Synthesis and Ring‐Opening Polymerization of Cyclic Butylene 2,5‐Furandicarboxylate

A new synthetic pathway for the polymerization of furan based polyesters is reported in this work. First, poly(butylene 2,5‐furandicarboxylate) cyclic oligoesters (COEs) are chemically synthesized by semi‐batch esterification. The structure of the COEs is confirmed by infrared spectroscopy, ¹H, and ¹³C‐NMR, while the molecular weight distribution of the COEs is determined by matrix‐assisted laser desorption/ionization time of flight mass spectroscopy. The cyclic oligoesters are then successfully polymerized via ring‐opening polymerization using tetrakis(2‐ethylhexyl)‐titanate as catalyst. Differential scanning calorimetry and ¹H‐NMR analysis unambiguously proves the formation of polymeric species. Both end‐group analysis from ¹H‐NMR spectrum and calculation through Flory–Fox equation give comparable estimates of the number average molecular weight: 5.8 × 10³ g mol^?1 and 7.8 × 10³ g mol^?1, respectively.

     

One‐Pot Synthesis of Polyester–Polyolefin Copolymers by Combining Ring‐Opening Polymerization and Carbene Polymerization

The ring‐opening polymerization (ROP) of a cyclic ester using alkyl acetate carbene (ROCOCH:) is generated from diazoacetate as organocatalyst under microwave irradiation, which enables the one‐pot preparation of copolymers of polyester and polyolefin. The chemical structure of the polymerized product is characterized by NMR, Fourier transformed infrared (FTIR), and UV–vis spectroscopy. The incorporation of the azo group into the obtained copolymer is determined by elemental analysis, which indicates that 1.38–6.21% nitrogen is contained in the obtained copolymers. The influences of catalyst and microwave irradiation parameters on the polymerization are investigated. Both the microwave power and irradiation time have great influences on the copolymerization. Moreover, the molar mass of the obtained polymers is calculated with polystyrene standards, which gradually increases from 600 to 36 100 g mol^?1 as the reaction temperature increases from 60 to 120 °C. Poly­mer with of 36 100 g mol^?1 and PDI of 1.86 is produced under optimized conditions. The combination of ROP and carbene polymerization offers a new and convenient pathway to synthesize copolymers of polyesters and polyolefins.

     

Poly(L‐lactide) Nanoparticles via Ring‐Opening Polymerization in Non‐aqueous Emulsion

The preparation of poly(L ‐lactide) nanoparticles via ring‐opening polymerization (ROP) of L ‐lactide is conducted in non‐aqueous emulsion. In this process, acetonitrile is dispersed in either cyclohexane or n‐hexane as the continuous phase and stabilized by a PI‐b‐PEO, respectively, a PI‐b‐PS copolymer as emulsifier. The air and moisture sensitive N‐heterocyclic carbene 1,3‐bis(2,4,6‐trimethylphenyl)‐2‐ididazolidinylidene (SIMes) catalyzes the polymerization of L ‐lactide at ambient temperatures. Spherical poly(L ‐lactide) nanoparticles with an average diameter of 70 nm and a tunable molecular weight are generated. Hence, the non‐aqueous emulsion technique demonstrates its good applicability toward the generation of well‐defined poly(L ‐lactide) nanoparticles under very mild conditions.     

Synthesis of Amphiphilic Comb‐Shape Copolymers Via Ring‐Opening Polymerization of a Macromonomer

Amphiphilic comb‐shape copolymers PCL‐co‐P(MTC‐mPEG₁₆) (where PCL, MTC, and mPEG refer to poly(ε‐caprolactone), 2‐methyltrimethylene carbonate, and methoxy poly(ethylene glycol), respectively) are synthesized by ring‐opening polymerization of ε‐caprolactone and cyclic carbonate‐terminated PEG macromonomer (MTC‐mPEG₁₆) with benzyl alcohol as an initiator and Sn(Oct)₂ as a catalyst. Amphiphilic copolymers PCL‐co‐P(MTC‐mPEG₁₆) can form micelles in aqueous solution by self‐assembly. The diameters of PCL‐co‐P(MTC‐mPEG₁₆) micelles characterized by dynamic light scattering area few dozens of nanometers with a narrow size distribution and the morphology of the micelles observed through transmission electron microscopy are nanosized spheres. The in vitro drug release of comb‐shape copolymer PCL‐co‐P(MTC‐mPEG₁₆) micelles is more stable and sustained than that of linear block copolymers mPEG‐b‐PCL.

