Structure Of Graft Copolymers Research Articles

Toughening poly(lactic acid) with novel polyolefin-graft-poly(lactic acid) copolymers maintaining high transparency and stiffness

The combination of well-balanced mechanical performance, high transparency and appealing eco-friendly attributes endows poly(lactic acid) (PLA) with significantly potential for wide-ranging applications in high-value packaging sectors. However, effectively toughening PLA without compromising its transparency and stiffness remains a formidable challenge. In this study, we synthesized a series of graft copolymers by incorporating hydroxyl-functionalized linear low density polyethylene (LLDPEOH) and copolymers of cycloolefin (COCOH) as the main chain and PLA as the side chain, which were subsequently employed as novel toughening agents for commercial PLA. The achievement of high-performance PLA blends with a balanced combination of toughness, strength, and transparency can be realized through meticulous tuning of the structure and mass fraction of the blended graft copolymers. The maximum elongation at break for the PLA blends increased by about 50 times that of neat PLA, reaching up to 300 %. Furthermore, these materials retained their high strength (54 MPa) and excellent transparency (light transmittance up to 90 %). The excellent properties of PLA blends could be ascribed to the well-designed chain structure of the graft copolymer which leaded to and excellent compatibility with the PLA matrix and unique phase morphology. This work is significant in guiding the design and synthesis of graft copolymers as toughening agents for PLA, thereby expanding its application range in areas where high transparency and toughness are required.

Synthesis and Antibiotic Activity of Chitosan-Based Comb-like Co-Polypeptides

Infections caused by multidrug-resistant Gram-negative bacteria have been named one of the most urgent global health threats due to antimicrobial resistance. Considerable efforts have been made to develop new antibiotic drugs and investigate the mechanism of resistance. Recently, Anti-Microbial Peptides (AMPs) have served as a paradigm in the design of novel drugs that are active against multidrug-resistant organisms. AMPs are rapid-acting, potent, possess an unusually broad spectrum of activity, and have shown efficacy as topical agents. Unlike traditional therapeutics that interfere with essential bacterial enzymes, AMPs interact with microbial membranes through electrostatic interactions and physically damage cell integrity. However, naturally occurring AMPs have limited selectivity and modest efficacy. Therefore, recent efforts have focused on the development of synthetic AMP analogs with optimal pharmacodynamics and an ideal selectivity profile. Hence, this work explores the development of novel antimicrobial agents which mimic the structure of graft copolymers and mirror the mode of action of AMPs. A family of polymers comprised of chitosan backbone and AMP side chains were synthesized via the ring-opening polymerization of the N-carboxyanhydride of l-lysine and l-leucine. The polymerization was initiated from the functional groups of chitosan. The derivatives with random- and block-copolymer side chains were explored as drug targets. These graft copolymer systems exhibited activity against clinically significant pathogens and disrupted biofilm formation. Our studies highlight the potential of chitosan-graft-polypeptide structures in biomedical applications.

Biodegradable composite material based on the starch-g-vinyl acetate copolymer

A native potato starch was modififi ed with vinyl acetate by graft polymerization in alkaline medium with pH 10 in the mode of temperature change from 70 to 80°C for 4 hours. The initiator of the process was ammonium persulfate (NH4)2S2O8. The conversion of vinyl acetate was 91,5%. The chemical structure of graft copolymer (Starch:Vinyl acetate) was confifi rmed by IR-spectroscopy. Composite materials of modififi ed starch and triethyl citrate with tensile strength of 24 MPa were obtained. Under natural environmental conditions, materials undergo biodegradation of 96% in 28 days.

