Mechanistic and synthetic considerations of cationic polymerizations of heterocylic and vinyl mon... more Mechanistic and synthetic considerations of cationic polymerizations of heterocylic and vinyl monomers will be covered, including conditions for the synthesis of well-defined polymers.
A model system of styrene (St) and methyl methacrylate (MMA) was copolymerized in an NMR tube at ... more A model system of styrene (St) and methyl methacrylate (MMA) was copolymerized in an NMR tube at 60 °C using 2,2′-azobis(isobutyronitrile) as the initiator and pyridazine as an internal standard to optimize an in situ 1 H NMR spectroscopic method for determining reactivity ratios by generating data at hundreds of instantaneous comonomer compositions (244 data points from 8 to 91 mol % St) starting with only nine initial comonomer compositions. The radical reactivity ratios of styrene (r St = 0.697 ± 0.010) and methyl methacrylate (r MMA = 0.491 ± 0.007) were determined by nonlinear least-squares fitting of a Mayo-Lewis plot of the instantaneous copolymer composition as a function of the comonomer feed composition using the terminal model and MINITAB statistical software, in which the copolymer composition was calculated by assuming that all comonomer consumed was converted to copolymer without side reactions; the results were similar to accepted literature values for the terminal and implicit penultimate models. After correcting for changes in the "lock" value at the initial stages of the copolymerization (because of solids formed in the sealed NMR tube), the same technique was used to determine the reactivity ratios of 2-(N-ethylperfluorooctanesulfonamido)ethyl acrylate (FOSA; r FOSA = 1.624 ± 0.048) and 2-(N-ethylperfluorooctanesulfonamido)ethyl methacrylate (FOSM; r FOSM = 2.876 ± 0.083) in their radical copolymerizations with N,Ndimethylacrylamide (DMA; r DMA = 1.126 ± 0.031 with FOSA; r DMA = 0.859 ± 0.026 with FOSM).
Brominated poly(lactic acid) (PLB) and brominated poly(lactic acid-co-glycolic acid) (PLGB) were ... more Brominated poly(lactic acid) (PLB) and brominated poly(lactic acid-co-glycolic acid) (PLGB) were synthesized by acid-catalyzed melt copolyesterifications of glycolic acid and/or lactic acid with 2-bromo-3-hydroxypropionic acid, which is a brominated constitutional isomer of lactic acid. Molecular weights up to M n = 10 4 Da were achieved by adding diphenyl ether to the copolymerizations (100% w/v comonomer concentration) performed at 90−130°C in vacuo. GPC PSt underestimates the molecular weight of PLB when it contains at least approximately 6 mol % brominated units. The bromine atoms of PLB5050 (M nPSt = 5.32 × 10 3 Da; absolute M n ∼ 1.70 × 10 4 Da) were replaced quantitatively with iodide using sodium iodide in acetone at room temperature, with a modest decrease in the molecular weight (M nPSt = 4.62 × 10 3 Da). PLB was also reacted with 0.25 equiv of sodium azide in DMF at 0°C to replace the corresponding amount of bromine atoms in 88% efficiency, again with a slight decrease in the apparent molecular weight (M nPSt = 4.15 × 10 3 Da). The resulting azido-functionalized PLA was reacted with dimethyl acetylenedicarboxylate, an activated alkyne, via a 1,3-dipolar azide−alkyne, microwave-assisted "click" cycloaddition at 56°C to generate poly(lactic acid) with 1,2,3-triazole rings and a corresponding increase in molecular weight (M nPSt = 5.05 × 10 3 Da), whereas copper-catalyzed "click" reactions involving basic amine ligands, such as a CuBr/PMDETA-catalyzed "click" reaction with propargyl alcohol, degraded the copolymer.
Industrial & Engineering Chemistry Research, 2016
Both soybean oil and linseed oil were cured in bulk with 1,1′-(methylene-di-1,4-phenylene)bismale... more Both soybean oil and linseed oil were cured in bulk with 1,1′-(methylene-di-1,4-phenylene)bismaleimide (MDA-BMI) and oligomeric bismaleimides (BMI-1700 and BMI-3000) at 150 °C for 45 min to yield bio-based thermoset polymers. 1H NMR spectroscopic characterization of a model reaction between soybean oil and N-phenylmaleimide confirmed that the products were formed only by an ene reaction. The curing reactions of bismaleimdes with soybean and linseed oils occurred in the absence of solvent and without added catalyst to produce cross-linked materials. Differential scanning calorimetry demonstrated that curing with MDA-BMI begins at 150 °C when the bismaleimide starts to melt, with maximum curing at 179 °C. The 5% weight loss decomposition temperature of the cross-linked thermosets, determined by thermogravimetric analysis (TGA), varied with the cross-linkers used, according to the following order: BMI-3000 > BMI-1700 > MDA-BMI. Glass fiber-reinforced composites with 45 wt % glass fibers were prepared by curi...
