Random copolymerization of ε-caprolactone and l-lactide with molybdenum complexes

Dioxomolybdenum complexes were examined as catalysts for the copolymerization of ε-caprolactone (ε-CL) and l-lactide (l-LA). The bis-[(5-OMe)salicylaldehydato]dioxomolybdenum complex completed the copolymerization after 20 h at 110 °C with 0.05 mol% of the catalyst to produce a copolymer in high yield. The microstructure of the copolymer was analyzed using ¹H and ¹³C NMR spectroscopy and was determined to have a random structure. The r values calculated from the heterodiad analysis of the ¹H NMR data were r _LA = 0.91 and r _CL = 0.93, and the L values calculated from the triad analysis of the ¹³C NMR data were L _LA = 1.58 and L _CL = 1.81. Other dioxomolybdenum complexes, such as cis-α MoO₂[(3-MeO)DiMeSaltn], MoO₂(acac)₂ and (NH₄)₈[Mo₁₀O₃₄] exhibited comparable or slightly lower reactivity for the copolymerization. Consecutive polymerization of ε-CL followed by l-LA afforded a block copolymer without trans-esterification.     

Ring-opening polymerization of ε-caprolactone initiated by heteropolyacid

In this work, phosphotungstic acid (PTA) as a novel initiator was reported for the ring-opening polymerization (ROP) of ε-caprolactone (ε-CL). It was found that PTA was an efficient initiator. ROP of ε-CL can be readily initiated by PTA at room temperature and form poly(ε-caprolactone) with narrow molecular weight distribution. Polymerization mechanism study indicates that the polymerization proceeds via acyl-oxygen bond cleavage.     

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     

Ring-opening copolymerization of ε-caprolactone with 2,2-dimethyltrimethylene carbonate using N-heterocyclic carbene organocatalysts

Random copolymer of ε-caprolactone with 2,2-dimethyltrimethylene carbonate has been synthesized by using N-heterocyclic carbene organocatalysts for the first time. A series of N-heterocyclic carbenes namely, imidazol-2-ylidenes substituted at 1,3 position by benzyl, isopropyl, ethyl and methyl were demonstrated to bring about the metal-free ring-opening copolymerization of ε-caprolactone and 2,2-dimethyltrimethylene initiated by benzyl alcohol in THF. The influences of reaction conditions, such as monomer, catalyst, and initiator concentration, as well as reaction temperature and time on the copolymerization have been examined in detail. The results show that 1-isopropyl-3-benzyl imidazol-2-ylidene carbene was potent organic catalyst for the ring-opening copolymerization of cyclic esters to generate well-defined linear polyesters of controlled molecular weight and narrow polydispersity. ¹H NMR spectral data of copolymer obtained showed that the polymerization mechanism is in agreement with the activated monomer mechanism.     

Ring-opening polymerization of ?-caprolactone by base catalyst for synthesis of grafted polysilsesquioxane

The polysilsesquioxane having amino and phenyl groups (APSQ) was prepared from the corresponding trimethoxysilanes by co-condensation under basic conditions. The amino group on APSQ was utilized as an initiator for graft polymerization of ?-caprolactone (CL). The ring-opening polymerization of CL, in the presence of a catalytic amount of the base prepared from triazabicyclodecene, proceeded effectively to afford the polysilsesquioxane having poly(CL) as the graft chains (GrPSQ). In the grafting, no formation of cross-linked product was observed. The grafted poly(CL) component in GrPSQ showed improved durability for heat as an advantage of the hybrid polymer containing polysiloxane structure.     

Ring-opening polymerization of ε-caprolactone and l-lactide using organic amino calcium catalyst

Poly (ε-caprolactone) (PCL) and poly (l-lactide) (PLA) were prepared by ring-opening polymerization catalyzed by organic amino calcium catalysts (Ca/PO and Ca/EO) which were prepared by reacting calcium ammoniate Ca(NH₃)₆ with propylene oxide and ethylene oxide, respectively. The catalysts exhibited high activity and the ring-opening polymerization behaved a quasi-living characteristic. Based on the FT-IR spectra and the calcium contents of the catalysts, and based on the ¹H NMR end-group analysis of the low molecular weight PCL prepared using catalysts Ca/PO and Ca/EO, it was proposed that the catalysts have the structure of NH₂-Ca-O-CH(CH₃)₂ and NH₂-Ca-O-CH₂CH₃ for Ca/PO and Ca/EO, respectively. The ring-opening polymerization of CL and LA follows a coordination-insertion mechanism and the active site is the Ca-O bond.     

