Chain End Groups Research Articles

Valencene as a naturally occurring sesquiterpene monomer for radical copolymerization with maleimide to induce concurrent 1:1 and 1:2 propagation

Valencene, a naturally occurring sesquiterpene that can be obtained from various citrus fruits, was copolymerized as an unconjugated 1,1-disubstituted bulky vinyl monomer by radical copolymerization with conjugated monomers possessing electron-withdrawing substituents, such as maleimides, acrylates, methacrylates, acrylonitrile, and methacrylonitrile, in toluene and PhC(CF3)2OH. The fluorinated alcohol increased the copolymerizability, as in the radical copolymerization of other unconjugated non-polar olefins with those electron-acceptor comonomers. In particular, the copolymerization of valencene and N-phenylmaleimide in PhC(CF3)2OH proceeded via concurrently occurring 1:1 and 1:2 propagation, in which the monomer reactivity ratio of maleimide and valencene to the maleimide radical with the penultimate valencene unit was close to 1 according to a kinetic analysis of the copolymerization based on the penultimate model. Therefore, the copolymerizability of valencene was higher than that of limonene, which is a similar unconjugated 1,1-disubstituted vinyl monomer with a smaller cyclohexenyl substituent that undergoes selective 1:2 radical copolymerization with maleimide derivatives under the same conditions. Reversible addition-fragmentation chain transfer RAFT copolymerization using a trithiocarbonate resulted in copolymers with controlled molecular weights and chain-end groups. The biobased copolymers of valencene and N-phenylmaleimide showed relatively high glass transition temperatures (Tg) of approximately 220–240 °C and relatively high thermal stability with 5% decomposition temperatures (Td5) of approximately 330–340 °C due to their rigid main-chain structures.

Orthogonally "Clickable" Biodegradable Nanofibers: Tailoring Biomaterials for Specific Protein Immobilization.

Multifunctionalizable polymeric nanofibers can be tailored for various biomedical applications by selective conjugation of small molecules and bioactive ligands. This study reports the design, synthesis, and application of novel biodegradable polyester-based nanofibers bearing metal-free “clickable” handles. Polylactide-based polymers were synthesized using organo-catalyzed ring-opening polymerization to contain “clickable” chain-end functional groups that specifically react through radical or nucleophilic thiol–ene reactions. A furan-protected maleimide-containing hydroxyl-bearing initiator yielded polymers containing strained oxanorbornene unit at their chain end. In addition, postpolymerization thermal treatment provides maleimide end group-containing polymers. Solution electrospinning method was utilized to obtain bead-free nanofibers. Efficient conjugation on these nanofibers was demonstrated using metal-free conjugation reactions. It was observed that polylactide nanofibers undergo extensive biofouling, which limits their possible utilization for specific biomolecular immobilization. To alleviate this problem, polymers were modified to contain two orthogonally reactive functional groups, namely, the oxanorbornene unit and an azide group at their chain ends. The former reactive handle was used for conjugation of poly(ethylene glycol) chains to impart hydrophilicity and thus an antibiofouling ability, whereas the azide group undergoes strain-promoted azide–alkyne cycloaddition to install a protein-binding ligand such as biotin. These nanofibers were able to specifically immobilize the protein streptavidin with minimal nonspecific adsorption.

Reduced bond length alternation and helical molecular orbitals in donor and acceptor substituted linear carbon chains

