Thermodynamics of polymer blends based on poly(ϵ-caprolactone)/poly(vinyl methyl ether)

The miscibility of the system poly(ϵ-caprolactone)/poly(vinyl methyl ether), PCL/PVME, was investigated using differential scanning calorimetry (DSC), solution calorimetry, optical microscopy (OM), Fourier transform infrared spectroscopy (FTIR), dilatometry, and internal pressure. The system is semicrystalline and the PCL crystallinity is sensitive to the composition of the blend and to the thermal treatment performed. The presence of a single glass transition temperature for all compositions is considered as an index of miscibility in the amorphous phase, but the evolution of crystallization and melting peaks shows that phase separation phenomena occur upon heating the system just above the PCL melting point, according to a `lower critical solution temperature' behaviour. The process of mixing is markedly endothermic and this means that the system is immiscible in the liquid phase, i. e. just above the PCL melting point. FTIR experiments demonstrate the absence of specific interactions between the two components. OM was used combined with DSC to investigate the occurrence of a melting point depression which can be used to evaluate the χ₁₂ parameter. Finally, dilatometric and internal pressure techniques were used to obtain the required data for the evaluation of the interaction parameter, χ₁₂, following the Patterson approach. The resulting value of the χ₁₂ parameter is always positive and higher than the critical value in the considered temperature range. This behaviour indicates, too, that the system is not miscible when it is heated above the PCL melting point.     

Synthesis of poly(ϵ-caprolactone) macromonomers

Macromonomers of poly(?-caprolactone) were synthesized according to a two-step method. ω-Hydroxypolycaprolactone was first obtained by protonic deactivation of the growing alkoxide site, under conditions such as to minimize the draw-backs of anionic polymerization of ?-caprolactone: slow initiation with respect to propagation, occurrence of reshuffling and backbiting reactions. In a second stage, the polymer was fitted with an endstanding unsaturation, according to methods derived from peptide chemistry. The macromonomers obtained were characterized accurately (control of MWD, functionalization).     

The Comparison of the Ringed Spherulite Morphology of PCL Blends with Poly(vinyl chloride), Poly(bisphenol A carbonate) and Poly(hydroxyether of bisphenol A)

The crystallization and ringed spherulite morphology of poly(ε‐caprolactone) (PCL) in the miscible blends of PCL/poly(vinyl chloride) (PVC), PCL/poly(hydroxyether of bisphenol A) (phenoxy resin) and PCL/poly(bisphenol A carbonate) (PC) were investigated by differential scanning calorimetry (DSC) and polarized light microscopy (PLM). Through the comparison of the PCL crystalline morphology with the interaction energy density B between the miscible components in these blends, it was found that the addition of the non‐crystallizable component had great effect on the regularity of the ringed spherulite, which was coincided with the change of the interaction energy density B. To grow regular ringed spherulites in the PCL miscible blends, it was most important that the crystallization rate of PCL in the blends must be matched with the diffusion rate of the non‐crystallizable component. Such a matching relation in the process of the ringed spherulite growth was a most important condition for the regular twisting of PCL lamellae.     

New poly(ester-carbonate) multi-block copolymers based on poly(lactic-glycolic acid) and poly(ϵ-caprolactone) segments

A new family of multi-block copolymers having the structure of poly(ester-carbonate)s was obtained by a chain-extension reaction involving poly(lactic-glycolic acid) oligomers (PLGA) and oligomeric α,ω-bishydroxy-terminated poly(ϵ-caprolactone)s (PCDT). The latter were first transformed into α,ω-bis(chloroformate)s, which were subsequently condensed in the presence of amines with both the hydroxylic and the carboxylic end-groups of PLGA oligomers. Several samples differing in the length of the PCDT segments and in the composition of the PLGA segments were prepared and characterized for their physico-chemical properties. All of them had high molecular weight, good solubility in organic solvents, and modest swellability in aqueous media. As regards their thermal behaviour, some samples showed evidence of the presence of a crystalline phase. Since these products are potentially useful as bioerodible materials in drug delivery systems, some preliminary results on their degradation behaviour under conditions mimicking those found in biological fluids are reported.     

