PCL Chains Research Articles

Candida Antarctica Lipase B-assisted top-down visualization of surface morphology of poly(ε-caprolactone)/poly(ethylene oxide) blend films

A series of enzymatic degradation experiments were designed to examine the surface morphology of phase separated poly(ε-caprolactone) (PCL)/poly(ethylene oxide) (PEO) blend films. Candida antarctica Lipase B (CALB), previously reported to have superior degradation selectivity when used at low concentrations, was utilized to selectively dissect interlamellar amorphous PCL chains and therefore to reveal the crystalline region of PCL phase. Water soluble PEO can be simultaneously removed by the CALB aqueous solutions, allowing one to envision the topological features of phase separated PCL/PEO films with various blend ratios. The transition of phase-separated PCL/PEO from nucleation and growth to spinodal decomposition was fully mapped out, along with the spatial distribution and surface morphological features of the crystalline PCL phase. The morphological characteristics of PCL/PEO blend films were further correlated to their reported physicochemical properties, demonstrating the impact of microscopic structures on the macroscopic properties of given semicrystalline polymer systems.

Effect of PCL chain length on rheological and mechanical properties of PCL‐PDMS‐PCL triblock copolymer films

AbstractThe polycaprolactone‐polydimethylsiloxane‐polycaprolactone (PCL‐PDMS‐PCL) triblock copolymer films of variable PCL chain are analyzed for rheological characteristics in this paper. The dynamics of viscoelastic behavior of photocrosslinked films above their crystal melting temperature (Tcm) is measured using oscillatory shear rheology experiments. The frequency sweep tests are analyzed at 0.1% strain as obtained from linear viscoelastic region. Shear thinning is observed in the study of complex viscosity. It has been noted that viscosity rises with increase in crosslink density and decrease in with PCL chain length. Time‐dependent effect on the copolymer films has been analyzed by creep recovery behavior. The Burgers model is fitted in creep compliance data to analyze its viscoelastic and viscous region. An examination of structure recovery revealed that recovery increased as PCL chain length decreased. Tensile strength and percentage elongation are studied at ambient conditions with a universal testing machine, while storage modulus and tan δ are analyzed by a dynamic mechanical analyzer at varying temperatures.

Efficient Synthesis of Hydrolytically Degradable Block Copolymer Nanoparticles via Reverse Sequence Polymerization‐Induced Self‐Assembly in Aqueous Media

AbstractHydrolytically degradable block copolymer nanoparticles are prepared via reverse sequence polymerization‐induced self‐assembly (PISA) in aqueous media. This efficient protocol involves the reversible addition‐fragmentation chain transfer (RAFT) polymerization of N,N′‐dimethylacrylamide (DMAC) using a monofunctional or bifunctional trithiocarbonate‐capped poly(ϵ‐caprolactone) (PCL) precursor. DMAC monomer is employed as a co‐solvent to solubilize the hydrophobic PCL chains. At an intermediate DMAC conversion of 20–60 %, the reaction mixture is diluted with water to 10–25 % w/w solids. The growing amphiphilic block copolymer chains undergo nucleation to form sterically‐stabilized PCL‐core nanoparticles with PDMAC coronas. 1H NMR studies confirm more than 99 % DMAC conversion while gel permeation chromatography (GPC) studies indicate well‐controlled RAFT polymerizations (Mw/Mn≤1.30). Transmission electron microscopy (TEM) and dynamic light scattering (DLS) indicate spheres of 20–120 nm diameter. As expected, hydrolytic degradation occurs within days at 37 °C in either acidic or alkaline solution. Degradation is also observed in phosphate‐buffered saline (PBS) (pH 7.4) at 37 °C. However, no degradation is detected over a three‐month period when these nanoparticles are stored at 20 °C in deionized water (pH 6.7). Finally, PDMAC30‐PCL16‐PDMAC30 nanoparticles are briefly evaluated as a dispersant for an agrochemical formulation based on a broad‐spectrum fungicide (azoxystrobin).

