Controlled ring‐opening polymerization of lactones and lactides

1,5‐dioxepan‐2‐one (DXO) is presented as a versatile component in biodegradable polymers for biomedical applications. Copolymerization of DXO and L‐lactide yielded a semi‐crystalline, yet flexible, material where the extent of crystallinity and erosion characteristics were controlled by an appropriate choice of copolymer composition. Crosslinked PDXO was polymerized as a novel biodegradable elastomer. The degradation behavior of these materials were explored in vitro. Microspheres from poly(DXO‐co‐L‐LA) were prepared and shown to be promising candidates for controlled release. The polymer composition and drug solubility provided effective means of controlling the drug delivery pattern.     

Radical ring‐opening polymerization

The radical ring‐opening polymerization (RROP) behavior of the following monomers is reviewed, and the possibility for application to functional materials is described: cyclic disulfide, bicyclobutane, vinylcyclopropane, vinylcyclobutane, vinyloxirane, vinylthiirane, 4‐methylene‐1,3‐dioxolane, cyclic ketene acetal, cyclic arylsulfide, cyclic α‐oxyacrylate, benzocyclobutene, o‐xylylene dimer, exo‐methylene‐substituted spiro orthocarbonate, exo‐methylene‐substituted spiro orthoester, and vinylcyclopropanone cyclic acetal. RROP is a promising candidate for producing a wide variety of environmentally friendly functional polymers. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 265–276, 2001     

Solvent‐free ring‐opening polymerization of lactones with hydrogen‐bonding bisurea catalyst

Development of effective organocatalysts for the living ring‐opening polymerization (ROP) of lactones is highly desired for the preparation of biocompatible and biodegradable polyesters with controlled microstructures and physical properties. Herein, a new class of hydrogen‐bond donating bisurea catalysts is reported for the ROP of lactones under solvent‐free conditions. ROP of lactones mediated by the bisurea/7‐methyl‐1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (MTBD) catalyst exhibits a living/controlled manner, affording the polymers and copolymers with the well‐defined structure, predictable molecular weight, narrow molecular weight distribution, and high selectivity for monomer at low catalyst loadings at ambient temperature. The possible mechanism of bisurea/MTBD‐catalyzed ROP of lactones is proposed, in which the bisurea activates the carbonyl group of lactones while MTBD facilitates the nucleophilic attack of the initiating/propagating alcohol by hydrogen bonding. Moreover, the poly(ε‐caprolactone‐co‐δ‐valerolactone) [P(CL‐co‐VL)] random copolymers with various compositions were synthesized using the bisurea/MTBD catalyst. The measurements of thermal properties and crystalline structure demonstrate that the CL and VL units are cocrystallized in the crystalline phase of P(CL‐co‐VL) copolymers. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 90–100     

Surface‐initiated ring‐opening polymerization of p‐dioxanone on Wang resin bead

Biodegradable poly(p‐dioxanone) (PPDO) was formed on Wang resin surface by surface‐initiated ring‐opening polymerization (SI‐ROP). The SI‐ROP of p‐dioxanone (PDO) was achieved by heating a mixture of Tin(II) bis(2‐ethylhexanoate) [Sn(Oct)₂], hydroxyl functionalized Wang resin, and PDO in anhydrous toluene at 80 °C. The resultant polymer‐grafted Wang resin (Wang‐g‐PPDO) was characterized by fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), optical microscopy (OM), and field‐emission scanning electron microscopy (FE‐SEM). The FTIR spectra of Wang‐g‐PPDO show peak characteristic of PPDO at 2943 cm^?1 (? C? H stretch), at 1741 cm^?1 (? C?O stretch), and 1136 cm^?1 (C? O? C stretch) indicating the formation of ester linkage between PPDO and hydroxyl terminated Wang resin. The DSC thermogram show melting peak corresponding to PPDO polymer on Wang resin surface. Thermogravimetric investigation shows increase in PPDO content on the Wang resin surface in terms of percentage of weight loss with increase in reaction time. The OM and SEM photographs clearly show the formation of PPDO polymer on the Wang resin surface without altering the spherical nature of Wang resin bead. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1178–1184, 2008     

