Functional End Groups Research Articles

Functionalized Biodegradable Polymers via Termination of Ring-Opening Polymerization by Acyl Chlorides

Aliphatic polyesters are an important class of polymeric materials for biomedical applications due to their versatile and tunable chemistry, biocompatibility and biodegradability. A capability of direct bonding with biomedically significant molecules, provided by the presence of the reactive end functional groups (FGs), is highly desirable for prospective polymers. Among FGs, N-hydroxysuccinimidyl activated ester group (NHS) and maleimide fragment (MI) provide efficient covalent bonding with –NH– and –SH containing compounds. In our study, we found that NHS- and MI-derived acyl chlorides efficiently terminate living ring-opening polymerization of ε-caprolactone, L-lactide, ethyl ethylene phosphonate and ethyl ethylene phosphate, catalyzed by 2,6-di-tert-butyl-4-methylphenoxy magnesium complex, with a formation of NHS- and MI-functionalized polymers at a high yields. Reactivity of these polymers towards amine- and thiol-containing model substrates in organic and aqueous media was also studied.

Synthesis of end group-functionalized PGMA-peptide brush platforms for specific cell attachment by interface-mediated dissociative electron transfer reversible addition-fragmentation chain transfer radical (DET-RAFT) polymerization

Polymer brush synthesis is a powerful approach to fabricate functional bio-interfaces. To enhance the control over brush synthesis and end groups, we have synthesized poly(glycidyl methacrylate) PGMA brushes with carboxylic acid end functional groups by interface-mediated dissociative electron transfer reversible addition-fragmentation chain transfer radical (DET-RAFT) polymerization on titanium surfaces. This method does not require the use of metals and occurs under mild conditions. The brushes obtained were analyzed comprehensively in order to understand how to control cell attachment behavior. The PGMA brushes synthesized by DET-RAFT polymerization were characterized by X-ray photoelectron spectroscopy (XPS), grazing angle Fourier transform infrared (GA-FTIR) spectroscopy, water contact angle measurements and variable angle spectroscopic ellipsometry. The terminal carboxylic acid functional groups were covalently conjugated with arginine-glycine-aspartic acid (RGD) and arginine-alanine-aspartic acid (RAD, negative control) peptides in one step. RGD selective attachment of NIH 3T3 fibroblasts was observed exclusively on PGMA-RGD brushes. Thus, a new versatile strategy has been validated to obtain functional biointerfaces for selective cell attachment in the absence of any metallic catalyst.

Kinetic importance of the missing step in dithiobenzoate-mediated RAFT polymerizations of acrylates

The effect of retardation exhibited in dithiobenzoate-mediated polymerizations is perhaps the most controversial kinetic phenomenon discussed in polymer chemistry in the last 20 years. However, the Missing Step reaction (MSR), which involves the termination between a propagating radical and a 3-arm star product, has emerged as a hypothesis to explain the full kinetic picture for acrylate polymerizations. Here, a kinetic model, the most detailed of its kind, is developed to describe and study the MSR. The model is based on the method of moments and includes RAFT pre-equilibrium and equilibrium, backbiting, cross-termination, MSR and chain-length dependent radical termination. After validation through comparison with experimental data available in the literature, the model is used to demonstrate that the kinetic behavior of the propagating and intermediates radicals can be described by the quasi-steady state assumption and that backbiting does not significantly influence predicted conversion profiles and product molecular weights. It is also shown that the induction period observed experimentally can be represented by either slow initiation/reinitiation of primary radicals or by assuming that radical intermediates formed by addition of primary radicals to the RAFT agent have increased stability; however, the associated rate constants for these reactions had to be adjusted from literature values. A comparison between the MSR and Intermediate Radical Termination (IRT) representations RAFT-mediated acrylate polymerization identifies chain end-group functionality (EGF) as a means to further discriminate between these theories.