Ring-closing depolymerization of poly(ε-caprolactone)

Ring-closing depolymerization of poly(ε-caprolactone) in toluene solution with catalytic amounts of Bu₂Sn(OMe)₂ results in a mixture of cyclic oligomers, the equilibrium concentration of which corresponds to the concentration predicted according to the Jacobson-Stockmayer theory. ε-Caprolactone, however, is absent from this reaction mixture. When poly(ε-caprolactone) is depolymerized in the melt at 260°C in the presence of a catalyst, beside ε-caprolactone its cyclic dimer and trimer are distilled off. The composition is dependent on the catalyst used, e.g., Bu₂Sn(OMe)₂ produces 95,4 wt.-% of ε-caprolactone and 3,7 wt.-% of its dimer while with Ti(OiPr)₄ (iPr: isopropyl) 51,4 wt.-% ε-caprolactone and 49,6 wt.-% of its dimer are obtained. Block copolymers containing poly(ε-caprolactone) result in a similar product distribution, however, the second block may influence the rate of decomposition. The activation energy of the catalysed (0,5 mol-% Bu₂Sn(OMe)₂) and uncatalysed ring-closing depolymerization were determined to be 63 kJ/mol, and 87 kJ/mol, respectively.     

Kuhn-Mark-Houwink-Sakurada-Beziehung für poly(ϵ-caprolactam)

The Kuhn-Mark-Houwink-Sakurada relationship for poly(?-caprolactam), (polyamide 6), is established, based on the absolute determination of the weight-average molecular weight by light scattering. It is obtained ([η] in cm³.g^?1): The unperturbed dimensions of this polymer in both solvents are also determined by using the Stockmayer-Fixman method.     

LCST phase separation in biodegradable polymer blends: poly(D,L‐lactide) and poly(ϵ‐caprolactone)

A lower critical solution temperature (LCST) phase transition is reported for blends of the biodegradable polymers poly(D,L ‐lactide) (PDLA) and poly(ε‐caprolactone) (PCL). From light scattering measurements the cloud point curve is determined to have a critical temperature of 86°C and a critical concentration of mass fraction 36 wt.‐% PCL. Optical microscopy of phase‐separated films indicates a spinodal morphology at the critical concentration, and droplet phases at off‐critical concentrations. After quenching phase separated blends below the melting temperature of PCL (60°C), the crystallization of PCL is used to positively identify PCL‐rich and PDLA‐rich phases. When cystallization of PCL follows LCST phase separation, the size, shape, and distribution of crystalline regions can be adjusted by the degree of PCL/PDLA phase separation. Thus, the LCST phase separation offers a novel method to control microphase structure in biodegradable materials. Applications to control of mechanical and physical properties in tissue engineering scaffolds are discussed in light of the results.     

Aliphatic polyesters II. The degradation of poly (DL-lactide), poly (ε-caprolactone), and their copolymers in vivo

The mechanisms of biodegradation of poly (DL-lactide), poly(ε-caprolactone), and copolymers of ε-caprolactone with DL-dilactide, δ-valerolactone, and DL-ε-decalactone in rabbit were shown to be qualitatively similar. However, the rate of the first stage of the degradation process, non-enzymatic random hydrolytic chain scission, varied by an order of magnitude and was dependent on morphological as well as chemical effects. Weight loss was generally not observed until the molecular weight had decreased to 15 000 or less. Poly (DL-lactide) differed from the other polyesters studied, the rate of chain scission increasing after the commencement of weight loss. The rate of weight loss was greater and the period prior to weight loss was shorter when the comonomer content of copolymers of ε-caprolactone was sufficient to reduce the melting point of ε-caproate sequences to body temperature.     

Synthesis of polypropene-graft-poly(ε-caprolactone)

The copolymerization of polypropene (PP) with maleic anhydride (MA) was carried out at 120°C in xylene with benzoyl peroxide (BPO) as initiator. The resulting product was identified as poly(propene-co-maleic anhydride) obtained by reaction of the double bond of maleic anhydride with free radicals created on the PP chain. In the next step this copolymer was reacted with functional poly(ε-caprolactone) (PCL) by a co-melting method to give rise to a graft copolymer. The optimum time for the second step was found to be around 6 h (at 120°C). X-ray diffraction measurements and DSC characterization of PP-g-PCL have shown that the melting point of the PP phase in the graft copolymers is lower than that of homopolypropene and that its glass transition temperature increases with increasing of PCL grafts.     

