Microwave‐improved polymerization of ϵ‐caprolactone initiated by carboxylic acids

The ring‐opening polymerization of ε‐caprolactone (ε‐CL), initiated by carboxylic acids such as benzoic acid and chlorinated acetic acids under microwave irradiation, was investigated; with this method, no metal catalyst was necessary. The product was characterized as poly(ε‐caprolactone) (PCL) by ¹H NMR spectroscopy, Fourier transform infrared spectroscopy, ultraviolet spectroscopy, and gel permeation chromatography. The polymerization was significantly improved under microwave irradiation. The weight‐average molecular weight (M_w) of PCL reached 44,800 g/mol, with a polydispersity index [weight‐average molecular weight/number‐average molecular weight (M_w/M_n)] of 1.6, when a mixture of ε‐CL and benzoic acid (25/1 molar ratio) was irradiated at 680 W for 240 min, whereas PCL with M_w = 12,100 and M_w/M_n = 4.2 was obtained from the same mixture by a conventional heating method at 210 °C for 240 min. A degradation of the resultant PCL was observed during microwave polymerization with chlorinated acetic acids as initiators, and this induced a decrease in M_w of PCL. However, the degradation was hindered by benzoic acid at low concentrations. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 13–21, 2003     

Photocatalyst-independent photoredox ring-opening polymerization of O-carboxyanhydrides: stereocontrol and mechanism

Photoredox ring-opening polymerization of O-carboxyanhydrides allows for the synthesis of polyesters with precisely controlled molecular weights, molecular weight distributions, and tacticities. While powerful, obviating the use of precious metal-based photocatalysts would be attractive from the perspective of simplifying the protocol. Herein, we report the Co and Zn catalysts that are activated by external light to mediate efficient ring-opening polymerization of O-carboxyanhydrides, without the use of exogenous precious metal-based photocatalysts. Our methods allow for the synthesis of isotactic polyesters with high molecular weights (>200 kDa) and narrow molecular weight distributions (M_w/M_n < 1.1). Mechanistic studies indicate that light activates the oxidative status of a Co^III intermediate that is generated from the regioselective ring-opening of the O-carboxyanhydride. We also demonstrate that the use of Zn or Hf complexes together with Co can allow for stereoselective photoredox ring-opening polymerizations of multiple racemic O-carboxyanhydrides to synthesize syndiotactic and stereoblock copolymers, which vary widely in their glass transition temperatures.

Photoredox ring-opening polymerization of O-carboxyanhydrides allows for the synthesis of functionalized polyesters with high molecular weights, narrow molecular weight distributions, and various tacticities.     

Anionic polymerization of styrenic macromonomers of polyisoprene,polybutadiene, and polystyrene

Anionic polymerization and high‐vacuum techniques were used to prepare a series of well‐defined polyisoprene, polybutadiene, and polystyrene polymacromonomers. The procedure involved (1) the synthesis of styrenic macromonomers in benzene by the selective reaction of the corresponding macroanion with the chlorine of 4‐(chlorodimethylsilyl)styrene (CDMSS) and (2) the in situ anionic polymerization of the macromonomer without previous isolation. The synthesis of the macromonomers [polyisoprene macromonomer: 11 samples, weight‐average molecular weight (M_w) = 1000–18,000; polybutadiene macromonomer: 5 samples, M_w = 2000–4000; and polystyrene macromonomer: 2 samples, M_w = 1300 and 3600] was monitored by size exclusion chromatography with refractive index/ultraviolet detectors. Selectivity studies with CDMSS indicated that polybutadienyllithum had the highest selectivity, and polystryryllithium the lowest. From kinetic studies it was concluded that the polymerization half‐life times were longer but comparable to those of styrene, and they appeared to only slightly depend on the molecular weight of the macromonomer chain (at least for low degrees of polymerization of the polymacromonomer and for M_w < 7000 for the macromonomer side chain). Dependence on the polymerization degree of the polymacromonomer product was also observed. All the prepared polymacromonomers were characterized by size exclusion chromatography with refractive index, ultraviolet and two‐angle laser light scattering detectors, and NMR spectroscopy. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1038–1048, 2005     