Efficient Synthesis of Hydrolytically Degradable Block Copolymer Nanoparticles via Reverse Sequence Polymerization-Induced Self-Assembly in Aqueous Media.

Hydrolytically degradable block copolymer nanoparticles are prepared via reverse sequence polymerization-induced self-assembly (PISA) in aqueous media. This efficient protocol involves the reversible addition-fragmentation chain transfer (RAFT) polymerization of N,N'-dimethylacrylamide (DMAC) using a monofunctional or bifunctional trithiocarbonate-capped poly(ϵ-caprolactone) (PCL) precursor. DMAC monomer is employed as a co-solvent to solubilize the hydrophobic PCL chains. At an intermediate DMAC conversion of 20-60 %, the reaction mixture is diluted with water to 10-25 % w/w solids. The growing amphiphilic block copolymer chains undergo nucleation to form sterically-stabilized PCL-core nanoparticles with PDMAC coronas. 1 H NMR studies confirm more than 99 % DMAC conversion while gel permeation chromatography (GPC) studies indicate well-controlled RAFT polymerizations (Mw /Mn ≤1.30). Transmission electron microscopy (TEM) and dynamic light scattering (DLS) indicate spheres of 20-120 nm diameter. As expected, hydrolytic degradation occurs within days at 37 °C in either acidic or alkaline solution. Degradation is also observed in phosphate-buffered saline (PBS) (pH 7.4) at 37 °C. However, no degradation is detected over a three-month period when these nanoparticles are stored at 20 °C in deionized water (pH 6.7). Finally, PDMAC30 -PCL16 -PDMAC30 nanoparticles are briefly evaluated as a dispersant for an agrochemical formulation based on a broad-spectrum fungicide (azoxystrobin).

Cationically photocured epoxy/polycaprolactone materials processed by solution electrospinning, melt electrowriting and 3D printing: Morphology and shape memory properties

Epoxy/polycaprolactone (PCL) blends containing cationic photo-initiator were prepared by both solution and melt blending. These materials were processed by solvent casting, solution electrospinning (SE), melt electrowriting (MEW), and Fused Deposition Modeling (FDM) 3D printing. The final materials were obtained after UV curing at room temperature. FTIR, and gel content measurements showed that all the materials were crosslinked and that the PCL was part of the network. The shape memory abilities (measured by DMA experiments) depended on the processing technique. Thus, the fixity and recovery ratios were optimal for electrospun fibers, while the 3D printed sample was not able to recover any shape, probably because of the poor adhesion between the printed layers. According to AFM images, samples obtained by MEW and 3D printing produced materials with spherulitic morphology, while solution electrospinning rendered fibers with Shish-Kebab-type crystalline morphology. The latter was highly anisotropic, and many chains were oriented along the nanofiber axis interdispersed with amorphous regions where the epoxy resin formed covalent links with the PCL chains. This morphology conferred extraordinary solvent resistance and shape memory properties to the electrospun mats. The latter manifested a very high affinity towards chloroform, and accordingly, they displayed potential applications as chloroform sensors.

Preparation, optimization, and characterization of chrysin-loaded TPGS-b-PCL micelles and assessment of their cytotoxic potential in human liver cancer (Hep G2) cell lines

In total, nine TPGS-b-PCL copolymers were synthesized employing distinct TPGS analogues (TPGS 2000, 3500, and 5000). In these copolymers, the length of the PCL chain varied according to the TPGS to PCL molecular weight ratio (1:1, 1:2, and 1:3). The formulation optimization was done by optimizing the drug to polymer ratio, encapsulation efficiency, drug loading, micelle diameter, and polydispersity index (PDI). TPGS3500-b-PCL7000 copolymer (TPGS to PCL ratio 1:2) with drug to polymer ratio 1:30 showed the best percentage encapsulation (63.50 ± 0.45 %) and drug loading (2.05 ± 0.07). The optimal micelle (CHR-M) diameter and PDI were determined to be 94.57 ± 13.40 nm and 0.16 ± 0.02, respectively. CHR-M showed slow release when compared with alcoholic solution of chrysin. Approximately 70.70 ± 6.4 % drug was released in 72 h. The CHR-M demonstrated considerably greater absorption in Hep G2 cells, which confirmed the reliability of the micellar carrier. The MTT assay results showed that the IC50 values for CHR-M were much lower after 24 and 48 h when compared to free chrysin. Therefore, CHR-M may be a viable carrier for active chrysin targeting with improved anticancer potential. Also, it could be a better alternative for the currently available treatment of hepatocellular carcinoma.

