Hydroxy End Groups Research Articles

Poly(lactic-co-glycolic acid) Networks with Dynamic Covalent Bonds: Synthesis and Characterization

Poly(lactic-co-glycolic acid) (PLGA) is an aliphatic polyester that degrades under environmental conditions making it interesting for replacing microplastic creating polyolefins in packaging and agricultural applications. However, linear PLGA exhibits unfavorable thermomechanical properties for use. Therefore, synthetic aspects, characterization, and reprocessing ability of PLGA in the form of dynamic covalent networks are studied in the present work. The dynamic covalent networks were synthesized from short-chain four-armed star-shaped PLGA with hydroxy end groups and 4,4′-methylene diphenyl diisocyanate as a cross-linker. Tin octanoate was used as a catalyst to promote the associative exchange reactions at elevated temperatures. The synthesized networks with dynamic bonding and debonding are insoluble in common organic solvents, have enhanced the thermomechanical properties, and have maintained the possibility of thermal reprocessing and recycling like thermoplastics.

On the Behavior of the Ethylene Glycol Components of Polydisperse Polyethylene Glycol PEG200.

Molecular dynamics (MD) simulations are reported for [polyethylene glycol (PEG)200], a polydisperse mixture of ethylene glycol oligomers with an average molar weight of 200 g·mol-1. As a first step, available force fields for describing ethylene glycol oligomers were tested on how accurately they reproduced experimental properties. They were found to all fall short on either reproducing density, a static property, or the self-diffusion coefficient, a dynamic property. Discrepancies with the experimental data increased with the increasing size of the tested ethylene glycol oligomer. From the available force fields, the optimized potential for liquid simulation (OPLS) force field was used to further investigate which adjustments to the force field would improve the agreement of simulated physical properties with experimental ones. Two parameters were identified and adjusted, the (HO)-C-C-O proper dihedral potential and the polarity of the hydroxy group. The parameter adjustments depended on the size of the ethylene glycol oligomer. Next, PEG200 was simulated with the OPLS force field with and without modifications to inspect their effects on the simulation results. The modifications to the OPLS force field significantly decreased hydrogen bonding overall and increased the propensity of intramolecular hydrogen bond formation at the cost of intermolecular hydrogen bond formation. Moreover, some of the tri- and more so tetraethylene glycol formed intramolecular hydrogen bonds between the hydroxy end groups while still maintaining strong intramolecular interactions with the ether oxygen atoms. These observations allowed the interpretation of the obtained RDFs as well as structural properties such as the average end-to-end distances and the average radii of gyration. The MD simulations with and without the modifications showed no evidence of preferential association of like-oligomers to form clusters nor any evidence of long-range ordering such as a side-by-side stacking of ethylene glycol oligomers. Instead, the simulation results support the picture of PEG200 being a random mixture of its ethylene glycol oligomer components. Finally, additional MD simulations of a binary mixture of tri-and hexaethylene glycol with the same average molar weight as PEG200 revealed very similar structural and physical properties as for PEG200.

End Group Dye-Labeled Polycarbonate Block Copolymers for Micellar (Immuno-)Drug Delivery.

Defined conjugation of functional molecules to block copolymer end groups is a powerful strategy to enhance the scope of micellar carriers for drug delivery. In this study, an approach to access well-defined polycarbonate-based block copolymers by labeling their end groups with single fluorescent dye molecules is established. Following controlled polymerization conditions, the block copolymers' primary hydroxy end group can be converted into activated pentafluorophenyl ester carbonates and subsequently aminolyzed with fluorescent dyes that are equipped with primary amines. During a solvent-evaporation process, the resulting end group dye-labeled block copolymers self-assemble into narrowly dispersed ∼25nm-sized micelles and simultaneously encapsulate hydrophobic (immuno-)drugs. The covalently attached fluorescent tracer can be used to monitor both uptake into cells and stability under biologically relevant conditions, including incubation with blood plasma or during blood circulation in zebrafish embryos. By encapsulation of the toll-like receptor 7/8 (TLR7/8) agonist CL075, immune stimulatory polymeric micelles are generated that get internalized by various antigen-presenting dendritic cells and promote their maturation. Generally, such end group dye-labeled polycarbonate block copolymers display ideal features to permit targeted delivery of hydrophobic drugs to key immune cells for vaccination and cancer immunotherapy.