In order to determine if the alternating tendency of styrene with fluorinated styrenes in free ra... more In order to determine if the alternating tendency of styrene with fluorinated styrenes in free radical copolymerizations correlates with the strength and/or extent of π-π stacking interactions between aromatic fluorocarbons and aromatic hydrocarbons, styrene (St) was copolymerized with 2,3,4,5,6-pentafluorostyrene (PFS) and 4-fluorostyrene (4FS) under a variety of conditions. For the copolymerization of styrene with PFS at 25°C, r St r FS) 0.048 and 0.069 in bulk and toluene, respectively, using tert-butylperoxy pivalate as the initiator. For the copolymerization of styrene with PFS at 70°C using benzoyl peroxide as the initiator, r St r FS) 0.17 in bulk and r St r FS) 0.14 in toluene. For the copolymerization of styrene with 4FS, r St r FS) 0.69 at 25°C under redox conditions and r St r FS) 0.62 at 70°C in bulk. As confirmed by 1 H, 13 C, and 19 F one-dimensional NMR and 1 H-13 C heteronuclear single quantum coherence and 1 H-1 H nuclear Overhauser effect two-dimensional NMR spectroscopy results, St and 4FS tend to form random copolymers whereas the St-PFS copolymers tend to alternate with the alternating tendency increasing with decreasing temperature. The glass-transition temperatures determined by differential scanning calorimetry of the St-PFS copolymers are elevated relative to their mole-average values, whereas those of the corresponding homopolymer blends and the St-4FS copolymers occur at mole-average values. The water and ethylene glycol contact angles of both the St-PFS and St-4FS copolymer films occur at their mole-average values.
Journal of Polymer Science Part A: Polymer Chemistry, 2009
2,3,4,5,6-Pentafluorostyrene (PFS) was copolymerized with 1-vinylnaphathalene (1VN) in bulk by ra... more 2,3,4,5,6-Pentafluorostyrene (PFS) was copolymerized with 1-vinylnaphathalene (1VN) in bulk by radical copolymerization at 25 C (r 1VN r PFS ¼ 0.070) using t-butylperoxy pivalate as the inititator, at 70 C (r 1VN r PFS ¼ 0.11) using benzyol peroxide as the initiator, and at 120 C (r 1VN r PFS ¼ 0.28) using t-butyl peroxide as the initiator; PFS was also copolymerized with 2-vinylnaphathalene (2VN) in bulk by radical copolymerization at 70 C (r 2VN r PFS ¼ 0.15) under similar conditions. Their reactivity ratios were determined at low monomer conversions using the nonlinear least-squares method of analysis, which demonstrated that both comonomer pairs tend to alternate, and that their alternating tendency increases with decreasing temperature, similar to the radical copolymerizations of PFS with styrene (St) in bulk. The glass transition temperatures determined by differential scanning calorimetry are elevated relative to their mole-average values, with the extent of elevation being greater for the 1VN-PFS copolymers than for the 2VN-PFS copolymers, which is greater than that for St-PFS copolymers. V
benzyl alcohol with less than 5% intramolecular transesterification using 2−3 equiv of NaBH 4 in ... more benzyl alcohol with less than 5% intramolecular transesterification using 2−3 equiv of NaBH 4 in the presence of 20−30 equiv of acetic acid
Several 1,2-(4,4'-dialkoxyary1)acetylene monomers containing similar or dissimilar substituents w... more Several 1,2-(4,4'-dialkoxyary1)acetylene monomers containing similar or dissimilar substituents were prepared by one of three variations of a one pot phase transfer Pd(O)/Cu(I) catalyzed coupling of aryl halides with a protected acetylene. The three steps within a single flask involved first coupling of the appropriate I-halo-4-alkoxybenzene derivative with 2-methyl-3-butyn-2-01, followed by cleavage of the carbinol group to form an aryl acetylide, and finally a second coupling of an aryl halide with the aryl acetylide. Best results were obtained when elevated temperatures and solid-liquid phase transfer reaction conditions were used. Some 1,4-bis[2-(4',4"-dial-koxypheny1)ethynyllbenzene compounds were also prepared.