Effects of methoxy polyethylene glycol‐polycaprolactone block copolymers and silica nanoparticles on the mechanical, tissue affinity and antibacterial properties of n‐butyl cyanoacrylate adhesive

AbstractCyanoacrylates are widely used as surgical tissue adhesives because of their high biodegradability, but they are brittle and have poor tissue affinity. In this study, methoxy polyethylene glycol‐polycaprolactone block copolymers (MPEG‐co‐PCLs) with different PCL chain lengths were synthesized by ring‐opening polymerization. Then, a new tissue adhesive with excellent mechanical properties, tissue affinity, antibacterial properties, and coagulation performances was prepared by incorporating MPEG‐co‐PCL and silica nanoparticles (SNPs) into n‐butyl cyanoacrylate (BCA). The optimal MPEG: PCL ratio is 1:4 (MP‐3), and the optimal mass ratio of MPEG‐co‐PCL and SNPs (0.5SNPs/0.5MP‐3) is 0.5 wt.%. Compared to BCA, the adhesion strength and flexibility of 0.5SNPs/0.5MP‐3 are dramatically improved by 110% and 244%, respectively. MPEG‐co‐PCL can fully exploit the advantages of homopolymers, and therefore, improve the tissue affinity and adhesion strength of the adhesive and avoid BCA polymerization initiated by MPEG and poor compatibility of PCL with BCA. SNPs can also compensate for the lack of antibacterial properties of BCA against Gram‐negative bacteria. The E. coli inhibition circle of 0.5SNPs/0.5MP‐3 is twice as large as BCA. SNPs can also improve coagulation by promoting platelet aggregation. This work provides an effective strategy for developing adhesives with potential clinical applications.

A wide range of poly(glycolic acid)‐based di‐ and tri‐block polyesters by a single organocatalyst: Synthesis and characterization

AbstractThe ring‐opening polymerization (ROP) of glycolide (GA), the copolymerization of GA with ε‐caprolactone (ε‐CL), and the terpolymerization of GA with ε‐CL and lactide (LA) were studied over the cheap non‐toxic metal‐free organocatalyst tetrabutylammonium 2‐(carbamyl)benzoate (TBACB). The catalyst with comparable catalytic activity to the comonomers afforded a series of well‐defined PGA‐based block polymers with ε‐CL, LA monomers at high yields by varying feeding methods under bulk and solution conditions. The poly(ɛ‐caprolactone‐b‐glycolic acid)s (PCGAs) and poly(ε‐caprolactone‐b‐lactide‐b‐glycolide) (PCLGAs) with controllable chain segment composition were obtained by “one‐pot” solution copolymerization in mixtures, or semi‐batch copolymerization. Due to the high thermal stability of TBACB, the PCGA and PCLGA with high molecular weight (Mn = 6.9 and 10.0 kg mol−1) could also be obtained by bulk polymerization at 120 °C by sequential addition of ε‐CL, (LA), and GA in a short time (<2.5 h). Compared to the polymers with similar compositions by different methods, the bulk polymerization showed more effective and higher molecular weight. The microstructure characterized by NMR showed highly ordered block polymers with defined chain segments. Two melting transitions (Tm) of PCGA suggested exclusively associated with PCL and PGA segmental chain in the product.

