Energy levels of ionized states in a polydiacetylene crystal (PTS) studied by photoemission

Electron emission from partially and fully polymerized PTS single crystals has been measured upon excitation in the photon energy range 7 <hv < 11 eV. The ionization thresholds are 5.5 ± 0.1 eV for PTS polymer and 7.1 ± 0.1 eV for TS monomer. The bottom of the conduction band in PTS is located at A^P_C = ?3.1 ± 0.1 eV.     

Thermal gelation or gel melting: (ethylene glycol)113‐(l‐alanine)12 and (ethylene glycol)113‐(l‐lactic acid)12

When PEG (M.W.～5000 Daltons) is conjugated to poly(l ‐alanine), the polymer aqueous solutions (<10.0 wt.%) undergo sol‐to‐gel (thermal gelation), whereas it is conjugated to poly(l ‐lactic acid), the polymer aqueous solutions (>30.0 wt.%) undergo gel‐to‐sol (gel melting) as the temperature increases. In the search for molecular origins of such a quite different phase behavior, poly(ethylene glycol)‐poly(l ‐alanine) (PEG‐PA; EG₁₁₃‐A₁₂) and poly(ethylene glycol)‐poly(l ‐lactic acid) (PEG‐PLA; EG₁₁₃‐LA₁₂) are synthesized and their aqueous solution behavior is investigated. PEG‐PAs with an α‐helical core assemble into micelles with a broad size distribution, and the dehydration of PEG drives the aggregation of the micelles, leading to thermal gelation, whereas increased molecular motion of the PLA core overwhelms the partial dehydration of PEG, thus gel melting of the PEG‐PLA aqueous solutions occurs. The core‐rigidity of micelles must be one of the key factors in determining whether a polymer aqueous solution undergoes sol‐to‐gel or gel‐to‐sol transition, as the temperature increases. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, , 52, 2434–2441     

Effect of polarity of the medium on the stereospecific polymerization of propylene by ansa-zirconocene catalyst

Propylene was polymerized with rac-ethylene-bis (1-η⁵-indenyl)dichlorozirconium/methylaluminoxane in solvents of different polarity. The poly (propylene) formed was separated by solvent extraction; ¹³C-NMR and DSC measurements were made on the polymer fractions. The poly(propylene) in each solvent fraction has its characteristic molecular weight steric pentad distributions, melting transition temperature, and enthalpy for fusion irrespective of the polymerization medium. The results suggest that the medium dielectric constant does not affect the polymerization rate or the intrinsic stereoselectivity, propagation and chain transfer rates a given catalytic species but can alter the occurrence of steric insertion errors through shifting of distributions of the propagating species producing poly(propylenes) of different stereoregularities. © 1994 John Wiley & Sons, Inc.     

Spectroscopic studies of solutions,suspensions, and precipitates of poly(1,6-di-p-toluene sulfonyloxy-2,4-hexadiyne)

Optical-absorption, fluorescence, and Raman spectra for solutions, suspensions, and precipitates of poly(1,6-di-p-toluene sulfonoxy-2,4-hexadiyne) in and from nitrobenzene, acetone, and chloroform are presented. These are interpreted in terms of the occurrence of two forms of the polymer chain; a quasicrystalline form with properties close to those of single crystal polymer and a chain-extended form occurring in solution and colloidal particles, with an absorption energy of about 2.5 eV (20,000 cm^?1). No evidence is found for the presence of very short polymer chains in partially polymerized monomer at low conversion. The relationship of these results to those for deformed single crystals is briefly discussed.     

Oxo‐crown‐ethers as comonomers for tuning polyester properties

2‐Oxo‐12‐crown‐4‐ether (OC) was procured in a novel, two‐step procedure in a 37% overall yield. This interesting hydrophilic lactone was effectively polymerized with Novozym 435 as the catalyst: within 10 min, the monomer conversion was greater than 95%. Poly(2‐oxo‐12‐crown‐4‐ether) [poly(OC)] was obtained as a viscous oil with a glass‐transition temperature of approximately ?40 °C, and it was soluble in water. Subsequently, OC was copolymerized with ω‐pentadecanolactone (PDL). A kinetic evaluation of both monomers showed that for OC, the Michaelis–Menten constant (K_M) and the maximal rate of polymerization (V_max) were 2.7 mol/L and 0.24 mol/L min, respectively, whereas for PDL, K_M and V_max were 0.5 mol/L and 0.09 mol/L min, respectively. Although OC polymerized five times faster than PDL, ¹H NMR analysis of the copolymers revealed a random copolymer structure. Differential scanning calorimetry traces of the copolymers showed that they were semicrystalline and that the melting temperature and melting enthalpy of the copolymers linearly decreased with an increasing amount of OC. The melting temperature of the copolymers could be adequately predicted by the Baur equation, and this suggested that poly (OC) was rejected from the poly(ω‐pentadecanolactone) [poly(PDL)] crystals. Solid‐state NMR studies confirmed that the crystalline phase exclusively consisted of poly (PDL), whereas the amorphous phase was a mixture of OC and PDL units. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2166–2176, 2006     