Application of low-grade recyclate to enhance reactive toughening of poly(ethylene terephthalate)

This paper presents a new recognition in reactive toughening of poly(ethylene terephthalate) (PET), namely the major effect of the molecular weight of PET on the evolution of the compatibilization and crosslinking reactions with ethylene‑butyl acrylate-glycidyl methacrylate (EBA-GMA) type reactive terpolymer, and thus indirectly on its toughening efficiency. It was found that the use of highly degraded recycled PET (rPET) grades, due to the available larger number of reactive functional end groups and increased mobility of the decreased-molecular-weight chains, multiplies the impact strength of the product compared to that of original PET (oPET) with identical EBA-GMA contents. The evinced noticeable difference between the toughening behaviour of rPET and oPET is explained by morphological and interfacial factors and connected to differences in rheological behaviour as well. The reactive oligomeric rPET macromolecules form a Toughening Enhancer Interphase (TEI) around the dispersed particles. Based on systematic analyses, conclusions were drawn regarding the quality, i.e. optimal intrinsic viscosity (IV) range, and quantity of rPET to be used to obtain high-impact-strength PET blends (notched Izod impact strength higher than 40 kJ/m2) with optimised mechanical properties, being suitable even for injection moulding applications, at significantly lower terpolymer contents (10.0–12.5 wt%) than expected. Besides, the proposed new way of utilisation of PET recyclates, especially the unmarketable highly degraded fractions, is believed to give a new driving force in PET recycling.

Bio-based ABA triblock copolymers with central degradable moieties

A set of (poly-α-methylene-γ-butyrolactone)–co-(poly-δ-decalactone)–co-(poly-α-methylene-γ-butyrolactone) (PMBL-co-PDL-co-PMBL) ABA block copolymers containing different stimuli cleavable groups at the central point of the poly(δ-decalactone) (PDL) block were synthesized by a combination of Ring Opening Transesterification Polymerization (ROTEP) of DL, diol end-group functionalization as α-bromoester and Atom Transfer Radical Polymerization (ATRP) of α -methylene-γ-butyrolactone (MBL). Diols containing acetal, spiroacetal, thioacetal and disulphide units were used as initiators for the bulk room temperature controlled polymerization of δ-decalactone (DL) using 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as catalyst. PDL diols were functionalized in a one-pot two-steps procedure using N-(2-bromoisobutyryl)imidazole (BiB-Im). The resulting macroinitiators were chain extended by atom transfer radical polymerization (ATRP) in DMF at 50 °C using MBL as methacrylic-like monomer and the conventional CuCl/CuCl2/2,2′-bipyridine catalyst system. The cleavage behaviour of the copolymers under reductive, acidic and photooxidative conditions has been studied and the resulting AB block copolymers structurally characterized.

Preparation and characterisation of liquid epoxidised natural rubber in latex stage by chemical degradation

Preparation and characterisation of liquid epoxidised natural rubber in latex by chemical degradation was successfully carried out. The effect of certain parameters, such as surfactant concentrations, incubation time of ENR latex in the presence of surfactant and pH condition on the reaction efficiency were studied. Effect of degrading agent concentrations and drying temperatures of LENR were also investigated. The molecular weight, i.e., Mw and Mn, which was determined by gel permeation chromatography (GPC) and gel content of LENR were decreased gradually as the degrading agent concentrations increased. Moreover, the drying temperatures, ranging from 333 to 423 K showed no significant changes in epoxidation levels and epoxy derivatives, as the drying period decreased from 24 to 4 h. The resulting LENR were further characterised using Fourier transform infra-red (FTIR) spectroscope, nuclear magnetic resonance (NMR) spectroscope, differential scanning calorimeter (DSC) and field emission-scanning electron microscope (FE-SEM). The glass transition temperature, Tg of LENR, i.e., 252 K was increased compared with ENR, i.e., 248 K. Besides, the latex particles morphology of LENR were found to be more uniform and larger compared with ENR. The functional groups such as carbonyl as functional end group, hydroxyl, epoxy, ester and furan groups were increased after degradation of ENR to form LENR. This indicates that the presence of functional polar groups at the LENR backbone play an important role which brings about the distinguished characters and properties of LENR.

