PCL Length Research Articles

Hybrid Single Crystals of Poly(ε‐caprolactone) Homopolymers and Poly(ε‐caprolactone)‐b‐Poly(ethylene oxide) Block Copolymers

AbstractHybrid single crystals (HSCs) of different poly(ε‐caprolactone) (PCL) homopolymers with a poly(ε‐caprolactone)‐b‐poly(ethylene oxide) (PCL‐b‐PEO) block copolymer (BCP) are prepared. The effects of PCL length, PCL/PCL‐b‐PEO molar ratio, crystallization temperature (Tc), and solvent on crystal morphology are investigated. The optimal Tc for the formation of more perfect HSCs is between those for homocrystals of individual PCL and PCL‐b‐PEO and roughly increases with the length of PCL and PCL/PCL‐b‐PEO molar ratio. The chain folding in the HSCs is studied by comparing the experimentally measured heights obtained by atomic force microscopy (AFM) and theoretically calculated ones based on a sandwich structure model. Under most situations, the PCL homopolymers adopt a larger chain folding number in the HSCs than that in their homocrystals, while the chain folding of BCP remains unaltered. However, when both PCL homopolymer and PCL‐b‐PEO BCP crystallize slowly and the overcrowding of the PEO is effectively alleviated, thicker HSCs can be formed, in which the PCL homopolymer preserves the chain folding in its homocrystals but the BCP adopts a reduced chain folding number as compared with that in its homocrystals. The relative crystallization rate of PCL homopolymer versus BCP also affects the real composition and overall height of the HSCs.

Poly(L‐lactide)‐b‐poly(ε‐caprolactone)‐b‐poly(D,L‐lactide) copolymers with enhanced toughness and strength by regulating crystallization and phase separation

AbstractCopolymerizing poly(lactide) with other materials to obtain better comprehensive performance is a effective way to expand its application range. In this work, the precursors of hydroxyl terminated (poly(L‐lactide) [PLLA], poly(ε‐caprolactone) [PCL], poly(D,L‐lactide) [PDLLA]) were prepared, and PLLA‐PCL‐PDLLA copolymer were synthesized by chain extension. The effects of the proportion and molecular weight of each component and the amount of chain extender on crystallization, phase structures, mechanical properties and thermal stabilities of PLLA‐PCL‐PDLLA copolymer were studied in detail. Based on small‐angle X‐ray scattering results, the competition between crystallization and microphase separation was regulated by the composition and chain length of prepolymers. As the ratio of PLLA/PDLLA was 1:1, crystallization was prevailing and no obvious peak was observed in SAXS pattern. The tensile test results showed that as the ratio of PLLA/PDLLA increased from 1:1 to 1:5, the elongation at break of the copolymer changed from 1.8% to 343%. By using shorter length of PCL and PLLA segments in chain extension, improvement in strength and flexibility were obtained due to moderate degree of crystallization and microphase separation. This work used biodegradable materials to prepare extraordinary toughness copolymers without losing the biocompatibility, which may provide a feasible method for obtaining high toughness and biodegradable PLA‐based materials.

MRI study of the cruciate ligaments and menisco-femoral ligaments of the knee.

It has been argued that the meniscus-femoral ligaments disappear with age. We therefore analyzed the presence of the meniscus-femoral ligaments, in MRI. We measured the PCL, ACL and MFL, noting their presence or absence in 120 Knee MRIs, 51 in women and 69 in men. All knees underwent MRI in the coronal, sagittal and axial planes. T1 and T2 weighted sequences were obtained. A descriptive statistical study of all the variables was carried out, and a comparative study was performed between sexes, sides and age groups. The MFLp was more frequent, found in 67 (55.8%) cases, than the MFLa, in 36 (30%) cases, and both together were present in 27 (22.5%) knees. We found a strong correlation between ACL length and PCL length (p = 0.001), we found no correlation between the presence of the posterior MFL either with age (p = 0.307) or with sex (p = 0.779) or side (p = 0.733). We also found no relationship between the presence of the anterior MFL and age (p = 0.553), or sex (p = 0.913), or laterality (p = 0.082). We found a strong correlation between ACL length and PCL length. In our study, the presence of the posterior MFL was more frequent, being present in 55.68%, while the anterior MFL was found in 30% of the knees. We did not observe that the presence of LMF decreases with age.

