Ring-opening polymerization of ε-caprolactone and δ-valerolactone using new Sm(III) μ-halo-bis(trimethylsilyl)amido complexes

New Sm(III) μ-halo-bis(trimethylsilyl)amido complexes [Sm(μ-X) {N(SiMe₃)₂}₂(THF)]₂ (X = Cl, Br) were synthesized and their crystal structures were analyzed. These complexes were used as catalysts for the homopolymerization of ε-caprolactone and δ-valerolactone and found to initiate ring-opening polymerization (ROP) of these monomers in high conversion over a short period, giving homopolymers with a moderate polydispersity index (∼ 2.0). The effect of temperature and the catalyst amount on the molecular weight distribution was also studied. Mechanistic studies were conducted using 1 : 1 and 1 : 6 molar ratios of μ-halo-bis-(trimethylsilyl)amido complexes and ε-caprolactone by ¹H-NMR and ¹³C-NMR spectroscopic techniques and revealed the presence of more than one initiating species. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1669–1674, 1999     

Crystallization of poly(ε-caprolactone)

The isothermal crystallization behaviour of poly(ε-caprolactone), PCL, has been investigated by dilatometry and optical microscopy. Nucleation rates and spherulitic growth rates have been measured. At all temperatures tested a change in nucleation rate was observed early during the crystallization. Growth rates were linear over the whole of the crystallization range. The experimental results were analysed using the Avrami equation in which the experimentally observed time dependence of nucleation is used. The equation contains integer values of the Avrami exponent and describes adequately the crystallization behaviour of PCL. The difference between the apparent and true nucleation rates is emphasized, and difficulties in the calculation of rate constants are discussed.     

Synthesis and characterization of poly(allyl methacrylate) obtained by γ‐radiation

Allyl methacrylate was polymerized by γ‐radiation under vacuum in solution and atom transfer radical polymerization (ATRP) methods and also in the presence of atmospheric oxygen in bulk. The kinetic curve is S‐type with a longer induction period, because of the presence of oxygen, in bulk polymerization. The curve for the solution polymerization is almost linear with a short induction period. The rate started to decrease after about 60% conversion and reached to a limiting conversion of 100%. The polymerization by ARTP method using γ‐radiation as initiator instead of conventional heating method gave a kinetic curve of linear character up to about limiting conversion of 100%. The polymers obtained were mostly gel type with linear chain fractions at lower conversions. The polymer characterizations were carried out by FTIR, differential scanning calorimetry, NMR, TGA, and XRD methods. The polymers were shown to proceed by the opening of vinyl groups. The allyl groups caused a limiting crosslinking, but 98–99% of the allyl groups are shown by FTIR and NMR, unchanged during the polymerization. The cyclic type polymer formation was not likely taking place. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1076–1083, 2007     

Synthesis and characterization of novel lipid functionalized poly(ε‐caprolactone)s

A series of novel lipid functionalized poly(ε‐caprolactone)s (PCLs) were synthesized through ROP of ε‐caprolactone in the presence of threo‐9,10‐dihydroxyoctadecanoic acid, synthesized from oleic acid. PCLs with different molecular weights were obtained by controlling the molar ratio of the initiator to the monomer. DSC and XRD analysis indicate that the crystallinity of PCLs decreased when compared to unfunctionalized PCL. The enzymatic degradation study shows that for samples with lower lipid derivatives content, a higher enzymatic degradation rate was observed because the lipase enzymes attack the ester bonds of the polymer; increased lipid content therefore inhibits the action of the lipase enzymes. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Enzyme-catalyzed polymerization and degradation of copolyesters of ε-caprolactone and γ-butyrolactone

Copolymers of γ-butyrolactone (γ-BL) and ε-caprolactone (ε-CL) were successfully synthesized by ring-opening polymerization using Novozyme-435 (immobilized lipase B from Candida antartica) as catalyst. Copolymers with different compositions were obtained and characterized by ¹H NMR, ¹³C NMR, GPC, DSC and X-ray diffraction. Increasing the [BL]/[CL] feed ratio resulted in decreases of molecular weight (M_n) of copolymers and reaction yield. Moreover, the BL contents in the copolymers varied according to the feed ratio. The T_m of the copolymers decreased from 58 to 49 °C with increase in BL content from 0 to 14%. The resulting copolymers were all semicrystalline with a PCL-type crystalline structure. Solution cast films were allowed to degrade in a pH 7.0 phosphate buffer solution containing Pseudomonas lipase. Weight loss data showed that the degradation rate of copolymers in the presence of Pseudomonas lipase decreased with the increase of BL contents.     