Glass transition temperatures in blends of poly(N-vinyl-2-pyrrolidone) with a copolymer of bisphenol A and epichlorohydrin or with poly(vinyl butyral)

Blends of poly(vinyl butyral) (PVB) and of a copolymer of bisphenol A and epichlorohydrin (Phenoxy) with poly(N-vinyl-2-pyrrolidone) (PVP) were prepared by solution casting. The glass transition temperatures T_g for different compositions of the blends were measured by differential scanning calorimetry (DSC). The T_g behaviour of PVB/PVP blends suggests the existence of a single phase for blends containing less than 50 wt.-% PVP, and of two phases in blends containing more than 50 wt.-% PVP. Phenoxy/PVP blends showed to be miscible over the entire composition range. It was found that the Gordon-Taylor equation predicts adequately the T_g-composition dependence with a K parameter equal to 0,5 and 1,25 for PVB/PVP and Phenoxy/PVP blends, respectively.     

A Novel Macroinitiator for the Synthesis of Triblock Copolymers via Atom Transfer Radical Polymerization: Polystyrene‐block‐poly(bisphenol A carbonate)‐block‐polystyrene and Poly(methyl methacrylate)‐block‐poly(bisphenol A carbonate)‐block‐poly(methyl methacrylate)

Summary: Bis(hydroxy)telechelic bisphenol A polycarbonate (PC) was prepared via melt polycondensation of bisphenol A (BPA) and diphenyl carbonate (DPC) using lanthanum(III ) acetylacetonate as a catalyst for transesterification. Subsequently, the polycarbonate was converted to a bifunctional macroinitiator for atom transfer radical polymerization (ATRP) with the reagent, α‐chlorophenylacetyl chloride. The macroinitiator was used for the polymerization of styrene (S) and methyl methacrylate (MMA) to give PS‐block‐PC‐block‐PS and PMMA‐block‐PC‐block‐PMMA triblock copolymers. These block copolymers were characterized by NMR and GPC. When styrene and methyl methacrylate were used in large excess, significant shifts toward high molecular weights were observed with quantitative consumption of the macroinitiator. Several ligands were studied in combination with CuCl as the ATRP catalyst. Kinetic studies reveal the controlled nature of the polymerization reaction for all the ligands used.

Formation of a bifunctional ATRP macroinitiator by esterification of bis(hydroxy)telechelic PC with α‐chlorophenylacetyl chloride.     

Telechelic poly(ε-caprolactone) terminated at both ends with OH groups and its derivatization

The synthesis of highly uniform (1,08 ≤ M _w/M _n ≤ 1,13) telechelic poly(ε-caprolactone) terminated at both ends with OH groups and its derivatization leading to poly(ε-caprolactone) with pyrene end-groups are described. The synthesis, carried out in THF at room temperature, involves initiation with (CH₃CH₂)₂AlO(CH₂CH₂O)₃Al(CH₂CH₃)₂, leading to poly(ε-caprolactone) macromolecules growing at both ends. The active centers were deactivated with acetic acid, giving macromolecules with OH end-groups. Reaction of α,ω-dihydroxypoly(ε-caprolactone), HO-poly(εCL)-OH, with 4-(1-pyrenyl)butyryl chloride yields α,ω-di-1-pyrenylpoly(ε-caprolactone), Py-poly(εCL)-Py. Polymers are characterized by GPC, ¹H NMR, and UV spectroscopies. The UV spectra of polymers with pyrene end-groups are compared with the UV spectra of the model compound.     

Chemical modification of poly(vinyl chloride) resin using poly(ethylene glycol) to improve blood compatibility