Correlations Between Precursor Molecular Weight and Dynamic Mechanical Properties of Polyborosiloxane (PBS)

AbstractIt is possible to tailor the dynamic response of polyborosiloxanes (PBS) based on picking the right molecular weight of a precursor. The molecular weight of hydroxy‐terminated polydimethylsiloxane (PDMS) defines the shear‐stiffening performance of PBS due to straightforward condensation reaction between hydroxy end groups of PDMS and boric acid. Introduced borono groups behave as stickers, hence, are prone to supramolecular interactions. New correlations are discovered for five PBS synthesized from hydroxy‐terminated PDMS with different molecular weights. Si─O─B infrared band intensities for all PBS follow the same trend with molecular weight as the number of PDMS hydroxy groups which confirms the full completion of the reaction. After synthesis, the molecular weight of PBSs remained almost the same, which indicates the absence of significant chain scissoring, polymerization, or crosslinking. During the rheological analysis, it is found that crossover point modulus follows the same trend as the number of PDMS hydroxy groups and Si─O─B band intensities. PBS demonstrates a linear increase in peak forces with molecular weight during the drop weight impact test. The low molecular weight of a precursor, hence, a high number of stickers is a primary requirement for effective protection against low‐velocity impact.

Grain size control of perovskite films based on β-alanine self-assembled monolayers surface treatment

The grain size of the perovskite layer can be tuned by the surface treatment of Ultraviolet ozone (UVO) with β-alanine self-assembled molecular films (SAMs) on the Nickel oxide (NiOx) substrate. The UVO treatment had been used to control the hydroxy (-OH) end-group on NiOx substrate and the condensation reaction of β-alanine SAMs, in which the end-group of the amino group (-NH2) correlates with the nucleation of the perovskite layer. The difference of surface end-group with/without the UVO treatment on the NiOx substrate was revealed by the shift of the oxidation peak of the SAMs layer in the cyclic voltammetry and the electrochemical impedance spectroscopy. It is found that the wettability of NiOx substrate was enhanced by the SAMs treatment time due to the increment of -NH2 end-group and the UVO treatment. Larger grain size of the perovskite layer was achieved on the NiOx substrate with SAMs 15 minutes treatment. Moreover, the optical absorbance of perovskite films in the short wavelength range was enhanced by the assembling time of SAMs. This study provides a method to control the surface morphology of the perovskite active layer in its solar cell device applications.

Unexpected Radical Telomerisation of Vinylidene Fluoride with 2-Mercaptoethanol.

The radical telomerisation of vinylidene fluoride (VDF) with 2-mercaptoethanol as chain transfer agent (CTA) was studied to synthesise fluorinated telomers which bear a hydroxy end-group, such as H(VDF)nS(CH2)2OH, under thermal (di-tert-butyl peroxide as the initiator) or photochemical initiations. A careful structural study of a typical H-VDF-S(CH2)2OH telomer was performed by 1H and 19F NMR spectroscopy. These analytical methods allowed us to explore the selective addition of the thiyl radical onto the hydrogenated side of VDF, and the telomer containing one VDF unit was obtained selectively. Surprisingly, for higher [VDF]o initial concentrations, a monoadduct telomer was produced as well as PVDF homopolymer. This feature was related to the fast consumption of the CTA. The kinetics of radical telomerisation led to a quite high transfer constant of the CTA (40 at 140 °C) that evidences the formation of a monoadduct as the only telomer formed.

