Efficient preparation and characterization of paraffin-based microcapsules by emulsion polymerization

Microencapsulated phase-change materials (MEPCMs) with paraffin as the core and poly(methyl methacrylate) (PMMA) and PMMA copolymers as the shell were prepared by emulsion polymerization using redox initiators at low temperatures. Fourier transform infrared spectroscopy was used to characterize the chemical composition of MEPCMs. The thermal properties and thermal stabilities of MEPCMs were tested by differential scanning calorimetry and thermogravimetric analysis. The morphologies and sizes of the microcapsules were investigated by scanning electron microscopy and particle size distribution analysis. The results indicated that the yield of microcapsules is as high as 96.2%, and the encapsulation efficiency of paraffin is nearly 100% when the paraffin content in MEPCM is 70%. The MEPCMs have good stability: the leakage ratios of MEPCMs can be less than 1% after 50 heating–cooling cycles. Therefore, the microencapsulation of paraffin using redox initiators has good production and application prospects. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47552.     

原子转移自由基乳液聚合研究进展

原子转移自由基聚合(ATRP)作为一种可控/活性聚合方法,可对聚合物结构进行精确控制;乳液聚合以水作为分散介质,具有经济、环保等特点。因此,乳液ATRP结合了两者的优点,具有工业化生产的潜力。首先分析了影响乳液ATRP的各种因素,然后综述了正向ATRP、RATRP(反向ATRP)、SR&NI ATRP(正向/反向同时进行的ATRP)和AGET ATRP(电子转移活化剂ATRP)等机制及研究进展,最后对乳液ATRP的发展方向进行了展望。     

Star polymers via atom transfer radical polymerization from adamantane-based cores

A series of novel multifunctional initiators derived from adamantane-based derivatives have been used in the syntheses of various styrenic and (meth)acrylic star polymers by atom transfer radical polymerization (ATRP). Conditions were identified in each system to produce star polymers with nearly monomodal molecular distributions. These synthesized star polymers have glass transition temperatures similar to those known for high-molecular-weight linear polymers. We obtained a series of adamantane-contained star polymers covering a wide range of molecular weights by adjusting the monomer-to-initiator ratio and the solvent polarity. Because of reaction heterogeneity and inevitable termination processes, the occurrence of star-star coupling led to a lower than predicted molecular weight polydispersity. When hydrolyzed from their cores by NaOH, the values of M_w of the arms of the PMMA star polymer did not change with reaction time, at least for the first 48 h of the reaction, which implies that no significant PMMA hydrolysis occurs within this interval of time.     

Well-defined dibenzocyclooctyne end functionalized polymers from atom transfer radical polymerization

The dibenzocyclooctyne end functionalized agent 1 was designed as atom transfer radical polymerization (ATRP) initiator. The ATRP was then explored on three types of monomers widely used in free radical polymerization: methyl methacrylate, styrene, and acrylates (n-butyl acrylate and tert-butyl acrylate). The living polymerization behaviors were obtained for the methyl methacrylate and styrene monomers. The SPAAC click reactivity of dibenzocyclooctyne end group were demonstrated by successfully reacting with azide functionalized small chemical agents and polymers. Various topological polymers such as block and brush polymers were produced from strain-promoted azide-alkyne cycloaddition reaction (SPAAC) using the resultant dibenzocyclooctyne end functionalized poly(methyl methacrylate)/polystyrene as building blocks. For the acrylates, however, the polymerization did not hold the living characteristics with the dibenzocyclooctyne end functionalized ATRP initiator 1.     

High-pressure atom transfer radical polymerization of methyl methacrylate for well-defined ultrahigh molecular-weight polymers

The feasibility of high-pressure atom transfer radical polymerization (ATRP) for synthesizing well-defined polymers of extraordinarily high molecular weights was demonstrated. ATRP of methyl methacrylate (MMA) under pressures up to 500 MPa was investigated at 60 °C. The addition of a small amount of a Cu(II)Cl₂/ligand complex along with the general benefits of high pressure of enhancing propagation and suppressing termination brought about an excellent control of polymerization even with an extremely low concentration of ATRP initiator. For example, there was produced PMMA with a number-average molecular weight M_n of 3.6 × 10⁶ and a polydispersity index of 1.24, which had never been achieved by conventional ATRP.     