First example of an unsymmetrical difunctional monomer polymerizable by two living/controlled methods

In this paper the synthesis and (co)polymerizations of 4‐(acryloyloxy)‐ε‐caprolactone are reported. This new monomer can be polymerized in a living/controlled way by two different polymerization mechanisms; atom transfer radical polymerization (ATRP) and ring‐opening polymerization (ROP). ATRP, which was carried out at 90°C using NiBr₂(PPh₃)₂, leads to new polyacrylates containing pendant caprolactone functionalities with controlled molecular weights and narrow polydispersities (M_w/M_n ˜1.1). Alternatively, ROP of this functional ε‐caprolactone bearing a pendant acrylate functionality leads to new poly(4‐(acryloyloxy) caprolactone) as well as random copolymers when ε‐caprolactone and L,L‐lactide are added as comonomers. The (co)polymerizations were carried out using either Al(OⁱPr)₃ in toluene at 25°C or Sn(Oct)₂ as a catalyst at 110°C producing (co)polymers with controlled molecular weights and narrow polydispersities (M_w/M_n ˜ 1.2). As a potential application, the introduction of acrylate pendant groups into the polyesters facilitated the preparation of cross‐linked biodegradable materials either thermally or by irradiation with ultraviolet light radical curing.     

Controlled polymerization of acrylic acid under 60Co irradiation in the presence of dibenzyl trithiocarbonate

The polymerization of acrylic acid (AA) was performed under ⁶⁰Co irradiation in the presence of dibenzyl trithiocarbonate at room temperature, and well‐defined poly(acrylic acid) (PAA) with a low polydispersity index was successfully prepared. The gel permeation chromatographic and ¹H NMR data showed that this polymerization displays living free‐radical polymerization characteristics: a narrow molecular weight distribution (M_w/M_n = 1.07–1.22), controlled molecular weight, and constant chain‐radical concentration during the polymerization. Using PAA? S? C(?S)? S? PAA as an initiator, the extension reaction of PAA with fresh AA was carried out under ⁶⁰Co irradiation, and the results indicated that this extension polymerization displayed controlled polymerization behavior. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3934–3939, 2001     

Solvent‐assisted anionic ring opening polymerization of glycidol: Toward medium and high molecular weight hyperbranched polyglycerols

Hyperbranched polyglycerols (HPGs) are globular structures with a large number of functionalizable hydroxyl groups and have excellent in vitro and in vivo biocompatibility profiles comparable to polyethylene glycol. This work introduces a facile method for the synthesis of medium molecular weights (M_ws) (50–300 kDa) HPGs, which has been difficult to synthesize with low polydispersity, with the assistance of solvents by ring opening polymerization. The influence of different solvents (1,4‐dioxane, tetrahydropyran (THP), ethylene glycol diethyl ether (EGDE) and decane), solvent to glycidol ratio, concentration of glycidol and the time of polymerization on M_w and polydispersity of HPGs has been studied. The M_w and polydispersity of HPGs are significantly affected by the nature of the polymerization phase (homogeneous or heterogeneous) and chemical structure of the solvent. The differences in the solvation of the potassium cations and change in the nucleophilicity of the alkoxide anion in various solvents may be responsible for the changes in M_w and PDI of the HPG. The M_w of the HPG decreases in the order 1,4‐dioxane > THP > EGDE >decane. The microstructure, solution and thermal properties of the HPG do not depend on the nature of solvent. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2614–2621     

Biocatalytic synthesis of polymers. II. Preparation of [AA–BB]x polyesters by porcine pancreatic lipase catalyzed transesterification in anhydrous,low polarity organic solvents