Can the Posterior Cruciate Ligament (Pcl) Predict Anterior Cruciate Ligament (Acl) Size For Planning During Acl Reconstruction?

Background:Pediatric Anterior Cruciate Ligament reconstruction (ACLR) has increased over the past several years. Estimating the native ACL size on pre-op imaging would ideally inform graft size during surgery and make it possible to individualize ACL graft size to each patient.Hypothesis/Purpose:To establish a correlation between the ACL and PCL size in normal pediatric knees, with the goal of informing appropriate graft size for ACL reconstruction.Methods:MRIs of 540 patients ages 8-18 years were assessed. Measurements included: ACL and PCL length, thickness and width (Figure 1). ACL footprint thickness and width at the tibial insertion was also measured. Inter-rater reliability was assessed with a random set of 25 patients. Pearson correlation coefficients were used to assess the correlation between ACL and PCL measurements. Linear regression models were used to test whether the relationship between ACL and PCL measurement differed by sex or age.Results:Demographic data for 540 patients are shown in Table 1. Inter-rater reliability was high for all measurements except PCL thickness at midsubstance. ACL length was most strongly correlated with PCL length (r=0.57, p<0.0001). ACL origin thickness was most strongly correlated with PCL mid-thickness (r=0.26, p<0.0001). ACL origin width was most strongly correlated with PCL insertion width (r=0.49, p<0.0001). ACL insertion thickness was most strongly correlated with PCL insertion thickness (r=0.27, p<0.0001). ACL insertion width was most strongly correlated with PCL mid-width (r=0.39, p<0.0001). Sample equations for estimating ACL size from each sex and age category are as follows: ACL Origin Thickness = 3.21 + 0.26PCL Origin Thickness (R2=0.07; 8-12yo males), ACL Origin Width = 1.35 + 0.15PCL Insert Width (R2=0.23; 8-12yo females), ACL Insert Thickness = 7.02 + 0.22PCL Mid Thickness – 0.17PCL Insert Width, (R2=0.10; 13-18yo males), ACL Insert Width = 2.31 – 0.09PCL Length + 0.39PCL Mid Thickness + 0.27PCL Mid Width + 0.25PCL Insert Width (R2=0.31; 13-18yo females).Conclusions:Correlations exist between ACL and PCL measurements with some moderated by sex and/or age. This study is the first step in potentially informing normal ACL size in pediatric patients based on an intact PCL on MRI.Table 1.Demographic data from 540 patients ages 8-18.Figure 1.Top row left to right: ACL length measured on sagittal view; ACL thickness – AP dimension at origin (femur), midpoint and insertion (tibia) measured on sagittal view; ACL width at ACL origin on femur – Transverse dimension on axial plane view; ACL width at ACL midpoint – Transverse dimension on axial plane view. Middle row left to right: ACL width at ACL tibia insertion – Transverse dimension on axial plane view; PCL length – measured on sagittal view – by adding 2 lines – one from origin to the PCL crimp and from PCL crimp to the tibia insertion; PCL thickness – AP dimension at origin (femur), midpoint and insertion (tibia) measured on sagittal view; PCL width at PCL origin on femur – Transverse dimension on axial plane view. Bottom row left to right: PCL width at PCL midpoint – Transverse dimension on axial plane view; PCL width at PCL tibia insertion – Transverse dimension on axial plane view; ACL thickness footprint – AP dimension on sagittal view; ACL footprint width at ACL origin on femur – Transverse dimension on axial plane view.