Isomorphic behavior of poly(aryl ether ketone) blends

Blends of various poly(aryl ether ketones) have been found to exhibit a range of miscibility and isomorphic behavior. This range is dependent on molecular weight; however, for poly(aryl ether ketones) with number-average molecular weight of 20,000, this range is about ±25% difference in ketone content. All miscible blends exhibit isomorphism, and all immiscible blends exhibit no evidence of isomorphism. The dependence of the glass transition temperature T_g versus composition exhibits a minimum deviation from linearity whereas the melting temperature T_m versus composition exhibits a pronounced maximum deviation from linear behavior. The crystalline melting point versus composition for isomorphic blends is considerably different than for random copolymers with isomorphic units. Homopolymers and random copolymers exhibit a melting point that is a linear function of ketone content (increasing ketone content increases T_m). For blends, the melting point is essentially the same as that of the higher melting constituent until high levels of the lower melting constituent are present. The observed melting point versus composition behavior will be interpreted using classical theory to calculate the components of the liquid and crystalline phase compositions. As a miscible blend is cooled from the melt, essentially pure component of the highest melting point crystallizes out of solution, as predicted by calculated solid-liquid phase diagrams. This occurs until the crystallization is complete owing to spherulitic impingement. At high concentrations of the lower melting constituent, lower melting points will be observed because the highest melting constituent will be depleted before the crystallization is complete. In many miscible blends involving addition of an amorphous polymer to a crystalline polymer, the degree of crystallinity of the crystalline polymer has been shown to increase. On the basis of evidence presented here, it is hypothesized that dilution by a miscible, amorphous polymer allows for a higher level of crystallinity.     

Solid-state polymerization of 1,2,3,4-diepoxybutane initiated by cobalt-60 γ-radiation

The solid-state polymerization of 1,2,3,4-diepoxybutane appears to proceed “insource” by an ionic mechanism and has an overall activation energy of 0.4 kcal./mole with an intensity dependency of 0.99. There is a rapid increase in the rate of polymerization just prior to the melting point and a very low rate for the liquid-phase reaction. Limiting conversions of 5% polymer are observed at ?196°C. for irradiation in vacuo. No limiting conversion was observed when the monomer was polymerized in the presence of air or in vacuo at ?78°C. Under all polymerization conditions the reactions were characterized by the absence of an induction period.     

(−)-Sparteine: The compound that most significantly influenced my research

A chiral diamine alkaloid, (−)-sparteine (Sp), has been found to be very effective as a ligand for Grignard reagents when used for the enantiomer-selective polymerization of racemic RS-1-phenylethyl methacrylate. The enantiomeric excess of the initially polymerized monomer is 93%, and at about a 60% conversion, nearly optically pure R-monomer is recovered. This enantiomer selectivity is today the highest in polymer chemistry. Triphenylmethyl methacrylate (TrMA) is a unique monomer that gives a highly isotactic polymer even during radical polymerization. When TrMA is polymerized with the Sp complex with n-butyllithium in toluene at −78 °C, an optically active, isotactic polymer [poly(triphenylmethyl methacrylate) (PTrMA)] with a one-handed helical conformation is obtained. The helical structure is maintained even at room temperature in solution. Analogous helical polymethacrylates that show various conformational changes have also been found. One-handed helical PTrMA exhibits high chiral recognition to a variety of racemates as a chiral stationary phase (CSP) for high-performance liquid chromatography. This finding has led to the development of very powerful CSPs based on polysaccharides, such as cellulose and amylose. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4480–4491, 2004     

Synthesis and characterization of a new soluble conducting polymer and its electrochromic device

