Core content and stability of n‐octadecane‐containing polyurea microencapsules produced by interfacial polymerization

Microencapsulation of phase change material (PCM) n‐octadecane was carried out by interfacial polymerization technique using core and bulk monomers as toluene‐2,4‐diisocyanate (TDI) and diethylene triamine (DETA), respectively. Cyclohexane was used as the solvent for TDI and n‐octadecane, which formed the oil phase. The effect of encapsulation procedure, core‐to‐monomer ratio (CM ratio) and PCM‐to‐cyclohexane (PC) ratio was investigated on core content, encapsulation efficiency, and stability of microcapsules. Using a modified procedure, the core content was found to increase with the increasing CM ratio and reached a maximum at 3.7, while the encapsulation efficiency continuously decreased with the increasing CM ratio. Also the encapsulation efficiency was found to have a strong dependence on PC ratio and a maximum encapsulation efficiency of 92%, along with the core content of 70% was obtained with CM ratio of 3.7 along with the PC ratio of 6. The microcapsules were well shaped, i.e., round and regular, with narrow size distribution at these conditions. The PCM microcapsules were found to be stable to heat treatment at 150°C for 8 h. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Improvements in the thermal conductivity and mechanical properties of phase‐change microcapsules with oxygen‐plasma‐modified multiwalled carbon nanotubes

The thermal properties and mechanical properties are the key factors of phase‐change microcapsules (microPCMs) in energy‐storage applications. In this study, microPCMs based on an n‐octadecane (C18) core and a melamine–urea–formaldehyde (MUF) shell supplemented with O₂‐plasma‐modified multiwalled carbon nanotubes (CNTs) were synthesized through in situ polymerization. Meanwhile, two different addition methods, the addition of modified CNTs into the emulsion system or into the polymer system, were compared and examined. Scanning electron microscopy micrographs showed that the microPCMs were spherical and had a broadened size distribution. Fourier transform infrared testing demonstrated that the modified CNTs did not affect C18 coated by MUF resin. The results indicate that the thermal conductivity and mechanical properties of the microPCMs were remarkably improved by the addition of a moderate amount of modified CNTs, but the heat enthalpy and encapsulated efficiency decreased slightly. Moreover, the thermal conductivity and mechanical properties of microPCMs modified with CNTs directly added to the polymer system were superior to those with CNTs added to emulsion system. In particular, when 0.2 g of modified CNTs were added to the polymer system, the thermal conductivity of the microPCMs was improved by 225%, and the breakage rates of the microPCMs at 4000 rpm for 5, 10, and 20 min decreased by 74, 72, and 60%, respectively, compared with that of the microPCMs without modified CNTs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45269.     

Preparation and properties of phase‐change heat‐storage UV curable polyurethane acrylate coating

Phase‐change heat‐storage UV curable polyurethane acrylate (PUA) coating was prepared by applying microencapsulated phase change materials (microPCMs) to PUA coating. MicroPCMs containing paraffin core with melamine‐formaldehyde shell were synthesized by in situ polymerization. The effect of stirring speed, emulsification time, emulsifier amount, and core/shell mass ratio on particle size, morphology, and phase change properties of the microPCMs was studied by using laser particle size analyzer, Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopic analysis, scanning electron microscopy, and differential scanning calorimetry. The results showed that the diameter of the microcapsules decreased with the increase of stirring speed, emulsification time, and emulsifier amount. When the mass ratio of emulsifier to paraffin is 6%, microcapsules fabricated with a core/shell ratio of 75/25 have a compact surface and a mean particle size of 30 μm. The sample made under the above conditions has a higher efficiency of microencapsulation than other samples and was applied to PUA coating. The dispersion of microPCMs in coating and heat‐storage properties of the coating were investigated. The results illustrated that the phase‐change heat‐storage UV curable PUA coating can store energy and insulate heat. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41266.     

Chain‐linked lactic acid polymers by benzene diisocyanate

Chain‐linked lactic acid polymers with high molecular weight were synthesized by two‐step polymerization method, including polycondensation and chain extending reactions. The effects of chain extender toluene diisocyanate (TDI) on the chain‐linked lactic acid polymers were studied. The polymers obtained were characterized by gel permeation chromatography, fourier transform infrared spectroscopy, ¹H NMR, and differential scanning calorimeter. Reactions between 1,4‐butanediol and lactic acid oligomers led to hydroxyl‐terminated prepolymer, which provided significant increase of molecular weight in the chain extending reaction. In addition, the glass transition temperature (T_g) and the melting temperature (T_m) were increased. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1045–1049, 2006     

Variations of the glass‐transition temperature in the imidization of poly(styrene‐co‐maleic anhydride)

