Molecular Weight Of PCL Research Articles

Phase behavior-microstructure-crystallization kinetics correlations in semi-crystalline/amorphous PCL/SAN mixtures filled with nanosilica

In this study, the effects of poly(ε-caprolactone) (PCL) molecular weight and the type and presence of nanosilica on the non-isothermal crystallization behavior of PCL in the PCL/poly(styrene-co-acrylonitrile) (SAN)/nanosilica systems have been quantitatively investigated. The PCL/SAN system have been chosen as an ideal model system because of the special phase behavior of the blends, which include a lower-critical solution temperature (LCST) phase diagram over a virtual upper-critical solution temperature. By this choose, the great importance of phase separation, mutual phase dissolution and preferential nanoparticle migration to one of the polymeric phases on the crystallization behavior during a commercial production process has been highlighted. The addition of both hydrophilic (Si) and hydrophobic (SiR) silica nanoparticles to virgin PCLs with different molecular weights retards the crystallization process. However, the presence of these nanoparticles in PCL/SAN blends impacts the PCL crystallization kinetics in opposite ways, depending on the nanosilica type, PCL molecular weight and melt cooling rate. The reasons for the observed opposite trends are the changes in the LCST-type phase diagram position by altering the PCL molecular weight and nanosilica type, the selective migration of nanoparticles as well as the dispersion state of nanofillers. The presence of both Si and SiR nanosilicas increases the crystallization activation energy, respectively, by 4.2% and 2.4% for the PCL/SAN blend conatining the PCL with lower molecular weight. While the addition of both Si (11%) and SiR (6.7%) reduces this energy for the blend conatining the PCL with higher molecular weight.

Correlation between non‐isothermal crystallization kinetics and morphology in poly(ε‐caprolactone)/poly(styrene‐co‐acrylonitrile) blends considering the blend phase behavior: Effects of poly(ε‐caprolactone) molecular weight

AbstractNon‐isothermal crystallization of poly(ε‐caprolactone) (PCL) in semi‐crystalline/amorphous PCL/poly(styrene‐co‐acrylonitrile) (SAN) blends with lower‐critical solution temperature (LCST) phase behavior at temperatures higher than the beginning of PCL crystallization has been studied and quantitatively modeled using different kinetics models. Near‐ and off‐critical PCL/SAN blends were prepared by using two different PCL molecular weights. The kinetics model results verified that the samples containing PCL with higher molecular weight have lower crystallinity and faster crystallization behavior, while adding amorphous SAN chains to PCL retards the crystallization process. A lower crystallization activation energy was relatively required for higher molecular weight, PCL‐2, in off‐critical PCL/SAN blends. However, the easier crystallization with higher degree of crystallinity was attained in near‐critical P80S20 blend containing PCL with lower molecular weight, indicating a shift of the LCST phase diagram of the PCL/SAN blend to higher temperatures by increasing the PCL molecular weight.

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.

Structure-property relationships in PCL porous scaffolds obtained by means of the TIPS and TIPS-PL methods

This study aims at characterization of porous poly(ε-caprolactone) (PCL) scaffolds prepared by the methods of thermally induced phase separation (TIPS) and TIPS supported by particulate leaching (PL). Both techniques were combined with freeze-drying. Two PCL grades (with different average molecular weight characterized by MFR 6.1 and 1.2 g/10 min) were employed in the fabrication of scaffolds. Three types of salt (sodium chloride) particles were used in the TIPS-PL preparation of the PCL sample: (i) smaller particles (S) measuring 200–315 μm, (ii) larger particles (B) measuring 500–600 μm, and (iii) mixture of S and B particles (S/B = 1/1 wt/wt). The crystallization behavior of the PCL solutions and the thermal properties of scaffolds were investigated by polarized light microscopy (PLM) and differential scanning calorimetry (DSC), respectively. The structural changes of PCL were studied by attenuated total reflectance infrared spectroscopy (ATR-FTIR). The scaffold structure was visualized by means of scanning electron microscopy (SEM) and X-Ray micro-computed tomography (X-ray micro-CT). Furthermore, the density, porosity, water uptake, contact angle and compressive properties of scaffold were investigated. The molecular weight of PCL had an impact on the crystallization of the PCL solutions and thereby on the crystallinity of scaffolds and the morphology of pore walls formed during TIPS. Sodium chloride grains had an influence on the pore size and overall morphology of foam scaffolds prepared by TIPS-PL. The addition of NaCl decreased significantly the density and compressive properties and increased the porosity and water uptake of scaffolds.

