Main-chain biodegradable liquid crystal derived from cholesteryl derivative end-capped poly(trimethylene carbonate): synthesis and characterisation

Main-chain biodegradable liquid crystal derived from cholesteryl derivative end-capped poly(trimethylene carbonate) was investigated. The novel liquid crystal was synthesised via ring-opening polymerisation of trimethylene carbonate initiated by cholesteryl derivative with an alkyl spacer and end primary hydroxyl group, without any catalyst. The chemical structure of resulting polymers was verified by ¹H NMR. Liquid crystalline properties were validated by X-ray diffraction, differential scanning calorimetry, and polarising optical microscopy. The results showed that all the synthesised polymers Chol-(CH₂)₂-(TMC)_n exhibited mesomorphism in particular temperature ranges because of the introduction of the cholesteryl derivative moiety.     

Synthesis and mesomorphism of new aliphatic polycarbonates containing side cholesteryl groups

New cholesterol side-functionalised polycarbonate polymers were synthesised by the ring-opening homo- and copolymerisation reaction of the cyclic monomer cholesteryl 5-methyl-2-oxo-1,3-dioxane-5-carboxylate and d,l-lactide using Sn(Oct)₂ as a catalyst. The chemical structures and average molecular weights of the cyclic monomer, homopolymer and block copolymers obtained in this study were characterised using FT-IR, ¹H NMR and gel permeation chromatographic measurement. The mesomorphism and mesophase structure were investigated with polarising optical microscopy, differential scanning calorimetry and X-ray diffraction measurement. As a result, the homopolymer and block copolymers showed an enantiotropic smectic A (SmA) phase. With the concentration of the lactide segment increasing, the glass transition temperature and isotropic temperature of the corresponding block copolymer all decreased. In addition, XRD suggested that the homopolymer and two block copolymers showed the SmA double-layer packing of side chains.     

Synthesis and properties of Pluronic-based pentablock copolymers with pendant amino groups

Amphiphilic Pluronic-based pentablock copolymers with pendant amino groups have been successfully synthesized via ring opening polymerization of γ-(carbamic acid benzyl ester)-ε-caprolactone (γCABεCL) and ε-caprolactone (εCL) using Pluronic F127 as macroinitiator and Sn(Oct)₂ as catalyst, and followed by hydrolysis of the Cbz protected groups under acidic conditions. The structure of the copolymer was confirmed by proton nuclear magnetic resonance (¹H NMR) and Fourier transform infrared spectroscopy spectra. In addition, gel permeation chromatography results demonstrated that the synthetic copolymer had a single and symmetrical peak. Moreover, the crystallinity and hydrophilicity could be well adjusted by the content of the functionalized monomer. Successful formation of aggregates was demonstrated by fluorescence method and transmission electron microscopy revealed that the micelles had a spherical morphology and the size was on nano scale according to the laser particle sizer results. The polymeric micelles had no obvious cytotoxicity even the micelles concentration reached 500 mg/L. Thus the Pluronic-b-poly(γ-amino-ε-caprolactone-co-ε-caprolactone) copolymers have great potential for the use in the biomedical fields.     

Amphiphilic poly(N,N-dimethylamino-2-ethyl methacrylate)-g-poly(ε-caprolactone) graft copolymers: synthesis and characterisation

Amphiphilic poly(N,N-dimethylamino-2-ethyl methacrylate)-g-poly(ε-caprolactone) graft copolymers (PDMAEMA-g-PCL) with various compositions and molecular weights were synthesised via a fully controlled three-step strategy. First, poly(ε-caprolactone) macromonomers (PCLMA) were prepared by ring-opening polymerization (ROP) of ε-caprolactone (CL) initiated by aluminum triisopropoxide (Al(OⁱPr)₃), followed in a second step by quantitative esterification of PCL hydroxy end-groups with a methacrylic acid derivative. Finally, the controlled copolymerization of PCLMA and N,N-dimethylamino-2-ethyl methacrylate (DMAEMA) was carried out by atom transfer radical polymerisation (ATRP) in THF at 60 °C using CuBr ligated with 1,1,4,7,10,10, hexamethyl triethylenetetramine and ethyl 2-bromoisobutyrate as catalyst and initiator, respectively. Furthermore, PDMAEMA-g-PCL graft copolymers were reacted with methyl iodide to convert the pendant tertiary amines into quaternary ammonium iodides increasing accordingly their water solubility. Some preliminary experiments was further carried out by tensiometry and dynamic light scattering in order to shed so light on the tensioactive behaviour of these amphiphilic graft copolymers (with protonated amines or quaternary ammonium cations).     

