Direct synthesis of terminally “clickable” linear and hyperbranched polyesters

1,3‐Dipolar cycloaddition of an organic azide and an acetylenic unit, often referred to as the “click reaction”, has become an important ligation tool both in the context of materials chemistry and biology. Thus, development of simple approaches to directly generate polymers that bear either an azide or an alkyne unit has gained considerable importance. We describe here a straightforward approach to directly prepare linear and hyperbranched polyesters that carry terminal propargyl groups. To achieve the former, we designed an AB‐type monomer that carries a hydroxyl group and a propargyl ester, which upon self‐condensation under standard transesterification conditions yielded a polyester that carries a single propargyl group at one of its chain‐ends. Similarly, an AB₂ type monomer that carries one hydroxyl group and two propargyl ester groups, when polymerized under the same conditions yielded a hyperbranched polymer with numerous “clickable” propargyl groups at its molecular periphery. These propargyl groups can be readily clicked with different organic azides, such as benzyl azide, ω‐azido heptaethyleneglycol monomethylether or 9‐azidomethyl anthracene. When an anthracene chromophore is clicked, the molecular weight of the linear polyester could be readily estimated using both UV–visible and fluorescence spectroscopic measurements. Furthermore, the reactive propargyl end group could also provide an opportunity to prepare block copolymers in the case of linear polyesters and to generate nanodimensional scaffolds to anchor a variety of functional units, in the case of the hyperbranched polymer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3200–3208, 2010     

Fully aromatic thermotropic liquid crystalline polyesters of 3,4′-dihydroxybenzophenone

A series of fully aromatic, thermotropic polyesters, derived from 3,4′-dihydroxybenzophenone and various aromatic dicarboxylic acids, was prepared by the high-temperature solution polycondensation method and examined for thermotropic behavior by a variety of experimental techniques. The aromatic dicarboxylic acids used in this study were 2,6-naphthalenedicarboxylic acid, 4,4′-bibenzoic acid, and terephthalic acid. The two homopolymers of 3,4′-DHB with either 2,6-NDA or 4,4′-BBA formed nematic LC phases at 285°C and 255°C and also exhibited isotropization transitions (T_i) at 317°C and 339°C, respectively. The copolymer of 3,4′-DHB with 50% TA and 50% 2,6-NDA also formed a nematic LC phase and had a broader range of LC phase than that of its respective homopolymers. Two other copolymers of 3,4′-DHB, both containing 50% 4,4′-BBA, also formed nematic LC phases at low T_f values. All of the thermotropic polyesters had high thermal stabilities. © 1994 John Wiley & Sons, Inc.     

Viscoelastic properties of blends of “entangled” polymers

The effect of molecular weight distribution on the viscoelastic properties of “entangled” polymers has been examined with blends of narrowly distributed polystyrene and broadly distributed polydimethylsiloxane. It is shown that blending laws established for nonentangled polymers do not apply to high molecular weight systems. The steady-state shear compliance of a blend is examined as a function of its molecular weight and the molecular weight of its components, and an approximation is given for the longtime viscoelastic response of entangled blends.     

Thermal conductivity and thermal expansivity of thermotropic liquid crystalline polymers

The thermal conductivity and thermal expansivity of a thermotropic liquid crystalline copolyesteramide with draw ratio λ from 1.3 to 15 have been measured parallel and perpendicular to the draw direction from 120 to 430 K. The sharp rise in the axial thermal conductivity K_par; and the drastic drop in the axial expansivity α_∥ at low λ, and the saturation of these two quantities at λ > 4 arise from the corresponding increase in the degree of chain orientation revealed by wide-angle x-ray diffraction. In the transverse direction, the thermal conductivity and expansivity exhibit the opposite trends but the changes are relatively small. The draw ratio dependences of the thermal conductivity and expansivity agree reasonably with the predictions of the aggregate model. At high orientation, K_par; of the copolyesteramide is slightly higher than that of polypropylene but one order of magnitude lower than that of polyethylene. In common with other highly oriented polymers such as the lyotropic liquid crystalline polymer, Kevlar 49, and flexible chain polymer, polyethylene, α_par; of the copolyesteramide is negative, with a room temperature value differing from those of Kevlar 49 and polyethylene by less than 50%. Both the axial and transverse expansivity show transitions at about 390 and 270 K, which are associated with large-scale segmental motions of the chains and local motions of the naphthalene units, respectively. ©1995 John Wiley & Sons, Inc.     