Fe‐mediated ARGET atom transfer radical polymerization of methyl methacrylate in ionic liquid‐based microemulsion

Poly(methyl methacrylate) (PMMA) was synthesized by activator regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP) of MMA in ionic liquid‐based microemulsion with polyoxyethylene sorbitan monooleate (Tween 80) as surfactant. The polymerization was carried out at 25°C with CCl₄ as initiator, FeCl₃·6H₂O/N,N,N′,N′‐tetramethyl‐1,2‐ethanediamine (TMEDA) as catalyst complex in the presence of reducing agent ascorbic acid (VC). The polymerization kinetics showed the feature of controlled/″living″ process as evidenced by a linear first‐order plot. The well‐controlled polymers were obtained with narrow polydispersity indices and the ionic liquid‐based microemulsions were transparent with a particle size less than 30 nm. The obtained polymer was characterized by ¹H NMR and gel permeation chromatography. The chain extension was successfully achieved by the obtained PMMA macroinitiator/FeCl₃·6H₂O/TMEDA/VC initiator system based on ARGET ATRP method. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthesis of heat- and solvent-resistant polymers by radical polymerization of trifluoromethyl-substituted N-phenylmaleimides

The radical polymerization of the three kinds of fluorine-containing maleimides, that is, N-[2-(trifluoromethyl)phenyl]maleimide (2TFPhMI), N-[3-(trifluoromethyl)phenyl]maleimide (3TFPhMI), and N-[4-(trifluoromethyl)phenyl]maleimide (4TFPhMI) was carried out in the presence of a radical initiator in benzene at 60°C. The polymerization reactivity of these fluorine-containing maleimides and the properties of the resulting polymers were examined in comparison with the results for the methyl-substituted phenylmaleimides. The trifluoromethyl-substituted maleimides readily polymerized to give polymers in high yields as well as a methyl-substituted one. The resulting polymers showed an excellent resistance against organic solvents; especially, poly(4TFPhMI) was insoluble in the most common solvents. The onset temperature of thermal decomposition of the fluorine-containing polymers (T_init> = 352–368°C) was similar to that of poly(N-phenylmaleimide) (T_init = 364°C) and slightly lower than those for the methyl-substituted one (T_init = 388–402°C). The glass transition temperature of the polymers was dependent on the position of the trifluoromethyl group. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1703–1708, 1998     

原子转移自由基法合成乙丙橡胶接枝物中的热聚合研究

采用原子转移自由基聚合法(ATRP)合成了三元乙丙橡胶与苯乙烯的接枝共聚物(EPDM-g-St),动力学研究表明聚合过程为“活性”聚合。在接枝聚合过程中发现了明显的苯乙烯热聚合现象。对接枝聚合中得到的均聚苯乙烯进行表征的结果表明,苯乙烯在ATRP接枝体系中的热聚合过程在一定程度上受到ATRP机理的控制;升高温度和延长反应时间使得热聚合更为显著。     

Grafting polymers from cellulose nanocrystals via surface-initiated atom transfer radical polymerization

Cellulose nanocrystals (CNC) are rod-like nanoparticles extracted from cellulose. Due to their fascinating properties—renewable, biocompatible, non-toxic, biodegradable, excellent mechanical performances, high specific surface area, water dispersible, can be assemble in chiral nematic phases—CNC have shown promise in various fields, including oil recovery, polymer composites reinforcing, hydrogels, aerogels, supercapacitors, energy saving buildings, cosmetics, papermaking, coatings, liquid crystals, and waste water treatment. However, the hydrophilic surface of CNC hinders their broader applications. In this context, surface modification of CNC via polymer grafting can be used to finely tune their surficial properties and endow CNC with a variety of functionalities, such as conductivity, pH or temperature responsiveness, reactivity…In particular, surface-initiated atom transfer radical polymerization (SI-ATRP) is a powerful tool to graft various polymers with a high grafting density and controlled chain length. In this review, the precise control of grafted polymers from CNC via SI-ATRP is first discussed, including issues related to the polymer grafting density, chain length and possibility to perform an asymmetric grafting. Then, the properties and applications of CNC grafted with a variety of polymers are presented. Finally, some challenges and outlook related to the SI-ATRP method applied to the field of CNC is discussed.     

Preparation of hyperbranched polymers by atom transfer radical polymerization

A cheap acrylic AB* monomer, 2‐(2‐chloroacetyloxy)‐isopropyl acrylate (CAIPA), was prepared from 2‐hydroxyisopropyl acrylate with chloroacetyl chloride in the presence of triethylamine. The self‐condensing vinyl polymerization by atom transfer radical polymerization (ATRP), a “living”/controlled radical polymerization, has yielded hyperbranched polymers. All the polymerization products were characterized by proton nuclear magnetic resonance spectroscopy (¹H NMR). CAIPA exhibited distinctive polymerization behavior that is similar to a classical step‐growth polymerization in the relationship of molecular weight to polymerization time, especially during the initial stage of the polymerization. However, a significant amount of monomer remained present throughout the polymerization, which is consistent with typical chain polymerization. Also, if a much longer polymerization time was used, the polymer became gel. As a result of the unequal reactivity of group A* and B*, the polymerization is different from an ideal self‐condensing vinyl polymerization: the branch structures of polymers prepared depend dramatically on the ratio of 2,2'‐bipyridyl to CAIPA. Hyperbranched polymers exhibit improved solubility in organic solvent, however, they have lower thermal stability than their linear analogs. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2114–2123, 2002     

