Main-chain Polyesters Research Articles

Synthesis of photodegradable polyesters from bio-based 3,4-dimethoxycinnamic acid and investigation of their degradation behaviors

To address the issue of petroleum resource depletion, it is desirable to develop recyclable materials from bio-based compounds. In addition, low-energy recycling methods such as light irradiation and hydrolysis should be considered. In this paper, bio-based materials, cinnamic acid (CA) derivatives, are introduced as repeating units in polyester main-chain, because CA derivatives undergo reversible [2 + 2] cycloaddition reactions to form dimers under light exposure. Photopolymerization of the monomer with CA moieties at both ends failed, probably because it was difficult to bring the two CA moieties closer together intermolecularly. Polycondensation between the CA dimer with two carboxylic acid moieties and diol compounds successfully provided the polyesters containing CA dimers as repeating units. Furthermore, orthogonal degradation methods, such as light exposure and hydrolysis, of the obtained polyester were investigated.

Thermal homeotropic self-alignment on a single substrate of new series of discotic nematic triphenylene-based main-chain polyesters

We present the synthesis, characterization, and study of Liquid Crystal properties of a new series of polyesters containing 2,7-di-functionalized triphenylene units in the main chain, whose distinctive feature is that the carboxyl moiety is distant from the aromatic core. Several molecular aspects, such as the distance between the carboxylic group to the core, the length of the connector, and the orientation of the carboxyls were analyzed. In addition, we have investigated the influence of these molecular parameters on the thermal self-alignment of the polymers on different substrates. We have found a simple method to obtain a monodomain homeotropic orientation of these polyesters on a single substrate.

Thermoresponsive Molecular Brushes with a Rigid-Chain Aromatic Polyester Backbone and Poly-2-alkyl-2-oxazoline Side Chains.

A new polycondensation aromatic rigid-chain polyester macroinitiator was synthesized and used to graft linear poly-2-ethyl-2-oxazoline as well as poly-2-isopropyl-2-oxazoline by cationic polymerization. The prepared copolymers and the macroinitiator were characterized by NMR, GPC, AFM, turbidimetry, static, and dynamic light scattering. The molar masses of the polyester main chain and the grafted copolymers with poly-2-ethyl-2-oxazoline and poly-2-isopropyl-2-oxazoline side chains were 26,500, 208,000, and 67,900, respectively. The molar masses of the side chains of poly-2-ethyl-2-oxazoline and poly-2-isopropyl-2-oxazoline and their grafting densities were 7400 and 3400 and 0.53 and 0.27, respectively. In chloroform, the copolymers conformation can be considered as a cylinder wormlike chain, the diameter of which depends on the side chain length. In water at low temperatures, the macromolecules of the poly-2-ethyl-2-oxazoline copolymer assume a wormlike conformation because their backbones are well shielded by side chains, whereas the copolymer with short side chains and low grafting density strongly aggregates, which was visualized by AFM. The phase separation temperatures of the copolymers were lower than those of linear analogs of the side chains and decreased with the concentration for both samples. The LCST were estimated to be around 45 °C for the poly-2-ethyl-2-oxazoline graft copolymer, and below 20 °C for the poly-2-isopropyl-2-oxazoline graft copolymer.

Advantage of graft architecture with a flexible main chain for implantation of ductile nature into brittle amorphous acrylic glass

Toughness enhancement of amorphous glassy polymers is required to expand the application range of thermoplastic polymers. This report describes the implantation of ductile nature into poly(methyl methacrylate) (PMMA) resins utilizing a graft architecture with a flexible polyester main chain, which was synthesized via atom transfer radical polymerization (ATRP) with a graft-from approach using a polyester macroinitiator bearing multiple bromo side groups. A comparison with a PMMA homopolymer and a blend PMMA containing a plasticizer revealed that the graft-type PMMA showed much higher elongation without sacrificing the modulus. The ductile nature of the graft-type PMMA was analyzed according to X-ray scattering, scanning electron microscopy observation, and rheological measurement. In the last section, effects of the length of both main chain and graft chain on the tensile properties were investigated.

Responsive Polyesters with Alkene and Carboxylic Acid Side-Groups for Tissue Engineering Applications.

