The catalysis of the reaction of carbon dioxide with epoxides (cyclohexene oxide or propylene oxide) using the (salen)Cr(III)Cl complex as catalyst, where H(2)salen = N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexenediimine (1), to provide copolymer and cyclic carbonate has been investigated by in situ infrared spectroscopy. As previously demonstrated for the cyclohexene oxide/CO(2) reaction in the presence of complex 1, coupling of propylene oxide and carbon dioxide was found to occur by way of a pathway first-order in catalyst concentration. Unlike the cyclohexene oxide/carbon dioxide reaction catalyzed by complex 1, which affords completely alternating copolymer and only small quantities of trans-cyclic cyclohexyl carbonate, under similar conditions propylene oxide/carbon dioxide produces mostly cyclic propylene carbonate. Comparative kinetic measurements were performed as a function of reaction temperature to assess the activation barrier for production of cyclic carbonates and polycarbonates for the two different classes of epoxides, i.e., alicyclic (cyclohexene oxide) and aliphatic (propylene oxide). As anticipated in both instances the unimolecular pathway for cyclic carbonate formation has a larger energy of activation than the bimolecular enchainment pathway. That is, the energies of activation determined for cyclic propylene carbonate and poly(propylene carbonate) formation were 100.5 and 67.6 kJ.mol(-1), respectively, compared to the corresponding values for cyclic cyclohexyl carbonate and poly(cyclohexylene carbonate) production of 133 and 46.9 kJ.mol(-1). The small energy difference in the two concurrent reactions for the propylene oxide/CO(2) process (33 kJ.mol(-1)) accounts for the large quantity of cyclic carbonate produced at elevated temperatures in this instance.

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The air-stable, chiral (salen)Cr(III)Cl complex (3), where H(2)salen = N,N'-bis(3,5-di-tert-butyl-salicylidene)-1,2-cyclohexene diamine, has been shown to be an effective catalyst for the coupling of cyclohexene oxide and carbon dioxide to afford poly(cyclohexenylene carbonate), along with a small quantity of its trans-cyclic carbonate. The thus produced polycarbonate contained >99% carbonate linkages and had a M(n) value of 8900 g/mol with a polydispersity index of 1.2 as determined by gel permeation chromatography. The turnover number (TON) and turnover frequency (TOF) values of 683 g of polym/g of Cr and 28.5 g of polym/g of Cr/h, respectively for reactions carried out at 80 degrees C and 58.5 bar pressure increased by over 3-fold upon addition of 5 equiv of the Lewis base cocatalyst, N-methyl imidazole. Although this chiral catalyst is well documented for the asymmetric ring-opening (ARO) of epoxides, in this instance the copolymer produced was completely atactic as illustrated by (13)C NMR spectroscopy. Whereas the mechanism for the (salen)Cr(III)-catalyzed ARO of epoxides displays a squared dependence on [catalyst], which presumably is true for the initiation step of the copolymerization reaction, the rate of carbonate chain growth leading to copolymer or cyclic carbonate formation is linearly dependent on [catalyst]. This was demonstrated herein by way of in situ measurements at 80 degrees C and 58.5 bar pressure. Hence, an alternative mechanism for copolymer production is operative, which is suggested to involve a concerted attack of epoxide at the axial site of the chromium(III) complex where the growing polymer chain for epoxide ring-opening resides. Preliminary investigations of this (salen)Cr(III)-catalyzed system for the coupling of propylene oxide and carbon dioxide reveal that although cyclic carbonate is the main product provided at elevated temperatures, at ambient temperature polycarbonate formation is dominant. A common reaction pathway for alicyclic (cyclohexene oxide) and aliphatic (propylene oxide) carbon dioxide coupling is thought to be in effect, where in the latter instance cyclic carbonate production has a greater temperature dependence compared to copolymer formation.