Microphase-separated morphology controlled polyimide graft copolymer membranes for CO2 separation

We report microphase-separated structured, 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA)–2,4,6-trimethyl-1,3-diaminobenzene (DAM) polyimide (PI)-based PI-POEM graft copolymer membranes with various poly(ethylene glycol)methyl ether methacrylate (POEM) grafting ratios for efficient CO2 separation. The brominated PI (PI-Br) was used as a macroinitiator to form amphiphilic microphase-separated PI-POEM graft copolymers via atom transfer radical polymerization (ATRP). The proton nuclear magnetic resonance (1H NMR) spectra demonstrate the chemical structure of PI-POEM graft copolymers with controllable POEM concentrations. The PI-POEM graft copolymers exhibit modified mechanical properties with a higher elongation at break and more hydrophilic membrane surface properties because of the relatively rubbery and hydrophilic POEM side chain addition. Notably, the PI-POEM graft copolymers exhibit microphase-separated morphology-controllable characteristics based on transmission electron microscope (TEM) images and X-ray scattering (small- and wide-angle) spectra. These structural properties enable the PI-POEM graft copolymer membranes to develop carbon dioxide (CO2)-gas-favorable transport characteristics with a high CO2 affinity. The PI-POEM graft copolymer membranes can exhibit controllable separation performance depending on the POEM concentrations. Consequently, the PI-POEM(3:1) graft copolymer membrane improves simultaneously in permeability and selectivity compared with the pure PI membrane. Thus, the PI-POEM(3:1) graft copolymer membrane exhibits CO2 permeability of 1,220 Barrer with selectivities of 27.5 and 23.5 for CO2/CH4 and CO2/N2, and H2 permeability of 810 Barrer with selectivities of 16.2 and 15 for H2/CH4 and H2/N2.

Graft Copolymerization of Methyl Methacrylate and Vinyltriethoxysilane onto Natural Rubber

Preparation and characterization of natural rubber grafted with methyl methacrylate (MMA) and vinytriethoxysilane (VTES) were performed in the present work. Graft copolymerization of methyl methacryate was carried out in latex stage, and VTES was added during the graft copolymerization of MMA. FTIR and NMR spectroscopy were used to investigate the structure of graft copolymer and determination of conversion and grafting efficiency of MMA. It confirmed that the poly(methyl methacrylate) (PMMA) and silica particles (PVTES) were successfully formed in NR-graft-PMMA-PVTES graft copolymer. Conversions of MMA were about 90-100%; however, MMA grafting efficiency decreased as the MMA concentrations increased. Tensile property of NR-graft-PMMA-PVTES was found to improve compared with that of pure NR.

Morphological evolution of self‐assembled PS‐g‐PA6 graft copolymer via in situ polymerization

AbstractThe self‐assembly behaviors of polystyrene graft polyamide‐6 (PS‐g‐PA6) copolymer obtained through incorporation of PA6 and PS segments with exact lengths via in situ polymerization were studied in this work. Copolymers were obtained via the bulk polymerization induced self‐assembly process without any external template or stabilizer. The morphological characteristics of PS‐g‐PA6 copolymer were probed using SEM and TEM techniques. Particular attention was paid to changing the PS‐g‐PA6 morphology from a simple nanospherical to the combined nano/microspherical phase structure by varying the [PA6]/[PS] mass ratio. At a [PA6]/[PS] mass ratio of 80:20, PS‐g‐PA6 copolymer revealed a specific phase structure, where the PS backbones formed a continuous phase and the PA6 side chains ensured the microspheres with dispersed nano‐scale inclusions. The grain diameter of a dispersed PA6 sphere phase was found to be about 75 nm. When the PS backbone mass ratio decreased to 10 wt%, the copolymer structure was self‐assembled into the 1–3 μm large microspheres with uniformly distributed nanospherical particles. A further decrease in the PS backbone content to 5 wt% led to the failure of phase inversion in the copolymers. The main feature of this project is that the structure of the main chain and branch chain of PS‐g‐PA6 copolymer can be reversed. The branched chain forms spherical phase and the main chain forms continuous phase structure. The strategy was proved to be effective to obtain the novel structure of graft copolymer.

