Large-scale microwave-assisted ring-opening polymerization of ɛ-caprolactone

To probe into the industrialization possibility of microwave-assisted ring-opening polymerization (ROP) of ?-caprolactone (?-CL), it was performed with monomer mass from 750 to 2450 g using a self-designed industrial microwave oven (6000 W) catalyzed by stannous octanoate (Sn(Oct)₂) (M/Cat = 1000). The large-scale ROP of ?-CL proceeded smoothly at various microwave power levels (850, 1700, and 2550 W) and produced poly(?-caprolactone) (PCL) with weight-average molar mass (M_w) from 66,000 to 12,2000 g/mol within 40 min in a yield over 93%. The structure of PCL was characterized by ¹H and ¹³C NMR, FT-IR, DSC and WAXD. We propose that the microwave ROP of ?-CL is a potential technology to prepare PCL commercially.     

Synthesis of polycarbonate containing in-chain 4-N,N-dimethylamino-4′-nitrostilbene via ring-opening polymerization

Summary We have successfully synthesized a new NLO chromophore based on 4-N,N-dimethylamino-4-nitrostilbene which contains bisphenol functionality for polycarbonate preparation. Chromophore-4 was used to make macrocyclic carbonate oligomers and the oligomers were converted to polycarbonate via ring-opening polymerization in solution.     

Hybrid dual-cure polymer networks via sequential thiol–ene photopolymerization and thermal ring-opening polymerization of benzoxazines

Dual-cure hybrid polymer networks were prepared by sequential thiol–ene photopolymerization followed by thermal ring-opening polymerization of benzoxazines with the aim of increasing the glass transition temperature range of thiol–ene based materials and improving the processibility of polybenzoxazines. The hybrid networks are derived from a multifunctional, dually-polymerizable monomer possessing both bis-“ene” and bis-benzoxazine moieties enabling the formation of two networks through a common constituent monomer when combined with a multifunctional thiol. The photopolymerization kinetics of the thiol–ene reaction were investigated by real-time infrared spectroscopy. Sequential thermal ring-opening polymerization of the benzoxazine moieties incorporated into the thiol–ene network was characterized by FTIR and differential scanning calorimetry. The glass transition of the hybrid material was observed at 150 °C; however, competing thiol–ene (radical-mediated) and thiol–benzoxazine (nucleophilic ring-opening) reactions during the UV cure yield a heterogeneous network structure.     

Patterning a π-conjugated polyelectrolyte through sequential polymerization of a bifunctional ionic liquid monomer

An electronically conductive polyelectrolyte is prepared by the sequential polymerization of a bifunctional imidazolium-based ionic liquid (IL) monomer, composed of a thienyl and vinyl containing cation paired with a tetrafluoroborate anion. In the first step, potentiodynamic electropolymerization of the thienyl moiety forms a cationic polyalkylthiophene that is soluble in select organic solvents. Cyclic voltammetry (CV) was used to determine the polymer p-doping potential (0.31 V) and the bipolaronic state (1.49 V). The polymer exhibits electrochromism, converting from red in the neutral state (λ_max = 443 nm) to dark blue in the polaronic state (λ_max = 819 nm). The solution-processable polymer can be cast into a film, masked and patterned by UV-initiated free radical polymerization of the vinyl moiety. Small-angle X-ray scattering (SAXS) revealed that the insoluble crosslinked polyalkylthiophene–polyvinylimidazolium adopts a lamellar structure with a lattice spacing of 3.3 nm. Four-probe d.c. conductivity measurements determined the de-doped electrical conductivity was 1.0 × 10⁻² S/cm. The results underscore the importance of the anion in controlling the polymerization of IL monomers.     

Molecular packing based on a π-stacked screw via self-assembly

A new platinum(II) complex, C₂₄H₁₆N₁₀S₂Pt·3H₂O, bis(4,5-diazafluorene-9-one thiosemicarbazato) platinum(II) trihydrate, has been synthesized. Crystals of it are trigonal, space group P3₂ with cell parameters of a=10.696(4), c=19.748(6) Å and Z=3. The ligands are coordinated to the platinum(II) atom by two imino nitrogen atoms N(3) and N(8), and two sulfur atoms S(1) and S(2) forming a rigid molecular tweezers maintained by intramolecular π–π stacking. Detailed crystal structure analyses exhibit that the one-dimensional 3₂ screw robust supramolecular aggregate was achieved by intermolecular π–π stacking interaction between the extensive delocalization π-system ligands via self-assembly and the aggregates were linked by hydrogen bonding.     