Enzyme-catalyzed degradation of poly(l-lactide)/poly(?-caprolactone) diblock, triblock and four-armed copolymers

Poly(l-lactide)/poly(?-caprolactone) diblock, triblock and four-armed copolymers with the same monomer feed ratio (50/50) were synthesised by two step ring opening polymerisation of successively added ?-caprolactone and l-lactide, using isopropanol, ethylene glycol, or pentaerythritol as initiator and zinc lactate as co-initiator. The resulting copolymers were characterised by ¹H NMR, DSC, SEC, and FT-IR, which confirmed the blocky characteristic of the copolymers. Solution cast films were allowed to degrade at 37 °C in the presence of proteinase K, and the degradation was monitored by gravimetry, DSC, SEC, ¹H NMR and ESEM. The effects of chain structure, block length and crystallinity on the degradation are discussed. The four-armed block copolymer degrades the most rapidly, while the diblock copolymer exhibited the slowest degradation rate. The difference was related to the crystallinity depending on both the molecular structure and block length. Little compositional or molar mass changes were obtained during degradation, which strongly supports a surface erosion mechanism, in agreement with ESEM observations.     

Chitooligosaccharide Copolymers: Synthesis and Aqueous Self-assembly

Novel water-soluble amphiphilic graft copolymers (COS-g-PCL-b-MPEG) were synthesized by the coupling reaction between chitooligosaccharide (COS) and MPEG-b-PCL-COOH, which was synthesized via ring-opening polymerization of ε-caprolactone (CL) using MPEG as an initiator and subsequent carboxylation by succinic anhydride. The chemical composition of the graft copolymers was confirmed by ¹H-NMR spectra and FT-IR spectrometry. The thermal properties and crystallinity of the copolymers were observed by DSC and XRD measurements, which showed the existence of separate backbone and graft chain phases in the copolymer. The micellar behavior via self-assembly of the graft copolymers in aqueous solution was studied using pyrene fluorescence dye technique. AFM measurements showed that the micelles had a spherical morphology at the critical micelle concentration (CMC) and ranged in size from 20–45 nm. The amphiphilic ternary biodegradable graft copolymer endows the hydrophilic outer shell of micelles with structural and functional diversification, which might be desirable for drug delivery applications.     

Ring-opening copolymerization of α-chloromethyl-α-methyl-β-propionolactone with ε-caprolactone

α-Chloromethyl-α-methyl-β-propionolactone (CMMPL) has been copolymerized with ε-caprolactone (CL) using a wide range of feed compositions and aluminium triisopropoxide [Al(OⁱPr)₃] as an initiator. Random copolymers of CMMPL with CL were obtained. The pendant chloromethyl groups of the copolymer were converted to quaternary ammonium salts by reaction with pyridine, resulting in an increased hydrophilicity of the copolymers.     

Amphiphilic Biodegradable Poly(ϵ-caprolactone)-Poly(ethylene glycol) – Poly(ϵ-caprolactone) Triblock Copolymer Synthesis by Maghnite-H+ as a Green Catalyst

Amphiphilic biodegradable (PCL-PEG-PCL) triblock copolymers have been successfully prepared by the ring opening polymerization of ?-caprolactone (CL) in the presence of poly(ethylene glycol) (PEG) at 80°C employing Maghnite-H⁺ a non-toxic Montmorillonite clay as catalyst. Maghnite-H⁺ reacts as a solid source of protons to induce ?-caprolactone polymerization. The triblock architecture, molecular weight and thermal properties of the copolymers were characterized by NMR spectra, GPC and DSC analyses. The effect of Maghnite-H⁺ proportion and PEGs on the rate of copolymerization and on average molecular weight of resulting copolymers was studied. A cationic mechanism for the copolymerization reaction was proposed.     

New side chain cholesterol-functionalised aliphatic polycarbonate copolymer: synthesis and phase behaviour

A new side cholesterol-functionalised liquid crystal (LC) copolymer based on aliphatic polycarbonate backbone was synthesised. The chemical structures of the block copolymers obtained in this study were characterised with Fourier Transform Infrared Spectroscopy (FT-IR) and Proton Nuclear Magnetic Resonance (¹H NMR) spectra. Their thermal stability and phase behaviours were investigated with thermogravimetric analysis (TGA) measurements, differential scanning calorimetry, and polarising optical microscopy. The molecular organisation in the mesophase was studied by temperature-dependent X-ray diffraction (XRD). As a result, the block copolymer bearing side cholesteryl groups showed a glass transition at 15.8°C and a smectic A (SmA) to isotropic phase transition at 151.3°C on heating cycle. XRD indicated that the block LC copolymer showed an interdigitated molecular arrangement of the mesogenic units within the smectic layers. This partial bilayer structure was similar to the SmA phase formed by polar mesogens.     