Main chain polyesters have been extensively used in the biomedical field. Despite their many advantages, including biocompatibility, biodegradability, and others, these materials are rather inert and lack specific functionalities which will endow them with additional biological and responsive properties. In this work, novel pH-responsive main chain polyesters have been prepared by a conventional condensation polymerization of a vinyl functionalized diol with a diacid chloride, followed by a photo-induced thiol-ene click reaction to attach functional carboxylic acid side-groups along the polymer chains. Two different mercaptocarboxylic acids were employed, allowing to vary the alkyl chain length of the polymer pendant groups. Moreover, the degree of modification, and as a result, the carboxylic acid content of the polymers, was easily tuned by varying the irradiation time during the click reaction. Both these parameters, were shown to strongly influence the responsive behavior of the polyesters, which presented adjustable pKα values and water solubilities. Finally, the difunctional polyesters bearing the alkene and carboxylic acid functionalities enabled the preparation of cross-linked polyester films by chemically linking the pendant vinyl bonds on the polymer side groups. The biocompatibility of the cross-linked polymers films was assessed in L929 fibroblast cultures and showed that the cell viability, proliferation, and attachment were greatly promoted on the polyester surface, bearing the shorter alkyl chain length side groups and the higher fraction of carboxylic acid functionalities.

Reversible photo-responsive gel-sol transitions of robust organogels based on an azobenzene-containing main-chain liquid crystalline polymer.

Stimuli-responsive supramolecular gels have been widely investigated, but the construction of a liquid crystalline gel with a high mechanical property and reversible photo-response still remains a challenge. This is due to the difficulty of designing gelators with liquid crystal properties and gelation abilities in organic solvents simultaneously. In this study, an azobenzene-containing main-chain polyester (Azo-mLCP) with a pendant amide group was synthesized. The organogel of Azo-mLCP via a hydrogen bond in dioxane possessed reversible thermal- and photo-responsive behaviours. The organogel exhibited a good self-supporting ability when the concentration of the gelator was more than 7.5 wt%. The rapid trans-to-cis isomerization of Azo-mLCP in solution was studied via UV-Vis absorption spectra. In addition, the gel-to-sol transition of the organogel could be triggered efficiently by an incomplete trans-to-cis conversion strategy. This study opens a way for the main-chain liquid crystalline polymers to serve in potential applications in photo-responsive robust actuators, electro-optical devices, and so on.

Extremely rapid postfunctionalization of maleate and fumarate main chain polyesters in the presence of TBD

Unsaturated polyester (UP) scaffold, poly (butylene maleate) (P1), possessing an electron-deficient double bond in the main chain was prepared and utilized as a precursor for thiol- and aza-Michael addition reactions. From a detailed catalyst search (amidine and guanidine bases), 1,5,7-triazabicyclo [4.4.0]dec-5-ene (TBD) proved to be the most efficient catalyst for thiol-Michael addition reactions since pendant thioether functional polyesters were achieved quantitatively within 1 min. Furthermore, P1 was allowed to react with primary and secondary amines through aza-Michael addition reactions, followed by thiol-Michael addition reaction thus affording the synthesis of pendant amine and thioether functional polyesters.

Transition of liquid crystal anchoring at the microdomain interface observed for main-chain nematic polyester segments of block copolymers

The microdomain structures and liquid crystal (LC) orientations of ABA triblock copolymers comprising poly(styrene) (PS) A blocks and a main-chain LC polyester B block were examined via small-angle X-ray scattering and electron microscopy in the form of fibrous samples. The LC polyester blocks were segregated from the PS blocks to form a nematic LC in the lamellar microdomains of the copolymers, with the PS volume fraction (φ) ranging from 13 to 38%. As φ decreased, the nematic director was always positioned along the fiber axis, but the microdomain lamellae changed their direction from parallel to perpendicular with respect to the fiber axis and began to adopt a zigzag configuration. These lamellar orientations were attributed to the main-chain nematic LC segments lying along the microdomain interface but extending perpendicularly to the interface as the occupying interface area was reduced. The lamellar microdomains parallel to the nematic director increased the LC and PS lamellar thicknesses reversibly by 48 and 16%, respectively, at the same time as the isotropization of the nematic LC. Such changes in lamellar thickness suggest that both the PS and LC segments were elongated along the direction of the LC orientation.