Enzyme-catalyzed preparation of polymers offers several potentially valuable advantages over the usual polymerization procedures. (1) Such polymerizations may allow the polymer to retain functionality that would be destroyed under normal polymerization conditions. (2) The selectivity provided by enzyme catalysts may permit polymers, including optically active polymers, to be prepared that are either not accessible or accessible only with difficulty by other methods. (3) The characteristics of the enzyme and the mild polymerization conditions may permit formation of polymers having highly regular sizes and backbone structures. This report describes the first successful use of an enzyme-catalyzed polycondensation to prepare a chiral (AA–BB)_x polyesters of more than a few repeat units. Polymerization of bis(2,2,2-trichloroethyl) alkanedioates (BB) with diols (AA) using the enzyme porcine pancreatic lipase (PPL) as a catalyst is detailed. The polycondensations were carried out at ambient temperature in anhydrous, low polarity organic solvents such as ether, THF, and methylene chloride. End group analysis by NMR provided M_n values of 1300–8200 daltons while GPC provided M_w values of 2800–14900 daltons for the polymers. Based on proton NMR spectra obtained during the polymerization, relatively rapid formation of an AA–BB “dimer” and an AA–BB–AA “trimer,” slower formation of a BB–AA–BB “trimer,” and subsequent condensation of these to give higher polymers are suggested to be components of the polymerization mechanism.     

Synthesis of arborescent styrene homopolymers and copolymers from epoxidized substrates

The synthesis of arborescent styrenic homopolymers and copolymers was achieved by anionic polymerization and grafting. Styrene and p‐(3‐butenyl)styrene were first copolymerized using sec‐butyllithium in toluene, to generate a linear copolymer with a weight‐average molecular weight M_w = 4000 and M_w/M_n = 1.05. The pendant double bonds of the copolymer were then epoxidized with m‐chloroperbenzoic acid. A comb‐branched (or arborescent generation G0) copolymer was obtained by coupling the epoxidized substrate with living styrene‐p‐(3‐butenyl)styrene copolymer chains with M_w ≈ 5000 in a toluene/tetrahydrofuran mixture. Further cycles of epoxidation and coupling reactions while maintaining M_w ≈ 5000 for the side chains yielded arborescent copolymers of generations G1–G3. A series of arborescent styrene homopolymers was also obtained by grafting M_w ≈ 5000 polystyrene side chains onto the linear and G0–G2 copolymer substrates. Size exclusion chromatography measurements showed that the graft polymers have low polydispersity indices (M_w/M_n = 1.02–1.15) and molecular weights increasing geometrically over successive generations. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis of periodic copolymers via ring‐opening copolymerizations of cyclic anhydrides with tetrahydrofuran using nonafluorobutanesulfonimide as an organic catalyst and subsequent transformation to aliphatic polyesters

To synthesize polyesters and periodic copolymers catalyzed by nonafluorobutanesulfonimide (Nf₂NH), we performed ring‐opening copolymerizations of cyclic anhydrides with tetrahydrofuran (THF) at 50–120 °C. At high temperature (100–120 °C), the cyclic anhydrides, such as succinic anhydride (SAn), glutaric anhydride (GAn), phthalic anhydride (PAn), maleic anhydride (MAn), and citraconic anhydride (CAn), copolymerized with THF via ring‐opening to produce polyesters (M_n = 0.8–6.8 × 10³, M_n/M_w = 2.03–3.51). Ether units were temporarily formed during this copolymerization and subsequently, the ether units were transformed into esters by chain transfer reaction, thus giving the corresponding polyester. On the other hand, at low temperature (25–50 °C), ring‐opening copolymerizations of the cyclic anhydrides with THF produced poly(ester‐ether) (M_n = 3.4–12.1 × 10³, M_w/M_n = 1.44–2.10). NMR and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectra revealed that when toluene (4 M) was used as a solvent, GAn reacted with THF (unit ratio: 1:2) to produce periodic copolymers (M_n = 5.9 × 10³, M_w/M_n = 2.10). We have also performed model reactions to delineate the mechanism by which periodic copolymers containing both ester and ether units were transformed into polyesters by raising the reaction temperature to 120 °C. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

SYNTHESIS OF POLYPROPYLENE-POLY(METH)ACRYLATE BLOCK COPOLYMERS USING METALLOCENE CATALYZED PROCESSES AND SUBSEQUENT ATOM TRANSFER RADICAL POLYMERIZATION