A mixture of isomers 2,5-di(4-methyl-thiophen-2-yl)-1-(4-nitrophenyl)-1H-pyrrole, 2-(4-methyl-thiophen-2-yl)-5-(3-methyl-thiophen-2-yl)-1-(4-nitrophenyl)-1H-pyrrole and 2,5-di(3-methyl-thiophen-2-yl)-1-(4-nitrophenyl)-1H-pyrrole (Me-SNS(NO₂)) were synthesized. Resulting monomers were polymerized chemically, producing soluble polymers in common organic solvents. The average molecular weight has been determined by gel permeation chromatography (GPC) as Mn=5.6×10³ for the chemically synthesized polymer. The monomers were also electrochemically polymerized in the presence of LiClO₄, NaClO₄ (1:1) as the supporting electrolyte in acetonitrile solvent. Resulting polymers were characterized via CV, FTIR, NMR, SEM and UV–Vis spectroscopy. Spectroelectrochemistry analysis of polymer revealed Π–Π^* transition below 300 nm, with an electronic band gap of 2.18 ev. Switching ability of the polymer was evaluated by kinetic study measuring percent transmittance (%T) at the maximum contrast point, indicating that poly(Me-SNS(NO₂)) is a suitable material for electrochromic devices.     

Ring‐opening polymerization of lipoic acid and characterization of the polymer

Thermal polymerization of DL ‐α‐lipoic acid (LPA) in bulk without any initiator proceeded easily above the melting point of LPA. The molecular weight polymer determined by GPC was high. From the ¹H NMR spectra of polymers, poly(LPA) obtained from polymerization of high purity LPA was to consist of cyclic structures, which was confirmed by ESI‐MS. Interlocked polymer consisting of poly(LPA) and dibenzo‐30‐crown‐10 entangled with each other was synthesized by the polymerization of LPA in the presence of dibenzo‐30‐crown‐10. From the DSC analysis of the polymers, glass transition temperature was estimated to be about ?11 °C, but melting point was not observed, indicating that poly(LPA) is an amorphous polymer. By photodecomposition of poly(LPA), M_n was rapidly decreased at the early stage of the decomposition. After that, the M_n of the polymer kept and then was almost constant even for a prolonged reaction time. On the basis of the results, it would be presumed that poly (LPA) obtained form polymerization of high purity LPA includes an interlocked structure. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Thermal behavior of polytriazole films: A thermal analysis study

The thermal behavior of poly(1,3-phenyl-1,4-phenyl)-4-phenyl-1,2,4-triazole has been investigated using different scanning calorimetry (DSC) and thermogravimetry (TG). Processes are studied for this thermally stable polymer that take place between 200 and 500°C. While the polycondensation reaction product in powder from appeared to be partially crystalline, films prepared by casting from a formic acid solution appeared to be completely amorphous. A thermal treatment between T_g(～ 270°C) and T_m(～ 430°C) can introduce crystallinity in the films because of the polymer's ability to cold crystallize. The cold crystallization temperature T_c seems to be dependent on the preparation history of the solid polymer phase. Thermal annealing of the films just below T_g does not introduce crystallinity but inhibits subsequent cold crystallization at higher temperatures. Crystallization upon cooling from the crystalline melt has not been observed either. At temperatures just above the crystalline melting point the polymer starts to decompose in an exothermic reaction.     

Vacuum pyrolysis study of graphite-like pyropolymers from 1,4-diphenyl-1-buten-3-yne

1,4-Diphenyl-1-buten-3-yne was metathesis polymerized over NbCl₅- or TaCl₅-based catalysts followed by pyrolysis to obtain graphite-like pyropolymers. The brown metathesis polymer, poly(1,4-diphenyl-1-buten-3-yne), has the structure of fully conjugated backbone and was annealed at 250°C to obtain partially crosslinked polymer which showed 20% increase of carbon residue on pyrolysis over 400°C than the pyrolyzed poly(1,4-diphenyl-1-buten-3-yne) without annealing. The polymers were characterized by GPC, EA, NMR, XPS, TGA, DSC, FT-IR, laser-Raman, x-ray diffraction, and SEM studies. © 1996 John Wiley & Sons, Inc.     

