Preparation and Characterization of Anthracene End-Capped Polystyrene via Reversible Addition-Fragmentation Chain Transfer Polymerization

Summary A novel benzodithioate compound with an anthracene structure (anthracen-9-ylmethyl benzodithioate, AMB) was synthesized. Using AMB as the chain transfer agent, the RAFT polymerizations of styrene with AIBN as an initiator were carried out in difference reaction conditions. The polymerization results showed that AMB was an effective RAFT agent for the RAFT polymerizations of styrene with the characteristics of “living”/controlled free radical polymerization. The structure of the obtained polymers was characterized by ¹H NMR. The results showed that the polymers contained an anthrancene moiety of AMB in the end and showed enhanced fluorescence property than AMB in DMF solution. The chain extension experiments of the obtained polymer with two different monomers (styrene and methyl acrylate) were successfully carried out.     

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.     

Synthesis of polystyrene end-capped with pyrene via reversible addition-fragmentation chain transfer polymerization

A novel benzodithioate compound with a pyrene structure in the R group, pyrenylmethyl benzodithioate (PMB) was synthesized. Using PMB as the chain transfer agent (CTA), the RAFT polymerizations of styrene with AIBN as an initiator were carried out in different reaction conditions. The results indicated that PMB was an effective CTA for the RAFT polymerizations of styrene with the “living”/controlled characteristics. The structures of the obtained polymers were characterized by ¹H NMR. The results showed that majority of the polymer chains contained the pyrene moiety in the chain end. The enhanced fluorescence property in CHCl₃ solution was observed. The chain-extension experiments of the obtained polystyrene (PS) with the monomers of styrene and methyl acrylate were successfully carried out.     

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.     

(S)-2-(ethyl propionate)-(O-ethyl xanthate)- and (S)-2-(Ethyl isobutyrate)-(O-ethyl xanthate)-mediated RAFT polymerization of vinyl acetate

(S)-2-(Ethyl propionate)-(O-ethyl xanthate) (X1) and (S)-2-(Ethyl isobutyrate)-(O-ethyl xanthate) (X2) were used as the reversible addition-fragmentation chain transfer (RAFT) agents for the radical polymerization of vinyl acetate (VAc). The former showed the better chain transfer ability in the polymerization at 60°C. Kinetic study with both RAFT agents showed pseudo-first order kinetics up to around 85% monomer conversion. Molecular weight of the resulting polymer increased linearly with increase in the monomer conversion up to around 85%. The observed molecular weights calculated from ¹H-NMR spectrum [M_n(NMR)] are close to the corresponding theoretical molecular weights [M_n(theor)]. The corresponding polydispersity index (PDI) of the resulting polymers remained almost constant at around 1.2 up to ∼ 65% monomer conversion and then increased gradually with the further increase in the monomer conversion. Chain-end analysis of the resulting polymers by ¹H-NMR showed clearly that polymerization started with the radical forming out of the xanthate mediator. The negligible homo-chain extension and the hetero-chain extension involving synthesis of poly(VAc)-b-poly(NVP) diblock copolymer were occurred. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis of 1,3‐benzodioxole end‐functionalized polymers via reversible addition–fragmentation chain transfer polymerization

Reversible addition–fragmentation chain transfer (RAFT) polymerization of styrene was carried out in the presence of a novel RAFT reagent, bearing 1,3‐benzodioxole group, benzo [1,3]dioxole‐5‐carbodithioic acid benzo [1,3]dioxol‐5‐ylmethyl ester (BDCB), to prepare end‐functionalized polystyrene. The polymerization results showed that RAFT polymerization of styrene could be well controlled. Number–average molecular weight (M_n(GPC)) increased linearly with monomer conversion, and molecular weight distributions were narrow (M_w/M_n < 1.4). The successful reaction of chain extension and analysis of ¹H NMR spectra confirmed the existence of the functional 1,3‐benzodioxole group at the chain‐end of polystyrene. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3535–3539, 2006     

Preparation of star polymers based on polystyrene or poly(styrene-b-N-isopropyl acrylamide) and divinylbenzene via reversible addition-fragmentation chain transfer polymerization