Atom transfer radical polymerization of n‐butyl methacrylate in an aqueous dispersed system

Atom transfer radical polymerization of n‐butyl methacrylate (BMA) was conducted in an aqueous dispersed system with different kinds of copper complexes. The partitioning behavior of the copper complexes, including CuCl/4,4′‐di(5‐nonyl)‐2,2′‐bipydine (dNbpy), CuCl₂/dNbpy, CuCl/2,2′‐bipydine (bpy), CuCl₂/bpy, CuCl/bis(N,N′‐dimethylaminoethyl)ether (bde), and CuCl₂/bde between the monomer (BMA), and water was studied in detail with ultraviolet‐visible spectroscopy. The results show that with a less hydrophobic ligand, such as bpy or bde, most of the Cu(I) or the Cu(II) complexes migrated from the BMA phase to the aqueous phase, the atom transfer equilibrium was destroyed, and the polymerization was nearly not controlled; it converted to classical emulsion polymerization. As to the very hydrophobic ligand dNbpy, although the partitioning study of the copper complexes indicated that not all the copper species were restricted to the organic phase, the linear correlation between the molecular weight and the monomer conversion and the narrow polydispersities confirmed that the polymerization was still quite well controlled. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3175–3179, 2003     

Thermal characterization of poly(vinyl chloride) samples prepared by living radical polymerization: Comparison with poly(vinyl chloride) prepared by free radical polymerization

Poly(vinyl chloride) (PVC) samples were synthesized by a living radical polymerization (LRP) method and compared with commercial PVC prepared by the conventional free radical polymerization (FRP). The differences were assessed, for the first time, in terms of viscosimetry parameters and thermal analysis. The LRP method used to prepare the PVC‐LRP samples is the only one available to obtain this polymer free of structural defects, being of commercial interest in a view of preparing a new generation of PVC‐based polymer with outstanding performance. The polymerization temperature selected (35°C) to prepare the LRP samples is currently used in the industry to prepare PVC‐FRP grades with moderate to high molecular weight. Since the thermal stability is a direct consequence of the polymer structure, this study is of vital importance to understand the potential of new PVC‐LRP. The thermoanalytical measurements demonstrate an enhanced thermal stability of PVC‐LRP when compared with its FRP counterpart. The PVC‐LRP sample with very low molecular weight reveals a higher thermal stability than the most stable PVC‐FRP sample. It is the first report dealing with thermal analysis of PVC prepared by LRP. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis of well-defined star polymers and star block copolymers from dendrimer initiators by atom transfer radical polymerization

Novel polyarylether dendrimers with 1,3,5-tri(4-hydroxyphenoxy)benzene core, polybenzylether interior, and benzyl 2-bromoisobutyrate surface group (CMGn-Br, n=1-3, with functionality of 6, 12, and 24, respectively) were prepared by convergent procedure. ATRP of tert-butyl acrylate (tBA) and styrene (St) with CMGn-Br dendrimer initiators in the presence of CuBr/pentamethyldiethylenetriamine catalytic system was investigated in detail, and a series of well-defined dendrimer-like star PtBA and PSt with precise arm numbers were synthesized under suitable conditions. The quantitative initiation of the dendrimer initiators was demonstrated by high initiation efficiency, ¹H NMR spectra, hydrolysis, and MALLS/SEC approach. Star block copolymers comprising PSt and PtBA segments with low polydispersity (1.08<M_w/M_n<1.18) were also successfully synthesized using functional macroinitiators by block copolymerization. In addition, the thermal properties of the resultant polymers were characterized by DSC and TGA.     

Thermal and morphological stability of polystyrene microcapsules containing phase‐change materials

Polystyrene microcapsules with paraffin wax as the active agent [phase‐change material (PCM)] were produced by a Shirasu porous glass emulsification technique and a subsequent suspension‐like polymerization process. The suitability of the obtained microcapsules for textile applications was studied. The thermal properties, surface morphology, and structural stability of the PCM microcapsules were investigated with differential scanning calorimetry, thermogravimetric analysis, and environmental scanning electron microscopy. The microcapsules could be used without any appreciable damage or irreversible changes in their integrity until 135°C. Furthermore, these microcapsules were heat‐resistant and could endure the curing conditions of textile coating up to 140°C for 30 min. In addition, the stability of the microcapsules under common laundering conditions was tested. It was confirmed that the microcapsules were durable enough and maintained their stability during stirring in hot water and alkaline solutions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of Pickering stabilization on radical entry in emulsion polymerization