We investigate the change in ER response of a nematic solvent on dissolution of an end-on polyacr... more We investigate the change in ER response of a nematic solvent on dissolution of an end-on polyacrylate side-chain liquid crystal polymer (PA-SCLCP), and compare the results with an earlier study of a polysiloxane SCLCP(PSil-SCLCP). For each species, we find a weak enhancement of the ER response,δη =η_on-η_off. Equating η_on and η_off to the Miesowicz viscosities ηc and η_b, and using molecular hydrodynamic theory, which deduces δη_c/δηb =R_allel^4/R_⊥^4, where R_allel and R_⊥ are the rms end-to-end distances of the chain, parallel and perpendicular to the director, we infer that the conformation of each SCLCP is weakly prolate. The molecular weight dependence of the conformational relaxation time, τ_r, also extracted via the hydrodynamic model, is, however, stronger for PA-SCLCP than for PSil-SCLCP. Remarkably, in each case, the molecular weight scaling of τr is identical to that deduced from the GPC hydrodynamic volumes. This implies that the nematic conformations are similar to those in isotropic solution. The different molecular weight dependences of τr appear to reflect different rigidities of each backbone. Estimates of the anisotropic chain dimensions in the nematic solvent, viz. radii of gyration (R_g,allel , R_g,⊥) and hydrodynamic radii (R_h,allel , R_h,⊥) were computed via the hydrodynamic theory. We find R_g,allel and R_h,allel exhibit similar molecular weight dependences, which is weaker, however, than that of R_g,⊥ and R_h,⊥. These results agree with a recent SANS study of the conformation of a PA-SCLCP in the nematic melt.
04ld 1'e'44? I hojur Or ' CWsOnsC including tile tine to, reviewingq ifltruCt,0n1l %earthingq tri... more 04ld 1'e'44? I hojur Or ' CWsOnsC including tile tine to, reviewingq ifltruCt,0n1l %earthingq tri'It data I I~t'~ IIII~~ii itltniiii ij ll .h4P th~e .3Ijecjop of ,nforn'art If end comments regarding thr$ burden #trflnatC 0t any ot 4.PC 0 otrllII(I'IIII~IC I lii rden. t0 tVash,n 1 ,o, Had .at r i'ce. Directorate fior informino pe'tons and Repo(., "is t II~~~~iI~~I IIiI IIIIII i~ii.e o' maaq~emn md Budget. Paperwork Reduction Pro~ect (O7O4_C1BS). Washrrngton. OC 20503
04ld 1'e'44? I hojur Or ' CWsOnsC including tile tine to, reviewingq ifltruCt,0n1l %earthingq tri... more 04ld 1'e'44? I hojur Or ' CWsOnsC including tile tine to, reviewingq ifltruCt,0n1l %earthingq tri'It data I I~t'~ IIII~~ii itltniiii ij ll .h4P th~e .3Ijecjop of ,nforn'art If end comments regarding thr$ burden #trflnatC 0t any ot 4.PC 0 otrllII(I'IIII~IC I lii rden. t0 tVash,n 1 ,o, Had .at r i'ce. Directorate fior informino pe'tons and Repo(., "is t II~~~~iI~~I IIiI IIIIII i~ii.e o' maaq~emn md Budget. Paperwork Reduction Pro~ect (O7O4_C1BS). Washrrngton. OC 20503
alkoxy)benzoyl)oxy]benzyl]oxy]carbonyl]bicyclo[2.2.1]hept-2-enes with short fluorocarbon segments... more alkoxy)benzoyl)oxy]benzyl]oxy]carbonyl]bicyclo[2.2.1]hept-2-enes with short fluorocarbon segments were polymerized by ring-opening metathesis polymerization in THF at room temperature using Mo(CHCMe 2Ph)(N-2,6-i Pr2Ph)(O t Bu)2 as the initiator. Although hydrocarbon and fluorocarbon segments as short as three methylenic units each induce smectic layering in the corresponding 2,5-bis{[4′-(n-(perfluoroalkyl)alkoxy)benzoyl]oxy}toluene model compounds, the polymers require at least eight and three, or five and four methylenic units in the hydrocarbon and fluorocarbon segments, respectively, to organize into smectic layers; polymers with shorter hydrocarbon and/or fluorocarbon segments are nematic.