Abiotic and biotic degradation of aliphatic polyesters from “petro” versus “green” resources

Aliphatic polyesters are degradable by abiotic and/or biotic hydrolysis. The accessibility of a polymer to degradative attack by living organisms is not dependent on its origin, but on its molecular composition and architecture. Synthetic polymers with intermittent ester linkage (e.g. polyesters, polyurethanes etc.) are accessible to biodegradative attack of esterase. On the other hand aliphatic polyesters are also quickly degraded by a pure abiotic hydrolysis. The results from abiotic and biotic hydrolyses of polycaprolactone (PCL) (from “petro” resource), poly(L-lactide) (PLLA) and polyhydroxyalkanoates (PHA) (from “green” resources) are presented and discussed with the respect to rate of degradation, molecular weight changes and degradation product pattern. For the environmental consequences, the type of formed degradation products are of importance and not the origin of the polymer.     

Thermal properties of some fully aromatic thermotropic liquid crystal polyesters

Wholly aromatic liquid crystalline main chain polyesters derived from terephthalic acid, phenyl- or (1-phenylethyl)hydroquinone modified with either 3,4′- or 4,4′-dicarboxydiphenylether and p-hydroxybenzoic acid, have been prepared by acidolysis and thermally investigated. All prepared polyesters exhibit excellent thermal stability up to about 400°C, however, the (1-phenylethyl)hydroquinone polyesters generally showed lower stability. Melting points could be decreased to around 200°C without any decrease in the thermal stability or the nematic range.     

New polymer synthesis. LXXXIII. Synthesis of chiral and cholesteric polyesters from silylated “sugar diols”

A series of polycondensation was conducted with the purpose to optimize the reaction conditions for the polycondensation of silylated 2,3-isopropylidene D -threitol with a dicarboxylic acid dichloride. Polycondensation in o-dichlorobenzene or 1-chloronaphthalene at 180–230°C were found to be most satisfactory. Trifluoroacetic acid/H₂O allow an easy cleavage of the isopropylidene group without hydrolysis of the polyester. Ten cholesteric copolyesters were prepared by polycondensation of mixtures of silylated methylhydroquinone and isosorbide, isomannide, or 2,3-isopropylidene threitol with the dichloride of 1,10-bis(4′-carboxyphenoxy)decane. All these copolyesters form a broad cholesteric phase above 200°C. The copolyesters containing 5 or 10 mol % of a sugar diol display a blue Grandjean texture. © 1996 John Wiley & Sons, Inc.     

“intelligent” polymers in medicine and biotechnology

One can define “intelligent” polymers as those polymers which respond with large property changes to small physical or chemical stimuli. These polymers may be in various forms, such as in solution, on surfaces, or as solids. One may also combine “intelligent” aqueous polymer systems with biomolecules, to yield a large family of polymers which respond “intelligently” to physical, chemical or biological stimuli. This article overviews such interesting and versatile polymer systems.     

