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The synthesis of random and block copolypolyeptides derived from γ-methylglutamate and leucine N-carboxyanhydrides using Al-Schiff's base complexes and allylamine as initiators is here reported. The copolymer structures were confirmed by ¹H and ¹³C NMR. The calculation of the statistical average block lengths reveals the presence of longer methylglutamate units in the copolymer. The determination of the reactivity ratios indicated a slightly higher reactivity of γ-methylglutamateNCA as compared to leucineNCA. Block copolypeptides containing glutamate and leucine units were obtained by sequential polymerization of the two NCAs using Al-Schiff's base complexes or allylamine in dioxane as solvent. Based on ¹³C NMR spectra of copolymers exhibiting two signals corresponding to peptide linkages, we confirmed the block structure and concluded that the copolymerization proceeds by attack of an amino group present on a glutamate chain end onto a LeuNCA. The copolymerization with allylamine was also shown, from calculation of the average block lengths of sequences, to exhibit living behavior. Viscometry analysis further showed that molar masses of the copolypeptides obtained with Al-Schiff's base were quite close to those derived from allylamine, supporting the proposed mechanism of copolymerization.

In an attempt to find a novel catalyst system for atom transfer radical polymerization (ATRP), a parameter estimation method based on nonlinear regression was developed to evaluate various catalyst systems by determining kinetic parameters of polymerization. From our model system considering small molecular atom transfer addition reaction, we found that equilibrium constant of atom transfer reaction could be successfully determined using our parameter estimation method. However, the each value of activation rate constant and deactivation reaction constant is hard to be determined ubiquitously because of the poor sensitivities of them and the local minima trapping. By applying second minimization algorithm, the parameter estimation algorithm achieves higher propensity to reach global minimum, yet not all the time. The simulation results using kinetic rate constants determined by our method shows better agreement with the experimental data than that using literature values. This is because the current method uses fewer assumptions than other literature methods in determining rate constants. We also demonstrated the determination of kinetic constants in the polymerization of styrene and MMA using various metal catalysts, and the simulations using these kinetic constants agree well with the experimental data.

Modified polyguanidines were prepared, and their liquid crystalline properties were studied using optical polarizing microscopy and X-ray diffraction. Parameters examined include chirality, the uniformity of the lengths of side chains, and attached side-chain mesogens. If the side chains on the repeat units are identical, then polymer has a more ordered structure in both solution and the solid state. Uniform lengths of the side chains are also important. Poly(N,N‘-di-n-hexylguanidine), poly-I, exhibited a lyotropic smectic texture in contrast to a nematic texture of poly(N-(rac)-2-phenylethyl)-N‘-methylguanidine) (poly-(rac-II)). Optically pure poly(N-((R)-2-phenylethyl)-N‘-methylguanidine) (poly-(R-II)) formed a cholesteric texture, whereas the corresponding racemic polyguanidine, poly-(rac-II), formed a nematic texture. Additionally, poly-(R-II) displayed a mesophase at a lower critical concentration than either poly-I or poly-(rac-II), implying that poly-(R-II) is stiffer than these two other derivatives. Poly(N-6-((4‘-methoxyphenylazo)phenyl-4-oxy)hexyl-N‘-n-hexylguanidine) (poly-IV), one of combined liquid crystalline structures (liquid crystalline backbone plus liquid crystalline side chains), displayed a lyotropic nematic texture presumably due to the strong dipolar−dipolar interaction between the main chain and side chains that folds the appendages parallel to the molecular axis. Poly(N-12-((4‘-methoxybiphenyl-4-oxy)dodecyl-N‘-n-dodecylguanidine) (poly-V) and poly(N,N‘-di-n-dodecylguanidine) (poly-VI) exhibited thermotropic liquid crystalline behavior.

Palladium ester enolates have been prepared and characterized using IR, NMR, and single-crystal X-ray diffraction techniques. The X-ray diffraction established a dimeric crystal structure for complex {[N^∧N]PdCH2C(O)OCH3}2 (N^∧N = 1-[1-(5-methylpyrrole-2-yl)ethylidne]amino-2,6-diisopropylbenzene), 2, which contains C,O-bridging enolato groups. Upon reaction with donor molecules (acetonitrile, phosphines), the dimeric 2 cleaves to form monometallic C-bound enolate complexes, 3‘ and 4.

Neutral palladium complexes bearing pyrrole−imine ligands (I−III) have been synthesized, and their use as catalysts for olefin and vinyl monomer (co)polymerizations was investigated. Methyl acrylate (MA) has been homopolymerized in excellent yields (>95%) using these complexes. Copolymerizations of MA with norbornene or 1-hexene in the presence of these catalysts produce acrylate-enriched copolymers. Hypothesizing that metal enolates are potential intermediates in some of these polymerizations, palladium enolate complexes (IV−VII) containing ligand 1 were tested for their catalytic activity. Surprisingly, these complexes proved inactive toward acrylate and/or olefin polymerizations. Further mechanistic studies have shown that the homo- and copolymers obtained using these complexes arise from a radical mechanism rather than the anticipated metal-mediated process.