Star polymers based on styrene/divinyl benzene (St/DVB) and PSt-b-poly(N-isopropyl acrylamide) (NIPAAM)/DVB have been successively prepared by ‘arm-first’ method via reversible addition-fragmentation chain transfer (RAFT) polymerization. The linear macro RAFT agent PSt-SC(S)Ph was prepared by RAFT polymerization of St using benzyl dithiobenzoate and AIBN as RAFT agent and initiator. Successive RAFT polymerization of NIPAAM with PSt-SC(S)Ph as macro RAFT agent to afford diblock copolymer, PSt-b-PNIPAAM-SC(S)Ph. The coupling reactions of PSt-SC(S)Ph or PSt-b-PNIPAAM-SC(S)Ph in the presence of DVB produced the star copolymers, C(PSt)_n or C(PSt-b-PNIPAAM)_n. The molar ratio of DVB/PSt-SC(S)Ph and polymerization time influenced the yields, molecular weight and distribution of the star-shaped polymers, which was characterized by ¹H NMR and IR spectra, GPC measurements as well as DLS.     

Preparation of nano-TiO2/polyurethane emulsions via in situ RAFT polymerization

Stable nano-TiO₂/polyurethane (PU) emulsions were prepared via in situ reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization of 2-hydroxyethyl acrylate (HEA)-capped PU macromonomer, using azobisisobutyronitrile (AIBN) as a radical initiator and 2-{[(butylsulfanyl)carbonothioyl]sulfanyl} propanoic acid (BCSPA) anchored onto TiO₂ nanoparticles (TiO₂-BCSPA) as a RAFT agent. When the molar ratio of AIBN to TiO₂-BCSPA was changed from 1:3 to 1:10, the polydispersity index (PDI) of polymers in the emulsions decreased from 1.83 to 1.06, due to more effective RAFT polymerization in the emulsions. The TiO₂ nanofillers were well-dispersed throughout the polymer films. The tensile strengths of the nanocomposite films were significantly enhanced due to coordination bonding between the TiO₂ nanofillers and the –COOH end groups of the polymers, as evidenced by the FT-IR spectral data.     

Reversible addition-fragmentation chain transfer polymerization of 7-(4-(acryloyloxy)butoxy)coumarin

The light sensitive vinyl monomer with coumarin unit, 7-(4-(acryloyloxy)butoxy)coumarin (7AC), was synthesized. The reversible addition-fragmentation chain transfer (RAFT) polymerization of 7AC, initiated by 2,2′-azobisisobutyronitrile (AIBN), was carried out using 2-cyanoprop-2-yl dithiobenzoate (CPDB) as a RAFT agent in N,N-dimethylformamide (DMF) solution. The kinetics exhibited first-order relationship with respect to the monomer concentration. The molecular weight of the polymer increased linearly with the monomer conversion. The chain extension of poly(7-(4-(acryloyloxy)butoxy)coumarin) (P7AC) using styrene (St) as the second monomer demonstrated that the obtained polymers were almost “living”. The fluorescence intensity of P7AC increased with the molecular weight of P7AC and was stronger than that of the monomer. The obtained polymer had strong ultraviolet (UV) absorption at 322 nm. The molecular weights of the polymer had no effect on its ultraviolet absorption intensity. The coumarin structure existing in P7AC underwent [2 + 2] cycloaddition reaction (photodimerization) under UV irradiation in tetrahydrofuran (THF) solution, which can be further used to prepare small particles from the single polymer.     

Synthesis and Characterizations of Triphenylamine End-Functionalized Polymers via Reversible Addition-Fragmentation Chain Transfer Polymerization

A novel reversible addition-fragmentation chain transfer (RAFT) reagent bearing triphenylamine (TPA) group, 4-diphenylamino-dithiobenzoic acid benzyl ester (DDABE), was designed and synthesized. It was used in the RAFT polymerizations of styrene (St) and methyl acrylate (MA) to prepare end-functionalized polymers. The results of the polymerization showed that the RAFT polymerizations could be well controlled using DDABE as the RAFT agent. Number-average molecular weight (M_n,GPC) increased linearly with monomer conversion, and molecular weight distributions were relatively narrow (PDI< 1.50). The results of chain-extension reaction, ¹H NMR spectra and UV/Vis spectra confirmed that most of the polymers chains were end-capped by the functional triphenylamine (TPA) groups. The effect of feed molar ratios of St/DDABE/AIBN on polymerization was investigated.     

