Lactone polymers. III. Polymerization of ε-caprolactone

Polymerization of ε-caprolactone catalyzed by dibutylzine and triisobutylaluminum has been examined. Monomer conversion and polymer molecular weight increase simultaneously during the polymerization suggesting a living polymer system. Also, molecular weight is proportional to the reciprocal of catalyst concentration. However, the polymer molecular weights are three to five times that which would be calculated from the catalyst concentration assuming a living polymer system. In addition, fractionation of poly-ε-caprolactone prepared with dibutylzinc revealed that the distribution is considerably broader than expected for a Poisson distribution. While no mechanistic explanation for the broad molecular weight distribution observed has been defined, examination of the metal alkyl-catalyzed polylactones shows that the molecular weight distributions can and do change with time. This change is due to an ester interchange process occurring subsequent to polymerization. This phenomenon can be used to change the molecular weight distribution from very broad to the most probable distribution.     

Lactone polymers. II. Hydrodynamic properties and unperturbed dimensions of poly-ε-caprolactone

Poly-ε-caprolactone prepared by a dibutylzinc-catalyzed bulk polymerization process was fractionated, and the solution properties of the fractions were studied in benzene and in dimethylformamide. In these solvents at 30°C the Mark-Houwink relations were [η] = 9.94 × 10^?5 M and [η] = 1.91 × 10^?4 M , respectively. The value of K_Θ was found to vary from 1.1 to 1.2 × 10^?3 when determined by three known extrapolation techniques. Poly-ε-caprolactone chains appear to be quite flexible in solution, and the steric hindrance parameter σ had the low value of 1.37. Root-mean-square end-to-end dimensions were approximated from the experimental data and calculated from the Debye-Bueche and the Kirkwood-Riseman theories.     

Ternary blends of phenoxy/SAN/poly(-ε-caprolactone)

The compatibilizing effect of poly(ε-caprolactone) (PCL) on the blends of two immiscible polymers, poly(hydroxy ether of bisphenol A) (phenoxy) and poly(styrene-co-acrylonitrile) (SAN) has been investigated. The phase behavior of the ternary blends was affected by the AN content in the SAN copolymers and a maximum miscible region was observed at 19.5 wt % of AN. The effect of AN content on the phase behavior of the ternary blends was interpreted in terms of the relative magnitude of the segmental interaction energy densities, which were obtained by combining a melting point depression and an extended binary interaction model. When a small amount of PCL was added to the phenoxy/SAN blends, the phase morphology showed a finer phase dispersion, indicating that the interfacial tension between the phenoxy and SAN is considerably reduced. However, the improvement in tensile properties was limited despite the morphological change with the PCL content. From the results of the DSC measurements, SEM, and tensile testing, it was understood that the PCL acted as a compatibilizer for the immiscible phenoxy/SAN blends. © 1994 John Wiley & Sons, Inc.     

Binary and ternary poly(lactic acid)/poly(ϵ-caprolactone) blends: The effects of oligo-ϵ-caprolactones upon mechanical properties

Oligo-ε-caprolactones(o-CL) have been utilized as principle secondary components within poly(lactic acid)[PLA]-based blends as well as additives within larger-sized PCL/PLA blends in an effort to fully complement the mechanical attributes of the respective polyesters. Dynamic mechanical thermal analysis(DMTA) shows that the presence of o-CL plasticizes the PLA non-crystalline phase with a more pronounced effect seen as the size of o-CL is reduced. Moreover, it appears that the size of o-CL could also affect the static mechanical properties of the ternary systems as material stiffness and strength reside between those properties measured for high molecular weight PCL/PLA binary blends and the PLA homopolyester. Future work will examine the ability of these blends to sustain these properties during hydrolytic exposure.     