Reactivity of Sm(II) compounds as ring‐opening polymerization initiators for lactones

Successful room temperature ring‐opening polymerization (ROP) of ε‐caprolactone and δ‐valerolactone has been carried out using SmX₂ (X = I, Br, and cyclopentadienyl (Cp)) catalysts. SmI₂ in the presence of metallic Sm was found to have enhanced reactivity as room temperature ROP initiator for lactones as compared to pure SmI₂. SmBr₂ and SmCp₂ showed increased reactivity compared with the Sm/SmI₂ system due to their higher reductive power. The catalyst concentration and time of polymerization showed a marked effect on number‐average molecular weight (M_n). There was a decrease in M_n on increasing reaction time and decreasing catalyst concentration. The initiation mechanism is discussed based on end group analysis of low molecular weight polymers.     

Computational evaluation of radical ring‐opening polymerization

The tendencies of ring‐opening processes in radical ring‐opening polymerizations were evaluated by AM1 and PM3 semi‐empirical calculations and 6‐31G*‐level calculations based on the density functional theory (DFT) B3LYP models. Sixteen cyclic monomers bearing vinyl or exomethylene groups were categorized into ring‐opening and no‐ring‐opening monomers by the evaluation of the differences of the internal energies and the lengths of the cleaving bonds between the ground states of the initial radicals and the activated states in the ring‐opening processes. Although the semi‐empirical calculations not parameterized to radical reactions resulted in the moderate categorization of the ring‐opening monomers, the DFT calculation clearly distinguished the ring‐opening and no‐ring‐opening monomers. The ring‐opening tendencies were also evaluated with the changes in the internal energies throughout the ring‐opening processes, but this method could not group the ring‐opening and no‐ring‐opening monomers clearly. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2827–2834, 2007     

Rapid ring‐opening polymerization of 1,4‐dioxan‐2‐one initiated by titanium alkoxides

Ring‐opening polymerization of 1,4‐dioxan‐2‐one in bulk was initiated by three titanium alkoxides, titanium dichlorodiisopropoxide (TiCl₂(OiPr)₂), titanium chlorotriisopropoxide (TiCl(OiPr)₃), and titanium tetraisopropoxide (Ti(OiPr)₄). The results indicate that the polymerization rate increased with number of OiPr groups in the initiator. High conversion of monomer (90%) and high molecular weight (11.9 × 10⁴ g/mol) of resulting polymer can be achieved in only 5 min at 60 °C with Ti(OiPr)₄ as an initiator. Analysis on nuclear magnetic resonance (NMR) spectra suggests the initiating sites for TiCl₂(OiPr)₂, TiCl(OiPr)₃, and Ti(OiPr)₄ to be 1.9, 2.6, and 3.8, respectively. Coordination‐insertion mechanism for the polymerization via cleavage of the acyl–oxygen bonds of the monomer was proved by NMR investigation. Kinetic studies indicate that polymerization initiated by Ti(OiPr)₄ followed a first‐order kinetics, with an apparent activation energy of 33.7 kJ/mol. It is noteworthy that this value is significantly lower than earlier reported values with other catalysts, namely La(OiPr)₃ (50.5 kJ/mol) and Sn(Oct)₂ (71.8 kJ/mol), which makes it an attractive catalyst for reactive extrusion polymerization. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Microwave‐assisted ring‐opening polymerization of p‐dioxanone

The ring‐opening polymerization (ROP) of p‐dioxanone (PDO) under microwave irradiation with triethylaluminum (AlEt₃) or tin powder as catalyst was investigated. When the ROP of PDO was catalyzed by AlEt₃, the viscosity‐average molecular weight (M_v) of poly(p‐dioxanone) (PPDO) reached 317,000 g mol^?1 only in 30 min, and the yield of PPDO achieved 96.0% at 80 °C. Tin powder was successfully used as catalyst for synthesizing PPDO by microwave heating, and PPDO with M_v of 106,000 g mol^?1 was obtained at 100 °C in 210 min. Microwave heating accelerated the ROP of PDO catalyzed by AlEt₃ or tin powder, compared with the conventional heating method. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3207–3213, 2008     