“Living”/controlled polymerization of methyl acrylate mediated by dithiocarbamates under γ‐ray irradiation

γ‐Ray initiated reversible addition–fragmentation chain transfer (RAFT) polymerizations of methyl acrylate (MA) were investigated in bulk using five different dithiocarbamate structures, 2‐phenyl‐benzoimidazole‐1‐carbodithioic acid benzyl ester ( 1b ), 2‐methyl‐benzoimidazole‐1‐carbodithioic acid benzyl ester ( 1c ), 2‐pheny‐indole‐1‐cardithioic acid benzyl ester ( 1d ), 2‐(carbazole‐9‐carbothioylsulfanyl)‐2‐methyl‐propionic acid ester ( 1e ), and carbazole‐9‐carbodithioic acid naphthalene‐1‐ylmethyl ester ( 1f ), as RAFT agents. The experiment results showed that MA polymerized in a controlled way under a low irradiation dose rate, i.e., first‐order kinetic plots, the experimental molecular weights increased linearly with monomer conversions. The polydispersity indices of polymers generally remained at a relatively low value (lower than 1.4). The effect of irradiation dose on the polymerization results was investigated. The obtained polymers were characterized with ¹H NMR and GPC. Chain‐extension reaction was also successfully carried out using the obtained polymer as the macro‐RAFT agent and styrene as the second monomer. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1769–1775, 2007     

Synthesis of alkyne‐terminated xanthate RAFT agents and their uses for the controlled radical polymerization of N‐vinylpyrrolidone and the synthesis of its block copolymer using click chemistry

Two new alkyne‐terminated xanthate reversible addition‐fragmentation chain‐transfer (RAFT) agents: (S)‐2‐(Propynyl propionate)‐(O‐ethyl xanthate) (X₃) and (S)‐2‐(Propynyl isobutyrate)‐(O‐ethyl xanthate) (X₄) were synthesized and characterized and used for the controlled radical polymerization of N‐vinylpyrrolidone (NVP). X₃ showed better chain transfer ability in the polymerization at 60°C. Molecular weight of the resulted polymer increased linearly with the increase in monomer loading. Kinetics study with X₃ showed the pseudo‐first order kinetics up to 67% monomer conversion. Molecular weight (M_n) of the resulting polymer increased linearly with the increase in the monomer conversion up to around 67%. With the increase in the monomer conversion, polydispersity of the corresponding poly(NVP)s initially decreased from 1.34 to 1.32 and then increased gradually to 1.58. Chain‐end analysis of the resulting polymer by ¹H‐NMR and FTIR showed clearly that polymerization started with radical forming out of xanthate RAFT agent. Living nature of the polymerization was also confirmed from the successful homo‐chain extension experiment and the hetero‐chain extension experiment involving synthesis of poly(NVP)‐b‐polystyrene amphiphilic diblock copolymer. Formed alkyne‐terminated poly(NVP) also allowed easy conjugation to azide‐terminated polystyrene by click chemistry to prepare well‐defined poly(NVP)‐b‐polystyrene block copolymers. Resulting polymers were characterized by GPC, ¹H‐NMR, FTIR, and thermal study. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthesis and self-assembly behaviors of three-armed amphiphilic block copolymers via RAFT polymerization

The novel trifunctional reversible addition-fragmentation chain transfer (RAFT) agent, tris(1-phenylethyl) 1,3,5-triazine-2,4,6-triyl trithiocarbonate (TTA), was synthesized and used to prepare the three-armed polystyrene (PS₃) via RAFT polymerization of styrene (St) in bulk with thermal initiation. The polymerization kinetic plot was first order and the molecular weights of polymers increased with the monomer conversions with narrow molecular weight distributions (M_w/M_n ≤ 1.23). The number of arms of the star PS was analyzed by gel permeation chromatography (GPC), ultraviolet visible (UV-vis) and fluorescence spectra. Furthermore, poly(styrene-b-N-isopropylacrylamide)₃ (PS-b-PNIPAAM)₃, the three-armed amphiphilic thermosensitive block copolymer, with controlled molecular weight and well-defined structure was also successfully prepared via RAFT chain extension method using the three-armed PS obtained as the macro-RAFT agent and N-isopropylacrylamide as the second monomer. The copolymers obtained were characterized by GPC and ¹H nuclear magnetic resonance (NMR) spectra. The self-assembly behaviors of the three-armed amphiphilic block copolymers (PS-b-PNIPAAM)₃ in mixed solution (DMF/CH₃OH) were also investigated by high performance particle sizer (HPPS) and transmission electron microscopy (TEM). Interestingly, the lower critical solution temperature (LCST) of aqueous solutions of the three-armed amphiphilic block copolymers (PS-b-PNIPAAM)₃ decreased with the increase of relative length of PS in the block copolymers.     