High molecular weight poly(l-lactide) via ring-opening polymerization with bismuth subsalicylate–The role of cocatalysts

The catalytic potential of bismuth subsalicylate (BiSub), a commercial drug, for ring-opening polymerization of l -lactide was explored by variation of cocatalyst and polymerization time. Various monofunctional phenols or carboxylic acids, aromatic ortho-hydroxy acids, and diphenols were examined as potential cocatalysts. 2,2′-Dihydroxybiphenyl proved to be the most successful cocatalyst yielding weight average molecular weights (uncorrected M_w values up to 185,000) after optimization of reaction time and temperature. Prolonged heating (>1-2 h) depending on catalyst concentration) caused thermal degradation. In polymerization experiments with various commercial Bi(III) salts a better alternative to BiSub was not found. By means of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry a couple of unusual and unexpected transesterification reactions were discovered. Finally, the effectiveness of several antioxidants and potential catalyst poisons was explored, and triphenylphosphine was found to be an effective catalyst poison.     

Calcium methoxide initiated ring-opening polymerization of ε-caprolactone and L-lactide

Summary A commercial calcium dimethoxide and an in-situ generated calcium methoxide prepared from bis(tetrahydrofuran)calcium bis[bis(trimethylsilyl)amide] and methanol, were investigated as initiators for the ring-opening polymerization of ε-caprolactone and L-lactide. Commercial calcium dimethoxide initiated rapid ε-caprolactone polymerization at 120°C in bulk to give quantitatively a polymer with a polydispersity index around 1.3. Significant racemization was observed for L-lactide polymerization. The In-situ formed calcium methoxide promoted the solution polymerization of both ε-caprolactone and L-lactide to high conversion at room temperature over a short time period, yielding the corresponding polyesters with narrow molecular weight distribution. NMR spectra showed that the poly(L-lactide) isolated had a purely isotactic microstructure. The initiator efficiency could be tuned by varying the molar ratio of methanol and bis(tetrahydrofuran)calcium bis[bis(trimethylsilyl)amide]. Received: 11 August 2000/Revised version: 21 December 2000/Accepted: 3 January 2001     

Molecular architecture effect on reactivity of polynorbornenes with pendant α,β-unsaturated amide or ester bridged chains via ring-opening metathesis polymerization

The molecular architecture effect on active structure of miscellaneous polynorbornenes (Scheme 1) was investigated with pendant α,β-unsaturated amide or ester groups via ring-opening metathesis polymerization (ROMP). Remarkable differences in the reactivity and polymerization behavior of active norbornenes depend on various molecular architectures. Polynorbornenes derived from active norbornenes with ethylene between urethane group and ester group such as 3a,b (Scheme 1) showed excellent solubility. Organo-insoluble precipitate was obtained after ROMP of 5c with the amide group. Random copolymerization technique of bicyclo[2.2.1]hept-2-ene (NB) and 5c with amide group was considered to be a strategy to overcome the formation of precipitates, which expected to decrease the hydrogen bonding between two amide groups. High performance polynorbornenes with active groups could be designed with high potential of application for photoresist, UV curing and elastomers. Functional poly(5b) was incorporated into poly(methyl methacylate) [poly(MMA)] to produce AB cross-linked materials. The AB cross-linked material [15 wt% poly(5b), T_d10=355 °C in nitrogen] had higher thermal stability than pure poly(MMA) (T_d10=250 °C in nitrogen).     

