Free Radical Copolymerization Reaction Research Articles

Utilizing methacrylated lignin as a sustainable macro-crosslinker for synthesizing innovative PVA/AMPS composites crosslinked hydrogel nanofibers: A potential application for lithium-ion battery separators

There are significant issues with commercial separators that must be resolved before they can be used in high-energy-density batteries. These problems include low porosity, poor electrolyte wetting, and low mechanical properties. This study presents a facile method for preparing composite crosslinked hydrogel nanofibers of polyvinyl alcohol (PVA) with 2-acrylamide-2-methylpropanesulfonic acid (AMPS) for lithium-ion battery separators by utilizing methacrylated lignin (LMA) as a bio-based crosslinker. Initially, LMA was synthesized by grafting glycidyl methacrylate (GMA) onto lignin via esterification. Subsequently, a crosslinked hydrogel nanofiber membrane (PVA/AMPS-LMA) was electrospun with varying LMA fractions, which were polymerized by combining free radical copolymerization and esterification reactions. The effectiveness of LMA as a crosslinker was assessed against the N, N′-methylene bisacrylamide (MBA). The study showed that using LMA as a crosslinker significantly improved the membrane's properties. The PVA/AMPS-LMA separator displayed superior features such as mechanical strength, thermal stability, porosity, electrolyte uptake, ionic conductivity, and lithium-ion transference number, when compared with PVA/AMPS, PVA, and Celgard separators. Specifically, the PVA/AMPS-LMA separator demonstrated a high mechanical strength of 24.9 MPa, strong thermal stability at 170 °C with no shrinkage, high porosity (84.3 %), and electrolyte uptake (661.4 %). It also exhibited exceptional ionic conductivity (2.75 mS/cm) and a notable lithium-ion transference number (tLi+ = 0.717). In coin batteries, the PVA/AMPS-LMA separator retained over 96 % capacity (142.4 mAh/g) after 200 cycles at 1C. This performance exceeded that of PVA/AMPS, PVA, and Celgard separators, suggesting that PVA/AMPS-LMA separators have the potential to replace their commercial counterparts.

Electrical and Electromagnetic Characteristics of Poly (Methyl Methacrylate)/Polyaniline PMMA/PANi Conductive Film

In this study, a conductive film of poly (methyl methacrylate)/polyaniline (PMMA/PANi) was fabricated through a free radical copolymerization reaction using methyl methacrylate (MMA) and aniline monomers at different aniline-to-MMA ratios, namely, 1:1, 1:3, and 1:5. The PMMA/PANi copolymer films exhibited a total electromagnetic interference (EMI) shielding effectiveness (SET) of 0.45, 0.60, and 1.22 dB, respectively, which is more than twice that of the pure PMMA film (0.16 dB). The copolymer films possess the highest conductivity of 2.34 x 10−6 S/cm at the optimum value of aniline for films polymerized with a 1:3 PMMA:PANi ratio. Higher conductivity materials exhibited lower resistance and, thus, absorbed more EM energy, resulting in better EMI shielding

Study on Preparation of Slow-release Polycarboxylate Superplasticizer by Macromonomer EPEG at Room Temperature

Slow-release polycarboxylate superplasticizer was synthetic under room-temperature conditions, a free radical copolymerization reaction occurred under the action of a redox initiator, and the optimal preparation process and temperature effect were discussed in detail. The results show that the best preparation process (EP-15) is: acid-to-ether ratio is 1.89, the amount of NaH2PO2 is 2.27%, the appropriate reaction temperature is 15-25°C, and the suitable macromonomer is EPEG-3000 of OXIRANCHEM. Tests have verified that compared to a commercially available slow-release polycarboxylate superplasticizer (PCE-1), EP-15’s dispersion retention performance and the strength growth of concrete in 3 d, 7 d, and 28 d are significantly better.

