Well-defined Functional Polymers Research Articles

Synthesis, characterization and thermal degradation kinetics of a new pyrazole derived methacrylate polymer, poly(1,3-diphenyl-1H-pyrazol-5-yl methacrylate).

A new pyrazole derived methacrylate monomer, 1,3-diphenyl-1H-pyrazol-5-yl methacrylate, was synthesized from the reaction of 1,3-diphenyl-5-pyrazolone with methacryloyl chloride in the presence of triethylamine. After that, its homopolymerization was carried out by free radical polymerization method at 60 °C initiated with benzoyl peroxide. Spectral characterizations were achieved by 1H-NMR andFTIR spectroscopies. The kinetics of thermal degradation of the new polymer, poly(1,3-diphenyl-1H-pyrazol-5-yl methacrylate), poly(DFPMA), were investigated by thermogravimetric analysis (TGA) at different heating rates. The initial decomposition temperature of the polymer changed from 216.3 °C to 243.5 °C depending on the increasing heating rate. The thermal decomposition activation energies in a conversion range of 7-19% were 79.45 kJ/mol and 81.56 kJ/mol by the Flynn-Wall-Ozawa and Kissinger methods, respectively. Thermodegradation mechanism of the poly(DFPMA) were investigated in detail by using different kinetic methods available in the literature such as Coats-Redfern, Tang, Madhusudanan and Van Krevelen. Among all these methods, the best result was obtained for Coats-Redfern method (E =90.93 kJ/mol) at the optimum heating rate of 15 °C/min for D1 mechanism. That means the thermodegradation mechanism of poly(DFPMA) proceeds over a one-dimensional diffusion type deceleration mechanism.

RAFT-Based Polymers for Click Reactions.

The parallel development of reversible deactivation radical polymerization and click reaction concepts significantly enriches the toolbox of synthetic polymer chemistry. The synergistic effect of combining these approaches manifests itself in a growth of interest to the design of well-defined functional polymers and their controlled conjugation with biomolecules, drugs, and inorganic surfaces. In this review, we discuss the results obtained with reversible addition–fragmentation chain transfer (RAFT) polymerization and different types of click reactions on low- and high-molar-mass reactants. Our classification of literature sources is based on the typical structure of macromolecules produced by the RAFT technique. The review addresses click reactions, immediate or preceded by a modification of another type, on the leaving and stabilizing groups inherited by a growing macromolecule from the chain transfer agent, as well as on the side groups coming from monomers entering the polymerization process. Architecture and self-assembling properties of the resulting polymers are briefly discussed with regard to their potential functional applications, which include drug delivery, protein recognition, anti-fouling and anti-corrosion coatings, the compatibilization of polymer blends, the modification of fillers to increase their dispersibility in polymer matrices, etc.

Oxygen-Tolerant RAFT Polymerization Catalyzed by a Recyclable Biomimetic Mineralization Enhanced Biological Cascade System.

An enzyme cascade system including glucose oxidase (GOx) and iron porphyrin (DhHP-6) is encapsulated in a metal-organic framework called zeolitic imidazolate framework-8 (ZIF-8) through one-step facile synthesis. The composite (GOx&DhHP-6@ZIF-8) is then used to initiate oxygen-tolerant reversible addition-fragmentation chain-transfer polymerization for different methacrylate monomers, such as 2-diethylaminoethyl methacrylate, 2-hydroxyethyl methacrylate, and poly(ethylene glycol) methyl ether methacrylate (Mn = 500g mol-1 ). The composite shows the robustness toward solvent and temperatures, all polymerizations using above monomers and catalyzing by GOx&DhHP-6@ZIF-8 exhibits high monomer conversion (>85%) and narrow molar mass dispersity (<1.3). Besides, acrylic and acrylamide monomers such as 2-hydroxyethyl acrylate and N,N-dimethylacrylamide are also carried to demonstrate the broad applicability. Proton nuclear magnetic resonance characterization and chain extension experiments confirm the retaining end groups of the resultant polymers, which is a significant feature of living polymerization. More importantly, the process of recycling the composite through a centrifuge is simplistic, and the composite still maintains similar activity compared to the original composites after five times. This low-cost and easily separated composite catalyst represents a versatile strategy to synthesize well-defined functional polymers suitable for industrial-scale production.