Increasing chain length and end group substitution of polyynes play a crucial role in molecular electronics and nanomaterials. The studies on linear carbon chains are lesser when compared to other carbon allotropes like graphene, fullerenes, nanotube, etc. This prompted us to study the linear carbon chains of different lengths and substitutions. The electronic and optical properties of X–C[Formula: see text]–X ([Formula: see text]–15 and [Formula: see text], NH2, CN, OH) molecules have been studied by using CAM-B3LYP/6-31G* level of theory of DFT methods. Linear carbon chains with odd values of n show lower bond length alternation (BLA) values similar to that of cumulenes and may have metallic property, but the substitution of donor/acceptor molecules does not decrease the BLA significantly. Molecular orbital analysis of linear carbon chains shows that NH2 or NO2 substituted polyynes have helical molecular orbitals for smaller chain lengths which may make a good candidate for molecular wires in molecular devices. As the chain length increases, the helicity decreases and finally disappears. Also, it is seen that for smaller odd values of [Formula: see text] for donor, substituted polyynes have a singlet ground, whereas all the odd [Formula: see text] values of acceptor substitution have triplet ground state.

Developing a nontoxic and biocompatible polymeric self-assembly by using RAFT methodology for biomedical application

The amphiphilic block copolymer poly(N-vinylpyrrolidone)-b-poly(N-vinylcarbazole) (PVP-b-PVK) was synthesized by reversible-deactivation radical polymerization (RDRP)using reversible addition-fragmentation chain transfer (RAFT) methodology by new chain transfer agent (CTA) i.e. benzyl piperidine dithiocarbamate (BPDC). The pseudo-first-order kinetics and linear evolution of the molar mass with N-vinylpyrrolidone (NVP) conversion were obtained with the molar mass dispersity (Ð) 1.30–1.41 in toluene. 1H NMR spectrum indicates the presence of chain-end functional groups on homopolymer and block copolymer. The above block copolymer get self-assembled and form micelles in the aqueous medium, the size of micelles is characterized by 1H NMR, transmission electron micrographs (TEM) and dynamic laser light scattering (DLS) analyses, and critical micelles concentration (CMC) was determined by UV–vis spectroscopy. Trypan blue exclusion and MTT assay were done to ensure the cytotoxic effect of PVP-b-PVK on different types of normal cells (thymocytes, splenocytes and macrophage), and no cytotoxic effect was shown by block copolymer on cells, while observed biocompatibility with cells was 200 mg/mL. Further, the beads of block copolymer releases (65%) highly water-soluble levofloxacin drug up to 8 h in a controlled manner at pH 7.4 (37 ± 0.2 °C), while loading of levofloxacin drug was 62% (w/w).

Facile synthesis of ultrasmall polydopamine-polyethylene glycol nanoparticles for cellular delivery

Very small polydopamine (PDA) polyethylene glycol (PEG) crosslinked copolymer (PDA-PEG) nanoparticles have been prepared following a convenient one-step procedure in aqueous solution. Particle sizes and colloidal stabilities have been optimized by varying PEG in view of chain length and end group functionalities. In particular, amine-terminated PEG3000 [PEG3000(NH2)2] reacted with polydopamine intermediates so that very small, crosslinked PDA-PEG nanoparticles with sizes of less than 50 nm were formed. These nanoparticles remained stable in buffer solution and no sedimentation occurred. Chemical functionalization was straight-forward as demonstrated by the attachment of fluorescent dyes. The PDA-PEG nanoparticles revealed efficient cellular uptake via endocytosis and high cytocompatibility, thus rendering them attractive candidates for cell imaging or for drug delivery applications.

Alkyl Chain End Group Engineering of Small Molecule Acceptors for Non-Fullerene Organic Solar Cells

Alkyl chain engineering is widely used to prepare high-performance donor materials. However, relatively few studies have been focused on the alkyl chain optimization of acceptor materials. Herein, a series of new A–D–A (acceptor–donor–acceptor) type small molecule acceptors (ITBTR-C2, ITBTR-C4, ITBTR-C6, and ITBTR-C8) with indacenodithieno[3,2-b]thiophene (IDTT) as the core, benzothiadiazole (BT) as the π bridge, and ethyl-, butyl-, hexyl-, and octyl-substituted 2-(1,1-dicyanomethylene) rhodanine as the end groups, respectively, are successfully synthesized to systematically investigate the alkyl substituent effects on the physical, chemical, and electronic properties of A–D–A type small molecule acceptors. All molecules exhibit a strong and broad absorption from 600 to 800 nm as well as similar HOMO and LUMO energy levels. ITBTR-C6 with hexyl substitution shows the highest electron mobility and better phase separation morphology after blending with a donor polymer (PBDB-T). Therefore, inverted bulk heter...