ABSTRACT

The synthesis of block copolymers containing low molar mass polypropylene and poly(meth)acrylates is reported. Vinyl-terminated polypropylene (M_n SEC=3,100; M_w/M_n=1.45) was used to prepare a macroinitiator for atom transfer radical polymerization (ATRP) via hydrosilation with 1-(2-bromoisobutyryloxy)propyl-tetramethyldisiloxane. Polar segments were then incorporated to polypropylene by chain extension using either methyl methacrylate, or n-butyl acrylate. While blocking efficiency was limited in this system, well-defined PP-b-PMMA (M_n=22,220; M_w/M_n=1.14) was obtained by extraction of unreacted polypropylene with diethyl ether.     

Living cationic polymerization of vinyl ethers in the presence of a strong base: Poisonous or helpful?

A quite small dose of a poisonous species was found to induce living cationic polymerization of isobutyl vinyl ether (IBVE) in toluene at 0 °C. In the presence of a small amount of N,N‐dimethylacetamide, living cationic polymerization of IBVE was achieved using SnCl₄, producing a low polydispersity polymer (weight–average molecular weight/number–average molecular weight (M_w/M_n) ≤ 1.1), whereas the polymerization was terminated at its higher concentration. In addition, amine derivatives (common terminators) as stronger bases allow living polymerization when a catalytic quantity was used. On the other hand, EtAlCl₂ produced polymers with comparatively broad MWDs (M_w/M_n ～ 2), although the polymerization was slightly retarded. The systems with a strong base required much less quantity of bases than weak base systems such as ethers or esters for living polymerization. The strong base system exhibited Lewis acid preference: living polymerization proceeded only with SnCl₄, TiCl₄, or ZnCl₂, whereas a range of Lewis acids are effective for achieving living polymerization in the conventional weak base system such as an ester and an ether. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6746–6753, 2008     

Microwave‐assisted suzuki coupling reaction for rapid synthesis of conjugated polymer–poly(9,9‐dihexylfluorene)s as an example

Long reaction period (dozens of hours) is often required for the synthesis of conjugated polymers by palladium‐catalyzed Suzuki polymerization reaction. This work shows that microwave can accelerate Suzuki polymerization to realize the ultra‐rapid synthesis of conjugated polymers, here poly(9,9‐dihexylfluorene)s (PDHFs) as an example. The effects of reaction conditions on the polymerization have been systematically investigated, including the mode of microwave irradiation, microwave power, reaction temperature, reaction time, solvents, catalyst species, and catalyst concentrations. Compared with the conventional heating method (oil bath) for the synthesis of PDHFs (48 h, M_w = 20,000 g/mol), Suzuki polymerization under optimized microwave condition can yield PDHFs with higher molecular weight (M_w = 40,000 g/mol) in a much shorter time (14 min). The structures of obtained PDHFs samples are fully characterized spectroscopically, demonstrating well‐defined PDHFs have been prepared through microwave‐assisted (MA) Suzuki polymerization reaction. In addition, the mechanism of MA Suzuki polymerization is proposed preliminarily. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Junction‐Controlled Topological Polymerization

Methodology that enables the controlled synthesis of linear and branched polymers from an identical monomer will be a novel pathway for polymer synthesis and processing. Herein we first describe the control of one or both of the C(3)‐C(3′) and C(6)‐C(6′) coupling reactions of carbazolyl. In a second approach, an identical monomer containing two carbazolyls is polymerized using chemical and electrochemical oxidizers, leading to topologically controllable growth of linear polymers in weak oxidizer or of cross‐linked polymer chains in strong oxidizer, with satisfactory long chain propagation of step growth polymerization (M_n=6.0×10⁴ g mol^?1, M_w/M_n=2.3). This very simple polymerization with cheap reagents and low levels of waste has provided a flexible pathway for synthesis and processing of polymers.     