Synthesis,purification, and characterization of “perfect” star polymers via “Click” coupling

The copper (I)‐catalyzed azide‐alkyne cycloaddition “click” reaction was successfully applied to prepare well‐defined 3, 6, and 12‐arms polystyrene and polyethylene glycol stars. This study focused particularly on making “perfect” star polymers with an exact number of arms, as well as developing techniques for their purification. Various methods of characterization confirmed the star polymers high purity, and the structural uniformity of the generated star polymers. In particular, matrix‐assisted laser desorption ionization‐time‐of‐flight mass spectrometry revealed the quantitative transformation of the end groups on the linear polymer precursors and confirmed their quantitative coupling to the dendritic cores to yield star polymers with an exact number of arms. In addition to preparing well‐defined polystyrene and poly(ethylene glycol)homopolymer stars, this technique was also successfully applied to amphiphilic, PCL‐b‐PEG star polymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis and clustering of supramolecular “graft” polymers

The synthesis and melt rheology of supramolecular poly(isobutylene) polymers bearing statistically distributed hydrogen‐bonding moieties is reported, aiming at understanding the formation of the underlying supramolecular networks for self‐healing polymers. Two different hydrogen bonds were incorporated into a poly(isobutylene) (PIB) copolymer, one based on a (weak) pyridinium/pyridine interaction, the other based on a (stronger) 2,6‐diaminotriazine/thymine interaction. A direct copolymerization based on living cationic polymerization of isobutene and the comonomers 1 , 2 , and 4 in amounts of 1 mol % lead to the copolymers PIB‐ 1 , PIB‐ 2 , and PIB‐ 4 with a content of ～1 mol % of comonomer and molecular weights ranging from ～2000 to 19,000 g mol^?1 (M_w/M_n ～ 1.2–1.5). Subsequent azide/alkyne “click” chemistry enabled the attachment of 2,6‐diaminotriazine‐ and thymine‐moieties to yield the copolymers PIB‐ 5 , PIB‐ 6 , and PIB‐ 7 . Proof of the statistical incorporation of ～1 mol % of hydrogen‐bonding moieties was achieved by ¹H NMR spectroscopy and matrix‐assisted laser desorption ionization measurements. The true presence of a supramolecular network in PIB‐ 1 (pyridinium/pyridine interaction) as well as with 1/1 blends of PIBs interacting via the 2,6‐diaminotriazine/thymine interaction (PIB‐ 5 /PIB‐ 6 ) was proven via the increasing plateau modulus with increasing molecular weights (5.5k, 9.9k, 12.4k, 16k, and 19k). Dynamics of the hydrogen bonds in the melt state was investigated by determining the effective cluster lifetime ( τ ) observing a clear difference in the (weaker) pyridinium/pyridine interaction ( τ ～ 1 s) to the 2,6‐ (stronger) diamintriazine/thymine interaction ( τ ～ 100 s). The so‐generated materials will be useful as a basis for self‐healing polymers, as dynamics plays a major role in such polymers. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis and characterization of “umbrella” shaped polymers

A new strategy has been developed to prepare umbrella polymer, i.e. star polymers with one heteroarm. The synthesis uses living anionic polymerization to prepare a short segment of 1,2-polybutadiene at the end of a linear polystyrene. The vinyl groups of 1,2-polybutadiene are hydrosilylated with dichloro(methyl)silane. The umbrella polymer is then formed by nucleophilic displacement of the silicon-chlorine with 1,4-polybutadienyllithium. An umbrella polymer with poly(2-vinylpyridine) arms is prepared in the same way after hydrosilylation with chlorodimethylsilane. The umbrella polymers are characterized by light scattering, size-exclusion chromatography (SEC), ultraviolet/visible spectroscopy (UV/vis), nuclear magnetic resonance (NMR) and intrinsic viscosity.     

“Click polyester”: Synthesis of polyesters containing triazole units in the main chain via safe and rapid “click” chemistry and their properties

Click Cu(I)‐catalyzed polymerizations of diynes that contained ester linkages and diazides were performed to produce polyesters (click polyesters) of large molecular weights [(～1.0–7.0 ) × 10⁴], that contained main‐chain 1,4‐disubstitued triazoles in excellent yields. Incorporation of triazole improved the thermal properties and magnified the even‐odd effect of the methylene chain length. We also found that, by changing the positions of the triazole rings, the thermal properties of the polyesters could be controlled. The use of in situ azidation was a safe reaction, as explosive diazides are not used. In addition, the microwave heating was found to accelerate the polymerization rates. This is the first study that has applied click chemistry for the synthesis of a series of polyesters. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4207–4218, 2010     

Liquid crystal polymers. 15. Synthesis and liquid crystalline properties of alkyl-substituted polyesters

Alkyl substitution in a series of main chain, liquid crystal polyesters strongly depressed their glass temperatures, melting points, clearing points, and mesophase thermal stabilities. Polymers with pendant n-alkyl substituents eight carbon atoms or longer did not form a liquid crystal phase.     