Poly(vinyl chloride) (PVC) was aminated by treating the resin with a concentrated aqueous solution of ethylenediamine. The aminated PVC was then reacted with hexamethylene diisocyanate to incorporate the isocyanate group onto the polymer backbone. The isocyanated PVC was further reacted with poly(ethylene glycol) (PEG) of molecular weight 600 Da. The modified polymer was characterized using infrared and X-ray photoelectron spectroscopy (XPS) and thermal analysis. Infrared and XPS spectra showed the incorporation of PEG onto PVC. The thermal stability of the modified polymer was found to be lowered by the incorporation of PEG. Contact angle measurements on the surface of polymer films cast from a tetrahydrofuran solution of the polymer demonstrated that the modified polymer gave rise to a significantly hydrophilic surface compared to unmodified PVC. The solid/water interfacial free energy of the modified surface was 3.9 ergs/cm(2) as opposed to 18.4 ergs/cm(2) for bare PVC surface. Static platelet adhesion studies using platelet-rich plasma showed significantly reduced platelet adhesion on the surface of the modified polymer compared to control PVC. The surface hydrophilicity of the films was remarkably retained even in the presence of up to 30 wt% concentration of the plasticizer di-(2-ethylhexyl phthalate). The study showed that bulk modification of PVC with PEG using appropriate chemistry can give rise to a polymer that possesses the anti-fouling property of PEG and such bulk modifications are less cumbersome compared to surface modifications on the finished product to impart anti-fouling properties to the PVC surface.     

Kinetics of ϵ-caprolactone polymerization and formation of cyclic oligomers

The kinetics of the anionic polymerization of ?-caprolactone, including the kinetics of macrocyclization and the kinetics of macrocycles propagation in THF solution, initiated with (CH₃)₃SiONa, were investigated. Rate constants of propagation (k_p(n)) and of back-biting (k_d(n)) involving monomer and cyclic oligomers (macrocycles) with n = 2, 3, … monomeric units were determined for n ≤ 7. It was found that starting from the tetramer k_d(n) ～ n^?1,4±0,1 and k_p(n) ～ n^0,7±0,15 (in Jacobson-Stockmayer's theory k_p(n) ～ n). This discrepancy is explained in terms of “conformational hindrance”, increasing for small cycles with the increase of the ring size until a certain ring size is reached. This hindrance decreases the availability of some of the ester groups in the macrocyclics for attack of the growing species, lowering in this way the exponent in the dependence of k_p(n) on n from one to a lower value.     

Blends of poly(hydroxy ether of bisphenol-A) with poly(2-vinylpyridine) and poly(4-vinylpyridine)

Poly(hydroxy ether of Bisphenol-A), so-called Phenoxy resin (structure-based IUPAC name: poly[oxy(2-hydroxytrimethylene)oxy-1,4-phenyleneisopropylidene-1,4-phenylene]), is shown to be miscible with poly(4-vinylpyridine) (P4VPy, poly[1-(4-pyridyl)ethylene]) and poly(2-vinylpyridine) (P2VPy, poly[1-(2-pyridyl)ethylene]) over the entire composition range. Miscibility of the blends is evidenced by their glass transition temperatures being intermediate between the pure polymers for the blends of P4VPy and Phenoxy but being higher than the average for the case of the P2VPy/Phenoxy blends. Hydrogen bonding between the components was detected through infrared spectroscopy, which was also used in the study of mixtures of low-molecular-weight analogues, in order to calculate the free energies of mixing according to the association model of Painter and Coleman.     

Analysis and characterization of unusual ternary polymer miscibility in poly(ether diphenyl ether ketone), poly(ether ether ketone), and poly(ether imide)

A rare case of ternary polymer miscibility has been demonstrated in the mixture (in the glassy amorphous domains) comprising three polymers: polyetherimide (PEI), a new semicrystalline meta‐linked poly(ether diphenyl ether ketone) (PEDEKm), and semicrystalline poly(ether ether ketone) (PEEK). The T_g‐composition relationship for the ternary miscible blend system was treated by extension of the conventional models. The narrow T_g breadth also suggests that the scale of mixing was fine. The ternary blend exhibit no cloud point transition within the wide temperature range (50–400°C) studied. The interactions between any pairs among the three polymers were estimated using the Flory‐Huggins theory. The FT‐IR result gave further evidence that no significant specific interactions existed in any of the three binary pairs. The results collectively supported that no significant binary Δχ existed in the ternary polymer blend, which is favorable for leading this rare ternary miscibility.     