Tunable plasticization of sustainable ethyl cellulose toward thermoplastic elastomers through ATRP grafting

Thermoplastic elastomers (TPEs) derived from sustainable cellulose and its derivatives have attracted a great deal of attention, because of their abundance, renewable nature, rigid backbone and good mechanical properties. To fabricate TPEs with tunable performance, a series of sustainable ethyl cellulose (EC)-grafted poly(methyl methacrylate (MMA)) (EC-g-P(MMA)) and poly(MMA-co-butyl methacrylate (BMA)) (EC-g-P(MMA-co-BMA)) were fabricated by way of atom-transfer radical polymerization (ATRP). By tuning the molar ratio of MMA/BMA in the copolymer side chains, tunable performance of TPEs with tunable glass transition temperatures (118–47.8°C) was achieved. The chemical structures of EC-bromide and EC graft copolymers were identifiable by Fourier transform infrared spectroscopy and hydrogen-1 (1H) nuclear magnetic resonance spectroscopy. The EC graft copolymers exhibited a higher molecular weight and good thermal stability and mechanical properties. These results suggested that these tunable-performance copolymers with a sustainable cellulose backbone and an acrylate side chain were potential candidates for service as TPEs in some applications.

Combining Renewable Ethyl Cellulose and Acrylate to Fabricate Sustainable TPEs via Controlled Polymerization

A series of ethyl cellulose (EC) grafted copolymers were fabricated with methyl methacrylate (MMA), stearyl methacrylate (SMA) and EC grafted 2-bromoisobutyryl bromide(EC-Br) as macroinitiator via atom transfer radical polymerization (ATRP). The chemical structures of EC-Br and EC graft copolymers were identified by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (1H NMR) spectroscopy. The EC graft copolymers exhibited higher molecular weight and polydispersity index value. With the dosage of SMA increased, EC grafted copolymers exhibited glass transition temperatures in a broad temperature range from 119.1 to 42.3 ℃. And the initial decomposition temperature (Ti) of EC grafted copolymers were increased (148.2 ℃ to 199.4 ℃). The stresses at break of EC grafted copolymers were decreased with the increase of SMA content. However, the elongation at break of all EC grafted copolymers were increased with the dosage of MMA decreased. These results suggested that the sustainable copolymers with cellulose backbone, acrylate side-chain were potential candidates for service as TPEs in some applications.

Formation of the Adhesive Layer's Graft-Copolymer Structure in the Garment Duplicated Parts

Formation of the Adhesive Layer's Graft-Copolymer Structure in the Garment Duplicated Parts

Chain architectures of various cellulose-based antiscalants on the inhibition of calcium carbonate scale

Two series of cellulose-based antiscalants with different chain architectures, i.e., linear carboxymethyl cellulose (CMC) and branch-shaped carboxymethyl cellulose-graft-poly(acrylic acid) (CMC-g-PAA), were synthesized. The carboxyl groups were distributed on CMC backbone but mainly on the grafted chains of CMC-g-PAA. The addition of CMC and CMC-g-PAA can both increase the surface energy of CaCO3 scale and decrease its crystal nucleation rate, thereby inhibiting CaCO3 scale formation. The structural effects of these cellulose-based antiscalants, especially the chain architectures, on the scale inhibition were investigated in detail. High degree of carboxymethyl substitution caused better inhibition effect of linear CMC. However, CMC-g-PAA with an appropriate content of carboxyl groups but high average number of PAA grafted chains can achieve high inhibition performance. Besides, with similar contents of carboxyl groups, CMC-g-PAA showed much better inhibition performance than CMC due to the distinct multi-dimensional spatial structure of graft copolymer in solution, causing the enhanced chelation and dispersion effects. Characterization of CaCO3 crystal by scanning electron microscopy and X-ray diffraction confirmed that crystal distortion effect obviously existed in CMC but quite minor in CMC-g-PAA. The differences between the scale-inhibition performance of CMC and CMC-g-PAA should be attributed to the different scale-inhibition mechanisms originated in their distinct chain architectures.

Synthesis, Structure, Hydrodynamics and Thermoresponsiveness of Graft Copolymer with Aromatic Polyester Backbone at Poly(2-isopropyl-2-oxazoline) Side Chains.