The ring-opening metathesis polymerization of cyclobutene-containing monomers based on the endo-tricyclo[4.2.2.0^2,5]deca-3,9-diene structure bearing cyclic anhydride and N-alkyl- or N-phenyl-substituted succinimides at the 7- and 8-positions was investigated. Well-defined molybdenum and ruthenium complexes were used as catalysts. Cl2Ru(CHPh)(PCy3)2 (III) was shown to be the most suitable catalyst as a well-controlled and even living polymerization was observed. Mainly cis stereochemistry (≈75%) was observed in the main chain. Kinetic studies with different substituted succinimide moieties indicated that the polymerization rate depended on electronic effects in the monomer. ¹⁹F NMR of fluorinated polymers suggests that through-space interactions between fluorine groups and the main polymer chain occur. These new polymers have a good thermal stability (304 °C < Td < 344 °C). Upon hydrogenation, the N-methylsuccinimide functionalized polymer exhibited a Tg at 285 °C, and the thermal stability increased by about 100 °C.

We have previously reported the use of titanium alkoxide complexes as initiators for the living polymerization of isocyanates. In this paper, we present the synthesis of a trimetallic initiator, 2, comprised of three titanium alkoxides connected to a central organic core and the use of this catalyst to form three-arm star polymers which contain rigid polyisocyanate arms. Kinetic and molecular weight experiments confirm that the trimetallic complex 2, like its monometallic analogue, 6, initiates the living polymerization of n-hexyl isocyanate and that the three-arm stars obtained from 2 are completely symmetrical. The number-average molecular weight of polymer obtained from 2 increases linearly with the monomer-to-catalyst ratio used, which indicates a lack of chain transfer during polymerization. A comparison of the rates of polymerization of n-hexyl isocyanate by 2 and 6 at fixed initial monomer and titanium concentrations (k2 = (3.99 ± 0.2) × 10^-3 M min^-1, k6 = (3.84 ± 0.1) × 10^-3 M min^-1) demonstrates that all three titanium centers in 2 are active and propagate independently of one another. The solution properties of these new three-arm star polymers were examined through tandem GPC/light scattering and solution viscometry experiments. Light scattering shows that there is a 55% reduction in the mean-square radius of gyration (g = 〈RG²〉star/〈RG²〉linear = 0.45 ± 0.05) of the three-arm star polyisocyanate from that of a linear polyisocyanate of the same molecular weight. The experimental value of g approaches the rod limit of g that indicates that the arms of the three-arm star can be construed as stiff, wormlike chains. Additionally, there is a 28% reduction in the intrinsic viscosity of three-arm polyisocyanate star from that of its linear equivalent. Finally, a 30% w/w solution of three-arm star polyisocyanate displays a nematic, lyotropic liquid crystalline mesophase.

In certain fire situations, a structural or load-bearing polymer matrix composite (PMC) may be exposed to excessive thermal loads that degrade the matrix. In this paper, we report the results of a study to assess the utility of ultrasonic spectroscopy as a means of assessing the residual physical and mechanical characteristics of PMCs exposed to excessive thermal loads. We show that the measured power spectra of ultrasonic energy correlates with performance of graphite fiber epoxy matrix composites exposed to thermal degradation. Unidirectional composites were exposed to short term–high intensity thermal loads at one end of the specimen. Thus, inducing a thermal gradient along the length of the specimen. Simultaneous thermogravimetric analysis–differential scanning calorimetry (TGA/DSC) and Fourier transform infrared spectroscopy (FTIR) analysis of the aged specimens revealed a gradient in thermal degradation. The thermal loads induced substantial degradation of the composite. However, the amplitude of the power spectra is observed to increase gradually then sharply prior to its complete attenuation due to delaminations. Mode I fracture toughness tests correlate with the observed changes in the ultrasonic spectra. FTIR, TGA/DSC, fracture toughness, and ultrasonic spectral analysis all indicate the same critical temperature at which thermally induced damage sharply increased. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2601–2610, 1999

Bimetallic complexes of the type (C5Me5)2Sm−R−Sm(C5Me5)2 were used for the living bis-initiated polymerization of methyl methacrylate and ε-caprolactone, giving polymers with discrete functionalities at the center of the backbone (“link-functionalized”). Poly(methyl methacrylate) containing olefin units was prepared from [(C5Me5)2Sm]2(μ-η³-CH2CHCH−)2 and related allyl compounds, although slow and/or inefficient initiation of polymerization is observed for complexes in which R is a bulky, heteroatom, or coordinating group. In contrast, the polymerization of ε-caprolactone may be carried out with good control in the presence of both sterically hindering and electron-rich moieties. Polylactones incorporating aromatic, cumulene, and amine/imine groups were synthesized through one-step bimetallic initiation in this manner. Differences between lanthanide(III) methacrylate and lactone polymerizations, differences between lanthanide(III) and aluminum(III) lactone polymerizations, and the presence of transesterification in the lactone system are discussed.