Ethylene–co–norbornene copolymerization in the presence of a chain transfer agent

Ethylene (E)-co-norbornene (N) copolymerizations were conducted by using two ansa-metallocenes, isopropyliden(η5-cyclopentadienyl)(η5-indenyl)zirconium dichloride (1) and isopropyliden(η5-3-methylcyclopentadienyl)(η5-fluorenyl)zirconium dichloride (2), activated with dimethylanilinium tetrakis(pentafluorophenyl)borate, in presence of TIBA and variable amounts of Zn(Et)2 as a potential chain transfer agent (CTA). The study evaluated the effect of CTA on microstructure, molecular weight, chain end group and structural, thermal and mechanical properties of poly(E-co-N)s. The analysis of the data revealed that in all copolymerization reactions with metallocenes 1 and 2 in presence of diethyl zinc chain transfer to zinc alkyl occurs along with the typical chain transfers of E-co-N polymerization. The chain transfer to zinc alkyl is more efficient at low N content in copolymers. The two catalysts show different behavior in copolymerization at high N content: molar masses of copolymers produced by 2 are more affected by CTA concentration, that is, the chain shortening with increasing CTA content is greater in copolymers obtained with catalyst 2. The analysis of mechanical properties revealed that CTA affects the polymer chain structure. An increase of CTA caused a change of ductility, rigidity, and mechanical strength; chains produced in presence of Zn(Et)2 are, at least in part, characterized by segments produced as a result of exchange between different metal centers, possibly jointed through ethylene units.

Characterizations of radicals formed in radical polymerizations and transfer reactions by electron spin resonance spectroscopy

Abstract Electron spin resonance (ESR, aka electron paramagnetic resonance, EPR) investigations have been conducted on radicals formed during radical polymerizations and provide a detailed characterization of the active radical species. Active propagating radicals can be observed during actual radical polymerizations by ESR/EPR. The chain lengths of the observed radicals were estimated by a combination of atom transfer radical polymerization (ATRP) and ESR/EPR. The structures of the chain end radicals were determined by analysis of the ESR/EPR spectra. An increase in the dihedral angles between terminal p-orbital of radical and Cβ–H bonds was observed with increasing chain lengths of methacrylate polymers. Radical transfer reactions were observed during radical polymerization of acrylates. A combination of ATRP and ESR/EPR clarified a 1,5-hydrogen shift mechanism of the radical transfer reactions using model adamantyl acrylate radicals. Penultimate unit effects were also observed. Time-resolved ESR/EPR (TR ESR) spectroscopy clarified the initiation processes of an alternating copolymerization of styrene with maleic anhydride and the copolymerization of styrene with 1,3-butadiene. Several unsolved problems in conventional radical polymerization processes have been clarified using combinations of ATRP with ESR/EPR and TR ESR. Characterization of the radicals in radical polymerizations using various ESR techniques would definitely provide interesting and useful information on conventional radical polymerizations.

Micelles Protect Intact Metallo-supramolecular Block Copolymer Complexes from Solution to Gas Phase during Electrospray Ionization

