Effect of comonomer composition on the controlled free-radical copolymerization of styrene and maleic anhydride by reversible addition-fragmentation chain transfer (RAFT)

Controlled free-radical copolymerization of styrene and maleic anhydride was performed in 1,4-dioxane or tetrahydrofurane solution at 60 °C using the RAFT technique. The effect of monomer feed ratio on copolymerization kinetics and on control over molar mass distribution was examined. It was shown that polymerization was faster and quality of control was poorer when the proportion of maleic anhydride in the monomer feed was larger. These features were assigned to a decrease in the chain transfer constant of the polymeric RAFT agent, most probably due to an increase in the apparent rate constant of propagation with the proportion of maleic anhydride.     

Polymer-layered silicate nanocomposites prepared through in situ reversible addition-fragmentation chain transfer (RAFT) polymerization

Reversible addition-fragmentation chain transfer (RAFT) polymerizations were performed in the presence of organically modified clays and successfully prepared polystyrene-, poly(methyl methacrylate)-, and poly(n-butyl acrylate)-layered silicate nanocomposites. The polymers had well-defined molecular weights and low polydispersities, as expected from RAFT polymerizations. The morphology of polystyrene-, and poly(n-butyl acrylate)-nanocomposites were found to be exfoliated using montmorillonite modified with N,N-dimethyl-n-hexadecyl-(4-vinylbenzyl) ammonium (MMT-VB16). In the case of PMMA nanocomposite, the structure was a mixture of intercalated and exfoliated when MMT-VB16 was used, while the use of montmorillonite modified with 2-methacryloyloxyethyl-hexadecyldimethyl ammonium (MMT-MA16) resulted in exfoliation.     

Cellular uptake of tailored copolymer synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization

The tailored copolymer poly(methoxy-PEG acrylate-co-N-hydroxysuccinimide-co-fluorescein diacetate 5-maleimide) (P1) and block copolymer poly(N-isopropylacrylamide)-b-poly(methoxy-PEG acrylate-co-N-hydroxysuccinimide-co-fluorescein diacetate 5-maleimide) (P2) were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization, which were both water-soluble, fluorescent and containing active group N-hydroxysuccinimide (NHS). Due to the temperature-sensitive poly(N-isopropylacrylamide) unit, the latter copolymer P2 formed nanoparticles at 37 °C in aqueous medium. Both P1 and P2 were taken up by cultured human umbilical vein endothelial cells (HUVECs) and localized mainly in the cytoplasm, which could subsequently be detected by confocal laser scanning microscopy (CLSM).     

Dispersion of calcite by poly(sodium acrylate) prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization

Calcite is dispersed into nanoparticles with the use of polysodium acrylate, PAANa. The molecular weight distribution of PAANa greatly influences the characteristics of the dispersion. Near-monodisperse PAANa adsorbs irreversibly and totally onto the CaCO₃ surface, but for polydisperse PAANa, a mass segregation occurs, where only chains with a selected molecular weight are adsorbed. With polydisperse samples, small spherical CaCO₃ particles are generated in addition to calcite crystals. This bimodal dispersion is less viscous than the dispersion containing only calcite crystals.     

The direct polymerization of 2-methacryloxyethyl glucoside via aqueous reversible addition-fragmentation chain transfer (RAFT) polymerization

A preliminary study on the direct controlled radical polymerization of a glycomonomer, namely 2-methacryloxyethyl glucoside (MAGlu), under reversible addition-fragmentation chain transfer (RAFT) polymerization conditions in aqueous media has been conducted. This represents the first example detailing the direct polymerization of a sugar monomer via RAFT and, significantly, has been conducted without protecting group chemistry. 4-Cyano-4-methyl-4-thiobenzoylsulfanyl butyric acid (CTP) was employed as the RAFT chain transfer agent (CTA) due to its inherent water-solubility and its applicability for methacrylic monomers. The homopolymerization displays all the characteristics of a controlled/‘living’ polymerization—linear increase in M_n with conversion, pseudo-first order kinetics, the final polymers have narrow molecular distributions and novel block copolymers can be prepared.     