Reorientation of Crystalline Block Copolymer Membranes by Phospholipid Hybridization

Block copolymer (BCP) self-assembly and crystallization determine their fundamental mechanical, optical, and transport properties. Multiple physical and chemical routes to control BCP self-assembly have been developed over the years. In contrast, modulating the crystallization behavior, particularly crystallite size and orientation, has received considerably less attention. This paper underpins that 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) phospholipid additives enable precise control of BCP crystallization via a combination of interfacial and confinement effects. The assembly and crystallization behavior of methoxy-poly(ethylene glycol)-b-poly(ε-caprolactone) (mPEG-b-PCL) hybridized with DPPC was elucidated in solid-supported dry-film forms. mPEG-b-PCL/DPPC hybrid films coassemble into multilamellar structures with BCP and lipid domains stacked in registry across the film thickness. With small amounts of DPPC (3 wt %), mPEG-b-PCL/DPPC hybrid films unexpectedly exhibit nonadditive thermal conductivity, reaching ∼0.1 W m–1 K–1, a value considerably lower than pure BCP or DPPC films. Hybridization alters DPPC chain packing and induces specific PCL crystallite orientation at the nanoscale. PCL chains on the folding plane of an orthorhombic lattice optimize molecular interactions with vertically aligned DPPC alkyl chains by orienting PCL crystallites at a 20° tilt. These results enable new applications of polymeric systems in which switchable crystallization routes are used to tune heat transport.

Photocrosslinked Poly(ϵ‐caprolactone) – Polydimethylsiloxane – Poly(ϵ‐caprolactone) Triblock Copolymeric Films: Structural, Thermal and Shape Memory Properties

AbstractThe shape memory triblock photocrosslinked copolymeric films of varying poly(ϵ‐caprolactone) (PCL) chain length and constant polydimethylsiloxane (PDMS) content are synthesized. The effect of PCL chain length on structural, thermal and shape memory properties of triblock copolymeric films is studied. The structural properties are analyzed by X‐ray diffraction (XRD) and optical microscope. Discrete crystal morphology is observed with increase in PCL chain length. Thermal properties are evaluated by differential scanning calorimetry (DSC) using non‐isothermal and isothermal modes. The crystallinity and crystal melting point of triblock polymer increases with increase in PCL chain length. The crystallization kinetics of triblock PCL‐PDMS‐PCL copolymeric films are studied with the help of Avrami model and Lauritzen‐Hoffman (LH) model. The three‐dimensional growth of PCL crystals is observed in triblock copolymers. Inclusion of PDMS block resulted in longer crystallization time, higher energy barrier and affects the crystal growth rate of PCL block, which further affect the shape fixity and shape recovery ratio accordingly.

Poly(ε-Caprolactone)-Methoxypolyethylene Glycol (PCL-MPEG)-Based Micelles for Drug-Delivery: The Effect of PCL Chain Length on Blood Components, Phagocytosis, and Biodistribution.

BackgroundThe main challenge of polymeric micelles as drug delivery systems is that the actual delivery efficiency is not as high as expected, which is closely related with the interactions with the complex biological environments such as blood components, phagocytosis, and biodistribution. Herein, we expect to understand these concerns for the clinically relevant micelles that composed of methoxypolyethylene glycol (MPEG) with identical chain length And poly(ε-caprolactone) (PCL) with tunable chain length (PCLn-MPEG) (n=20, 30, and 40) wherein doxorubicin was encapsulated as a model drug.MethodsThe doxorubicin-loaded PCLn-MPEG micelles were prepared by a dialysis method and characterized by dynamic light scattering and transmission electron microscopy. The surface PEG density and chain conformation were investigated by dissipative particle dynamics simulation. The stability of the micelles was detected by nanoparticle tracking analysis. The effects of PCL chain length on the blood components, phagocytosis, and biodistribution were assayed in vitro and in vivo.ResultsThe micelles exhibited spherical morphology with a diameter about 30nm. The PEG chain conformation from “mushroom-like” to “brush-like” was evident. The micelles have no remarkable effect on the red blood cells, blood coagulation, and platelet activation. Interestingly, the protein adsorption was affected and dependent on the chain conformation, with lowest adsorption for PCL30-MPEG, which also has the loWest phagocytosis. The stability of the micelles was in the order of PCL40-MPEG>PCL30-MPEG>PCL20-MPEG which was dependent on the PCL chain length. The micelles mainly accumulated in liver, with the order consistent with their stability, indicating that, besides the phagocytosis, the stability of the micelle plays an important role in biodistribution as well. The related mechanisms were proposed and discussed.ConclusionManipulating the PEG/PCL ratio of the micelle is an effective approach to modulate the protein adsorption, phagocytosis, and biodistribution, which may be a prerequisite for clinical applications.