Correlation of the Abbe Number, the Refractive Index, and Glass Transition Temperature to the Degree of Polymerization of Norbornane in Polycarbonate Polymers.

The influences of the average degree of polymerization (Dp), which is derived from Mn and terminal end group, on optical and thermal properties of various refractive indexed transparent polymers were investigated. In this study, we selected the alicyclic compound, Dinorbornane dimethanol (DNDM) homo polymer, because it has been used as a representative monomer in low refractive index polymers for its unique properties. DNDM monomer has a stable amorphous phase and reacts like a polymer. Its unique reaction allows continuous investigation from monomer to polymer. For hydroxy end group and phenolic end group polymers, the refractive index (nd) decreased with increasing Dp, and both converged to same value in the high Dp region. However, the Abbe number (νd) of a hydroxy end group polymer is not dependent on Dp, and the νd of a phenolic end group polymer is greatly dependent on Dp. As for glass transition temperatures (Tg), both end group series were increased as Dp increased, and both converged to the same value.

Synthesis and Properties of Thermotropic Poly(oxybenzoate-co-oxynaphthoate) Copolyester Modified by a Third AB Type Monomer

The synthesis and modification of high performance thermotropic liquid crystal polyesters (TLCP) are still being investigated due to their excellent properties. In this study modification of poly(oxybenzoate-co-oxynaphthoate) (P-HBA/HNA), a random copolymer of 4-hydroxybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid (HNA), by 5 mol% of one of three AB type monomers (AB type monomers are those who have hydroxy and carboxylic end groups), vanillic acid (VA), 4-hydroxyphenylacetic acid (HPA) and 4-hydroxycinnamic acid (HCA), was conducted. The influence of the AB type third monomer on the liquid crystal properties, melting behavior, thermal stability, microstructure and fiber morphology of the resulting modified terpolyesters was comparatively studied relative to the parent copolymer. When 5 mol% of the HBA units were replaced, the resulting terpolyesters had much lower melting temperatures and could be easily melt processed, while the modified terpolyesters exhibited higher melting and glass transition temperatures when 5 mol% of the HNA units were replaced. Weaker melting peaks and larger melting ranges were observed for the modified terpolyesters, attributed to the existence of nonperiodic layer crystallites caused by the modifiers. The obtained terpolyesters showed good thermal stability and could be melt processed in a broad nematic phase temperature region. The molecular chain packing of the modified terpolyesters was almost destroyed by the third AB type reactants. Fibers prepared from the resulting terpolyesters exhibited well developed fibrillar structure and higher orientation factors, indicating that modification of the P-HBA/HNA by using the AB type monomers to improve its properties would be useful.

Nonmigratory Poly(vinyl chloride)-block-polycaprolactone Plasticizers and Compatibilizers Prepared by Sequential RAFT and Ring-Opening Polymerization (RAFT-T̵-ROP)

Well-defined nonmigrating polymeric plasticizers, poly(vinyl chloride)-block-polycaprolactone (PVC-b-PCL), were synthesized by sequential reversible addition–fragmentation chain transfer (RAFT) polymerization and ring-opening polymerization (ROP) with 2-hydroxyethyl 2-(ethoxycarbonothioylthio)propanoate (HECP) as RAFT agent and incipient initiator for ROP of e-caprolactone (CL, oxepan-2-one). Kinetic experiments demonstrated that HECP provided good control in RAFT polymerization of vinyl chloride (VC) with dispersity (Đ) ∼ 1.2 for 3400 < Mn < 11000. Chain extension experiments with VC and vinyl acetate proved the high end-group fidelity of the macroRAFT agent formed. The hydroxy end-group of the PVC macroRAFT agent allowed its use as a ROP initiator in forming a series of PVC-b-PCL with different PCL block lengths by RAFT-T-ROP. Characterization by wide-angle X-ray diffraction (WAXD), polarized light microscopy (PLM), and differential scanning calorimetry (DSC) indicates that there is enhanced chain enta...

