法,二者是用不同的催化剂体系合成的。另外,对两种聚合方法 TPI的力学性能研究发现,溶液聚合TPI的力学性能要优于本体沉淀聚合法。     

Theoretical investigation of the mechanism of cis-trans regulation for the allylnickel(II)-catalyzed 1,4 polymerization of butadiene

In this Account we summarize the recent progress in the computational modeling of the transition-metal-catalyzed 1,3-diene polymerization. We present a comprehensive and theoretically well-founded view of the cis-trans regulation mechanism of the intriguing C-C coupling for the allylnickel(II)-catalyzed 1,4 polymerization of butadiene. The crucial elementary reactions of the entire polymerization process were theoretically explored for typical trans-1,4- and cis-1,4-regulating catalysts. As a result, the catalytic structure-activity relationships are deduced, which are responsible for opening that reaction channel which yields trans-1,4 and cis-1,4 polymer units.     

Plastic scintillators with efficient light output and pulse shape discrimination produced via photoinitiated polymerization

Poly(vinyl toluene) (PVT) overdoped with 2,5-diphenyloxazole and using 1,4-bis(5-phenyloxazol-2-yl)benzene as a fluorescent secondary dopant can be used to detect and differentiate neutron and gamma radiation via scintillation. The low cost of PVT makes these plastic scintillators attractive for both portable and larger sized first line detection of special nuclear materials. Current fabrication methods rely on thermally initiated radical polymerization that generally requires an approximately 5-day heating process in order to produce high quality scintillators. In this work, we report a proof-of-concept photopolymerization process to prepare plastic scintillators up to 20 g in size in 1 day. These plastic scintillators were comparable to standard thermally polymerized samples in terms of their physical properties and response to various radiation sources. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47381.     

Polymerization of olefins through heterogeneous catalysis,I. Low pressure propylene polymerization in slurry with Ziegler–Natta catalyst

Propylene was polymerized in slurry over a TiCl₃·? AICI₃ (Stauffer Type AA) catalyst with Al—Et₂Cl cocatalyst at 60 psig pressure both with and without H₂ present. The effects of polymerization temperature, catalyst poisons, and type of slurry liquid were investigated, with particular emphasis on the yield, tacticity, and MWD of the resulting polymer. The highest yields and isotactic content were obtained with decane–heptane mixtures as a slurry liquid, while slurry liquids in which polypropylene was most soluble gave the narrowest MWD.     

Ultralow percolation graphene/polyurethane acrylate nanocomposites

Polyurethane acrylate (PUA) are widely used as coating for automobile industry. Making these coatings electrically conductive would open up new applications. Using thermally reduced graphene (TRG) and in-situ polymerization we have created PUA nanocomposites with an ultralow percolation concentration of 0.15 wt% (0.07 vol%) graphene. Urethane-acrylate oligomer (UAO) was synthesized and diluted by tripropyleneglycol diacrylate (TPGDA) to form flowable UAO/TPGDA mixture (UA). TRG was solvent-blended in UA to form uncured TRG/UA liquids and were polymerized by free radical polymerization with azobisisobutyronitrile (AIBN) initiator. Percolation concentrations of polymerized TRG/PUA nanocomposites occurred at 0.15 wt% (0.07 vol%), as determined by surface resistance measurements, bulk electrical conductivity, and modulus. TEM images revealed a homogeneous dispersion of TRG in PUA. Differential scanning calorimetry (DSC) was used to monitor the polymerization of TRG/UA uncured liquids and thermal properties of polymerized TRG/PUA nanocomposites. Polymerization heat, glass transition temperature, and polymerization temperature are independent of TRG loading, though polymerization temperature is ～10 °C lower in the absence of TRG.     

Synthesis and characterization of thermally curable polyacetylenes by polymerization of propargyl benzoxazine using rhodium catalyst

A novel acetylene monomer containing benzoxazine group was synthesized and polymerized with [(norbornadiene)rhodium(I) chloride]₂ ([(nbd)RhCl]₂) to give the corresponding polymer. The effect of triethylamine as co-catalyst in the polymerization was investigated. The spectral and thermal analyses confirmed the presence of benzoxazine functionality in the resulting polymer. It is shown that polyacetylene containing benzoxazine side groups undergoes irreversible cis–trans isomerization and thermally activated curing in the absence of any catalyst forming polyacetylene thermoset with high thermal stability.