The conventional approach to prevention of marine biofouling has been the use of antifouling paints and coatings which function through the release of toxins in the immediate vicinity of the ship. Such technology, while admittedly effective, has proven to be responsible for an alarming increase in the levels of organotin and other toxic materials in and around dry docks, harbors, and shipping lanes which experience significant commercial and tourist traffic. Therefore, our objective is the rational design of minimally adhesive, mechanically stable, nontoxic fouling release coatings as responsible and practical alternatives to antifouling technologies. Herein we report on the synthesis and characterization of a series of cross-linkable perfluoropolyether (PFPE) graft terpolymers containing various alkyl (meth)acrylate monomers with glycidal methacrylate as the cure-site monomer. These materials were targeted for use as coatings to prevent marine biofouling. A series of terpolymers were prepared through application of the macromonomer approach, allowing for control of crosslink density, T g , and modulus. Structure/property relationships were established through compositional variation with regard to the three classes of monomers. The first monomer class was an alkyl (meth)acrylate used to create the continuous phase of the microphase-separated graft terpolymers. Variation between methyl methacrylate (MMA) and n-butyl acrylate (BA) provided materials with a low (-10 °C) and a high (95 °C) T g for the continuous phase. This was a means of isolating the effect of modulus and T g on surface properties, while the basic chemical nature of the monomer remained unchanged. The second monomer class contained a curable functional group. Through incorporation of glycidyl methacrylate (GMA) in the monomer feed and manipulation of curing conditions, the relative effect of cross-link density on surface dynamics has been evaluated. The third monomer class was the PFPE macromonomer itself. The incorporation of this macromonomer was used to enhance the release properties of the resulting materials which relied on surface enrichment of the low surface energy PFPE component. Dynamic surface properties of these materials have been evaluated through dynamic surface tensiometry (DST). Herein, it has been demonstrated that contact angle hystersis can be significantly mitigated (i.e., θ r is maximized) by as much as 50°through variation in bulk polymer composition, the chemical nature of monomers, cross-link density, modulus, and environmental conditions at the time of cure. The antifouling and fouling-release potential of the experimental coatings were also evaluated by laboratory assays employing the green fouling macroalga UlVa. The results from these initial studies suggest promising antifouling properties, especially with regard to spore settlement which was strongly inhibited on the experimental surfaces. Additionally, those that did settle were only weakly attached with one sample set exhibiting fairly moderate release of the young...

A series of salicylaldimine ligands of the general formula (NR 2 C 7 H 5-x (R 1 ) x OH) [x ) 1 or 2; R 1 ) Me, t Bu, Cl, OMe; R 2 ) 2,6-i Pr 2 C 6 H 3 , or 3,5-(CF 3 ) 2 C 6 H 3 ] have been synthesized and characterized via 1 H and 13 C NMR, elemental analysis, and X-ray crystallography. The concomitant series of zinc bis(salicylaldiminato) complexes of the general formula (NR 2 C 7 H 5-x (R 1 ) x O) 2 Zn have been synthesized and characterized in the solid state by X-ray crystallography. All complexes crystallized as four coordinate monomers with distorted tetrahedral geometry about the zinc center. The O-Zn-O angles range between 105 and 112.5°, and the N-Zn-N bond angles were more obtuse spanning the range 122.9-128.9°. The only deviation from distorted tetrahedral geometry occurred when R 2 ) 3,5-(CF 3 ) 2 C 6 H 3 which crystallized as a distorted trigonal bipyramidal dimeric species with O ax -Zn-O ax bond angles of 165.00(15)°. The equatorial angles approach 120°except for the N eq -Zn-N eq angle of 110.54( 16)°which is attributed to the strain of the bridging ligands. The zinc bis(salicylaldiminato) complexes showed varying activities as catalyst precursors for the copolymerization of CO 2 and cyclohexene oxide. Activation is proposed to occur via CO 2 insertion in the phenolic Zn-O bond with simultaneous ring-opening resulting in a site for epoxide binding. The difference in activity has been ascribed to the different steric/electronic effects provided by the R 1 and R 2 substituents on the various steps of the copolymerization mechanism. The activity of the zinc bis(salicyaldiminato) catalyst precursors (<16 g‚polym/g‚Zn/hr) were similar to the activities of the previously reported zinc phenoxide complexes for this reaction; however, unlike the zinc phenoxide catalysts, the zinc bis(salicylaldiminato) complexes produced poly(cyclohexane carbonate) with greater than 99% carbonate linkages.

The reactions of zinc halides with 2,6-di-methoxypyridine or 3-trifluoromethylpyridine in dichloromethane have led to the formation of quite different complexes. Specifically, reactions involving pyridine containing electron donating methoxy substitutents have provided salts of the type [Zn(2,6-dimethoxypyridine)4][Zn2X6], as revealed by elemental analysis and X-ray crystallography. On the other hand, simple bis-pyridine adducts of zinc halides were isolated from the reactions involving the pyridine ligand with electron withdrawing substituents and characterized by X-ray crystallography, for example, Zn(3-trifluoromethylpyridine)2Br2. These zinc complexes were shown to be catalytically active for the coupling of carbon dioxide and epoxides to provide high molecular weight polycarbonates and cyclic carbonates, with the order of reactivity being Cl > or = Br > I, and 2,6-di-methoxypyridine > 3-trifluoromethylpyridine. Polycarbonate production from carbon dioxide and cyclohexene oxide was shown to be first-order in both metal precursor complex and cyclohexene oxide, as monitored by in situ infrared spectroscopy at 80 degrees C and 55 bar pressure. For reactions carried out in CO2 swollen epoxide solutions in the absence of added quantities of pyridine, the copolymer produced contained significant polyether linkages. Alternatively, reactions performed in the presence of excess pyridine or in hydrocarbon solvent, although slower in rate, afforded completely alternating copolymers. For comparative purposes, zinc chloride was a very effective homopolymerization catalyst for polyethers. Additionally, zinc chloride afforded copolymers with 60% carbonate linkages in the presence of high carbon dioxide pressures. In the case of cyclohexene oxide, the copolymer back-biting reaction led exclusively to the production of the trans cyclic carbonate as shown by infrared spectroscopy in v(C=O) region and X-ray crystallography. The unique feature of these catalyst systems is their simplicity.