Molecular-weight dependence of phase structure and viscosity in a liquid crystalline polyester with strong π–π interaction

ABSTRACTIn this article, the molecular-weight dependence of the phase structure, rheological behaviour and thermal stability of a main-chain liquid crystalline polyester (PBDPS) with strong π–π interaction was investigated in details by differential scanning calorimetry, polarising optical microscopy, wide-angle X-ray diffraction, dynamic oscillatory rheological measurements and thermogravimetric analysis. While the molecular weight of PBDPS is 5.2k, it shows smectic B and smectic A phases prior to isotropic phase. With increasing molecular weight, smectic B phase of PBDPS gradually disappeared. Moreover, the smecitc B to smectic A (Tlc) and smectic A to isotropic (Ti) phase transition temperatures decreased as increased molecular weight. The rheology results suggested that fluid type of PBDPSs changed from Newtonian fluid to pseudo-plastic fluid as the molecular weight of PBDPS increased. In addition, the zero-shear viscosity (η0) of PBDPS showed a power law relationship () with molecular weight of PBDPS. All the PBDPSs showed good thermal stability with an initial decomposition temperature higher than 360°C.

Behavior of thermosensitive graft copolymer with aromatic polyester backbone and poly-2-ethyl-2-oxazoline side chains in aqueous solutions

ABSTRACTThermoresponsive graft copolymers with alkylene-aromatic polyester main chain and poly-2-ethyl-2-oxazoline side chains were synthesized. Two copolymer samples which differed in grafting density (0.5 and 0.7) were studied using dynamic and static light scattering and turbidimetry in aqueous solutions at concentration 0.0053 g cm−3. Hydrodynamic radii of scattering objects and their contribution to light scattering were obtained as a function of temperature in a wide temperature interval. Temperatures of phase separation were found out. Effect of grafting density on the copolymer behavior in aqueous solutions upon heating was determined. In particular, the phase separation temperature reduces with the decreasing grafting density.

Modification of microbial polymers by thiol-ene click reaction: Nanoparticle formation and drug encapsulation

Comb-like amphiphilic polymers were obtained by grafting long paraffinic chains on microbial poly(γ,dl-glutamic acid) and poly(β,l-malic acid) through two steps, i.e. allylation of the carboxylic side groups followed by UV-initiated thiol-ene click reaction with 1-alkanethiols bearing 8, 12 and 16 carbon atoms, and their characterization was accomplished by 1H NMR, GPC and DSC. The grafted polymers were capable of self-assembling in nanoparticles with diameters in the 80–240nm range. Incubation in water under physiological conditions led to hydrolysis of the lateral ester bonds followed by scission of the polyamide or polyester main chain. The model drugs, Theophylline and Carbamazepine, were efficiently encapsulated in these systems with much better results attained for the later. Drug release from nanoparticles incubated under physiological conditions occurred with a burst effect and were completely discharged in 24h. Release profiles recorded from drug-loaded films suggested that the drug was delivered in both cases through a diffusion process.

Cybotactic nematic phase in main-chain polyesters with bent-core mesogens

New six main-chain polyesters containing bent-core mesogens with various central units (Ar = 1,2- or 1,3-phenylene and 1,6-, 1,7-, 2,3- or 2,7-naphthylene) were synthesized. All of the polymers were soluble in a mixture of phenol/p-chlorophenol/TCE (25/40/35 w/w/w). The inherent viscosities were in the range of 0.18–0.38 dL/g. Despite the existence of bent-core mesogens eliciting a remarkable diminution of molecular packing, polymer with Ar = 2,7-naphthylene formed a smectic phase, and polymers with both Ar = 1,2-phenylene and 2,3-naphthylene formed nematic phases. Moreover, most of the polymers were distinctly semi-crystalline. Herein, we report our findings regarding the first detection of cybotactic groups from the nematic phases of main-chain polyesters with bent-core mesogens.

Polyester-Containing α-Cyclodextrin-Based Polyrotaxane: Synthesis by Living Ring-Opening Polymerization, Polypseudorotaxanation, and End Capping Using Nitrile N-Oxide

The first synthesis of polyrotaxanes consisting of polyester axles and α-cyclodextrin (α-CD) wheels was achieved by the catalyst-free click end-capping reaction of polypseudorotaxanes using nitrile N-oxide. The polypseudorotaxanes contain acrylate-functionalized polyesters that are obtained by the living ring-opening polymerization of lactones. The yield and coverage ratio of polyrotaxanes are highly dependent on the reaction time, molecular weight of the polyester, polyester structure, and solvent used. From the thermal properties of the resulting polyrotaxanes, it was found that coverage with α-CDs efficiently suppresses the crystallization of the polyester main chain.