Recent Advances in 3D Printing of Polyhydroxyalkanoates: A Review

Abstract In the 21st century, additive manufacturing technologies have gained in popularity mainly due to benefits such as rapid prototyping, faster small production runs, flexibility and space for innovations, non-complexity of the process and broad affordability. In order to meet diverse requirements that 3D models have to meet, it is necessary to develop new 3D printing technologies as well as processed materials. This review is focused on 3D printing technologies applicable for polyhydroxyalkanoates (PHAs). PHAs are thermoplastics regarded as a green alternative to petrochemical polymers. The 3D printing technologies presented as available for PHAs are selective laser sintering and fused deposition modeling. Stereolithography can also be applied provided that the molecular weight and functional end groups of the PHA are adjusted for photopolymerization. The chemical and physical properties primarily influence the processing of PHAs by 3D printing technologies. The intensive research for the fabrication of 3D objects based on PHA has been applied to fulfil criteria of rapid and customized prototyping mainly in the medical area.

Influence of the addition of organo-montmorillonite nanofiller on cross-linking of polysiloxanes – FTIR studies

The main aim of the present work was to investigate the effect of organo-montmorillonite nanofiller on the cross-linking process of polysiloxane. Two series of model polysiloxane nanocomposites were prepared by incorporating organoclay at different amounts such as 0, 1, 2, 4, and 8 wt% in relation to the weight of the polymer matrix. Poly(methylhydrosiloxane) (PMHS) was cross-linked with two linear vinylsiloxanes of different chain lengths between functional end-groups through hydrosilylation. This reaction was carried out in the presence of Karstedt’s catalyst at equimolar ratios of reactive groups. Fourier-transform infrared (FTIR) spectroscopic measurements obtained during the cross-linking processes as well as for the reaction products revealed that the rate of hydrosilylation and its efficiency are influenced by the type of the cross-linking agent used and the amount of organo-montmorillonite introduced into the polysiloxane network. Quantitative analysis of the recorded FTIR spectra showed that as the amount of nanofiller in the polysiloxane matrix increased, the rate and efficiency of the cross-linking process decreased. Swelling measurements confirmed that the increase in the amount of unreacted Si-H groups in the system resulted in a lower cross-link density of the studied materials. Furthermore, X-ray diffraction and transmission electron microscopy were performed to determine the nature of dispersion of organoclay within the studied systems.

Wertheim's thermodynamic perturbation theory with double-bond association and its application to colloid-linker mixtures.

We extend Wertheim's thermodynamic perturbation theory to derive the association free energy of a multicomponent mixture for which double bonds can form between any two pairs of the molecules' arbitrary number of bonding sites. This generalization reduces in limiting cases to prior theories that restrict double bonding to at most one pair of sites per molecule. We apply the new theory to an associating mixture of colloidal particles ("colloids") and flexible chain molecules ("linkers"). The linkers have two functional end groups, each of which may bond to one of several sites on the colloids. Due to their flexibility, a significant fraction of linkers can "loop" with both ends bonding to sites on the same colloid instead of bridging sites on different colloids. We use the theory to show that the fraction of linkers in loops depends sensitively on the linker end-to-end distance relative to the colloid bonding-site distance, which suggests strategies for mitigating the loop formation that may otherwise hinder linker-mediated colloidal assembly.

Polymorphic arrangement of an organic molecule in its hydration environment.

We investigate the polymorphism of complexes formed by the hydration of a functionalized azobenzene molecule by low-temperature scanning tunneling microscopy. Under conditions at which the water-less azobenzene molecules remain as monomers on Au(111), co-adsorption of water leads to water-azobenzene complexes. These complexes prefer to adopt linear arrangements of the azobenzene mediated by its functionalized end groups. Such structures may serve as model systems for investigating the influence of a solvent on a surface reaction.