Lactone polymers. I. Glass transition temperature of poly-ε-caprolactone by means on compatible polymer mixtures

Dynamic mechanical properties determined with a torsion pendulum were used to ascertain the glass transition temperature T_g of poly-ε-caprolactone. By measurements on compatible blends of poly-ε-caprolactone and poly(vinyl chloride), the T_g of amorphous poly-ε-caprolactone was shown to be 202°K at about 1 cps. This is 16°K lower than the T_g of annealed, crystalline polymer. The blend transition data were well fitted by both the Fox and the Gordon-Taylor expressions. The Fox expression was also used to describe the decrease from 233°K of the secondary low-temperature relaxation due to poly(vinyl chloride) by assuming the low temperature relaxation of poly-ε-caprolactone, 138°K, was responsible for the decrease in the blends. The 138°K relaxation due to poly-ε-caprolactone was decreased when more than 50% poly(vinyl chloride) was present.     

Mechanical and dynamic viscoelastic properties of hydroxyapatite reinforced poly(ε-caprolactone)

Poly(ε-caprolactone)/hydroxyapatite (PCL/HA) composites as potential bone substitutes were prepared by melt-blending. The melting, crystallization and glass transition temperatures deduced from differential scanning calorimetery and dynamic mechanical thermal analysis (DMTA) were all changed by the addition of HA, suggesting an interaction at the interface of these two phases. Quasi-static mechanical testing shows that the yield strength and Young's modulus of PCL were increased by the addition of the reinforcement filler, HA. Dynamic viscoelastic properties were investigated using DMTA and an advanced rheometric expansion system. The results show that both the storage modulus and viscous modulus are enhanced by HA, and the PCL composite melts still behave like pseudo-plastic liquid.     

Synthesis and barrier properties of poly(ε-caprolactone)-layered silicate nanocomposites

A new polymer-ceramic nanocomposite has been synthesized consisting of well-dispersed, two-dimensional layers of an organically modified mica-type silicate (MTS) within a degradable poly(ε-caprolactone) matrix. A protonated amino acid derivative of MTS was used to promote delamination/dispersion of the host layers and initiate ring-opening polymerization of ε-caprolactone monomer, resulting in poly(ε-caprolactone) chains that are ionically bound to the silicate layers. The polymer chains can be released from the silicate surface by a reverse ion-exchange reaction and were shown to be spectroscopically similar to pure poly(ε-caprolactone). Thick films of the polymer nanocomposite exhibit a significant reduction in water vapor permeability that shows a linear dependence on silicate content. The permeability of nanocomposite containing as low as 4.8% silicate by volume was reduced by nearly an order of magnitude compared to pure poly(ε-caprolactone). © 1995 John Wiley & Sons, Inc.     

Polycaprolactone-based block copolymers. II. Morphology and crystallization of copolymers of styrene or butadiene and ε-caprolactone

Three series of amorphous semicrystalline poly(styrene-b-ε-caprolactone)s have been synthesized with polystyrene blocks of 6000 (series A), 40000 (series B), and 70000 (series C) molecular weight, respectively. In these materials, the polymer miscibility evolves from a situation where a diffuse interphase involves the major part of the volume of the copolymer (series A) to a sharp phase separation as observed for copolymers with the longest PS block (series C). The crystallization of PCL blocks is mainly governed by the phase morphology. In copolymers of series A, the crystallization rate of PCL blocks is slowed down the more as the miscibility with PS increases, and ultimately the degree of crystallinity X_c decreases significantly. When phase separation is sharp, X_c changes dramatically at the phase inversion and decreases when PS forms the continuous phase. At the inversion X_c depends on the mean size of the PCL microdomains as compared with the thickness of the crystalline lamellae. The periodicity of the phase morphology as observed by TEM is influenced by the solvent used in casting films, whereas monolamellar monocrystals can be obtained by a self-seeding technique.     

Polymerization and properties of optically active α-(p-substituted benzenesulfonamido)-β-lactones

Optically active α-(p-substituted benzenesulfonamido)-β-lactones having as para substituents OMe, Me, H, and Cl were polymerized in bulk, in ethyl acetate solution with triethylamine or betaine, and in dioxane with butyllithium as initiators. The rate of polymerization was followed by the change of specific rotation with time and was decreasing in following order of para substituents: OMe > Me > H > Cl. The relative reactivity in logarithmic form was plotted against Hammett's σ functions showing a linear relationship with reaction constant ρ = ?0.57.     