High-Throughput Synthesis of Oligo(εcaprolactone) / Oligotetrahydrofuran Based Polyurethanes

ABSTRACTRobot assisted synthesis as part of high-throughput (HT) technology can assist in the creation of polymer libraries, e.g. polymers with a variety of molecular weights, by automatizing similar reactions. Especially for multiblock copolymers like polyurethanes (PUs) synthesized from telechels via polyaddition reaction, the adjustment of equivalent molar amounts of reactants requires a comprehensive investigation of end group functionality.In this work, PUs based on oligo(ε-caprolactone) (OCL) / oligotetrahydrofuran (OTHF) as model components were designed utilizing HT synthesis enabling the quantitative determination of the optimized ratio between reactive end-groups via fully automated syntheses without major characterization effort of end group functionality. The semi-crystalline oligomeric telechelics were connected with a diisocyanate and OCL with a molecular weight of 2, 4, or 8 kg∙mol-1 was integrated. Here, optimized molecular weights between 90 ± 10 kg∙mol-1 (in case of OCL 8 kg∙mol-1) and 260 ± 30 kg∙mol-1 (in case of OCL 2 kg∙mol-1) were obtained with an isocyanate content of 120 mol%, whereby 100 mol% of isocyanate groups resulted only in molecular weights between 60 ± 6 kg∙mol-1 (OCL 8 kg∙mol-1) and 80 ± 10 kg∙mol-1 (OCL 2 kg∙mol-1). In addition to the optimized ratio between isocyanate and hydroxy end groups, quantitative influences of the OCL chain length and overall molecular weights of PUs on thermal and mechanical properties were detected. The melting temperatures (Tms) of OCL and OTHF domains were well separated for PUs of low molecular weight, the temperature interval between the Tms decreased when the molecular weight of the PUs was increased, and were even overlapping towards one broad Tm, when OCL 2 kg∙mol-1 was incorporated. The storage modulus E’ was highly dependent on OCL chain length exhibiting an increase with increasing molecular weight of OCL from 220 MPa to 440 MPa at 0 °C and decreased with increasing chain length of PUs. The elongation at break (εb) was analyzed below and above Tm of OTHF resulting in εb = 780-870% at 0 °C and εb = 510-830% at 30 °C for PUs of high molecular weight. Accordingly, stretchability of PUs was almost independent of the state of OTHF (semi crystalline or amorphous) but correlated with the OCL precursor chain length (increasing εb with increasing chain length) and overall molecular weight of PUs (PUs at higher molecular weight exhibited higher εb). Hence, the analysis of these quantitative influences between macromolecular structure of multiblock copolymers and the resulting properties (well separated Tms versus overlapping melting transition, improvement of stretchability) would enable the design of new tailored PUs.

Substrate chemistry regulates the surface phase separation of polyurethane films

The effect of substrate chemistry on surface phase separation of polyurethane films were investigated by using self-assembled monolayer (SAM) with chemically different modifications, i.e. hydroxy (–OH) and methyl (–CH3) end groups. Results showed that hydrophilic (–OH) and hydrophobic end groups (–CH[Formula: see text] could respectively promote the aggregation of hard and soft segments at polyurethane–substrate interface, which further regulates the phase separation of polyurethane surface that contacts the substrate. The aggregation of hard segments tended to enhance the surface smoothness of polyurethane films, especially on hydrophilic substrates with hydroxy modification. Further analysis of tensile testing revealed that the regulation of surface phase separation had no effect on the shape memory effect of polyurethane films. These findings suggest that the chemical properties of the substrates could regulate the phase separation and may provide some guidance on the design of specific polyurethane with desired morphology and properties.

Reduced-mobility layers with high internal mobility in poly(ethylene oxide)-silica nanocomposites.