     

One‐Pot Sequential Ring‐Opening Metathesis Polymerization and Acyclic Diene Metathesis Polymerization Synthesis of Unsaturated Block Polyphosphoesters

A novel divergent approach is presented for the one‐pot synthesis of unsaturated block poly­phosphoester (PPE) structures by a sequential ring‐opening metathesis polymerization (ROMP) and acyclic diene metathesis (ADMET) polymerization. A linear functional PPE bearing one or two terminal acrylate groups is first prepared through the third generation Grubbs catalyst‐mediated ROMP of seven‐membered cyclic phosphate monomer, in the presence of a symmetrical multifunctional terminating agent or chain transfer agent. The functional PPE is then utilized as a selective macromolecular chain stopper in subsequent ADMET polymerization of phosphoester functional asymmetric α,ω‐diene monomer, yielding unsaturated block PPEs. The thermal properties of block PPEs are studied and their thermal degradation and flame‐retardant properties are evaluated. Furthermore, the prepared block PPEs can spontaneously self‐assemble in a selective solvent to form polymeric micelles, which are characterized in detail by dynamic light scattering, atom force microscopy, transmission electron microscopy, and scanning electron microscopy analyses.

     

Synthesis of Functional Polydepsipeptides via Direct Ring‐Opening Polymerization and Post‐Polymerization Modification

This contribution explores different strategies for the synthesis of side chain functional polydepsipeptides. First, the ring‐opening polymerization of side chain functional morpholine‐2,5‐diones is revisited and the optimized reaction conditions used for the polymerization of (Z)‐L ‐Lys, (Boc)‐L ‐Lys and L ‐allylglycine based morpholine‐2,5‐diones. As a first approach towards side chain functional polydepsipeptides, the deprotection of poly(Glc‐alt‐(Z)‐L ‐Lys) and poly(Glc‐alt‐(Boc)‐L ‐Lys) is evaluated. Although under appropriate conditions, the side chain protecting groups can be quantitatively removed, the reaction conditions used here were found to lead to backbone degradation. As an alternative approach, the thiol‐ene post‐polymerization modification of poly(Glc‐alt‐allylglycine) is explored. Free radical addition of various ω‐functional thiols was found to proceed without backbone degradation and in several cases with quantitative allyl group conversion. The post‐polymerization modification strategy is attractive as it obviates the need for protecting group chemistry and facilitates the synthesis of diverse libraries of side chain functional polydepsipeptides.

     

High Molecular‐Weight Cyclic Polyesters from Solvent‐Free Ring‐Opening Polymerization of Lactones with a Pyridyl‐Urea/MTBD

(Thio)urea/base systems have been widely used in the ring‐opening polymerization (ROP) of lactones based on their superior performance in activity and selectivity. Herein, a pyridyl‐urea ( 6C‐PU )/7‐methyl‐1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene catalytic system is used to prepare the polyesters with cyclic topology via the ROP of lactones in the absence of initiator under solvent‐free conditions. The catalytic system shows high activity in the ROP of δ‐valerolactone (δ‐VL) and cyclic polyvalerolactones (PVLs) with high molecular weights and narrow molecular weight distribution are obtained despite the existence of some linear products generated during the precipitation process. The structure of the resulting polymers is determined by proton and carbon nuclear magnetic resonance spectra, matrix assisted laser desorption/ionization time of flight mass spectrometry, and intrinsic viscosity studies. A possible mechanism is proposed on the basis of NMR analysis and characteristics of polymerization. Thermal and mechanical properties of cyclic PVLs are investigated through differential scanning calorimetry, thermogravimetric analysis, and tensile test.     

Controlled Ring‐Opening Polymerization of Lactones and Lactide Initiated by Lanthanum Isopropoxide, 2. Mechanistic Studies

The mechanism of ring‐opening polymerization of some lactones and lactide initiated by lanthanum isopropoxide has been comprehensively investigated. NMR and viscosity analyses demonstrated that three active polymer chains grow per lanthanum atom and that, depending on the coordinating ability of the monomer, propagation proceeds on aggregated or unaggregated active species. It is also demonstrated that inter‐ and intramolecular side reactions are limited and that lanthanum‐based initiator selectivity in ring‐opening polymerization is analogous to that of aluminum ones.

Part of the proposed mechanism for the lanthanum alkoxide initiated polymerization of ε‐caprolactone.     