New thermoresponsive graft copolymers with an aromatic polyester backbone and poly(2-isopropyl-2-oxazoline) (PiPrOx) side chains are synthesized and characterized by NMR and GPC. The grafting density of side chains is 0.49. The molar masses of the graft-copolymer, its backbone, side chains, and the modeling poly-2-isopropyl-2-oxaziline are 74,000, 19,000, 4300, and 16,600 g·mol−1, respectively. Their conformational properties in nitropropane as well as thermoresponsiveness in aqueous solutions are studied and compared with that of free side chains, i.e., linear PiPrOx with a hydrophobic terminal group. In nitropropane, the graft-copolymer adopts conformation of a 13-arm star with a core of a collapsed main chain and a PiPrOx corona. Similarly, a linear PiPrOx chain protects its bulky terminal group by wrapping around it in a selective solvent. In aqueous solutions at low temperatures, graft copolymers form aggregates due to interaction of hydrophobic backbones, which contrasts to molecular solutions of the model linear PiPrOx. The lower critical solution temperature (LCST) for the graft copolymer is around 20 °C. The phase separation temperatures of the copolymer solution were lower than that of the linear chain counterpart, decreasing with concentration for both polymers.

Combination of atom transfer radical polymerization and click chemistry toward cellulose-rosin derived UV-absorbent copolymers

UV absorption coating is an important function material, which can protect the substrates from photoaging. In this work, a class of sustainable UV-absorbent copolymers derived from ethyl cellulose (EC), fatty acid and rosin were prepared by a combination of atom transfer radical polymerization (ATRP) and click chemistry. To fulfill this strategy, the pendant azides were first attached onto the backbone of EC. Then, ATRP was applied to fabricate well-defined poly(lauryl methacrylate) (PLMA) bearing terminal alkynes. Finally, click chemistry between the pendant azides in EC and the alkynes in PLMA as well as in rosin esters (DAPE), was performed to achieve the cellulose-rosin graft copolymers (EC-(g-DAPE)-g-PLMA) with UV absorption property. The chemical structure of cellulose-rosin graft copolymers was confirmed by FTIR, 1H NMR and GPC. Thermodynamic performance analysis indicated that these EC-rosin graft copolymers showed better thermal stability than EC. Due to the synergistic hydrophobic interaction of rosin and the hydrophobic lauryl groups in PLMA, these graft copolymers showed excellent hydrophobic property, and the static contact angles were all above 90°. In addition, all the EC-rosin graft copolymers showed outstanding and stable UV absorption capability, and maintained excellent UV absorption capability after continuous UV-irradiation for 1 h or being heated to 100 °C for 0.5 h, which had potential application in UV absorption materials.

Thermoplastic Superelastomers Based on Poly(isobutylene)-graft-Poly(l-lactide) Copolymers: Enhanced Thermal Stability, Tunable Tensile Strength, and Gas Barrier Property

A mechanically adjustable reinforced thermoplastic superelastomer system, with tunable gas-permeability, was developed. The superelastomer is based on a graft copolymer structure, using commercial ...

Reverse poly(ε-caprolactone)-g-dextran graft copolymers. Nano-carriers for intracellular uptake of anticancer drugs

A new fully biodegradable “reverse” oligosaccharide-based amphiphilic graft copolymer structure with a hydrophobic backbone and hydrophilic side chains, poly(ε-caprolactone)-g-dextran (PCL-g-Dex) was synthetized. For this purpose, “clickable” propargylated PCL (PCL-yne) and azido-dextran (Dex-N3) were prepared to further synthesize PCL-g-Dex copolymer by a Huisgen’s cycloaddition. This “reverse” copolymer architecture self-assembled in biodegradable nano-carriers, in the shape of dynamic polymeric micelles, and were loaded with doxorubicin (Dox) anti-cancer drug. Dox-loaded micelles showed different drug releases depending on the pH. Cytotoxicity tests showed that Dox-loaded micelles can selectively kill colon cancer cells (HCT-116) while they have no cytotoxic effect towards healthy cells (CCD-45SK). Fluorescent micelles based on FITC-labelled PCL-g-Dex copolymer were used for fluorescence imaging and flow cytometry assays. These experiments proved the effective and specific internalization of micelles by cancer cells, whereas healthy cells showed a very poor uptake. These results show that PCL-g-Dex micelles may be a promising Dox nano-carrier in cancer chemotherapy.

