Novel synthesis of branched polystyrenes by quasi‐living radical copolymerization using photofunctional inimer

Branched polystyrenes were prepared by quasi‐living radical copolymerization of N,N‐diethylaminodithiocarbamoylmethylstyrene (inimer: DTCS) with styrene under UV irradiation. DTCS monomers play an important role in this copolymerization system as an inimer capable of initiating living radical polymerization of the vinyl group. Two monomers (DTCS and styrene) showed equal reactivity toward both propagating species, and the copolymer composition was the same as the comonomer feed. This result means that both the branching and chain length of the hyperbranched molecules can be controlled statistically by the feed monomer ratios. The compact nature of the branched macromolecules is demonstrated by viscosity measurements compared to the linear analogues. © 2001 Society of Chemical Industry     

Controlled radical polymerization of p-(iodomethyl)styrene—a route to branched and star-like structures

p-(Iodomethyl)styrene was polymerized under the action of a radical initiator (AIBN). The polymerization proceeds with degenerative chain transfer and leads to well defined branched polymers with functional primary and secondary iodomethyl groups as revealed by NMR studies. The obtained polymer can be further used as macroinitiator for radical polymerization of styrene. This polymerization proceeds in controlled way to polystyrene star polymers with reactive groups at the end of their arms. The characterization of branched and star structures was performed by NMR and GPC with absolute molar mass detection (MALLS).     

Formation of a soluble hyperbranched polymer via initiator–fragment incorporation radical copolymerization of divinyl adipate and isobutyl vinyl ether

The copolymerization of divinyl adipate (DVA) with isobutyl vinyl ether (IBVE) was conducted at 70 and 80 °C in benzene using azobisisobutyronitrile (AIBN), at a concentration as high as 0.50 mol l^?1 as the initiator, where the concentrations of DVA and IBVE were 0.40 and 0.60 mol l^?1, respectively. The copolymerization proceeded homogeneously, without any gelation, to yield soluble copolymers in spite of the high molar ratio of DVA as an excellent cross‐linker for IBVE. The copolymer yield increased with time, and the number‐average molecular weight (M_n = 0.9–2.4 × 10⁴ g mol^?1) from gel permeation chromatography (GPC) and molecular weight distribution (M_w/M_n = 1.5–7.6) of the resulting copolymer increased with copolymer yield. The cyanopropyl group, as a fragment of AIBN, was incorporated as a main constituent in the copolymer, the fraction of which increased from ca 10 to ca 20 % with copolymer yield, hence indicating that the copolymerization is an initiator–fragment incorporation radical polymerization. The copolymers also contained IBVE units (10–30 %) and DVA units with intact double bond (8–36 %) and without double bond (45 %). The intrinsic viscosity of the copolymer was very low (0.1 dl g^?1) at 30 °C in tetrahydrofuran. The results from GPC–multi‐angle laser light scattering (MALLS), transmission electron microscopy (TEM) and MALLS revealed that individual copolymer molecules were formed as hyperbranched nanoparticles. Copyright © 2004 Society of Chemical Industry     

Initiator‐fragment incorporation radical polymerization of ethylene glycol dimethacrylate in the presence of 1,1‐diphenylethylene: synthesis and characterization of soluble hyperbranched polymer nanoparticles

The polymerization of ethylene glycol dimethacrylate (EGDMA) as crosslinker was carried out at 70 and 80 °C in benzene using dimethyl 2,2′‐azobisisobutyrate (MAIB) as initiator at concentrations as high as 0.50–0.70 mol l^?1 in the presence of 1,1‐diphenylethylene (DPE), where the concentrations of EGDMA and DPE were 0.50–0.70 and 0.25–0.50 mol l^?1, respectively. The polymerization proceeded homogeneously, without gelation, to give soluble polymers. The yield and molecular weight of the resulting polymers increased with time. The homogeneous polymerization system involved ESR‐observable DPE‐derived radicals of considerably high concentration (3.6–5.3 × 10^?5 mol l^?1). The methoxycarbonylpropyl groups as MAIB‐fragments were incorporated as a main constituent (35–50 mol%) into the polymers (initiator‐fragment incorporation radical polymerization). The polymers also contained DPE units (15 mol%) and EGDMA units with double bonds (10–25 mol%) and without double bonds (20 mol%). Results from gel permeation chromatography (GPC)–multiangle laser light scattering (MALLS), transmission electron microscopy (TEM) and viscometric measurements revealed that the individual polymer molecules were formed as hyperbranched nanoparticles. Copyright © 2004 Society of Chemical Industry     