AB2 Functional Polyesters via Ring Opening Polymerization: Synthesis and Characterization

Aliphatic AB₂ functional polyesters were conveniently prepared by the ring opening polymerization of ε‐caprolactone and L ‐lactide in the presence of the AB₂ functional initiator 2,2‐bis(hydroxymethyl)propionic acid (bis‐MPA) and Sn(Oct)₂ as the catalyst. In L ‐lactide polymerization, both bis‐MPA hydroxyl groups initiated the polymerization reaction, but for ε‐caprolactone polymerization this depended on the monomer to initiator to catalyst ratio. Initiation at two hydroxyl groups occurred at high monomer to initiator ([M]/[I]) ratio and at high Sn(Oct)₂ to monomer ratio. The melting temperatures of the AB₂‐functional PLLA and PCL polymers were comparable to linear polymers with a equal to the per arm in the polymer.

     

Selectivity of PEO‐block‐PPO Diblock Copolymers in the Microwave‐Accelerated,Anionic Ring‐Opening Polymerization of Propylene Oxide with PEG as Initiator

Diblock copolymers of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) were synthesized by the anionic ring‐opening polymerization of propylene oxide (PO), with controlled microwave heating in sealed vessels. A detailed study was carried out to investigate the effects of different parameters on the formation of unwanted byproducts. Parameters that were considered include temperature; the concentration of NaH, monomer and hydroxy groups in the feed; and the polarity of the reaction medium. A continuous decrease of internal pressure during the sealed‐vessel experiment reflected the consumption of PO monomer and the completion of the reaction was confirmed by a drop of the internal pressure to zero when reactions were performed in bulk. The products were characterized by using different chromatographic techniques. A comparison of the reaction times and composition of the polymers prepared by microwave and conductive heating is given.

     

Cationic Bottlebrush Polymers from Quaternary Ammonium Macromonomers by Grafting‐Through Ring‐Opening Metathesis Polymerization

Cationic bottlebrush homopolymers are polymerized using a grafting‐through approach by ring‐opening metathesis polymerization (ROMP) to afford well‐defined polymers. Quaternary ammonium macromonomers (MMs) are prepared by quaternizing tertiary amine MMs synthesized by reversible addition‐fragmentation chain transfer (RAFT) polymerization. The quaternary ammonium MMs undergo ROMP to target molecular weights (M_n = 30 000–100 000 g mol^?1) and a low dispersity (? = 1.10–1.30). Halide‐ligand exchange between the third generation Grubbs catalyst (G3) and halide counter ions (bromide and iodide ions) of MMs changes the catalyst activity throughout ROMP, causing it to deviate from pseudo‐first order kinetic behavior; however, the polymerization still follows controlled behavior without significant catalyst termination. Increasing steric bulk of the MMs decreases the polymerization rate as well. Amphiphilic block copolymers are synthesized by sequential polymerization of quaternary ammonium MMs and polystyrene (PS) MMs. Using a PS macroinitiator affords block copolymers with lower ? values as compared to the less active cationic macroinitiator.     

Amphiphilic Polyoxazoline‐block‐Polypeptoid Copolymers by Sequential One‐Pot Ring‐Opening Polymerizations

Amphiphilic block copolymers possess great potential as biomaterials in drug delivery and gene therapy. Herein, pseudopeptidic‐type diblock copolymer of poly(2‐oxazoline)‐block‐polypeptoid (POx‐b‐POI) is presented and synthesized. Poly[2‐(3‐butenyl)‐2‐oxazoline]‐block‐poly(sarcosine) (PBuOx‐b‐PSar) comprising hydrophobic POx segment bearing alkenyl side chain and hydrophilic POI segment of N‐methyl glycine, viz., sarcosine, is prepared by ring‐opening polymerization (ROP) through a one‐pot and three‐step route. Diphenyl phosphate initiates ROP of BuOx, and then the living chain end of PBuOx is quenched by ammonia to obtain PBuOx‐ammonium phosphate in situ, the active ammonium group initiates ROP of sarcosine N‐carboxy anhydride. PBuOx‐b‐PSar with controlled molecular weights (4.7–10.8 kg mol⁻¹) and narrow dispersities (Ð _M 1.15–1.21) are characterized by ¹H NMR, ¹³C NMR, and size‐exclusion chromatography. Dynamic light scattering and transmission electron microscopy analysis reveal that PBuOx‐b‐PSar self‐assembles into nanostructures of average diameter D _H of 37–109 nm in aqueous solution. 3‐(4,5‐Dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide test demonstrates the cytocompatibility (relative cell viability > 80%) of the PBuOx‐b‐PSar. In view of the self‐assembly and biocompatibility, the readily prepared diblock copolymers may hopefully be used in biomedical applications.

