Rheological properties of poly(ε-caprolactone) and poly(styrene-co-acrylonitrile) blends

Summary Rheological properties of poly(-caprolactone) (PCL) and Poly (styrene-co-acrylonitrile) (SAN) blends were examined as a function of the acrylonitrile (AN) content in SAN, to systematically understand the correlation between the interaction parameter and the theological properties of miscible polymer blends. When the plateau modulus (G _N ⁰) and zero shear viscosity ( ₀) of the PCL/SAN blends are plotted against the AN content in SAN, a minimum is observed. Qualitatively, the results obtained parallel the variation of the interchain interaction with the AN content. The negative deviation ofG _N ⁰ and ₀ from linearity seems to be attributed to the increase in the entanglement molecular weight between dissimilar chains which results from the chain extension caused by interchain interaction.     

DSC studies of poly(vinyl chloride)/poly(ε-caprolactone)/poly(ε-caprolactone)-b-poly(dimethylsiloxane) blends

Poly(vinyl chloride)/poly(ε-caprolactone)/poly(ε-caprolactone)-b-poly(dimethylsiloxane) [PVC/PCL/(PCL-b-PDMS)] blends were prepared by solvent casting from tetrahydrofuran. The content of PVC was kept constant (60 wt%); the PCL and PCL-b-PDMS contents were varied by replacing different amounts of PCL [0–20 wt% from the PVC/PCL (60/40) blend] with PCL-b-PDMS copolymer having different molecular weights of the PCL blocks. The thermal properties of prepared blends were investigated by differential scanning calorimetry in order to analyse miscibility (through glass transition temperature) and crystallinity. Differential scanning calorimetry analyses show that the PVC/PCL/PCL-b-PDMS blends are multi-phase materials which contain a PVC plasticized with PCL phase, a block copolymer PCL-b-PDMS phase (with crystalline and amorphous PCL and PDMS domains) and a PCL phase (preponderantly crystalline).     

Single-component poly(ε-caprolactone) composites

Non-covalently bonded crystalline inclusion compounds (ICs) have been formed by threading host cyclic starches, α-cyclodextrins (α-CDs), onto guest poly(ε-caprolactone) (PCL) chains and by co-crystallization of guest PCL and host urea (U). PCLs were coalesced from both ICs by appropriate removal of the α-CD and U hosts. When added at low concentrations, PCL coalesced from its α-CD–IC served as an effective self-nucleating agent for the bulk crystallization of as-received PCL from the melt. Film sandwiches consisting of two layers of as-received (asr) (control), and one layer each of asr and self-nucleated (nuc) (composite) PCLs were produced by melt pressing. A composite sandwich consisting of a film of neat PCL coalesced from its U–IC (c-PCL) and a film of asr-PCL was also melt pressed. DSC showed that both composite films maintain their characteristic structures and properties even after melt-pressing them together. Both single component film sandwiches exhibited strong interfaces and better mechanical properties than the asr-PCL/asr-PCL control composite sandwiches. These results are similar to those previously obtained on similarly prepared nylon-6 (N-6) sandwich composites made with asr- and nuc-N-6 films with the same levels of crystallinity. However, while the elongation at break was greatly reduced in the asr-N-6/nuc-N-6 composite, asr-/asr-, asr-/c-, and asr-/nuc-, PCL/PCL-composites all showed similarly large elongations at break. The above room temperature and well below room temperature glass-transition temperatures of N-6 and PCL are likely the cause of their widely different elongations at break.     

Synthesis and crystallization kinetics of silsesquioxane-based hybrid star poly(ε-caprolactone)

