Radical‐initiated polymerization of β‐methyl‐α‐methylene‐γ‐butyrolactone

β‐Methyl‐α‐methylene‐γ‐butyrolactone (MMBL) was synthesized and then was polymerized in an N,N‐dimethylformamide (DMF) solution with 2,2‐azobisisobutyronitrile (AIBN) initiation. The homopolymer of MMBL was soluble in DMF and acetonitrile. MMBL was homopolymerized without competing depolymerization from 50 to 70 °C. The rate of polymerization (R_p) for MMBL followed the kinetic expression R_p = [AIBN]^0.54[MMBL]^1.04. The overall activation energy was calculated to be 86.9 kJ/mol, k_p/k_t^1/2 was equal to 0.050 (where k_p is the rate constant for propagation and k_t is the rate constant for termination), and the rate of initiation was 2.17 × 10^?8 mol L^?1 s^?1. The free energy of activation, the activation enthalpy, and the activation entropy were 106.0, 84.1, and 0.0658 kJ mol^?1, respectively, for homopolymerization. The initiation efficiency was approximately 1. Styrene and MMBL were copolymerized in DMF solutions at 60 °C with AIBN as the initiator. The reactivity ratios (r₁ = 0.22 and r₂ = 0.73) for this copolymerization were calculated with the Kelen–Tudos method. The general reactivity parameter Q and the polarity parameter e for MMBL were calculated to be 1.54 and 0.55, respectively. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1759–1777, 2003     

Cationic copolymerization of racemic‐β‐butyrolactone with L,L‐lactide: One‐pot synthesis of block copolymers

Cationic copolymerization of racemic‐β‐butyrolactone (β‐BL) with l,l ‐lactide (LA) initiated by alcohol and catalyzed by trifluoromethanesulfonic acid proceeding by activated monomer (AM) mechanism was investigated. Although both comonomers were present from the beginning in the reaction mixture, polymerization proceeded in sequential manner, with poly‐BL formed at the first stage acting as a macroinitiator for the subsequent polymerization of LA. Such course of copolymerization was confirmed by following the consumption of both comonomers throughout the process as well as by observing the changes of growing chain‐end structure using ¹H NMR. ¹³C NMR analysis and thermogravimetry revealed the block structure of resulting copolymers. The proposed mechanism of copolymerization was confirmed by the studies of changes of ¹H NMR chemical shift of acidic proton in the course of copolymerization, providing an indication that indeed protonated species and hydroxyl groups are present throughout the process, as required for AM mechanism. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4873–4884     

Acid‐promoted double ring‐opening reaction of bicyclobis (γ‐butyrolactone) with alcohol and its application to polyester synthesis

Bicyclobis(γ‐butyrolactone) (BBL) bearing methyl group 1a reacted with benzyl alcohol (BnOH) in the presence of p‐toluenesulfonic acid (p‐TsOH) through the double ring‐opening of the bislactone structure to afford the corresponding adduct 2a bearing carboxyl group. The resulting carboxyl group underwent condensation with BnOH to afford the corresponding diester 3a . The second step was quite slow at ambient temperature; however, it was efficiently accelerated by elevating temperature to 120 °C or performing under reduced pressure at 80 °C to afford 3a in an excellent yield. Based on these results, the reaction of 1a with xylene‐α,α‐diol (XyD) was carried out in chlorobenzene at 120 °C to obtain the corresponding polyester bearing ketone group in the side chain. The condensation reaction in the second step was effectively promoted by simultaneous removal of water under reduced pressure. BBLs 1b and 1c bearing reactive groups, isopropenyl and chloromethyl, respectively, were also employed as monomers efficiently. Their reactions with XyD gave the corresponding reactive polyesters bearing methacryloyl and chloroacetyl moieties, respectively. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Aluminum salen and salan complexes in the ring‐opening polymerization of cyclic esters: Controlled immortal and copolymerization of rac‐β‐butyrolactone and rac‐lactide