Grafted polytriphenylamines synthesized by atom transfer radical polymerization in tandem with oxidative polycondensation

Arylamine polymers are among the most studied conducting polymers due to a whole range of interesting properties and applications. In this paper, we describe the synthesis of soluble and processable electroactive poly(triphenylamine-g-oligostyrene) by two polymerization methods in tandem. In the first step, oligostyrene macromonomers with well-defined molecular weight, polydispersity and chain-end functionality were obtained by radical-controlled polymerization (i.e., atom transfer radical polymerization, ATRP) of styrene. The styrene oligomerization was carried out using a new triphenylamine-based initiator, [4-(diphenylamino)benzyl 2-bromo-2-methylpropanoate], cuprous bromide as co-initiator and bipyridine as ligand, at 100 °C, in bulk. Using two feed molar ratios of components: [styrene]₀:[initiator]₀:[CuBr]₀:[bipyridine]₀, two macromonomers with M _n = 9,900; M _w/M _n = 1.25 and M _n = 3,460; M _w/M _n = 1.22, respectively, were synthesized. The presence of triphenylamine moiety at one end of the macromonomer allowed the chemical and electrochemical polymerization of macromonomers to polytriphenylamine brushes having short oligostyrene grafts in every structural unit. The oligostyrene substituents confer processability and good solubility in common organic solvent characteristics for polystyrene while preserving the optoelectronic properties of arylamine-conjugated main chain. The chemical oxidative polymerization of macromonomer was carried out using iron (III) chloride dissolved in nitrobenzene. The redox behavior of the initiator, macromonomer and graft polymer was investigated by cyclic voltammetry. In all cases, it was observed that the reversible oxido-reduction of arylamine sites was accompanied by irreversible oxidative electropolymerization by free-para positions of triphenylamine substituents and deposition of thin films on working electrode. The structures of the initiator, macromonomers and graft copolymers were determined by Fourier transform infrared, ¹H and ¹³C NMR spectroscopy. The absorption and fluorescence spectroscopy have revealed absorption and emission maxima characteristics for triphenylamine group. DSC studies have confirmed glass transitions characteristics for styrene oligomers.     

Synthesis and characterization of novel copolymer containing pyridylazo-2-naphthoxyl group via reversible addition–fragmentation chain transfer (RAFT) polymerization

A novel monomer containing pyridylazo-2-naphthoxyl group, 1-(1-(4-vinylbenzyloxy)naphthalen-2-yl)-2-(pyridin-2-yl)diazene (VBNPA), was successfully synthesized and copolymerized with styrene (St) in N,N-dimethyl formamide (DMF) via reversible addition–fragmentation chain transfer (RAFT) polymerization using 2-cyanoprop-2-yl-1-dithionaphthalate (CPDN) as RAFT agent. The polymerization behavior exhibited “living”/controlled characters. The obtained copolymer, poly(St-co-VBNPA), with pre-determinable molecular weight and narrow molecular weight distribution can be used as a carrier in metal ion detection and analysis via pre-concentration technique. The copolymer–metal ion (copper (Cu) and europium (Eu)) complexes were prepared and characterized.     

Visual recognition of supramolecular graft polymer formation via phenolphthalein–cyclodextrin association

Visual recognition of the formation of supramolecular graft polymers in aqueous solution driven by host-guest assembly is presented. The interaction between β-cyclodextrin (β-CD) and phenolphthalein moieties can be followed via a distinctive change of color in basic media by optical inspection. The phenolphthalein-containing lateral polymer chain was obtained via reversible addition-fragmentation chain transfer (RAFT) copolymerization of N,N-dimethylacrylamide and N-(2-hydroxy-5-(1-(4-hydroxyphenyl)-3-oxo-1,3-dihydroisobenzofuran-1-yl)benzyl)acrylamide. The RAFT polymerizations afforded statistical copolymers with molecular masses between 6900 and 8800 g mol⁻¹ and molar mass dispersities (?) between 1.1 and 1.2. β-CD-functionalized building blocks were synthesized using a propargyl-functionalized chain transfer agent for the polymerization of N,N-diethylacrylamide followed by a copper(I)-catalyzed cycloaddition with β-CD-azide (M_n = 8200 g mol⁻¹; ? = 1.2). Self-assembly of both polymers to form supramolecular graft polymers was evidenced by 2D NOESY NMR, UV–vis spectroscopy and dynamic light scattering.     

