Grafting Of PCL Research Articles

Enzymatic PCL-grafting to NH2-end grouped silica and development of microspheres for pH-stimulated release of a hydrophobic model drug

This study set out to evaluate novel PCL-based silica containing nanohybrids as the polymer matrix in a hydrophobic drug-loaded microsphere system. Nanohybrids were synthesized by PCL-grafting to NH2-end grouped silica by in situ enzymatic ring opening polymerization of ε-caprolactone. Molecular weight and monomer conversion, PCL grafting percentage, thermal properties and crystallinity of the nanohybrids were determined by 1H NMR, TGA, DSC and XRD. Synthesized nanohybrids had low crystallinity percentage (32 and 39 %) and molecular weight (4800 and 8700 g/mol), promising for controlled drug release applications. The nanohybrids were used for fabrication of trans-chalcone-loaded microspheres by O/W single emulsion solvent evaporation. Mean particle diameter of the microspheres were between 15 and 30 µm. The result of release studies showed that optimum microsphere formulations (AP4 and A2, respectively) had 61 and 64 % encapsulation efficiency. One of the more significant findings to emerge from this investigation is that TC release was extended to 16 and 37 days, in a controlled manner. TC release was significantly enhanced in acidic pH media (pH 3.6 and 5.6) indicating pH-dependent release from nanohybrid microspheres; releasing 80–100 % of the loaded drug in 4–14 days. Drug/polymer interactions and molecular structures were investigated by FT-IR spectroscopy and DSC analysis. According to the results obtained, enzymatically synthesized nanohybrids have potential for pH-dependent release of the model drug, trans-chalcone.

Chain-End Functionalization of Poly(ε-caprolactone) for Chemical Binding with Gelatin: Binary Electrospun Scaffolds with Improved Physico-Mechanical Characteristics and Cell Adhesive Properties.

Composite biocompatible scaffolds, obtained using the electrospinning (ES) technique, are highly promising for biomedical application thanks to their high surface area, porosity, adjustable fiber diameter, and permeability. However, the combination of synthetic biodegradable (such as poly(ε-caprolactone) PCL) and natural (such as gelatin Gt) polymers is complicated by the problem of low compatibility of the components. Previously, this problem was solved by PCL grafting and/or Gt cross-linking after ES molding. In the present study, composite fibrous scaffolds consisting of PCL and Gt were fabricated by the electrospinning (ES) method using non-functionalized PCL1 or NHS-functionalized PCL2 and hexafluoroisopropanol as a solvent. To provide covalent binding between PCL2 and Gt macromolecules, NHS-functionalized methyl glutarate was synthesized and studied in model reactions with components of spinning solution. It was found that selective formation of amide bonds, which provide complete covalent bonding of Gt in PCL/Gt composite, requires the presence of weak acid. With the use of the optimized ES method, fibrous mats with different PCL/Gt ratios were prepared. The sample morphology (SEM), hydrolytic resistance (FT-IR), cell adhesion and viability (MTT assay), cell penetration (fluorescent microscopy), and mechanical characteristics of the samples were studied. PCL2-based films with a Gt content of 20 wt% have demonstrated the best set of properties.

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.

Strongly Improved Mechanical Properties of Thermoplastic Biocomposites by PCL Grafting inside Holocellulose Wood Fibers

Chemical wood cellulose fiber modification is performed with the purpose to improve compatibility and induce nanofibrillation of the fibers during melt compounding of thermoplastic biocomposites. C...

Surface modification for nano‐lignocellulose fiber through vapor‐phase‐assisted surface polymerization

ABSTRACTThis study addresses the inherent issues surrounding surface modification methods of nanofibers and proposes an environmentally friendly and less toxic strategy for the surface modification of hydrophilic nanofiber. From the continuation of our previous work, which discussed the easy production of nanofiber (average size: 127 nm) from oil palm mesocarp fiber (OPMF), in this work, the surface of nanofibers (M‐IL‐OPMF) were modified through vapor‐phase‐assisted surface polymerization (VASP) to improve the affinity of interface between the polymer grafted M‐IL‐OPMF and non‐polar matrix. VASP of ε‐caprolactone was successfully proceeded from the [M‐IL‐OPMF] at 70 °C for 24 h and 72 h, and compositions were estimated to be 35.7% fiber/64.3% polymer and 27.8% fiber/72.2% polymer. To confirm the grafting of PCL, size‐exclusion chromatography (SEC) and Fourier transform infrared (FT‐IR) spectroscopy, thermogravimetry (TG), and dispersibility test in hydrophobic solvent were carried out. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2575–2580

