Resulting Graft Copolymers Research Articles

Synthesis of Thermoresponsive Chitosan-graft-Poly(N-isopropylacrylamide) Hybrid Copolymer and Its Complexation with DNA.

A hybrid synthetic-natural, thermoresponsive graft copolymer composed of poly(N-isopropyl acrylamide) (PNIPAM) side chains, prepared via RAFT polymerization, and a chitosan (Chit) polysaccharide backbone, was synthesized via radical addition-fragmentation reactions using the "grafting to" technique, in aqueous solution. ATR-FTIR, TGA, polyelectrolyte titrations and 1H NMR spectroscopy were employed in order to validate the Chit-g-PNIPAM copolymer chemical structure. Additionally, 1H NMR spectra and back conductometric titration were utilized to quantify the content of grafted PNIPAM side chains. The resulting graft copolymer contains dual functionality, namely both pH responsive free amino groups, with electrostatic complexation/coordination properties, and thermoresponsive PNIPAM side chains. Particle size measurements via dynamic light scattering (DLS) were used to study the thermoresponsive behavior of the Chit-g-PNIPAM copolymer. Thermal properties examined by TGA showed that, by the grafting modification with PNIPAM, the Chit structure became more thermally stable. The lower critical solution temperature (LCST) of the copolymer solution was determined by DLS measurements at 25-45 °C. Furthermore, dynamic and electrophoretic light scattering measurements demonstrated that the Chit-g-PNIPAM thermoresponsive copolymer is suitable of binding DNA molecules and forms nanosized polyplexes at different amino to phosphate groups ratios, with potential application as gene delivery systems.

Effect of short-chain architecture on the resulting thermal properties of polypropylene

Polypropylene (PP) is a versatile commodity polymer with a plethora of potential applications, in this work, short-chain branches of anhydride, amine, and various acrylate monomers with varying molecular weights were grafted onto PP using reactive extrusion. It was envisioned that such graft co-polymers can enhance the performance of PP making it a viable material such as water heating applications. The main interest herewith is to evaluate the occurrence of the grafting reaction and its effect on the thermal properties of the resulting graft co-polymers. Fourier Transform Infrared (FTIR), Differential Scanning Calorimeter (DSC), Polarized Optical Microscopy (POM), Thermogravimetric Analysis (TGA), gel content, and rheology tests were conducted to evaluate the effect of grafting on the performance of PP. DSC results showed a novel increase in crystallinity and crystallization temperature indicating a nucleating effect by the grafted chains. This is correlated with TGA and rheology results, where an increase in the temperature of maximum degradation and a reduction in the viscosity proved to be converging confirmations of grafting. The results clearly indicated successful grafting of PP which resulted in improved thermal stability that is essential for use in energy applications.

Preliminary study on polyisoprene-modified natural rubber via in-situ polymerization of isoprene in deproteinized natural rubber latex

Modification of natural rubber (NR) using vinyl monomers, particularly styrene, has been widely studied. Compared to unmodified NR, the resulting graft copolymer is stronger and stiffer but sacrificed on NR elasticity. This is because of the higher glass transition temperature (Tg) of styrene as compared to NR. Therefore, the modification of NR via isoprene monomer was investigated as isoprene will have the same Tg as NR. The focus of this research is to study the effect of in-situ polymerization of isoprene in deproteinized natural rubber (DPNR) latex with unmodified DPNR latex. The success of the modification was evidenced by the degree of conversion and Fourier Transform Infrared (FTIR). The average degree conversion of polyisoprene modified natural rubber (I-DPNR) obtained was 81.42%. Comparing the FTIR of I-DPNR and DPNR, the presence of trans-1,4 polyisoprene peaks and lower transmission of cis-1,4 polyisoprene was observed. The dynamic mechanical analysis (DMA) showed that I-DPNR and DPNR has a similar Tg. Stress–strain curves obtained from the tensile test of both the unvulcanized and vulcanized rubbers revealed that I-DPNR is more elastic as compared to the DPNR. These results obtained are consistent with the hypothesis that modification of NR with the isoprene monomer can result in similar properties as the DPNR. Higher elasticity reported for I-DPNR is a result of its higher entanglement as compared to unmodified NR.