Polymer nanocomposite ADA@SM as a high-temperature filtrate reducer for water-based drilling fluids and its filtration loss mechanism

High temperatures degrade drilling fluid performance and endanger drilling safety when drilling deep and ultra-deep wells. The development of a new high-temperature drilling fluid additive to maintain drilling fluid performance in high-temperature environments is critical. A polymer nanocomposite (ADA@SM) was synthesized from the monomers styrene (St), methyl methacrylate (MMA), acrylamide (AM), 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), and diallyldimethylammonium chloride (DMDAAC) through a free-radical copolymerization reaction. Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (1H NMR) were used to characterize the structure of ADA@SM, and transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to characterize the microstructure of ADA@SM, indicating that it had a "star-net" structure. TGA analysis showed that the thermal decomposition temperature of ADA@SM was above 274 °C. The rheological and filtration properties of drilling fluids with ADA@SM were studied before and after aging at high temperatures (150–240 °C). The rheological model of the drilling fluid containing 2.5 wt% ADA@SM was found to be consistent with the Herschel-Buckley model. After aging at 220 °C, the filtration loss for API and HTHP was 8.4 mL and 29.8 mL, respectively. Using particle size analysis and zeta potential analysis, ADA@SM produced a drilling fluid with good particle size distribution and colloidal stability in high temperature environments. SEM analysis showed that ADA@SM adsorbed on the surface of the bentonite particles, which improved the compactness of the filter cake. The relative molecular weight (Mn) of ADA@SM decreased from 59671 to 5908 after degradation at high temperatures, and ADA@SM released polymer nanospheres, which effectively reduced the filtration loss of the drilling fluid.

Synthesis of a new high temperature and salt resistant zwitterionic filtrate reducer and its application in water-based drilling fluid

To overcome the negative effects of high temperature and salt pollution on the performance of drilling fluid in deep and ultra-deep wells, it is imperative to develop a high- temperature-and salt-resistant filtrate reducer. A zwitterionic quaternary copolymer (DADN) of N, N-dimethylacrylamide (DMAA), 2-acrylamido-2-methylpropane sulfonic acid (AMPS), diallyl dimethyl ammonium chloride (DMDAAC), and N-vinylcaprolactam (NVCL) was synthesized in an aqueous solution by free radical copolymerization reaction. The composition, structure, and thermal stability of the copolymers were characterized by Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance (1H NMR), Gel Permeation Chromatography (GPC), elemental analysis and thermogravimetric analysis (TGA), respectively. Furthermore, the filtration loss reduction performance of DADN was evaluated according to the American Petroleum Institute (API) standard. The mechanisms of filtrate loss reduction and salt resistance were revealed based on the transmission electron microscopy (TEM) analysis, adsorption isotherm and zeta potential analysis for the water-based drilling fluid (WBDF) containing DADN, and the scanning electron microscopy (SEM) analysis, energy-dispersive spectrometry (EDS) analysis and Brunner–Emmet–Teller (BET) analysis for the corresponding filter cake. The results showed that the thermal decomposition of DADN mainly happened over 298 ℃. Meanwhile, DADN exhibited the most outstanding filtration loss reduction ability compared to three commercially filtrate reducers (Driscal D, CMC and PAC-Lv). Specifically, the filtration losses of Driscal D/WBDF, CMC/WBDF and PAC-Lv/WBDF were 18.2, 31.2 and 24.8 mL after hot rolling at 220 °C for 16 h, respectively, while the filtration loss of DADN was only 6.5 mL. It was found that 2% DADN showed excellent filtration loss reduction ability at 220 °C and 15% NaCl. As confirmed by the SEM, EDS and adsorption isotherm results, strong adsorption of DADN on bentonite was obtained even under a high temperature and high-salinity environment. In particular, in the high-salinity environment, a firm “star network” structure formed by bentonite/DADN was observed by TEM, significantly improving the colloidal stability and filter cake compactness of WBDF.