Facile Preparation of Well-Defined Uniform Hydrophilic Hairy Hollow Functional Polymer Micro- and Nanoparticles

A facile, general, and highly efficient strategy for preparing well-defined uniform hydrophilic hairy hollow functional polymer micro- and nanoparticles by combining RAFT polymerization techniques and sacrificial template method is described. Two synthetic routes have been developed for this purpose. The first route involves one-pot synthesis of uniform “living” poly(methacrylic acid) (PMAA) micro/nanospheres with surface-bound dithioester groups via RAFT precipitation polymerization (RAFTPP), their successive grafting of cross-linked functional polymer layers and hydrophilic polymer brushes via surface-initiated RAFT (SI-RAFT) polymerization, and rapid etching of the PMAA core by simply washing the resulting core-shell-corona-structured particles with methanol. Alternatively, such hairy hollow polymer particles can also be prepared by synthesis of uniform “living” hollow polymer particles (through controlled grafting of cross-linked functional polymer layers onto “living” PMAA particles prepared via RAFT...

A Facial Strategy for Catalyst and Reducing Agent Synchronous Separation for AGET ATRP Using Thiol-Grafted Cellulose Paper as Reducing Agent.

Atom Transfer Radical Polymerization (ATRP) has been a powerful tool to synthesize well-defined functional polymers, which are widely used in biology, drug/gene delivery and antibacterial materials, etc. However, the potential toxic residues in polymer reduced its service life and limited its applications. In order to overcome the problem, in this work, a novel polymerization system of activators generated by electron transfer for atom transfer radical polymerization (AGET ATRP) for synchronous separation of the metal catalyst and byproduct of reducing agent was developed, using thiol-grafted cellulose paper (Cell-SH) as a solid reducing agent. The polymerization kinetics were investigated in detail, and the “living” features of the novel polymerization system were confirmed by chain-end analysis and chain extension experiment for the resultant polymethyl methacrylate (PMMA). It is noted that the copper residual in obtained PMMA was less than 20 ppm, just by filtering the sheet-like byproduct of the reducing agent.

One-Enzyme Triple Catalysis: Employing the Promiscuity of Horseradish Peroxidase for Synthesis and Functionalization of Well-Defined Polymers

We demonstrate a new concept in polymer chemistry that the promiscuity of enzymes, as represented by horseradish peroxidase, can be employed for RAFT polymerization and thiol-ene and Diels-Alder reactions to synthesize well-defined functional polymers, via three different catalytic reactions mediated by one single enzyme.

Well-defined single-chain polymer nanoparticles via thiol-Michael addition

A synthetic strategy has been developed giving facile access to well-defined single-chain polymer nanoparticles (SCNPs) from styrene-, acrylate- and methacrylate-based polymers. Random copolymers (polydispersity indices 1.10–1.15) of methyl (meth)acrylate, benzyl methacrylate or styrene containing protected thiol monomers (xanthate and thioacetate vinyl monomers) were obtained via reversible addition–fragmentation chain transfer (RAFT) polymerization. Through aminolysis of the xanthate and thioacetate moieties, copolymers with free thiol moieties were obtained. The thiol bearing polymers were cross-linked with bifunctional acrylates under mild conditions. Precursor polymer dependent size-reductions between 30 and 90% were verified by gel permeation chromatography (GPC) measurements. Furthermore, the SCNPs were characterized by 1H NMR, atomic force microscopy (AFM) and dynamic light scattering (DLS). Characteristic patterns for SCNPs were observed in the AFM phase mode. Thiol-Michael addition is demonstrated to be a versatile tool, which can easily be employed in the preparation of versatile well-defined functional polymer nanoparticles in the 3–10 nm size range.

