Synthesis of emulsion styrene butadiene rubber by reversible addition–fragmentation chain transfer polymerization and its properties

Emulsion polymerization is generally used to synthesize styrene butadiene rubber (SBR), and the molecular weight of this rubber can be easily increased. However, the broad molecular weight distribution (MWD) of SBR increases energy loss and adversely affects the dynamic viscoelastic properties. To overcome this disadvantage, reversible addition–fragmentation chain transfer (RAFT) polymerization, which is a type of living polymerization, is applied to emulsion polymerization for preparing RAFT emulsion SBR (ESBR). The molecular weight and microstructure of RAFT ESBR are compared to those of commercially available ESBR 1502 by gel permeation chromatography and proton nuclear magnetic resonance spectroscopy. The aforementioned two polymers are used to prepare unfilled ESBR compounds, which are compared in terms of key physical properties (abrasion resistance, mechanical properties, and dynamic viscoelastic properties). It is confirmed that various physical properties of RAFT ESBR are improved due to its narrow MWD. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47069.     

Grafting modification of ramie fibers with poly(2,2,2-trifluoroethyl methacrylate) via reversible addition–fragmentation chain transfer (RAFT) polymerization in supercritical carbon dioxide

Reversible addition–fragmentation chain transfer (RAFT) polymerization was used to control the grafting of 2,2,2-trifluoroethyl methacrylate (TFEMA) with ramie fibers in supercritical carbon dioxide (scCO₂). The hydroxyl groups of the ramie fibers were converted to 2-dithiobenzoyl isobutyrate as the RAFT chain transfer agent (cellulose-CTA). Then, the subsequent grafting with TFEMA was mediated by RAFT polymerization in the presence of 2-(ethoxycarbonyl)prop-2-yl dithiobenzoate (ECPDB) as the free RAFT chain transfer agent (free CTA). The modified ramie fibers were highly hydrophobic with water contact angles of up to 149°. Size exclusion chromatography showed narrow polydispersity (PDI = 1.28) of the grafted poly(TFEMA) chains. This grafting polymerization process is a novel and environmentally friendly approach for the preparation of functional grafted copolymers utilizing ramie fiber biomass.     

Synthesis of 9H-fluoren-9-yl benzodithioates and their application as reversible addition–fragmentation chain transfer agents in living radical polymerization of styrene

The reversible addition–fragmentation chain transfer (RAFT) polymerization is one of living radical polymerizations. In this study, four different 9H-fluoren-9-yl benzodithiolates (FBDTs) were synthesized, and used along with azobis(isobutyronitrile) (AIBN), a radical initiator, in polymerization of styrene (ST) at the molar ratio of 3:1. This new transfer agent exhibited the typical characteristic living free radical polymerization behaviors such as good control of molecule weight and narrow molecule weight distribution. It was concluded that the FBDTs can be used as the RAFT agents in free radical polymerization of vinyl monomers.     

Preparation of acid-cleavable branched polymers for argon fluoride photoresists via reversible addition–fragmentation chain-transfer polymerization

A series of branched polymers for chemically amplified resists (CARs) were prepared through the reversible addition–fragmentation chain-transfer (RAFT) copolymerization of three monomers with lithographic functionalities and an acid-cleavable dimethacrylate monomer. The three monomers with lithographic functionalities were 2-ethyl-2-adamantyl methacrylate, α-γ-butyrolactone methacrylate, and 3-hydroxy-1-adamantyl methacrylate. The acid-cleavable monomer was 2,5-dimethyl-2,5-hexanediol dimethacrylate (DMHDMA), and 2-cyanoprop-2-yl-1-dithionaphthalate was used as a chain-transfer agent. Because DMHDMA contains two methacrylate groups, it induced the branched structures of the polymers. The degree of branching could be controlled by the molar fraction of DMHDMA in the monomer mixtures. The size and structure of the polymers obtained after hydrolysis were very close to those of linear polymers prepared by RAFT copolymerization with the same amount of reagents, only without the acid-cleavable monomer. A preliminary lithography test using an argon fluoride source demonstrated that the acid-cleavable branched polymers could be promising candidates for CAR materials. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Molecular control of polystyrene in the reverse iodine transfer polymerization (RITP) – Suspension process