A series of silsesquioxane-based hybrid star poly(ε-caprolactone) with different arm length (SHPCL-4, SHPCL-10, SHPCL-40) were synthesized from ring-opening polymerisation of ε-caprolactone as a monomer initiated by silsesquioxane-based hybrid polyol (SBOH). Two linear poly(ε-caprolactone)s, LPCL-25 and LPCL-35, were also prepared for comparison. The sequence of LPCL-25<LPCL-35<SHPCL-4<SHPCL-10<SHPCL-40 for total molecular weights (M_n) and the sequence of SHPCL-4<SHPCL-10<LPCL-25<LPCL-35<SHPCL-40 for average molecular weight per arm were determined by ¹H NMR and GPC measurements. The ¹H NMR data also suggested that SHPCLs possess a spheric architecture with 29.2 arms in average. The crystallization kinetics study by non-isothermal DSC showed that the starting temperature of crystallization (T_s), the ending temperature (T_e) and the peak temperature of exothermic curve (T_p) are in the order as: SHPCL-4<SHPCL-10<LPCL-25<SHPCL-40≈LPCL-35, while the crystallinity (X_c) follows the order of SHPCL-4<SHPCL-10<SHPCL-40<LPCL-25<LPCL-35. The corrected overall crystallization rate constant (K_c) calculated from Avrami equation were found to be in the order as: SHPCL-4<SHPCL-10<LPCL-35<LPCL-25≈SHPCL-40, which was further evidenced by the real time morphological observation with polarized light microscopy (POM). It is also found by the POM measurements that the inorganic core and star architecture greatly retards the nucleation of SHPCLs with short arms, while it helps the nucleation of SHPCL with longer arms.     

Synthesis and characterization of polyrotaxanes comprising α-cyclodextrins and poly(ε-caprolactone) end-capped with poly(N-isopropylacrylamide)s

Biodegradable polyrotaxane (PR)-based triblock copolymers were synthesized via the atom transfer radical polymerization (ATRP) of N-isopropylacrylamide (NIPAAm) initiated with polypseudorotaxanes (PPRs) consisting of a distal 2-bromopropiomyl bromide end-capping poly(ε-caprolactone) (Br-PCL-Br) and a varying amount of α-cyclodextrins (α-CDs) in the presence of Cu(I)Br/PMDETA at 25 °C in aqueous solution. The copolymers were featured by relatively higher yields from 46.0% to 82.8% as compared with previous reports. Their structure was characterized in detail by using ¹H NMR, ¹³C CP/MAS NMR, GPC, WXRD, DSC and TGA analyses. When a feed molar ratio of NIPAAm to Br-PCL-Br was changed from 50 to 200, the degree of polymerization of PNIPAAm blocks attached to two ends of PPRs was in a range of 158–500. About one third of the added α-CDs were still entrapped on the central PCL chain after the ATRP process. Attaching PNIPAAm rendered the copolymers soluble in aqueous solution showing the thermo-responsibility as evidenced by turbidity measurements.     

Synthesis and characterization of a novel amphiphilic poly (ethylene glycol)–poly (ε-caprolactone) graft copolymers

A series of amphiphilic graft copolymers PEO-g-PCL with different poly (ε-caprolactone) (PCL) molecular weight were successfully synthesized by a combination of anionic ring-opening polymerization (AROP) and coordination-insertion ring-opening polymerization. The linear PEO was produced by AROP of ethylene oxide (EO) and ethoxyethyl glycidyl ether initiated by 2-(2-methoxyethoxy) ethoxide potassium, and the hydroxyl groups on the backbone were deprotected after hydrolysis. The ring-opening polymerization of CL was initiated using the linear poly (ethylene oxide) (PEO) with hydroxyl group on repeated monomer as macroinitiator and Sn(Oct)₂ as catalyst, then amphiphilic graft copolymers PEO-g-PCL were obtained. By changing the ratio of monomer and macroinitiator, a series of PEO-g-PCL with well-defined structure, molecular weight control, and narrow molecular weight distribution were prepared. The expected intermediates and final products were confirmed by ¹H NMR and GPC analyzes. In addition, these amphiphilic graft copolymers could form spherical aggregates in aqueous solution by self-assemble, which were characterized by transmission electron microscopy, and the critical micelle concentration values of graft copolymers PEO-g-PCL were also examined in this article.     

Synthesis and self-assembly of a new amphiphilic thermosensitive poly(N-vinylcaprolactam)/poly(ε-caprolactone) block copolymer

New amphiphilic thermosensitive poly(N-vinylcaprolactam)/poly(ε-caprolactone) (PNVCL-b-PCL) block copolymers were synthesized by ring-opening polymerization of ε-caprolactone with hydroxy-terminated poly(N-vinylcaprolactam) (PNVCL-OH) as a macroinitiator. The structures of the polymers were confirmed by IR, ¹H NMR and GPC. The critical micelle concentrations of copolymer in aqueous solution measured by the fluorescence probe technique reduced with the increasing of the proportion of hydrophobic parts, so did the diameter and distribution of the micelles determined by dynamic light scattering. The shape observed by transmission electron microscopy (TEM) demonstrated that the micelles are spherical. On the other hand, the UV–vis measurement showed that polymers exhibit a reproducible temperature-responsive behavior with a lower critical solution temperature (LCST). The LCST of PNVCL-OH can be adjusted by controlling the molecular weights, and that of copolymers can be adjusted by controlling the compositions and the concentration. Variable temperature TEM measurements demonstrated that LCST transition was the result of transition of individual micelles to larger aggregates.     