The product distribution of cyclooligomerizations of 3,4-bis(methyloxy)benzyl chloride, 3,4bis(me... more The product distribution of cyclooligomerizations of 3,4-bis(methyloxy)benzyl chloride, 3,4bis(methy1oxy)benzyl alcohol, N-veratrylethanolamine-N-tosylate, and 1,2-bis(methyloxy)benzene with formaldehyde and with paraformaldehyde using a large variety of reaction conditions waa determined in order to find conditions selective for either cyclotriveratrylene (CTV) or cyclotetraveratrylene (CTTV) formation. CTV, which is the kinetic cyclization product, is formed almost exclusivelywhen 3,4-bis(methyloxy)benzyl chloride is reacted stoichiometrically with AgBF, in methylene chloride. CTV is also formed in high yield when 3,4-bis(methyloxy)benzyl alcohol is cyclooligomerized with superacids (HClOd and CF~SOSH), especially if the reaction is performed in a nonsolvent. CTTV, which can be considered the thermodynamic product, is obtained in the highest yield when 3,4-bis(methyloxy)benzyl alcohol is cyclized by using a large excess of CF&OOH and dilute CH&lz solution. Higher molecular weight analogues were also obtained in almost all reactions.
ABSTRACT Recently, we described a coarse-grained model of poly(ethylene oxide) (PEO) and then emp... more ABSTRACT Recently, we described a coarse-grained model of poly(ethylene oxide) (PEO) and then employed that model to study the amount of spontaneous threading of cyclic molecules by linear chains in the melt (Helfer et al Macromolecules at press). We now use that coarse-grained model to determine how the amount of threading is affected by dilution of the PEO melt with good, Θ, or poor solvents. We employ two distinctly different methods for incorporating the solvent. One method employs explicit coarse-grained solvent molecules, which have the same size as a coarse-grained bead of the polymer. Solvents of different quality are produced by changes in the values of the interaction energies between solvent and polymer beads. The other method does not employ explicit solvent particles but simply modifies the attractive part of the discretized Lennard-Jones potential that describes the pair-wise long-range interaction of coarse-grained PEO while leaving unchanged the rotational isomeric state model that describes the short-range intramolecular interactions. The thermodynamic quality of this implicit solvent is inferred from its effect on the mean square radius of gyration of PEO. The intermolecular pair correlation functions show that cyclic and linear molecules aggregate together in a poor solvent, which contributes to the increase in the amount of threading, relative to the situation found at the same concentration in a good solvent. However, the magnitude of this effect of the poor solvent is insufficient to overcome the decrease in threading upon increasing dilution expected from simple application of the law of mass action. Although the qualitative effects are similar for the two different methods of treating the solvent, quantitative comparison suggests that the use of explicit solvent particles gives a stronger connection with the anticipated behaviour of real systems. The present results for equilibrium structures in a Monte Carlo simulation are not as sensitive to the details of the treatment of the solvent as were earlier results (Chang and Yethiraj 2001 J. Chem. Phys. 114 7688) for the dynamics of the collapse of a single chain in a poor solvent.
Page 1. Liquid Crystals, 2001, Vol. 28, No. 7, 991±1001 Induction of smectic layering in nematic ... more Page 1. Liquid Crystals, 2001, Vol. 28, No. 7, 991±1001 Induction of smectic layering in nematic liquid crystals using immiscible components IV. The eŒect of bulky lateral carboxyl substituents on the thermotropic behaviour of ...
alkoxy)benzoyl)oxy]benzyl]oxy]carbonyl]bicyclo[2.2.1]hept-2-enes with short fluorocarbon segments... more alkoxy)benzoyl)oxy]benzyl]oxy]carbonyl]bicyclo[2.2.1]hept-2-enes with short fluorocarbon segments were polymerized by ring-opening metathesis polymerization in THF at room temperature using Mo(CHCMe 2Ph)(N-2,6-i Pr2Ph)(O t Bu)2 as the initiator. Although hydrocarbon and fluorocarbon segments as short as three methylenic units each induce smectic layering in the corresponding 2,5-bis{[4′-(n-(perfluoroalkyl)alkoxy)benzoyl]oxy}toluene model compounds, the polymers require at least eight and three, or five and four methylenic units in the hydrocarbon and fluorocarbon segments, respectively, to organize into smectic layers; polymers with shorter hydrocarbon and/or fluorocarbon segments are nematic.