A novel nano-lignin-based amphoteric copolymer as fluid-loss reducer in water-based drilling fluids

In the study, nano-lignin (Nano-LS) was gradually formed from inside to outside via layer-by-layer self-assembly owing to the interaction of π-π bonds, and a novel amphoteric polymer, Nano-LS-g-DAD, was synthesized by grafting N, N-dimethylacrylamide (DMAM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), diallyl dimethyl ammonium chloride (DMDAAC) onto the Nano-LS in an aqueous solution using ammonium persulfate and sodium bisulfite as initiators. The structure of the resulting graft copolymer was characterized via Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (1H-NMR) methods. Thermogravimetric analysis (TGA) revealed the thermal stability of Nano-LS-g-DAD, and the thermal decomposition of Nano-LS-g-DAD was observed above 281 ℃. Nano-LS-g-DAD were prepared also for water-based drilling fluids (WBDFs), and rheological and filtration properties were evaluated before and after aging at 260 ℃ for 16 h. The results revealed that the fluid loss (FLAPI) of WBDFs with Nano-LS-g-DAD was only 8.0 mL after aging at 260 ℃ for 16 h in a filtration test conducted as per American Petroleum Institute (API) standards. It indicated that the Nano-LS-g-DAD still maintained positive filtration reduction performance in WBDFs at ultra-high temperature. The fluid-loss control mechanism of Nano-LS-g-DAD for WBDFs was investigated via Zeta potential analysis and clay particle size distribution measurement. Simultaneously, WBDFs with Nano-LS-g-DAD also maintained positive rheological and filtration properties under the invasion of salt and calcium ions. Furthermore, the acute toxicity value (EC50) of Nano-LS-g-DAD was 54,800 mg/L, which indicated that it was environmentally friendly.

DETERMINATION OF A SUITABLE CONDITION OF GRAFT COPOLYMERIZATION OF VINYLTRIETHOXYSILANE ONTO NR TO FORM NANOMATRIX STRUCTURE

ABSTRACT Graft copolymerization of vinyltriethoxysilane (VTES) onto NR particles in the latex stage is a unique reaction, since it occurs together with hydrolysis and condensation of the triethoxysilane group of VTES to form a colloidal silica linking to the rubber particles. These reactions may contribute to the formation of a silica nanomatrix structure that consists of a dispersoid of rubber particles as the major component and a silica matrix as the minor component. Here, the graft copolymerization of VTES followed by hydrolysis and condensation is investigated to determine a suitable condition to prepare NR with a silica nanomatrix structure. The mechanical properties of the resulting graft copolymer are discussed in relation to the morphology, silica content, and gel content of the rubber. Based on morphological observations, NR particles with an average diameter of approximately 1 μm are well dispersed in a nanomatrix consisting of silica nanoparticles. The thickness of the silica nanomatrix increases as the monomer concentration increases, and a long incubation time generates large silica nanoparticles. The tensile strength and viscoelastic properties are significantly improved by forming the silica nanomatrix structure, with its continuous structure that prevents the NR particles from merging.

Thermoresponsive behavior of sodium alginate grafted with poly(N-isopropylacrylamide) in aqueous media

Thermoresponsive graft copolymers were synthesized. Thermally induced properties were introduced by grafting poly (N-isopropylacrylamide) (PNIPAM) side chains onto a sodium alginate backbone. The resulting graft copolymers cover a broad range in PNIPAM composition and molecular weight. Remarkable thermothickening behavior in water and 0.1 M NaCl is observed by viscometry when the temperature, concentration, weight ratio of PNIPAM side chains to backbone, and PNIPAM molecular weight are higher than certain critical values. This behavior is reversible and could have applications in oil rigs and drug delivery systems.