Reactivity of 2,3-Dichloropropene in free-radical copolymerization reactions

The copolymers of 2,3-Dichloropropene with vinyl chloride, methyl methacrylate, and styrene of different compositions were obtained via free-radical copolymerization. The copolymerization constants for the comonomers were found from the dependence of the copolymer composition on the initial mixture content. An increase in the content of 2,3-Dichloropropene in the initial mixture was found to decrease the yield and intrinsic viscosity of the copolymer for all systems. The reactivity of 2,3-Dichloropropene in copolymerization reactions was assessed according to the reciprocals of the copolymerization constants of vinyl chloride, methyl methacrylate, and styrene, which indicate the reactivity of the dichlorinated monomer when interacting with comonomer radicals. It was found that 2,3-dichloropropene is the most active in the reaction with a styrene radical. However, its reactivity with a methyl methacrylate radical decreases by a factor of 0.88 as compared to the styrene radical. The lowest reactivity of 2,3-Dichloropropene is observed when interacting with a vinyl chloride radical. The synthesized copolymers can be further modified by replacing chlorine atoms with functional groups.

A Novel N-Halamine Biocidal Nanofibrous Membrane for Chlorine Rechargeable Rapid Water Disinfection Applications.

Disinfecting pathogenic contaminated water rapidly and effectively on sites is one of the critical challenges at point-of-use (POU) situations. Currently available technologies are still suffering from irreversible depletion of disinfectants, generation of toxic by-products, and potential biofouling problems. Herein, we developed a chlorine rechargeable biocidal nanofibrous membrane, poly(acrylonitrile-co-5-methyl-5-(4'-vinylphenyl)imidazolidine-2,4-dione) (P(AN-VAPH)), via a combination of a free radical copolymerization reaction and electrospun technology. The copolymer exhibits good electrospinnability and desirable mechanical properties. Also, the 5-methyl-5-(4'-vinylphenyl)imidazolidine-2,4-dione (VAPH) moieties containing unique hydantoin structures are able to be chlorinated and converted to halamine structures, enabling the P(AN-VAPH) nanofibrous membrane with rapid and durable biocidal activity. The chlorinated P(AN-VAPH) nanofibrous membranes showed intriguing features of unique 3D morphological structures with large specific surface area, good mechanical performance, rechargeable chlorination capacity (>5000 ppm), long-term durability, and desirable biocidal activity against both bacteria and viruses (>99.9999% within 2 min of contact). With these attributes, the chlorinated P(AN-VAPH) membranes demonstrated promising disinfecting efficiency against concentrated bacteria-contaminated water during direct filtration applications with superior killing capacity and high flowing flux (5000 L m-2 h-1).

Design, synthesis, characterization, and surface activities of comb-like polymeric fluorinated surfactants with short fluoroalkyl chains

Compared to hydrocarbon surfactants, fluorinated surfactants exhibit excellent surface activity. But long-chain linear perfluoroalkyl derivatives containing more than six CFn units have raised environmental concerns because they are persistent, bio accumulative, and highly toxic. Therefore, the development of new, environmentally friendly fluorinated surfactants is urgently required. Given that shortening the fluorocarbon chains of fluorinated surfactants can enhance their environmental safety, we designed and prepared a series of novel comb-like polymeric fluorinated surfactants by means of one-step free-radical copolymerization reactions of fluorinated methacrylates (FMAs) as hydrophobic monomers (containing two, four, or six CF2 groups; denoted FMA-4, FMA-8, and FMA-12, respectively) and poly(ethylene glycol) methyl ether methacrylates (PEGMEMAs) as hydrophilic monomers (Mn = 300, 500, or 950 Da; denoted PEGMEMA-300, PEGMEMA-500, and PEGMEMA-950, respectively) with initiation by 2,2-azobis(2-methylpropionitrile). The resulting surfactants, designated poly(PEGMEMAm-FMAn)x, were characterized by 1H and 19F nuclear magnetic resonance spectroscopy, gel permeation chromatography, static surface tension analysis, dynamic light scattering and transmission electron microscopy. The surface activities of the surfactants could be regulated by adjusting the ratio of the hydrophilic and hydrophobic monomers. A result that differs from that for previously reportedly fluorinated surfactants, we found for the first time that under certain conditions, the surface activities of these short-fluorocarbon-chain surfactants exceeded the activities of long-fluorocarbon-chain surfactants. The lowest static surface tension achieved with these poly(PEGMEMAm-FMAn)x surfactants in water was 30.12 mN/m.