The imidization of poly(styrene‐co‐maleic anhydride) (SMA) was conducted, and the glass‐transition temperatures (T_g's) of the resulting products were measured with differential scanning calorimetry. The contributions from functional groups of maleic anhydride, N‐phenylmaleamic acid, and N‐phenylmaleimide to T_g were examined. T_g increased in the order of SMA < styrene–N‐phenyl maleimide copolymer < styrene–N‐phenyl maleamic acid copolymer and followed the Fox equation. T_g of the imidized products of SMA could be controlled by the conversions of both ring‐opening and ring‐closing reactions. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2418–2422, 2007     

Preparation of phase change materials microcapsules by using PMMA network‐silica hybrid shell via sol‐gel process

Encapsulation of phase change materials (PCM) using a poly(methyl methacrylate) network‐silica hybrid as the shell material has been developed. n‐Octadecane melted at 28°C was used as PCM. Based on the suspension polymerization process, the microcapsules were prepared successfully by mixing and by the reaction of ethylene glycol dimethacrylate with precopolymer solution with tetraethoxysilane (TEOS), whose resultant microcapsules had higher latent heat (ΔH = 151 J/g) than those without TEOS (ΔH = 88.3 J/g). The average size of the PCM microcapsules was about 10 μm. The silica content, n‐octadecane content, and latent heat of microcapsules were changed with varying ageing conditions, ageing time, and temperature. The highest amount of latent heat (ΔH = 178.9 J/g) and n‐octadecane content (73.3%) of the microcapsule were obtained when the inorganic/organic ratio of the microcapsule was 5%. It was difficult to increase n‐octadecane content (74% to 55.7–67.9%) and latent heat (180.5 J/g to 135.9–165.7 J/g) of the microcapsules by introducing different functional groups of coupling agents. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Core/shell SiOx@PAM nanospheres from UV‐assisted surface‐initiated free radical polymerization

The core/shell SiO_x@polyacrylamide (SiO_x@PAM) nanospheres were successfully prepared by the in situ surface‐initiated free radical polymerization of acrylamide (AM) from the silica nanoparticles with self‐assembled monolayers (SAMs) of N‐methyl aniline (NMA) in presence of benzophonone via a precipitation polymerization method under the ultraviolet (UV) irradiation. The conversion of monomer (C%) and the percentage of encapsulating (PE%), calculated from the elemental analyses (EA) results, reached 20.9 and 51.0% after 150 min of UV‐irradiation, respectively. It is consistent with the analyses of TGA. Fourier transform infrared (FTIR) analyses also confirmed the formation of the core/shell SiO_x@PAM nanospheres. And it was investigated that the silica nanoparticles had been encapsulated with PAM from the X‐ray photoelectron spectrometer (XPS) analyses. The analysis results of transmission electron microscope (TEM) showed that the diameters of the SiO_x@PAM nanospheres were in the range of 50–200 nm. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3433–3438, 2006     

Interface stability behaviors of methanol‐melamine‐formaldehyde shell microPCMs/epoxy matrix composites

Microcapsules containing phase change materials (microPCMs) have been widely applied in smart temperature‐controlling materials. Interface stability plays a key role in these microPCMs/matrix composites. The aim of this study was to investigate the interface stability behaviors of methanol‐melamine‐formaldehyde (MMF) shell microPCMs containing paraffin/epoxy matrix composites. MMF prepolymer can be applied to fabricated microcapsules with smooth shells. The average diameter of the microPCMs could be controlled in the range of 5–45 μm by stirring speed of 500–6,000 r min⁻¹. From the SEM morphologies of the interphase between the microPCMs and the epoxy‐matrix, it is concluded that the interaction may be enhanced by MMF graft structure due to the increasing of molecular interaction in the interface. During a repeated heat‐transmission process, not only the repeated‐times of thermal absorbing‐releasing process will damage the interface bonding, but also higher thermal conductive speed will make the interface bearing more debonding stress. Large microPCMs in matrix may supply better interface stability. Moreover, the numerical and experimental results are consistent to obtain a clear insight into the rule of interface debonding for microPCMs/matrix composites that the interface perfection can be enhanced by increasing the thickness of interphase. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Narrow‐disperse or monodisperse crosslinked and functional core–shell polymer particles prepared by two‐stage precipitation polymerization