Living ring-opening polymerization of ɛ-caprolactone with combinations of tert-butyllithium and bilky aluminium phenoxides

Summary The polymerization of ɛ-caprolactone (ɛ-CL) with a combination of tert-butyllithium (t-BuLi) and bis(2,6-di-t-butylphenoxy)methylaluminum [MeAl(ODBP)₂] in toluene at 0°C proceeded in a living manner to give polymers with narrow molecular weight distributions (MWD) within a few minutes, while the polymerization with t-BuLi alone gave a polymer with much broader MWD. The yield of the polymer did not reach 100 % at the Al/Li ratio of 5, because the excess MeAl(ODBP)₂ coordinates with ɛ-CL to protect it from the attack by the propagating species. The polymerization with t-BuLi/EtAl(ODBP)₂ gave polymers in quantitative yields regardless of Al/Li ratio, and also narrower MWD even for higher molecular weight polymers. Received: 1 August 2000/Accepted: 11 August 2000     

Biological quorum sensing molecule-metal complex produces π-conjugated polymer

Quorum sensing (QS) is bacterial communication system. We consider that β-diketon moiety in the QS materials may have important role in the biological communications. The β-diketon part has functionality of coordination to metals and gives stimuli to individual organism as a message. This function allows to response environmental change for survival and prosperity. In this research, we apply quorum sensing materials for catalysts. Two kinds of metals, rhodium and palladium, were employed for combination with the QS-based catalytic system to produce a cis-rich polyacetylene derivative. This approach may contribute evaluation of biological communication mechanism based on QS materials.     

Synthesis of π-conjugated organoboron polymers by haloboration-phenylboration polymerization of aromatic diynes

π-Conjugated organoboron polymers were prepared by haloboration-phenylboration polymerization beween diyne monomers and bromodiphenylborane. The polymerization was carried out by adding a slightly excess amount of bromodiphenylborane to a tetrachloroethane solution of diynes at room temperature under nitrogen and stirring the reaction mixture for 4 hours at 100°C. The obtained polymers were soluble in common organic solvents such as THF and chloroform. Their molecular weights were estimated to be several thousands by gel permeation chromatographic analysis. In UV-vis absorption spectra, bathochromic shift of λ_max and absorption edge in comparison with the corresponding monomers were observed, which indicates the π-conjugation via vacant p-orbital of boron atom.     

Fluorinated ?-caprolactone: Synthesis and ring-opening polymerization of new α-fluoro-?-caprolactone monomer

Fluorinated polyester was synthesized from a novel α-fluoro-?-caprolactone monomer (α-FCL). The monomer was synthesized from commercially available cyclohexene oxide in three steps. Baeyer-Villiger reaction using 3-chloroperoxybenzoic acid of the corresponding 2-fluorocyclohexanone resulted in formation of two isomeric lactones α-and-?-fluoro-?-caprolactones in 1:1.2 molar ratio, respectively. Poly(α-fluoro-?-caprolactone) was synthesized by bulk ring-opening polymerization of α-fluoro-?-caprolactone monomer (α-FCL) catalyzed by stannous octanoate, Sn(Oct)₂ at 120 °C for 6 h. Relationships between reaction time, polymer yield, and molecular weight were established. The ring-opening polymerization of ?-fluoro-?-caprolactone (?-FCL) produce geminal fluorohydrin, which is not stable and it is subsequently dehydrofluorinated to give the corresponding aldehyde. Copolymerization of α-FCL with ?-caprolactone (?-CL) in various feed ratios was also investigated. Detail microstructure analyses of the copolymers were accomplished from ¹H, ¹³C and 2-D NMR data. Presence of fluorine atoms is expected to regulate the chemical and physical properties of the polyester.     

Synthesis, characterization and fluorescence adjustment of well-defined polymethacrylates with pendant π-conjugated benzothiazole via atom transfer radical polymerization (ATRP)