Supramolecular diblock copolymers using metal-ligand coordination can be synthesized under ambient conditions by delicate design of the end groups of the homopolymer chains. However, mass spectrometric analysis of such metallo-supramolecular copolymers is challenging. One of the reasons is the nonpolarity of the polymer chains, making it hard to disperse the complexes in electrospray ionization (ESI)-friendly environments. The other difficulty is the noncovalent nature of such copolymers, which is easily disrupted during the ionization. Here, we demonstrate that the intact metallo-supramolecular diblock copolymers can be maintained sufficiently during the ESI process in aqueous solution within micelles. The high-resolution mass spectrometric evidence revealed that the surfactant molecules effectively protect the noncovalent binding of the complexes into gaseous ions. Intriguingly, surfactant molecules were sufficiently detached away from the copolymer complexes, giving unambiguous mass spectra that were predominated by intact diblock copolymers. This ESI-based approach allowed us to investigate the relative bond strengths of metal-to-ligand complexation using collision-induced dissociation (CID) in the ion trap mass spectrometry. Conformational features and collision cross sections of the copolymers were thus obtained using subsequent ion mobility spectrometry mass spectrometry (IMS-MS). Remarkable environment-dependent conformations of the denoted diblock copolymers were found using this mass spectrometric platform.

Polyphenylsulfone (PPSU) for baby bottles: a comprehensive assessment on polymer-related non-intentionally added substances (NIAS)

ABSTRACTPolyphenylsulfone (PPSU) is a new material for the production of baby bottles. PPSU is a polyether plastic formally composed of bisphenol S (BPS) and 4,4ʹ-dihydroxybiphenyl (DHBP), which both have slight endocrine activities in in vitro tests. So far, little is known about the presence and the release of potentially hazardous substances from PPSU baby bottles. In this study, we present a three-step approach for the analysis of PPSU starting with polymer characterisation in terms of chemical structure, total oligomer content and hydrolytic stability. Second is the determination of extractables focussing on monomers, monomer derivatives, linear and cyclic oligomers below 1000 Da and residual solvent. Third is a risk assessment on migration-related substances in accordance to European Union plastics regulation no. 10/2011 based on triplicate consecutive migration experiments using official milk simulant 50% ethanol. We analysed five types of PPSU baby bottles from different brands as well as corresponding raw materials from different manufacturers by various analytical techniques (high-performance liquid chromatography (HPLC)-diode array detector /fluorescence detector/Corona/electrospray ionisation-MS, HPLC-size exclusion chromatography, gas chromatography-mass spectrometry (GC-MS), 1H-NMR). We found significant variations of PPSU materials from different producers with regard to polymer and oligomer chain end groups (methoxylation, chlorination), while total oligomer content below 1000 Da was similar (mean about 0.48%). BPS was not detected above 0.3 mg/kg polymer in any PPSU sample. Residual DHBP content ranged between 1.7 and 15.5 mg/kg polymer. The most common oligomer in all PPSU samples was the cyclic tetramer (about 1200 mg/kg polymer), which is the only cyclic compound below 1000 Da. Residual solvent, sulfolane, was determined to a maximum of 1300 mg/kg polymer. In migration tests, we detected exceedances of neither specific migration limits for listed substances nor of thresholds of toxicological concern for non-listed substances (monomer derivatives, oligomers). Based on our analytical results, no concerns exist regarding migration of polymer-related substances from PPSU baby bottles.

Comb-shaped polysulfones containing sulfonated polytriazole side chains for proton exchange membranes

Comb-shaped polysulfone copolymers were synthesized by the click reaction, copper(I) catalyzed azide-alkyne 1,3-dipolar cycloaddition, using polysulfone having azidomethyl side group (PSf-N3) and sulfonated polytriazole having one ethynyl chain-end group. PSf-N3 was prepared by the substitution reaction of polysulfone through chloromethylation followed by azidation, and sulfonated polytriazoles having one ethynyl chain-end group was synthesized via the click reaction using 1,4-diethynylbenzene and 4,4′-diazido-2,2′-stilbenedisulfonic acid disodium salt tetrahydrate with CuI followed by end-capping process. Tough, flexible, and transparent membranes could be prepared by solution casting from the comb-shaped polysulfone copolymers and ion exchange capacity (IEC) of the resulting membranes could be controlled by changing the chain length of the sulfonated polytriazoles. The comb-shaped polysulfone membranes showed enhanced physicochemical stability and significantly higher proton conductivity when compared with a sulfonated poly(arylene ether sulfone) (SPAES) membrane having a similar IEC due to the distinct hydrophilic-hydrophobic phase separated morphology. The fuel cell performance of membrane electrode assembly with the comb-shaped polysulfone membrane is superior to those with the SPAES and Nafion-212 membranes at the various operating conditions.