Synthesis of poly(ε-caprolactone)-grafted guar gum by surface-initiated ring-opening polymerization

This study reports the grafting of poly(ε-caprolactone) (PCL) on guar gum (GG) by in-situ ring-opening polymerization using tetra(phenylethynyl)tin (Sn(C≡CPh)4) as catalyst. The hydroxyl groups of guar gum act as initiators for ε-caprolactone ring-opening polymerization and the resulting poly(ε-caprolactone) binds covalently to the polysaccharide. The highest stability of Sn(C≡CPh)4 allows the reaction in open-air, thereby reducing the cost of the synthesis and provides polymers with high molar mass. Fourier transform infrared (FTIR) and the long-term stability of the suspension PCL-g-GG in dichloromethane confirmed the effectiveness of grafting of PCL into GG. The size exclusion chromatography (SEC) results show that the molar masse of grafted PCL could be modulated by varying the amount of guar gum. From thermogravimetric analysis and differential scanning calorimetry results the thermal stability of PCL-g-GG is greatly improved with different content of guar gum, also the melting temperature and crystallinity increased by increasing the GG content. The scanning electron microscopy (SEM) analyses showed the good adhesion between GG and PCL with 5% of GG contents. It was also revealed by contact angle measurements that the grafting of PCL to GG leads to a decrease of hydrophobicity of PCL. The micro-indentation hardness properties of the prepared PCL-g-GG were significantly improved, as compared to neat PCL.

Investigation of the effect of graphene oxide functionalization on the physical, mechanical and shape memory properties of polyurethane/reduced graphene oxide nanocomposites

At the present study, two types of graphene oxide nanosheets, including reduced graphene oxide (RGO) and reduced functionalized graphene oxide (R(GO-PCL)), were synthesized to investigate the effect of graphene nanosheets functionalization on physical, mechanical, and shape memory properties of PU-Reduced Graphene Oxide nanocomposites. Two types of nanocomposites containing 1 phr RGO and R(GO-PCL) nanosheets were prepared. Fourier transform infrared (FTIR) method confirmed the chemical grafting of PCL to GO by the esterification reaction. Thermal gravimetric analysis (TGA) results exhibited that GO nanosheets were functionalized by roughly 10 wt% of PCL-diols. According to X-ray diffraction (XRD) patterns, the gap of nanosheets in R(GO-PCL) has increased. It could be deduced from XRD and DSC results that nanocomposites crystalline structure has changed compared to neat PU. Field emission scanning electron microscopy (FE-SEM) images confirmed the proper dispersion of R(GO-PCL) nanosheets. Tensile results indicated that the modulus and strain at break of the functionalized nanocomposites were increased.

Synthesis of Multiarm Star Polymer Based on Hyperbranched Polyester Core and Poly(ε-caprolactone) Arms and Its Application in UV-Curable Coating.

Hyperbranched polymers have attracted much attention in the field of UV-curable coatings because of its low viscosity, highly branched structure, and rich functional moieties. However, hyperbranched polymers also have some limitations. For example, the spherical structure increases the crosslinking hindrance, resulting in surplus functional moieties. In this study, a multiarm star polymer with hyperbranched polyester core and linear polymer arms was synthesized and used as UV-curable coating. H40, the fourth generation of the hyperbranched polyester, was chosen as the core owing to its low viscosity and high chemical reactivity. Poly(ε-caprolactone) (PCL) arms were introduced to increase the content of flexible segments and reduce the cross-linking hindrance. The terminal hydroxyls were then replaced with methacrylate groups to endow the star polymer with UV curable ability, yielding HPCLn-M. This multiarm star polymer was considered as a promising candidate to make up for the shortcomings of UV-curable coating made from the hyperbranched polymer. The properties, such as hardness, adhesion, acid resistance, and alkali resistance of cured films were enhanced obviously after the grafting of PCL. Moreover, to further explore the effect of the length of PCL grafts on the coating, star polymers with different degree of polymerization (DP) were synthesized. Through the performance tests of cured films, it was found that the multiarm star polymer HPCLn-M could make up for the limitations of the hyperbranched polymer when the DP of PCL was suitable, and the comprehensive performance of cured film reached the best when the DP of PCL was 20. Overall, this multiarm star polymer could combine the advantages of the hyperbranched polymer and linear polymer and has the potential to be the next environmentally friendly UV-curable coating.

