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An A2B2-type miktoarm star copolymer with two linear poly(ε-caprolactone) (PCL) and two linear poly(cyclohexene oxide) (PCHO) arms was synthesized by using ring-opening polymerization (ROP), click chemistry, and photoinduced cationic polymerization, respectively. The ROP of ε-CL with a dihydroxy functional initiator, 3-cyclohexene-1,1-dimethanol, p...
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A multi-step reaction process was applied for the synthesis of a novel and well-defined star-shaped telechelic macrophotoinitiator with four poly(L-lactide) (PLLA) arms connected to photoinitiating benzoin groups at the chain ends (PLLA-PI)4. To achieve this, 2,2-bis(hydroxymethyl)-1,3-propanediol was used as the initiator which constitutes the cor...
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... The former method entails the controlled/living polymerization of a monomer with a photoreactive initiator [14][15][16]. The latter approach involves introducing a photoactive molecule to a well-defined polymer chain [17,18]. We have previously synthesized a wide variety of well-defined macrophotoinitiators via controlled/living polymerization methods such as atom transfer radical polymerization (ATRP) [19] and ring-opening polymerization (ROP) [20,21]. ...
In this study, two novel photoactive xanthates, which bear a photoinitiator (PI) group in the middle and an S-alkyl dithiocarbonate group (–O–C(S)–S–R) at each of the two ends of the molecule, were synthesized as chain transfer agents (CTA) to be used in reversible addition-fragmentation chain transfer/macromolecular design via the interchange of xanthate (RAFT/MADIX) polymerization. Having the same central photoinitiator group, two chain transfer agents (CTA-PI-CTA 1 and CTA-PI-CTA 2) differ from each other in their R leaving groups; C6H5–CH2– and C6H5–CH(COOEt)–, respectively. The structures of CTA-PI-CTAs were elucidated via elemental analysis and spectroscopic techniques, such as 13C NMR, 1H-NMR, and FT-IR. Styrene (St) was used as the model monomer in MADIX polymerization. Its RAFT/MADIX polymerization with these chain transfer agents successfully produced mid-chain functional polystyrene macrophotoinitiators (PSt-PI-PSt 1 and PSt-PI-PSt 2) with well-defined structures. The GPC, FT-IR, 1H-NMR, UV, and fluorescence spectroscopic studies revealed that low-dispersity polystyrenes with desired photoinitiator functionality in the middle of the chain were obtained. Finally, these macrophotoinitiators were used as prepolymers in photoinitiated free radical polymerization of methyl methacrylate (MMA) to obtain polystyrene-poly(methyl methacrylate) (PSt-PMMA) block copolymers.
... There are two general ways offered for the synthesis of well-defined macrophotoinitiators so far: (i) controlled/living polymerization of monomers in the presence of the initiators with photoreactive groups [12,13]; (ii) covalently bonding a photoreactive group to a polymer chain synthesized by one of the controlled/living polymerization methods [14][15][16]. The development of controlled/living polymerization techniques in the past two decades has notably opened new routes for preparing well-defined polymers including macrophotoinitiators with predictable molecular weight, low polydispersity, and tunable architectures [17,18]. ...
An alternative approach for the synthesis of well-defined macrophotoinitiators of polystyrene and polyacrylonitrile with an end-chain photofunctional group via reversible addition-fragmentation chain transfer/macromolecular design via the interchange of xanthate (RAFT/MADIX) polymerization has been described. For this purpose, a novel photoreactive chain transfer agent (CTA-PI), namely S-benzyl O-(2-oxo-1,2-diphenylethyl) carbonodithioate, was prepared with an efficient one-pot, two-step synthesis by first reacting benzoin photoinitiator (PI) with CS2 in the presence of NaH and then reacting this intermediate with benzyl bromide in THF. The structure of CTA-PI was determined by FT-IR, ¹H NMR, and ¹³C NMR spectroscopy and confirmed by elemental analysis. Here, we used this xanthate based CTA in conjunction with 4,4′-azobis(4-cyanovaleric acid) (ACVA), as the initiating species, to investigate RAFT/MADIX polymerization of styrene (St), acrylonitrile (AN), methyl methacrylate (MMA), the so-called more activated monomers (MAMs), and vinyl acetate (VAc), one of the less activated monomers (LAMs). While RAFT/MADIX polymerization of styrene and acrylonitrile progressed in a controlled manner producing well-defined macrophotoinitiators with benzoin end-chain functional group, polymerization of methyl methacrylate proceeded uncontrollably. Polymerization of vinyl acetate under the same reaction conditions, on the other hand, did not occur at all. Spectroscopic and GPC measurements indicated that syntheses of polystyrene and polyacrylonitrile macrophotoinitiators bearing a photoreactive benzoin end group, PSt-PI and PAN-PI, respectively, with well-defined structures were achieved. These unique macrophotoinitiators were then used as prepolymers in photoinitiated free radical promoted cationic polymerization of cyclohexene oxide (CHO) and butyl vinyl ether (BVE) monomers to obtain PSt-PCHO, PSt-PBVE, PAN-PCHO, and PAN-PBVE di-block copolymers.