Effect of Block Length and Stereocomplexation on the Thermally Processable Poly(ε-caprolactone) and Poly(Lactic acid) Block Copolymers for Biomedical Applications

The current research concentrates on the synthesis of linear block copolymers with their backbone consisting of hard and soft segments, that is, poly(L-lactic acid) (PLLA)/ poly(D-lactic acid) (PDLA) and poly(e-caprolactone) (PCL), with the detailed investigation of the effect of block length on the thermal, mechanical, and crystallization behavior followed by their processing and biocompatibility evaluation. In the current work, sequential ring opening polymerization has been employed wherein PCL is used as a macroinitiator for the synthesis of diblock (PCL-PDLA and PCL-PLLA) and stereotriblock copolymers (PCL-PLLA-PDLA) of targeted molecular weight, which is confirmed by 1H NMR spectroscopy. The block length of PCL, in the case of diblock copolymer, is fixed; however, that of PLLA or PDLA is varied, and the enantiomeric blends thereof are made to achieve the merits of stereocomplexation. The length of the individual blocks is the same in the case of stereotriblock copolymer. The presence of two crystall...

Y-shaped copolymers of poly(ethylene glycol)-poly(ε-caprolactone) with ketal bond as the branchpoint for drug delivery

In this study, a Y-shaped amphiphilic block copolymer consisting of hydrophilic poly(ethylene glycol) (mPEG) and two poly(ε-caprolactone) (PCL) as the hydrophobic arms with a ketal linker was synthesized (mPEG-Ketal-(PCL)2). The structure of the copolymer with different compositions was characterized by 1H NMR, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). The amphiphilic property endows the copolymer with the ability to be self-assembled into micelles for encapsulating anticancer drug doxorubicin (DOX), and the effect of copolymer with different PCL length on drug loading properties were tested. The morphology, size, pH responsiveness, drug release profile and in vitro anticancer activity of the DOX loaded micelles were also studied. In vitro drug release studies showed that over 50% of the DOX was released at pH 5.0 in 24 h because of hydrolysis of ketal linker in the copolymers. The confocal laser microscopy and flow cytometry experiments showed that the DOX-loaded micelles could be effectively internalized by Hela cells, the ketal bond in the backbone was broken in acid endo/lysosomal compartments and triggered the fast release of DOX. The in vitro antitumor efficacy of the DOX loaded mPEG-Ketal-(PCL)2 micelles was better than that of non-pH sensitive ones. In vivo studies showed that the mPEG-Ketal-(PCL)2 micelles enhanced the DOX blood circulation time and had good tumor-targeting efficiency.

Adjustable Intermolecular Interactions Allowing 2D Transition Metal Dichalcogenides with Prolonged Scavenging Activity for Reactive Oxygen Species.

There is an increasing demand for control over the dimensions and functions of transition metal dichalcogenides (TMDs) in aqueous solution toward biological and medical applications. Herein, an approach for the exfoliation and functionalization of TMDs in water via modulation of the hydrophobic interaction between poly(ε-caprolactone)-b-poly(ethylene glycol) (PCL-b-PEG) and the basal planes of TMDs is reported. Decreasing the hydrophobic PCL length of PCL-b-PEG from 5000 g mol-1 (PCL5000 ) to 460 g mol-1 (PCL460 ) significantly increases the exfoliation efficiency of TMD nanosheets because the polymer-TMD hydrophobic interaction becomes dominant over the polymer-polymer interaction. The TMD nanosheets exfoliated by PCL460 -b-PEG5000 (460-WS2 , 460-WSe2 , 460-MoS2 , and 460-MoSe2 ) show excellent and prolonged scavenging activity for reactive oxygen species (ROS), but each type of TMD displays a different scavenging tendency against hydroxyl, superoxide, and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radicals. A mechanistic study based on electron paramagnetic resonance spectroscopy and density functional theory simulations suggests that radical-mediated oxidation of TMDs and hydrogen transfer from the oxidized TMDs to radicals are crucial steps for ROS scavenging by TMD nanosheets. As-prepared 460-TMDs are able to effectively scavenge ROS in HaCaT human keratinocytes, and also exhibit excellent biocompatibility.

Influence of Chain Length on the Self-Assembly of Poly(ε-caprolactone)-Grafted Graphene Quantum Dots.