Formation of an in situ nanosilica nanomatrix via graft copolymerization of vinyltriethoxysilane onto natural rubber

Natural rubber (NR) with an in situ nanosilica nanomatrix was characterized in present work. The in situ nanosilica nanomatrix was prepared via graft copolymerization of a silane monomer, vinyltriethoxysilane (VTES), onto deproteinized NR (DPNR) in latex stage using tetrapentamine (TEPA)/tert‐butylhydroperoxide (TBHPO) as initiators. VTES conversion of more than 80% was obtained, and it depended on VTES concentration. The graft copolymer structure was characterized by Fourier transform infrared (FT‐IR), solution‐state proton nuclear magnetic resonance (1H‐NMR), and solid‐state 29Si‐NMR spectroscopy. FT‐IR analysis of the graft copolymer confirmed the formation of in situ silica particles, while solution‐state 1H‐NMR and solid‐state 29Si‐NMR revealed the partial hydrolysis of the ethoxy groups and polycondensation of the silanol groups. The formation of nanosilica particles enhanced thermal and mechanical properties of the graft copolymer. Morphology observations of the in situ nanosilica nanomatrix through scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicated that the spherical nanosilica particles form a nanomatrix surrounding NR particle. The formation of the nanomatrix was proved to enhance mechanical properties for NR materials.

Ultrasound-assisted synthesis of the β-cyclodextrin based cationic polymeric flocculants and evaluation of flocculation performance: Role of β-cyclodextrin

In this work, the novel β-cyclodextrin based polymeric flocculants (CADs) were synthesized and applied on the treatment of humic acid (HA)-kaolin wastewater. Acrylamide (AM) and acryloyloxyethyltrimethyl ammonium chloride (DAC) were grafted onto β-cyclodextrin (β-CD) by ultrasound assisted initiation using ceric ammonium nitrate as initiator. The synthesized conditions were optimized by evaluating the intrinsic viscosity and grafting efficiency of CADs. Furthermore, the characterization methods including Fourier transform infrared spectroscopy (FTIR), 1H nuclear magnetic resonance spectroscopy (1H NMR), thermogravimetric/differential scanning calorimetry (TG/DSC) and scanning electron microscopy (SEM) were used to evaluate and analyze the molecular structure and surface morphology of graft copolymers. In flocculation experiments, the effects of dosage, flocculant types, solution pH and flocs properties on flocculation performance were investigate in detail. CADs exhibited more satisfactory turbidity and HA removal performance than the synthetic cationic flocculants (PAD) and the non-ionic graft polymers (CAM). At the optimum dosage 4 mg/L, the maximum turbidity and HA removal rate of CAD 1# was 97.5% and 68.3%, respectively. Furthermore, CAD 1# exhibited a good flocculation performance and wide flocculation window in the pH range of 2.0–8.0. Lastly, the flocculation mechanism of CAD was detailed discussed by the investigation of zeta potential, surface tension, flocs FTIR and XPS spectra. Results indicated the unique hydrophobic internal structure of β-CD played an important role in improving the removal rate HA of CAD.

Synthesis and characterization of lignosulfonate/acrylamide graft copolymers and their application in environmentally friendly water- based drilling fluid

Acrylamide (AAm) was grafted onto lignosulfonate (LS) in the aqueous medium using two different H2O2/CaCl2 redox and potassium persulfate (KPS) thermal initiating systems at 30 and 55 °C, respectively. Resulting LS-g-PAAm graft copolymers were characterized by gravimetric, FT-IR and 1H NMR methods, from which initiator type and AAm concentration dependency of the AAm conversion (XAAm), grafting percentage (G(%)), grafting efficiency (GE) and copolymer structure were systematically evaluated. It was found that XAAm and G(%) can be affected significantly by the initiator type and AAm concentration while GE can mostly be affected only by the initiator type. Highest GE of 100% and grafting length of the PAAm chains onto LS was observed in the reaction LA-2 performed using redox initiator at 30 °C and initial weight ratio of AAm to LS of 20 while highest XAAm was observed in the reaction LA-3 performed using KPS initiator at 55 °C. Graft copolymers as well as LS with different amounts were used to prepare bentonite-based tap water (TWF), sea water (SWF) and NaCl salt saturated water (SSWF) fluids. Rheological and fluid loss (FL) properties of the above fluids were evaluated before and after hot rolling at 250 °F for 4 h. It was found that when an amount of 2.45–3.5 g/350 ml water is used; graft copolymers obtained from reactions LA-2 and LA-3 are able to improve rheological properties and to control FL and pH values in the TWF and SSWF, respectively, at low and high temperatures. All fluids showed shear thinning behavior with a gel-like structure under static conditions. Results revealed that thermal stability and salt resistance of the graft copolymers are high enough to be used as an effective additive in the high temperature and high salty water-based drilling fluids (WBDFs). An attempt was made to establish a relationship between the graft copolymer structure and its aqueous solution properties in the various water-based fluids. It was found that simultaneous higher GE (preferentially as high as 100%) and XAAm (as high as possible) in the graft polymers can results in a structure with the best performance in the WBDFs.

