Visible‐light induced RAFT polymerization of styrenic monomers with aromatic aldehydes as organophotoredox catalysts

A photoinduced electron transfer‐reversible addition‐fragmentation chain transfer (PET‐RAFT) polymerization of p‐methylstyrene (p‐MS) and styrene (St) with 2‐(dodecylthiocarbonothioylthio)‐2‐methylpropionic acid as the chain transfer agent (CTA) and aromatic aldehydes, including 4‐cyanobenzaldehyde (PC1), 2,4‐dimethoxy benzaldehyde, and 4‐methoxy benzaldehyde, as organic photocatalysts has been demonstrated via irradiation with 23 W compact fluorescent lamps. The kinetics of the polymerizations shows first order with respect to monomer conversions. Linear evolution of the M_n of the produced polymers with the monomer conversion is observed. Meanwhile, the as‐prepared polymers are of relatively narrow polydispersity (PDI = M_w/M_n). For instance, the polymerization of p‐MS shows living polymerization features using PC1 within a range of solvents. Especially, the M_n of PpMS increased from about 2100 to 12,700 g/mol with the monomer conversion from 8% to 52% in tetrahydrofuran. The controlled polymerization of St is also observed under optimal reaction conditions. However, the M_n discrepancy between the experimental readings and theoretical calculations is greater at the monomer conversions greater than 40% and the PDI increased gradually over the monomer conversion. This is probably because that CTA is strongly sensitive to the light irradiation with wave range around its characteristic absorption wavelength, leading to significant decomposition of CTA moieties during the RAFT polymerization. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2072–2079     

Visible light‐induced RAFT polymerization of methacrylates with benzaldehyde derivatives as organophotoredox catalysts

The benzaldehyde derivatives, such as 2,4‐dimethoxy benzaldehyde (PC1) and p‐anisaldehyde (PC2), were successfully used as photoredox catalysts (PCs) in combination with typical RAFT agent 4‐cyano‐4‐(phenylcarbonothioylthio)pentanoic acid (CTP) for the controlled photoinduced electron transfer RAFT polymerization (PET‐RAFT) of methyl methacrylate (MMA) and benzyl methacrylate (BnMA) at room temperature. The kinetics of the polymerizations showed first order with respect to monomer conversions. Besides, the average number molecular weights (M_n) of the produced polymers increased linearly with the monomer conversions and kept relatively narrow polydispersity (PDI = M_w/M_n). For example, the M_n of PMMA increased from about 3400 to 17,300 g mol⁻¹ with the increasing in monomer conversion from 11% to 85%, and the PDI maintained around 1.36. The living features of polymerizations with the PC1 and PC2 as catalysts have also been further supported by chain extension and synthesis of PMMA‐b‐PBnMA diblock copolymer. As a result, the simplicity and efficiency of benzaldehyde derivatives catalyzed PET‐RAFT polymerization have been demonstrated under mild conditions. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 229–236     

Perfluorocyclobutyl-containing Amphiphilic Block Copolymers Synthesized by RAFT Polymerization

Amphiphilic block copolymers containing hydrophobic perfluorocyclobutyl‐based (PFCB) polyacrylate and hydrophilic poly(ethylene glycol) (PEG) segments were prepared via reversible addition‐fragmentation chain transfer (RAFT) polymerization. The PFCB‐containing acrylate monomer, p‐(2‐(p‐tolyloxy)perfluorocyclobutoxy)‐phenyl acrylate, was first synthesized from commercially available compounds in good yields, and this kind of acrylate monomer can be homopolymerized by free radical polymerization or RAFT polymerization. Kinetic study showed the 2,2′‐azobis(isobutyronitrile) (AIBN) initiated and cumyl dithiobenzoate (CDB) mediated RAFT polymerization was in a living fashion, as suggested by the fact that the number‐average molecular weights (M_n) increased linearly with the conversions of the monomer, while the polydispersity indices kept less than 1.10. The block polymers with narrow molecular weight distributions (M_w/M_n≦1.21) were prepared through RAFT polymerization using PEG monomethyl ether capped with 4‐cyanopentanoic acid dithiobenzoate end group as the macro chain transfer agent (mPEG‐CTA). The length of the hydrophobic segment can be tuned by the feed ratio of the PFCB‐based acrylate monomer and the extending of the polymerization time. The micellization behavior of the block copolymers in aqueous media was investigated by the fluorescence probe technique.     