Zinc complexes derived from benzoic acids containing electron-withdrawing substituents have been synthesized from Zn(II)(bis-trimethylsilyl amide)(2) and the corresponding carboxylic acid (2,6-X(2)C(6)H(3)COOH, where X = F, Cl, or OMe) in THF and structurally characterized via X-ray crystallography. The 2,6-difluorobenzoate complex crystallizes from THF or CH(3)CN as a seven membered zinc aggregate, where the metal atoms are interconnected by a combination of 10 mu-benzoates and mu(4)-oxo ligands, that is, [(2,6-difluorobenzoate)(10)O(2)Zn(7)](solvent)(2), solvent = THF (1) and CH(3)CN (1a). On the other hand, the 2,6-dichlorobenzoate zinc derivative crystallizes from THF as a dimer, [(2,6-dichlorobenzoate)(4)Zn(2)](THF)(3) (2), where the two zinc centers are bridged by three benzoate ligand. One of the zinc centers possesses a tetrahedral ligand environment where the fourth ligand is a unidentate benzoate, and the other zinc center has an octahedral arrangement of ligands which is accomplished by the additional binding of three THF molecules. Upon dissolution of complex 1 or 2 in the strongly binding pyridine solvent, disruption of these zinc carboxylates occurs with concomitant formation of mononuclear zinc bis-benzoates with three pyridine ligands in the metal coordination sphere. Complexes 1 and 2 were found to be effective catalysts for the copolymerization of cyclohexene oxide and carbon dioxide to afford polycarbonates devoid of polyether linkages, that is, completely alternating copolymers. Although these catalysts or catalyst precursors in the presence of CO(2)/propylene oxide afforded mostly propylene carbonate, they did serve as efficient catalysts for the terpolymerization of carbon dioxide/cyclohexene oxide/propylene oxide. The reactivities of these zinc carboxylates were very similar to those previously reported analogous complexes which have not been structurally characterized. Hence, it is suggested here that all of these zinc carboxylates provide similar catalytic sites for CO(2)/epoxide coupling processes.

The reaction of Cd[N(SiMe(3))(2)](2) with 2 equiv of the corresponding phenol in toluene has led to the isolation of [Cd(O-2,6-R(2)C(6)H(3))(2)](2) derivatives, where R represents the sterically bulky (t)Bu and Ph substituents. The dimeric nature of these complexes in the solid state has been established via X-ray crystallography, i.e., trigonal geometry around cadmium is observed in 1 (R = (t)Bu) where the two cadmium centers are bridged by two phenoxides with each metal containing a terminal phenoxide. Complex 2 (R = Ph) contains an additional interaction of the metal centers with carbon atoms of the aromatic substituents on the phenoxide ligands. These dimeric structures are maintained in weakly coordinating solvents as revealed by (113)Cd NMR in d(2)-methylene chloride, which displays (111)Cd-(113)Cd coupling. Nevertheless, because of the excessive steric requirements of these phenoxide ligands, these dimers are easily disrupted in solution by weak donor ligands such as epoxides. Three bisepoxide adducts have been isolated as crystalline solids and characterized by X-ray crystallography. As previously observed in other Cd(O-2,6-(t)Bu(2)C(6)H(3))(2) x L(2) complexes, these epoxide adducts adopt a crystallographically imposed square-planar geometry about the cadmium centers, with the exception of the exo-2,3-epoxynorbornane derivative, which displays a distorted tetrahedral geometry. Temperature-dependent (113)Cd NMR studies have established that there is little difference in the binding abilities of these epoxides with either complex 1 or complex 2. Importantly, it is concluded from these studies that the lack of reactivity of alpha-pinene oxide and exo-2,3-epoxynorbornane toward copolymerization reactions with carbon dioxide, in the presence of zinc bisphenoxide catalysts, is not due to differences in epoxide metal binding. This is further affirmed by the isolation and crystallographic characterization of the very stable Zn(O-2,6-(t)Bu(2)C(6)H(3))(2) x (exo-2,3-epoxynorbornane)(2) derivative.