Aluminum‐based salen and salan complexes mediate the ring‐opening polymerization (ROP) of rac‐β‐butyrolactone (β‐BL), rac‐lactide, and ε‐caprolactone. Al‐salen and Al‐salan complexes exhibit excellent control over the ROP of rac‐β‐butyrolactone, yielding atactic poly(3‐hydroxybutyrate) (PHB) with narrow PDIs of <1.15 for Al‐salen and <1.05 for Al‐salan. Kinetic studies reveal pseudo‐first‐order polymerization kinetics and a linear relationship between molecular weight and percent conversion. These complexes also mediate the immortal ROP of rac‐β‐BL and rac‐lactide, through the addition of excess benzyl alcohol of up to 50 mol eq., with excellent control observed. A novel methyl/adamantyl‐substituted Al‐salen system further improves control over the ROP of rac‐lactide and rac‐β‐BL, yielding atactic PHB and highly isotactic poly(lactic acid) (P_m = 0.88). Control over the copolymerization of rac‐lactide and rac‐β‐BL was also achieved, yielding poly(lactic acid)‐co‐poly(3‐hydroxybutyrate) with narrow PDIs of <1.10. ¹H NMR spectra of the copolymers indicate a strong bias for the insertion of rac‐lactide over rac‐β‐BL. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Efficient catalysts for ring‐opening polymerization of ε‐caprolactone and β‐butyrolactone: Synthesis and characterization of zinc complexes based on benzotriazole phenoxide ligands

A series of efficient zinc catalysts supported by sterically bulky benzotriazole phenoxide ( BTP ) ligands are synthesized and structurally characterized. The reactions of diethyl zinc (ZnEt₂) with ^CMe2PhBTP ‐H, ^t‐BuBTP ‐H, and ^TMClBTP ‐H yield monoadduct [(μ‐ BTP )ZnEt]₂ ( 1 – 3 ), respectively. Bisadduct complex [( ^t‐BuBTP )₂Zn] ( 4 ) results from treatment of ZnEt₂ with ^t‐BuBTP ‐H (2 equiv.) in toluene, but treatment of ^TMClBTP ‐H with ZnEt₂ in the same stoichiometric proportion in Et₂O produces five‐coordinated monomeric complex [( ^TMClBTP )₂Zn(Et₂O)] ( 5 ). The molecular structures of compounds 1 , 4 , and 5 are characterized by X‐ray crystal structure determinations. All complexes 1 – 5 are efficient catalysts for the ring‐opening polymerization of ε‐caprolactone (ε‐CL) in the presence of 9‐anthracenemethanol. Experimental results indicate that complex 3 exhibits the greatest activity with well‐controlled character among these complexes. The polymerizations of ε‐CL and β‐butyrolactone catalyzed by 3 are demonstrated in a “living” character with narrow polydispersity indices (monomer‐to‐initiator ratio in the range of 25–200, PDIs ≤ 1.10). The “immortal” character of 3 provides a way to synthesize as much as 16‐fold polymer chains of poly(ε‐CL) (PCL) with narrow PDI in the presence of a catalyst in a small proportion. The controlled fashion of complex 3 also enabled preparation of the PCL‐b‐poly(3‐hydroxybutyrate) copolymer. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Organometallic and enzymatic catalysis for ring opening copolymerization of ε‐caprolactone and 4‐methyl‐ε‐caprolactone

A series of copolymers containing ε‐caprolactone (CL) and 4‐methyl‐ε‐caprolactone (MeCL) were synthesized by ring‐opening polymerization (ROP) using Tin(II) bis(2‐ethylhexanoate)(Sn(Oct)₂) or Novozym 435 as catalyst. The molecular structure and weight of copolymers were determined by nuclear magnetic resonance (NMR) and size exclusion chromatography (SEC), respectively. Our kinetic study showed that the monomer reactivity ratios for CL (r₁) and MeCL (r₂) using Sn(Oct)₂ as catalyst were estimated to be near unity and r₁ × r₂ = 1, indicating the random distribution of the monomers in the final copolymer. The results of DSC and XRD consistently indicated that the copolymers were inclined to be amorphous with the increasing of MeCL fraction. Microspheres were prepared from copolymers and characterized by SEM. The preliminary degradability and biocompatibility studies on these copolymers were also assessed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Hydroxyl‐tolerated polymerization of N‐phenoxycarbonyl α‐amino acids: A simple way to polypeptides bearing hydroxyl groups