Amphiphilic olefin block copolymers synthesized by successive coordinative chain transfer and ring-opening polymerizations

Introducing polarity is a necessity for widening the application scope of polyolefins specifically for developing biocompatible products. To this end, we exploit a two-step polymerization process to synthesize poly(ethylene‑b‑caprolactone) PE‑PCL block copolymers, which contain both polar and non-polar segments. First ethylene is polymerized by a generic metallocene catalyst in the presence of ZnEt2 as the chain transfer agent according to the coordinative chain transfer polymerization (CCTP) technique. Terminal zinc atoms are subsequently replaced by hydroxyl groups (PE‑OH) by exposing dormant polymer chains to oxygen. Afterward, ring-opening polymerization (ROP) of ε‑caprolactone is initiated by PE‑OH to form PE‑PCL block copolymers. Successful formation of both blocks is verified by FTIR and NMR spectroscopy. The presence of PCL blocks greatly lowers the crystallinity of ethylene sequences according to XRD and DSC results. Moreover, a second type of PE crystals with more chain folds and lower lamella thickness is found in block copolymers, which is absent in the equivalent physical blend. The diverse crystal structure of block copolymers suggest that phase separation exists between PE and PCL segments. The SEM image of the equivalent physical blend confirms the tendency of PCL and PE chains to phase separate, and infers a compatibilization in the presence of PE‑PCL block copolymers. This phase separation is detected by rheological measurements, as well, where block copolymers show deviations from Maxwell behavior in the terminal relaxation zone at low frequencies. Rheology results also show that the order-disorder transition temperature (TODT) of these block copolymers is higher than 180 °C. These results provide a clear picture from the morphology and utility of such block copolymers specifically for compatibilizing blends of polar polymers and non-polar polyolefins, which significantly broaden the utility of polyolefins.

Reducing the crystallinity of PCL chains by copolymerization with substituted δ/ε-lactones and its impact on the phase separation of PCL-based block copolymers

Different self-segregation behavior of ABA triblock copolymers with central PBD or PBD H blocks and semi-crystalline or amorphous PCL-like external blocks.

Nanocomposites of PCL and SBA-15 Particles Prepared by Extrusion: Structural Characteristics, Confinement of PCL Chains within SBA-15 Nanometric Channels and Mechanical Behavior.

A study of different nanocomposites based on poly(ε-caprolactone) (PCL) and mesoporous SBA-15 silica that were prepared by melt extrusion was carried out by analyzing the possible effect of this filler on the crystalline details of PCL, on its mechanical behavior, and on the eventual observation of the confinement of the polymeric chains within the hollow nanometric silica channels. Thus, simultaneous Small-Angle and Wide-Angle X-ray Scattering (SAXS/WAXS) synchrotron experiments at variable temperature were performed on these PCL nanocomposites with different mesoporous silica contents. The importance of the morphological and structural features was assessed by the changes that were observed during the mechanical response of the final materials, which determined that the presence of mesoporous particles leads to a noticeable reinforcing effect.

The effect of incorporating graphene and polycaprolactone-grafted graphene oxide nanosheets on thermal and physico-mechanical properties, microstructure and biocompatibility of electrospun polyurethane nanocomposite mats