Thermal polymerization of methyl (meth)acrylate via reversible addition-fragmentation chain transfer (RAFT) process

Thermal polymerization of methyl (meth)acrylate (MMA) was carried out using 2-cyanoprop-2-yl-1-dithionaphthalate (CPDN) and cumyl dithionaphthalenoate (CDN) as chain transfer agents. The kinetic study showed the existence of induction period and rate retardation, especially in the CDN mediated systems. The molecular weights of the polymers increased linearly with the monomer conversion, and the molecular weight distributions (M_w/M_ns) of the polymers were relatively narrow up to high conversions. The maximum number-average molecular weights (M_ns) reached to 351?900 g/mol (M_w/M_n = 1.47) and 442?400 g/mol (M_w/M_n = 1.29) in the systems mediated by CPDN and CDN, respectively. Chain-extension reactions were also successfully carried out to obtain higher molecular weight PMMA and PMMA-block-polystyrene (PMMA-b-PSt) copolymer with controlled structure and narrow M_w/M_n. Thermal polymerization of methyl acrylate (MA) in the presence of CPDN, or benzyl (2-phenyl)-1-imidazolecarbodithioate (BPIC) also demonstrated “living”/controlled features with the experimented maximum molecular weight 312?500 g/mol (M_w/M_n = 1.57). The possible initiation mechanism of the thermal polymerization was discussed.     

Synthesis of carboxylic acid functionalized nanoparticles by reversible addition-fragmentation chain transfer (RAFT) miniemulsion polymerization of styrene

In this study, an addition-fragmentation chain transfer agent bearing carboxylic acid, 4-toluic acid dithiobenzoate (TADB), was used to synthesize carboxylic acid functionalized PS nanospheres via the miniemulsion polymerization. In addition, non-functionalized RAFT agent, benzyl dithiobenzoate (BDB), was also used to compare the surface properties of the PS nanoparticles. For the TADB system, the rate of polymerization was approximately two-fold faster than the BDB system, while the molecular weights and PDI of PS remain intact.With increasing the molar ratio of [TADB]/[AIBN] from 0 to 3.0, the average particle diameter is substantially increased from 90 to 126 nm. The absolute value of zeta potential and conductivity also correspondingly increase from 49.1 mV and 3.47 mS/cm to 53.9 mV and 4.21 mS/cm, respectively. The results indicate that the surface of PS nanospheres could be functionalized by means of a carboxylic acid group on the RAFT agent and the stability of the PS miniemulsion latex could be significantly improved.     

马来酸酐/苯乙烯多单体接枝低等规聚丙烯

低等规聚丙烯（LIPP）是由等规立构和间规立构组成的嵌段共聚物，具有低的结晶性能，良好的粘接性和加工性能，在胶粘剂领域有着广阔的应用前景。然而LIPP的非极性和低的机械性能限制了它的应用。本文采用溶液法，以过氧化二异丙本（DCP）为引发剂，以苯乙烯（St)作为共聚单体，将马来酸酐（MAH）接枝到低等规聚丙烯（LIPP）大分子链上，采用化学滴定法测定产物（LIPP－g-MAH-St)的接枝率（GR），并系统地研究了加料方式，单体用量，引发剂用量，反应时间等因素对GR的影响，结果表明，采用先加入引发剂的加料方式有利于马来酸酐对低等规聚丙烯的接枝反应，反应的最佳条件是：反应时间7h，MAH的加入量为9份（以100份LIPP计），引发剂DCP的加入量为0．45份。     

Microwave radiation copolymerization in solid state of maleic anhydride and allylthiourea

Microwave radiation copolymerization of maleic anhydride and allylthiourea was studied in solid state. Composition of the monomer feed and the power and time of microwave radiation on conversion and intrinsic viscosity were discussed. Reactivity ratios for maleic anhydride and allylthiourea were also determined. Values of r₁ and r₂ were 0.875 and 0.650 for maleic anhydride and allylthiourea, respectively. The copolymer can be used as soluble macromolecular complexing agents for metal ions. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1563–1566, 1998     

New chain transfer agents for reversible addition-fragmentation chain transfer (RAFT) polymerisation in aqueous solution

New chain transfer agents for free radical polymerisation via reversible addition-fragmentation chain transfer (RAFT) were synthesised that are particularly suited for aqueous solution polymerisation. The new compounds bear dithioester and trithiocarbonate moieties as well as permanently ionic groups to confer solubility in water. Their stability against hydrolysis was studied, and compared with the one of a frequently employed water-soluble RAFT agent, using UV-Vis-spectroscopy and ¹H-NMR measurements. An improved resistance to hydrolysis was found for the new RAFT agents compared to the reference one, providing good stabilities in the pH range between 1 and 8, and up to temperatures of 70 °C.     