Ceric-ion-initiated grafting of methyl methacrylate onto (1 → 5)-α-D-ribofuranan and (1 → 5)-α-D-xylofuranan

We report herein studies of grafting of MMA onto (1 → 5)-α-D -ribofuranan and (1 → 5)-α-D -xylofuranan by ceric ion initiation both in water and in dimethyl sulfoxide (DMSO). In aqueous medium, the graft polymer having high grafting (%) can be obtained easily without adding any nitric acid. The degradation of polysaccharide by the acidic ceric ion solution is not serious; 73–82% of its original molecular weight remained after the polymerization. In DMSO, graft polymers having lower grafting (%) and lower molecular weight of grafts were obtained.     

Stereocomplex formation in AB DI-block copolymers of poly(ϵ-caprolactone) (a) and poly(lactide)(B)

The thermal properties of two series of AB di-block copolymers of poly(ϵ-caprolactone) (A) and poly(lactide) (B) and their blends were studied. Each series contained poly(lactide) blocks of opposite chirality. The length of the poly(ϵ-caprolactone) blocks was not varied (DP = 70), whereas the poly(lactide) blocks were of varying length (DP = 5 − 80). Blends of polymers containing blocks of opposite chirality were prepared by mixing in solution. The melting temperature of the PLA phase was raised by approximately 55 °C in the blends due to stereocomplex formation. The melting temperatures of the crystalline PCL and PLA phases strongly depended on the composition of the block copolymers.     

Photodegradation behavior of tert-butyl vinyl ketone polymers and copolymers with styrene and α-methylstyrene

Photodegradation behavior of atactic and isotactic polymers of tert-butyl vinyl ketone (t-BVK) and its copolymers with styrene and α-methylstyrene was studied in dioxane as a solvent at room temperature. The quantum yield of main-chain scission of atactic poly(t-BVK) was found to be larger than that of isotactic poly(t-BVK) and atactic poly(methyl vinyl ketone). From the Stern-Volmer plots on the quenching study of atactic poly(t-BVK) with naphthalene and 2,5-dimethyl-2,4-hexadiene, it was found that 60–70% of its photochemical reaction underwent main-chain scission from the triplet state. It was also found that the increase in t-BVK contents of both copolymers accelerated the photodegradation, and the copolymer with styrene was more photodegradable than that with α-methylstyrene. These results seemed to suggest that the main-chain scission of these vinyl ketone polymers and copolymers proceeded through a Norrish type II photoelimination mechanism.     

Ring-opening metathesis polymerization of new α-norbornenyl poly(ε-caprolactone) macromonomers

Poly(ε-caprolactone) (PCL) macromonomers capped by a polymerizable norbornene end-group have been synthesized and (co)polymerized by ring-opening metathesis with formation of graft copolymers and polymacromonomers. α-Norbornenyl PCL macromonomers have been synthesized by ring opening polymerization (ROP) of ε-caprolactone (εCL) initiated by 2-diethylaluminoxymethyl-5-norbornene. Copolymerization of these PCL macromonomers with norbornene and polymerizable derivatives has been catalyzed by the [RuCl₂(p-cymene)]₂ PCy₃/(trimethylsilyl)diazomethane complex yielding a series of poly(norbornene)-graft-poly(ε-caprolactone) copolymers. These new graft copolymers have been characterized by a set of analytical methods, i.e., SEC, ¹H-NMR, FTIR, DSC, and TGA. Furthermore, PCL macromonomers have been polymerized into high molecular weight comb chains of narrow molecular weight distribution (M_w/M_n = 1.10) within high yields (90%). © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2447–2455, 1999     

Complex formation of poly(ε-caprolactone) with cyclodextrin

Poly(ε-caprolactone) was found to form inclusion complexes with α-cyclodextrin to give crystalline compounds. The complexes are stoichiometric one-to-one (cyclodextrin: monomer unit) compounds. The yields of the complexes decreased with increasing the molecular weight of the polymer. They were characterized by IR, ¹H NMR, ¹³C CP/MAS NMR, and X-ray diffraction. The inclusion modes are discussed.