Differing from the moisture‐sensitive α‐amino acid N‐carboxyanhydrides (AA‐NCAs) monomers, N‐phenoxycarbonyl α‐amino acids (AA‐NPCs) can be prepared and stored in open air. In this contribution, we report that the controlled polymerizations of AA‐NPC monomers of O‐tert‐butyl‐dl ‐serine (BRS‐NPC), N^ε‐benzyloxycarbonyl‐l ‐lysine (ZLL‐NPC) and N^ε‐trifluoroacetyl‐l ‐lysine (FLL‐NPC) initiated by amines are surprisingly able to tolerate common nucleophilic impurities such as water and alcohols at a level of monomer concentration. The structures of polypeptides synthesized in the presence of water or alcohols agree well with the designed ones in the case of repeated chain extensions. Detailed mechanism study and density functional theory calculation reveal that the low concentration of AA‐NCA and the high activity of amines are the key factors to the controllability of AA‐NPC polymerizations. The water‐ and alcohol‐tolerant property in polymerizations of AA‐NPCs encourages the following studies on unprotected (phenolic) hydroxyl groups containing AA‐NPCs. The controllable polymerizations of N‐phenoxycarbonyl l ‐tyrosine (LT‐NPC) and N‐phenoxycarbonyl S‐(3‐hydroxypropyl)‐l ‐cysteine (HLC‐NPC) initiated by amines are confirmed and reported for the first time, which extends the library of AA‐NPCs and polypeptides as well. All the universality of library, the convenience of monomer preparation, and the controllability and water‐ and alcohol‐tolerant property of polymerization of AA‐NPCs significantly enhance the feasibility of polypeptide synthesis, making AA‐NPC approach a promising synthetic method of polypeptides. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 907–916     

Ring‐opening polymerization of β‐butyrolactone catalyzed by efficient magnesium and zinc complexes derived from tridentate anilido‐aldimine ligand

Magnesium (Mg) and zinc (Zn) complexes incorporating tridentate anilido‐aldimine ligand, (E)‐2, 6‐diisopropyl‐N‐(2‐((2‐(piperidin‐1‐yl)ethylimino)methyl)phenyl)aniline ( AA ^Pip ‐H, 1 ), were synthesized and structurally characterized. The reaction of AA ^Pip ‐H ( 1 ) with MgⁿBu₂ or ZnEt₂ in equivalent proportions afforded the monomeric complex [( AA ^Pip )MgⁿBu] ( 2 ) or [( AA ^Pip )ZnEt] ( 3 ), respectively. The coordination modes of these complexes differ in the solid state: Mg complex 2 shows a four‐coordinated and distorted tetrahedral geometry, whereas Zn complex 3 adopts a trigonal planar geometry with a three‐coordinated Zn center. Complexes 2 and 3 are efficient catalysts for the ring‐opening polymerization of β‐butyrolactone (β‐BL) in the presence of 9‐anthracenemethanol (9‐AnOH). The polymerization of β‐BL with the Zn catalyst system is demonstrated in a living fashion with a narrow polydispersity index, PDI = 1.01–1.10. The number‐averaged molecular weight (M_n) of the produced poly(3‐hydroxybutyrate) (PHB) is quite close to the expected M_n over diverse molar ratios of monomer to 9‐AnOH. A greater ratio of monomer to alcohol catalyzed by Zn complex 3 served to form PHB with a large molecular weight (M_n > 60000). An effective method to prepare PHB‐b‐PCL and PEG‐b‐PHB by the ring‐opening copolymerization of β‐BL catalyzed by zinc complex 3 is reported. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Synthesis and Ring Opening Polymerization of a New Functional Lactone, α‐Iodo‐ε‐caprolactone: A Novel Route to Functionalized Aliphatic Polyesters

A new functional lactone, α‐iodo‐ε‐caprolactone (αIεCL), was synthesized from ε‐caprolactone by anionic activation using a non‐nucleophilic strong base (lithium diisopropylamide) followed by an electrophilic substitution with iodine chloride. Ring‐opening (co)polymerizations of the resulting monomer with ε‐caprolactone were carried out using tin 2‐ethylhexanoate as a catalyst in toluene at 100 °C. Homopolymerization of αIεCL was achieved, and poly(αIεCL) was fully characterized by SEC, ¹H NMR and elemental analysis. Random copolymerizations of αIεCL with εCL were controlled with experimental molecular weights close to the theoretical values, narrow molecular weight distributions and a good agreement between experimental and theoretical molar compositions of αIεCL.