Fabrication of highly porous poly (ε-caprolactone) microfibers via electrospinning

Highly porous Poly (ε-caprolactone; PCL) microfibers were successfully fabricated by collecting the fibers into a water bath during electrospinning. The morphology of the fibers collected with and without the water bath was investigated. We observed that altering the pH of the water bath affected both the fiber diameter and the size of pores on the fibers. Acidic or basic condition was found to be more favorable than neutral conditions for the formation of well-porous fibers. The morphology and pore size of the microfibers were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The average diameter of the fibers and the pore size on the surface of the microfibers were found to be 12–14.5 and 0.3–0.7 μm, respectively. The crystallinity and thermal properties of the PCL mats were investigated by DSC. This highly porous nature of the microfibers makes PCL less crystalline and increases the surface to volume ratio of the mat. Therefore, the PCL mat obtained by water bath electrospinning may be more effective for tissue scaffolds and drug delivery than the mat obtained without water bath.     

Two-way reversible shape memory behaviour of crosslinked poly(ε-caprolactone)

Polymers capable of reversible “two-way” shape memory behaviour are of great interest for applications where reversible actuation is demanded, and semicrystalline crosslinked systems have been indicated as an interesting solution towards this end. In this work we have explored the two-way shape memory response of semicrystalline poly(ε-caprolactone)-based polymer networks, prepared with various macromolecular architectures starting from linear, three- and four-arm star poly(ε-caprolactone) functionalized with methacrylate end-groups. All the materials have revealed two-way shape memory capabilities. The effect arises from an elongation process that takes place when the material is cooled under an applied load below the crystallization temperature, and that is completely reversed when heated again above melting temperature, in a manner that strongly depends on the applied load and on the material crosslink density. Two-dimensional XRD analysis, carried out on elongated specimens, shows that the elongation on cooling is accompanied by a change in the crystallinity orientation along the direction of stretch.     

In vitro degradation of poly(l-lactide)/poly(ε-caprolactone) blend reinforced with MWCNTs

The physical and mechanical properties of poly(l-lactide)/poly(??-caprolactone) (PLLA/PCL) blends reinforced with multiwalled carbon nanotubes (MWCNTs) before and after in vitro degradation were investigated. Because of brittleness, PLLA needs to be plasticized by PCL as a soft polymer. The MWCNTs are used to balance the stiffness and the flexibility of PLLA/PCL blends. The results showed that with incremental increase in concentration of MWCNTs in composites, the agglomerate points of MWCNTs were increased. The physical and mechanical properties of prepared PLLA/PCL blends and MWCNT/PLLA/PCL nanocomposites were characterized. The X-ray diffraction analysis of the prepared blends and composites showed that MWCNTs, as heterogeneous nucleation points, increased the lamella size and therefore the crystallinity of PLLA/PCL. The mechanical strength of blends was decreased with incremental increase in PCL weight ratio. The mechanical behavior of composites showed large strain after yielding and high elastic strain characteristics. The tensile tests results showed that the tensile modulus and tensile strength are significantly increased with increasing the concentration of MWCNTs in composites, while, the elongation-at-break was decreased. The in vitro degradation rate of polymer blends in phosphate buffer solution (PBS) increased with higher weight ratio of PCL in the blend. The in vitro degradation rate of nanocomposites in PBS increased about 65% when the concentration of MWCNTs increased up to 3% (by weight). The results showed that the degradation kinetics of nanocomposites for scaffolds can be engineered by varying the contents of MWCNTs.     