Mechanistic and synthetic considerations of cationic polymerizations of heterocylic and vinyl mon... more Mechanistic and synthetic considerations of cationic polymerizations of heterocylic and vinyl monomers will be covered, including conditions for the synthesis of well-defined polymers.
A model system of styrene (St) and methyl methacrylate (MMA) was copolymerized in an NMR tube at ... more A model system of styrene (St) and methyl methacrylate (MMA) was copolymerized in an NMR tube at 60 °C using 2,2′-azobis(isobutyronitrile) as the initiator and pyridazine as an internal standard to optimize an in situ 1 H NMR spectroscopic method for determining reactivity ratios by generating data at hundreds of instantaneous comonomer compositions (244 data points from 8 to 91 mol % St) starting with only nine initial comonomer compositions. The radical reactivity ratios of styrene (r St = 0.697 ± 0.010) and methyl methacrylate (r MMA = 0.491 ± 0.007) were determined by nonlinear least-squares fitting of a Mayo-Lewis plot of the instantaneous copolymer composition as a function of the comonomer feed composition using the terminal model and MINITAB statistical software, in which the copolymer composition was calculated by assuming that all comonomer consumed was converted to copolymer without side reactions; the results were similar to accepted literature values for the terminal and implicit penultimate models. After correcting for changes in the "lock" value at the initial stages of the copolymerization (because of solids formed in the sealed NMR tube), the same technique was used to determine the reactivity ratios of 2-(N-ethylperfluorooctanesulfonamido)ethyl acrylate (FOSA; r FOSA = 1.624 ± 0.048) and 2-(N-ethylperfluorooctanesulfonamido)ethyl methacrylate (FOSM; r FOSM = 2.876 ± 0.083) in their radical copolymerizations with N,Ndimethylacrylamide (DMA; r DMA = 1.126 ± 0.031 with FOSA; r DMA = 0.859 ± 0.026 with FOSM).
Brominated poly(lactic acid) (PLB) and brominated poly(lactic acid-co-glycolic acid) (PLGB) were ... more Brominated poly(lactic acid) (PLB) and brominated poly(lactic acid-co-glycolic acid) (PLGB) were synthesized by acid-catalyzed melt copolyesterifications of glycolic acid and/or lactic acid with 2-bromo-3-hydroxypropionic acid, which is a brominated constitutional isomer of lactic acid. Molecular weights up to M n = 10 4 Da were achieved by adding diphenyl ether to the copolymerizations (100% w/v comonomer concentration) performed at 90−130°C in vacuo. GPC PSt underestimates the molecular weight of PLB when it contains at least approximately 6 mol % brominated units. The bromine atoms of PLB5050 (M nPSt = 5.32 × 10 3 Da; absolute M n ∼ 1.70 × 10 4 Da) were replaced quantitatively with iodide using sodium iodide in acetone at room temperature, with a modest decrease in the molecular weight (M nPSt = 4.62 × 10 3 Da). PLB was also reacted with 0.25 equiv of sodium azide in DMF at 0°C to replace the corresponding amount of bromine atoms in 88% efficiency, again with a slight decrease in the apparent molecular weight (M nPSt = 4.15 × 10 3 Da). The resulting azido-functionalized PLA was reacted with dimethyl acetylenedicarboxylate, an activated alkyne, via a 1,3-dipolar azide−alkyne, microwave-assisted "click" cycloaddition at 56°C to generate poly(lactic acid) with 1,2,3-triazole rings and a corresponding increase in molecular weight (M nPSt = 5.05 × 10 3 Da), whereas copper-catalyzed "click" reactions involving basic amine ligands, such as a CuBr/PMDETA-catalyzed "click" reaction with propargyl alcohol, degraded the copolymer.
Industrial & Engineering Chemistry Research, 2016
Both soybean oil and linseed oil were cured in bulk with 1,1′-(methylene-di-1,4-phenylene)bismale... more Both soybean oil and linseed oil were cured in bulk with 1,1′-(methylene-di-1,4-phenylene)bismaleimide (MDA-BMI) and oligomeric bismaleimides (BMI-1700 and BMI-3000) at 150 °C for 45 min to yield bio-based thermoset polymers. 1H NMR spectroscopic characterization of a model reaction between soybean oil and N-phenylmaleimide confirmed that the products were formed only by an ene reaction. The curing reactions of bismaleimdes with soybean and linseed oils occurred in the absence of solvent and without added catalyst to produce cross-linked materials. Differential scanning calorimetry demonstrated that curing with MDA-BMI begins at 150 °C when the bismaleimide starts to melt, with maximum curing at 179 °C. The 5% weight loss decomposition temperature of the cross-linked thermosets, determined by thermogravimetric analysis (TGA), varied with the cross-linkers used, according to the following order: BMI-3000 > BMI-1700 > MDA-BMI. Glass fiber-reinforced composites with 45 wt % glass fibers were prepared by curi...