RAFT polymerization and thiol-ene modification of 2-vinyloxyethyl methacrylate: Towards functional branched polymers

A vinyl functional polymer, viz, poly(vinyloxyethyl methacrylate) (poly(VEMA) was synthesized by the RAFT polymerization of an asymmetric divinyl monomer, VEMA. This polymer, with pendant vinyloxyl groups, was subsequently reacted with three thiol compounds; 2-mercaptoethanol, cysteamine and 3-mercaptoproponic acid via the thiol-ene reactions. The resulting branched polymers contained hydroxyl, amino and carboxylic acid functionalities suitable for further reactions and conjugations.     

Preparation of branched polyacrylonitrile through self‐condensing vinyl copolymerization

Branched polyacrylonitrile (PAN) was prepared through a self‐condensing vinyl copolymerization of acrylonitrile and 2‐(2‐bromopropionyloxy)ethyl acrylate (BPEA). The branched architecture of the product was confirmed by NMR spectra and the average degree of branching (DB ) was estimated. Through a comparison of the intrinsic viscosity of the product with that of its linear analogue, the contraction factor g′ was calculated. It was found that the viscosity of the branched PAN was obviously lower that that of linear PAN. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Semibatch RAFT polymerization for branched polyacrylamide production: Effect of divinyl monomer feeding policies

Star and hyperbranched polyacrylamides (s‐PAMs and b‐PAMs) were synthesized via semibatch RAFT copolymerization of acrylamide (AM) and N,N′‐methylenebisacrylamide (BisAM) using four monomer feeding policies. The BisAM to chain transfer agent (CTA) ratios from 1 to 40 at a constant [AM]₀/[CTA]₀ of 600 were investigated at 60°C. The s‐PAMs with the number of arms of 1.4–12.8 and 1.8–8.4 were, respectively, produced by arm‐first (AF) and core‐first (CF) approaches, whereas the b‐PAMs having the branching density of 1.34–13.1C/1000Cs were synthesized by constant BisAM feeding (semibatch polymerization, SB) and batch (batch polymerization, BA). Soluble b‐PAMs were produced with the four feeding policies at [BisAM]₀/[CTA]₀ of 5. However, when the [BisAM]₀/[CTA]₀ was increased to 30, the gelation occurred with the CF and BA approaches while the AF and SB synthesized soluble branched PAMs. The AF and SB approaches appeared to be practical in producing the respective s‐PAM and b‐PAM at high [BisAM]₀/[CTA]₀ ratios or low CTA usages. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1322–1333, 2013     

Synthesis and solution properties of alternating maleimide/styrene hyperbranched copolymers via controlled radical mechanism

Copolymerizations of (N,N‐diethyldithiocarbamyl)methylstyrene (inimer: DTCS) with maleimide (MI) were carried out under UV irradiation. DTCS monomers play an important role in this copolymerization system as an inimer that is capable of initiating radical polymerization of the vinyl group. Reactivity ratios (r₁ = 0.15 and r₂ = 0) were estimated by the curve‐fitting procedure (DTCS [M₁]; MI[M₂]). These reactivities show strong alternation, and the propagating copolymer radicals proceed with homopolymerization of 1:1 complexes formed between the donor and acceptor monomers. These alternating copolymers exhibit highly branched structure and are actually hyperbranched copolymers. The compact nature of the hyperbranched molecules was demonstrated by comparison of their dilute‐solution properties with those of the linear analogues. The hyperbranched macromolecules behave as single, well‐separated molecules (even in good solvent) and as hard spheres. Copyright © 2003 Society of Chemical Industry     

End‐functional polymers,thiocarbonylthio group removal/transformation and reversible addition–fragmentation–chain transfer (RAFT) polymerization