     

New aliphatic poly(ester‐carbonates) based on 5‐methyl‐5‐allyloxycarbonyl‐1,3‐dioxan‐2‐one

The synthesis, characterization, and ring‐opening polymerization of a new cyclic carbonate monomer containing an allyl ester moiety, 5‐methyl‐5‐allyloxycarbonyl‐1,3‐dioxan‐2‐one (MAC), was performed for the first time. MAC was synthesized in five steps in good yield beginning from the starting material, 2,2‐bis(hydroxymethyl)propionic acid. Subsequent polymerization and copolymerizations of the new cyclic carbonate with rac‐lactide (rac‐LA) and ?‐caprolactone (CL) were attempted. Rac‐LA copolymerized well with MAC, but CL copolymerizations produced insoluble products. Oligomeric macroinitiators of MAC and rac‐LA were synthesized from stannous ethoxide, and both macroinitiators were used for the controlled ring‐opening polymerization of rac‐LA. The polymerization kinetics were examined by monitoring the disappearance of the characteristic C? O ring stretch of the monomer at 1240 cm^?1 with real‐time in situ Fourier transform infrared spectroscopy. Postpolymerization oxidation reactions were conducted to epoxidize the unsaturated bonds of the MAC‐functionalized polymers. Epoxide‐containing polymers may allow further organic transformations with various nucleophiles, such as amines, alcohols, and carboxylic acids. NMR was used for microstructure identification of the polymers, and size exclusion chromatography and differential scanning calorimetry were used to characterize the new functionalized poly(ester‐carbonates). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1978–1991, 2003     

Synthesis of bicyclic bis(γ‐butyrolactone) derivatives bearing sulfide moieties and their alternating copolymers with epoxide

A series of bicyclic bis(γ‐butyrolactone)s (BBL) bearing sulfide moiety 2 were readily synthesized from a precursor BBL bearing isopropenyl group 1. This efficient and versatile synthesis of 2 was achieved by a highly reliable radical addition reaction of thiols to the C‐C double bond in the isopropenyl group 2 underwent anionic copolymerization with glycidyl phenyl ether in a 1:1 alternating manner to give a series of the corresponding polyester 3, of which side chains inherited the sulfide group from 2. The glass transition temperatures (T_g) of 3 showed clear dependence on the flexibility of the sulfide side chains. The scope of this copolymerization system was further expanded by synthesizing a bifunctional BBL 4 from 1 with using hexanedithiol and performing its copolymerization with bisphenol A diglycidyl ether 5. The copolymerization gave the corresponding networked polymer in high yield. During the copolymerization, the volume expanding nature of the double ring‐opening reaction of 4 contributed to the efficient compensation of the intrinsic volume shrinkage of the ring‐opening of epoxide to achieve a shrinkage‐free curing system. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Ring‐opening polymerization of lactides catalyzed by magnesium complexes coordinated with NNO‐tridentate pyrazolonate ligands