In order to determine if the alternating tendency of styrene with fluorinated styrenes in free ra... more In order to determine if the alternating tendency of styrene with fluorinated styrenes in free radical copolymerizations correlates with the strength and/or extent of π-π stacking interactions between aromatic fluorocarbons and aromatic hydrocarbons, styrene (St) was copolymerized with 2,3,4,5,6-pentafluorostyrene (PFS) and 4-fluorostyrene (4FS) under a variety of conditions. For the copolymerization of styrene with PFS at 25°C, r St r FS) 0.048 and 0.069 in bulk and toluene, respectively, using tert-butylperoxy pivalate as the initiator. For the copolymerization of styrene with PFS at 70°C using benzoyl peroxide as the initiator, r St r FS) 0.17 in bulk and r St r FS) 0.14 in toluene. For the copolymerization of styrene with 4FS, r St r FS) 0.69 at 25°C under redox conditions and r St r FS) 0.62 at 70°C in bulk. As confirmed by 1 H, 13 C, and 19 F one-dimensional NMR and 1 H-13 C heteronuclear single quantum coherence and 1 H-1 H nuclear Overhauser effect two-dimensional NMR spectroscopy results, St and 4FS tend to form random copolymers whereas the St-PFS copolymers tend to alternate with the alternating tendency increasing with decreasing temperature. The glass-transition temperatures determined by differential scanning calorimetry of the St-PFS copolymers are elevated relative to their mole-average values, whereas those of the corresponding homopolymer blends and the St-4FS copolymers occur at mole-average values. The water and ethylene glycol contact angles of both the St-PFS and St-4FS copolymer films occur at their mole-average values.
Journal of Polymer Science Part A: Polymer Chemistry, 2009
2,3,4,5,6-Pentafluorostyrene (PFS) was copolymerized with 1-vinylnaphathalene (1VN) in bulk by ra... more 2,3,4,5,6-Pentafluorostyrene (PFS) was copolymerized with 1-vinylnaphathalene (1VN) in bulk by radical copolymerization at 25 C (r 1VN r PFS ¼ 0.070) using t-butylperoxy pivalate as the inititator, at 70 C (r 1VN r PFS ¼ 0.11) using benzyol peroxide as the initiator, and at 120 C (r 1VN r PFS ¼ 0.28) using t-butyl peroxide as the initiator; PFS was also copolymerized with 2-vinylnaphathalene (2VN) in bulk by radical copolymerization at 70 C (r 2VN r PFS ¼ 0.15) under similar conditions. Their reactivity ratios were determined at low monomer conversions using the nonlinear least-squares method of analysis, which demonstrated that both comonomer pairs tend to alternate, and that their alternating tendency increases with decreasing temperature, similar to the radical copolymerizations of PFS with styrene (St) in bulk. The glass transition temperatures determined by differential scanning calorimetry are elevated relative to their mole-average values, with the extent of elevation being greater for the 1VN-PFS copolymers than for the 2VN-PFS copolymers, which is greater than that for St-PFS copolymers. V
benzyl alcohol with less than 5% intramolecular transesterification using 2−3 equiv of NaBH 4 in ... more benzyl alcohol with less than 5% intramolecular transesterification using 2−3 equiv of NaBH 4 in the presence of 20−30 equiv of acetic acid
Several 1,2-(4,4'-dialkoxyary1)acetylene monomers containing similar or dissimilar substituents w... more Several 1,2-(4,4'-dialkoxyary1)acetylene monomers containing similar or dissimilar substituents were prepared by one of three variations of a one pot phase transfer Pd(O)/Cu(I) catalyzed coupling of aryl halides with a protected acetylene. The three steps within a single flask involved first coupling of the appropriate I-halo-4-alkoxybenzene derivative with 2-methyl-3-butyn-2-01, followed by cleavage of the carbinol group to form an aryl acetylide, and finally a second coupling of an aryl halide with the aryl acetylide. Best results were obtained when elevated temperatures and solid-liquid phase transfer reaction conditions were used. Some 1,4-bis[2-(4',4"-dial-koxypheny1)ethynyllbenzene compounds were also prepared.