Synthesis of emulsion styrene butadiene rubber by reversible addition–fragmentation chain transfer polymerization and its properties

Emulsion polymerization is generally used to synthesize styrene butadiene rubber (SBR), and the molecular weight of this rubber can be easily increased. However, the broad molecular weight distribution (MWD) of SBR increases energy loss and adversely affects the dynamic viscoelastic properties. To overcome this disadvantage, reversible addition–fragmentation chain transfer (RAFT) polymerization, which is a type of living polymerization, is applied to emulsion polymerization for preparing RAFT emulsion SBR (ESBR). The molecular weight and microstructure of RAFT ESBR are compared to those of commercially available ESBR 1502 by gel permeation chromatography and proton nuclear magnetic resonance spectroscopy. The aforementioned two polymers are used to prepare unfilled ESBR compounds, which are compared in terms of key physical properties (abrasion resistance, mechanical properties, and dynamic viscoelastic properties). It is confirmed that various physical properties of RAFT ESBR are improved due to its narrow MWD. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47069.     

Mechanism of ?-caprolactone polymerization and ?-caprolactone/trimethylene carbonate copolymerization carried out with Zr(Acac)4

The paper presents the mechanism of the polymerization of ?-caprolactone with the use of Zr(Acac)₄. At the first stage of the initiation of the polymerization, a reaction consisting of proton transfer from caprolactone to acetylacetonate ligand and then ligand exchange reaction with release of free acetylacetone (HAcac) occur. Complex 1, arisen as a product of this reaction, is the actual initiator of the observed polymerization. During the conducted polymerization the molar mass increase is directly proportional to monomer conversion degree. On the basis of observed phenomenon, the polymerization of cyclic trimethylene carbonate (TMC) applying ?-caprolactone as a co-initiator is possible. Complex 1 arose in the initial phase of this reaction as well, being an equally efficient initiator for TMC polymerization. Using Zr(Acac)₄ as an initiator for an ?-caprolactone/TMC copolymerization resulted in obtaining a series of copolymers with varied, predicted composition and high molar mass values.     

Precipitation polymerization of ε-caprolactone in water using metal triflates as catalysts

The precipitation polymerization of ε-caprolactone has been assessed in water using various commercial metal triflates as catalysts. The reaction is quantitative at 70 and 100?°C, leading to number-average molecular weights up to 5,400?g/mol and dispersities around 1.5–2.0. A polycondensation mechanism operating from in situ generated 6-hydroxyhexanoic acid is proposed. Among various salts, aluminum and tin(II) triflates lead to the higher molecular weight after 24?h reaction at 70?°C.     

Highly active rare earth catalysts for the solution polymerization of ε-caprolactone

Summary By using -butyrolactone (-BL) as the reaction media, highly active catalysts--light rare earth chloride-epoxidy---BL-for the solution polymerization of -caprolactone, have been obtained for the first time. With these catalyst, PCL with molecular weight as his as 40x10⁴(Mv) can be prepared at 60°C for 1.5 hr. The amount of epoxide in catalyst solution, catalyst aging temperature and time affect the catalyst activity significantly. The mechanism study shows that in -BL, the weakening of Ln-Cl bonds by the donation of coordinated -BL with Ln³⁺ and the homogenous effect promote the reaction between light rare earth chloride and epoxide. The produced rare earth alkoxide initiates CL polymerization via a coordination-insertion mechanism with Acyl-oxygen bond cleavage.     

Preparation of single-site tin(IV) compounds and their use in the polymerization of ε-caprolactone

Butyltin(IV) carboxylate compounds were obtained by reactions of butyltrichlorotin(IV) with potassium pivalate, perfluoroheptanoate, methacrylate, 2,6-pyridinedicarboxylate, and phthalate. The synthesized complexes were fully characterized by nuclear magnetic resonance (¹H-, ¹³C-NMR), Fourier transform infrared (FTIR), mass spectroscopies (MS) and elemental analysis. These tin complexes were used as catalysts for the ring opening polymerization of ε-caplolactone and the conversion of monomers to polymers was completed in just 1 h. The structures of polymers were characterized by a combination of spectroscopic techniques (NMR, FTIR, MS), differential scanning calorimeter (DSC) and gel permeation chromatography. In this study, the ε-caplolactone polymers with different average molecular weights between 5000 and 40,000 Da having a regular structure were obtained.     

Homopolymerization of ε-caprolactone Initiated by a Scandium Aryloxide

Summary Ring-opening polymerization of -caprolactone (CL) has been firstly achieved by a novel rare earth initiator of scandium tris(2,6-di-tert-butyl-4-methylphenolate), producing PCL with M_v of 75,700 in solution polymerization under mild conditions. Kinetics study indicates that the apparent activation energy is 58.0 kJ/mol. Mechanism study reveals that the monomer ring is opened via acyl-oxygen bond cleavage leading to a Sc-0 active center.     