Photoswitching of the melting point of a semicrystalline polymer by the azobenzene terminal group for a reversible solid-to-liquid transition

We report the photoswitching of the amorphization and the melting point of a semi-crystalline polymer through the introduction of end functional groups.

Solid electrolyte membranes prepared from poly(arylene ether sulfone)-g-poly(ethylene glycol) with various functional end groups for lithium-ion battery

A series of poly(arylene ether sulfone)-g-poly(ethylene glycol)s (PAES-g-PEG)s with different functional groups of –CH3, –OH, -2OH, and –CN were synthesized for the application of solid polymer electrolyte membranes in the lithium-ion battery. Several essential material and membrane properties, including thermal, mechanical, dimensional stability, lithium-ion conductivity, interfacial compatibility, Li-ion transference number, and cell performance, were investigated. The phase separation behavior in the presence of ionic liquid was also examined using small-angle X-ray scattering. As this provision of functional groups led to the suppression of crystallinity but the increment of dielectric permittivity of the electrolytes, both the lithium-ion conductivity and Li-ion transference number were significantly affected. Among them, the PAES-g-PEG membrane containing –CN end group showed the highest lithium-ion conductivity of 8.97 × 10−4 S cm−1 and the Li-ion transference number of tLi+ = 0.4, maintaining the rigid solid-state with the tensile strength beyond 1.5 MPa at room temperature. These excellent physical and electrochemical properties of solid-state electrolyte membranes led to quite a high cell capacity of over 138 mAh g−1 during the 50 charge-discharge cycling tests and stable lithium stripping/plating cyclic performance during 500 cycles.

A library of thermoresponsive PEG‐based methacrylate homopolymers: How do the molar mass and number of ethylene glycol groups affect the cloud point?

AbstractIn this study, a novel library of thermoresponsive homopolymers based on poly (ethylene glycol) (EG) (m)ethyl ether methacrylate monomers is presented. Twenty‐seven EG based homopolymers were synthesized and three parameters, the molar mass (MM), the number of the ethylene glycol groups in the monomer, and the chemistry of the functional side group were varied to investigate how these affect their thermoresponsive behavior. The targeted MMs of these polymers are varied from 2560, 5000, 8200 to 12,000 g mol−1. Seven PEG‐based monomers were investigated: ethylene glycol methyl ether methacrylate (MEGMA), ethylene glycol ethyl ether methacrylate (EEGMA), di(ethylene glycol) methyl ether methacrylate (DEGMA), tri(ethylene glycol) methyl ether methacrylate (TEGMA), tri(ethylene glycol) ethyl ether methacrylate (TEGEMA), penta(ethylene glycol) methyl ether methacrylate (PEGMA), nona(ethylene glycol) methyl ether methacrylate (NEGMA). Homopolymers of 2‐(dimethylamino) ethyl methacrylate (DMAEMA) were also synthesized for comparison. The cloud points of these homopolymers were tested in different solvents and it was observed that it decreases as the number of EG group was decreased or the MM increased. Interestingly, the end functional group (methoxy or ethoxy) of the side group has an effect as well and is even more dominant than the number of EG groups.

Comparison study on surface and thermo-chemical properties of PFPE lubricants on DLC film through MD simulations

Molecular dynamics simulations are performed using four types of PFPE lubricants (Zdol, Ztetraol, TA-30, and ZTMD) to investigate their spreadability, airshear behavior, surface contamination, and friction. The more functional end groups in PFPE lubricants the less spreadability on DLC surface, which agrees with the experimental results. The airshear simulation shows that the tangential shear movement of lubricants reduces as the number and the polar strength of functional end group increases. The higher temperature, the more shear displacement due to the increasing mobility. In HDI contact simulations, the PFPE lubricant with more and stronger functional end groups results in higher friction force and less head contamination by lubricant transfer. The higher temperature, the more head contamination but lower friction force.