A CTA-shuttled R-group approach: a versatile synthetic tool towards well-defined functional cylindrical polymer brushes via RAFT polymerization

We report a novel three-step strategy toward polyCTA for the synthesis of cylindrical polymer brushes via “CTA-shuttled” RAFT R-approach polymerization. Post functionalizations on the CTA residue are also discussed.

Tetrazine-Mediated Postpolymerization Modification

A new and highly efficient polymer, postpolymerization, modification platform based on an inverse electron demand Diels–Alder reaction is reported. Well-defined polymers were synthesized from allyl glycidyl ether and glycidol by anionic ring-opening polymerization with postpolymerization modifications conducted with a number of tetrazine derivatives that carried functional groups spanning from carboxylates and esters to primary amines. Analysis of polymerization kinetics by real-time 1H NMR, and GPC revealed a rapid and high degree of side-chain conversion (>99%), with the generation of well-defined functional polymers, in both organic and aqueous solvents, without the need for additives or catalysts.

Polymer Functional Nanodiamonds by Light-Induced Ligation

A light-triggered strategy to functionalize nanodiamonds (NDs) with well-defined functional polymers is presented. The employed grafting approach is based on o-methylbenzaldehydes, which upon UV irradiation form o-quinodimethanes that undergo Diels–Alder reactions with dienophiles. A series of well-defined maleimide end-group functional polymers, i.e., poly(styrene) (Mn = 5800 g mol–1; Đ = 1.2), poly(N-isopropylacrylamide) (Mn = 5800 g mol–1, Đ = 1.2), and poly(2-(2′,3′,4′,6′-tetra-O-acetyl-α-d-mannosyloxy)ethyl methacrylate) (Mn = 24 300, 39 000, and 58 800 g mol–1, Đ ≤ 1.3), were prepared via reversible addition–fragmentation chain transfer (RAFT) polymerization of protected maleimide functional RAFT agents. After deprotection of the furan-protected maleimide end groups, the polymers were photografted to o-methylbenzaldehyde functional NDs and characterized in detail via infrared (IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). The grafting density decreas...

Synthesis of well-defined catechol polymers for surface functionalization of magnetic nanoparticles

Well-defined fluorescent functional polymers with terminal catechol groups were synthesized by SET-LRP under aqueous conditions for “grafting to” modification of iron oxide nanoparticles.

Micelle stabilization via entropic repulsion: balance of force directionality and geometric packing of subunit.

Nanoparticles, 10-30 nm in size, have shown great prospects as nanocarriers for drug delivery. We designed amphiphiles based on 3-helix peptide-PEG conjugate forming 15 nm micelles (defined as "3-helix micelles") with good in vivo stability. Here, we investigated the effect of the site of PEG conjugation on the kinetic stability and showed that the conjugation site affects the PEG chain conformation and the overall molecular architecture of the subunit. Compared to the original design where the PEG chain is located in the middle of the 3-helix bundle, micelle kinetic stability was reduced when the PEG chain was attached near the N-terminus (t(1/2) = 35 h) but was enhanced when the PEG chain was attached near the C-terminus (t(1/2) = 80 h). Quantitative structural and kinetic analysis suggest that the kinetic stability was largely dictated by the combined effects of entropic repulsion associated with PEG chain conformation and the geometric packing of the trimeric subunits. The modular design approach coupled with a variety of well-defined protein stucture and functional polymers will significantly expand the utility of these materials as nanocarriers to meet current demands in nanomedine.

Multicomponent Polymerization System Combining Hantzsch Reaction and Reversible Addition-Fragmentation Chain Transfer to Efficiently Synthesize Well-Defined Poly(1,4-dihydropyridine)s.