A series of poly(ethylene oxide) nanocomposites with spherical silica was studied by proton NMR spectroscopy, identifying and characterizing reduced-mobility components arising from either room-temperature lateral adsorption or possibly end-group mediated high-temperature bonding to the silica surface. The study complements earlier neutron-scattering results for some of the samples. The estimated thickness of a layer characterized by significant internal mobility resembling backbone rotation ranges from 2 nm for longer (20 k) chains adsorbed on 42 nm diameter particles to 0.5 nm and below for shorter (2 k) chains on 13 nm particles. In the latter case, even lower adsorbed amounts are found when hydroxy endgroups are replaced by methyl endgroups. Both heating and water addition do not lead to significant changes of the observables, in contrast to other systems such as acrylate polymers adsorbed to silica, where temperature- and solvent-induced softening associated with a glass transition temperature gradient was evidenced. We highlight the actual agreement and complementarity of NMR and neutron scattering results, with the earlier ambiguities mainly arising from different sensitivities to the component fractions and the details of their mobility.

Synthesis and Properties of Oligomers with Hydroxy End-Groups

Methods of oligomers (polymers) with hydroxy end-groups obtaining are examined. The synthesis of hydroxy-containing oligomers based on epoxy resins is of special attention. The molecules of mentioned oligomers apart from free primary and secondary hydroxy groups contain epoxy, peroxy, carboxy or acrylic groups.

Carbon Dioxide-Derived Immortal Brush Macromolecules with Poly(propylene carbonate) Side Chains

Brush macromolecules (BMs) are unique because of their distinct properties from linear or other nonlinear polymers, relying on side chain steric repulsions and backbone stiffness. BMs with densely grafted side chains have been synthesized either by cationic, anionic, or controlled radical polymerization, yet CO2–epoxide immortal alternating copolymerization has rarely been applied for the synthesis of BMs via the “grafting-from” approach. Here we report synthesis of BMs by alternating copolymerization of CO2 and propylene oxide (PO) initiated from poly(acrylic acid) as a multifunctional macroinitiator. The copolymerization afforded ultrahigh-molecular-weight BMs with poly(propylene carbonate) (PPC) side chains (molecular weight >106), and the side chain length was tunable via further CO2–PO alternating copolymerization initiated from hydroxy end groups of the resulting side chain PPCs. These BMs were directly observed by atomic force microscopy, demonstrating that the BMs have ellipsoidal morphologies wit...

Selective and thermodynamic properties of supramolecular liquid-crystalline derivatives of azobenzene and biphenyl as stationary phases for gas chromatography

Smectic phase of formyl derivatives of azobenzene has been identified by means of polarization thermomicroscopy using a miscibility criterion. The study of dielectric properties and simulation of dipole moments and Kirkwood correlation factors have revealed that azobenzene and biphenyl derivatives containing hydroxy end group in the aliphatic terminal substituent can form supramolecules and linear associates stabilized by hydrogen bonds. The sorbents based on the studied liquid crystals have exhibited high structural selectivity with respect to isomers of various organic compounds. Thermodynamic manifestations of the specific mesogen–non-mesomorphic sorbate interactions have been revealed.

Synthesis and characterization of isosorbide-based α,ω-dihydroxyethersulfone oligomers

Functionalization of bio-based oligomers is a relevant approach in order to allow these materials to replace more conventional and nonbiodegradable polymers in a wider range of applications. This article will report on the hydroxylation of isosorbide-based ethersulfone oligomers. The hydroxy end-group was controlled by the variation of polycondensation parameters. Comparative study was conducted to assess the effect of isosorbide excess and the monomer concentration on structural composition and molecular weights of produced oligomers. Depending on reaction conditions, various products were synthesized, mainly α,ω-dihydroxyethersulfone oligomers. The characterization of the synthesized polyethersulfone was demonstrated by MALDI–TOF, NMR spectroscopy, differential scanning calorimetry, and size exclusion chromatography.