Degradable precision polynorbornenes via ring‐opening metathesis polymerization

In an attempt to introduce monomer sequence control in a growing polynorbornene via ring‐opening metathesis polymerization, we employ dioxepins to efficiently determine the location of the monomers on the macromolecule backbone. Owing to the acid‐labile acetal group, dioxepins allow scission of the polymer at the point of the dioxepin insertion and thus provide an indirect way to determine the monomer location. Additionally, dioxepins are used as spacers in the synthesis of multiblock polynorbornenes that are readily cleavable to afford the individual polynorbornene blocks. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1236–1242     

Synthesis of thioether‐functional poly(olefin)s via ruthenium‐alkylidene initiated ring‐opening metathesis polymerization

Ring‐opening metathesis polymerization (ROMP) of thioether‐derived oxanorbornene imide ( M1 ) and its copolymerization with various cycloolefin comonomers such as cyclopentene ( M2 ), cyclopent‐3‐en‐1‐ol ( M3 ), cycloheptene ( M4 ), and cyclooctene ( M5 ) using Hoveyda–Grubbs second generation catalyst has been investigated. Polymerizations were performed at two different temperatures (0 and 25 °C) and the obtained functional poly(olefin)s were characterized by nuclear magnetic resonance ¹H and ¹³C (NMR), and infrared spectroscopy as well as size exclusion chromatography, differential scanning calorimetry, and thermogravimetric analysis analyses. Additionally, the dependence of the polymer composition on the reaction temperature and monomer feed was studied with time‐dependent ¹H NMR experiments. Copolymerization of M1 with a five‐membered cycloolefin monomer M2 showed relatively low ROMP reactivity irrespective of the reaction conditions in comparison to M3 , M4 , and M5 monomers. In general, the degree of monomer incorporation into poly(olefin)s were determined in the order of M5 > M3 > M4 > M2 , and that sheds light on the effect of cycloolefin ring strain energies in the ruthenium‐alkylidene initiated ROMP. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1741–1747     

A novel acid promoted ring‐opening polymerization of a seven‐membered cyclic carbonate initiated with BCl3

Ring‐opening polymerization of a seven‐membered cyclic carbonate, 1,3‐dioxepan‐2‐one, was investigated with a novel initiator system, BCl₃‐HCl·Et₂O. Addition of HCl·Et₂O promoted the polymerization even at 0°C to produce the corresponding polycarbonate with controlled molecular weight and narrow polydispersity ratio (< 1.2).     

Chemistry of 2‐oxazolines: A crossing of cationic ring‐opening polymerization and enzymatic ring‐opening polyaddition

Chemistry of 2‐oxazolines is involved in the polymer synthesis fields of cationic ring‐opening polymerization (CROP) and enzymatic ring‐opening polyaddition (EROPA), although both polymerizations look like a quite different class of reaction. The key for the polymerization to proceed is combination of the catalyst (initiator) and the design of monomers. This article describes recent developments in polymer synthesis via these two kinds of polymerizations to afford various functional polymers having completely different structures, poly(N‐acylethylenimine)s via CROP and 2‐amino‐2‐deoxy sugar unit‐containing oligo and polysaccharides via EROPA, respectively. From the viewpoint of reaction mode, an acid‐catalyzed ring‐opening polyaddition (ROPA) is considered to be a crossing where CROP and EROPA meet. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1251–1270, 2010     

Organocatalysis applied to the ring‐opening polymerization of β‐lactones: A brief overview