Copolymers with soft and hard segments based on 2,2-dimethyltrimethylene carbonate and ε-caprolactone

Thermoplastic elastomers with ABA-block structure, A representing the hard segment and B the soft segment, were prepared by ring-opening polymerization from 2,2-dimethyltrimethylene carbonate (DTC, 1 ) and ε-caprolactone (ECL, 2 ) as monomers. Typical anionic initiators, viz. the dilithium salt of hydroxytelechelic poly(ethylene oxide) 200 ( 4 ) and of polytetrahydrofuran 1000 ( 5 ) and as an insertion initiator the bis(diethylaluminium) salt of triethylene glycol were used. The soft block is formed by a sequence of random (or tapered) structure comprising equimolar amounts of the two monomers and obtained by simultaneous polymerization of DTC and ECL. The hard blocks consist of highly crystalline poly(2,2-dimethyltrimethylene carbonate) sequences. The thermal properties of the polymers depend on the sequence length, the content of heterodiads in the soft block and the thermal history of the samples. Copolymer films with short end blocks and high content of heterodiads show rubber-elastic properties at normal conditions.     

Polylactones, 15. Reactions of δ-valerolactone and ϵ-caprolactone with acidic metal bromides

δ Valerolactone and ?-caprolactone were reacted with BBr₃, AIBr₃, TiBr₄, SnBr₄ or Bu₂SnBr₂ in dichloromethane or chloroform in a 1 : 1 mole ratio. When these exothermic reactions were conducted with cooling, complexation of the lactones at the exocyclic oxygen was detectable by means of IR and ¹H NMR spectroscopy as the first reaction step. However, heating to 60°C causes in all cases ring cleavage, and after hydrolytic removal of the metal bromides ω-bromocarboxylic acids or oligomers with ω-bromoalkanoyl end groups were obtained. SnBr₄, Bu₂SnBr₂ and ZnBr₂ proved to be good initiators of the polymerization of both lactones. At low monomer/initiator (M/I)-ratios (high initiator concentrations) most of the initiator remained unchanged, and the average degrees of polymerization of the resulting polylactones largely exceeded the value expected for the M/I-ratio. By means of viscosity and GPC measurements weight-average molecular weights up to 70 000 were found. All polylactones obtained by initiation with these three metal bromides contain ?-bromoalkanoyl end groups. Furthermore, high-molecular-weight poly(?-caprolactone) could be prepared at polymerization temperatures up to 150°C. The results do not indicate a cationic polymerization mechanism, but an insertion mechanism involving the metal-O bond formed after the first cleavage of the lactone rings.     

Block polymers obtained by means of anionic polymerization. Polystyrene-block-poly(ε-caprolactone) and polystyrene-block-poly(2,3-dimethyltrimethylene carbonate)

The anionic ring-opening polymerization of ε-caprolactone and 2,2-dimethyltrimethylene carbonate in toluene as solvent with polystyryllithium or lithium polystyrylethoxide resp. lithium polystyrylmethoxide as initiators, results in the formation of the corresponding block polymers as major products, beside small amounts of homopolymer. The block copolymers were isolated chromatographically from the mixture and analyzed spectroscopically.     

Kinetics of the anionic polymerization of ϵ-caprolactone with K+ · (dibenzo-18-crown-6 ether) counterion. Propagation via macroions and macroion pairs

Following our earlier work on the polymerization of lactones involving crowned cations, kinetics of the anionic polymerization of ?-caprolactone (?CL) with K⁺ · (dibenzo-18-crown-6 ether) (K⁺DB18C6) counterion was studied calorimetrically in THF solution in the temperature range from 0 to 20°C. Dissociation constants of CH₃(CH₂)₅O^?K⁺DB18C6, modelling the active centers, were determined conductometrically: K_D (20°C) = 7,7 · 10^?5 mol · dm^?3, ΔH = 9,3 ± 0,2 kJ · mol^?1, ΔS = ?47 ± 2J · mol^?1 · K^?1. From kinetic measurements and from measurements of the dissociation constant of CH₃(CH₂)₅O^? K⁺DB18C6, rate constants of propagation via macroions and via macroion pairs were determined. Activation parameters for propagation via these species are equal to: ΔH = 39,2 ± 0,2 kJ · mol^?1, ΔS = ?63 ± 1 J · mol^?1 · K^?1, ΔH = 13,7 ± 0,1 kJ · mol^?1, ΔS = ?185 ± 2 J · mol^?1 · K^?1. At 20°C, k = 3,50 · 10² dm³ · mol^?1 · s^?1 and k = 5,2 dm³ · mol^?1 · s^?1. Due to the large difference of ΔH^≠ for propagation via macroions and macroion pairs (vide supra), the isokinetic point (k = k) would appear at ?65°C.