The reverse iodine transfer polymerization (RITP)-suspension polymerization of styrene was carried out in the presence of molecular iodine (I₂) using AIBN as an initiator and polyvinylalcohol (PVA) as a stabilizer under argon atmospheres at 70 °C for 10 h in the absence of light. The effect of iodine and styrene contents on the molecular characteristics was investigated. The result was summarized into three categories; (1) the two different polymerizations, the emulsion and suspension, simultaneously occurred in the RITP-suspension polymerization. (2) The emulsion fraction decreased, whereas the suspension fraction increased with the I₂ content from 0 to 0.25 mmol, resulting in the decreased molecular weight of the resultant polymer from 320,000 to 59,000 g/mol, respectively. This was arisen from the higher reaction rate of the RITP-suspension polymerization due to the better solubility of AIBN in the monomer droplet in the suspension phase than in the micelle in the emulsion phase upon the increased I₂ content. (3) As the styrene content increased up to 40 wt% under fixed I₂ content, the suspension fraction dominated, resulting in the reduced molecular weight from 59,000 to 38,000 g/mol, respectively. This was rationalized that the temperature increment upon the relatively small amount of solvent, which means due to the large amount of monomer, induced the rapid polymerization in the monomer droplets where the suspension polymerization was favorable. Thus, the RITP-suspension process dramatically decreased the molecular weight of PS not only by the presence of I₂, but also by the dominated suspension fraction.     

Effect of π-π stacking on the atom transfer radical polymerization of styrene

The atom transfer radical polymerization (ATRP) of styrene (St) was carried out in the presence of varying equivalents (eq) of hexafluorobenzene (HFB) to probe the effect of pi-pi stacking on the rate of the polymerization and the resulting tacticity of polystyrene (PSt) formed. The extent of interaction between the electron deficient face of the HFB and the electron rich face of the styrenic or polystyrenic phenyl ring was also examined as a function of reaction solvent, incorporating both non-aromatics (hexanes and THF) and aromatics (benzene and toluene). It was found that in all cases the rate of the ATRP of St was slowed by the addition of HFB to the reaction mixture, with increasing amounts of HFB (1 full eq. compared to St) retarding the rate to a relatively greater extent compared to smaller amounts (0.5 eq). Additionally, when aromatic solvents were used instead of hydrocarbons the effect of HFB on the rate of the ATRP was minimized, consistent with the solvent itself competing with the styrenic phenyl groups for pi-pi stacking interactions with HFB. The decreased rate in the presence of HFB is consistent with a reduced ability of the terminal phenyl group on the PSt chain to stabilize the active polymer radical, pushing the equilibrium further to the dormant alkyl halide. This interaction between the dormant alkyl bromide and HFB was verified by ¹H NMR, with 1-bromoethylbenzene used as the alkyl bromide. When the ATRP of non-aromatic vinyl monomers was studied (butyl acrylate and methyl methacrylate), the effect of HFB on the system was almost unnoticeable as expected due to their inability to participate in pi-pi stacking interactions. The tacticity of the PSt formed in the presence of HFB was compared to PSt formed in its absence by observing the C1 resonance on ¹³C NMR, but no change in the shape or chemical shift of the signal was observed.     

Thermo-responsive block copolymer micelle-supported (S)-α,α-diphenylprolinol trimethylsilyl ether for asymmetric Michael addition of nitroalkenes and aldehydes in water

An amphiphilic block copolymer PNIPAM₅₃-b-(PS₃₀-co-P4AMS₁₀) was facilely prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization. The immobilization of (S)-α,α-diphenylprolinol trimethylsilyl ether onto the block copolymers was then performed through using copper-catalyzed alkyne-azide cycloaddition (CuAAC), and the generating amphiphilic diblock copolymer supported chiral catalyst PNIPAM₅₃-b-(PS₃₀-co-P4AMS₁₀)/proTMS was self-assembled into micelles with regular diameters about 50 nm in aqueous solution. The micellar catalyst was further used for the asymmetric Michael reaction between propanal and trans-β-nitrostyrene in water. Using only 1 mol% micellar catalyst, the corresponding Michael addition products could be obtained in good yields and high enantioselectivities as well as good diastereoselectivities. In addition, this micellar catalyst could be reused at least for four times. Moreover, the micellar catalyst could be applied for the asymmetric addition reaction of 4-chlorocinnamyl aldehyde and nitromethane, and thus constructing the baclofen pharmaceutical intermediate.     