Heat resistance of radiation crosslinked poly(ε-caprolactone)

Polycaprolactone (PCL) was gamma-irradiated at different phases such as solid state at 30 to 55°C, molten state, and supercooled state, under vacuum or air atmosphere, to elucidate its crosslinking behavior. Irradiation in the molten state (80°C) gave higher gel content compared to room temperature. The resulting gel, however, contains many voids due to the gas evolved during irradiation. Conversely, irradiation of PCL in the supercooled state led to the highest gel content among the three irradiation conditions and it was free of voids. Based on these findings, to evaluate heat resistibility of crosslinked PCL prepared by irradiation in supercooled state, the crosslinked PCL was hot pressed at 200°C to form a film. Unirradiated PCL melted at 60°C. The film prepared from 160 kGy irradiated PCL (crosslinked sample) under an applied load of 0.667 MPa, at a temperature of 110°C did not break even after 3 h. At a temperature of 120°C, the film has a tensile strength of 3 MPa. Furthermore, the film extended by hot pressing is transparent and has high heat shrinkability. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 581–588, 1998     

Synthesis and characterization of polyrotaxanes comprising α‐cyclodextrins and poly(ε‐caprolactone) end‐capped with poly(butyl methacrylate)s

Biodegradable polyrotaxane‐based triblock copolymers were synthesized via the bulk atom transfer radical polymerization (ATRP) of n‐butyl methacrylate (BMA) initiated with polypseudo‐rotaxanes (PPRs) built from a distal 2‐bromoisobutyryl end‐capped poly(ε‐caprolactone) (Br‐PCL‐Br) with α‐cyclodextrins (α‐CDs) in the presence of Cu(I)Br/N,N,N′,N″,N″‐pentamethyldiethylenetriamine at 45 ºC. The structure was characterized in detail by means of ¹H NMR, gel permeation chromatography, wide‐angle X‐ray diffraction, DSC and TGA. When the feed molar ratio of BMA to Br‐PCL‐Br was changed from 128 to 300, the degree of polymerization of PBMA blocks attached to two ends of the PPRs was in the range 382 ? 803. Although about a tenth of the added α‐CDs were still threaded onto the PCL chain after the ATRP process, the movable α‐CDs made a marked contribution to the mechanical strength enhancement, blood anticoagulation activity and protein adsorption repellency of the resulting copolymers. Meanwhile, they could also protect the copolymers from the attack of H₂O and Lipase AK Amano molecules, exhibiting a lower mass loss as evidenced in hydrolytic and enzymatic degradation experiments. © 2013 Society of Chemical Industry     

Mechanical behavior of poly(ε-caprolactone)/poly(styrene-co-acrylonitrile) blends

The mechanical properties of compatible poly(ε-caprolactone)/poly(styrene-co-acrylonitrile) blends were studied for samples prepared from both the melt and solution. The mechanical response was observed to be primarily dependent upon the variation of the glass transition temperature with blend composition. For certain compositions, varying the sample preparation scheme resulted in specimens of different modulus. This behavior was associated with differences in the degree of crystallinity.     

Synthesis and thermal characterization of macromonomeric azo initiator containing poly(ε-caprolactone): Styrene and methyl methacrylate copolymerization

Macromonomeric azo initiator containing biodegradable poly(ε-caprolactone, (PCL) was synthesized by the condensation reaction of PCL with 4,4′-azobis(4-cyanopentanoyl chloride) and methacryloyl chloride. This macromonomeric azo initiator (MIM–PCL) was further used in the polymerization of styrene (St) or methylmethacrylate (MMA) via a radical initiated process at 60°C in bulk in order to obtain polystyrene (PS)-b-PCL or poly(methyl methacrylate) (PMMA)-b-PCL crosslinked block copolymers. Thermal decomposition kinetics of MIM–PCL and its copolymers were studied by using thermogravimetric analysis and differential scanning calorimetry (DSC). DSC traces of MIM–PCL showed two different exotherms, at 98 and 127°C. The first exotherm, observed at 98°C, was due to the polymerization of the terminal methacrylic groups; the other was due to the exothermic decomposition of azo groups of MIM–PCL. PCL-b-PS and PCL-b-PMMA crosslinked block copolymers showed single glass transition temperatures due to the compatibility of the crosslinked block segments. The polymer–solvent interaction parameter of PCL in chloroform was determined by vapor pressure osmometry to be 0.1 for the PCL–chloroform system at 30°C. The average molecular weights between junction points of crosslinked homo PCL were calculated by using the Flory–Rehner equation. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1149–1157, 1998     

Synthesis and properties of novel biodegradable triblock copolymers of poly(5-methyl-5-methoxycarbonyl-1,3-dioxan-2-one) and poly(ethylene glycol)

Novel biodegradable triblock copolymers of poly(5-methyl-5-methoxycarbonyl-1,3-dioxan-2-one) (PMMTC) with poly(ethylene glycol) (PEG), PMMTC-b-PEG-b-PMMTC, were synthesized by the ring-opening polymerization of MMTC in bulk, using the dihydroxyl PEG as initiator and Sn(Oct)₂ as catalyst. The triblock copolymers with different compositions were characterized by IR and ¹H NMR, their molecular weight was measured by gel permeation chromatography (GPC). The results showed that the molecular weight of triblock copolymers increased either with the increase of the molar ratio of MMTC in feed while the PEG chain length kept constant, or by lengthening the backbone chain of PEG block with the same ratio of MMTC in feed. The hydrophilicity of copolymers was greatly improved by incorporation of PEG block into polycarbonate. The in vitro hydrolytic/enzymatic degradation and controlled drug release properties of the triblock copolymers were also investigated.     