Poly(vinylidene fluoride-co-chlorotrifluoroethylene) Modification via Organocatalyzed Atom Transfer Radical Polymerization.

To address the challenge of metal contamination, a "graft from" approach via organocatalyzed atom transfer radical polymerization (O-ATRP) is developed to synthesize poly(vinylidene fluoride-co-chlorotrifluoroethylene) (P(VDF-co-CTFE)) graft copolymers. N-phenylphenothiazine is utilized as a model organic photoredox catalyst for catalyzing the (co)polymerization of methyl methacrylate (MMA), methacrylate (MA), and n-butyl acrylate (BA). By employing this technique, high temporal control of polymerization and graft content are achieved. A series of P(VDF-co-CTFE)-g-PMMA, P(VDF-co-CTFE)-g-PMA, and P(VDF-co-CTFE)-g-PBA is prepared under mild conditions. The resultant graft copolymer can be used as macroinitiator to re-initiate O-ATRP to synthesize P(VDF-co-CTFE)-g-(PMMA-b-PMA), which might exhibit the potential application as novel dielectric material.

Synthesis and characterization of maleylated cellulose-g-polyacrylamide hydrogel using TiO2 nanoparticles under sunlight

Graft polymerization onto the cellulose is one way to produce semisynthetic copolymers and semiconductors were hardly used as initiators. Maleylated cellulose (MC) with different degree of carboxyl groups was synthesized and degree of carboxyl groups was determined using titration method. Then the graft copolymers of acrylamide (AM) on MC were synthesized by titanium dioxide semiconductor photoinitiator in aqueous suspension under sunlight. The effect of different parameters, such as the degree of carboxyl groups, degassing of atmosphere, reactor type, light source, MC/AM ratio, and initiator concentration, was evaluated in the synthesis of graft copolymers. MC with a high degree of carboxyl groups about 2.8 mmol g−1 was selected for graft photopolymerization. Maximum monomer conversion (55%) for Maleylated cellulose-g-polyacrylamide (MC-g-PAM) was achieved with 0.5 mg TiO2, MC/AM = 0.056, argon atmosphere, sunlight source, and double quartz tube reactor. The maximum amount of equilibrium swelling (41 g g−1) was achieved for MC-g-PAM with 34% monomer conversion. The resulting graft copolymers were characterized by FT-IR, SEM, and TGA. Synthesis of MC-g-PAM using TiO2 nanoparticles (NPs) as the initiator was done successfully that shows the TiO2 NPs are useable in graft polymerization of acrylamide monomers onto the MC under sunlight.

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 and orthogonal postmodification of dual‐clickable polymer precursors bearing both aldehyde and alkyne groups

ABSTRACTA new styrenic monomer 2‐propargyloxy‐5‐vinylbenzaldehyde (PVB) containing both aldehyde and alkyne reactive groups was designed for the synthesis and subsequent orthogonal postfunctionalization of dual‐clickable polymer precursor. Reversible addition‐fragmentation chain transfer polymerization of PVB afforded a structurally well‐defined polymer poly(2‐propargyloxy‐5‐vinylbenzaldehyde) (PPVB) bearing alkyne and aldehyde functionalities that are reactive towards azide‐ and aminooxy‐containing molecules, respectively. Therefore, the resulting PPVB can be served as a dual‐clickable polymer scaffold for construction of multiple functional polymers via orthogonal alkyne–azide and aldehyde–aminooxy click reactions. Postpolymerization modification of PPVB sequentially with aminooxy‐terminated poly(ethylene oxide)s (H2NO‐PEO) and azide‐functionalized imidazolium‐type ionic liquid (N3‐IL·TFSI, having bis(trifluoromethane)sulfonamide, TFSI, counter‐anion) yielded an interesting multicomponent graft polymer PPVB‐g‐(PEO‐and‐IL·TFSI). After anion exchange of hydrophobic TFSI counter‐anion by bromide (Br) anion, the resulting graft copolymer PPVB‐g‐(PEO‐and‐IL·Br) becomes soluble in water, and its imidazolium units can capture negatively charged tetraphenylethylene disulfonate derivative (TPE‐2 ) guest molecule via electrostatic complexation to form in situ self‐assembled fluorescent nanoaggregates with colloidal stability imparted by hydrophilic PEO chains. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 2650–2656