We investigate the change in ER response of a nematic solvent on dissolution of an end-on polyacr... more We investigate the change in ER response of a nematic solvent on dissolution of an end-on polyacrylate side-chain liquid crystal polymer (PA-SCLCP), and compare the results with an earlier study of a polysiloxane SCLCP(PSil-SCLCP). For each species, we find a weak enhancement of the ER response,δη =η_on-η_off. Equating η_on and η_off to the Miesowicz viscosities ηc and η_b, and using molecular hydrodynamic theory, which deduces δη_c/δηb =R_allel^4/R_⊥^4, where R_allel and R_⊥ are the rms end-to-end distances of the chain, parallel and perpendicular to the director, we infer that the conformation of each SCLCP is weakly prolate. The molecular weight dependence of the conformational relaxation time, τ_r, also extracted via the hydrodynamic model, is, however, stronger for PA-SCLCP than for PSil-SCLCP. Remarkably, in each case, the molecular weight scaling of τr is identical to that deduced from the GPC hydrodynamic volumes. This implies that the nematic conformations are similar to those in isotropic solution. The different molecular weight dependences of τr appear to reflect different rigidities of each backbone. Estimates of the anisotropic chain dimensions in the nematic solvent, viz. radii of gyration (R_g,allel , R_g,⊥) and hydrodynamic radii (R_h,allel , R_h,⊥) were computed via the hydrodynamic theory. We find R_g,allel and R_h,allel exhibit similar molecular weight dependences, which is weaker, however, than that of R_g,⊥ and R_h,⊥. These results agree with a recent SANS study of the conformation of a PA-SCLCP in the nematic melt.
04ld 1'e'44? I hojur Or ' CWsOnsC including tile tine to, reviewingq ifltruCt,0n1l %earthingq tri... more 04ld 1'e'44? I hojur Or ' CWsOnsC including tile tine to, reviewingq ifltruCt,0n1l %earthingq tri'It data I I~t'~ IIII~~ii itltniiii ij ll .h4P th~e .3Ijecjop of ,nforn'art If end comments regarding thr$ burden #trflnatC 0t any ot 4.PC 0 otrllII(I'IIII~IC I lii rden. t0 tVash,n 1 ,o, Had .at r i'ce. Directorate fior informino pe'tons and Repo(., "is t II~~~~iI~~I IIiI IIIIII i~ii.e o' maaq~emn md Budget. Paperwork Reduction Pro~ect (O7O4_C1BS). Washrrngton. OC 20503
04ld 1'e'44? I hojur Or ' CWsOnsC including tile tine to, reviewingq ifltruCt,0n1l %earthingq tri... more 04ld 1'e'44? I hojur Or ' CWsOnsC including tile tine to, reviewingq ifltruCt,0n1l %earthingq tri'It data I I~t'~ IIII~~ii itltniiii ij ll .h4P th~e .3Ijecjop of ,nforn'art If end comments regarding thr$ burden #trflnatC 0t any ot 4.PC 0 otrllII(I'IIII~IC I lii rden. t0 tVash,n 1 ,o, Had .at r i'ce. Directorate fior informino pe'tons and Repo(., "is t II~~~~iI~~I IIiI IIIIII i~ii.e o' maaq~emn md Budget. Paperwork Reduction Pro~ect (O7O4_C1BS). Washrrngton. OC 20503
alkoxy)benzoyl)oxy]benzyl]oxy]carbonyl]bicyclo[2.2.1]hept-2-enes with short fluorocarbon segments... more alkoxy)benzoyl)oxy]benzyl]oxy]carbonyl]bicyclo[2.2.1]hept-2-enes with short fluorocarbon segments were polymerized by ring-opening metathesis polymerization in THF at room temperature using Mo(CHCMe 2Ph)(N-2,6-i Pr2Ph)(O t Bu)2 as the initiator. Although hydrocarbon and fluorocarbon segments as short as three methylenic units each induce smectic layering in the corresponding 2,5-bis{[4′-(n-(perfluoroalkyl)alkoxy)benzoyl]oxy}toluene model compounds, the polymers require at least eight and three, or five and four methylenic units in the hydrocarbon and fluorocarbon segments, respectively, to organize into smectic layers; polymers with shorter hydrocarbon and/or fluorocarbon segments are nematic.