Bead-free electrospun polyurethane/graphene (PU-G) and polyurethane/reduced polycaprolactone-grafted graphene oxide (PU-GPCL) nanofiber mats were prepared for wound dressing application. The facilitated electron signal diffusion throughout the scaffolds boosted the proliferation, cell attachment, and cell viability of the 3T3 fibroblast cells on the PU-G and PU-GPCL nanofiber mats. The partial electrical conductivity induced in PU-G nanocomposites, due to the presence of G nanosheets , reduced the diameters of nanofibers compared to other samples. In addition, the lower tendency of G nanosheets to localize into the nanofibers decreased the mechanical properties of PU-G scaffolds which might restrict their practical applications. On the other hand, the localization of GPCL nanosheets into nanofibers, because of their high affinity with PU matrix, improved the mechanical properties of the PU-GPCL nanofiber mats. Considering the results of different analyses, including mechanical and MTT studies, it could be deduced that PU-GPCL electrospun nanofiber mat containing 1 wt% of GPCL nanosheets could be selected as the potential candidate for wound dressing application. • Bead-less PU/G and PU/GPCL electrospun nanofiber mats were prepared. • SEM images show that GPCL are embedded into the nanofibers due to grafted PCL chains. • MTT assay show cell-interaction of scaffolds with 3T3 fibroblast cells were boosted. • SEM images show PU/G scaffolds have smaller diameters due to electrical conductivity.

Grafting of poly(ε‐caprolactone) from Abaca cellulose fibers via ring‐opening polymerization resulting in facile one‐pot biocomposites

AbstractAs efforts to replace nonsustainable plastics increase, biocomposites from cellulose fibers and biodegradable polymers like poly(ε‐caprolactone) (PCL) are promising candidates. The necessary adhesion between fibers and matrix can be achieved by grafting polymeric chains onto the fibers. Herein, we report grafting of PCL onto Abaca fibers (AFs), a one‐pot method to obtain a composite containing grafted fiber and free PCL, and the characterization of prepared composite films. Three parameters for pretreatment (disintegration, drying, and solvent exchange) of AF were compared. Short and long PCL chains with molecular weights below and close to the chain entanglement weight of PCL were grafted from AFs. Using benzyl alcohol as an additional initiator, free PCL was simultaneously prepared. The unreacted monomer was removed by precipitation in water, resulting in ready‐made one‐pot composites. The biocomposites containing the free PCL and PCL‐grafted AFs were further processed by a combination of compounding and hot‐pressing. The analyzed mechanical (tensile) and rheological properties show a large dependence on the lengths of the PCL grafts. The herein‐reported composites pave the way for interesting bio‐based alternatives to plastic, especially looking at the tailoring of material properties.

Tuned interactions within inclusion complex to generate electrospun matrices of superior strength

The utilization and applications of biopolymer based electrospun matrices has expanded in various fields because of their advantageous features, however due to the poor mechanical strength their true potential has still not been realized. Enhancing mechanical strength of electrospun matrices is a long sought-after goal which is achieved by maximizing the interactions in inclusion complex (IC) of poly(ɛ-caprolactone) (PCL) with urea, in this work. The ratio of urea was varied with respect to PCL and changes in the enthalpy of fusion (ΔHf) for IC thus formed were analyzed using DSC. Binding efficiency (BE) of PCL and urea within the IC was calculated using ΔHf, which was reproducibly altered by varying urea to PCL ratio. The extent of hydrogen bonding between PCL and urea, varied in this way, was also confirmed by FTIR and XRD analysis. PCL and urea-based IC samples were electrospun to fabricate uniform fibrous matrices which upon selective removal of urea showed superior mechanical strength as compared to neat PCL matrix. The crystallinity of coalesced PCL was found to be significantly enhanced, up to 34%, in IC with urea as a result of better orientation of PCL chains. A memory effect on crystallization was ultimately seen where characteristics of coalesced PCL matrix were found to be retained even after dissolution of matrix in acetic acid and electrospinning it again.