Synthesis and Emission Behavior of Liquid-Crystalline Main-Chain Polyesters Containing Carbazole and Oxadiazole Moieties

Organic light-emitting diodes (OLEDs) based on chromophore-containing liquid crystals (LCs) can emit polarized light due to self-assembly of mesogenic chromophores. The stability of LC phases in LC polymers with a mesogenic group in the main chain is higher than that in the polymers containing a mesogenic group in the side chain. In this study, a novel family of polyesters containing a carbazole moiety as a hole-transporting unit and an oxadiazole (OXD) moiety as an electron-transporting unit in the main chain, P10-DOXDCz and P16-DOXDCz, were designed and synthesized. These polyesters were prepared by transesterification of N-hexyl-3,6-di[2-([1,3,4]oxadiazol-5-yl)-4-methylbenzoate]carbazole and 1,10-decanediol or 1,16-hexadecanediol at 220 °C for 20 h. They showed a nematic phase. Both P10-DOXDCz and P16-DOXDCz emitted intense blue fluorescence with a maximum at 439 nm and 450 nm in thin films, respectively, and their fluorescence quantum yields were 0.74 and 0.81 in solution, respectively. Both compounds exhibited polarized emission in a LC phases, and the order parameters estimated from the polarized emission spectra were 0.10 for P10-DOXDCz and 0.14 for P16-DOXDCz. Fabricated devices, ITO/PEDOT:PSS/P10-DOXDCz and P16-DOXDCz/MgAg, emitted blue light when a positive voltage was applied to the ITO electrode.

Twin liquid crystals and segmented thermotropic polyesters containing azobenzene—effect of spacer length on LC properties

AbstractWe report systematic studies on a homologous series of twin liquid crystalline (LC) molecules based on phenyl and naphthyl azobenzene (PnP and NpnNp) as well as segmented copolyesters based on them. The twin series had the structure azobenzene–oligooxyethylene–azobenzene, where the ethyleneoxy length was varied from 2 to 6 units. The LC properties of the twin series depended on the chemical structure of the azochromophore and also the length of the central oligooxyethylene segment. The PnP series exhibited smectic LC properties for n > three oligooxyethylene units. Conversely, NpnNp series exhibited spherulitic phases only for the shortest member –Np2Np. One non‐LC short spacer twin (P2P) and one LC long spacer twin (P6P) were incorporated as part of a main chain polyester composed of fully aliphatic segments of sebacate and di or tetraethylene glycol (DEG/TEG) units by melt polycondensation. Non‐LC P2P formed LC polymers even at low (5 mol %) incorporation in DEG‐based copolymers, whereas the LC‐P6P could do so only at 30 mol % incorporation. The LC properties of the twin molecules as well as copolymers were studied using differential scanning calorimetry, polarized light microscopy (PLM) along with variable temperature wide angle X‐ray diffraction. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Synthesis of linear functionalized polyesters by controlled atom transfer radical polyaddition reactions

We report on the facile synthesis of a range of new linear functionalized polyesters by controlled atom transfer radical polyaddition reactions. One bis-styrenic type monomer, 1,2-bis(4-vinylbenzyloxy)ethane (AA), and two bis-methacrylate type ATRP initiators, 1,2-bis(2-bromoisobutyryloxy)ethane (BB) and bis[2-(2-bromoisobutyryloxy)ethyl]disulfide (BssB), were synthesized. The polymerizations of monomer AA with BB and BssB were carried out in anisole at 0 °C, using Cu/CuBr2 coupled with N,N-bis(2-pyridylmethyl)octylamine (BPMOA) as the catalyst. The polymerization kinetics were investigated and the polymers were characterized by GPC and NMR, both confirming the step-wise mechanism with the formation of the expected linear polyesters having pendent bromides. When BssB was used, additional disulfide groups were incorporated in the polyester main chain, imparting a tunable degradation mechanism to the polyester. Moreover, the pendent bromides on the polymers could serve as initiation sites or precursors to azides to prepare biodegradable graft copolymers. This has been proven by two examples, reactivating the pendent bromides at room temperature to initiate the ATRP of other methacrylates, and transforming these groups into azido-groups by substitution reaction followed by click chemistry with alkynyl-terminated polyethylene glycol.