Chemical Modification of Butyl Rubber with Maleic Anhydride via Nitroxide Chemistry and Its Application in Polymer Blends.

Butyl rubber (isobutylene–isoprene–rubber, IIR) was functionalized in solution with a nitroxide moiety taking advantage of the unsaturations present in the isoprene units of IIR, and was further grafted with maleic anhydride (MA) or styrene–MA (SMA) to produce IIR-g-MA and IIR-g-SMA. In one of the functionalization techniques used, the molecular structure of the IIR was preserved as the chain-breaking reactions are prevented from occurring. The resulting graft copolymers were tested as compatiblizers/impact modifiers blended with Nylon-6, and one of them was preliminarily tested as a coupling agent in the preparation of nanocomposites of IIR and an organo-clay. Blends of PA-6/IIR-g-MA exhibited a significant increase in impact resistance at increasing loads of the modified IIR, as well as a good rubber particle dispersion in the polyamide matrix. On the other hand, the performance of IIR-g-SMA as an impact modifier of PA, or as a coupling agent in the preparation of rubber-organoclay nanocomposites, is marginal.

Modification of the water-insoluble hemicelluloses via free radical copolymerization in diluted alkali aqueous medium

The synthesis of hemicelluloses-g-polyacrylamide (PAM) was carried out in diluted alkaline aqueous solution via free radical copolymerization initiated by redox initiator composed of potassium persulfate (KPS)/sodium thiosulfate (Na2S2O3). The less substituted hemicelluloses, l-arabino-4-O-methyl-d-glucurono-d-Xylan (wis-AGX), are the main components of the hemicelluloses isolated from corncobs by the ultrasound-assisted diluted alkali extraction method and exhibit poor water solubility, which largely limit their applications. The factors, such as the initiator dosage, the monomer concentration, and the reaction time, which influenced both the grafting percent and the grafting efficiency, were investigated. The chemical structure and thermal and macromolecular weight properties of the graft copolymers were characterized by Fourier transform infrared spectrometer (FT-IR), 1H nuclear magnetic resonance spectroscopy (NMR), thermogravimetric analysis (TGA), and gel permeation chromatography (GPC). The results indicated that the PAM moieties were successfully introduced into the side chains of the hemicelluloses, and the graft copolymers showed good solubility in water. Such modification is suggested to find a possible new way for broadening applications of water-insoluble hemicelluloses, and the resultant graft copolymers might have potential applications, such as gels, films, adsorbents, coatings, or drug delivery systems.

Dynamic Mechanical Properties of Vietnam Modified Natural Rubber via Grafting with Styrene

The dynamic mechanical behavior of modified deproteinized natural rubber (DPNR) prepared by graft copolymerization with various styrene contents was investigated at a wide range of temperatures. Graft copolymerization of styrene onto DPNR was performed in latex stage using tert-butyl hydroperoxide (TBHPO) and tetraethylene pentamine (TEPA) as redox initiator. The mechanical properties were measured by tensile test and the viscoelastic properties of the resulting graft copolymers at wide range of temperature and frequency were investigated. It was found that the tensile strength depends on the grafted polystyrene; meanwhile the dynamic mechanical properties of the modification of DPNR meaningfully improved with the increasing of both homopolystyrene and grafted polystyrene compared to DPNR. The dynamic mechanical properties of graft copolymer over a large time scale were studied by constructing the master curves. The value of bT has been used to prove the energetic and entropic elasticity of the graft copolymer.