End-group functionalization of homopolymers is a valuable way to produce high-fidelity nanostructured and functional soft materials when the structures obtained have the capacity for self-assembly (SA) encoded in their structural details. Herein, an end-functionalized PCL with a π-conjugated EDOT moiety, (EDOT-PCL), designed exclusively from hydrophobic domains, as a functional “hydrophobic amphiphile”, was synthesized in the bulk ROP of ε-caprolactone. The experimental results obtained by spectroscopic methods, including NMR, UV-vis, and fluorescence, using DLS and by AFM, confirm that in solvents with extremely different polarities (chloroform and acetonitrile), EDOT-PCL presents an interaction- and structure-based bias, which is strong and selective enough to exert control over supramolecular packing, both in dispersions and in the film state. This leads to the diversity of SA structures, including spheroidal, straight, and helical rods, as well as orthorhombic single crystals, with solvent-dependent shapes and sizes, confirming that EDOT-PCL behaves as a “block-molecule”. According to the results from AFM imaging, an unexpected transformation of micelle-type nanostructures into single 2D lamellar crystals, through breakout crystallization, took place by simple acetonitrile evaporation during the formation of the film on the mica support at room temperature. Moreover, EDOT-PCL’s propensity for spontaneous oxidant-free oligomerization in acidic media was proposed as a presumptive answer for the unexpected appearance of blue color during its dissolution in CDCl3 at a high concentration. FT-IR, UV-vis, and fluorescence techniques were used to support this claim. Besides being intriguing and unforeseen, the experimental findings concerning EDOT-PCL have raised new and interesting questions that deserve to be addressed in future research.
Linoleic acid modified with auto-oxidation, hydroxylation, bromination and azidation was used to synthesis graft copolymers using ω-alkyne-terminated poly(ε-caprolactone) (alk-PCLs) via “click” reaction. In the first step, the polymeric linoleic acid (PLina) as macroinitiator was obtained by the autoxidation of linoleic acid. Hydroxylation of the PLina was then carried out using diethanolamine to produce hydroxylated polymeric linoleic acid (PLina-OH). The PLina-OH was chemically modified with 2-bromopropionyl bromide to obtain bromo-functionalized polymeric linoleic acid (PLina-Br). This macroinitiator was then modified with sodium azide, resulting in azide polymeric linoleic acid (PLina-N3). In a parallel process, ω-alkyne-terminated poly(ε-caprolactone) (alk-PCLs) were prepared via ROP of the ε-caprolactone monomer in the presence of propiolic acid, 3-butyn-1-ol, 5-hexynoic acid, and propargyl alcohol as the precursors and tin(II) 2-ethyl hexanoate (Sn(Oct)2) as the catalyst. These preliminary steps involved the synthesis of azide and alkyne compounds capable of being linked together via the alkyne-azide cycloaddition reaction catalyzed by copper (Cu(I)), which led to poly(linoleic acid)-g-poly(ε-caprolactone) (PLina-g-PCL). The obtained polymers were characterized by proton nuclear magnetic resonance (1H NMR), Fourier-transform infrared (FTIR), differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA) and elemental analysis. JCSC-D-21-00100
A novel and well-defined four-arm star-type telechelic macrophotoinitiator of poly(ε-caprolactone) carrying benzoin photofunctional end-groups (PCL-BPI)4 was successfully synthesized by the combination of ring opening polymerization (ROP) and click chemistry techniques. First, hydroxyl end-functionalized four-arm (PCL-OH)4 was synthesized by ROP of ε-caprolactone (ε-CL) with pentaerythritol initiator. Then, the hydroxyl groups at the chain ends were converted to terminal alkyne groups by the condensation reaction between (PCL-OH)4 and 4-pentynoic acid to give an alkyne end-functionalized four-arm poly(ε-caprolactone), (PCL-alkyne)4, as the first click couple compound. Separately, an azido end-functionalized benzoin photoinitiator (BPI-N3) was prepared in two steps to be used as the other click couple compound. (PCL-alkyne)4 and BPI-N3 were coupled via “click chemistry” to prepare a well-defined four-arm star-type telechelic macrophotoinitiator, (PCL-BPI)4. In addition, the obtained (PCL-BPI)4 macrophotoinitiator was used in the photoinitiated free radical promoted cationic polymerization of cyclohexene oxide (CHO) to produce an (AB)4-type star shaped block copolymer, (PCL-PCHO)4. All the polymers prepared were characterized by different spectral and analytical methods and their thermal behaviors were investigated.