Degradable and biocompatible aldehyde-functionalized glycopolymer conjugated with doxorubicin via acid-labile Schiff base linkage for pH-triggered drug release

Well-defined aldehyde-functionalized glycopolymers were synthesized via reversible addition-fragmentation chain transfer (RAFT) copolymerization of 1,2:3,4-di-O-isopropylidene-6-O-(2′-formyl-4′-vinylphenyl)-D-galactopyranose (IVDG) and 5,6-benzo-2-methylene-1,3-dioxepane (BMDO) using dicumyl peroxide as the initiator and 1-phenylethyl phenyldithioacetate as the RAFT agent at 130 °C in anisole. The resulting copolymers were found to be hydrolytically degradable due to their main-chain polyester structures. Removal of the protective isopropylidene groups from the sugar residues resulted in a novel amphiphilic copolymer with low cytotoxicity as confirmed by MTT assay against L929 cells. The deprotected copolymer could conjugate anticancer drug DOXvia an acid-labile Schiff base linkage to form DOX-loaded micelles in a high drug loading level (∼14 wt%) with pendent galactose moieties covering the surface. The size of the DOX-conjugated polymeric micelle was determined to be about 125 nm by dynamic light scattering. The in vitro release studies demonstrated that the release of DOX from the micelles manifested a strong dependence on the environment pH due to the acid-cleavable Schiff base linkage between the DOX and micelles. The DOX release was significantly faster at pH 5.0 compared to pH 7.4.

Preparation of Main-Chain Thermotropic Polyesters With Two Types of Mesogens Connected Alternatively by Aliphatic Spacers

A homologous series of main-chain thermotropic polyesters (PBTn, n = 2, 4, 6) containing biphenyl and triad aromatic ester mesogenic units interconnected by n-methylene spacers in the main chain were prepared from terephthaloyl bis(4-oxybenzoyl chloride) (TOBC) and 4,4′-bis(ω-hydroxyalkyloxy)biphenyls (n-BP, n = 2, 4, 6) by solution polycondensation. The chemical structures of the monomers and PBTn were characterized by spectroscopic techniques and elemental analysis. The solubility, supermolecular structures, thermal and liquid crystalline properties of PBTn were investigated by differential scanning calorimetry (DSC), polarizing microscopy (PLM), small-angle X-ray scattering (SAXS), thermogravimetric analyses (TGA), and wide-angle X-ray diffraction (WAXD), and they were found to be closely dependent on the length of the methylene spacers. The increasing methylene units led to improved solubility, broader liquid crystalline range, reduced mesophase-isotropic transition point, higher thermal stability, and decreasing crystallinity. The decomposition temperatures (5% mass loss) of the polymers were above 380°C in nitrogen atmosphere and only PBT4 and PBT6 exhibited smectic mesophases as well as high viscosity in the mesophase.

Nanosized Shape‐Changing Colloids from Liquid Crystalline Elastomers

A method to prepare shape-changing nanospheres from liquid crystalline elastomers is reported. The nanosized colloids are prepared by a miniemulsion process. During this process, colloids are prepared from a liquid crystalline (LC) main-chain polyester and subsequently crosslinked into a nanometer-sized LC elastomer. The ability of these LC elastomers to change their shape at the phase transition temperature from the smectic A to the isotropic phase was detected by temperature-dependent transmission electron microscopy. The phase transition-induced shape change leads to strongly shape anisotropic nanosized elastomer particles.

Spontaneous deformation of main-chain liquid-crystalline elastomers composed of smectic polyesters

We observe the spontaneous shape change of a uniaxially deformed liquid-crystalline elastomer composed of smectic main-chain liquid-crystalline polyesters in a cyclic heating–cooling process. Although the elastomer contracts by about 115% on heating up to the isotropic phase, the sample length recovers by 55% on cooling to room temperature in the first heating–cooling process, and the elastomer exhibits an almost complete reversible deformation in the second heating–cooling process. By a comparison of the results of sample observation with those of X-ray analysis, we recognise that the strain λ was linearly coupled with the orientational order parameter S. In addition, the results of the X-ray analysis imply that a cybotactic nematic state, in which smectic clusters lie scattered in a nematic-like matrix, emerges after exposure to the isotropic phase.