This review focuses on processes for thiocarbonylthio group removal/transformation of polymers synthesized by radical polymerization with reversible addition‐fragmentation‐chain transfer (RAFT). A variety of processes have now been reported in this context. These include reactions with nucleophiles, radical‐induced reactions, thermolysis, electrocyclic reactions and ‘click’ processes. We also consider the use of RAFT‐synthesized polymers in the construction of block or graft copolymers, functional nanoparticles and biopolymer conjugates where transformation of the thiocarbonylthio group is an integral part of the process. This includes the use of RAFT‐synthesized polymers in other forms of radical polymerization such as atom transfer radical polymerization or nitroxide‐mediated polymerization, and the ‘switching’ of thiocarbonylthio groups to enable control over polymerization of a wider range of monomers in the RAFT process. With each process we provide information on the scope and, where known, indicate the mechanism, advantages and limitations. Copyright © 2011 Society of Chemical Industry     

Soluble hyperbranched copolymer via initiator-fragment incorporation radical copolymerization using a trivinyl monomer

The initiator-fragment incorporation radical polymerization was extended to a copolymerization system of a trivinyl monomer. The copolymerization of trimethylolpropane trimethacrylate (TMPTM) as a trivinyl monomer with α-methylstyrene (MSt) was examined at 70 and 80 °C in toluene using dimethyl 2,2′-azobisisobutyrate (MAIB) of high concentrations as initiator. When the concentrations of TMPTM, MSt and MAIB were 0.30, 0.60 and 0.50 mol/l, the copolymerization proceeded homogeneously without gelation at 80 °C to yield soluble hyperbranched copolymer in a yield of 65%. The copolymer formed for 8 h consisted of 37 mol% of the TMPTM unit, 42 mol% of the MSt unit and 21 mol% of the methoxycarbonylpropyl group as initiator-fragment, where 22% of the vinyl groups of the incorporated TMPTM units remained unreacted. The copolymer showed an upper critical solution temperature (32 °C on cooling) in a tetrahydrofuran(THF)-water [44:10 (wt/wt)]. Reflecting the hyperbranched structure, the viscosity of a copolymer solution in toluene was very low. The porous film was prepared directly by casting a THF solution of the hyperbranched copolymer on a cover glass. The copolymer molecules are radially arranged on the surface layer of the spherical pores as showed by polarized optical microscope imaging.     

An all ATRP route to PMMA-PEO-PS and PMAA-PEO-PS miktoarm ABC star terpolymer

An all Atom Transfer Radical Polymerization (ATRP) route to synthesize miktoarm ABC star terpolymer, μ-(poly(methyl methacrylate)-poly(ethylene oxide)-polystyrene) (μ-(PMMA-PEO-PS)), was demonstrated. Poly(methyl methacrylate) (PMMA) with a halide end group was first prepared by ATRP of MMA. It was then activated under ATRP conditions at 30 °C to add a styrenic-terminated PEO macromonomer, resulting in the formation of PMMA-b-PEO. Finally, the active halide at the junction point of the diblock copolymer was used to initiate the ATRP of St at higher temperature. By a similar approach, μ-(poly(phenyl methacrylate)-poly(ethylene oxide)-polystyrene) (μ-(PhMA-PEO-PS)) was synthesized, hydrolysis of which in basic medium gave μ-(PMAA-PEO-PS). The polymers were characterized by ¹H NMR spectroscopy and gel permeation chromatography.     

Solution properties of hyperbranched polymers and synthetic application for amphiphilic star‐hyperbranched copolymers by grafting from hyperbranched macroinitiator

Hyperbranched polystyrenes (PS) were prepared by living radical photopolymerization of N,N‐diethyldithiocarbamoylmethylstyrene (DTCS) as an inimer under UV irradiation. Branched PS with an average chain length between branching points of four styrene units was also prepared by living radical copolymerization of DTCS with styrene. The ratio of radius of gyration to hydrodynamic radius R_G/R_H for these hyperbranched polymers was in the range 0.82–0.89 in toluene. The translational diffusion coefficient D(C) showed a constant value in the range of 0–14 × 10^?3 g ml^?1 in toluene. It was found from these dilute solution properties that hyperbranched PSs formed a unimolecular structure even in a good solvent because of their compact nature. These hyperbranched PSs exhibited large amounts of photofunctional carbamate (DC) groups on their outside surfaces. Subsequently, we derived amphiphilic star‐hyperbranched copolymers by grafting from hyperbranched macroinitiator with 1‐vinyl‐2‐pyrrolidinone. These star‐hyperbranched copolymers were soluble in water and methanol. © 2001 Society of Chemical Industry     

原子转移自由基聚合合成支化聚丙烯腈

以二乙烯苯为支化单体,α-溴代异丁酸叔丁酯为引发剂,CuBr和2,2'-联吡啶为催化体系,利用本体和溶液原子转移自由基聚合合成了支化聚丙烯腈.采用核磁共振谱仪、凝胶渗透色谱仪和多角度激光光散射仪等测试了聚合物结构、相对分子质量及其分布.用无水乙酸钠对支化聚丙烯腈进行末端改性,得到了在硫氰酸钠水溶液中性能稳定、可长期保存的支化聚丙烯腈,而改性对聚合物的耐热性能没有影响.     