Potential Biodegradable Implants from ϵ-Caprolactone and D,L-Lactide Copolymers: Synthesis,Properties, and In Vivo Degradation

Random copolymers of ?-caprolactone (CL) and D, L-lactide (DLLA) were synthesized by ring-opening polymerization using stannous octoate as catalyst. The effect of polymerization conditions, such as feeding dose, reaction temperature, polymerization time, and catalyst content on the properties of the copolymers was evaluated to prepare suitable copolymers with controlled properties for biodegradable implant applications. The results showed that the polymerization conditions influenced the thermal and mechanical properties of the copolymers strongly and controllable and tunable properties of random copolymers could be obtained by adjusting the copolymer compositions. The optimum reaction conditions to prepare the CL-DLLA copolymers for implant applications are 30–87 mol.% DLLA content in feeding dose, 110°C reaction temperature, and 24 h polymerization time. The results of in vivo implantation revealed the excellent degradability of CL-DLLA copolymers. Copolymers of CL and DLLA with different compositions and properties would be suitable for the application of biodegradable implants.     

Synthesis and characterization of poly(ɛ-caprolactone-co-ethylene glycol) star-type amphiphilic copolymers by “click” chemistry and ring-opening polymerization

Abstract

The synthesis of poly(?-caprolactone-co-ethylene glycol) AAB star-type amphiphilic copolymers were carried out by use of a “click” chemistry reaction to block propargyl polyethylene glycol (propargyl-PEG) to terminally azide poly(?-caprolactone) (PCL-N₃). For this purpose, propargyl-PEG was synthesized by the reaction of PEGs (3000?Da, 2000?Da, 1500?Da, and 1000?Da) and propargyl chloride. Terminally chloride poly(?-caprolactone) (PCL-Cl) was carried out by means of ring-opening polymerization (ROP) of ?-caprolactone (CL) and 3-chloro-1,2-propanediol. Synthesis of PCL-N₃ was obtained by the chemical interaction of PCL-Cl and sodium azide. By reacting propargyl-PEG and PCL-N₃, the star-type amphiphilic copolymers were obtained. The characterization of products was accomplished by using multiple instruments including ¹H-NMR, FT-IR, GPC, TGA, contact angles, and elemental analysis techniques.     

Synthesis,liquid crystalline mesophases and morphologies of diblock copolymers composed of a poly(dimethylsiloxane) block and a nematic liquid crystalline block

In this study, a series of liquid crystalline diblock copolymers, composed of a soft poly(dimethylsiloxane) (PDMS) block with a de?ned length and a side-on liquid crystalline poly(3??-acryloyloxypropyl 2,5-di(4?-butyloxybenzoyloxy) benzoate) (P3ADBB) block with different lengths, are synthesised by the atom transfer radical polymerisation. The macromolecular structures, liquid crystalline properties and the microphase-separated morphologies of the diblock copolymer are investigated by ¹H NMR, FT-IR, GPC, POM, DSC and TEM. The results show that the well-de?ned diblock copolymers (PDMS_n-b-P3ADBB_m) possess four different soft/rigid ratios (n = 58, m = 10, 25, 42, 66) and relatively narrow molecular distributions (PDI ≤ 1.30). P3ADBB blocks of the copolymers show nematic sub-phases, which are identical to the mesomorphic behaviour of the homopolymer P3ADBB. After being annealed at 90°C in a vacuum oven for 48 h, the copolymers form a lamellar morphology when m = 10 and morphologies of PDMS spheres embedded in P3ADBB matrix when m = 25, 42 and 66.     

Liquid crystalline polymers XV. Synthesis,properties and cytotoxicity of photoresponsive thermotropic liquid crystalline copoly(arylidene-ether)s based on 4-tert-butylcyclohexanone and cyclohexanone moieties in the main chain