Highly processable, rubbery poly(n-butyl acrylate) grafted poly(phenylene vinylene)s

In this study, we have demonstrated a suitable methodology towards tailoring the optical and physical properties of poly(phenylene vinylene)s (PPVs) by grafting poly(n-butyl acrylate) side chains to yield highly processable PPVs with the physical characteristics of the grafted polymer. Grafting from the PPV macroinitiators was conducted using activators regenerated by electron transfer (ARGET) atom transfer radical polymerisation (ATRP) technique. The resulting graft copolymers showed significant enhancement of photoluminescence quantum yield in both solution and in the solid state while exhibiting lower glass transition temperature and dry adhesive properties compared to the ungrafted PPVs, thereby signifying the methodology as an attractive tool for fabricating functional conjugated polymers with desired physical characteristics.

Enzymatic Synthesis and Characterization of Hydrophilic Sugar Based Polyesters and Their Modification with Stearic Acid.

Biodegradable and hydrophilic functional polyesters were synthesized enzymatically using xylitol or d-sorbitol together with divinyl adipate and lipase B from Candida antartica (CAL-B). The resulting polyesters had pendant OH-groups from their sugar units which were esterified to different degrees with stearic acid chloride. The structure and the degrees of polymerization of the resulting graft copolymers based on poly(xylitol adipate) and poly(d-sorbitol adipate) were characterized by 1H NMR spectroscopy and SEC. DSC, WAXS and SAXS measurements indicated that a phase separation between polymer backbone and stearoyl side chains occurred in the graft copolymers, and, additionally, the side chains were able to crystallize which resulted in the formation of a lamellar morphology. Additionally, nanoparticles of the graft copolymers in an aqueous environment were studied by DLS and negative stain TEM.

Correction to Synthesis and Remarkable Efficacy of Model Polyethylene-graft-poly(methyl methacrylate) Copolymers as Compatibilizers in Polyethylene/Poly(methyl methacrylate) Blends

Polyethylene-graft-poly(methyl methacrylate) (PE-g-PMMA) copolymers were prepared using a combination of ring-opening metathesis polymerization (ROMP), hydrogenation, and atom transfer radical polymerization (ATRP). Approximately 20 PMMA side chains per molecule with average degrees of polymerization 6, 12, and 24 were grown via a “grafting from” approach from a Br-substituted linear PE backbone with Mw = 56 000. The resulting graft copolymers were evaluated as compatibilizing agents for binary PE/PMMA homopolymer blends. The roles of PMMA side chain length and different compatibilizer concentration in the polymer blends were investigated, and the mechanical and morphological properties of blends containing 70% PE and 30% PMMA by weight were examined. The presence of the compatibilizer reduced the average PMMA droplet size substantially, even at compatibilizer loadings as low as 1%. Furthermore, the compatibilized blends exhibited significant improvements in elastic modulus, yield strength, and scratch re...

Development of thermo-sensitive poly N-isopropyl acrylamide grafted chitosan derivatives

In this study, the thermo-sensitive copolymers were synthesized by graft copolymerization of poly N isopropyl acrylamide (PNIPAm) onto chitosan (Ch) and aminated chitosan (AmCh) derivative. Free radical polymerization using potassium persulphate (KPS) as initiator was used for performing the grafting process. FTIR, TGA and DSC analysis were used to verify the structure of the resulting graft copolymers. The thermal sensitivity of the prepared copolymers was determined by monitoring the phase transition temperature at 550nm using a UV–VIS spectrophotometer. The results show that the transition of the PNIPAm-g-Ch is sharper than that of the PNIPAm-g-AmCh and the transition, in both cases, became sharper as increase the PNIPAm grating percentage.