Isotactic sequence lengths by ozonation of poly(propylene oxide)

Ozonation followed by lithium aluminum hydride reduction cleaved high molecular weight isotactic poly(propylene oxide) to crystalline polyglycols. From the melting point and molecular weight of the latter, the molar freezing point depression produced by end groups is found to be ca. 18°C./mole, as compared to that estimated for poly(ethylene glycols), K_f = 12°C./mole, from earlier data. By assuming syndiotactic placements (or other irregularities) would produce the same molar depression, the melting point of isotactic poly(propylene oxides) produced by various catalysts has been used to estimate the isotactic sequence lengths.     

Melting behavior of highly stretched isotactic polypropylene film

Isotactic polypropylene film was stretched in poly(ethylene glycol) at 140°C and its melting behavior was investigated by using a differential scanning calorimeter (DSC-1B). The shape of the melting curve depends largely on the stretching ratio, v. A sample stretched to moderate extension (1 < v < 3.5–4) has only a single melting peak (163°C) in the thermogram. When the sample is stretched beyond v = 3.5–4, the thermogram becomes more and more complex with increase of v, and some peaks appear when stretched to 10 < v < 13. The lowest peak which is considered to be the melting peak of the intermolecular crystals produced by the unfolding of chain molecules in the lamellae develops gradually with increase of v. In the thermogram for v = 18 the lowest temperature peak is most pronounced, in contrast to the highest temperature peak which decreases markedly in intensity. The phenomenon shows that large amounts of lamellar crystals are converted to intermolecular crystals in this region. On further stretching (v > 20) a very sharp high temperature peak appears, whose half-width is about 1°C. Qualitatively similar results were obtained for the samples stretched in poly(ethylene glycol) at 150°C and in air at 140 and 150°C.     

Stereoregularity of poly(vinyl ether)

α-Methylvinyl isobutyl and methyl ethers were polymerized cationically and the structure of the polymers was studied by NMR. Poly(α-methylvinyl methyl ether) polymerized with iodine or ferric chloride as catalyst was found to be almost atactic, whereas poly(α-methylvinyl isobutyl ether) polymerized in toluene with BF₃OEt₂ or AlEt₂Cl as catalyst was found to be isotactic. In both cases, the addition of polar solvent resulted in the increase of syndiotactic structure as is the case with polymerization of alkyl vinyl ether. tert-Butyl vinyl ether was polymerized, and the polymer was converted into poly(vinyl acetate), the structure of which was studied by NMR. A nearly linear relationship between the optical density ratio D₇₂₂/D₇₃₆ in poly(tert-butyl vinyl ether) and the isotacticity of the converted poly(vinyl acetate) was observed.     

The crystalline character of atactic poly(p-biphenyl acrylate) and poly(p-cyclohexylphenyl acrylate) in their dynamic mechanical response

Dynamic mechanical properties have been determined in atactic poly(p-biphenyl acrylate) (PPBA) and poly(p-cyclohexylphenyl acrylate) (PPCPA) in the temperature range from 80 to 540°K at frequencies in the range 10³–10⁴ Hz. The general behavior of the dynamic elastic modulus as a function of temperature shows a transition region from the glassy state at about 390°K for both polymers, a plastic region extending over a temperature interval of about 100°K, and another transition to the melt situated at 540 and 480°K for PPBA and PPCPA, respectively. The experimental data show that the mechanical behavior of both polymers strongly resembles that of crystalline polymers. The loss spectrum of PPBA shows the presence of several important maxima: one corresponding to the melting point, characterized by a very rapid increase of losses with increasing temperature (α′ relaxation), one in the glass-temperature range, characterized by a rather broad peak (α′ relaxation), and others below T_g, associated with secondary relaxation effects. The analysis of the different transitions and relaxations indicates that some of these processes can be ascribed to motions taking place in the ordered regions of the polymer. PPCPA shows a similar loss pattern; however, owing to the lower melting point the α maximum is partially submerged in the α′ relaxation associated with the melting process. Of particular interest is the γ process in the glassy state of this polymer, caused by the chair–chair transition of the cyclohexyl rings. The limited intensity of this relaxation as compared with that of most polymers containing cyclohexyl side groups, has been interpreted as due to the high ΔF associated with such a transition for cyclohexyl rings linked to phenylene groups. This leads to some interesting conclusions about the conformation of the side groups in PPCPA.     

