A number of new polymers have been studied. They include polymers obtained by chain reaction polymerization of olefins and epoxides with functional groups where the polymerizable group was separated from the functional group by an inert spacer group, the preparation of head-to-head polymers, and the preparation of optically active polymers based on the macromolecular asymmetry.

Azobenzene-modified polyesters and poly(ester amide)s fitted with chiral, atropisomeric binaphthylene segments were prepared by a series of low-temperature polycondensation reactions carried out in polar solvent media. When compared with their polyaramide counterparts studied earlier, these materials had significantly improved solubility behaviors and were readily dissolved by a wide range of organic solvents. In solution, each of these constructs underwent photoinduced oscillations in optical rotatory power when subjected to multiple UV-light/visible-light illumination cycles that drove trans <-> cis isomerization reactions along their polymer chains. Light-regulated chiroptical perturbations were dependent on polymer backbone structures and were further modulated by well-coordinated temperature fluctuations and by the nature of the solvent medium employed. (c) 2005 Wiley Periodicals, Inc.

Conformationally restricted copolyaramides containing a combination of 4,4'-azobenzene, 1,4-phenylene, and chiral 2,2'-binaphthylene main-chain segments exhibit photoresponsive chiroptical behavior stemming from multiple trans-cis-isomerization reactions triggered within their polymer backbones. In contrast to their more randomly constructed counterparts, copolymer variants endowed with periodic backbone structures undergo reversible, wavelength-dependent inversions in their optical rotations in response to multiple ultraviolet-light/visible-light illumination cycles. Similar behavior is also observed for a smaller oligomer fitted with a periodic arrangement of its monomer units. In their present forms, the periodic constructs constitute a new class of solution-based, photomodulated chiroptical switches that may be suitable for applications in a number of emerging technological areas. (C) 2003 Wiley Periodicals, Inc.

Computer-based calculations were used to simulate the mass spectra for a number of uniform macromolecules having fixed, well-defined chain lengths. The presence of naturally occurring carbon, hydrogen, oxygen, and halogen isotopes introduced significant levels of mass heterogeneity into these systems. For a given polymer, mass variability was demonstrated to be a function of both the elemental composition and degree of polmerization of the polymer chain. In many cases, these natural variations in mass exceeded the molecular weight of one or more monomeric repeat units along the polymer backbone, effectively blurring the mass distinction between uniform polymer constructs formed from N and N+1 repeat units, The significance of isotopic diversity and its potential impact on the synthesis and physiochemical properties of highly uniform macromolecules is also discussed. (C) 2002 Wiley Periodicals, Inc.

Azobenzene modified polyaramides and several model compounds fitted with atropisomeric 2,2 ' -binaphthyl linkages exhibit thermo- and photoresponsive chiroptical behavior when evaluated in dilute solution environments. The trans-azobenzene modified polymers were characterized by CD spectra with intense molar ellipticities in the 300-400 nm spectral window. Specific rotation magnitudes at the sodium D-line ranged into the hundreds of degrees and were dependent upon the extent of binaphthyl loading along the polymer chain. The irradiation of the polymer samples to drive the trans --> cis isomerization process resulted in an immediate chiroptical response, with CD band intensities and optical rotations significantly diminished. These effects were fully reversible and were attributed to the presence of one-handed helical conformations in the trans-azobenzene modified polymers that were severely disrupted following the trans --> cis isomerization reaction.

A series of azobenzene-modified polyamides fitted with main chain spirobiindane turns and chiral binaphthyl bends was prepared from the solution polycondensation of trans-azobenzene-4,4′-dicarbonyl chloride with appropriate diamine monomers. When evaluated in their all trans-azobenzene configurations, these materials exhibited a good mix of physical properties suitable for high performance applications. Photoinduced trans→cis isomerization reactions were effected by irradiating polymer solutions with near UV light. Reverse cis→trans isomerization of the backbone azobenzene segments was triggered by either photochemical or thermal means and was monitored by optical absorbance spectroscopy. Thermally induced cis→trans reorganization within each polymer followed the first-order rate law. Activation energies calculated for this process in DMAC all fell near 21–23kcalmol−1 and were not strongly correlated to backbone content. Polymers containing axially asymmetric S-(−)- or R-(+)-2,2′-binaphthyl main chain linkages exhibited thermo- and photo-responsive chiroptical behavior when evaluated in dilute THF solutions. Specifically, the trans-azobenzene-modified materials were all characterized by CD spectra showing intense molar ellipticities within the 300–400nm spectral window. Specific rotation magnitudes determined for the trans-polymers at the sodium D-line ranged into the hundreds of degrees and were dependent on the extent of binaphthyl loading along the polyamide backbone. The irradiation of the polymer samples to drive the trans→cis isomerization reaction resulted in an immediate chiroptical response, with CD band intensities and optical rotations significantly diminished. These effects were fully reversible and were attributed to the presence of putative one-handed helical conformations in the trans-azobenzene-modified polymers that were severely disrupted following the trans→cis isomerization reaction.