     

Synthesis of Poly(L‐lactide)‐Functionalized Multiwalled Carbon Nanotubes by Ring‐Opening Polymerization

MWNTs are modified to possess hydroxy groups and are used as coinitiators to polymerize L ‐lactide by the surface‐initiated ring‐opening polymerization. FT‐IR and TEM observations reveal that the PLLA is covalently attached to the MWNTs (MWNT‐g‐PLLA), and the weight gain as a result of the functionalization is determined by TGA analysis. Two kinds of solvents, namely DMF and toluene, are used to carry out the two series of polymerizations at 140 and 70 °C, respectively, for 2–20 h. The amount of grafted PLLA increases with the reaction time either in DMF or in toluene, but it increases more significantly in DMF at 140 than in toluene at 70 °C, with the reaction time being the same. The grafted PLLA layer on the MWNT is more uniform when the reaction is performed in DMF than in toluene, and some bare surfaces are observed in the TEM image of the MWNT‐g‐PLLA prepared in toluene. The MWNT‐g‐PLLAs are well dispersed in the organic solvents as well as in the PLLA matrix. Incorporation of MWNT‐g‐PLLA greatly improves the tensile modulus and strength without a significant loss of the elongation at break. The specific interaction between the MWNT‐g‐PLLA and the polymer matrix is quantified by way of the Flory‐Huggins interaction parameter, B, which is determined by combining the melting point depression and the binary interaction model.

     

Novel Polyesteramide‐Based Diblock Copolymers: Synthesis by Ring‐Opening Copolymerization and Characterization

Block copolymers based on a polyesteramide sequence and a polyether block were synthesized in bulk at 250 °C by ring‐opening copolymerization (ROP) of ε‐caprolactone (CLo) and ε‐caprolactam (CLa) as initiated by Jeffamine® M1000, i.e., ω‐NH₂ copoly[(ethylene oxide)‐co‐(propylene oxide)] copolymer [P(EO‐co‐PO)‐NH₂]. For an initial molar ratio of [CLa]₀/[CLo]₀ = 1, the copolymerization allowed for the formation of a diblock copolymer with a statistical polyesteramide sequence, as evidenced by ¹³C NMR. Investigation of the ROP mechanism highlighted that CLo was first polymerized, leading to the formation of a diblock copolymer P(EO‐co‐PO)‐b‐PCLo‐OH, followed by CLa hydrolysis to aminocaproic acid that inserted into the ester bonds of PCLo via aminolysis and subsequent condensation reactions. The outcome is the selective formation of P(EO‐co‐PO)‐b‐P(CLa‐co‐CLo)‐OH diblock copolymers where the composition and length of the polyesteramide sequence can be fine‐tuned by the [CLa]₀/[CLo]₀ and ([CLa]₀ + [CLo]₀)/[P(EO‐co‐PO)‐NH₂]₀ initial molar ratios.     

Low Temperature Ring‐Opening Polymerization of Diglycolide Using Organocatalysts with PEG as Macroinitiator

Polyglycolide (PGA) is synthesized via ring‐opening polymerization (ROP) of diglycolide using the organocatalysts 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU), 1,5‐diazabicyclo[4.3.0]non‐5‐ene, or 1,5,7‐ triazabicyclo[4.4.0]dec‐5‐ene. ROP is carried out at low temperatures ranging from ?20 to 50 °C without adding any alcohol as initiator. All polymers are fully soluble in hexafluoroisopropanol. At ambient temperature number average molecular weights up to 27 000 g mol^?1 are obtained. With DBU the highest molecular weights and conversions are accessible at ?20 °C. Melting temperature and glass transition temperature are independent of PGA molecular weight. Carrying out the reactions in the presence of polyethylene glycol serving as macroinitiator yields polymers with improved thermal stability and lowered melting temperatures.