Two compounds containing the benzothiazole moiety, 4-(2-benzothiazole-2-yl-vinyl)-phenyl methacrylate (BVMA) and 2-bromo-2-methyl-propionic acid 4-(2-benzothiazole-2-yl-vinyl)-phenyl ester (BPBVE) were synthesized. Atom transfer radical polymerization (ATRP) of BVMA was conducted at 60 °C using BPBVE and CuBr/2,2′-bipyridine (BPY) as initiator and catalyst, respectively. Chain extension with 4-methacryloxy-hexyloxy-4′-nitrostilbene (MHNS) was conducted using PBVMA as the macroinitiator. The homopolymer PBVMA in DMF solution emitted blue fluorescence, and the copolymer PBVMA-b-PMHNS emitted orange fluorescence at about 610 nm due to the intramolecular energy transfer. ATRP of BVMA was also conducted using 2-bromo-2-methyl-propionic acid 4-nitrostilbene-hexyloxy ester (BPNHE) as an initiator. The obtained polymer was characterized via ¹H NMR and the fluorescence intensity was found to change with increasing number average molecular weight (M_n). The polymer with M_n = 15900 emitted white fluorescence in DMF solution.     

Grafting of poly(ε-caprolactone) on electrospun gelatin nanofiber through surface-initiated ring-opening polymerization

Gelatin–polycaprolactone hybrid materials are being used in medicinal applications such as drug delivery, tissue engineering applications nowadays. In this study, gelatin–polycaprolactone graft copolymer was synthesized through ring-opening polymerization process instead of conventional grafting methods using potentially cytotoxic crosslinkers, or applying plasma, aminolysis reactions. Gelatin nanofiber (GNF) was produced by electrospinning process before immobilization of poly(ε-caprolactone). Ring-opening polymerization of ε-caprolactone was successfully initiated on the surface of GNF using tin(IV) isopropoxide and gelatin (primary amine functional groups) as an initiator and a coinitiator, respectively. The growing of polymer chains on GNF was indicated by both scanning electron microscope and energy-dispersive X-ray spectroscopy. Chemical structure was characterized through infrared spectrum, thermal behaviors and the material composition was analyzed with thermogravimetric analysis, wettability and hydrophilicity were determined by water contact angle measurements.     

HNTs/GO composite as efficient catalyst for ring-opening polymerization of ε-Caprolactone

Polycaprolactone (PCL) has been widely applied based on the biocompatibility and biodegradability. It is important to investigate the safe and efficient catalyst system for ring-opening polymerization of monomer ε-caprolactone (ε-CL). In our work, Halloysite/Graphene Oxide (HNTs/GO) composite is successfully prepared by electrostatic self-assembly and used as an effective catalyst for the ring-opening polymerization of ε-CL. The structures, morphologies and thermal properties of the products are subsequently characterized. The results show that the synthesized PCL are semi-crystalline and observed to be lamellar, which depend on the template effects of HNTs/GO composite. The HNTs/GO composite serves as an effective catalyst and a reinforcing filler simultaneously to improve the thermal stability of the prepared PCL.     

Synthesis of amphiphilic polycyclooctene-graft–poly(ethylene glycol) copolymers by ring-opening metathesis polymerization

In this paper, a novel monomer of 4-methyl-3-(carbamate)–carbanilic acid-4-cyclooctene ester (MCCCE) was synthesized and characterized by FTIR, NMR and ESI-MS. Polycyclooctene-graft-blocked isocyanate copolymers were prepared by the copolymerization of MCCCE and cyclooctene via ring-opening metathesis polymerization (ROMP). Amphiphilic polycyclooctene-graft–PEG copolymers were prepared by melt mixing the polycyclooctene-graft-blocked isocyanate copolymers with poly(ethylene glycol) (PEG) at 200 °C. The blocked isocyanate group on MCCCE can be dissociated to produce free isocyanate group, which will react with the end hydroxyl groups on PEG molecules. The effects of monomer-to-catalyst, monomer-to-chain transfer agent ratios on molecular weight of the copolymer were detailedly studied. The water contact angle of polycyclooctene-graft–PEG copolymer is much smaller than that of polycyclooctene.     