Development of 3D-printed vaginal devices containing metronidazole for alternative bacterial vaginosis treatment

Bacterial vaginosis (BV) is an abnormal condition caused by the change of microbiota in the vagina. One of the most common bacteria found in the case of BV is Gardnerella vaginalis, which is categorised as anaerobic facultative bacteria. Currently, the available treatment for BV is the use of antibiotics, such as metronidazole (MTZ), in topical and oral dosage forms. The limitation of the currently available treatment is that multiple administration is required and thus, the patient needs to apply the drug frequently to maintain the drug efficacy. To address these limitations, this research proposed prolonged delivery of MTZ in the form of intravaginal devices made from biodegradable and biocompatible polymers. Semi-solid extrusion (SSE) 3D printing was used to prepare the intravaginal devices. The ratio of high and low molecular weight poly(caprolactone) (PCL) was varied to evaluate the effect of polymer composition on the drug release. The versatility of SSE 3D printer was used to print the intravaginal devices into two different shapes (meshes and discs) and containing two different polymer layers made from PCL and a copolymer of methyl vinyl ether and maleic anhydride (Gantrez™-AN119), which provided mucoadhesive properties. Indeed, this layer made from Gantrez™-AN119 increased ca. 5 times the mucoadhesive properties of the final 3D-printed devices (from 0.52 to 2.57 N). Furthermore, MTZ was homogenously dispersed within the polymer matrix as evidenced by scanning electron microscopy analysis. Additionally, in vitro drug release, and antibacterial activity of the MTZ-loaded intravaginal devices were evaluated. Disc formulations were able to sustain the release of MTZ for 72 h for formulations containing 70/30 and 60/40 ratio of high molecular weight/low molecular weight PCL. On the other hand, the discs containing a 50/50 ratio of high molecular weight/low molecular weight PCL showed up to 9 days of release. However, no significant differences in the MTZ release from the MTZ-loaded meshes (60/40 and 50/50 ratio of high molecular weight/low molecular weight PCL) were found after 24 h. The results showed that the different ratios of high and low molecular weight PCL did not significantly affect the MTZ release. However, the shape of the devices did influence the release of MTZ, showing that larger surface area of the meshes provided a faster MTZ release. Moreover, MTZ loaded 3D-printed discs (5% w/w) were capable of inhibiting the growth of Gardnerella vaginalis. These materials showed clear antimicrobial properties, exhibiting a zone of inhibition of 19.0 ± 1.3 mm. Based on these findings, the manufactured represent a valuable alternative approach to the current available treatment, as they were able to provide sustained release of MTZ, reducing the frequency of administration and thus improving patient compliance.

An Evaluation of the Effect of Reaction Conditions in the Enzymatically Catalyzed Synthesis of Poly(ϵ‐Caprolactone)

AbstractPolycaprolactone (PCL) is a biocompatible polymer that degrades slowly in physiological environments. Properties, including flexibility and easy processability, endow PCL with a high potential for being used in biomedical and pharmaceutical applications. Typically, PCL is synthesized by high energy‐consuming ring‐opening polymerization processes catalyzed by metallic compounds. In addition, obtaining safe PCL requires tedious purification procedures that, in turn, reduce yield and generate large amounts of toxic emissions. As an alternative, PCL can be synthesized by employing lipases as enzymatic catalysts. However, the properties of the resulting polymer are highly dependent on the experimental conditions. In this paper, we studied the effect of synthesis variables, such as solvent, temperature, the concentration of monomer and catalyst, and lipase source, on the molecular weight of PCL and the reaction yield. According to the results, the highest molecular weight and monomer conversion were obtained when ϵ‐caprolactone was polymerized by 10 % of heterogeneous catalyst that contains Candida Antarctica lipase B in toluene at 70 °C. Under these conditions, polymerization exhibited controlled characteristics and allowed obtaining a polymer with a molecular weight of 14.12 kDa while the dispersion index was 1.34. The enzymatic catalyst was stable and allowed PCL formation over five usage cycles with minor activity loss. The reported findings suggest that immobilized Candida Antarctica lipase B is a suitable catalyst for the synthesis of PCL and could be employed at a large scale with minor energy consumption and shorter reaction times compared with the conventional processes.