A novel zwitterionic quaternary copolymer as a fluid-loss additive for water-based drilling fluids

ABSTRACT Wellbore instability and formation collapse are crucial issues in the process of well excavation in the oil industry under extreme high temperature conditions. A novel zwitterionic quaternary copolymer (PDANV) of 4-vinylpyridine (VP), N, N-dimethylacrylamide (DMAA), 2-acrylamido-2-methylpropane sulfonic acid, N-vinylcaprolactam (NVCL) was synthesized in aqueous solution by free radical copolymerization reaction. The structure of PDANV was characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (1 H NMR), and the results indicated that ideal product are obtained. Thermal stability of PDANV was revealed by thermogravimetric analysis (TGA) and result showed that thermal degradation of PDANV mainly happened over 301°C. Simultaneously, PDANV was prepared to further evaluate its effect on rheological and filtration properties of water-based drilling fluids (WBDFs). The results showed that the fluid loss (FLAPI) of PDANV/WBDFs was only 3.4 mL, 6.0 mL before and after hot rolling at 260°C for 16 h, respectively. Compared with the 19.2% and 57.9% reduction of traditional fluid-loss additives CMC and Driscal, the fluid-loss reduction rate of PDANV/WBDFs was 87.5% in ultra-high temperature environment. Additionally, PDANV performed satisfactorily with great properties in WBDFs even at high concentration of salts and calcium. Therefore, it can be used for applications where the PDANV is subjected to certain harsh environments, such as extreme salinity and ultra-high temperature conditions.

Styrene-co-butyl acrylate copolymers with potential application as membranes in PEM fuel cell

Styrene-butyl acrylate (St-BuA) copolymers were obtained by mass free radical copolymerization reactions, using BPO as initiator. A 70:30 (St-BuA) comonomer composition was selected. Three different molar concentrations of sulfonating agent (50, 100 and 150%) were considered to obtain the sulfonated copolymer (sSt-BuA) and membranes were casted from sSt-BuA copolymers. Copolymers were characterized with FTIR, TGA and NMR 1H and mechanically by TMA. The sSt-BuA sulfonation degree (SD) effect on the ion-exchange capacity (IEC) was evaluated by titration and water uptake (WU) by gravimetry. Microstructure was also observed using scanning electron microscopy (SEM), and its electrochemical properties were evaluated by electrochemical impedance spectroscopy (EIS). The chemical composition of St-BuA copolymer was confirmed by proton nuclear magnetic resonance (NMR 1H) spectroscopy. Fourier transformed infrared spectroscopy (FT-IR) and thermal gravimetric analysis (TGA) analysis also confirmed the existence of both comonomers and a successful sulfonation up to an actual 30% level, as well as a good thermal stability over 300 °C for the molecular structure and over 150 °C for sulfonated membranes. TMA indicate an increase in flexure modulus along degree of sulfonation. SEM images show a highly dense material with low pore size for the sulfonated copolymer. The IEC values obtained varied from 0.83 to 1.18 meq g−1, depending on sulfonation degree. The proton conductivity for St-BuA 50% membrane (9.77 × 10−5 S cm−1) was a two order of magnitude lower than the commercial Nafion membrane (4.53 × 10−3 S cm−1). Thermal, mechanical and electrochemical results demonstrate that these sSt:BuA copolymers are promising materials to be used as membranes in fuel cells applications.

Effect of fixed charge group concentration on salt permeability and diffusion coefficients in ion exchange membranes