Toughening of semi-IPN structured epoxy using a new PEEK-type polymer via in situ azide–alkyne click polymerization

A new poly(ether ether ketone)-type polymer prepared from 1,4-bis(azidomethyl)benzene (p-BAB), 4,4′-bis(2-propynyloxy)benzophenone (PBP) or 4,4′-sulfonylbis(propynyloxy)-benzene (SBP) via azide–alkyne click polymerization was used as a toughening agent to improve the fracture toughness, thermal stability of the toughened epoxy and reduce its viscosity during processing. The epoxy was toughened by the polymer [poly(p-BAB/PBP)] via in situ polymerization during the curing process, which largely decreased viscosity during the epoxy mixing process compared to that of a neat epoxy. The fracture toughness of 5 wt % poly(p-BAB/PBP) toughened epoxy is two times higher than that of the neat epoxy, and even higher than that of the polyethersulfone-type [poly(p-BAB/SBP)] toughened epoxy using the same amount of toughening agents. In addition, the T _g of this toughened epoxy is higher than that of engineering plastic, which could be regarded as the evidence for the excellent thermal resistance. These phenomena might be attributed to the formation of semi-interpenetrating polymer networks composed by the epoxy network and the linear poly(p-BAB/PBP). In situ poly(p-BAB/PBP) has unique advantages such as decreased viscosity and improved thermal stability in comparison with in situ poly(p-BAB/SBP). These features are significant for the development of carbon-fiber-reinforced plastics as alternate materials to metals. Therefore, in situ poly(p-BAB/PBP) is a promising toughener for epoxy systems. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48178.     

Effect of π-π stacking on the atom transfer radical polymerization of styrene

The atom transfer radical polymerization (ATRP) of styrene (St) was carried out in the presence of varying equivalents (eq) of hexafluorobenzene (HFB) to probe the effect of pi-pi stacking on the rate of the polymerization and the resulting tacticity of polystyrene (PSt) formed. The extent of interaction between the electron deficient face of the HFB and the electron rich face of the styrenic or polystyrenic phenyl ring was also examined as a function of reaction solvent, incorporating both non-aromatics (hexanes and THF) and aromatics (benzene and toluene). It was found that in all cases the rate of the ATRP of St was slowed by the addition of HFB to the reaction mixture, with increasing amounts of HFB (1 full eq. compared to St) retarding the rate to a relatively greater extent compared to smaller amounts (0.5 eq). Additionally, when aromatic solvents were used instead of hydrocarbons the effect of HFB on the rate of the ATRP was minimized, consistent with the solvent itself competing with the styrenic phenyl groups for pi-pi stacking interactions with HFB. The decreased rate in the presence of HFB is consistent with a reduced ability of the terminal phenyl group on the PSt chain to stabilize the active polymer radical, pushing the equilibrium further to the dormant alkyl halide. This interaction between the dormant alkyl bromide and HFB was verified by ¹H NMR, with 1-bromoethylbenzene used as the alkyl bromide. When the ATRP of non-aromatic vinyl monomers was studied (butyl acrylate and methyl methacrylate), the effect of HFB on the system was almost unnoticeable as expected due to their inability to participate in pi-pi stacking interactions. The tacticity of the PSt formed in the presence of HFB was compared to PSt formed in its absence by observing the C1 resonance on ¹³C NMR, but no change in the shape or chemical shift of the signal was observed.     

Synthesis and characterization of ferrocene end-capped poly(ε-caprolactone)s by a combination of ring-opening polymerization and “click” chemistry techniques

Ferrocene (Fc) end-capped linear and star-shaped poly(ε-caprolactone)s (PCLs) with different numbers of arms were synthesized by a combination of ring-opening polymerization (ROP) and “click” chemistry techniques in a four-step reaction procedure. In the first step, the polymer backbones were prepared via ROP of the ε-caprolactone (ε-CL) monomer in bulk by employing the compounds with different numbers of hydroxyl groups as the multisite initiators and stannous octoate (Sn(Oct)₂) as the coordination-insertion catalyst. The hydroxyl end-groups of the obtained PCLs were then converted into a bromides and azides consecutively. In the final step, the Fc moiety was attached to the termini of the PCLs using a Cu(I)-catalyzed 1,3-dipolar cycloaddition reaction between the azide end-groups of the PCLs and the acetylene group of ethynylferrocene under ambient conditions. In all cases, the FT-IR and ¹H NMR spectra indicated a successful and quantitative transformation of the desired end-functional groups. The electrochemical properties of the Fc end-capped PCLs were also investigated via cyclic voltammetry (CV).