Synthesis of (S)-α-amino oleic acid

An efficient synthesis of (S)-α-amino oleic acid was developed. The fully protected FA derivative was obtained in four steps starting from methyl (2S)-2-[bis(tert-butoxycar-bonyl)amino]-5-oxopentanoate. These steps are (i) olefination of the starting aldehyde with the appropriate phosphonate anion, (ii) hydrogenation of the double bonds, (iii) controlled reduction of ω-ethyl ester to an aldehyde in the presence of α-methyl ester, and (iv) a Wittig reaction of the latter aldehyde with the suitable ylide. Free α-amino oleic acid was prepared after deprotection of the amino group followed by saponification in a total yield of 24%. N-tert-Butoxycarbonyl-protected amino oleic acid and the corresponding amino alcohol were prepared in high yield. The structures of the products have been established by various spectroscopic techniques.     

Study of macroinitiator efficiency and microstructure–thermal properties in the atom transfer radical polymerization of methyl methacrylate

The atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) with poly vinylacetate macroinitiator (PVAc-CCl₃) and CuCl/PMDETA as catalyst was successfully carried out in bulk and solution. The apparent propagation rate constant () and concentration of active species ([P°]) were higher in the bulk. In solution they increased with polarity of solvent. Two different molecular weights of macroinitiators were used in ATRP of MMA. The linear relation of Ln[M]₀/[M] versus time was only confirmed for the low molecular weight macroinitiator. The ratio of was calculated in the bulk reaction with the low molecular weight macroinitiator, this ratio was 1.77 × 10¹⁴ M⁻¹ s⁻¹ for larger macroinitiator in solution. The MWD of block copolymers were sharper with lower molecular weight macroinitiator in the solution, but it appeared broader in the bulk polymerization. Our results indicated that smaller molecular weight macroinitiator was more efficient and formed a block copolymer with lower PDI. Thermal analysis and microstructure of the block copolymers are investigated by ¹H NMR, FT-IR, TGA and DSC. The chain tacticity of the MMA units is found not to be sensitive to the kinetic of the reactions with two different molecular weights of macroinitiator. DSC measurement shows two different transitions at 39 and 108 °C assigned to PVAc and PMMA blocks. The TGA profile shows a three-step degradation. The initial small weight loss that occurs around 220 °C and two large weight loss around 238 and 310 °C are attributed to dechlorination step and decomposition of the PMMA and PVAc blocks.     

Preparation of poly(methyl methacrylate) macromonomer by radical polymerization in the presence of methyl α-(bromomethyl)acrylate and copolymerization of the resultant macromonomer

Radical polymerization of methyl methacrylate (MMA) in the presence of methyl -(bromomethyl) acrylate yielded poly-(MMA) bearing the 2-methoxycarbonylallyl end group through chain reaction involving bimol ecular termination. The molecular weight of the resultant polymer was effectively controlled with a small amount of the bromomethylacrylate added; the chain transfer constant was estimated to be 0.9. The poly (MMA) with the unsaturated end group (

N-(4-(N-取代氨磺酰基)苯基)-α-龙脑烯酸酰胺化合物

为了寻找天然产物基抑菌剂,以α-蒎烯(I)为原料,经环氧化和催化异构得到α-龙脑烯醛(III),进一步转化为α-龙脑烯酸(IV)和α-龙脑烯酸酰氯(V),然后与4-(N-取代氨磺酰基)苯胺类化合物发生N-酰化反应,以32.8~78.1%的收率合成得到8个N-(4-(N-取代氨磺酰基)苯基)-α-龙脑烯酸酰胺化合物VIa～VIh。采用FTIR、1HNMR、13CNMR和ESI-MS对目标产物进行结构表征。抑菌活性测试表明,在50 µg/mL质量浓度下,目标化合物显示一定的抑菌活性,其中化合物N-[4-(N-(噻唑-2-基)氨磺酰基)苯基]-α-龙脑烯酸酰胺(Ⅵe)对小麦赤霉病菌和黄瓜枯萎病菌的抑制率分别为71.3%（活性级别为B级）和68.0%（活性级别为C级）。     