This report presents a systematic investigation of the influence of fixed charge group concentration on salt diffusion coefficients in ion exchange membranes. Cross-linked cation and anion exchange membranes (CEMs and AEMs) having different fixed charge group concentrations and similar water content were synthesized via a one-step free radical copolymerization reaction. Concentration gradient-driven ion transport through the membranes was probed by measuring salt permeability coefficients as a function of salt concentration in the upstream solution. For all membranes, salt permeability coefficients increased by approximately one order of magnitude as external solution salt concentration increased from 0.01 to 1 M, predominantly due to similar increases in salt partition coefficients. On average, salt permeability coefficients for both series of membranes decreased with increasing fixed charge group concentration to nearly the same extent. Apparent salt diffusion coefficients, which were extracted from salt permeability and salt partition coefficients via the solution-diffusion model, changed to a greater extent for the AEMs than those for the CEMs despite similar changes in membrane fixed charge group concentration. The relative changes in apparent salt diffusion coefficients between AEMs and CEMs were attributed to differences in free volume of the membranes. This hypothesis was supported by positron annihilation lifetime spectroscopy measurements, which demonstrated variation in ortho-positronium lifetime values (a measure of free volume element size) for these membranes that correlated with variations in apparent salt diffusion coefficients.

Amino acid and ionic liquid modified polyhedral oligomeric silsesquioxane-based hybrid monolithic column for high-efficiency capillary liquid chromatography

In this study, a novel amino acid and ionic liquid dual organically functionalized reagents modified polyhedral oligomeric silsesquioxane methacryl substituted (POSS-MA) based hybrid monolithic column (POSS-VBI-Cys) was designed and reported. With amino acid L-cysteine and ionic liquid 1-vinyl-3-butylimidazolium bromide as dual monomers, POSS-MA as the crosslinker, the new POSS-VBI-Cys hybrid monolithic column could be facilely fabricated via the “one-pot” free radical copolymerization and thiol-ene click reaction. Because of the introduction of polar amino acid L-cysteine, the new POSS-VBI-Cys column exhibited attenuated hydrophobicity in reversed-phase liquid chromatography separation. Polar amides, nucleosides and nucleic acid bases displayed strong retention on the POSS-VBI-Cys column and could be successfully separated. Furthermore, the new POSS-VBI-Cys column displayed good separation selectivity for model glycoproteins and non-glycoproteins mixture and it was also successfully used for the purification and separation of TARG1 protein from its originally expressed sample. In the future research, we will further exploit its performances for separation of intact proteins and in-depth proteome applications.

Fabrication and Characterization of Nanoenergetic Hollow Spherical Hexanitrostibene (HNS) Derivatives.

The spherization of nanoenergetic materials is the best way to improve the sensitivity and increase loading densities and detonation properties for weapons and ammunition, but the preparation of spherical nanoenergetic materials with high regularization, uniform size and monodispersity is still a challenge. In this paper, nanoenergetic hollow spherical hexanitrostibene (HNS) derivatives were fabricated via a one-pot copolymerization strategy, which is based on the reaction of HNS and piperazine in acetonitrile solution. Characterization results indicated the as-prepared reaction nanoenergetic products were HNS-derived oligomers, where a free radical copolymerization reaction process was inferred. The hollow sphere structure of the HNS derivatives was characterized by scanning electron microscopy (SEM), transmission electron microscope (TEM), and synchrotron radiation X-ray imaging technology. The properties of the nanoenergetic hollow spherical derivatives, including thermal decomposition and sensitivity are discussed in detail. Sensitivity studies showed that the nanoenergetic derivatives exhibited lower impact, friction and spark sensitivity than raw HNS. Thermogravimetric-differential scanning calorimeter (TG-DSC) results showed that continuous exothermic decomposition occurred in the whole temperature range, which indicated that nanoenergetic derivatives have a unique role in thermal applications. Therefore, nanoenergetic hollow spherical HNS derivatives could provide a new way to modify the properties of certain energetic compounds and fabricate spherical nanomaterials to improve the charge configuration.

Adsorption and Desorption of Na<sup>+</sup> and NO<sub>3</sub><sup>−</sup> Ions on Thermosensitive NIPAM-<i>co</i>-DMAAPS Gel in Aqueous Solution

Adsorbent gel with the ability to absorb and to desorb Na+ and NO3− ions simultaneously with temperature swing was synthesized by free radical copolymerization reaction of N-isopropylacrylamide (NIPAM) and N,N-dimethyl-(acrylamidopropyl)ammonium propane sulfonate (DMAAPS). In this study, NIPAM acts as a thermosensitive agent and DMAAPS as an adsorbent agent. The purpose of this research is to investigate the effect of temperature and solution concentration on the swelling, adsorption, and desorption behaviors of NIPAM-co-DMAAPS gel. The relationship between adsorption and desorption behaviors of the gel was also elucidated. NaNO3 solution was selected as the target solution in swelling, adsorption, and desorption test. It was observed that the swelling degree of the gel increased as temperature and solution concentration raised. The adsorption amount of ions decreased with the increase of temperature. In contrast, the amount of ions desorbed from the gel increased linearly with temperature.