Compatibility of isotactic polypropylene/poly(ε-caprolactone) blends

Blends of poly(ε-caprolactone) (PCL)/isotactic polypropylene (iPP), in the solid state and at compositions spanning the complete range, were characterized using the dynamic mechanical, DSC, and optical microscopy techniques. Morphology examination revealed that increasing the PCL content causes a decrease of spherulitic size. The loss modulus spectra at isochronous conditions (110 Hz) reveal an heterophase system with limited phase mixing between the amorphous components of the blend constituents. Melt-mixing and quenching using the DSC causes a considerable melting point depression of the PCL component, attributed to its miscibility with the polypropylene amorphous phase. Addition of PCL caused an increase of iPP crystallinity at intermediate compositions, while at low PCL levels the presence of iPP crystals hinders the growth of PCL crystallites.     

Phase behavior of poly(ε-caprolactone)/ poly (vinylidene fluoride) blends

The miscibility of blends of poly (ε-caprolactone) (PCL)/poly(vinylidene fluoride) (PVDF) was studied by measuring the cloud point, melting point depression and crystallization kinetics. Lower critical solution temperature (LCST) behavior was observed at PCL-rich compositions, whilst it was not observed at high compositions of PVDF. However it is possible that an LCST could exist below the melting point of PVDF. From analysis of the melting point depression, the Flory interaction parameter x₁₂, was calculated from the Nishi-Wang equation and the value was found to be-1.5. The crystallization rate of PCL increased with increasing amount of PVDF in the blend. The spinodal curve for PCL/PVDF blends was simulated by using the lattice-fluid theory.     

Compatibility of low-density polyethylene–poly(ε-caprolactone) blends

The compatibility of low-density polyethylene (LDPE)–poly(ε-caprolactone) (PCL) was examined using the microscopic, the dynamic mechanical, and the DSC techniques. Morphological examination revealed that at low PCL concentrations, when specimens are severaly quenched, a uniform microspherulitic structure is formed. The dynamic mechanical spectra, at isochronous conditions (110 Hz), indicate very limited mixing of the amorphous phase of the two components at the intermediate compositions. More drastic relaxation shifts were observed at the extremes of the composition range. Ultimate strength and elongation at break are characteristic of a mechanically compatible system at high and low PCL contents. In the intermediate composition range their low value indicates phase separation. DSC measurements showed a nonlinear dependence of bulk crystallinity on blend composition; also, that the presence of PE enhances the degree of PCL crystallinity. Thermal history strongly affects bulk crystallinity. At elevated temperatures, near the mp of PE, thermal treatment affects considerably the melting point of the PE crystals.     

Synthesis and characterization of fullerene grafted poly(ε‐caprolactone)

The fullerene grafted poly(ε‐caprolactone) (PCL) was successfully synthesized with a graft efficiency of 80%. The fullerene moieties grafted onto the PCL chain aggregate into 1–2 μm particles so that a physical pseudo‐network is formed. Because of the existence of the network structure, the fullerene grafted PCL film can retain its shape at much higher temperatures than that of pure PCL film, as observed in dynamic mechanical tests. It shows a hydrophobic gelling behavior in chloroform solution. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Ring-opening polymerization of ε-caprolactone initiated by cyclopentadienyl sodium

Polymerization of ε-caprolactone had been investigated with cyclopentadienyl sodium as an initiator. The effects of reaction time, temperature, and concentration of the initiator on the yield and molecular weight of the polymer were discussed. It was shown that the high molecular weight of poly(ε-caprolactone) (13 × 10⁴) was obtained with cyclopentadienyl sodium initiator, and the mechanism of polymerization was also discussed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1273–1276, 1998     

Syntheses and characterization of poly(butylene terephthalate) copolyesters modified with p‐acetoxybenzoic acid