Towards thermoplastic hemicellulose: Chemistry and characteristics of poly-(ε-caprolactone) grafting onto hemicellulose backbones

Hemicellulose is a highly available polysaccharide but with poor industrial applications attributed mainly to difficulties in processability, owing to extensive intermolecular hydrogen bonds. In the current study, hemicellulose was subjected to a chemical modification by ring-opening graft polymerization of ε-caprolactone (CL) to improve its processability for value-added applications. Hemicellulose-graft-poly-(ε-caprolactone) (HCgPCL) copolymers were synthesized using 1,5,7-triazabicyclodecene [4.4.0] (TBD) as an organic catalyst. The extent and length of grafted PCL sidechains in HCgPCL copolymers were controlled by adjusting the molar ratios of CL monomer to anhydroxylose residues. The various characterization analysis of the physicochemical and mechanical properties of HCgPCL materials revealed a successful grafting. The NMR analyses indicated that the degree of polymerization (DP) of the grafted PCL can range between 1.82 and 4.26 based on the changes in the molar ratio of the reactants. Furthermore, results indicated that the mechanical and the hydrophobic properties of the materials were enhanced by PCL grafting onto hemicellulose. Finally, biodegradability measurements indicated a remarkable (95.3–99.7%) materials biodegradation. We anticipate that the HCgPCL copolymers will have great potential to be an eco-friendly part of the bioplastic industry.

Grafting polycaprolactone diol onto cellulose nanocrystals via click chemistry: Enhancing thermal stability and hydrophobic property

Hydrophobic and thermally-stable cellulose nanocrystals (CNCs) were synthesized by polycarpolactone diol (PCL diol) grafting via click chemistry strategy. The synthesis was designed as a three-step procedure containing azide-modification of CNCs, alkyne-modification of PCL diol and sequent copper(I)-catalyzed azide–alkyne cycloaddition reaction. The structure of azide-modified CNCs and alkyne-modified PCL diol, the structure, hydrophobic ability and thermal stability of click products CNC-PCL were characterized. FTIR, XPS and H1 NMR results indicated a successful grafting of the N3 groups onto the CNCs, synthesis of PCL diol-CCH, and formation of the CNC-PCL material. CNC-PCL had enhanced dispersion in the non-polar solvent chloroform owing to the well-maintained microscale size and PCL-induced hydrophobic surface. The thermal stability of CNC-PCL was largely increased due to the grafting of thermally-stable PCL. This work demonstrates that click chemistry is an attractive modification strategy to graft CNCs with polyester chains for further potential application in polymer composites.

Enhancing the grafting amount of Poly(ε-caprolactone) on MgO nanoparticles by modifying with ethylene glycol for improving mechanical properties of Poly(ε-caprolactone)

A new surface modification method to improve the graft polymerization of e-caprolactone (CL) on MgO surface was developed. The MgO nanoparticles were first modified with ethylene glycol (EG), and then used for initiating graft polymerization of CL. The modified MgO nanoparticles were attested by fourier transform infrared spectroscopy, thermal gravimetric analysis and dispersion stability test. The results showed that EG was successfully grafted onto the MgO surface, the hydroxyl group of the grafted EG initiated the graft polymerization of CL onto the MgO surface in the presence of stannous octanoate. The PCL grafting amount (11.13%) on MgO modified with EG (MgO-EG) is much higher than that of unmodified MgO (3.95%). MgO-EG-PCL with 11.13 wt% of grafted PCL exhibited the most excellent dispersibility in chloroform. The MgO-EG-PCL/PCL composites exhibited the most significant improvement, tensile strength and the elongation at break of PCL increased from 15.64 to 19.58 MPa and from 272.34% to 420.73%, respectively.

The effect of dense polymer brush on the microfibrillated cellulose for the mechanical properties of poly(ε-caprolactone) biocomposites

Two different cellulosic fibers [pristine microfibrillated celluloses (MFCs) and 2,2-bis(hydroxymethyl)propionic acid-modified MFCs (bis-MPA-modified MFCs)] were grafted by poly(ε-caprolactone) (PCL) molecules through the ring-opening polymerization (ROP) method. The PCL-grafted MFCs were characterized using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and elemental analysis. The results showed that the grafting of PCL on the bis-MPA-modified MFCs was more efficient than that of the pristine MFCs due to the higher density of the activated hydroxyl groups on the bis-MPA-modified MFCs. Furthermore, the numerous PCL chains bound to the bis-MPA-modified MFCs (PCL-g-mMFC) demonstrated the stronger interfacial adhesion between the modified MFC fibers and the PCL matrix, as well as the greatly improved dispersion of the modified MFCs in the PCL matrix of the PCL/cellulose biocomposites.