Narrow‐disperse and monodisperse cross‐linked core–shell polymer particles containing different functional groups, such as esters, hydroxyls, chloromethyls, carboxylic acids, amides, cyanos, and glycidyls, in the shell layers in the micrometer size range were prepared by a two‐stage precipitation polymerization in the absence of any stabilizer. Commercial divinylbenzene (DVB), containing 80% DVB, was precipitation polymerized in acetonitrile without any stabilizer as the first‐stage polymerization and was used as the core. Several functional monomers, including methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2‐hydroxyethyl methacrylate, glycidyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, t‐butyl acrylate, i‐octyl acrylate, acrylic acid, acrylamide, acrylonitrile, styrene, and p‐chloromethyl styrene, were incorporated into the shells during the second‐stage polymerization. The resulting core–shell polymer particles were characterized with scanning electron microscopy and Fourier transform infrared spectroscopy. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1776–1784, 2006     

Preparation and properties of core [poly(styrene‐n‐butyl acrylate)]–shell [poly(styrene–methyl methacrylate–vinyl triethoxide silane)] structured latex particles with self‐crosslinking characteristics

Structured latex particles with a slightly crosslinked poly(styrene‐n‐butyl acrylate) (PSB) core and a poly(styrene–methacrylate–vinyl triethoxide silane) (PSMV) shell were prepared by seed emulsion polymerization, and the latex particle structures were investigated with Fourier transform infrared, thermogravimetric analysis, differential scanning calorimetry, transmission electron microscopy, and dynamic light scattering. The films that were formed from the structured core (PSB)–shell (PSMV) particles under ambient conditions had good water repellency and good tensile strength in comparison with films from structured core (PSB)–shell [poly(styrene–methyl methyacrylate)] latex particles; this was attributed to the self‐crosslinking of CH₂?CH? Si(OCH₂CH₃)₃ in the outer shell structure. The relationship between the particle structure and the film properties was also investigated in this work. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1824–1830, 2006     

Star‐shaped POSS–methacrylate copolymers with phenyl–triazole as terminal groups,synthesis, and the pyrolysis analysis

Star‐shaped polyhedral oligomeric silsesquioxane (POSS)–methacrylate hybrid copolymers with phenyl–triazole as terminal groups had been designed and synthesized via sequential atom transfer radical polymerization (ATRP), azidation, and phenylacetylene‐terminated procedures, and the hybrid copolymers here could be denoted as POSS–(PXMA‐Pytl)₈, where X can be M, B, L, and S, represented four different methacrylate monomers, such as methacrylate (MMA), butyl methacrylate (BMA), lauryl methacrylate (LMA), and stearyl methacrylate (SMA), respectively. Thermal gravimetric analysis (TGA) and in situ Fourier transform infrared spectroscopy (FTIR) were applied for studying the thermal stability and degradation mechanism, and it was found that all of the POSS–(PXMA‐Cl)₈ and POSS–(PXMA‐Pytl)₈ copolymers exhibited excellent thermal stabilities, which had great potential in heat‐resistant material application. Different tendencies of decomposition temperatures at 5% and 10% weight loss (T₅ and T₁₀) dependent on the side‐chain length and terminal group species were investigated respectively. The longer alkyl side chains of the monomers, the lower thermal stabilities, and enhanced T₅ and T₁₀ were also shown with the introduction of phenyl–triazole groups instead of chlorine groups. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40652.     

The microencapsulation of calcium chloride hexahydrate as a phase‐change material by using the hybrid coupler of organoalkoxysilanes

A novel method of microencapsulation for inorganic salt hydrates as phase‐change material (PCM), which is essential for their broad application, was pursued by combining sol–gel process with interfacial polymerization. Calcium chloride hexahydrate (CCH), chosen as a representative PCM of salt hydrates, was used as a core material, and organoalkoxysilane was applied to provide hybrid properties of mediating the hydrophilic core and hydrophobic shell material. The Fourier transform infrared spectra and SEM images confirmed that the siloxane and polyurea shell material successfully capsulated the CCH core. Fine morphology of microcapsules was further investigated with SEM, and it presented almost‐spherical shape and a well‐defined core–shell structure. Thermogravimetric analysis indicated that microcapsules containing CCH have sufficient thermal stability, which usually degraded in four steps. Differential scanning calorimeter investigation confirmed additionally that the microencapsulated CCH absorbs thermal energy with phase change during the melt process but undergo a severe super cooling phenomenon in the crystallizing process. In addition, the durability test was conducted to evaluate the siloxane polymer and polyurea as a shell material, protecting CCH from leaking. The effect of pH and the ratio of ingredients were studied in terms of encapsulation possibility and performance of core PCM, which include morphology of core–shell particles and essential thermal properties as a PCM. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45821.     