A novel multicomponent system has been constructed through the combination of Hantzsch reaction and reversible addition-fragmentation chain transfer (RAFT) polymerization in a one-pot manner. Compared to traditional stepwise methods, this one-pot system exhibits much more advantages to facilely and efficiently prepare well-defined poly(1,4-dihydropyridine)s (poly(1,4-DHP)s). A series of poly(1,4-DHP) derivatives have also been successfully prepared through this Hantzsch-RAFT system using different aldehydes as reactants, suggesting this system is a general and versatile approach to prepare well-defined functional polymers with 1,4-DHPs as side groups. Since 1,4-DHP derivatives are an important class of bioactive molecules in the pharmaceutical field, this simple method to prepare poly(1,4-DHP)s might have potential to prepare related functional polymers for biological and pharmaceutical applications.

‘One pot’ synthesis of well-defined poly(aminophosphonate)s: time for the Kabachnik–Fields reaction on the stage of polymer chemistry

A multicomponent reaction (MCR) has been carried out on the platform of controlled radical polymerization (CRP) to construct a ‘one pot’ MCR-CRP system for the facile preparation of well-defined functional polymers. In the current work, a novel ‘one pot’ system has been built through a combination of the Kabachnik–Fields (KF) reaction and reversible addition fragmentation chain transfer (RAFT) polymerization. Compared to a traditional stepwise method and polymer post-polymerization modification, this novel ‘one pot’ system exhibited distinct advantages to much more facilely and efficiently prepared well-defined poly(aminophosphonate)s (polyAPPs). A series of unique polyAPPs have also been successfully prepared through this KF–RAFT system, suggesting this novel method is a general and versatile approach to prepare well-defined organophosphorous polymers.

Controlled Radical Polymerization and Quantification of Solid State Electrical Conductivities of Macromolecules Bearing Pendant Stable Radical Groups

Macromolecules with aliphatic backbones that bear pendant stable radical groups (i.e., radical polymers) have attracted much attention in applications where a supporting electrolyte is capable of aiding charge transport in solution; however, the utilization of these materials in solid state applications has been limited. Here, we synthesize a model radical polymer, poly(2,2,6,6-tetramethylpiperidinyloxy methacrylate) (PTMA), through a controlled reversible addition-fragmentation chain transfer (RAFT) mediated polymerization mechanism to generate well-defined and easily-tunable functional polymers. These completely amorphous, electronically-active polymers demonstrate relatively high glass transition temperatures (Tg ∼170 °C) and, because of the aliphatic nature of the backbone of the radical polymers, are almost completely transparent in the visible region of the electromagnetic spectrum. Additionally, we quantify the conductivity of PTMA (∼1×10(-6) S cm(-1)) and find it to be on par with pristine π-conjugated polymers such as poly(phenylene vinylenes) (PPVs) and poly(3-alkylthiophenes) (P3ATs). Furthermore, we demonstrate that the addition of small molecules bearing stable radical groups provides for more solid state charge hopping sites without altering the chemical nature of radical polymers; this, in turn, allows for an increase in the conductivity of PTMA relative to neat PTMA thin films while still retaining the same high degree of optical transparency and device stability. Because of the synthetic flexibility and easily-controlled doping mechanisms (that do not alter the PTMA chemistry), radical polymers present themselves as promising and tunable materials for transparent solid-state plastic electronic applications.

Reactive thiol-ene emulsion-templated porous polymers incorporating pentafluorophenyl acrylate

Highly porous polymers (polyHIPEs) incorporating activated esters have been prepared by photopolymerisation of high internal phase emulsions (HIPEs) containing pentafluorophenyl acrylate (PFPA) in the monomer phase. The resulting materials have nominal porosity of 80% and a well-defined, interconnected pore morphology with average pore diameters ranging from 30 to 50 μm. PFPA could be added at up to 50 wt% of the monomer phase without destabilising the HIPE noticeably, however analysis of the polyHIPE materials revealed that only around half of this was incorporated into the final porous materials. The pentafluorophenyl groups were shown to be reactive towards a range of amines (tris-(2-aminoethyl)amine, benzylamine and Rhodamine 123), giving near complete loss of fluorine over the period of the reaction. The extent of functionalisation was however determined to be around 50% by elemental analysis, suggesting some loss of fluorine by hydrolysis of activated esters. We believe that this represents a facile method for the preparation of a variety of well-defined functional porous polymers by a post-polymerisation functionalisation route.