Studies on thermotropic liquid crystalline polymers. XV. Synthesis and properties of liquid crystalline copoly(imide-ester)s

Three series of the thermotropic liquid crystalline copoly(imide-ester)s were prepared by direct polycondensation. The first two series of the copoly(imide-ester)s were synthesized from N-(4-carboxyphenyl) trimellitimide with N,N-di(hydroxypropyl) pyromellitic diimide and various aromatic diols. The third series of copoly(imide-ester)s were prepared by N-(4-carboxyphenyl) trimellitimide with various imide-diols (methylene spacer = 2–6) and phenyl hydroquinone. The structures and thermal properties of the synthesized poly(imide-ester)s were examined by FTIR spectrum, wide-angle x-ray diffraction (WAXD), differential scanning calorimetry (DSC), thermal optical polarized microscope, and thermogravimetric analysis (TGA). The effects of the structures of the aromatic diols on the thermal properties of the resulting copoly(imide-ester)s were investigated. It was found that most of the copoly(imide-ester)s possessed excellent mesophase stabilities and thermostabilities. The mesophase stabilities of poly(imide-ester)s decreased with the increase of the size of lateral group, and the mesophase range increased with the increase of the amount of PhHQ. No significant odd-even effects were observed between the methylene spacer lengths and transition temperatures. © 1996 John Wiley & Sons, Inc.     

Studies on the thermotropic liquid crystalline polycarbonates. III. Synthesis and properties of fully aromatic liquid crystalline polycarbonates

Four series of fully aromatic thermotropic liquid crystalline polycarbonates were prepared by melt polycondensation from various novel phenylene diphenyl dicarbonates with monomers, such as hydroquinone, methylhydroquinone, chlorohydroquinone, resorcinol, bisphenol A, 4,4′-dihydroxydiphenylsulfone, or phenylhydroquinone, respectively. The thermotropic liquid crystalline properties were studied by polarizing microscope with a heating stage, differential scanning calorimeter (DSC), and wide-angle x-ray diffraction (WAXD). It was found that the nonlinearity of the carbonate group was compensated by resorcinol (1,3-phenylene unit), a bent shape unit. Nematic melts were found for the resulting polycarbonates. © 1993 John Wiley & Sons, Inc.     

Polymerizable liquid crystalline twin molecules: synthesis and thermotropic properties

The synthesis of 14 novel low molar mass liquid crystalline twin molecules is described and experimental details are given. The twin monomers contain two mesogenic units which are connected by a flexible spacer. Two terminal acrylate groups make these twins suitable for photopolymerization. The insertion of lateral groups into the mesogen leads to glassforming properties. We tested several substituents (-OCH₃, -CH₃) in different positions of the mesogenic unit and investigated their thermotropic properties as well as their crystallization behaviour by polarizing microscopy and DSC experiments. Some of the novel twin molecules with lateral substituents in the mesogenic core have unusually broad mesophases of about 150^oC. Below T _g stable LC glasses are formed. At room temperature a slow, kinetically hindered crystallization starts after about three hours. The broad mesophases of the twin molecules allow investigations of the photopolymerization kinetics over a wide temperature range. The addition of chiral non-liquid crystalline comonomers and subsequent photopolymerization leads to cholesteric networks with interesting optical properties. Last but not least, the twins are suitable mixing agents which suppress the crystallization of classical mono-rods.