The multifarious applications of graphene quantum dots (GQDs) necessitate surface modifications to enhance their solution processability. Herein, we report the synthesis and self-assembly of GQDs grafted with poly(ε-caprolactone) (PCL) of different degrees of polymerization (3, 7, 15, and 21) produced from ring-opening polymerization. Optical and morphological studies unveil the transformation of the assemblies from J-aggregates to H-aggregates, accompanied by an alteration in morphology from toroid to spheroid to rodlike structures with increasing chain length of PCL. Functionalized GQDs with lower chain lengths of PCL at higher concentration also assemble into liquid-crystalline phases as observed from birefringent textures, which are later correlated to the formation of columnar hexagonal (Colh) mesophases. However, no such behavior is observed at higher chain lengths of PCL under identical conditions. Therefore, it is evident that the variation in the PCL chain length plays a crucial role in the self-assembly, which is primarily triggered by the van der Waals force between the polymer chains dictating the π stacking of GQDs, resulting in different self- aggregated behavior.

Preparation of dual-drug conjugated polymeric micelles with synergistic anti-cancer efficacy in vitro

The traditional chemotherapy using single agent may suffer from serious drawbacks, particularly dose-limiting toxicity and relatively low antitumor efficacy, which can lead to failure of chemotherapy. Co-delivery of two or more therapeutic drugs in nanotechnology is a potential strategy to generate synergistic anticancer effects and reduce individual drug-related toxicity, but explosive release of each drug from multi-drug loaded nanoparticles has been a distinct obstacle. In this study, a novel amphiphilic and biodegradable triblock copolymer, named MPEG-b-norbornene functional PLA-b-P(α-BrCL), was constructed to covalently conjugate dual anticancer drugs, i.e., doxorubicin (DOX) and paclitaxel (PTX). The resultant P-PTX-DOX prodrugs were confirmed by 1H NMR and HPLC. By adjusting the length of PLA and PCL, it was shown that this polymer could carry relatively sufficient amount of both drugs (12.1 wt% of PTX and 15.8 wt% of DOX, respectively). Moreover, the drug release profile of P-PTX-DOX in vitro was also analyzed, which showed the desired drug release in a sustained manner. Cytotoxicity study indicated synergistic effects of P-PTX-DOX self-assembled micelles in suppression of proliferation of A549 cancer cells. In summary, a novel polyester-based copolymer was developed to covalently conjugate dual-drug, which exhibited controlled drug release behavior and synergistic anti-cancer efficacy in vitro.

A novel shape memory poly(ε-caprolactone) network via UV-triggered thiol-ene reaction

A facile method to prepare shape memory polymers crosslinked by SiO2 is described. A series of biodegradable shape memory networks were obtained through thiol-ene reaction triggered by UV irradiation between surface-thiol-modified SiO2 nanoparticles and end-acrylate poly (e-caprolactone) (PCL). The highly selective thiol-ene reaction ensured a uniform distribution of PCL chains between crosslinkers, contributing well-defined network architecture with enhanced mechanical and shape-memory properties. Thiol-functionalized silica nanoparticle was characterized by using FTIR and XPS analysis, and 1H NMR spectra was used to confirm the successful modification of terminal hydroxyl group of PCL diol. Surface-modified silica particles were found well dispersible in acrylate-capped PCL supported by SEM. Thermal and crystalline behaviors of the obtained polymers were analyzed by DSC and XRD, and DMA measurement proved good mechanical property. The shape memory behavior and tensile strength was somewhat tunable by the length of PCL. Acceptably, sample SiO2-SMP2k presented 99% recovery ratio and 97% shape fixity, and its relatively high tensile strength showed an attractive potential for biomedical application. Finally, a possible molecular mechanism accounting for the shape memory property was illustrated. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 692–701

PEO-b-PCL-b-PMOXA Triblock Copolymers: From Synthesis to Microscale Polymersomes with Asymmetric Membrane

We report a new family of amphiphilic ABC triblock copolymers: poly(ethylene oxide)-block-polycaprolactone-block-poly(2-methyl-2-oxazoline) (PEO-b-PCL-b-PMOXA). The synthesis is free of toxic reagents, well-controlled and results in polymers with ĐM < 1.25 and PMOXA length up to 25 units (2 kDa). We compare the self-assembly of PEO-b-PCL-b-PMOXA with PEO-b-PCL depending on PCL length and hydrophilic weight fraction (f) using the film rehydration method. Polymers self-assemble into different microscale structures, including polymersomes, which were studied by laser scanning microscopy. We proved the asymmetry of polymersome membrane by two independent methods, which confirmed the presence of a longer PEO block and the absence of a shorter PMOXA block on the outer surface of polymersomes.