Preparation of polylactide/poly(ε-caprolactone) microspheres enclosing acetamiprid and evaluation of release behavior

Reduction of the amount of pesticides applied to agricultural land is essential for environmental conservation. It can be accomplished by immobilization of the pesticides in polymer supports, which prevents their volatilization, degradation and leaching losses, and provides controlled release of the chemicals. In the present study, acetamiprid, a novel pesticide, was encapsulated in PLA-based microspheres using the solvent evaporation method via oil-in-oil (O/O) emulsion. Silicon oil and an acetonitrile solution with dissolved synthetic polymer(s) and acetamiprid were used as an outer and inner oil phases, respectively. The entrapment efficiency of the pesticide in the case of PLA microspheres decreased with increasing the concentration of the pesticide in the inner oil phase. The amount of acetamiprid released from the microspheres was less than 18 %. On the other hand, incorporation of poly(-caprolactone) (PCL) into the PLA microspheres resulted in increased amount of releasable pesticide (approximately 89 %). These results indicate that the PCL/PLA microsphere is a promising immobilization support of the acetamiprid for practical application.     

Evaluation of electron beam-induced crosslinking of poly(ε-caprolactone)—Effect of elevated temperatures

The effect of elevated temperatures (40, 80, and 170 °C) on the electron beam (EB)-induced crosslinking and degradation of poly(ε-caprolactone) (PCL) in nitrogen atmosphere without adding crosslinking agents has been investigated. The increased mass average molecular mass of EB modified masticated PCL (mPCL) samples were measured by size exclusion chromatography. The sol–gel investigation showed that mPCL tended to dominating crosslinking at a temperature of 170 °C. At this temperature, the maximum gel content of 56% was observed for an EB treatment with a dose of 100 kGy. In addition, the ratio of chain scission density to density of crosslinked units amounted to 0.25. The dynamic rheological test demonstrated that EB treatment at 170 °C led to the most remarkable elasticity enhancement behavior with enhanced viscosity, modulus, and decreased loss factor (tan δ). The occurrence of branching structure was evidently detected by van Gurp–Palmen plot in combination with the Cole–Cole plot for dose values ≤50 kGy. Less δ and a broadened relaxation process can be observed due to the introduction of some branched structures into mPCL. The results of enhanced molar mass and gel content analysis were confirmed by the dynamic rheological measurements. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47866.     

Thermal properties of di- and triblock copolymers of poly(l-lactide) with poly(oxyethylene) or poly(ε-caprolactone)

High molecular weight di- and triblock copolymers of poly(l-lactide), PLLA, (80 wt%) with a crystallizable flexible second component such as poly(ε-caprolactone), PCL, or poly(oxyethylene), PEO, (20 wt%) were obtained in nearly quantitative yields by ring opening of l-lactide initiated by PCL or PEO hydroxy terminated macromers. The copolymers were characterized by ¹H NMR and FTIR spectroscopy and size exclusion chromatography and showed unimodal and narrow molecular weight distributions. X-ray diffraction measurements revealed high crystallinity (38-56%) of the PLLA blocks and gave no clear evidences of PCL or PEO crystallinity. DMTA and DSC techniques showed a melting behaviour of the copolymers (T_m=174-175 °C; ΔH_m=19-37 J/g) quite similar to that of PLLA. PCL and PLLA segments are immiscible, while PLLA and PEO segments are partially miscible in the amorphous phase. Stress-strain measurements indicated a ductile behaviour of the copolymers, characterized by lower tensile moduli (225-961 Pa) and higher elongations at break (25-134%) with respect to PLLA.     

Impact of organoclays on the phase morphology and the compatibilization efficiency of immiscible poly(ethylene terephthalate)/poly(ε-caprolactone) blends

Adding nanofillers Cloisite 30B (C30B) and Cloisite 15A (C15A) to poly(ethylene terephthalate) (PET)/poly(ε-caprolactone) (PCL) (70/30, wt/wt) blends via melt blending can improve their phase morphology and change their interface properties. The effects of the different selective localization of clay on the structure and the morphologies are studied and evaluated by theoretical and experimental methods. It is found that C30B is selectively localized in PET and at the PET-PCL interface, whereas C15A is mainly localized at the interface. Moreover, the changes in the rheological behavior of the blends are attributed to the formation of clay network-like structures. X-ray diffraction, scanning electron microscope, and transmission electron micrograph observations also evidenced an exfoliated and/or intercalated structure of C30B, and intercalated structure of C15A in the blend, together with significant morphology changes of the initially immiscible blend. The relative permeability to PET/PCL of the nanocomposites decreased with the increasing of nanoclays content. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48812.     