Fabrication and thermal properties of microPCMs: Used melamine‐formaldehyde resin as shell material

An in‐situ polymerization process prepared a series of melamine formaldehyde (MF) microcapsules containing phase change material (PCM) as core material. The phase change temperature of this PCM was 24°C and its phase transition heat was 225.5 J/g. The microencapsulated phase change materials (MicroPCMs) were bedded in indoor‐wall materials to store and release heat energy, which would economize heat energy and make the in‐door condition comfortable. We investigated the structural formation mechanism by microscope and scanning electron microscopy (SEM). The superficial morphology measurements indicated the optimal shell material dropping rate 0.5 mL min^?1, double‐shell, and temperature elevating speed 2°C/10 min. The results obtained in the present investigation were reasonably understood on the basis of getting determinate rigidity and compacted shell. Also, the observed results were used to control the mass of shell material to get desired thickness of shell. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 2006     

Effects of TDI and FA‐703 on physico‐mechanical properties of polyurethane dispersion

A series of water dispersion polyurethanes dispersions (PUDs) were prepared by polyaddition reaction using isophorone diisocyanate (IPDI), toluene diisocyanate (TDI), poly(oxytetramethylene) glycol (PTMG), dimethylol propionic acid (DMPA), and triol (trade name FA‐703). Various formulations were designed to investigate the effects of process variables such as TDI and FA‐703 on the physico‐mechanical properties of PUD. IR spectroscopy was used to check the end of polymerization reaction and characterization of polymer. Evolution of the particle size distribution, contact angle, T_g, molecular weight, viscosity, and mechanical properties of the emulsion‐cast films were significantly affected by variable content of TDI and FA‐703. Average particle size of the prepared polyurethane emulsions and contact angle decrease with increase of content of FA‐703 and TDI. Molecular weight, T_g, tensile strength, tear strength, hardness, viscosity and elongation at break increase with increase of content of FA‐703 and TDI. The increase of molecular weight, tensile strength, tear strength and elongation at break properties are interpreted in terms of increasing hard segments, chain flexibility, and phase separation in high content of FA‐703 and TDI‐based polyurethane. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and properties of polystyrene‐b‐poly(ethylene oxide)‐b‐polystyrene triblock copolymers

A series of well‐defined and property‐controlled polystyrene (PS)‐b‐poly(ethylene oxide) (PEO)‐b‐polystyrene (PS) triblock copolymers were synthesized by atom‐transfer radical polymerization, using 2‐bromo‐propionate‐end‐group PEO 2000 as macroinitiatators. The structure of triblock copolymers was confirmed by ¹H‐NMR and GPC. The relationship between some properties and molecular weight of copolymers was studied. It was found that glass‐transition temperature (T_g) of copolymers gradually rose and crystallinity of copolymers regularly dropped when molecular weight of copolymers increased. The copolymers showed to be amphiphilic. Stable emulsions could form in water layer of copolymer–toluene–water system and the emulsifying abilities of copolymers slightly decreased when molecular weight of copolymers increased. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 727–730, 2006     

Preparation and characterization of flame retardant phase change materials by microencapsulated paraffin and diethyl ethylphosphonate with poly(methacrylic acid‐co‐ethyl methacrylate) shell

Microcapsules containing paraffin and diethyl ethylphosphonate (DEEP) flame retardant with uncrosslinked and crosslinked poly (methacrylic acid‐co‐ethyl methacrylate) (P(MAA‐co‐EMA)) shell were fabricated by suspension‐like polymerization. The surface morphologies of the microencapsulated phase change materials (microPCMs) were studied by scanning electron microscopy. The thermal properties and thermal stabilities of the microPCMs were investigated by differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA). The flame retarding performances of the microcapsule‐treated foams were calculated by using an oxygen index instrument. The DSC results showed that the crosslinking of the polymer shell led to an increase in the melting enthalpies of the microcapsule by more than 15%. The crosslinked P(MAA‐co‐EMA) microcapsules with DEEP and without DEEP have melting enthalpies of 67.2 and 102.9 J/g, respectively. The TGA results indicated that the thermal resistant temperature of the crosslinked microcapsules with DEEP was up to 171°C, which was higher than that of its uncrosslinked counterpart by ～20°C. The incorporation of DEEP into the microPCM increased the limiting oxygen index value of the microcapsule‐treated foams by over 5%. Thermal images showed that both microcapsule‐treated foams with and without DEEP possessed favorably temperature‐regulated properties. As a result, the microPCMs with paraffin and DEEP as core and P(MAA‐co‐EMA) as shell have good thermal energy storage and thermal regulation potentials, such as thermal‐regulated foams heat insulation materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41880.     