Mechanical properties and drug loading rate of a polycaprolactone 5-fluorouracil controlled drug delivery system

In the context of precision medicine, controlled drug delivery systems (CDDSs) have become a research focus. The structural integrity of CDDSs is critical for ensuring an acceptable drug release rule; hence, a CDDS must possess appropriate mechanical properties. In this study, a polycaprolactone/5-fluorouracil (PCL/5-Fu) CDDS was fabricated via solvent evaporation, and the effects of the PCL molecular weight and 5-Fu loading rate on the mechanical properties of the CDDS were evaluated. The results of tensile testing, scanning electron microscopy, and substance analysis indicated that when the content of 5-Fu was less than 9.09% in the developed CDDS, 5-Fu was completely compatible with PCL, and no crystal aggregation was induced. In addition, the maximum 5-Fu loading rate required to retain acceptable mechanical properties was 23.08%, and the corresponding tensile strength of the sample was 12.9 MPa. This strength is sufficient to prevent structural failure and instantaneous drug release due to strength reduction during application of the drug delivery system. In-vitro experimental results demonstrated that the PCL/5-Fu CDDS can achieve controlled drug release over 1000 h. These findings provide a basis for establishing a drug release model for the proposed CDDS.

Micellar Carriers Based on Amphiphilic PEG/PCL Graft Copolymers for Delivery of Active Substances

Amphiphilic copolymers of alkyne functionalized 2-hydroxyethyl methacrylate (AlHEMA) and poly(ethylene glycol) methyl ether methacrylate (MPEGMA) with graft or V-shaped graft topologies were synthesized. The functionalization of poly(ε-caprolactone) (PCL) with azide group enabled attachment to P(AlHEMA-co-MPEGMA) copolymers via a “click” alkyne-azide reaction. The introduction of PCL as a second side chain type in addition to PEG resulted in heterografted copolymers with modified properties such as biodegradability. “Click” reactions were carried out with efficiencies between 17–70% or 32–50% (for lower molecular weight PCL, 4000 g/mol, or higher molecular weight PCL, 9000 g/mol, respectively) depending on the PEG grafting density. The graft copolymers were self-assembled into micellar superstructures with the ability to encapsulate active substances, such as vitamin C (VitC), arbutin (ARB) or 4-n-butylresorcinol (4nBRE). Drug loading contents (DLC) were obtained in the range of 5–55% (VitC), 39–91% (ARB) and 42–98% (4nBRE). In vitro studies carried out in a phosphate buffer saline (PBS) solution (at pH 7.4 or 5.5) gave the maximum release levels of active substances after 10–240 min depending on the polymer system. Permeation tests in Franz chambers indicated that the bioactive substances after release by micellar systems penetrated through the artificial skin membrane in small amounts, and a majority of the bioactive substances remained inside the membrane, which is satisfactory for most cosmetic applications.

Thermal degradation of poly (ε-caprolactone) nanocomposites with soy lecithin-modified bentonite fillers

Thermal degradation of green nanocomposite films prepared from poly (ε-caprolactone) (PCL) and soy lecithin (SL)-modified bentonite (Bent) obtained by melt blending were studied through thermal degradation kinetics and molecular weight determinations by gel permeation chromatography (GPC). Kinetic of degradation processes were analyzed by dynamic thermogravimetric analysis (TGA). The apparent activation energies for the thermal degradation have been calculated using the kinetic methods of Friedman, Ozawa-Flynn-Wall, and Kissinger-Akahira-Sunose. Furthermore, a non-linear method was applied. The results showed that most of the used models were able to reproduce the experimental degradation behavior of PCL matrix, PCL/Bent and PCL/SL-Bent nanocomposites. The results from GPC and TGA demonstrated that the molecular weight of PCL was reduced by the presence of Bent-SL because SL acts as catalyzer of degradation reaction.

Poly(l‐glutamic acid)‐based micellar hydrogel with improved mechanical performance and proteins loading