Melting behavior of poly(ether ether ketone) in its blends with poly(ether imide)

We detail the melting behavior of poly(ether ether ketone) (PEEK) and investigate its melting behavior in miscible blends with poly(ether imide) (PEI). The determination of the equilibrium melting point (T_m⁰) of PEEK is discussed by considering its inhomogeneous morphology. T_m⁰ is obtained by a long extrapolation of a Hoffman–Weeks plot to 384°C. Hindrance of PEEK crystal reorganization induced by PEI during heating is observed over the blend composition investigated (20–75 wt % PEEK). This behavior is correlated with the incorporation of PEI in the interlamellar zones of PEEK crystals. The interaction parameter χ of PEEK/PEI blends is estimated by the equilibrium melting point depression. This gives the interaction density B = ?1.2 cal/cm³, and x = ?0.40 at 400°C. © 1993 John Wiley & Sons, Inc.     

poly(4,4′-oxybibenzoate): Polymerization,morphology, transitions,and crystal structures

4-Acetoxy 4′-carboxy biphenyl has been polymerized from solution, the bulk melt, and in constrained thin films, all below the melting point of the monomer as measured by differential scanning calorimetry (DSC). An isothermal sublimation–recrystallization–melting (and chemical change)–polymerization–crystallization process is proposed. From solution and in the thin films, single crystals consisting of ca. 100 Å thick lamellae are observed, with evidence for monomer addition–reaction on the end (top and bottom) surfaces. The bulk samples are fibrous, the “fibers” consisting of whisker-like single crystals. The polymer is highly heat and radiation (electron beam) resistant, with numerous successive electron diffraction (ED) patterns from the same crystal or sheared sample permitting comparison of the changes in ED patterns with transitions seen by DSC at ca. 350, 530, and 590°C. Phase I (a = 7.8, b = 5.5, c = 10.8 Å), a possible phase II (a = 15.6, b = 3.6 Å c = unknown), and a phase III (a = 9.0, b = 5.2 = √3a, c = 10.8 Å). Phases I and II are seen in samples polymerized at temperatures at and below 310°C; phase III is observed in samples polymerized at and above 350°C and in sheared samples. © 1993 John Wiley & Sons, Inc.     

Electrical conduction in olefin oxide polymers

The electrical conductivities in vacuo of poly(ethylene oxide) and two higher olefin oxide polymers have been found to be ～9 orders higher than for other saturated organic polymers. The possibility of ionic transport resulting from the presence of impurities (including water) has been eliminated, and it is proposed that an inherent ionic process is operative, involving the generation of protons and then subsequent transport by a handing-on process. The two general requirements are the presence of proton-accepting atoms (in this case oxygen) in the polymer chains; and proximity to the melting point to ensure adequate chain-mobility. These requirements are met by poly(ethylene oxide), poly(trimethylene oxide), and poly(tetramethylene oxide), which are all close to their melting points at room temperature. poly(methylene oxide), with a melting point of ～180°C., on the other hand, has the low conductivity of a typical insulator.     

Higher α‐olefin polymerizations catalyzed by rac‐Me2Si(1‐C5H2‐2‐CH3‐4‐tBu)2Zr(NMe2)2/Al(iBu)3/[Ph3C][B(C6F5)4]

Polymerizations of higher α‐olefins, 1‐pentene, 1‐hexene, 1‐octene, and 1‐decene were carried out at 30 °C in toluene by using highly isospecific rac‐Me₂Si(1‐C₅H₂‐2‐CH₃‐4‐^t Bu)₂Zr(NMe₂)₂ (rac‐1) compound in the presence of Al(iBu)₃/[CPh₃][B(C₆F₅)₄] as a cocatalyst formulation. Both the bulkiness of monomer and the lateral size of polymer influenced the activity of polymerization. The larger lateral of polymer chain opens the π‐ligand of active site wide and favors the insertion of monomer, while the large size of monomer inserts itself into polymer chain more difficultly due to the steric hindrance. Highly isotactic poly(α‐olefin)s of high molecular weight (MW) were produced. The MW decreased from polypropylene to poly(1‐hexene), and then increased from poly(1‐hexene) to poly(1‐decene). The isotacticity (as [mm] triad) of the polymer decreased with the increased lateral size in the order: poly(1‐pentene) > poly(1‐hexene) > poly(1‐octene) > poly(1‐decene). The similar dependence of the lateral size on the melting point of polymer was recorded by differential scanning calorimetry (DSC). ¹H NMR analysis showed that vinylidene group resulting from β‐H elimination and saturated methyl groups resulting from chain transfer to cocatalyst are the main end groups of polymer chain. The vinylidene and internal double bonds are also identified by Raman spectroscopy. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1687–1697, 2000