Biodegradable Polypeptide-based Vesicles with Intrinsic Blue Fluorescence for Antibacterial Visualization

Fluorescent imaging has been an indispensable tool to provide dynamic information about the localization and quantity of organisms. Meanwhile, due to the intrinsic hollow structure and modularized biofunctionalities, polymer vesicles have been widely applied in biomedical field. However, most polymer vesicles are embedded with organic fluorophores for fluorescent imaging, which have certain drawbacks such as leakage and possible cytotoxicity. Here, we present a biodegradable polypeptide-based vesicle with intrinsic blue fluorescence without introducing any fluorophore for real-time visualization of antibacterial process. Through modular design to integrate multiple functional fragments, poly(e-caprolactone)-block-poly(tryptophan)-block-poly(lysine-stat-phenylalanine) [PCL25-b-PTrp2-b-P(Lys13-stat-Phe4)] was synthesized, where PCL chains form the hydrophobic membrane, P(Lys-stat-Phe) and PTrp provide intrinsic fluorescence and broad-spectrum antibacterial activity. It is noteworthy that the fluorescence emission was shifted from invisible ultraviolet range of amino acids to visible range (emission maximum at 436 nm), which makes it possible to visualize the antibacterial process. In addition, through utilizing the intrinsic fluorescence of vesicles, confocal fluorescent imaging of vesicles with bacteria validated the specific adhesion of vesicle towards bacteria, and the bacterial death through membrane disruption. Overall, we provided a novel approach to develop biodegradable fluorescent polypeptide-based vesicles for real-time visualization of antibacterial process.

Effects of curing temperature on the structure and properties of epoxy resin-poly(ε-caprolactam) blends

Improving the toughness of epoxy resins (EP) with diverse thermoplastic polymers through curing reaction induced phase separation (RIPS) has been widely studied, with the prerequisite of designing and tailoring the phase morphology evolution of the blend. Herein, two typical amine-type curing agents, 4,4′-diamino diphenylmethane (DDM) with precuring temperature at around 150 °C and diethylenetriamine (DETA) at 80 °C were utilized to regulate and control the phase structures of EP-poly(ε-caprolactone) (PCL) blends. The curing temperature above or below the melting temperature (Tm) of PCL resulted in different states of PCL. The effect of curing temperature on the miscibility between EP matrix and PCL phase, and the correlation between phase morphology evolution and thermomechanical behavior, mechanical properties were comprehensively investigated for the first time. Results revealed that when the curing temperature of EPDDM-PCL blends was higher than the Tm of PCL, curing took place without phase separation; while distinct phase separation took place when EPDETA-PCL was cured at a temperature below the Tm of PCL. When the curing temperature was high, the PCL was able to dissolve completely in the resin before crosslinking began, so that semi-interpenetrating networks were formed; and that when the curing temperature was low, the PCL was unable to dissolve, and therefore formed separate particles. Consequently, the EPDDM-PCL blends exhibited all-leading mechanical properties due to the entanglement and slippage between PCL chains and EP networks. The strength of EPDETA-PCL was reduced but the toughness was improved for island-shaped PCL particles bridging or pinning the cracks during failure. These results elucidated the effect of the phase morphologies formed at different curing temperature on mechanical properties, and provided significant insights regarding the toughening of thermosets.

Morphological selectivity of the films of linear and star-shaped poly (ε-caprolactone)

Films created by poly (e-caprolactone) (PCL) have made a lot of consideration in biomedical applications because of their biodegradability, biocompatibility, incredible flexibility, and nontoxic degradation by-products. In this study, switching behavior of surface morphology of linear and star-shaped PCL as a function of polarity of the substrate, molecular weight of the polymer, solvent vapor annealing, solvent annealing, and thermal annealing were investigated. Films of PCL were prepared by drop casting method and their morphology was visualized through atomic force microscopy (AFM). Although, the whole study is based on AFM imaging, some of the basic morphologies of PCL films as obtained by AFM are also compared with SEM and TEM analysis. The substantial difference in polarity and roughness of mica and silicon wafers leads to different chain orientation of the polymer chains. Morphology transition strongly depends on the molecular weight of the polymer, low molar mass PCL presented larger surface domains compared to their higher molar mass analogs. Annealing of polymer with THF and ethanol vapors has improved the long-range ordering of PCL chains, while hexane and water vapors led to swelling of the films. The morphology of the film has also shown selectivity for the casting solvent. Thermal annealing around the melting temperature of the PCL made polymeric chains more extended and uniformly oriented.