ABSTRACTSoft tissues, such as fat and skin, present high flexibility and are capable of withstanding large deformation in various functions. Hydrogels that can resemble the mechanical performance of soft tissue are unique and widely demanded. In this study, micellar hydrogels based on biocompatible poly(l‐glutamic acid) (PLGA) were designed with the enhanced capacity to bear large deformation. Amphipathic triblock copolymer poly(ethylene glycol) acrylate‐co‐poly(ε‐caprolactone)‐co‐poly (ethylene glycol) acrylate (APEG‐PCL‐APEG) with two terminal double bonds was synthesized and self‐assembled into micelles. At the same time, graft copolymers, poly(l‐glutamic acid)‐g‐hydroxyethyl methacrylate (PLGA‐g‐HEMA) with double bonds were synthesized. APEG‐PCL‐APEG micelles and PLGA‐g‐HEMA were mixed to construct micellar hydrogel via radical polymerization. The crystalline structure and hydrophobic aggregation of copolymers (APEG‐PCL‐APEG) were found to associate with PCL molecular weight. Due to the hydrophobic stress dissipation and crystalline structure of the micelles, the softness and toughness of hydrogels were promoted, exhibiting a 25% increase in ultimate strain. Moreover, the micellar hydrogels were able to load proteins with long‐term retention. In addition, under dynamic mechanical stimulation, the release of proteins could be accelerated. Besides, the micellar hydrogels also supported rabbit adipose‐derived stem cells (rASCs) growth, thus exhibiting the potential toward soft tissue engineering. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1115–1125

Shape memory hydroxypropyl cellulose-g-poly (ε-caprolactone) networks with controlled drug release capabilities

Hydroxypropyl cellulose-g-poly (e-caprolactone) (HPC-g-PCL) derived networks from different lengths of PCL side chains have been prepared by crosslinking HPC-g-PCL, providing (X(HPC-g-PCL)) films with different gel contents, crystallinity, and morphology. Two networks with different e-cCaprolactone (CL) content (95 and 98%) named X(HPC-g-PCL)-95 and X(HPC-g-PCL)-98 were used for further study of thermo-mechanical properties and shape memory behavior. Young’s modulus (E), elongation at break (eb %) and tensile strength (σm) were examined at three different temperatures 22, 37 and 65 °C. The results revealed that E values significantly were controlled by crystallinity as well as crosslink density depending on the temperatures. Complete shape recovery was observed for both samples once the degree of crosslinking was increased over 95%, while a narrower recovery temperature ranges from 39 to 41 °C was found for the X(HPC-g-PCL)-98 sample. The shape fixity results showed a great dependence on the molecular weight of PCL. Therefore, the X (HPC-g-PCL)-98 sample demonstrated an excellent shape fixation. Naproxen-loaded shape memory films prepared using either the in situ (before crosslinking) or swelling (after crosslinking) methods (3 and 10 wt%), were also described as a model for controlled drug release device. The chemical composition of drug-loaded networks, drug concentration and the incorporation method greatly affected the crosslink density, morphology and mechanical properties. Importantly, loading via the in situ method resulted possibility to adjust the amount of incorporated drug and fast subsequent release, while drug-loaded films by the swelling method exhibited an initial burst release. Both networks exhibited slow sustained release of naproxen over two months.

Ultrathin film crystallization of poly(ε-caprolactone) in blends containing styrene-isoprene block copolymers: The nano-rose morphology

We report the discovery of a new nanostructured morphology in ultrathin blend films of semi-crystalline poly(ε-caprolactone) (PCL) and various styrene-isoprene block copolymers. The nano-rose morphology is visualized by atomic force microscopy as a monolayer of approximately 500 nm diameter crystalline spirals. Our finding that the nano-rose morphology occurs in a narrow film thickness window commensurate with the crystalline lamellar thickness suggests that this distinctive morphology results from redirection of growing PCL crystalline lamellae due to confinement effects during film casting. The nano-rose morphology was located in blends with several block copolymers of various architecture but was absent in blends with the individual homopolymer components. PCL molecular weight did not affect nano-rose size or film thickness window. However, solvent choice was an important factor, with nano-rose formation favored in non-polar and weakly polar solvents. This work supports theories that unbalanced surface stresses and impurity exclusion cause polymer crystals to grow unconventionally.

Preparation of dexamethasone ophthalmic implants: a comparative study of in vitro release profiles

Diseases affecting the posterior segment of the eye are the most common cause of visual disorders in industrialized countries. This scenario has encouraged the development of new treatment modalities for these diseases, such as drug loaded implants with prolonged drug release. The aim of the present work was to create a polymeric based biodegradable ophthalmic implant for the delivery of dexamethasone. For this purpose, we prepared and compared the in vitro release profiles of dexamethasone ophthalmic implants produced by two methods: melting casting and solvent casting. The type of the biodegradable polymer used – poly (ɛ-caprolactone) (PCL) and poly(lactic acid) (PLA); the drug loading (10% and 25%, w/w), the molecular weight of PCL (37 kDa and 14 kDa) and the form of the drug (dexamethasone and dexamethasone disodium phosphate) were also investigated. The results show that the preparation method has little influence on the obtained release profiles, being the type of polymer the most significant factor affecting the release profiles; nonetheless, a better distribution of dexamethasone was obtained for the devices prepared by melting casting.