Encapsulation of Antioxidant Gallate Derivatives in Biocompatible Poly(ε-caprolactone)-b-Pluronic-b-Poly(ε-caprolactone) Micelles.

Formulation of antioxidant agents is still a challenge that limits their application in the biomedical field. Pentablock copolymers obtained through modification of two common PEO-PPO-PEO copolymers (Pluronic F127 and F68) with poly(ε-carprolactone) (PCL) were evaluated regarding their capability to form nanocarriers suitable for gallic acid, methyl gallate, and ethyl gallate. Applying a dialysis method, PCL/F127/PCL and PCL/F68/PCL self-assembled into spherical micelles in 0.9% NaCl aqueous solution but notably differed in critical micellar concentration (CMC), micelle core hydrophobicity, and micelle size, as evidenced by pyrene fluorescence, transmission electron microscopy, and dynamic light scattering. Cytotoxicity studies showed that the copolymers were safe at concentrations well above the CMC. Transfer of gallic acid and derivatives from aqueous medium to the micelle phase was characterized in terms of distribution constant and free energy of transference, which were shown to be strongly dependent on the hydrophobicity of the gallate derivatives and the length of PCL in the pentablock copolymer. Antioxidant activity of gallates was challenged against DPPH previously loaded in PCL/F127/PCL and PCL/F68/PCL micelles. The more the hydrophobicity of the gallate derivative, the greater the capability to enter in the micelle and to consume free radicals. In vitro release studies of gallic acid, methyl gallate, and ethyl gallate from the pentablock copolymer micelles also evidenced the influence of the hydrophobicity of both the gallate derivative and the micelle core on release rate, recording a variety of release patterns. Overall, PCL/F127/PCL and PCL/F68/PCL appear as suitable nanocarriers of potent antioxidant agents in a wide range of polarities, which may be useful for diverse therapeutic applications.

Study on the crystallization of multiarm stars with a poly(ethyleneimine) core and poly(ϵ-caprolactone) arms of different length

Crystallization of multiarm star systems constituted by a core of poly(ethyleneimine) (PEI) and arms of poly(ϵ-caprolactone) (PCL) was studied by transmission electron microscopy, calorimetry and optical microscopy techniques. Three systems differing on the degree of polymerization of PCL were studied as well as binary mixtures constituted by systems differing on the length of PCL arms. Samples were able to crystallize from both diluted solutions and the melt state giving rise to well-formed lamellae and spherulites, respectively. Lamellae of samples with large PCL arms were highly regular and corresponded to elongated hexagonal crystals with an aspect ratio that decreased with the length of PCL arms.A significant decrease on equilibrium melting temperatures, degree of crystallinity and glass transition temperature was detected for samples having short PCL arms. Crystallization kinetics were also highly influenced by the length of PCL arms, being both nucleation density and secondary nucleation constant increased as the length of PCL arms decreased. Crystallization of star mixtures having different PCL lengths was determined by the larger arms since they initiated the process and subsequently shorter arms were progressively incorporated. A thermal nucleation was characteristic of multiarm star mixtures due to the different crystallization temperature ranges of samples with large and short PCL arms, whereas samples with a homogeneous arm length rendered an athermal nucleation.

Four-armed PCL-b-PDLA diblock copolymer: 1. Synthesis, crystallization and degradation

Abstract A series of four-armed poly(e-caprolactone)- b -poly( d -lactic acid) diblock copolymers (4a-PCL- b -PDLA) with well controlled composition were synthesized. The effect of length of PCL and PDLA blocks on the crystallization and enzymatic/alkaline degradation was studied. It was found that the PDLA blocks have great influence on the crystallization of PCL blocks under two different crystallization conditions. The copolymers with shorter PDLA blocks showed faster degradation rate but different spherulite structures after enzymatic degradation or alkaline degradation. The morphological changes of spherulites depended on the PCL chains which were trapped inside or excluded from the spherulites of PDLA when the copolymer crystallized at 80 °C or 30 °C (i.e. above or lower the glass transition temperature of PDLA chains). The spherulite morphology and porous morphology of copolymer films after degradation were well discussed. This work revealed that the crystalline morphology and degradation rate of PCL- b -PDLA films could be well controlled by copolymer composition and confined crystallization of PCL chains within the previously formed lamellar stacks of PDLA.