Synthesis of Diverse Well-Defined Functional Polymers Based on Hydrozirconation and Subsequent Anti-Markovnikov Halogenation of 1,2-Polybutadiene

For the first time, hydrozirconation and halogenolysis of 1,2-polybutadiene (1,2-PBD, by living anionic polymerization) were studied to synthesize reactive poly-halohydrocarbons, which provide a platform for preparing well-defined functional polymers via macromolecular substitution. Hrirozirconation and halogenolysis afforded quite convenience for anti-Markovnikov hydrohalogenation of 1,2-PBD with controllable degree of functionalization. Diverse functional polymers and branched polymers were synthesized after macromolecular substitution reaction with a broad range of commercially available nucleophiles (amines, phenols, alcohols, carbanions, carboxylates, and azide) or macromolecular nucleophiles. NMR and GPC characterizations confirmed high conversion in substitution reaction and narrow molecular weight distribution of the resultant functional polymers, respectively. The methodology utilizing Schwartz's reagent for hydrozirconation of macromolecules could greatly facilitate the modification of vinyl groups containing polymers with high efficiency.

Stimuli-responsive star polymers through thiol–yne core functionalization/crosslinking of block copolymer micelles

Thiol–yne photochemistry is applied in a convenient non-“click” fashion to produce well-defined functional star polymers in water.

Synthesis and use of a new alkene-functionalized SG1-based alkoxyamine

A new alkene-functionalized SG1-based alkoxyamine was synthesized and used to prepare well-defined functional polymers by nitroxide mediated polymerization. The latter were characterized by NMR, SEC and MALDI-TOF mass spectrometry. Livingness was assessed by chain extension toward AB-type block copolymer. The alkene functionality located at the α-chain-end allowed the post-modification of the polymer by thiol–ene coupling reaction.

Design, syntheses and evaluation of hemocompatible pegylated-antimicrobial polymers with well-controlled molecular structures

In this paper, we have designed and synthesized well-defined pegylated-polymers with tertiary amines from readily available commodity monomers 2-(dimethylamino)ethyl methacrylate (DMAEMA) and oligo(ethylene glycol) methyl ether methacrylate (OEGMA, M n ∼ 475 Da) by reversible addition–fragmentation chain transfer (RAFT) polymerisation. By employing a simple and efficient post-polymerisation functionalization strategy, tertiary amines were quaternized to result in cationic polymers. By the careful selection of the functional halide, X–(CH 2) q–R, (where in X = halide; R = the chemical functionality; q = the number of alkyl spacer between the quaternary ammonium group and R), a series of polymers with well-controlled molecular weight, different amphiphilic balance and chemical functionalities (such as alkyl, primary alcohol, primary amine and carboxylic acid) were readily synthesized. The antimicrobial activities of these cationic polymers were determined against Gram-positive bacteria Bacillus subtilis. Minimum inhibitory concentration (MIC), the polymer concentration to completely inhibit the bacterial growth, was found to be dependent both on the nature of functional group and the hydrophobicity of the polymer. Amongst the functional groups, both the alkyl and the alcohol groups were found to be effective, with MIC values in the range of 20–80 mg/L. The haemolytic properties of polymers were analyzed against mouse red blood cells. The poymers with a short alkyl or hydroxyl group demonstrated little haemolysis, yet retained strong antimicrobial activity. The overall hydrophobicity of the polymer influenced its haemolytic behavior. These polymers can be promising antimicrobial agents. In addition, the approach proposed in this study to atom-efficient design and synthesis of antimicrobial polymers from the commercially available monomers can also be applied to develop well-defined functional cationic polymers for various biomedical applications.