Properties and Biodegradability of Thermoplastic Starch Obtained from Granular Starches Grafted with Polycaprolactone

Granular starches grafted with polycaprolactone (St-g-PCL) were obtained using N-methylimidazole (NMI) as a catalyst. The effect of the starch/monomer ratio and catalyst content was studied to obtain different levels of grafted PCL. The highest grafting percentage (76%) and addition (43%) were achieved for reactions with a starch/monomer ratio of 50/50 and 25% catalyst. The grafting of PCL on the starch granule was verified by the emergence of the carbonyl group in the FTIR spectra and the increased diameter of the grafted starch granule. Thermoplastic starch from ungrafted starch (TPS) and grafted starch (TPGS) was obtained by mixing ungrafted or grafted starch granules with water, glycerol, or sorbitol in a mixer. TPS and TPGS behave as plastic materials, and their mechanical properties depend on the type of plasticizer used. Materials with glycerol as the plasticizer exhibited less rigidity. The presence of starch-g-PCL results in a dramatic increase in the elongation of the thermoplastic material. The starch present in the TPS or TPGS was completely biodegraded while the grafted PCL was partially biodegraded after the enzymatic degradation of the materials.

Functionalization of Miscanthus by Photoactivated Thiol–Ene Addition to Improve Interfacial Adhesion with Polycaprolactone

The fast thiol–ene reaction between the unsaturated groups of the Miscanthus fibers, MIS, and poly(mercaptopropyl)methylsiloxane, PMMS, was activated in the presence of a photoinitiator. The evidence of the grafting was studied by energy-dispersive X-ray (EDX), X-ray photoelectron spectrometry (XPS), and FTIR-ATR spectroscopy. Then, grafting of polycaprolactone, was conducted in a lab-scale twin-screw extruder with benzoyle peroxide to initiate radical reactions at high temperature. Mechanical properties of biocomposites based on coated or grafted Miscanthus, MIS, and polycaprolactone, PCL, were tested. PCL grafting was found to have a significant influence on the mechanical properties of biocomposites with an increase of modulus (E) from 322 to 847 MPa for PCL80MIS20 blend and PCL79.5MIS 20 PMMS0.5, respectively. The presence of grafted PCL at the interfaces of MIS, evaluated by FTIR-ATR spectroscopy, performed as an efficient interfacial coupling agent between MIS and the PCL matrix. This in situ reactive extrusion grafting offers an effective approach to functionalize MIS fibers.

Optimized synthesis of hydroxypropyl cellulose-g-poly(ε-caprolactone) network

The objective of this study was the synthesis of copolymer networks based on poly (e-caprolactone) (PCL), hydroxypropyl cellulose (HPC) and hexamethylene diisocyanate (HDI) via bulk graft copolymerization followed by crosslinking (using routes I and II), and subsequent optimization of the process by response surface methodology (RSM). The studied reaction parameters were: (i) monomer content (weight ratio of CL/HPC), (ii) amount of catalyst, and (iii) amount of crosslinker. FT-IR and 1H NMR results confirmed that the grafting of PCL onto HPC and subsequent crosslinking through terminal hydroxyl groups of PCL grafts by HDI were performed successfully. Through differential scanning calorimetry (DSC) and X-ray diffraction analysis (XRD), it was found that the crystallinity of grafted polymers depended on the amount of grafted PCL and degree of crosslinking. In modeling of the process using RSM, the coefficient of determination (R2) for the models (97.3 and 93.3 % for two routes) as well as the probability (p < 0.0001) revealed high significance of the regression models. Also it was found that the obtained systems possessed T m s between 42.94 and 54.57 °C (route I) and 32.49–46.30 °C (route II) that were tunable by the monomer content, catalyst and crosslinker amounts. RSM provided a useful tool to select in a fast way the proper experimental conditions to synthesize crossinked HPC-g-PCL copolymer as a novel biocompatible and biodegradable shape memory polymer with adjustable switching temperature and potential biomedical applications, which would be further studied in the future.

Extraordinary reinforcement effect of three-dimensionally nanoporous cellulose gels in poly(ε-caprolactone) bionanocomposites.

Three-dimensionally nanoporous cellulose gels (NCG) were prepared by dissolution and coagulation of cellulose from aqueous alkali hydroxide-urea solution, and used to fabricate NCG/poly(ε-caprolactone) (PCL) nanocomposites by in situ ring-opening polymerization of ε-CL monomer in the NCG. The NCG content of the NCG/PCL nanocomposite could be controlled between 7 and 38% v/v by changing water content of starting hydrogel by compression dewatering. FT-IR and solid-state (13)C NMR showed that the grafting of PCL onto cellulose are most likely occurred at the C6-OH groups and the grafting percentage of PCL is 25 wt % for the nanocomposite with 7% v/v NCG. (1)H NMR, XRD, and DSC results indicate that the number-average molecular weight and crystal formation of PCL in the nanocomposites are remarkably restricted by the presence of NCG. AFM images confirm that the interconnected nanofibrillar cellulose network structure of NCG are finely distributed and preserved well in the PCL matrix after polymerization. DMA results show remarkable increase in tensile storage modulus of the nanocomposites above glass transition and melting temperatures of the PCL matrix. The percolation model was used to evaluate the mechanical properties of the nanocomposites, in which stress transfer among the interconnected nanofibrillar network is facilitated through strong intermolecular hydrogen bonding and entanglement of cellulose nanofibers.