Highly stereoselective epoxidation of (−)-α-pinene over chiral transition metal (salen) complexes occluded in zeolitic hosts

Various transition metal complexes of seven different salen ligands have been incorporated in specially modified zeolitic host materials. The thus immobilized sterically demanding complexes have been tested in the diastereoselective epoxidation of (–)--pinene in the liquid phase in an autoclave at room temperature and elevated pressure using O₂ as oxidant. In most cases conversions of 100% could be achieved. Best results so far – 100% conversion, 96% epoxide chemoselectivity and 91% diastereomeric excess – have been obtained in the presence of the entrapped [(R,R)-(N,N)-bis(3,5-di-tert-butylsalicylidene)-1,2-diphenylethylenediamino]cobalt(II) = Co(salen-5) complex. Computer simulations were done in order to prove that the reaction can take place inside the pore system, i.e., (–)--pinene is able to diffuse through the microporous entrances of the carrier material.     

Ring-opening polymerization of ?-caprolactone by poly(propyleneglycol) in the presence of a monomer activator

The ring-opening polymerization of ?-caprolactone (CL) was induced by using polypropylene glycol (PPG) as an initiator in the presence of the monomer activator HCl·Et₂O to synthesize triblock copolymers composed of PPG and poly(?-caprolactone) (PCL). The degree of CL conversion and the molecular weight of PCL increased linearly with the polymerization time or with the feed ratio of CL to PPG in the presence of HCl·Et₂O in CH₂Cl₂ at 25 °C. The PCLs obtained had molecular weights close to the theoretical values calculated from the CL:PPG molar ratios and exhibited monomodal GPC curves with narrow polydispersity indexes. The apparent rate constant (k_app) for the polymerization of CL activated by HCl·Et₂O was greatly affected by the ratio of HCl·Et₂O/PPG. The activation energy for the polymerization of CL in this system was estimated to be 49.8 kJ/mol K. We successfully prepared PPG and PCL triblock copolymers using this activated monomer mechanism.     

Preparation of single-site tin(IV) compounds and their use in the polymerization of ε-caprolactone

Butyltin(IV) carboxylate compounds were obtained by reactions of butyltrichlorotin(IV) with potassium pivalate, perfluoroheptanoate, methacrylate, 2,6-pyridinedicarboxylate, and phthalate. The synthesized complexes were fully characterized by nuclear magnetic resonance (¹H-, ¹³C-NMR), Fourier transform infrared (FTIR), mass spectroscopies (MS) and elemental analysis. These tin complexes were used as catalysts for the ring opening polymerization of ε-caplolactone and the conversion of monomers to polymers was completed in just 1 h. The structures of polymers were characterized by a combination of spectroscopic techniques (NMR, FTIR, MS), differential scanning calorimeter (DSC) and gel permeation chromatography. In this study, the ε-caplolactone polymers with different average molecular weights between 5000 and 40,000 Da having a regular structure were obtained.     

Controlled/“living” atom transfer radical polymerization of styrene in the synthesis of amphiphilic diblock copolymers from a poly(ethylene glycol) macroinitiator

Summary   Atom transfer radical polymerization (ATRP) of styrene was initiated by a poly(ethylene glycol) macroinitiator prepared by quantitative esterification of MPEG2000 with 2-chloropropionyl chloride. The polymerization carried out at 130°C catalyzed by addition of cuprous chloride and 2,2'-bipyridine has been found to comply to the criteria for a “living” polymerization, since a linear