Poly(butylene terephthalate) (PBT) copolyesters modified with seven compositions of p‐acetoxybenzoic acid (PABA) ranging from 10 to 70 mol % were prepared. The X‐ray diffraction patterns, the polarizing microscopy behaviors, and thermal analysis showed that the modified PBT contained more PABA homopolymer units (PABA–PABA) than PBT–PABA units in the copolyesters. On increasing PABA mole percenage, PBT crystallinity decreased and thermal stability increased. It was found that although the PBT copolyesters did not exhibit a clear liquid crystalline texture like the copolyester of poly(ethylene terephthalate) modified with PABA did, the PBT copolyester containing 70 mol % of PABA exhibited the typical shear thinning behavior of a liquid crystalline polymer. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1085–1095, 2001     

Crystallization kinetics of poly-ε-caprolactone from poly-ε-caprolactone/poly(vinyl chloride) solutions

The polymer–polymer solution of poly(vinyl chloride) and poly-ε-caprolactone yields an excellent system for studying the crystallization kinetics of a crystallizable component from a polymer–polymer solution. Unlike previous studies of isotactic–atactic polystyrene solutions for which the glass transition temperature is invariant with composition, this system exhibits a marked dependence of T_g on the composition. The experimental data dE^?(modulus)/dt (psi^?/min) were obtained over a composition range of 40 to 70 wt-% poly-ε-caprolactone. With the appropriate modification of the spherulitic growth rate equation, the expression approximated a reasonable fit of the experimental data. This demonstrates a marked dependence of the crystallization rate on concentration. Secondary observations of this investigation show a slower crystallization rate for high molecular weight poly-ε-caprolactone and a slow secondary crystallization step. Both homopolymer poly-ε-caprolactone and poly-ε-caprolactone in the poly-ε-caprolactone/poly(vinyl chloride) solution show a slow (relative to the nucleation-controlled step) crystallization stage considered to involve a slow diffusion mechanism.     

Synthesis and thermal characterization of random poly(butylene terephthalate‐co‐2‐methyl‐ethylene terephthalate) copolyesters

Poly(butylene terephthalate‐co‐2‐methyl‐ethylene terephthalate) (PBT/MET) was synthesized by incorporating 1,2‐propandiol(1,2‐PDO) into PBT chains. The molar composition and chemical structure of PBT/MET copolyesters were confirmed by means of FT‐IR and ¹H‐NMR. To investigate the effect of 1,2‐PDO on the thermal properties of PBT/MET copolyesters, the copolymerizations were carried out by varying various contents of MET units, and the prepared materials were evaluated by differential scanning calorimetry and thermogravimetric analysis. Results suggested that with the increase of the content of 1,2‐PDO, the amount of crystallinity and the melting temperature decline, while the glass transition temperature increases and the copolyesters become more transparent and brittle with respect to PBT homopolymer. In addition, the T_g‐composition and T_m‐composition data are well subjected to the Wood equation and Flory's equation, respectively. All these copolyesters are found to consist of the general trend displayed by copolymers reported elsewhere. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis and characterization of the novel block copolymer poly(ε‐caprolactone)‐b‐poly(4‐vinyl pyridine) by the combination of coordination and controlled free‐radical polymerizations

A novel block copolymer, poly(ε‐caprolactone)‐b‐poly(4‐vinyl pyridine), was synthesized with a bifunctional initiator strategy. Poly(ε‐caprolactone) prepolymer with a 2,2,6,6‐tetramethylpiperidinyloxy (TEMPO) end group (PCL_T) was first obtained by coordination polymerization, which showed a controlled mechanism in the process. By means of ultraviolet spectroscopy and electron spin resonance spectroscopy, the TEMPO moiety was determined to be intact in the polymerization. The copolymers were then obtained by the controlled radical polymerization of 4‐vinyl pyridine in the presence of PCL_T. The desired block copolymers were characterized by gel permeation chromatography, Fourier transform infrared spectroscopy, and NMR spectroscopy in detail. Also, the effects of the molecular weight and concentration of PCL_T on the copolymerization were investigated. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2280–2285, 2004     

Hydrolytic degradation of poly(oxyethylene)–poly-(ε-caprolactone) multiblock copolymers

The degradation of poly(oxyethylene)–poly(ε-caprolactone) (POE–PCL) multiblock copolymers was investigated at 37°C in a 0.13M, pH 7.4 phosphate buffer selected to mimic in vivo conditions. The copolymers were obtained by coupling polycaprolactone diols and poly(ethylene glycol) diacids using dicyclohexylcarbodiimide as coupling agent. Various techniques, such as weighing, size exclusion chromatography, infrared, ¹H nuclear magnetic resonance, differential scanning calorimetry, and X-ray diffractometry, were used to monitor changes in total mass, water absorption, molar mass, thermal properties, degree of crystallinity, and composition. The results showed that introduction of POE sequences considerably increased the hydrophilicity of the copolymers as compared with PCL homopolymers. Nevertheless, the degradability of PCL sequences was not enhanced due to the phase separation between the two components. Significant morphological changes were also observed during the degradation. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 989–998, 1998