Metallosalen-Based Ionic Porous Polymers as Bifunctional Catalysts for the Conversion of CO2 into Valuable Chemicals.

A series of new metallosalen-based ionic porous organic polymers (POPs) were synthesized for the first time using a simple unique strategy based on the free-radical copolymerization reaction. Various techniques were used to characterize the physicochemical properties of these catalysts. These well-designed materials endowed high surface area, hierarchical porous structures, and enhanced CO2 /N2 adsorptive selectivity. Moreover, these POPs having both metal centers (Lewis acid) and ionic units (nucleophile) could serve as bifunctional catalysts in the catalytic conversion of CO2 into high value-added chemicals without any additional co-catalyst under mild and solvent-free conditions, for example, CO2 /epoxides cycloaddition and Nformylation of amines from CO2 and hydrosilanes. The results demonstrated that the irregular porous structure was very favorable for the diffusion of substrates and products, and the microporous structural property resulted in the enrichment of CO2 near the catalytic centers in the CO2 -involved transformations. Additionally, the superhydrophobic property could not only enhance the chemoselectivity of products but also promote the stability and recyclability of catalysts.

Hypercrosslinked polymers incorporated with imidazolium salts for enhancing CO2 capture

Hypercrosslinked polymers (ILHCPs) incorporated with imidazolium salts were prepared using 4-vinylbenzyl chloride, divinylbenzene, and imidazole ionic liquid monomers with various alkyl groups and anions by free radical copolymerization and Friedel-Crafts alkylation reaction. The structures of ILHCPs were characterized by using FT-IR, solid state 13C CP/MAS NMR spectroscopy, TGA, and gas adsorption. ILHCPs exhibit excellent capability of CO2 adsorption compared with that of nonfunctional hypercrosslinked polymers (HCPs), although both the BET surface area (447–667 m2/g) and pore volume (0.24–0.28 cm3/g) of ILHCPs are less than HCPs. The synergistic effect from mirco/mesopore structures and imidazolium salts are proved to play a key role in enhancing the CO2 adsorption capability and selectivity over other gases for ILHCPs. It can be found that the imidazolium salts content in HCPs is more important compared with the pore texture for adsorbing CO2. An optimal molar content of imidazolium salts groups is found to be 10.5% with the maximum CO2 uptake capability of 7.56 wt% and best CO2 adsorption selectivity (CO2/N2) of 47.9/1 (273 K, 1 bar), while those of the HCPs are only 5.93 wt% and 27.9/1. Such results strongly suggest that ILHCPs can be promising applied in selective CO2 separation. POLYM. ENG. SCI., 2016. © 2016 Society of Plastics Engineers

Studies on copra oil self-cured ester as a sustainable material for surface coatings

In this paper, synthesis, characterization, and optimization of a copra oil self-cured ester have been studied. The oil was first analyzed to examine the physico-chemical properties (iodine value, viscosity, refractive index, acid value, and specific gravity) and subsequently neutralized and dehydrated. The synthesis of self-cured ester was accomplished by reduction of the triglycerides in the oil by alcoholysis and functional group modification with phthalic anhydride and styrene via free radical co-polymerization reaction. Structural elucidation of the resin was enhanced by the Fourier transform infrared (FT-IR) spectroscopic technique. The response surface methodology (RSM) based on a central composite rotatable design (CCRD) involving 30 experiments of four process variables at five levels was employed for the optimization study as an economical way of obtaining an optimal response with fewest number of experiments. The studied process parameters were reaction temperature, reaction time, catalyst concentration, and phthalic anhydride-to-monoglyceride oil (PA:MGO) ratio. A predictive model describing the fractional conversion in terms of process variables was derived from multiple regression analysis. An optimum fractional conversion of 96.55% was predicted at a reaction temperature of 241.94 °C, reaction time of 124.2 min, catalyst concentration of 0.1% and PA:MGO ratio of 0.38:1, for the process. The extent of reaction at 135 min of polycondensation of the monomers was more than 85%. A model validation experiment shows a good agreement between the actual (97.19%) and predicted (96.55%) values. Physico-chemical properties and performance characteristics of the ester indicate its suitability in surface coating applications.