Controlling Enzymatic Polymerization from Surfaces with Switchable Bioaffinity.

The affinity of surfaces toward proteins is found to be a key parameter to govern the synthesis of polymer brushes by surface-initiated biocatalytic atom transfer radical polymerization (SI-bioATRP). While the "ATRPase" hemoglobin (Hb) stimulates only a relatively slow growth of protein repellent brushes, the synthesis of thermoresponsive grafts can be regulated by switching the polymer's attraction toward proteins across its lower critical solution temperature (LCST). Poly(N-isopropylacrylamide) (PNIPAM) brushes are synthesized in discrete steps of thickness at temperatures above LCST, while the biocatalyst layer is refreshed at T < LCST. Multistep surface-initiated biocatalytic ATRP demonstrates a high degree of control, results in high chain end group fidelity and enables the synthesis of multiblock copolymer brushes under fully aqueous conditions. The activity of Hb can be further modulated by tuning the accessibility of the heme pocket within the protein. Hence, the multistep polymerization is accelerated at acid pH, where the enzyme undergoes a transition from its native to a molten globule conformation. The controlled synthesis of polymer brushes by multistep SI-bioATRP highlights how a biocatalytic synthesis of grafted polymer films can be precisely controlled through the modulation of the polymer's interfacial physicochemical properties, in particular of the affinity of the surface toward proteins. This is not only of importance to gain a predictive understanding of surface-confined enzymatic polymerizations, but also represents a new way to translate bioadhesion into a controlled functionalization of materials.

Propene Polymerization with C1-Symmetric Fluorenyl-Metallocene Catalysts

Propene homopolymers have been produced by employing three C1-symmetric metallocene molecules (1, 2 and 3), each having t-butyl substituent(s) on the Cp, on the fluorenyl or on both aromatic moieties activated with methylaluminoxane at different polymerization temperatures and monomer concentrations. Polymers’ microstructures determined by 13C NMR spectroscopy suggest that the otherwise dominant alternating mechanism governed by the chain migratory insertion is largely replaced by the competing site epimerization mechanism, as a direct result of the imposing steric bulk of the t-butyl substituent on one of the distal positions of the Cp moiety. This phenomenon is more pronounced with 3 when a second t-butyl is present in the same half-space of the molecule making the site epimerization mandatory. The lower activity of catalyst 3 with respect to catalyst 2 is also in line with the necessity for the polymer chain to back-skip (or the site to epimerize) to its original position before the subsequent monomer insertion. Chain end group analyses by 1H NMR spectroscopy have revealed that the formation of vinylidene end groups, either via β-H elimination or as a result of direct chain transfer to the monomer after an ordinary 1,2-insertion is the prevailing chain termination route. A correlation between the relative concentrations of vinylidene end groups of polypropene (PP) polymers produced with each catalyst and the corresponding polypropenes’ molar masses was found, indicating the lower the relative concentrations of vinylidene end groups, the higher the molar masses.

Efficient Homodifunctional Bimolecular Ring-Closure Method for Cyclic Polymers by Combining RAFT and Self-Accelerating Click Reaction.