Roadmap for Monomer Conversion and Chain Length-Dependent Termination Reactivity Algorithms in Kinetic Monte Carlo Modeling of Bulk Radical Polymerization

Radical polymerization is prone to diffusional limitations on termination, leading to a rate acceleration by the gel-effect and molecular changes, with strong increases in average chain length in free radical polymerization (FRP) and improvement of the end-group functionality in reversible deactivation radical polymerization. What complicates the correct implementation of the termination rates in kinetic modeling studies is (i) the chain length and monomer conversion dependence of the individual (apparent) termination rate coefficients (k(t,app,ij) values; i,j: chain length) and (ii) the wide variations in macroradical chain length distribution (CLD) types and shapes along the polymerization and upon altering the reaction conditions, including variations in CLD modality and broadness. In this work, we compare four major kinetic Monte Carlo modeling algorithms to sample termination reaction events in bulk radical polymerization, using literature k(t,app,ij) values. We present a roadmap allowing one to select the most suited algorithm depending on the radical polymerization technique and reaction conditions, therefore opening the pathway to more correct representations of chain length and monomer conversion dependencies in radical polymerization. Case studies are related to bulk nitroxide-mediated polymerization, FRP, and pulsed laser polymerization, following an increasing complexity in the active macroradical CLD type and shape.

Development of Flame Retarding Separator for Lithium Ion Battery By Crosslinkable Binder Coating

Conventional polyolefin separators undergo thermal shrinkage under abnormal conditions such as overcharging and overheating, and this may induce catastrophic thermal runaway in LIBs, resulting in gas venting, fire, rupture, or explosion. Ceramic-coated separators (CCSs) have been widely used because inorganic materials with high heat resistance protect the polyolefin surface to prevent thermal shrinkage of the separator. However, without the use of highly adhesive and thermally stable polymeric binders, the ceramic coating layer is incapable of functioning properly to maintain the thermal stability of the CCSs when exposed to heat.As one method for securing the thermal stability of the separator, we propose crosslinking of the binder in the ceramic coating layer. This study presents a thermally stable crosslinkable silsesquioxane-based ceramic-coated separator (x-CCS) with flame-retarding capabilities for the fabrication of safe Li-ion batteries. The binder used for crosslinking is ePOSS (inorganic polyhedral oligomeric silsesquioxane with epoxy functional end groups) with high thermal stability, which can form crosslinks with each other through UV irradiation. The x-CCS was fabricated by applying a 3 μm thick composite layer of Al2O3/ePOSS/PVdF-HFP to both sides of a conventional polyethylene separator. This remarkably improved the thermal stability of the separator at 140°C, with the original form of the separator maintained even after an ignition test. Because ePOSS, which has high thermal stability, is crosslinked like a net in the coating layer and maintains its shape after combustion. Although the permeability of the CCS was slightly decreased by the applied coating, the resultant improved wettability towards liquid electrolyte thereby enhancing the ionic conductivity, cycle performance, and rate capability when used in a Li-ion battery.

Enzymatic synthesis and characterization of muconic acid‐based unsaturated polymer systems