Controlled ring‐opening polymerization of l‐lactide and ε‐caprolactone catalyzed by aluminum‐based Lewis pairs or Lewis acid alone

Ring‐opening polymerization of cyclic esters was studied using catalysts composed of bulky Lewis acids (LA) and Lewis bases (LB). Controlled polymerization of l ‐lactide (l ‐Lac) was proceeded by Al(C₆F₅)₃·THF in combination with trimesitylphosphine (Mes₃P) or triphenylphosphine (Ph₃P) using BnOH as an initiator to produce poly(l ‐Lac) with narrow molecular weight distribution (MWD; M_w/M_n = 1.1). Both the LA and the LB were indispensable to promote the polymerization. The molecular weights of the resulting poly(l ‐Lac)s were controlled by the feed monomer to initiator ratio. ε‐Caprolactone (CL) was rapidly polymerized by Al(C₆F₅)₃·THF with or without Mes₃P, although the resulting polymer had rather broad MWD (M_w/M_n = 1.7). The CL polymerization by Al(C₆F₅)₃·THF alone at r.t. gave poly(CL) with relatively narrow MWD (M_w/M_n = 1.2). © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 297–303     

Ring-Opening Polymerization of Cyclic Monomers with Aluminum Triflate

A green method for the controlled synthesis of aliphatic polymers is presented. The ring-opening polymerizations of cyclic monomers including several lactones, such as caprolactone (CL) or pentadecalactone (PDL), and cyclic anhydride monomers, such as succinic anhydride (SUC) and tetrahydrofuran (THF), catalyzed by a series of metal triflates (trifluoromethanesulfonate) were studied. Aluminum triflate was found to be an advantageous candidate to catalyze the ring-opening polymerization of cyclic monomers. The details of the ring-opening polymerization of CL catalyzed by aluminum triflate were studied. The maximum number average molecular weight (M_n), polydispersity (M_w/M_n) and yield of the obtained poly(-caprolactone) (PCL) at 60 °C for 6 hours were 18,400, 1.94 and 89 wt%, respectively. Those of poly(pentadecalactone) (PPDL) at 100 °C for 6 hours were 12,400, 2.24 and 49 wt%, respectively. The M_n, M_w/M_n and yield of the obtained poly(butylene succinate) (PBS) from SUC and THF at 100 °C for 48 hours were 4,900, 2.03 and 84 wt%, respectively. Furthermore, the mechanism of the polymerization was discussed based on the relationship between the conversion of CL and time. The molecular weight buildup of PCL was linear with a conversion in 50 min before the conversion reached 100 % and with M_w/M_n stabilized at about 1.5. The M_w/M_n of PCL then gradually increased. From these data, a living polymerization with a small transesterification was suggested from the PCL polymerization by aluminum triflate.     

Precision synthesis of (1→6)-α-D-glucopyranan by cationic ring-opening polymerization of 1,6-anhydro-2,3,4-tri-O-allyl-β-D-glucopyranose

The ring-opening polymerization of 1,6-anhydro-2,3,4-tri-O-allyl-β-D-glucopyranose ( 2 ) has been carried out using various cationic initiators. For the condition of [ 2 ]/[BF₃·OEt₂] = 20 at −15°C for 90 h, the polymer yield, M_w and M_w/M_n of the polymer obtained were 79%, 215,600 and 3.45, respectively. In order to study the living characteristic of the polymerization of 2 , the cationic ring-opening bulk polymerization initiated by trimethylsilyl trifluoromethanesulfonate (TMSOTf) was carried out under the condition of [ 2 ]/[TMSOTf] = 1000 at −15 °C. The M_w value increased in proportion to conversion until c.a. 30% and below. The M_w/M_ns of resulting polymers were very narrow, e.g., the M_w/M_n value was 1.2 and below, which was smaller than that for the solution polymerization using BF₃·OEt₂. These results indicated that the ring-opening bulk polymerization of 2 using TMSOTf was living-like.     