Biodegradable polymer networks via triazolinedione-crosslinking of oleyl-functionalized poly(ε-caprolactone)

The formation of biodegradable polymer networks by the crosslinking of tailor-made poly(ε-caprolactone) (PCL) via the ultrafast 1,2,4-triazoline-3,5-dione (TAD) chemistry has been demonstrated. First, a series of α,ω-oleyl terminated PCL was prepared by a two-step, one-pot synthesis that was initiated by the coordination ring opening polymerization of ε-caprolactone, resulting in prepolymers bearing both an oleyl and hydroxyl end group, which were subsequently coupled by means of a diisocyanate. Network formation was performed via Alder-ene reaction of two different bifunctional triazolinediones (bisTADs) with the oleyl end groups. Different crosslinking parameters were studied in order to find the optimal conditions for the preparation of sufficiently strong polymer networks. Besides the determination of thermal and mechanical properties, as well as the susceptibility to hydrolytic degradation, of the obtained PCL-network, also the influence of the PCL molecular weight, nature of the TAD crosslinker and crosslinking stoichiometry were determined.

Phase separation and segregation morphology of PCL/PS blends: Quantitative effect of the crystallization temperature, composition, and molecular weight of PS

The phase diagrams for blends of semicrystalline poly(ε‐caprolactone) (PCL) with amorphous polystyrene (PS) were determined and it was noticed that when molecular weight increases, the critical composition diminishes while its temperature increases. That is the same effect that produces the increase in the polydispersity of PS. From the fitting of phase diagrams of blends of PCL with oligomers and homopolymers of PS, taking into account the polydispersity, it was possible to conclude that the miscibility in these systems is due only by entropic effects. The crystalline fraction as well as the interlamellar spacing increased with crystallization temperature while the volume fraction of the amorphous PCL in the interfibrillar regions increases for the pure PCL and in its blends with low concentration of PS. Increasing the mass fraction of PS increases the average long spacing (L) till a weight fraction of 60%, for higher mass fractions L is almost constant indicating the interfibrillar segregation of PS. The PCL lamellar morphology is not affected when the molecular weight of PS employed is similar or higher than the molecular weight of PCL. If the PS has a higher molecular weight its penetration into the structure is inhibited. POLYM. ENG. SCI., 57:1062–1072, 2017. © 2016 Society of Plastics Engineers

Engineering of endothelial cell response on biphasic polyurethane matrix

Polyurethanes (PUs) are composed of soft and hard segments, and segmental interactions induce biphasic morphologies which can influence endothelial cell (EC) organization by regulating cell–matrix and cell–cell interactions. In this study, we explored this effect using poly(caprolactone) (PCL)-based PU, where the soft segment was composed of PCL and the hard segment was composed of hexamethylene diisocyanate (HDI) and L-tyrosine-based dipeptide (DTH). The composition of the PUs was varied by altering the PCL molecular weight and correspondingly, different phase morphologies were observed. Organization and functional state of ECs on these PUs showed that composition and phase morphology of PU have a significant effect on cellular response. The ECs formed an organized network with cord-like structures which resulted in interconnected loops when soft and hard segment fractions were phase-separated. VE-cadherin (for cell–cell adherence) and vinculin (for cell–matrix focal adhesion) localized at the tip of interconnecting cells in the tube structures indicated synchronized cell–cell and cell–matrix interactions.

Poly(ε-caprolactone)/triclosan loaded polylactic acid nanoparticles composite: A long-term antibacterial bionanocomposite with sustained release