An efficient metal-free homodifunctional bimolecular ring-closure method is developed for the formation of cyclic polymers by combining reversible addition-fragmentation chain transfer (RAFT) polymerization and self-accelerating click reaction. In this approach, α,ω-homodifunctional linear polymers with azide terminals are prepared by RAFT polymerization and postmodification of polymer chain end groups. By virtue of sym-dibenzo-1,5-cyclooctadiene-3,7-diyne (DBA) as small linkers, well-defined cyclic polymers are then prepared using the self-accelerating double strain-promoted azide-alkyne click (DSPAAC) reaction to ring-close the azide end-functionalized homodifunctional linear polymer precursors. Due to the self-accelerating property of DSPAAC ring-closing reaction, this novel method eliminates the requirement of equimolar amounts of telechelic polymers and small linkers in traditional bimolecular ring-closure methods. It facilitates this method to efficiently and conveniently produce varied pure cyclic polymers by employing an excess molar amount of DBA small linkers.

Termination, Transfer, and Propagation Kinetics of Trimethylaminoethyl Acrylate Chloride Radical Polymerization in Aqueous Solution

The SP–PLP–EPR (single pulse–pulsed laser polymerization–electron paramagnetic resonance) method has been used to measure the rate coefficients of termination, intramolecular transfer, and propagation for the radical polymerization of 20 wt % trimethylaminoethyl acrylate chloride (TMAEA) in the temperature range 0–90 °C. The high complexity of this acrylate system is due to water being the solvent, to the monomer being a strong electrolyte, and to both secondary chain-end radicals and tertiary midchain radicals being simultaneously present. The termination kinetics, which was analyzed by a chain-length-dependent scheme, largely differs from the situation met with nonionized radicals. The reliability of the rate coefficients obtained from the SP–PLP–EPR experiments has been demonstrated by the almost perfect agreement of TMAEA conversion vs time data from simulation, on the basis of these coefficients, and from the chemically initiated TMAEA polymerization experiment at 70 °C.

Non-random bonding of mono/divalent cations in mixed phosphate glasses

Incorporation of Sr to biocompatible Ca-phosphate glasses opened many possibilities for clinical applications. Transport properties relevant to the cation release in physiological conditions depend, among other factors, on the interaction with the PO4 forming groups. To understand these issues, three series of mixed glasses with mono (Na+) and divalent (Ca2+/Sr2+) cations were considered here: polyphosphates (0.57−x) Na2O∙x MO∙0.43 P2O5 (MCa, Sr; 0≤x≤0.57), and metaphosphate (0.50−x) Na2O∙x SrO∙0.50 P2O5 (0≤x≤0.50). Molar volumes and glass transition temperatures were analyzed as a function of the concentration of the alkaline earth. 31P and 23Na nuclear magnetic resonance techniques were applied to analyze local structure around phosphate groups and Na sites. As a function of the alkaline earth content, transitions in the evolution of properties (molar volume, glass transition temperature and 31P resonance of Q1 chain-end tetrahedra) were detected in the polyphosphate series. This behavior can be interpreted in terms of preferential bonding of the divalent cation to the oxygens in (PO3.5)2− anions (Q1), instead of (PO3)− (Q2). This non-statistical bonding to the available O is only possible up to a maximum concentration of the alkaline earth oxide (x=0.28), in good agreement with the observed break in properties of NaSr polyphosphate (x=0.30). A similar behavior seems plausible for Ca2+ in NaCa polyphosphate, but changes in the medium range order and progressive structural distortions induced by the stronger ion cause smooth variations of the molar volume. These findings may be relevant to understand the ion dissolution rates in biocompatible glasses, as the more hydrolysable Q2 groups concentrate the weaker cations, while the stronger Sr2+ or Ca2+ are located near chain-end Q1 groups.

Polihydroksyalkaniany – zastosowanie i recykling

The rising amount of plastic waste derived from non-biodegradable polymeric materials generate the need to find alternative materials which could be biodegraded via composting. One of possible solutions are polyhydroxyalkanoates, biodegradable polyesters obtained by fermentation from renewable resources. They can also serve as valuable raw material for the production of bio-based chemicals as well as oligomeric products with different chain structure and end groups applicable as drug carriers.

Interfacial and topological effects on the glass transition in free-standing polystyrene films.