A series of magnesium benzylalkoxide complexes, [LⁿMg(μ‐OBn)]₂ ( 1 – 14 ) supported by NNO‐tridentate pyrazolonate ligands with various electron withdrawing‐donating subsituents have been synthesized and characterized. X‐ray crystal structural studies revealed that Complexes 1 – 3 , 5 , 7 , 9 , and 10 are dinuclear bridging through benzylalkoxy oxygen atoms with penta‐coordinated metal centers. All of these complexes acted as efficient initiators for the ring‐opening polymerization of L‐lactide and rac‐lactide. Based on kinetic studies, the activity of these metal complexes is significantly influenced by the electronic effect of the ancillary ligands with the electron‐donating substituents at the phenyl rings enhancing the polymerization rate. In addition, the “living” and “immortal” character of 6 has paved a way to synthesize as much as 40‐fold polymer chains of polylactides with a very narrow polydispersity index in the presence of a small amount of initiator. Among all of magnesium complexes, Complex 6 exhibits the highest stereoselectivity toward ring‐opening polymerization of rac‐lactide with Pr up to 88% in THF at 0 °C. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Two‐Step Backbiting Reaction in the Ring‐Opening Polymerization of γ‐Acryloyloxy‐ε‐caprolactone Initiated with Aluminium Isopropoxide

γ‐Acryloyloxyethyl‐γ‐butyrolactone is formed as a byproduct when the polymerization of γ‐acryloyloxy‐ε‐caprolactone is initiated with aluminium isopropoxide in toluene. The extent of this side reaction decreases with decreasing temperature and is dependent on whether the reaction is stopped as soon as monomer conversion is complete or not. A two‐step backbiting mechanism is proposed for this intramolecular transesterification reaction.     

The effect of microwave irradiation on the kinetics and activation thermodynamics of ring‐opening polymerization of ε‐caprolactone

We examined the ring‐opening polymerization of ε‐caprolactone in toluene between 50 and 70 °C, and catalyzed by some Lewis and Brønsted acids to investigate the effects of microwave versus conventional heating on the kinetics and activation thermodynamics of the reaction. The polymerizations proceeded more rapidly when microwave heating, instead of conventional heating, was used to control the temperature. The number‐average molecular weight (M_n) of the polymer could be controlled even when microwave heating was used. To identify which thermodynamic activation constants were responsible for the accelerated polymerizations, we performed the reaction at different temperatures to obtain data for the Arrhenius and Eyring equations. Although the values for the activation energies and the activation enthalpies were larger when microwave heating rather than conventional heating was used, the frequency factors and the activation entropies (ΔS^?) over compensated for the less favorable activation energies and enthalpies. The more favorable ΔG^? found for the microwave‐assisted polymerizations mainly reflect the larger ΔS^? values, and the rate accelerations appear to be a consequence of differently arranged intermediates and/or transition states. © 2013 Wiley Periodicals, Inc. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3732–3739     

Ring‐opening polymerization of lactide, ε‐caprolactone and their copolymerization catalyzed by β‐diketiminate zinc complexes

A series of zinc silylamido complexes bearing non‐symmetric β ‐diketiminate ligands were synthesized and structurally characterized. Ring‐opening polymerization (ROP) of rac ‐lactide catalyzed by these zinc complexes afforded heterotactic polylactides at room temperature (P _r = 0.79 ~ 0.83 in THF). The steric and electronic characteristics of the ancillary ligands showed significant influence on the polymerization performance of the corresponding zinc complexes. All these zinc complexes also showed moderate activities toward the polymerization of ε ‐caprolactone at ambient temperature in toluene, producing polycaprolactones (PCLs) with high molecular weights and moderate polydispersities. PCL‐b ‐PLLA copolymers could be obtained via three different copolymerization strategies (one‐pot polymerization, and sequential addition of the two monomers in either order) by adopting complex 6 as the initiator through the adjustment of reaction temperatures. The diblock nature of the copolymers was confirmed by ¹³C NMR spectroscopy and DSC analysis.     

Investigation of Cationic Polymerization of β‐Pinene Using Calorimetric Measurements

An experimental investigation of the kinetics of cationic polymerization of β‐pinene was performed using two different initiator systems under two different operating conditions (shot additions of initiator, and continuous feeding of monomer). The experiments were done using calorimetric measurements under isoperibolic conditions. The heat of polymerization of β‐pinene was found to be ?30.6 kcal · mol^?1. A simple kinetic model was tentatively proposed, and the model fit reasonably well to the different experimental runs. Different values of the fitting parameters were obtained for runs carried out under different conditions, which can probably be ascribed to the presence of adventitious impurities in the commercial‐grade monomer used.