Synthesis of well‐defined cyclodextrin‐core star polymers

The synthesis of 21‐arm methyl methacrylate (MMA) and styrene star polymers is reported. The copper (I)‐mediated living radical polymerization of MMA was carried out with a cyclodextrin‐core‐based initiator with 21 independent discrete initiation sites: heptakis[2,3,6‐tri‐O‐(2‐bromo‐2‐methylpropionyl]‐β‐cyclodextrin. Living polymerization occurred, providing well‐defined 21‐arm star polymers with predicted molecular weights calculated from the initiator concentration and the consumed monomer as well as low polydispersities [e.g., poly(methyl methacrylate) (PMMA), number‐average molecular weight (M_n) = 55,700, polydispersity index (PDI) = 1.07; M_n = 118,000, PDI = 1.06; polystyrene, M_n = 37,100, PDI = 1.15]. Functional methacrylate monomers containing poly(ethylene glycol), a glucose residue, and a tert‐amine group in the side chain were also polymerized in a similar fashion, leading to hydrophilic star polymers, again with good control over the molecular weight and polydispersity (M_n = 15,000, PDI = 1.03; M_n = 36,500, PDI = 1.14; and M_n = 139,000, PDI = 1.09, respectively). When styrene was used as the monomer, it was difficult to obtain well‐defined polystyrene stars at high molecular weights. This was due to the increased occurrence of side reactions such as star–star coupling and thermal (spontaneous) polymerization; however, low‐polydispersity polymers were achieved at relatively low conversions. Furthermore, a star block copolymer consisting of PMMA and poly(butyl methacrylate) was successfully synthesized with a star PMMA as a macroinitiator (M_n = 104,000, PDI = 1.05). © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2206–2214, 2001     

Polymerization of styrene in alcohol/water mediated by a macro‐RAFT agent of poly(N‐isopropylacrylamide) trithiocarbonate: From homogeneous to heterogeneous RAFT polymerization

The reversible addition fragmentation chain transfer (RAFT) polymerization of styrene in alcohol/water mixture mediated with the poly(N‐isopropylacrylamide) trithiocarbonate macro‐RAFT agent (PNIPAM‐TTC) is studied and compared with the general RAFT dispersion polymerization in the presence of a small molecular RAFT agent. Both the homogeneous/quasi‐homogeneous polymerization before particle nucleation and the heterogeneous polymerization after particle nucleation are involved in the PNIPAM‐TTC‐mediated RAFT polymerization, and the two‐stage increase in the molecular weight (M_n) and nanoparticle size of the synthesized block copolymer is found. In the initial homogeneous/quasi‐homogeneous polymerization, the M_n and nanoparticle size slowly increase with monomer conversion, whereas the M_n and particle size quickly increase in the subsequent heterogeneous RAFT polymerization, which is much different from those in the general RAFT dispersion polymerization. Besides, the PNIPAM‐TTC‐mediated RAFT polymerization runs much faster than the general RAFT dispersion polymerization. This study is anticipated to be helpful to understand the polymer chain extension through RAFT polymerization under dispersion conditions. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Macromolecular brushes synthesized by “grafting from” approach based on “click chemistry” and RAFT polymerization

Well‐defined macromolecular brushes with poly(N‐isopropyl acrylamide) (PNIPAM) side chains on random copolymer backbones were synthesized by “grafting from” approach based on click chemistry and reversible addition‐fragmentation chain transfer (RAFT) polymerization. To prepare macromolecular brushes, two linear random copolymers of 2‐(trimethylsilyloxy)ethyl methacrylate (HEMA‐TMS) and methyl methacrylate (MMA) (poly(MMA‐co‐HEMA‐TMS)) were synthesized by atom transfer radical polymerization and were subsequently derivated to azide‐containing polymers. Novel alkyne‐terminated RAFT chain transfer agent (CTA) was grafted to polymer backbones by copper‐catalyzed 1,3‐dipolar cycloaddition (azide‐alkyne click chemistry), and macro‐RAFT CTAs were obtained. PNIPAM side chains were prepared by RAFT polymerization. The macromolecular brushes have well‐defined structures, controlled molecular weights, and molecular weight distributions (M_w/M_n ≦ 1.23). The RAFT polymerization of NIPAM exhibited pseudo‐first‐order kinetics and a linear molecular weight dependence on monomer conversion, and no detectable termination was observed in the polymerization. The macromolecular brushes can self‐assemble into micelles in aqueous solution. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 443–453, 2010     

Novel perfluorocyclobutyl aryl ether‐based well‐defined amphiphilic block copolymer