One-pot synthesis of hyperbranched polymers using small molecule and macro RAFT inimers

Two novel RAFT inimers, small molecule inimer 2-(methacryloyloxy)ethyl 4-cyano-4-(phenylcarbonothioylthio)pentanoate (MAE-CPP) and macro inimer PMMA-MAE-CPP were synthesized and used to prepare hyperbranched polymers via RAFT polymerization without the use of a divinyl cross-linker. The hyperbranched polymers synthesized included copolymers of MAE-CPP with styrene, copolymers of the macro inimer PMMA-MAE-CPP with styrene and the homopolymerization product of the macro inimer PMMA-MAE-CPP. The spectroscopic characteristics and polymerization kinetics of these RAFT polymers obtained under different polymerization conditions were systematically studied and the results compared with those obtained from the corresponding linear RAFT polymerizations as well as from hyperbranched polymerizations performed in the presence of a divinyl cross-linker which are reported in literature. The RAFT methodology reported here for the preparation of hyperbranched polymers is simpler than those reported previously using a divinyl cross-linker and provides good control over the hyperbranched polymers without the formation of insoluble gels.     

Synthesis of water-soluble single-walled carbon nanotubes by RAFT polymerization

Water-soluble single-walled carbon nanotubes (SWNTs) were synthesized by grafting poly(acrylamide) (PAM) from the surface of SWNT via reversible addition-fragmentation chain transfer (RAFT) polymerization. The RAFT agents were covalently attached to the SWNTs by functionalizing SWNTs with in situ generated diazonium compounds. The product was characterized by means of FT-IR, Raman, ¹H NMR, TGA and TEM. The results showed that PAM chains had successfully grafted from SWNT by RAFT polymerization. The amount of PAM grown from SWNT increased with the polymerization time. The acrylamide conversion increased linearly with the polymerization time, indicating the “living” characteristics of the RAFT polymerization. TEM was utilized to image PAM-g-SWNT, showing relatively uniform polymer coatings present on the surface of individual, debundled nanotubes.     

Reversible Addition Fragmentation Chain Transfer (RAFT) Emulsion Polymerization of Methyl Methacrylate via a Plasma-initiated Process

Summary The plasma-initiated emulsion polymerization of MMA in the presence of 2-cyanoprop-2-yl 1-dithionaphthalate (CPDN) was first investigated. The polymers were characterized by GPC, ¹H NMR, DSC and SEM. The results exhibit controlled polymerization characters: well-controlled molecular weight, relatively narrow polydispersity, molecular weight linearly increasing with conversion and successful chain extension reactions. The influence of the amount of the sodium dodecyl sulfate (SDS), CPDN concentration, plasma duration time on the polymerization rate, and micro-shape of the particle was investigated in this work. The plasma-initiation emulsion polymerization of octyl acrylate (OA) in the presence of CPDN is also carried out.     

Using dilatometry in the reversible addition fragmentation transfer polymerization of N-(S)-(−)-α-methylbenzyl methacryloylamine

Optically active polymers were prepared using reversible addition-fragmentation chain transfer polymerization (RAFT) of N-(S)-α-methylbenzylmethacryloylamine (N-(S)-α-MBMA), a functional optically active monomer. RAFT polymerizations were carried out at 70 °C in ethanol using AIBN as a thermal initiator and benzyl or (1-phenyl)ethyl dithiobenzoate (BDB and PEDB, respectively) as the RAFT agents. The kinetic study was performed by dilatometry. Plots of conversion vs time indicated that the polymerizations followed first order kinetics. ¹H NMR, IR, and UV–vis spectrophotometric studies confirmed the presence of thiocarbonylthio moieties (−SCS-) in the polymer chains. The molecular weight distributions (MWDs) were moderately narrow with polydispersity indices between 1.3 and 1.6, which indicated that the control of the reaction was not completely achievement using BDB or PEDB as RAFT agents. The optical activity [α]_D²⁵ measurements of synthesized polymers by RAFT did not show a noticeably linear increase dependence with respect to molecular weight, as was previously reported for another controlled free radical polymerization (CRP) system.