Microwave based synthesis and spectral characterization of thermo-sensitive poly(N,N-diethylacrylamide) grafted pectin copolymer

The functionalization of polysaccharides with synthetic polymers has attracted great attention owing to its application in many industrial fields. The aim of this work was to study the impact of pectin functionalization with N,N-diethylacrylamide (DEAAm). Pectin was modified via microwave-induced graft copolymerization of DEAAm using ceric ammonium nitrate (CAN) and N,N,N′,N′-tetramethylethylenediamine (TEMED). FTIR, 13C NMR, DSC/TGA, XRD, and SEM techniques were used to verify the structure of graft copolymers. Various reaction conditions such as microwave irradiation time, temperature, microwave power, monomer, initiator, and TEMED concentrations were investigated to get a maximum grafting yield of 192%. Lower critical solution temperatures (LCST) of graft copolymers were determined by UV spectroscopy. Graft copolymers were found to be thermo-sensitive, with LCST of 31°C and high thermal resistance. Biocompatibility test of copolymers showed that copolymers were not cytotoxic to L929 fibroblasts cells and can be used as a biomaterial.

Simple Radical Polymerization of Poly(Alginate-Graft-N-Isopropylacrylamide) Injectable Thermoresponsive Hydrogel with the Potential for Localized and Sustained Delivery of Stem Cells and Bioactive Molecules.

In this study, thermoresponsive copolymers that are fully injectable, biocompatible, and biodegradable and are synthesized via graft copolymerization of poly(N-isopropylacrylamide) onto alginate using a free-radical reaction are presented. This new synthesis method does not involve multisteps or associated toxicity issues, and has the potential to reduce scale-up difficulties. Chemical and physical analyses verify the resultant graft copolymer structure. The lower critical solution temperature, which is a characteristic of sol-gel transition, is observed at 32 °C. The degradation properties indicate suitable degradation kinetics for drug delivery and bone tissue engineering applications. The synthesized P(Alg-g-NIPAAm) hydrogel is noncytotoxic with both human osteosarcoma (MG63) cells and porcine bone marrow derived mesenchymal stem cells (pBMSCs). pBMSCs encapsulated in the P(Alg-g-NIPAAm) hydrogel remain viable, show uniform distribution within the injected hydrogel, and undergo osteogenic and chondrogenic differentiation under appropriate culture conditions. Furthermore, for the first time, this work will explore the influence of alginate viscosity on the viscoelastic properties of the resulting copolymer hydrogels, which influences the rate of medical device formation and subsequent drug release. Together the results of this study indicate that the newly synthesized P(Alg-g-NIPAAm) hydrogel has potential to serve as a versatile and improved injectable platform for drug delivery and bone tissue engineering applications.

Preparation of starch-g-PMMA, starch-g-P(MMA/BMA) and starch-g-P(MMA/MA) nanoparticles and their reinforcing effect on natural rubber by latex blending: a comparative study

Nanoparticles including starch-graft-methylmethacrylate, starch-graft-(methylmethacrylate/methyl acrylate), starch-graft-(methyl methacrylate/butyl methacrylate) were synthesized via emulsifier-free emulsion polymerization and were blended with natural rubber latex at various mass ratios. Chemical structure of graft copolymers was confirmed by Fourier transform infrared. Transmission electron microscopy demonstrated the core-shell structures of the nanoparticles distributed uniformly around the natural rubble particles. The tensile strength of blend films was significantly enhanced by addition of graft copolymers. Besides, scanning electron microscopy and atomic force microscopy showed the blend film had smooth surface.