N-(甲酰基吡嗪)-α-氨基酸甲酯的合成

以2,3-吡嗪二羧酸和α-氨基酸(甘氨酸、缬氨酸、亮氨酸)为原料,在氯化亚砜的作用下,采取分步法和一步法,得到不同的吡嗪酰胺类衍生物,其结构经1HNMR、13CNMR、IR和HR-MS等方法确定。探讨了不同反应条件对吡嗪酰胺类衍生物合成的影响。结果表明,在氯化亚砜的作用下,采用分步法和一步法,分别得到N-(2-羧基-3-甲酰基吡嗪)-α-氨基酸甲酯和N-(2,3-二甲酰基吡嗪)-α-氨基酸甲酯。其最优反应条件为:在分步法和一步法中,α-氨基酸甲酯盐酸盐与Et3N的摩尔比约为1∶2.1时,氨基释放完全,目标产物的收率最高;分步法2,3-吡嗪二甲酰氯盐酸盐的制备采用直接抽滤为最优方法,收率达75%以上;一步法N-(2,3-二甲酰基吡嗪)-α-氨基酸甲酯的制备中,氯化亚砜的量为6 mL时,收率最高。从整体来看,分步法的收率较高,均50%以上。     

ω-Iodinated poly(dimethylsiloxane) as a chain transfer agent in iodine transfer radical polymerization of vinyl acetate and dibutyl maleate: synthesis and structural characterization

Iodine transfer radical homo- (ITP) and copolymerization (ITCP) of vinyl acetate (VAc) with dibutyl maleate (DBM) initiated by 2,2?-azobis(isobutyronitrile) (AIBN) were performed in bulk at 80 °C in the presence of ω-iodo- terminated poly(dimethylsiloxane) (PDMS-I) as a macro-chain transfer agent (macro-CTA). ¹H-NMR and gel permeation chromatography (GPC) results confirmed formation of the PDMS-b-PVAc diblock copolymer. Moreover, the results of ¹H-NMR showed that the iodo-terminated chain ends are unstable and decompose to the aldehyde moieties. On the other hand, different behaviour was observed in the ITCP of the VAc and DBM. ¹H-NMR and GPC results showed that presence of DBM in the reaction medium leads to degradation of the C-I bond of the PDMS-I, resulting in the generation of HI. In fact, PDMS-I acts as in situ generator of the CTA in the presence of DBM via reaction between the generated HI and VAc. In other words, it was found that P(VAc-co-DBM) copolymer chains are synthesised by ITP mechanism in the presence of in situ generated 1-iodoethyl acetate as a CTA. Therefore, a mixture of PDMS and P(VAc-co-DBM) chains was obtained.     

Hydrophobic interaction-mediated reversible adsorption–desorption of nanoparticles in the honeycomb-patterned thermoresponsive poly(N-isopropylamide) hydrogel surface

Hydrophobic interaction-mediated reversible adsorption–desorption of Ag nanoparticles in water solutions was studied in surface-tailored poly(N-isopropylacrylamide) (PNIPAAm) hydrogel film. Surface-tailoring of PNIPAAm hydrogel was performed by the preparation of the hydrogel as a honeycomb-patterned film using a honeycomb-patterned PS film as a template. The surface morphology and hydrophobic interaction of the patterned hydrogel surface were significantly altered by temperature change of the aqueous solution that came in contact with the gel. The surface of the hydrogel became hydrophobic for adsorption at a higher temperature than the lower critical solution temperature of 32 °C, but became hydrophilic with decreased adsorptivity at lower temperature condition. Adsorptivity was obtained through measuring the concentration of the silver nanoparticles using UV–vis spectroscopy in an aqueous solution. A reversible adsorption–desorption of nanoparticles dependent on the temperature in the hydrogel surface obtained in this study clearly suggested that the hydrophobic interaction was reversibly changed in the patterned temperature-responsive hydrogel surface, similar to various biological systems in nature.     

Selective Photo-epoxidation of (R)-(+)- and (S)-(−)-Limonene by Chiral and Non-Chiral Dioxo-Mo(VI) Complexes Anchored on TiO2-Nanotubes

Topics in Catalysis - Selective epoxidation of the (R) and (S) isomers of limonene by dioxomolybdenum(VI) complexes anchored covalently on TiO2 nanotubes using UV–Vis light and O2 as the...