Preparation and characterization of poly(styrene)/metal composites via reversible addition-fragmentation chain transfer (RAFT) polymerization

The expectant dithiocarbamate group end-functional poly(styrene) (PS) with a controlled molecular weight and low molecular weight distribution was synthesized conveniently via reversible addition-fragmentation chain transfer (RAFT) polymerization and was used to prepare polymer/metal composites with coordination chemistry. By the self-assembly technique, PS coordinated with the rare earth metal in N,N-dimethylformamide (DMF) to generate the fluorescent Eu–PS and Sm–PS complexes. Furthermore, PS-coated spherical silver nanoparticles (AgNPs) were prepared by reducing Ag⁺ to Ag⁰ under ultrasound irradiation in the presence of DMF and H₂O. The well core/shell structure of the AgNPs was characterized by transmission electron microscopy (TEM).     

Characterization of pH-dependent micellization of polystyrene-based cationic block copolymers prepared by reversible addition-fragmentation chain transfer (RAFT) radical polymerization

A series of block copolymers composed of a fixed length of an (ar-vinylbenzyl)trimethylammonium chloride (Q) block (the number average degree of polymerization of the Q block, DP_n,Q=57) and varying lengths of an N,N-dimethylvinylbenzylamine (A) block (the number average degrees of polymerization of the A blocks, DP_n,A, ranging 11-50) were prepared by reversible addition-fragmentation chain transfer (RAFT) radical polymerization, and their pH-dependent micellization was characterized by potentiometric titration, ¹H NMR spectroscopy, dynamic and static light scattering, and fluorescence techniques as a function of the A block length. At pH<5.5, the A block is fully protonated, and hence the block copolymers act as a simple polyelectrolyte, dissolving molecularly in acidic water. At pH>7, the A block becomes deprotonated, and thereby the block copolymers aggregate into a micelle composed of hydrophobic microdomains formed from the deprotonated A blocks. Results of light scattering and fluorescence measurements indicated that the micellization behavior depended strongly on the length of the A block. The number of polymer chains comprising one micelle (i.e. mean aggregation number, N_agg) increased from 3 to 12 as DP_n,A increased from 11 to 50 at pH 10.0. In the case of a random copolymer of Q and A with an A/Q molar ratio similar to that of a block copolymer with DP_n,A=50, N_agg∼1 (i.e. unimolecular micelle) was confirmed by static light scattering at pH 10.0.     

Recycling of polycarbonate by blending with maleic anhydride grafted ABS

Recycling of used polycarbonate (PC) was conducted via melt blending with maleic anhydride grafted ABS (ABS-g-MA) using a twin-screw extruder. The toughness of waste PC was greatly improved through the modification of ABS-g-MA. The toughening mechanism was explored based on the morphology of the blends. The grafting of MA onto ABS was considered a key factor, which resulted in a special morphology of ABS domains dispersed in PC matrix. At a certain PC/ABS-g-MA weight ratio, the ABS domains connected together forming a network and gave rise to a maximum of the notched impact strength.     

Novel W(II) complexes for reversible addition-fragmentation chain transfer (RAFT) polymerizations

Alkylation of the phosphorus coordination of the diphenyl(dithioformato)phosphine ligand in [W(CO)₅(PPh₂CS₂)]NEt₄ (1) at the S atom results in the formation of the novel RAFT agent S═C[W(CO)₅PPh₂]S–R (2a, R = CH₂Ph; 2b, R = CH₂CH═CH₂). These compounds have been shown to be highly effective in reversible addition-fragmentation chain transfer (RAFT) polymerization to produce polymers (homopolymer and diblock copolymer) of predetermined molecular weight and narrow polydispersity (< 1.3). Electron-withdrawing organometallic substituents can increase the activity of RAFT agents. To the best of our knowledge, this is the first report of their use as RAFT agents in polymerization.     

苯乙烯可逆加成-断裂链转移聚合动力学

为了实现可逆加成-断裂链转移(RAFT)聚合过程中,苯乙烯均聚、高分子量聚苯乙烯的合成及苯乙烯与其他单体共聚时,对苯乙烯转化率、共聚时组成和分子量大小的控制,进行了二硫代苯乙酸-1-苯基乙酯(PEPDTA)调控苯乙烯本体和细乳液聚合动力学分析。在本体聚合中,反应速率慢,链增长自由基与中间态自由基的终止反应对聚合速率影响较小,很难合成窄分布、高转化率、高分子量的聚苯乙烯;在细乳液聚合中,反应速率快、转化率高,随着PEPDTA含量增加,乳胶粒数量减少、粒径分布变宽,诱导期和缓聚现象明显;聚合物的数均分子量随转化率线性增长,RAFT试剂浓度越高,分子量分布越窄,反应时间越长,分布越宽。以Smith-Ewart方程为基础,建立了苯乙烯RAFT细乳液聚合动力学模型,模型动力学曲线与实验数据相符合,能较好地预测实验过程。     