     

Synthesis and Ring‐Opening Metathesis Polymerization of New Oxanorbornene Dicarboximides with Fluorine Pendant Groups

The synthesis of exo‐N‐3,5‐bis(trifluoromethyl)phenyl‐7‐oxanorbornene‐5,6‐dicarboximide (TFMPhONDI, 2a ), exo‐N‐4‐fluorophenyl‐7‐oxanorbornene‐5,6‐dicarboximide (FPhONDI, 2b ), and exo‐N‐pentafluorophenyl‐7‐oxanorbornene‐5,6‐dicarboximide (PFPhONDI, 2c ) monomers is described. Poly(norbornene dicarboximide)s were obtained via ROMP using bis(tricyclohexylphosphine)benzylidine ruthenium(IV) dichloride ( I ) and tricyclohexylphosphine [1,3‐bis(2,4,6‐trimethylphenyl)‐4,5‐dihydroimidazolilydene][benzylidene] ruthenium dichloride ( II ). Poly‐TFMPhONDI ( 3a ) bearing a trifluoromethylaryl moiety showed a higher T_g and improved mechanical properties as compared to poly‐FPhONDI ( 3b ) and poly‐PFPhONDI ( 3c ).

     

Soluble Phenylenevinylene Polymers Containing Tetraphenylethene Units by Ring‐Opening Metathesis Polymerization

Soluble phenylenevinylene polymers containing tetraphenylethene units are synthesized by ring‐opening metathesis polymerization of 4‐triphenylvinylphenyl‐[2.2]paracyclophane‐1,9‐diene in the presence of the second generation Grubbs’ initiator. Various polymer molecular weights can be obtained by altering the monomer to initiator ratio. Isomerization is successfully conducted in dilute polymer solution under a UV light irradiation. The as‐prepared polymers with longer chain lengths show relatively strong emission with a photoluminescence quantum yield of up to 43% in solution. Aggregation induced emission is observed for the polymers containing the cis–trans microstructures when the water fraction reached 80% in water/THF mixture. The morphologies of the polymers containing the cis–trans and trans microstructures are distinctive which reveal sphere‐like particles and network‐like structures, respectively. These polymers are promising candidates for potential uses in fluorescence applications.     

Fast Ring‐Opening Polymerization of 1,2‐Disubstituted Epoxides Initiated by a CoIII‐Salen Complex

Polyethers are an important class of polymers that find numerous applications. Ring‐opening polymerization of various 1,2‐disubstituted epoxides initiating a commercial, and well‐defined Co^III‐Salen complex is investigated in this paper. Remarkable reactivity (0.01% Co^III loadings, TOF up to 19200 h^?1) is discovered in this transformation. High molecular weight polymers (up to 80 kg mol^?1) are produced. In particular, polyether from ring‐opening polymerization of 1,4‐dihydronaphthalene oxide exhibits a glass transition temperatures (T_g) of up to 108 °C. By investigating the relationship between polymerization reactivity and counter ion in the Co^III complex, as well as the properties of the resultant polyethers, a cationic mechanism through an oxonium species is proposed.     

One‐Pot Combination of eROP and ROMP for the Synthesis of Block Copolymers

The one‐pot combination of enzymatic ring‐opening polymerization (eROP) and ring‐opening metathesis polymerization (ROMP) is successfully established to construct block copolymers. cis‐1,4‐Diacetoxy‐2‐butene is employed both as a precursor to initiate eROP of ε‐caprolactone or 15‐pentadecanolide and as a chain transfer agent in ROMP. The obtained polymers are systematically characterized by NMR, GPC, DSC, and microTOF‐QII MS. An evaluation of the reaction kinetics indicates the presence of two stages during the one‐pot eROP/ROMP process. Compared with cascade methods, this one‐pot method exhibits many advantages for preparing well‐defined block copolymers, such as mild reaction conditions and the elimination of complex purification steps for intermediates. Thus, this one‐pot combination approach has the potential to be widely used in preparing biocompatible polymeric materials, especially for biological and pharmaceutical applications.

     

Counterion Effect of Amine Salts on Ring‐Opening Polymerization of 1,3‐Benzoxazines

The effect of nucleophilicity of counterions of amine HX salts as catalysts on the ring‐opening polymerization (ROP) of 1,3‐benzoxazines is investigated. The significant reduction observed for the ROP temperature is related to the nucleophilicity of counterions and found to show a general trend as I^? > Br^? > Cl^?, as studied by differential scanning calorimetry and Fourier transform infrared spectroscopy. Moreover, the latent character of the amine salts is also demonstrated by tracking the benzoxazine–amine salt mixtures using ¹H NMR spectroscopy. The spectral analysis gives evidences for the dormant nature of the amine HX salts toward benzoxazine at room temperature in solvent. Besides, thermal stabilities of the cured benzoxazine monomers with and without catalysts are investigated by thermogravimetric analysis.