A series of fluorine‐containing amphiphilic diblock copolymers comprising hydrophobic poly(p‐(2‐(p‐tolyloxy)perfluorocyclobutoxy)phenyl methacrylate) (PTPFCBPMA) and hydrophilic poly(2‐(diethylamino)ethyl methacrylate) (PDEAEMA) segments were synthesized via successive reversible addition fragmentation chain transfer (RAFT) polymerizations. RAFT homopolymerization of p‐(2‐(p‐tolyloxy)perfluorocyclobutoxy)phenyl methacrylate was first initiated by 2,2′‐azobisisobutyronitrile using cumyl dithiobenzoate as chain transfer agent, and the results show that the procedure was conducted in a controlled way as confirmed by the fact that the number‐average molecular weights increased linearly with the conversions of the monomer while the polydispersity indices kept below 1.30. Dithiobenzoate‐capped PTPFCHPMA homopolymer was then used as macro‐RAFT agent to mediate RAFT polymerization of 2‐(diethylamino)ethyl methacrylate, which afforded PTPFCBPMA‐b‐PDEAEMA amphiphilic diblock copolymers with different block lengths and narrow molecular weight distributions (M_w/M_n ≤ 1.28). The critical micelle concentrations of the obtained amphiphilic diblock copolymers were determined by fluorescence spectroscopy technique using N‐phenyl‐1‐naphthylamine as probe. The morphology and size of the formed micelles were investigated by transmission electron microscopy and dynamic light scattering, respectively. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

“Living”/controlled free radical polymerization of MMA in the presence of cobalt(II) 2‐ethylhexanoate: A switch from RAFT to ATRP mechanism

A metal complex, cobalt(II) 2‐ethylhexanoate (CEH), was added to the system of thermal‐initiated reversible addition‐fragmentation chain transfer (RAFT) polymerization of methyl methacrylate (MMA) with 2‐cyanoprop‐2‐yl 1‐dithionaphthalate (CPDN) as the RAFT agent at 115 °C. The polymerization rate was remarkably enhanced in the presence of CEH in comparison with that in the absence of CEH, and the increase of the CPDN concentration also accelerated the rate of polymerization. The polymerization in the concurrence of CPDN and CEH demonstrated the characters of “living”/controlled free radical polymerization: the number‐average molecular weights (M_n) increasing linearly with monomer conversion, narrow molecular weight distributions (M_w/M_n) and obtained PMMA end‐capped with the CPDN moieties. Meanwhile, CEH can also accelerate the rate of RAFT polymerization of MMA using the PMMA as macro‐RAFT agent instead of CPDN. Similar polymerization profiles were obtained when copper (I) bromide (CuBr)/N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine was used instead of CEH. Extensive experiments in the presence of butyl methacrylate, bis(cyclopentadienyl) cobalt(II) and cumyl dithionaphthalenoate were also conducted; similar results as those of MMA/CPDN/CEH system were obtained. A transition of the polymerization mechanism, from RAFT process without CEH addition to atom transfer radical polymerization in the presence of CEH, was possibly responsible for polymerization profiles. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5722–5730, 2007     

Preparation of α,ω‐telechelic hexyl acrylate polymers with ?OH, ?COOH,and ?NH2 functional groups by RAFT

The design, synthesis, and use of two new, stable, functionalized chain transfer agents (CTA's) containing OH and amine end groups for the RAFT polymerization is reported: 2‐hydroxyethoxy‐carbonylphenylmethyl dithiobenzoate and 2‐(2‐(tert‐butoxycarbonyl)ethylamino)‐2‐oxo‐1‐phenylethyl benzodithioate, respectively. The RAFT polymerization of n‐hexyl acrylate (HA) using those CTA's, were compared to several other functionalized dithiobenzoate esters reported in the literature containing COOH and Ester groups. The performances of the dithiobenzoates were compared in terms of kinetics and molecular weight distribution control. Good control in polymerization of n‐hexyl acrylate with a linear increase of M_n with conversion mantaining polydispersity indices (PDI) below 1.1 was obtained by use of the new functionalized CTA's developed and also by use of some other CTA's tested, to produce well‐defined linear polymers with one specific chain‐end functionality: ? OH, ? COOH or Amine. Using a postpolymerization reaction with functionalized azocompounds in a 5 to 1 ratio, α,ω‐telechelic polymers, with ? OH or ? COOH as functional group at the second end were obtained. By using this synthetic strategy α,ω‐homotelechelic and heterotelechelic polymers were readily prepared. The chemical availability of functional end‐groups in the telechelics was demonstrated by reaction with methacrylic anhydride. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3033–3051, 2010     