Thermal‐initiated reversible addition–fragmentation chain transfer polymerization of methyl methacrylate in the presence of oxygen

A novel reversible addition–fragmentation chain transfer polymerization (RAFT) of methyl methacrylate (MMA) in the presence of oxygen was carried out for the first time without added chemical initiators. The polymerization was mediated by 2‐cyanoprop‐2‐yl 1‐dithionaphthalate (CPDN) or cumyl dithionaphthalenoate (CDN) as RAFT agent. The polymerization demonstrated the features of a living/controlled radical polymerization. The polymerization rate increased with oxygen concentration. Polymers with molecular weight M_n up to 520,000 g/mol, polydispersity M_w/M_n ～1.46 and RAFT efficiency M_n,th/M_n,GPC ～1.026 in the case of CPDN and M_n ～331,500 g/mol, M_w/M_n ～1.35, and M_n,th/M_n,GPC ～1.137 in the case of CDN were obtained. The possible mechanism of the thermal‐initiated RAFT polymerization of MMA in the presence of oxygen was discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3343–3354, 2006     

Synthesis of Dendrigraft Poly(ϵ‐Caprolactone)s Using Side Hydroxyl Groups for the Grafting of Branch Chains

Dendrigraft poly(ϵ‐caprolactone)s with high molecular weight and narrow polydispersity are synthesized via a convenient generation‐growth approach. Copolymerization of ϵ‐caprolactone (CL) and 4‐(2‐benzoxyethoxy)‐ϵ‐caprolactone (BECL) with stannous octanoate as a catalyst affords a functionalized poly(ϵ‐caprolactone) (PCL) with benzyl‐protected hydroxyl side groups. After removal of benzyl groups by palladium‐catalyzed hydrogenolysis, the graft copolymerization of CL and BECL onto the hydroxyl‐bearing linear polyester (zero‐generation) affords the first‐generation graft polyester. Further deprotection and graft polymerization cycles led to dendrigraft polyesters. Molecular weights are multiplied in each graft copolymerization. The second‐generation dendrigraft poly(ϵ‐caprolactone) has an M_w of 236 000 g·mol⁻¹ and M_w/M_n of 1.53.     

Scale Inhibitor and Dispersant Based on Poly(Acrylic Acid) Obtained by Redox‐Initiated Polymerization

Low molar mass poly(acrylic acid) (PAA) is generally obtained by free radical polymerization of acrylic acid (AA) in aqueous solution, using thermal initiators and some chain transfer agent. However, under such conditions it is rather difficult to efficiently produce molar masses as low as those required for obtaining an effective dispersant. In this work, the semibatch polymerization of AA at 45 °C is considered, using potassium persulfate (KPS) and sodium metabisulfite (KPS/NaMBS), or alternatively KPS and sodium hypophosphite (KPS/NaHP) as redox initiators to produce PAA of controlled low molar masses. These initiation systems allow the production of PAA with M_n as low as 2.0 kDa, relatively narrow molar mass distribution (1.5 < M_w/M_n < 3.0), and low branching degree. Most of the investigated polymerizations reach almost complete conversions (>95%); and it is verified that both reductants, NaMBS and NaHP, also behave as chain transfer agents. Finally, the investigated process with redox couples allowed the production of PAA with acceptable dispersant and antiscaling properties.     

Preparation of thermoresponsive polymers bearing amino acid diamide derivatives via RAFT polymerization

We report here the synthesis of well‐defined homopolymer bearing amino acid diamide, poly(N‐acryloyl‐L ‐valine N′‐methylamide), via reversible addition fragmentation chain transfer (RAFT) polymerization using alkynyl‐functionalized 2‐dodecylsulfanylthiocarbonylsulfanyl‐2‐methyl‐propionic acid propargyl alcohol ester as chain transfer agent (CTA) and 2,2′‐azobis(isobutyronitrile) as initiator. The effects of a variety of parameters, such as temperature and solvent, on RAFT polymerization were examined to determine the optimal control of the polymerization. The controlled nature of RAFT polymerization was evidenced by the controllable molecular weight and low‐molecular‐weight polydispersity index (M_w/M_n) of resulting homopolymers and further demonstrated to have retained end‐group functionality by the fact of the successful formation of block copolymers from further RAFT polymerization by using the resultant polymer as macro‐CTA, as well as from “click” chemistry. Thermoresponsive property of the prepared polymer was evaluated in terms of the lower critical solution temperature in aqueous solution by measuring the transmittance variation at 500 nm from UV/vis spectroscopy. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3573–3586, 2010