The production of latexes stabilized by solid particles, so‐called Pickering stabilizers, has attracted considerable attention due to its benefits, including the enhanced mechanical properties of the polymer films. Clays for instance were found to enhance particle stabilization in emulsion polymerization, in a comparable way to conventional surfactants. Their concentration thus determines the polymer particles size and number, and consequently the reaction rate. In this work, we investigate the impact of the presence of such rigid and big platelets at the polymer particle's surface on radical exchange between the aqueous phase and the polymer particles. It was found for the system underhand that the average number of radicals per particle ( ) was independent of the stabilizer layer. Therefore, a radical capture model independent of the clay concentration could be used to simulate reactions involving different clay concentrations and predict the evolution of the monomer conversion, particle size, and . © 2018 American Institute of Chemical Engineers AIChE J, 64: 2612–2624, 2018     

Reverse atom transfer radical polymerization of n‐butyl methacrylate in an aqueous dispersed system

Reverse atom transfer radical polymerization (ATRP) of n‐butyl methacrylate (BMA) was conducted in an aqueous dispersed system. The influence of the surfactant, catalyst, reaction time and temperature on the colloidal stability and the control of polymerization was investigated. As a result, using an azo initiator (AIBN), a non‐ionic surfactant (Brij 35) and a hydrophobic ligand (dNbpy) to complex a copper halide, polymers with predetermined molecular weight and low polydispersity were obtained as stable latexes. Copyright © 2004 Society of Chemical Industry     

Synthesis of binary mixed homopolymer brushes by combining atom transfer radical polymerization and nitroxide-mediated radical polymerization

This communication describes a novel strategy to synthesize binary mixed homopolymer brushes from mixed self-assembled monolayers (SAMs) on silica substrates by combining atom transfer radical polymerization (ATRP) and nitroxide-mediated radical polymerization (NMRP). Mixed SAMs terminated by ATRP and NMRP initiators were prepared by coadsorption of two corresponding organotrichlorosilanes from toluene solutions. Mixed poly(methyl methacrylate) (PMMA)/polystyrene (PS) brushes were synthesized by ATRP of MMA at 80 °C followed by NMRP of styrene at 115 °C. Corresponding ‘free’ initiators were added into the solutions to control the polymerizations. We have found that the brush thickness increases with molecular weight in a nearly linear fashion. For a series of binary brushes consisting of PMMA of molecular weight of 26,200 and PS of various molecular weights, we have observed a transition in water contact angles with increasing PS molecular weight after CH₂Cl₂ treatment. Moreover, binary mixed polymer brushes with comparable molecular weights for two grafted polymers undergo reorganization in response to environmental changes, exhibiting different wettabilities.     

Synthesis and characterization of hyperbranched azobenzene-containing polymers via self-condensing atom transfer radical polymerization and copolymerization

We report on the synthesis of an azobenzene-containing inimer 6-{4-[4-(2-(2-bromoisobutyryloxy)hexyloxy)phenylazo]phenoxy}hexyl methacrylate (I) and used it to prepare hyperbranched homopolymer and copolymers by self-condensing vinyl polymerization (SCVP) and copolymerization (SCVCP) with its precursor 6-{4-[4-(6-hydroxyhexyloxy)phenylazo]phenoxy}hexyl methacrylate (M) using atom transfer radical polymerization (ATRP). Depending on the comonomer ratio, γ=[M]₀/[I]₀, branched polymethacrylates with number-average weights between 8000 and 20,000 and degree of branching (DB) between 0.08 and 0.49 were obtained by SCVCP, as evidenced by GPC and ¹H NMR analysis. In addition, the photochemical properties of the polymers were also studied by UV-vis spectra and found the structure of polymers affect obviously the trans-cis isomerization properties of the branched polymers.     

用电子转移活化再生原子转移自由基聚合制备含氟丙烯酸酯共聚物及其表征

在水分散介质中,以非离子乳化剂Tween-80和十二烷基磺酸钠作为复合乳化剂,通过电子转移活化再生原子转移自由基聚合,采用ab二次引发乳液聚合法制备了含氟丙烯酸酯三元共聚物,用傅里叶变换红外光谱、拉曼光谱、核磁共振波谱及凝胶渗透色谱等对其结构、组成和相对分子质量及其分布进行了表征。结果表明,含氟丙烯酸酯聚合物的分子结构及组成可控,转化率高达95%,相对分子质量分布较窄。优选憎水性配体和惰性乳化剂可提高反应的可控性。