Comparison of styrene reversible addition–fragmentation chain‐transfer polymerization in a miniemulsion system stabilized by ammonlysis poly(styrene‐alt‐maleic anhydride) and sodium dodecyl sulfate

In this study, we conducted the reversible addition–fragmentation chain‐transfer (RAFT) polymerization of styrene (St) in a miniemulsion system stabilized by two different stabilizers, ammonlysis poly(styrene‐alt‐maleic anhydride) (SMA) and sodium dodecyl sulfate (SDS), with identical reaction conditions. The main objective was to compare the polymerization kinetics, living character, latex stability, and particle morphology. The macro‐RAFT agent used in both systems was SMA, which was obtained by RAFT solution polymerization mediated by 1‐phenylethyl phenyldithioacetate. The experimental results show that the St RAFT miniemulsion polymerization stabilized by SDS exhibited a better living character than that stabilized by ammonlysis SMA. The final latices were very stable in two systems, but different stabilizers had an obvious effect on the polymerization kinetics, living character, and particle morphology. All of the particles obtained by RAFT miniemulsion polymerization stabilized by SDS were solid, but an obvious core–shell structure was observed in the miniemulsion system stabilized by ammonlysis SMA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Polyacrylate‐core/TiO2‐shell nanocomposite particles prepared by in situ emulsion polymerization

We report the preparation of polyacrylate‐core/TiO₂‐shell nanocomposite particles through in situ emulsion polymerization in the presence of nano‐TiO₂ colloid obtained by the hydrolysis of titanium tetrachloride. The resultant colloidal system can be stable for months without any precipitation. In a typical sample, the diameter of nanocomposite particles was about 150 nm, and the thickness of TiO₂‐shell was 4–10 nm. Only cetyltrimethylammonium bromide was employed to provide the latex particles with positive charge, which was enough for the formation of fine TiO₂ coatings. Three initiators were tested. Ammonia persulfate was the most suitable one, because the cooperative effect was formed by the negatively charged TiO₂ particles and the terminal anionic group (SO₄^2?, the fraction of Ammonia persulfate) of the polymer chain on the surface of latex particles to maintain the stability of nanocomposite system. The pH value played a vital role in obtaining a tight TiO₂ coating. Transmission electron microscopy, X‐ray diffraction and Atomic force microscopy were used to characterize this nanocomposite material. It was found that rutile and anatase coexisted in the nanocomposite film. This may suggest a potential application in the field of photocatalytic coating. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1466–1470, 2006     

Microstructure and glass‐transition temperature of novel star N‐SIBR

In this study, a polymeric N‐functionalized mutilithium (N‐M‐Li) compound was prepared from commercial divinylbenzene (DVB) and lithiohexamethyleneimine (LHMI), and star‐shaped copoly(styrene–butadiene–isoprene) was obtained by anionic polymerization using preformed N‐M‐Li as initiator, tetramethylethlenediamine (TMEDA) as polar modifier, and cyclohexane as solvent. The microstructure and the glass–transition temperature (Tg) of copolymers were characterized by ¹H NMR and differential scanning calorimetry (DSC), respectively. It showed that the non‐1,4‐structure content and the Tg of copolymers increased with the increase of TMEDA dosage or the decrease of polymerization temperature; however, the effects of the initiator concentration and DVB dosage on them were not obvious. We also obtained the relationships between the non‐1,4‐structure content of copolymers and the Tg of copolymers respectively, and between the ln(T/Li) (TMEDA/N‐M‐Li, mole ratio) and the non‐1,4‐structure content of copolymers, as follows: Tg (°C) = 0.6258C_{non 1,4}?55.93 and C_{non 1,4} = 20.79 ln K+59.11, where K is T/Li value. Therefore on the basis of experimental results, we realize polymer design according to our practical requirements. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5848–5853, 2006     

Soybean‐ and castor‐oil‐based thermosetting polymers: Mechanical properties

Maleic anhydride modified soybean‐ and castor‐oil‐based monomers, prepared via the malination of the alcoholysis products of the oils with various polyols, such as pentaerythritol, glycerol, and bisphenol A propoxylate, were copolymerized with styrene to give hard rigid plastics. These triglyceride‐based polymers exhibited a wide range of properties depending on their chemical structure. They exhibited flexural moduli in the 0.8–2.5 GPa range, flexural strength in the 32–112 MPa range, glass transition temperatures (T_g) ranging from 72 to 152°C, and surface hardness values in the 77–90 D range. The polymers prepared from castor oil exhibited significantly improved modulus, strength, and T_g values when compared with soybean‐oil‐based polymers. These novel castor and soybean‐oil‐based polymers show comparable properties to those of the high‐performance unsaturated polyester (UP) resins and show promise as an alternative to replace these petroleum‐based materials. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1497–1504, 2006