Various catalysts for the polymerization of carbodiimide have been investigated. In early studies, anionic polymerization techniques were employed, but the products obtained were low molecular weight oligomers. More recently, a living route using titanium(IV) complexes as initiators has been employed and the high molecular weight polymers obtained exhibit a well-ordered helical, extended-chain conformation. However, the titanium complexes are sensitive to high temperatures and the presence of oxygen or water. Herein, we report that more robust catalysts based on copper(I) and copper(II) complexes also initiate living carbodiimide polymerizations. The tolerance of these complexes to impurities is illustrated by the fact that they cleanly initiate the polymerization of carbodiimides under air and oxygen. They are even active in the presence of water, but both molecular weights and yields tend to be lower than in dry solvents. It has been shown that the catalytic activity of a copper(II) amidinato complex is almost equal that of reported titanium(IV) initiators. Analysis of these systems by gel permeation chromatography−light scattering measurements (GPC−LS) and preliminary kinetic analysis suggest this system to be living.

The compounds bis(phenylmethyl) cis-cyclobutene-3,4-dicarboxylate (1) and cis-3,4-bis(2-oxa-3-phenylpropyl)cyclobutene (2) were polymerized by ring-opening metathesis polymerizations using Mo(CHC(CH3)2R¹)(NC6H3-2,6-diisopropyl)(OR²)2 (R¹ = Ph, R² = C(CH3)3, I; R¹ = CH3, R² = C(CF3)2CH3, II) as the initiator. For I as initiator, no chain termination or chain transfer processes were observed during the lifetime of the polymerization, showing that the polymerizations of 1 and 2 by I are living. Block copolymers containing 1 and 2 and diethyl cis-cyclobutene-3,4-dicarboxylate (5) were synthesized. The double bonds of the poly-2 and poly-3 ranged from 70% trans to 92% cis depending on the initiator and monomer used. Poly-1 and poly-2 were treated with iodotrimethylsilane and converted to the acid-functionalized and alcohol-functionalized poly-4 and poly-6, respectively. Block copolymers were treated with iodotrimethylsilane and converted to materials with blocks bearing protic functionalities and blocks bearing polar aprotic groups.

Soluble derivatives of poly(p-phenylene) of high molecular weight were synthesized via Suzuki coupling reactions catalyzed by palladium(0) precursors in the presence of either triphenylphosphine (TPP) or tri(o-tolyl)phosphine (TOTP). Syntheses involving the former ligand resulted in the formation of polymers in which the incorporation of phosphine was clearly observable by ³¹P NMR. However, polymers formed utilizing the latter ligand in a hydrophobic solvent such as CH2Cl2 exhibited no signals in the ³¹P NMR spectrum, even after 20 000 scans. Analyses by tandem GPC−light scattering and tandem GPC−light scattering−viscometry showed that polymers synthesized by utilizing a large amount of TPP-based catalyst (2%) possessed a considerably lower molecular weight than did the other samples and exhibited markedly different dependencies of the radius of gyration and intrinsic viscosity on molecular weight. From these studies, it does appear that the aryl−aryl interchange reaction known to occur in ArPdL2I complexes significantly affects the architecture of these polymers.

Soluble precursor polymers 8 and 14 were successfully synthesized via the palladium-mediated condensation of 4,4‘-(1,3,2-dioxaborolan-2-yl)biphenyl (7) with the bis(p-bromophenyl)norbornadiene monomer 5 and the bis(p-bromophenyl)norbornene monomer 13, respectively. The number-averaged molecular weights of these materials were determined by GPC−LS to be 34 000 for 8 and 75 000 for 14. Thermolysis of 8 by a retro-Diels−Alder reaction began at 260 °C and appeared (by GC−MS analysis of the volatile byproducts) to yield a conjugated polymer with both alkyne and cyclopentadiene functionalities in the polymer backbone; however, TGA analysis indicated that the transformation was accompanied by some decomposition. The analogous thermolysis of 14 to yield the polymer with a double bond in the backbone began at 230 °C and appeared to proceed without the concomitant decomposition.

Organopalladium ArPdL2I (L = tertiary phosphine) complexes (1) can be synthesized in one step from the precursors Pd2(dba)3·C6H6 (2) (dba = t,t-dibenzylideneacetone) and (η³-allyl)PdCp (3) (Cp = η⁵-cyclopentadienide). Two advantages over previous synthetic methods are that this route requires only stoichiometric amounts of phosphine and that the desired complexes are easily isolated from reaction byproducts. The scope and generality of these reactions are investigated, and the synthesis of a number of new organic- and water-soluble complexes utilizing this methodology is discussed. Improved syntheses of water-soluble ligands P(C6H5)2(4-SO3KC6H4) (5) and As(C6H5)2(4-SO3KC6H4) (6) are presented as well.