Synthesis and microstructure of a novel graft copolymer from poly(vinylidene fluoride–chlorotrifluoroethylene–trifluoroethylene)

A novel graft copolymer of poly(vinylidene fluoride–chlorotrifluoroethylene–trifluoroethylene)-graft-poly(6-((4-cyano-4-biphenyl)oxy) hexyl methacrylate) (P(VDF-CTFE-TrFE)-graft-PCBHM) using P(VDF-CTFE-TrFE) as the initiator was successfully synthesized via atom transfer radical polymerization. It was found that the crystallinity of resultant graft copolymer increased slightly after grafting from the P(VDF-CTFE-TrFE), and the crystalline regions in the graft copolymer contained more (β phase which has all-trans chain conformation) trans chain conformation. Upon the introduction of PCBHM side chains, the thermal stability of the graft copolymer was lower than that of pristine terpolymer, but the storage modulus was enhanced significantly, which is beneficial for breakdown field-strength enhancement, and dielectric properties simultaneously decreased.

Isothermal crystallization behavior of PP and PP-g-GMA copolymer at high undercooling

The study involves synthesis of polypropylene grafted with glycidyl methacrylate (PP-g-GMA) using three different initiators, benzoyl peroxide, dicumyl peroxide and tertiary butyl cumyl peroxide (TBSP). Among the peroxides used, dicumyl peroxide resulted in considerable reduction of molecular weight of the resulting graft copolymer. The melting/crystallization behavior and isothermal crystallization kinetics of PP homopolymer and PP-g-GMA copolymers were studied with differential scanning calorimetry (DSC) at high undercooling (44–60°C). The results showed that the degree of crystallinity and overall crystallization rate of copolymers is greater than that of virgin PP. Among the three initiators used, TBCP exhibited lowest half crystallization time. The isothermal crystallization kinetics of the PP and copolymers was described with the Avrami equation and Sestak-Berggren (SB) equation. The Avrami exponent n of the PP and copolymers were found to be in the range 1.03 to 1.41 at high undercooling conditions employed in this study. The agreement between the values of n calculated from SB kinetics and Avrami equation is satisfactory with few exceptions. The crystallization rate of PP-g-GMA copolymer was found to be more sensitive to temperature. The isothermally crystallized samples showed a single melting peak for PP while a double peak at lower temperature was recorded for PP-g-GMA copolymer samples. The equilibrium melting point was deduced according to Hoffman-Weeks theory. The decrease of recorded for the PP modified with GMA suggests that the thermodynamic stability of the PP crystals is influenced by the chemical interactions.

Synthesis and structure–property relationships of polypropylene-g-polystyrene and polypropylene-g-poly(n-butyl acrylate) graft copolymers with well-defined molecular structures

Several polypropylene-g-polystyrene (PP-g-PS) and polypropylene-g-poly(n-butyl acrylate) (PP-g-PnBA) graft copolymers with well-defined molecular structures, basing on the same PP-Br precursor, were synthesized via a combination of metallocene-catalyzed polymerization and ATRP. The structure–property relationships of the resultant graft copolymers were systematically investigated. The crystallization temperatures of the obtained PP-g-PS and PP-g-PnBA graft copolymers decreased first and increased then with the enhancement of branch lengths. Compared to PP-Br, the introduction of PS or PnBA branches onto PP backbones both led to increased η0, more pronounced shear-thinning behavior, elevated value of G′ at low shear frequencies, and reduced loss angle. Under the same foaming conditions, the resulting PP-g-PS and PP-g-PnBA foams exhibited closed cell structure, increased cell density, and uniformized cell size distribution compared to the PP-Br foam. The cell density of PP-g-PS foam increased first and decreased then with the enhancement of branch length, and the cell size increased as the branch length increased. However, the cell density of the obtained three PP-g-PnBA foams was almost the same regardless of the PnBA branch length, and the cell size decreased first and increased then with increasing the branch length.