The product distribution of cyclooligomerizations of 3,4-bis(methyloxy)benzyl chloride, 3,4bis(me... more The product distribution of cyclooligomerizations of 3,4-bis(methyloxy)benzyl chloride, 3,4bis(methy1oxy)benzyl alcohol, N-veratrylethanolamine-N-tosylate, and 1,2-bis(methyloxy)benzene with formaldehyde and with paraformaldehyde using a large variety of reaction conditions waa determined in order to find conditions selective for either cyclotriveratrylene (CTV) or cyclotetraveratrylene (CTTV) formation. CTV, which is the kinetic cyclization product, is formed almost exclusivelywhen 3,4-bis(methyloxy)benzyl chloride is reacted stoichiometrically with AgBF, in methylene chloride. CTV is also formed in high yield when 3,4-bis(methyloxy)benzyl alcohol is cyclooligomerized with superacids (HClOd and CF~SOSH), especially if the reaction is performed in a nonsolvent. CTTV, which can be considered the thermodynamic product, is obtained in the highest yield when 3,4-bis(methyloxy)benzyl alcohol is cyclized by using a large excess of CF&OOH and dilute CH&lz solution. Higher molecular weight analogues were also obtained in almost all reactions.
ABSTRACT Recently, we described a coarse-grained model of poly(ethylene oxide) (PEO) and then emp... more ABSTRACT Recently, we described a coarse-grained model of poly(ethylene oxide) (PEO) and then employed that model to study the amount of spontaneous threading of cyclic molecules by linear chains in the melt (Helfer et al Macromolecules at press). We now use that coarse-grained model to determine how the amount of threading is affected by dilution of the PEO melt with good, Θ, or poor solvents. We employ two distinctly different methods for incorporating the solvent. One method employs explicit coarse-grained solvent molecules, which have the same size as a coarse-grained bead of the polymer. Solvents of different quality are produced by changes in the values of the interaction energies between solvent and polymer beads. The other method does not employ explicit solvent particles but simply modifies the attractive part of the discretized Lennard-Jones potential that describes the pair-wise long-range interaction of coarse-grained PEO while leaving unchanged the rotational isomeric state model that describes the short-range intramolecular interactions. The thermodynamic quality of this implicit solvent is inferred from its effect on the mean square radius of gyration of PEO. The intermolecular pair correlation functions show that cyclic and linear molecules aggregate together in a poor solvent, which contributes to the increase in the amount of threading, relative to the situation found at the same concentration in a good solvent. However, the magnitude of this effect of the poor solvent is insufficient to overcome the decrease in threading upon increasing dilution expected from simple application of the law of mass action. Although the qualitative effects are similar for the two different methods of treating the solvent, quantitative comparison suggests that the use of explicit solvent particles gives a stronger connection with the anticipated behaviour of real systems. The present results for equilibrium structures in a Monte Carlo simulation are not as sensitive to the details of the treatment of the solvent as were earlier results (Chang and Yethiraj 2001 J. Chem. Phys. 114 7688) for the dynamics of the collapse of a single chain in a poor solvent.
Page 1. Liquid Crystals, 2001, Vol. 28, No. 7, 991±1001 Induction of smectic layering in nematic ... more Page 1. Liquid Crystals, 2001, Vol. 28, No. 7, 991±1001 Induction of smectic layering in nematic liquid crystals using immiscible components IV. The eŒect of bulky lateral carboxyl substituents on the thermotropic behaviour of ...
alkoxy)benzoyl)oxy]benzyl]oxy]carbonyl]bicyclo[2.2.1]hept-2-enes with short fluorocarbon segments... more alkoxy)benzoyl)oxy]benzyl]oxy]carbonyl]bicyclo[2.2.1]hept-2-enes with short fluorocarbon segments were polymerized by ring-opening metathesis polymerization in THF at room temperature using Mo(CHCMe 2Ph)(N-2,6-i Pr2Ph)(O t Bu)2 as the initiator. Although hydrocarbon and fluorocarbon segments as short as three methylenic units each induce smectic layering in the corresponding 2,5-bis{[4′-(n-(perfluoroalkyl)alkoxy)benzoyl]oxy}toluene model compounds, the polymers require at least eight and three, or five and four methylenic units in the hydrocarbon and fluorocarbon segments, respectively, to organize into smectic layers; polymers with shorter hydrocarbon and/or fluorocarbon segments are nematic.
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Papers by Coleen Pugh