Silica “SHB” chiral Pc-L* copper complexes for halogen-free solvent cyclopropanation reactions

The grafting of the preformed Pc-L* (pyridine containing macrocyclic ligands) copper(I) complexes on different ordered and non-ordered silicas, and their use, under heterogeneous batch conditions, as catalysts for the olefin cyclopropanation are reported. High yields (up to 99%) and good recyclability in halogen-free solvent reactions were obtained, together with negligible copper leaching (0.1% of total copper).

Synthesis, self‐assembly, and cytotoxicity of well‐defined trimethylated chitosan‐O‐poly(ε‐caprolactone): Effect of chitosan molecular weight

Structurally well-defined trimethylated chitosan-O-poly(ε-caprolactone) (TMC-O-PCL) was synthesized under mild homogeneous conditions, using sodium dodecyl sulfate-dimethylated chitosan complex (SDC) as an organosoluble intermediate. The effect of chitosan molecular weight (MW) on the preparation, organosolubility, self-assembly, and cytotoxicity of the copolymers was investigated. The copolymers with low-MW chitosan backbone had improved solubility in common organic solvents. Spherical micelles with average diameter of 25-55 nm and uniform morphology were formed through self-assembly of TMC-O-PCL in pH 7.4 PBS. When trimethylation degree of the copolymers was above 44%, the micelles could remain stable in neutral aqueous media. The critical aggregation concentration of TMC-O-PCL slightly increased with a decrease in the MW of chitosan backbone. The cytotoxicity of the cationic micelles could be suppressed by increasing PCL grafting levels, reducing trimethylation degree, and MW of the chitosan backbone.

Synthesis of Polycaprolactone-Grafted Microfibrillated Cellulose for Use in Novel Bionanocomposites–Influence of the Graft Length on the Mechanical Properties

In the present work, microfibrillated cellulose (MFC) made from bleached sulfite softwood dissolving pulp was utilized to reinforce a poly(ε-caprolactone) (PCL) biopolymer matrix. To improve the dispersibility of the hydrophilic MFC in the nonpolar matrix and the interfacial adhesion in the composite material, we covalently grafted the MFC with PCL via ring-opening polymerization (ROP) of ε-caprolactone (ε-CL). To be able to investigate the effect of the PCL graft length on the mechanical properties of the composite material, we performed ROP to different molecular weights of the grafts. Bionanocomposites containing 0, 3, and 10 wt % MFC were prepared via hot pressing using both unmodified and PCL grafted MFC (MFC-g-PCL) as reinforcement. PCL grafting resulted in improved dispersion of the MFC in a nonpolar solvent and in the PCL matrix. The mechanical testing of the biocomposites showed an improvement in the mechanical properties for the PCL grafted MFC in comparison to ungrafted MFC. It was also shown that there was an impact on the mechanical properties with respect to the PCL graft lengths, and the strongest biocomposites were obtained after reinforcement with MFC grafted with the longest PCL graft length.

Submicrometer Thermoplastic Vulcanizates Obtained by Reaction-Induced Phase Separation of Miscible Poly(Ε-Caprolactone)/Dimethacrylate Systems

Abstract Reaction-induced phase separation of initially miscible mixtures of poly(Ε-caprolactone) (PCL) and elastomer precursors based on difunctional methacrylate resins was applied to prepare thermoplastic vulcanizates (TPVs) with rubber particle sizes ranging from 80 to 900 nm. The radicals formed by the peroxide decomposition initiate the formation of a cross-linked rubber network with gel contents exceeding 90%, but also abstract hydrogen atoms from the aliphatic moieties in PCL. This leads to the formation of PCL-grafted rubber particles, which show a high nucleating efficiency for crystallization of the PCL matrix. It is demonstrated that the tensile and elastic properties of these TPVs are determined by a complex interplay of the morphology, the type of elastomer precursor, the extent of PCL grafting, the crystallinity, and the lamellar thickness. The materials showed a rheological behavior that is typical for TPVs, for which the melt changes from an elastic to a viscous behavior above a critical stress.