A new series of photoresponsive thermotropic liquid crystalline copoly(arylidene-ether)s based on both 4-tert-butylcyclohexanone and cyclohexanone moieties in the main chain were synthesised using solution polycondensation technique of both with different 4,4?-diformyl-α,ω-diphenoxyalkane derivatives. Two model compounds were synthesised from the reaction of each cycloalkanone monomer with benzaldehyde, and their structures were determined using single crystal X-ray diffraction. The structure of the monomers and copolymers was confirmed by elemental and spectral analyses. In addition, the thermal stabilities of these copolymers were evaluated by thermogravimetric analysis. We performed both differential scanning calorimertric and polarised optical microscopic measurements to investigate the thermotropic liquid crystalline properties of synthesised copolymers. The UV?Vis absorption spectroscopy of the liquid crystalline copoly(arylidene-ether) 6f revealed that the system undergoes Entgegen/Zusammen (E/Z) photoisomerisation using UV lamp (450 nm). Moreover, the various characteristics of the prepared copolymers including: solubility, X-ray diffraction analysis, gel permeation chromatography (GPC) and scanning electron microscopy were determined and discussed. The cytotoxicity of the model compounds and selected examples of these copolymers was tested against MCF-7 breast cancer cells. All tested samples showed considerable results, where 6c copolymer gave the best result; it showed cytotoxicity against MCF-7 cell line with IC₅₀ of 0.26 µM.     

Synthesis and enzymatic degradation of end-functionalized biodegradable polyesters

End-functionalization of biodegradable polymers/oligomers based on L-lactide and glycolide by cholesteryl moiety was investigated. We established the feasibility of preparing the functionalized polymers/oligomers, Chol-(LG)_m+n, through ring-opening copolymerization initiated by cholesterol bearing a hydroxyl group, without adding any catalyst. The functionalized polymers/oligomers of different molecular weights were obtained by controlling the feed ratio of the initiator cholesterol to the monomers. The chemical structure of end-functionalized polymers/oligomers was confirmed by FTIR and ¹H NMR. Incorporation of cholesteryl moiety into the polymer chains induces liquid crystallinity in the resultant oligomers when the molecular chains are not very long. The enzymatic degradation studies, for all the samples, were carried out using enzyme, proteinase K. Interestingly, the enzymatic degradation of cholesteryl end-functionalized polymers/oligomers resulted in a lamella-like porous structure on the sample surface, which is altogether different from the commonly reported spherical-pore structure formed during the degradation of conventional polyesters.     

Controlled polymerization of ϵ-caprolactone -from macromolecules to microspheres

Pseudoanionic polymerization of ϵ-caprolactone (CL), initiated with dialkylaluminum alkoxides, was used for the tailored synthesis of poly(CL) with M̄_n ≤ 100 000 and M̄_w /M̄_n < 1. 20. Macromolecules with functional groups at one or at both ends were obtained in this way. Controlled polymerization of CL allowed to prepare poly(dodecyl acrylate)-g-poly(ϵ-caprolactone) (poly(DAC)-g-poly(CL)) with well defined poly(CL) grafts. These copolymers were used as the surface active agents for the direct synthesis of poly(CL) microspheres. The number average diameter (D̄_n ) of poly(CL) microspheres varied from 0.628 μm to 0.94 μm and the diameter polydispersity (D̄_v /D̄_n ) varied from 1.038 to 1.26, depending on the composition of poly(DAC)-g-poly(CL). Human serum albumin (HSA) and human gamma globulins (_γ G) were attached to the poly(CL) microspheres. The maximal surface concentrations of HSA and _γ G adsorbed onto the microspheres were equal to 9·10⁻⁴ g/m² and 2.0·10⁻³ g/m² respectively.     

Ring-opening metathesis polymerization of new α-norbornenyl poly(ε-caprolactone) macromonomers

Poly(ε-caprolactone) (PCL) macromonomers capped by a polymerizable norbornene end-group have been synthesized and (co)polymerized by ring-opening metathesis with formation of graft copolymers and polymacromonomers. α-Norbornenyl PCL macromonomers have been synthesized by ring opening polymerization (ROP) of ε-caprolactone (εCL) initiated by 2-diethylaluminoxymethyl-5-norbornene. Copolymerization of these PCL macromonomers with norbornene and polymerizable derivatives has been catalyzed by the [RuCl₂(p-cymene)]₂ PCy₃/(trimethylsilyl)diazomethane complex yielding a series of poly(norbornene)-graft-poly(ε-caprolactone) copolymers. These new graft copolymers have been characterized by a set of analytical methods, i.e., SEC, ¹H-NMR, FTIR, DSC, and TGA. Furthermore, PCL macromonomers have been polymerized into high molecular weight comb chains of narrow molecular weight distribution (M_w/M_n = 1.10) within high yields (90%). © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2447–2455, 1999     

Synthesis and characterization of aba-type block copolymer of poly(ϵ-caproplactone) with poly(ethylene glycol), by mean of activation end groups