A smart micellar system with an amine-containing polycarbonate shell

The present paper reports the design and preparation of an amphiphilic triblock co-polymer poly(ε-caprolactone) (PCL)–poly(6,14-dimethyl-1,3,9,11-tetraoxa-6,14-diaza-cyclohexadecane-2,10-dione) (PADMC)–PCL and the use of micelles composed of them as carriers for pH-sensitive drug release. The triblock co-polymers were synthesized via two-step ring-opening polymerization with catalysis by Novozym-435 lipase. By adjusting the feed ratio, three co-polymers with different PCL lengths and the same PADMC length were produced. The block structure of the co-polymers obtained was confirmed by comparative studies on PCL–PADMC–PCLs and the corresponding random poly(ε-caprolactone-random-6,14-dimethyl-1,3,9,11-tetraoxa-6,14-diaza-cyclohexadecane-2,10-dione) (poly(CL- r-ADMC)) by means of nuclear magnetic resonance and differential scanning calorimetry. Cell cytotoxicity tests showed that the co-polymer displayed no apparent cytotoxicity to 293T and HeLa cells. Transmissions electron microscopy indicates that the self-assembled micelles exhibited a well-defined spherical shape with a diameter between ∼30 and 50 nm. The critical aggregation concentration was dependent on the block composition. Due to the presence of ionizable tertiary amine groups in the PADMC block, acid-induced variation in the micellar morphology was evident with respect to micelle size and size distribution. The size–pH curve was characterized by a smooth sigmoid form, and had a dramatic upward shift with decreasing pH from 6.5 to 4.5, which correlated well with the buffer range of hydrophilic PADMC. As a demonstration of the potential of PCL–PADMC–PCL micelles to control drug delivery, acid induced drug release for prednisone acetate-loaded micelles was explored. PCL–PADMC–PCL micelles show good promise as smart drug carriers, sensing the local specific pH decrease around lesion sites.

Tibio-femoral joint constraints for bone pose estimation during movement using multi-body optimization

When using skin markers and stereophotogrammetry for movement analysis, bone pose estimation may be performed using multi-body optimization with the intent of reducing the effect of soft tissue artefacts. When the joint of interest is the knee, improvement of this approach requires defining subject-specific relevant kinematic constraints. The aim of this work was to provide these constraints in the form of plausible values for the distances between origin and insertion of the main ligaments (ligament lengths), during loaded healthy knee flexion, taking into account the indeterminacies associated with landmark identification during anatomical calibration.Ligament attachment sites were identified through virtual palpation on digital bone templates. Attachments sites were estimated for six knee specimens by matching the femur and tibia templates to low-dose stereoradiography images. Movement data were obtained using stereophotogrammetry and pin markers. Relevant ligament lengths for the anterior and posterior cruciate, lateral collateral, and deep and superficial bundles of the medial collateral ligaments (ACL, PCL, LCL, MCLdeep, MCLsup) were calculated. The effect of landmark identification variability was evaluated performing a Monte Carlo simulation on the coordinates of the origin-insertion centroids. The ACL and LCL lengths were found to decrease, and the MCLdeep length to increase significantly during flexion, while variations in PCL and MCLsup length was concealed by the experimental indeterminacy.An analytical model is given that provides subject-specific plausible ligament length variations as functions of the knee flexion angle and that can be incorporated in a multi-body optimization procedure.