Resisting protein adsorption on biodegradable polyester brushes

The protein adsorption and degradation behaviors of poly(lactic acid), poly(glycolic acid) (PGA) and poly(ε-caprolactone) (PCL) brushes and their co-polymer brushes with oligo(ethylene glycol) (OEG) were studied. Both brush structure and relative amount of OEG and polyester were found to be important to the protein resistance of the brushes. A protein-resisting surface can be fabricated either by using OEG as the top layer of a copolymer brush or by increasing the amount of OEG relative to polyester when using a hydroxyl terminated OEG (OEG-OH) and a methoxy terminated OEG (OEG-OMe) mixture as the substrate layer. The degradation of single polyester brushes and their co-polymer brushes using OEG-OH as a substrate layer or using OEG as a top layer was hindered. This phenomenon was rationalized by the inhibition of the proposed back-biting process as the hydroxy end groups of polyester were blocked by OEG molecules. Among these brushes tested, PGA co-polymer brushes using the methoxy/hydroxyl OEG mixture as the substrate layer proved to be both protein-resistant and degradable due to the relatively large amount of OEG moieties and the good biodegradability of PGA.

Role of end-groups and catalyst in polyester cyclodepolymerization and cycle-chain equilibria

The influence of polyesters end-groups on cyclic oligoester formation is investigated using a series of hydroxy-, carboxy- and methylester-terminated aliphatic polyesters, in the presence of various ester interchange catalysts. The presence of hydroxy end-groups is the preponderant factor on cyclodepolymerization kinetics. This indicates that the main reaction is the intramolecular hydroxy–ester interchange reaction between hydroxy end-groups and ester functions in the chain. Carboxy-ester and ester–ester interchanges play a minor role, as the cycle-chain equilibrium is reached only very slowly when carboxy- or ester-terminated polyesters are reacted. High temperature and the presence of tin catalysts are also favorable factors, while, as expected, dilution shifts the equilibrium toward the formation of high yields of cyclic oligoesters. A mechanism is proposed, based on the reverse of the “coordination-insertion” mechanism established for the ring-opening polymerization of lactones.

Treelike Polymeric Ionic Liquids Grafted onto Graphene Nanosheets

Herein we report on a versatile grafting-to process combined with end group modification to prepare treelike polymeric ionic liquids which are covalently attached to graphene nanosheets. When cationic 3-ethyl-3-hydroxymethyloxetane (EHO) polymerization is initiated in the presence of dispersed hydroxy-functional graphene (FG) nanosheets, chain termination reactions account for highly effective grafting of hyperbranched poly(3-ethyl-3-hydroxymethyloxetane) (PEHO) onto FG. Tosylated PEHO hydroxy end groups are highly reactive alkylating agents for N-alkylimidazoles, thus enabling the incorporation of alkylimidazolium cations with tosylate counteranions as outer shell of the treelike FG-PEHO graft copolymer. In sharp contrast to FG, treelike FG-PEHO containing methylimidazolium tosylates as shell are readily dispersed in water to form stable dispersions without requiring either surfactant addition or high shear mixing. Moreover, these novel carbon/polymer hybrid materials self-assemble on surfaces and form films. In view of the facile tuning of their structures and properties, such treelike graphene polyelectolytes qualify for manifold applications.

Oligonorbornenes with Hammock‐Like Crown Ether Pendants as Artificial Transmembrane Ion Channel

Trimeric oligonorbornenes with hammock-like crown ether pendants 3b and 3c were selectively synthesized by cascade metathetical cyclopolymerization upon treatment with the first generation Grubbs catalyst. These crown-ether-containing oligonorbornenes are impregnated in egg yolk phosphatidylcholine (EYPC) liposome as an artificial ion channel. The efficiency of the sodium ion transport properties has been examined. Oligomer 3c having a polar hydroxy end group exhibits the highest transport efficiency, which is comparable with the best efficiencies reported in literature. The orientation of the crown ether moieties in these oligomers may be critical for the ion transport properties.