Poly(?-caprolactone)-b-poly(ethylene glycol)-b-poly(?-caprolactone) (PCL-b-PEG-b-PCL) triblock copolymer were synthesized by mean anionic activation of the hydroxyl end groups of poly(ethylene glycol) in presence of diphenylmethylsodium. Copolymers were characterized by SEC, FT-IR and ¹H-NMR spectroscopy, TGA and DSC. Size exclusion chromatographic analysis of obtained copolymers indicated incorporation of CL monomer into PEG without formation of PCL homopolymer. Characterization by FT-IR and ¹H NMR spectroscopy of the resulting polymeric products, with respect to their structure, end-groups and composition, showed that they are best described as ester-ether-ester triblock copolymers, whose compositions can be adjusted changing the feeding molar ratio of PEG to CL. The thermal stability of triblock copolymers was less that PEG precursor, but higher that PCL homopolymer. Analysis by mean DSC showed that all copolymers were semi-crystalline and their thermal behavior depending on their composition.     

Synthesis and properties of side-chain liquid crystalline polymers grafted with chiral dimers containing cholesteryl groups

ABSTRACT

Two series of novel side-chain liquid crystal (LC) polysiloxanes grafted with chiral liquid crystalline dimers containing cholesteryl mesogens were synthesised. The chemical structure and LC properties of comonomers and polymers were characterised by FTIR, ¹H-NMR, DSC, TGA, POM and XRD. M₁ and M₂ were chiral nematic (N*) dimers, and M₃ was an achiral LC monomer displaying nematic mesophase in a narrow mesomorphic temperature range, while the copolymers exhibited N* mesophase whose mesomorphic temperature ranges were much wider than those of the comonomers. Moreover, the glass transition temperatures and isotropization temperatures of the polymers all decreased with decreasing the dimer components. Reflection spectra showed that P_a series tend to attain wide-band selective reflection at long wavelengths, while P_b series were more potential at short wavelengths with narrow bandwidths. Decreasing the dimer components led the wavelength of the selective reflection to blue shift, which was an abnormal phenomenon in chiral mixture system.     

New symmetric azobenzene molecules of varied central cores: Synthesis and characterisation for liquid crystalline properties

A new series of azobenezene liquid crystals (LCs) was designed and synthesised by known and straightforward methods. The central connecting cores of the molecules varied viz., benzene/naphthalene/biphenyl. The molecular structures were confirmed by infrared, UV, nuclear magnetic resonance spectroscopic techniques. The LC texture and thermal phase behaviours were investigated by polarising optical microscopy and differential scanning calorimetry. Smectic B phase was found in biphenyl-derived azobenzene ester. The effect of central core on LC properties was investigated. The decreased angle at central connecting core suppressed the melting points, phase transition temperatures without losing LC properties, whereas, in moderate angle compounds LC properties were suppressed. The compounds with increased angle at central core favours rich mesomorphism.     

Preparation and Characterization of Linear and Miktoarm Star Side-Chain Liquid Crystalline block Copolymers with p-Methoxyazobenzene Moieties via a Combination of ATRP and ROP

One linear and two miktoarm star side-chain liquid crystalline (LC) block copolymers with p-methoxyazobenzene moieties were prepared by a combination of ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP) techniques. First, ROPs of ε -caprolactone (ε -CL) were carried out catalyzed by Sn(Oct)₂ using three multifunctional initiators, hydroxyethyl 2-bromoisobutyrate (AB type), 3-hydroxy-2-(hydroxymethyl)-2-methylpropyl 2-bromo-2-methylpropanoate (A₂B type) and 2,2-bis(hydroxymethyl)propane-1,3-diyl bis(2-bromo-2-methylpropanoate) (A₂B₂ type), at 110°C in toluene, respectively. Second, the previously obtained poly(ε -caprolactone)s (PCLs) with bromines functionalities were used as the macroinitiators to conduct ATRP of 6-(4-methoxy-4-oxy-azobenzene) hexyl methacrylate (MMAZO) with CuBr/PMDETA as the catalyst systems at 85°C in anisole to prepare the linear and miktoarm side-chain LC block copolymers (PCL-b-PMMAZO, (PCL)₂-(PMMAZO) and (PCL)₂-(PMMAZO)₂). The produced polymers were well-controlled with the controlled molecular weights and the relatively narrow molecular weight distributions (M _w/M _n ≤ 1.35). The structures of the obtained polymers were all characterized by NMR, FT-IR and GPC analysis. Furthermore, the LC properties of the linear and miktoarm star block copolymers were also investigated by differential scanning calorimetry (DSC) and thermal polarized optical microscopy (POM).