Block Copolymers of Methoxypoly(Ethylene Oxide) and Poly(ϵ-Caprolactone): Synthesis, Structure, Micellization, and Interaction with Prednisolon

A series of MOPEO-b-PCL diblock copolymers (DBCs) with M nMOPEO = 2.5 · 103 and M nPCL = (0.28 ÷ 2.43) · 104 was synthesized using the anionic ring-opening block copolymerization. A bulk structure of the copolymers was studied with DSC. One glass transition and three melting peaks for MOPEO-b-PCL were found, thus implying the existence of separate crystalline domains of both blocks in a copolymer structure. The intense micellization of DBCs in dioxane/aqueous solutions was found with a spectrophotometry, a static light scattering, and photography. A reduction in CMC and an increase in −ΔG° values with growth of the PCL length and at the addition of prednisolon (PS) were established. The hydrogen bonding of PS with DBCs was confirmed with FTIR spectroscopy.

UV-cured epoxy coatings modified with perfluoropolyether-based materials

Hydroxy terminated PFPE were chain extended with short PCL segments in order to enhance the compatibility towards the epoxy resin. The obtained PFPE–PCL block copolymers were used as additives to modify toughness of a UV curable bisphenol-A-based epoxy coating. A certain degree of phase separation was achieved during UV curing. The morphology of the obtained cured materials depends on the polycaprolactone PCL length. The perfluoropolyether PFPE additive, without any PCL segment (additive TX), clearly showed a biphasic morphology with separated domains within 50–100 μm. By increasing the PCL segment it was not identified any second distinct phase. It was shown that the addition of TX additive can generate a strong phase separation and this allowed to achieve an improvement of the toughness properties of the cured samples without affecting the thermo-mechanical properties.

Chitosan‐graft‐poly(ϵ‐caprolactone)s: An optimized chemical approach leading to a controllable structure and enhanced properties

AbstractA novel synthetic approach was developed for the controllable modification of chitosan (CS) with poly(ϵ‐caprolactone) (PCL). 6‐O‐Triphenylmethyl‐chitosan (TMCS) was synthesized as a highly soluble intermediate in organic solvents to facilitate an efficient grafting reaction of PCL onto CS in a homogeneous reaction medium. Subsequently, the syntheses of CS‐g‐PCL copolymers with different degrees of substitution (ds) and various chain lengths of PCL (number‐average molecular weight = 1200–11,000) were carried out by a coupling reaction between the carboxylic terminal groups of PCL chains and the amino groups of TMCS. The successful grafting reaction was confirmed by GPC measurements, which indicated that the products were graft copolymers rather than physical blends. The ds, defined as the number of PCL chains per saccharide unit, of the graft copolymers could be adjusted simply by changes in the molar feed ratios of PCL to CS, and graft copolymers with different ds values ranging from 0.28 to 0.49 were synthesized, as calculated by 1H NMR and elemental analysis. DSC and X‐ray measurements showed that the melting temperature and enthalpy of the PCL grafts of these graft copolymers could be adjusted by the ds and the chains length of PCL, respectively. Meanwhile, the CS‐g‐PCL copolymers exhibited better solubility in various solvents, such as in chloroform for some of the resultant graft copolymers, than the original CS. Finally, nanoparticles of 100–200 nm, having hydrophobic PCL domains and cationic hydrophilic surfaces, were obtained through the self‐assembly of the copolymers in selective solvents. These types of graft copolymers have great potential in various applications, such as targeted drug and gene delivery as well as tissue engineering. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2556–2568, 2007

Amphiphilic biodegradable poly(CL- b-PEG- b-CL) triblock copolymers prepared by novel rare earth complex: Synthesis and crystallization properties

Amphiphilic biodegradable poly(CL- b-PEG- b-CL) triblock copolymers have been successfully prepared by the ring-opening polymerization of ε-caprolactone (CL) employing yttrium tris(2,6-di-tert-butyl-4-methylphenolate) [Y(DBMP) 3] as catalyst and double-hydroxyl capped PEGs (DHPEG) as macro-initiator. The triblock architecture, molecular weight, thermal and crystallization properties of the copolymers were characterized by NMR spectra, SEC, DSC and WAXD analyses. The isothermal crystallization behavior of the copolymers was investigated by POM analysis in detail, which is greatly influenced by the length of PCL and PEG blocks. On the POM micrograph of PEG 10,000–(PCL 8600) 2, a unique morphology of concentric spherulites was observed due to the sequent crystallization of the PCL and PEG blocks.