Branched architecture profoundly influences the physical properties of polymers, making it an important topic in the field of polymer science. Herein, we report a facile synthetic strategy to introduce one site-specific side chain at the junction point to fabricate a series of bolaform giant surfactants with branched architecture. By tuning the volume fraction and the ratio between the linking chain and side chain, various phases have been identified, including three-phase-four-layer lamellae, graphene-like honeycombs, tetragonally packed cylinders, and two-phase lamellae. Notably, the lattice dimension of obtained columnar structures is ∼12 nm, corresponding to sub-10 nm cylinder diameters. As revealed by temperature-dependent small-angle X-ray scattering profiles, a branched architecture significantly decreases the order-disorder transition temperature by ∼90 °C. We also use semi-quantitative calculations to analyze the thermodynamic properties of the observed phases and build rational connections between phase behaviors and the corresponding branching ratios. This study shed light on fine-tuning the macromolecular assembly via molecular topology engineering.

A number of azobenzene modified poly(aryl ether ketone amide)s with differing backbone geometries wereevaluated for their photo- and thermo-regulated behaviour in dilute solution. Photoinduced trans → cis isomerization reactions were carried out by irradiating the polymer samples with ultraviolet light at wavelengths between 370 and 400 nm. Photostationary state compositions achieved under these conditions typically consisted of about 70% of the higher energy cis isomer distributed along the polymer main chain. Reverse cis → trans isomerization of the backbone azobenzene moieties was triggered by either photochemical or thermal means and was monitored by optical absorbance and 1H n.m.r. spectroscopies. Thermally induced cis → trans return in each of the polymers obeyed the first-order rate law. Activation energies calculated for the ‘dark’ isomerization reaction fell near 21 kcal mol−1 for each of the polymer samples evaluated. These values were not dependent on the overall structure or molecular weight of the polymer backbone and were nearly identical to those determined for several lower molecular weight model compounds. Calculated half-lives for the isomerization of cis-azobenzene linkages buried in the polymer backbone ranged from 1 day near room temperature to about 1 h at the 60°C isotherm. Data gleaned from SEC experiments suggested that polymers endowed with conformationally restricted geometries underwent a two-fold reduction in hydrodynamic radius in response to ultraviolet light exposure. Photo-contractions in more flexible polymer samples appeared to be less dramatic, consistent with molecular modelling and dilute solution viscosity measurements.

Minimum potential energy helical conformations for a family of four isotactic polyacetaldehydes have been determined. Our results indicate that all of the polymers form irrational helices. Comparisons have been made with the reported structures for two of these stereoregular polymers based on earlier X-ray diffraction data. c-Axis values associated with the pitch of the helix for polyacetaldehyde and for polytrichloroacetaldehyde (polychloral) were experimentally measured to be 0.48 and 0.51 nm, respectively. Our calculated conformations afforded values for a helix pitch of 0.47 and 0.52 nm, respectively, which derive from a 3.9/1 helix for polyacetaldehyde and a 3.7/1 helix for polychloral. The structure for polytribromoacetaldehyde (polybromal) was predicted to be similar to that for polychloral. For polytrifluoroacetaldehyde (polyfluoral) and polyacetaldehyde, a number of helical conformations with similar energies were found. All of these conformations could be related to the polychloral helical structure. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1855–1860, 1998

A series of azobenzene modified poly(aryl ether ketone amide)s was prepared by the low temperaturepolycondensation of trans-azobenzene-4,4′-dicarbonyl chloride with bis-1,4-(3-aminophenoxy-4′-benzoyl)-benzene and other aromatic diamines containing ether and keto groups. The polymers were amorphous, possessed glass transition temperatures between 167 and 218°C and displayed good thermal stabilities under nitrogen and air up to about 400°C. They dissolved readily in a number of organic solvents giving stable solutions. By employing conventional solvent casting techniques, mechanically robust polymer films were obtained with excellent levels of optical clarity. The poly(aryl ether ketone amide)s described here appear to be well suited for photochemical studies in both the solid state and in solution.

The low-temperature polycondensation of trans-azobenzene-4,4'-dicarbonyl chloride with (S)-(-)-1,1'-binaphthyl-2,2'-diamine and/or 1,4-bis(3-aminophenoxy-4'-benzoyl)benzene afforded a new series of poly(aryl ether ketone amide)s with both fixed and photoinducible kinking elements positioned randomly along the main chain. In their lower energy, trans-azobenzene configurations, the orange, film-forming materials were amorphous, highly tractable, and thermally stable under air or nitrogen up to about 420 degrees C. Variants endowed with higher loadings of the bent binaphthyl monomer were soluble in a variety of organic solvent media including THF and acetone. The introduction of cis-azobenzene backbone kinks into these materials was carried out by irradiating the polymer solutions with near-UV light. Up to 10% of the azobenzene moieties in these polymers were capable of assuming the higher energy cis-configuration, thus greatly increasing the number of bent or kinked sites positioned along each polymer backbone. In solution, reverse cis --> traits isomerization reactions were triggered thermally and were quantitatively tracked by both optical absorbance and H-1 NMR spectroscopies. Activation parameters calculated for cis --> trans reorganization of the polymer backbone were not dependent upon the chemical composition or molecularweight of the polymers but did exhibit a small dependence upon the nature of the solvent medium used to conduct the isomerization experiment. (C) 1998 John Wiley & Sons, Inc.

The crystallization of agitated aqueous solutions of sodium chlorate and sodium bromate was nucleated with levo- or dextrorotatory crystal powders of sodium chlorate and sodium bromate to furnish new crystals with a high degree of chiroptical purity.