Novel synthesis and solution properties of hyperbranched poly(ethyl methacrylate)s by quasi‐living radical copolymerization using photofunctional inimer

Hyperbranched poly(ethyl methacrylate)s (PEMA) were prepared by quasi‐living radical copolymerization of 2‐(N,N‐diethylaminodithiocarbamoyl)‐ethyl methacrylate (inimer: DTEM) with ethyl methacrylate (EMA) under UV irradiation. DTEM monomers play an important role in this copolymerization system as inimers capable of initiating living radical polymerization of the vinyl group. Two monomers (DTEM and EMA) showed almost equal reactivity toward both propagating species, and the copolymer composition was the same as the comonomer feed. This result means that both the branching and chain length of the hyperbranched molecules can be controlled statistically by the feed monomer ratios. The compact nature of the hyperbranched macromolecules is demonstrated by comparison of their solution properties with the linear analogues. Copyright © 2004 Society of Chemical Industry     

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.     

Using controlled radical polymerisation techniques for the synthesis of functional polymers containing amino acid moieties

There is great current interest in bridging the gap between robust synthetic polymers and complex biological polymers to allow for the preparation of novel functional, well‐defined, biocompatible and tailorable materials. In this mini‐review recent reports on the preparation of functional amino acid polymers using controlled radical polymerisation techniques are discussed. The future potential applications of these materials as well as the proposed further directions in the field are also highlighted. Copyright © 2010 Society of Chemical Industry     

Controlled radical copolymerization of vinyl acetate and dibutyl maleate by iodine transfer radical polymerization

Iodine transfer radical homo‐ and copolymerization of vinyl acetate (VAc) with dibutyl maleate (DBM) were carried out in the presence of ethyl iodoacetate (EtIAc) and 2,2′‐azobis(isobutyronitrile) (AIBN) as chain transfer agent and initiator, respectively, at 60 °C. Molecular weight and its distribution and (co)polymer structure (i.e. copolymer composition and chain end groups) were analysed using gel permeation chromatography and ¹H NMR spectroscopy, respectively. Homo‐ and copolymerization reactions proceed via a controlled characteristic with predetermined molecular weight and relatively narrow molecular weight distribution. The presence of DBM in the reaction mixture decreases the consumption rate of EtIAc as well as the polymerization rate. This is attributed to the effect of DBM on the transfer constant to the EtIAc and probably on the iodine exchange rate constant between the growing chains. The effect of the concentration of AIBN, EtIAc and overall monomers on the conversion, molecular weight and its distribution was studied. Simultaneously high conversion and molecular weight with a relatively narrow molecular weight distribution can be achieved only when equimolar and intermediate concentration of EtIAc and AIBN is used in the reaction mixture. End‐group analysis by ¹H NMR reveals that iodinated VAc end groups in the (co)polymer chains are unstable, resulting in aldehyde end groups. Thermogravimetric analysis shows that the thermal stability of the VAc‐based polymer increases on incorporating DBM units into the copolymer chains. © 2013 Society of Chemical Industry     

A replicated investigation of nitroxide‐mediated radical polymerization of styrene over a range of reaction conditions

A comprehensive experimental investigation of nitroxide‐mediated radical polymerization (NMRP) of styrene using 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO) as controller is presented. Polymerizations with a bimolecular initiator (benzoyl peroxide; BPO) were carried out at 120 and 130°C, with TEMPO/BPO molar ratios ranging from 0.9 to 1.5. Results indicate that increasing temperature increases the rate of polymerization while the decrease in molecular weights is only slight. It was also observed that increasing the ratio of TEMPO/BPO decreased both the rate of polymerization and molecular weights. Probably for the first time in the history of such investigations, the paper contains a comprehensive database, appropriate for parameter estimation in aid of future modelling studies, since it comes from a systematic data collection containing independent replication.