United-atom molecular-dynamics computer simulations of atactic polystyrene (PS) were performed for the bulk and free-standing films of 2 nm-20 nm thickness, for both linear and cyclic polymers comprised of 80 monomers. Simulated volumetric glass-transition temperatures (Tg) show a strong dependence on the film thickness below 10 nm. The glass-transition temperature of linear PS is 13% lower than that of the bulk for 2.5 nm-thick films, as compared to less than 1% lower for 20 nm films. Our studies reveal that the fraction of the chain-end groups is larger in the interfacial layer with its outermost region approximately 1 nm below the surface than it is in the bulk. The enhanced population of the end groups is expected to result in a more mobile interfacial layer and the consequent dependence of Tg on the film thickness. In addition, the simulations show an enrichment of backbone aliphatic carbons and concomitant deficit of phenyl aromatic carbons in the interfacial film layer. This deficit would weaken the strong phenyl-phenyl aromatic (π-π) interactions and, hence, lead to a lower film-averaged Tg in thin films, as compared to the bulk sample. To investigate the relative importance of the two possible mechanisms (increased chain ends at the surface or weakened π-π interactions in the interfacial region), the data for linear PS are compared with those for cyclic PS. For the cyclic PS, the reduction of the glass-transition temperature is also significant in thin films, albeit not as much as for linear PS. Moreover, the deficit of phenyl carbons in the film interface is comparable to that observed for linear PS. Therefore, chain-end effects alone cannot explain the observed pronounced Tg dependence on the thickness of thin PS films; the weakened phenyl-phenyl interactions in the interfacial region seems to be an important cause as well.

Precise molecular weight determination and structure characterization of end-functionalized polymers: An NMR approach via combination of one-dimensional and two-dimensional techniques

We present here the application of one-dimensional and two-dimensional NMR techniques to characterize the structure of methoxyl end-functionalized polystyrenes (PS). The peaks in 1H-NMR spectra corresponding to main-chain, side-chain and chain-end groups are assigned by 1H-1H gCOSY, 1H-13C gHSQC and gHMBC spectra. For the first time, the spin-lattice relaxation time (T1) of protons of the chain-ends is revealed to be affected more by polymer molecular weight (MW) than by the protons of the main-chains and the side-chains (almost independent from MW). As a result, a much higher delay time (d1) for chain-ends (d1 > 20T1) is needed for quantitative NMR measurement when using end-group estimation method to obtain the MW of PS, which is in accordance with the value estimated by GPC. An improved method for the polymer MW determination is established, by combination of different NMR techniques to distinguish the peaks, and a large d1 setting to achieve quantitative NMR analysis.

Photo-induced ATRP of MMA without ligands in ionic liquid

Fe-mediated photo-induced atom transfer radical polymerization (ATRP) of methyl methacrylate was studied with chlorophyll A as photoredox catalyst in the absence of ligands. This is the first report on photo-induced and FeBr3-mediated ATRP. A low-cost and environmentally friendly ATRP is provided in this system. A good linear semi-logarithmic plot of polymerization kinetics is the first-order time conversion, and narrow molecular weight distributions explain the well-controlled behavior. The measured number average molecular weight, Mn,GPC (determined by gel permeation chromatography), is increased with monomer conversion, and it is in good agreement with the theoretical values (Mn,th). The effect of FeBr3 is studied with respect to the polymerization. The values of the resultant PMMA increased with reduced FeBr3 concentration. In this system, the effect of periodic light/off process has been investigated through chain growth instantly turned on and off in response to the visible light. The polymerization was controllable even though the concentration of Fe-based catalyst was dropped to 4 ppm. The chain-end group having a functionality in the synthesized poly(methyl methacrylate) was characterized by nuclear magnetic resonance spectrometry (1H NMR). However, chain extension experiments show reserved chain-end functionality in the synthesized polymers and further confirm the “living” feature of the Fe-mediated photo-induced atom transfer radical polymerization.