Amine‐Reactive Polymers Synthesized by RAFT Polymerization Using an Azlactone Functional Trithiocarbonate RAFT Agent

A new azlactone‐derived trithiocarbonate is prepared and used as a chain‐transfer agent to mediate the reversible addition‐fragmentation chain transfer (RAFT) polymerization of styrene, ethyl acrylate, and N‐isopropyl acrylamide. Well‐defined polymers with controlled molecular weights (M _n = 1000–7000 g mol⁻¹) and narrow molecular weight distributions (PDI = 1.05–1.10) are thus obtained that retain the azlactone functionality at the chain end. The ability of the resulting end‐functionalized polymers to react quantitatively at room temperature with a stoichiometric amount of amino groups with retention of the thiocarbonylthio moiety is ascertained by using 4‐fluorobenzylamine and allylamine.     

Monte carlo simulations of polydisperse polymers grafted on spherical surfaces

This article presents effects of polydispersity in polymers grafted on spherical surfaces on grafted polymer chain conformations, grafted layer thickness, and free‐end monomer distribution within the grafted layer. At brush‐like grafting densities, as polydispersity index (PDI) increases, the scaling exponent of radius of gyration of grafted chains approaches that of a single chain grafted on the same nanoparticle, because polydispersity alleviates monomer crowding within the brush. At high PDI, the chains shorter than the number average chain length, N_n, have more compressed conformations, and the chains longer than N_n overall stretch less than in the monodisperse case. As seen in polydisperse flat brushes at high grafting densities, the grafted layer thickness on spherical nanoparticle increases with PDI. Polydispersity eliminates the region near the surface devoid of free‐end monomers seen in monodisperse cases, and it reduces the width of free‐end monomer distribution and shifts the free‐end monomer distribution close to the surface. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Hyperbranched polymers as scaffolds for multifunctional reversible addition–fragmentation chain‐transfer agents: A route to polystyrene‐core‐polyesters and polystyrene‐block‐poly(butyl acrylate)‐core‐polyesters

Polydisperse hyperbranched polyesters were modified for use as novel multifunctional reversible addition–fragmentation chain‐transfer (RAFT) agents. The polyester‐core‐based RAFT agents were subsequently employed to synthesize star polymers of n‐butyl acrylate and styrene with low polydispersity (polydispersity index < 1.3) in a living free‐radical process. Although the polyester‐core‐based RAFT agent mediated polymerization of n‐butyl acrylate displayed a linear evolution of the number‐average molecular weight (M_n) up to high monomer conversions (>70%) and molecular weights [M_n > 140,000 g mol^?1, linear poly(methyl methacrylate) equivalents)], the corresponding styrene‐based system reached a maximum molecular weight at low conversions (≈30%, M_n = 45,500 g mol^?1, linear polystyrene equivalents). The resulting star polymers were subsequently used as platforms for the preparation of star block copolymers of styrene and n‐butyl acrylate with a polyester core with low polydispersities (polydispersity index < 1.25). The generated polystyrene‐based star polymers were successfully cast into highly regular honeycomb‐structured microarrays. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3847–3861, 2003     

Design and property of thermoresponsive core–shell fluorescent nanoparticles via RAFT polymerization and suzuki coupling reaction

The polymerization of a 2,7‐dibromocarbazole‐containing functional monomer, 6‐(2,7‐dibromo‐9H‐carbazol‐9‐yl)hexyl methacrylate (DBCzMA), was successfully carried out via the reversible addition‐fragmentation chain transfer (RAFT) technology. The polymerization behavior possessed the feature of “living”/controlled radical polymerization, for example, the first‐order kinetics, the linear increase of the molecular weight of the polymer with the monomer conversion and relatively narrow molecular weight distribution (M_w/M_n ≤ 1.27). The amphiphilic copolymers, poly(DBCzMA_m‐b‐NIPAM_n), with different chain length of poly(DBCzMA) and poly(N‐isopropylacrylamide) (PNIPAM), were successfully prepared via RAFT chain‐extension reaction, using poly(DBCzMA) as the macromolecular chain transfer agent (macro‐CTA) and NIPAM as the second monomer. Modification of 2,7‐dibromide groups in amphiphilic copolymer poly(DBCzMA‐b‐NIPAM) via Suzuki coupling reaction employed 2,7‐bis(4′,4′,5′,5′‐tetramethyl‐1′,3′,2′‐dioxaborolan‐2′‐yl)‐N?9″‐heptadecanylcarbazole as the other reaction material to afford a poly(2,7‐carbazole)‐containing crosslinked materials. The stable and uniform core–shell fluorescent nanoparticles were successfully prepared in water. The formed fluorescent nanoparticles showed good thermoresponsive properties, which is confirmed by dynamic light scattering observation. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4021–4030     