Organocatalysis offers a number of prospects in the polymer community and presents advantages over metal based and bio‐organic methods. The use of organic molecules for performing chemical reactions is not a new concept, and any research into organocatalytic reactions builds on a respected history. Compared to the organocatalysis of large lactones, which began in the early 2000s, the examples presented here will demonstrate that few metal‐free initiating systems had been applied to β‐lactones well before the beginning of the current millennium. These metal‐free initiating systems present indisputable advantages over metal‐based processes. In the following paper, ring‐opening polymerizations (ROPs) of various β‐lactones for the preparation of poly(hydroxyalkanoate)s will be presented, as will the types of mechanisms involved, that is, zwitterionic and anionic, and cationic or supramolecular‐based ROPs. The advantages and drawbacks of the different technics will be discussed in the domain, which, for us, is important in the overall production of bioplastics. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 657–672     

Organocatalyzed ring‐opening polymerization of cyclic butylene terephthalate oligomers

In this study, various organic compounds, with different activation modes, have been tested as catalysts for the ring‐opening polymerization (ROP) of cyclic butylene terephthalate oligomers (CBT) in bulk at 210 °C, using tert‐butylbenzyl alcohol (tBnOH) as initiator. Among them, 1,3,5‐triazabicyclo[4.4.0]dec‐5‐ene (TBD) appeared to be the most efficient, achieving high monomer conversions in short reaction times (within minutes). Analysis by size‐exclusion chromatography (SEC) of the poly(butylene terephthalate) (PBT) synthesized using this catalyst also showed that the polymerization follows the expected theoretical M _n trend for molecular weights up to 50 kg·mol^?1. Chain‐end fidelity relatively to the alcohol initiator has been confirmed by MALDI‐TOF mass spectroscopy, which showed that all polymer chains possess the tert‐butylbenzyl moiety as chain‐end. Finally, to demonstrate the potential of this system for the synthesis of PBT‐based block copolymers, a monomethyl ether poly(ethylene glycol) (PEG) of 5000 g·mol^?1 has been employed as initiator for the ROP of CBT. A PEO‐b‐PBT block copolymer of 15,000 g·mol^?1 could thus been obtained, as confirmed by the shift of the SEC traces towards higher molecular weights and the same diffusion coefficient determined for ¹H NMR signals of the PEO block and the PBT block. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 1611–1619     

Tailored surface properties of monodispersed polymer particles with PCL hairy chains synthesized by hydroxyl‐initiated ring‐opening polymerization

Polymeric particles with hydrophobic PCL hairy chains were prepared by ring‐opening polymerization (ROP) from hydrophilic core particles, which were prepared by soap‐free emulsion polymerization of styrene, 2‐hydroxyethyl methacrylate, and divinylbenzene. Due to the incorporation of 2‐hydroxyethyl methacrylate in the core particles, hydroxyl groups on the surface of core particles could be obtained, and in the following ROP of ε‐caprolactone, the hydroxyl groups on the surface of the particles could effectively initiate the polymerization. Various reaction conditions were evaluated to produce hairy particles with optimal grafting efficiency. The presence of hydrophobic polymeric hairs on the surface of particles led to a dramatic improvement in their dispersibility in oil phase. By controlling the grafting amount of PCL on the surface of hydrophilic core particles, the surface properties of the hairy particles could be well tailored, represented the change of water contact angles from 75.0° to 114.6°. The prepared hairy particles were characterized by thermogravimetric analysis, scanning electron microscopy, differential scanning calorimetry, and Fourier transform infrared analysis. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4552–4563, 2007     

Rare earth metal initiated polymerization to give high polymers with narrow molecular weight distribution

Organolanthanide (III) initiated polymerization of alkyl acrylates gave high molecular weight poly(alkyl acrylate)s with extremely narrow molecular weight distribution in high yield. Molecular weight of the polymers increased linearly with the conversion. Random and block copolymerizations of acrylate monomers (alkyl acrylates and MMA) were successful. For development of olefin polymerization catalystsbased on lanthanide complexes, bulky substituents were introduced into Me₂Si bridged Cp rings and they were used as ligands of lanthanide complexes. Tri- and divalent lanthanide complexes with such a ligand system showed high activity for olefin polymerization and gave high molecular weight polyolefins.