Styrene copolymerization using a metallocenic initiator. Homo- and copolymerization of styrene with isoprene through zirconocene–MAO initiating systems

The copolymerization of styrene with isoprene (Ip) has been tested using combined zirconocene–methylaluminoxane (MAO) initiating system. Both “half-sandwich” and real zirconium-based metallocenes were used. Regardless of the metallocene employed, conversion to copolymer was much influenced by the proportion of Ip in the initial feed. As the proportion of Ip is enriched, conversion to copolymer decreases substantially. Results of NMR and DSC analyses indicate that the products obtained were truly copolymers and not a mixture of both homopolymers. The studied zirconocene–MAO initiating system produces atactic polystyrene. A small amount of Ip in the initial feed substantially diminishes the conversion and at best traces of poly(isoprene) were detected in the homopolymerization of Ip with these initiating systems.     

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     

Statistical Copolymers of l,l-lactide and ε-caprolactone

Summary Copolymers of l,l-lactide with -caprolactone have been investigated in order to develop valuable biodegradable materials for medical applications. The syntheses of homopolymers and copolymers of l,l-lactide and -caprolactone by ring-opening bulk polymerization were performed using stannous octoate as initiator at 120 °C. The compositions of the copolymers were systematically varied by polymerization of monomer mixtures containing from 10 to 90 95 of -caprolactone, at 10% step of variation. High polymerization conversions were observed for homopolymers and copolymers syntheses. Synthesized products were characterized by gel permeation chromatography (GPC) and nuclear magnetic resonance spectrometry (NMR). The analyses of the segment lengths by ¹³C-NMR spectroscopy indicated the predominance of random copolymers formation and the transesterification reaction was not detected.     

Estimation of the chain propagation rate constants of propylene polymerization and ethylene-1-hexene copolymerization catalyzed with MgCl2-supported Ziegler–Natta catalysts

In olefin polymerization with MgCl₂-supported Ziegler–Natta (Z–N) catalysts, the apparent propagation rate constant (k_p)_a calculated by R_p = (k_p)_a [C*] C_Me (C_Me is equilibrium monomer concentration in the reaction system) declines with reaction time for gradually developed monomer diffusion limitation in the polymer/catalyst particles. In this work, a simplified multi-grain particle model was proposed to build correlation between (k_p)_a and other kinetic parameters that can be determined experimentally. Rate profiles of propylene polymerization and ethylene-1-hexene copolymerization by three MgCl₂-supported Z–N catalysts were determined, and the (k_p)_a data was calculated using [C*] determined by quench-labelling the propagation chains with acyl chloride. Decline of (k_p)_a in each polymerization process was precisely fitted by the linear correlation between lg(k_p)_a and [(ρ_catm_p)/(ρ_pm_cat) + 1]^1/3 developed on the particle model. Real propagation rate constant (k_p) was estimated by extrapolating the fitting line to the starting point of polymerization, where no concentration gradient exists. According to the particle model, the slope of the lg(k_p)_a versus [(ρ_catm_p)/(ρ_pm_cat) + 1]^1/3 line (lgd) represents the degree of monomer diffusion limitation. Variations of parameter d found in the studied reaction systems can be reasonably explained based on the knowledge of olefin diffusion in the polymer phase.     

Ring-opening polymerization of γ-glycidoxypropyltrimethoxysilane catalyzed by multi-metal cyanide catalyst

Ring-opening polymerizations of γ-glycidoxypropyltrimethoxysilane (GPTMS) were carried out by using multi-metal cyanide (MMC) catalyst and the synthesized homopolymer was a comb-shaped polymer with regular structure. The structure of the polymer obtained (P-GPTMS) was characterized by FTIR, ¹H-NMR, and ²⁹Si-NMR spectroscopy, and the molecular weight and its distribution were analyzed by size-exclusion chromatography with multi-angle laser light scattering (SEC-MALLS). The thermal behavior of P-GPTMS was investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). P-GPTMS with high molecular weight (M _n = 18,000–80,000) and narrow molecular weight distribution (1.10–1.35) were synthesized when the dosage of MMC catalyst was 0.1% and polymerization temperature was 130 °C. The molecular weight of the product could be adjusted by controlling the polymerization time. The T _g of P-GPTMS is in the range of −34 to −30 °C. On the basis of the TGA data, the decomposition rate of P-GPTMS reached its peak at 374.14 °C and the entire decomposition stopped at 600 °C.     

Ethyl magnesium bromide as an efficient anionic initiator for controlled polymerization of ε-caprolactone

The ring-opening polymerization of ε-caprolactone initiated by ethyl magnesium bromide was studied. Because ring-opening polymerization is extremely fast in the monomer phase, we focused on solution polymerization in toluene. The solution polymerization of ε-caprolactone was characterized by the linear dependence of degree of conversion on polymerization time, which we described by a first-order kinetic equation. The molar mass, determined by SEC using a light scattering detector, was in agreement with that calculated from the degree of conversion attained and the ratio of ε-caprolactone to ethyl magnesium bromide. On this basis, we propose a mechanism for the effect of ethyl magnesium bromide on ε-caprolactone polymerization and provide evidence for this mechanism by isolating a novel stable complex of magnesium bromide with ε-caprolactone.