Monitoring the morphology development of polymer-monolithic stationary phases by thermal analysis

Thermal analysis and SEM were employed to gain insights in the different stages of morphology development and the thermal properties of polymer-monolithic stationary phases. The studied system was a thermally initiated free-radical copolymerization reaction at 70°C of styrene and divinylbenzene in the presence of tetrahydrofuran and 1-decanol. The key events in the early stages of morphology development are initiation, chain growth, branching, and cyclization, leading to microgel particles. Interparticle reactions through pendant vinyl groups lead to the formation of microgel clusters. The rapid increase in molecular weight and cross-link density of the microgel clusters causes a reaction-induced phase separation, and the formation of a macroscopic network of interconnected globules was observed (macrogelation) at around 45 min. After 3 h or 65% conversion, a space-filling macroporous monolithic network was observed. Afterwards, mainly growth of existing globules takes place, reducing the macropore size. The porogen ratio affects the timing of the reaction-induced phase separation, strongly influencing the morphology of the polymer material. The use of a mixture of divinylbenzene isomers yielded a monolithic material that is less cross-linked at the surface compared to the central part of the polymer backbone due to copolymerization-composition drift. The less cross-linked outer layer starts devitrifying at 100°C.

Incorporation of poly(glycidylmethacrylate) grafted bacterial cellulose nanowhiskers in poly(lactic acid) nanocomposites: Improved barrier and mechanical properties

Poly(glycidyl methacrylate) (PGMA) was grafted onto bacterial cellulose nanowhiskers (BCNW) by means of a redox-initiated free radical copolymerization reaction. The incorporation of PGMA chains decreased the thermal stability and crystallinity of BCNW. The neat and the PGMA-grafted BCNW were subsequently incorporated as fillers into the PLA matrix. PGMA grafting improved both matrix-filler adhesion and the dispersion of cellulose nanocrystals. However, the dispersion of the nanofiller was still not completely optimized and loadings higher than 3wt.% resulted in increased agglomeration. The incorporation of both neat and PGMA-grafted BCNW significantly reduced the oxygen permeability of PLA for low relative humidity conditions. However, due to the moisture sensitivity of cellulose, smaller improvements were attained when increasing the water activity. The detrimental effect of moisture on the oxygen permeability of nanocomposites was limited by the grafting copolymerization since PGMA-grafted BCNW seemed to present a more hydrophobic behavior. Furthermore, increased elastic modulus and tensile strength were observed for all the nanocomposites, especially when the concentration of nanocrystals was around the percolation threshold, i.e. 3wt.%, but only nanocomposites containing PGMA-grafted BCNW preserved the ductility of neat PLA.

Influences of soluble salts on adsorption properties of polycarboxylate superplasticizers

Polycarboxylate (PC) superplasticizers with different chemical structures were synthesized through free radical co-polymerization reaction. A total organic carbon analyzer was used to investigate adsorption behaviors of PCs, and to evaluate influences of soluble salts on absorption properties of PCs. It is found that adsorption ratios of PCs on cement particles decrease greatly with the addition of Na2SO4; the adsorption ratio of ethers PC with Hydroxyethyl methacrylate (HEMA) group first increases then decreases with the addition of NaCl; the adsorption ratio of esters PC with short side chains first decreases then increases, while the adsorption ratio of ethers PC with HEMA group decreases with the addition of CaCl2; the adsorption ratio of esters PC with short side chains decreases with the addition of Ca(NO3)2; AlCl3 causes the decrease of the adsorption ratio of ethers PC with HEMA group.