In this study, the antibacterial bionanocomposites of poly(ε-caprolactone) (PCL) with different concentrations of triclosan (TC) loaded polylactic acid (PLA) nanoparticles (30wt% triclosan) (LATC30) were fabricated via a melt mixing process in order to lower the burst release of PCL and to extend the antibacterial activity during its performance. Due to the PLA's higher glass transition temperature (Tg) and less flexibility compared with PCL; the PLA nanoparticles efficiently trapped the TC particles, reduced the burst release of TC from the bionanocomposites; and extended the antibacterial property of the samples up to two years. The melt mixing temperature was adjusted to a temperature lower than the melting point of LATC30 nanoparticles; therefore, these nanoparticles were dispersed in the PCL matrix without any chemical reaction and/or drug extraction. The sustained release behavior of TC from PCL remained unchanged since no significant changes occurred in the samples’ crystallinity compared with that in the neat PCL. The elastic moduli of samples were enhanced once LATC30 is included. This is necessary since the elastic modulus is decreased with water absorption. The rheological behaviors of samples showed appropriate properties for melt electro-spinning. A stable process was established as the relaxation time of the bionanocomposites was increased. The hydrophilic properties of samples were increased with increasing LATC30. The proliferation rate of the fibroblast (L929) cells was enhanced as the content of nanoparticles was increased. A system similar to this could be implemented to prepare long-term antibacterial and drug delivery systems based on PCL and various low molecular weight drugs. The prepared bionanocomposites are considered as candidates for the soft connective tissue engineering and long-term drug delivery.

Synthesis and structure-property behavior of polycaprolactone-polydimethylsiloxane-polycaprolactone triblock copolymers

Poly(ε-caprolactone)–polydimethylsiloxane–poly(ε-caprolactone) (PCL-PDMS-PCL) triblock copolymers with a wide range of block lengths (1000–32,000 g/mol) were synthesized by the ring-opening polymerization of ε-caprolactone using aminopropyl terminated PDMS oligomers as the initiator. Reactions were carried out in bulk or solution at 125 ± 5 °C under the catalytic action of tin octoate. Products obtained in high yields were characterized by FTIR spectroscopy, gel permeation chromatography, X-ray diffraction, temperature-dependent optical microscopy, differential scanning calorimetry, atomic force microscopy, scanning electron microscopy and static water contact angle measurements. Effect of the polymer composition and the molecular weight of the PDMS and PCL blocks on; (i) copolymer morphology and the extent of microphase separation, (ii) crystallization of PCL segments and (iii) surface properties of copolymers were investigated. Regardless of the block lengths, all PCL-PDMS-PCL copolymers displayed well microphase separated morphologies. The extent of microphase separation, resultant morphology and sizes of the microphases were strongly dependent on the copolymer composition and the block lengths of both PCL and PDMS segments. Crystalline PCL microphase was observed in all copolymers, which increased as a function of PCL content and molecular weight. Hydrophobicity of the copolymer surfaces was improved with increasing PDMS molecular weight, as determined by static water contact angle measurements.

Precision Polyolefin Nanoalloy Polypropylene/Poly(ε-caprolactone).

This communication reports the first example of precision polyolefin nanoalloys where an exotic immiscible polymer is nanometrically dispersed with stability in a polyolefin matrix in a highly controlled mode. Following the preparation of polypropylene/multiwalled carbon nanotubes nanocomposites (PP/MWCNTs) by in situ Ziegler-Natta polymerization, the hydroxyl groups on the surfaces of individual MWCNTs are used to initiate ring-opening polymerization of ε-caprolactone, resulting in PP/poly(ε-caprolactone) (PCL) alloy with PCL grafted on MWCNTs. Upon phase formation, the PP/MWCNTs-g-PCL alloys exhibit a unique PCL dispersion morphology, which is stable and solely governed by PCL molecular weight.

Cellulose acetate core–shell structured electrospun fiber: fabrication and characterization

This study explored the effect of type of core fluids on the fabrication of hollow and core–sheath cellulose acetate (CA) fiber. Tailoring the CA fiber with desirable features such as reinforced core, porous and hollow structure provides unique features for use in various applications. Fibers with such characteristics can be used for better controlled release drug delivery system or to promote cell adhesion in tissue engineering. Type of core material, tensile strength, and rheological properties were evaluated. DSC and FTIR analysis were performed to confirm the presence of core and sheath components. CA hollow structures were successfully obtained after selectively extracting the mineral oil. CA hollow fibers were twice the size of solid fiber despite similar solution and process conditions. Fiber morphologies indicated incomplete encapsulation by the CA when 80 kDa PCL molecular weight was used. This problem was not observed with 43 and 10 kDa PCL. DSC and FTIR analyses showed presence of both PCL and CA components. The rheology results suggest that the fibers could be formed when the viscosity of the core is less than that of sheath. Hydrated CA–43 kDa PCL fibers showed nearly ten-fold improvement in break point and stiffness. Human umbilical vein endothelial cells showed increased attachment and viability in both hollow CA and CA–PCL fibers relative to tissue culture plastic.