Synthesis and characterization of four- and six-arm star-shaped poly(ε-caprolactone)-b-poly(N-vinylcaprolactam): Micellar and core degradation studies

Star-shaped copolymers with four and six poly(ε-caprolactone)-block-poly(N-vinylcaprolactam) (S(PCL-b-PNVCL)) arms were successfully synthesized by combining ring opening polymerization (ROP) of ε-caprolactone (CL) and reversible addition-fragmentation chain transfer (RAFT) polymerization of N-vinylcaprolactam (NVCL). The resulting star copolymers were characterized using ¹H NMR, GPC and UV–vis. The numbers of arms in the star-shaped PCL-b-PNVCL block copolymers were demonstrated using degradation studies under acidic conditions, and the individual PNVCL chains were characterized by GPC and ¹H NMR. In aqueous solution, star-shaped PCL-b-PNVCL block copolymers self-assembled into large aggregates or micelles with sizes varying from 54 to 300 nm, depending on the molecular weight of the copolymer and the relative lengths of the hydrophobic and hydrophilic segments. Micelles were characterized by atomic force microscopy (AFM), dynamic light scattering (DLS) and scanning electron microscopy (SEM).     

Miscibility of poly(styrene-co-vinyl phenol) with poly(ɛ-caprolactone)

Summary Poly(styrene-co-vinyl phenol) (STVPh)/poly(-caprolactone)(PCL) blends showed enhanced miscibility over polystyrene/PCL blend, and showed single glass transition temperature when the contents of vinyl phenol (VPh) in copolymer were higher than 10 wt % (maximum content of VPh in STVPh used in this study was 20 wt%). STVPh 4, STVPh 7, STVPh 10 (4, 7, 10 were VPh wt%)/PCL blends showed cloud points on heating for miscible blend system, and this phase separation was reversible on cooling. From melting point depression of PCL, interaction parameter, B. for miscible STVPh 12/PCL blend system was evaluated.     

Preparation of curcumin loaded poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone) nanofibers and their in vitro antitumor activity against Glioma 9L cells

The purpose of this work was to develop implantable curcumin-loaded poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone) (PCL-PEG-PCL, PCEC) nanofibers, which might have potential application in cancer therapy. Curcumin was incorporated into biodegradable PCEC nanofibers by electrospinning method. The surface morphology of the composite nanofibers was characterized on Scanning Electron Microscope (SEM). The average diameter of the nanofibers was 2.3-4.5μm. In vitro release behavior of curcumin from the fiber mats was also studied in detail. The in vitro cytotoxicity assay showed that the PCEC fibers themselves did not affect the growth of rat Glioma 9L cells. Antitumor activity of the curcumin-loaded fibers against the cells was kept over the whole experiment process, while the antitumor activity of pure curcumin disappeared within 48 h. These results strongly suggested that the curcumin/PCEC composite nanofibers might have potential application for postoperative chemotherapy of brain cancers.     

Supernucleation and crystallization regime change provoked by MWNT addition to poly(ε-caprolactone)

In this work, the nucleation and crystallization behavior of melt mixed PCL/CNT nanocomposites has been studied. The mixtures of PCL and pristine MWNTs were prepared by extrusion with different nanofiller contents: 0.3, 0.5, 0.7, 1 and 3%. Standard DSC measurements demonstrated pronounced nucleation effects as well as increases in PCL crystallinity. The nucleation effect saturates at only 0.5% (a value much lower than those previously reported in the literature for similar nanocomposites) indicating that the dispersions obtained were excellent. This was corroborated by both TEM observations and by the determination of a very low dielectric percolation threshold (i.e., 0.3%). In self-nucleation experiments, supernucleation effects were obtained up to a maximum of approximately 200% efficiency. This is the first time that supernucleation effects of this order have been reported for PCL filled with untreated MWNTs, a result that we attribute to the excellent dispersion achieved. Isothermal crystallization experiments performed by DSC showed an increase in the crystallization kinetics of PCL with increases in MWNT content as a consequence of the supernucleation effect. The Avrami equation successfully described the overall crystallization kinetics and while neat PCL exhibited Avrami indexes close to 3, indicating that instantaneously nucleated spherulites were formed, the nanocomposite yielded mostly Avrami index values close to 2, as expected for axialites instantaneously nucleated on the surface of the MWNTs. Remarkably, the temperature dependence of the overall crystallization rate exhibited a dramatic change with MWNT content. This novel effect was described as a crystallization regime change (i.e., from Regime II to Regime III) induced by the presence of the MWNTs in terms of the Lauritzen and Hoffman theory.