AbstractThe design of unsaturated aliphatic (co)polyester systems, based on different diester‐modified muconic acid isomers, was performed via an eco‐friendly pathway by utilizing enzymatic polymerization using Candida antarctica lipase B (CALB) as catalyst. The obtained fully unsaturated oligoesters and polyesters reached lower molecular weights from 2210 to 2900 g mol−1 for the cis,cis‐(Z,Z)‐muconate isomer, and higher molecular weights of up to 21 200 g mol−1 for the polymers with cis,trans‐(Z,E) isomeric structures. The obtained (co)polyesters were thoroughly characterized and compared with their saturated polyester analogues. The applied biobased catalyst Novozym®435 (an immobilized form of CALB) showed higher selectivity towards the open cis,trans‐muconate compared to the more closed‐structure cis,cis‐muconate. Results of 1H NMR analysis showed that alkene functionality is present, and no stereo conformational changes were detected in the resulting polymers. The thermal properties of the muconate‐based polyesters showed a glass transition between −7 and 12 °C, and a one‐step degradation process with a maximum rate of weight loss between 415 and 431 °C, depending both on the conformation of the applied diester derivatives and on the segment lengths of the polyoxyalkylenes. Mass spectrometric analysis of the resulting saturated and unsaturated polyesters revealed five different microstructures with different terminal end groups, such as ester/hydroxyl, acid/ester, ester/ester and acid/hydroxyl, and cyclic polyesters without functional end groups. Overall, this study demonstrates that enzymatic polymerization is a robust approach for the synthesis of unsaturated polyesters. © 2020 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Industrial Chemistry.

Star-shaped polycaprolactone bearing mussel-inspired catechol end-groups as a promising bio-adhesive

The catechol groups in mussel adhesive proteins exhibit excellent adhesion property to the skin and tissue surfaces. Inspired by catechol groups, the aim of this study is to synthesize the star-shaped polycaprolactone bio-adhesive bearing catechol end-groups (s-PCL19-CA9). Firstly, star-shaped polycaprolactone was synthesized through ring-opening polymerization of caprolactone monomers initiated by β-cyclodextrin, and then the s-PCL19-CA9 was obtained through end-group functionalization using succinic anhydride and dopamine. The structure of s-PCL19-CA9 was characterized by 1H NMR, FTIR, and static light scattering. Adhesive strength measurements demonstrate that the incorporation of multifunctional catechol groups endows the crosslinked s-PCL19-CA9 with an excellent adhesion property (102 ± 10 kPa). The swelling ratio of crosslinked s-PCL19-CA9 is as low as 3.4 ± 0.2% owing to the hydrophobicity of PCL and the crosslinking structures. Besides, the cytotoxicity studies show that s-PCL19-CA9 is noncytotoxic. The TGA measurements indicate that s-PCL19-CA9 possesses a good thermal stability. Therefore, this work provides a new way for developing multifunctional bio-adhesives with excellent adhesion property and low swelling ratio.

Open-to-Air RAFT Polymerization on a Surface under Ambient Conditions.

Oxygen (O2)-mediated controlled radical polymerization was performed on surfaces under ambient conditions, enabling on-surface polymer brush growth under open-to-air conditions at room temperature in the absence of metal components. Polymerization of zwitterionic monomers using this O2-mediated surface-initiated reversible addition fragmentation chain-transfer (O2-SI-RAFT) method yielded hydrophilic surfaces that exhibited anti-biofouling effects. O2-SI-RAFT polymerization can be performed on large surfaces under open-to-air conditions. Various monomers including (meth)acrylates and acrylamides were employed for O2-SI-RAFT polymerization; the method is thus versatile in terms of the polymers used for coating and functionalization. A wide range of hydrophilic and hydrophobic monomers can be employed. In addition, the end-group functionality of the polymer grown by O2-SI-RAFT polymerization allowed chain extension to form block copolymer brushes on a surface.

Hetero-Diels-Alder Cycloaddition with RAFT Polymers as Bioconjugation Platform.

We introduce the bioconjugation of polymers synthesized by RAFT polymerization, bearing no specific functional end group, by means of hetero‐Diels–Alder cycloaddition through their inherent terminal thiocarbonylthio moiety with a diene‐modified model protein. Quantitative conjugation occurs over the course of a few hours, at ambient temperature and neutral pH, and in the absence of any catalyst. Our technology platform affords thermoresponsive bioconjugates, whose aggregation is solely controlled by the polymer chains.