Living radical dispersion photopolymerization of styrene by a reversible addition-fragmentation chain transfer (RAFT) agent

In this study, an addition-fragmentation chain transfer agent bearing dithioester group is synthesized and applied to conventional dispersion photopolymerization of styrene in ethanol medium in the presence of poly(N-vinylpyrrolidone) stabilizer with varying amounts of the RAFT agent and optionally with conventional initiator, azobisisobutyronitril (AIBN) at various temperatures. Monomer conversion, molecular weight evolution, polydispersity index (PDI), and final particle sizes are measured. The PDI of the formed polymer is between 1.5 and 2.5 in the presence of RAFT agent. Higher concentration of RAFT agent or elevated temperature leads to the acceleration of the polymerization rate resulting in fast conversion, and reducing molecular weight and PDI. Stable polystyrene beads above 1 μm in diameter are successfully prepared by means of RAFT method applied in dispersion polymerization. The weight average particle sizes are between 1.08 and 2.04 μm, and the uniformity (D_w/D_n) is ranged from 1.26 to 2.51.     

二釜串联连续本体法制备SMA

用二釜串联连续本体工艺制备苯乙烯-顺丁烯二酸酐无规共聚物,分别研究并获得了首釜和第二釜的启动操作策略和稳态工艺条件。     

Reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene in the presence of oxygen

Reversible addition-fragmentation chain transfer polymerization (RAFT) of styrene (St) was carried out in the presence of oxygen using 2-cyanoprop-2-yl 1-dithionaphthalate (CPDN) or benzyl (2-phenyl)-1-imidazolecarbodithioate (BPIC) as the RAFT agent. The characteristics of the “living”/controlled radical polymerization were observed at high concentration of RAFT agent and low polymerization temperature. A slight increase in the rate of polymerization was found when oxygen was added at high concentration to the polymerization system; however, the presence of oxygen incurred greater polydispersities of the polymer at the same monomer conversion compared to that obtained in the absence of oxygen. The possible mechanism of the RAFT polymerization of St in the presence of oxygen was discussed.     

Synthetic method of polyethylene-poly(methylmethacrylate) (PE-PMMA) polymer hybrid via reversible addition-fragmentation chain transfer (RAFT) polymerization with functionalized polyethylene

Summary Polyethylene-poly(methylmethacrylate) (PE-PMMA) polymer hybrid was synthesized via RAFT polymerization of MMA with PE chain transfer agent (PE-CTA) for the first time. The structure of PE-CTA produced by sequential functionalization of terminally hydroxylated PE was confirmed by ¹H NMR and FT-IR analyses. The results of GPC after MMA polymerization revealed that the molecular weight (M_w) of the resulting polymers increased compared with the one of the PE-CTA. ¹H NMR analysis of resulting polymers confirmed that the amounts of PMMA segments were in a range of 7.8 and 23 wt %. TEM images indicated the nanometer level microphase-separation morphology between the PE segment and PMMA segment.     

Kinetics study of living microemulsion polymerization mediated by reversible addition-fragmentation chain transfer

The present work focuses on the development of functional polyurethane hybrids through the incorporation of surface modified TiO₂ nanoparticles. For improving the nano-particle dispersion and increasing possible interactions between nano-particles and polyurethane matrix, the surface of the nano-particles was modified with 1,3,5-triazine core silane coupling agent. The surface modification of nanoparticles was confirmed by FESEM, FT-IR and Raman spectroscopic techniques. The functionalized nanoparticles were then inscribed in 0, 1 and 2 weight percentages into polyurethane matrix. The as prepared composite coatings were investigated for various anti-microbial, thermo-mechanical and anticorrosive properties. The tensile strength of polyurethane was improved by 300 % upon addition of 2 wt% of modified TiO₂ nanoparticles as compared to neat polyurethane. Fog test and electrochemical polarization studies suggest that the corrosion resistance increases with increase of the modified TiO₂ content in the coating formulation. The composite coatings also have good resistance towards various bacterial and fungal stains as compared to the pure polyurethanes. The coatings substantially gain hydrophilic nature symbiotically with TiO₂ content suggesting its potential application as self-cleanable material.