Controlled polymerization of carbazole‐based vinyl and methacrylate monomers at ambient temperature: A comparative study through ATRP,SET, and SET‐RAFT polymerizations

The polymerization of N‐vinylcarbazole (NVK) and carbazole methacrylate (CMA) was carried out using controlled radical polymerization methods such as atom transfer radical polymerization (ATRP), single electron transfer (SET)‐LRP, and single electron transfer initiation followed by reversible addition fragmentation chain transfer (SET‐RAFT). Well‐controlled polymerization with narrow molecular weight distribution (M_w/M_n) < 1.25 was achieved in the case of NVK by high‐temperature ATRP while ambient temperature SET‐RAFT polymerization was relatively slow and controlled. In the case of CMA, SET‐RAFT is found to be more suitable for the ambient temperature polymerization. The polymerization rate followed first order kinetics with respect to monomer conversion and the molecular weight of the polymer increased linearly with conversion. The controlled nature of the polymerization is further demonstrated by the synthesis of diblock copolymers from PNVK and PCMA macroinitiators using a new flavanone‐based methacrylate (FMA) as the second monomer. All the polymers exhibited fluorescence. The excimer bands in the homopolymers of PNVK and PCMA were very broad, which may be attributed to the carbazole–carbazole overlap interaction. The scanning electron microscopy analysis of the block copolymer reveals interesting morphological features. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Orthogonally functionalizable copolymers based on a novel reactive carbonate monomer

A novel N‐hydroxy succinimide‐based carbonate monomer that allows direct synthesis of polymers incorporating a reactive carbonate group in the side chain was synthesized. This new monomer was copolymerized with methyl methacrylate and poly(ethylene glycol) methylether methacrylate using free‐radical polymerization to obtain organo‐ and water‐soluble reactive copolymers. Copolymerization of the activated carbonate monomer with an azide‐containing monomer and N‐hydroxy succinimide‐containing activated ester monomer provided orthogonally functionalizable copolymers. The pendant reactive carbonate groups of the copolymers were functionalized with amines to obtain carbamates. Polymers capable of orthogonal functionalization could be selectively functionalized as desired using subsequent 1,3‐dipolar cycloaddition or amidation reactions. The novel monomer and the copolymers were characterized by ¹H‐NMR, ¹³C‐NMR, and infrared spectroscopy. The efficient stepwise orthogonal functionalization of the copolymers were examined via ¹H‐NMR spectroscopy. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Synthesis of tetrazole‐containing azo polymers with properties of photo‐induced birefringence and surface‐relief‐gratings via RAFT polymerization

A novel optically active monomer, 6‐{4‐[4‐(1‐phenyl‐1H‐tetrazol‐5‐yloxy)‐phenylazo] ‐phenoxy}‐hexyl methacrylate (PTPPHMA) bearing tetrazole and azobenzol moieties, was synthesized and polymerized by reversible addition‐fragmentation chain transfer (RAFT) polymerization using 2‐cyanoprop‐2‐yl dithiobenzoate (CPDB) as the RAFT agent and 2, 2′‐azobis(isobutyronitrile) (AIBN) as the initiator. Well‐defined optically active photochromic polyPTPPHMA(PPTPPHMA) was obtained. “Living”/controlled characteristics were observed in the polymerization: well‐controlled molecular weights (M_ns), narrow molecular weight distributions (M_w/M_n) of the polymers and successful chain‐extension of PPTPPHMA with styrene (St) as the second monomer. The photochemical interconversion between trans and cis isomers of PPTPPHMA in N,N′‐dimethyl formamide (DMF) solution was explored under irradiation of ultraviolet light. The photoinduced birefringence on the thin films of PPTPPHMA was investigated. A maximum birefringence of 0.1 was obtained, and no significant change of profiles of the birefringence after several cycles of writing/erasing/rewriting sequences was observed. The surface‐relief‐gratings (SRGs) were induced on the polymer films by interference of Kr⁺ laser beams at 413.1 nm with 35 mW/cm² intensity, the diffraction efficiencies from SRGs were measured to be in the range of 2.0–2.5%. The atomic force microscopy (AFM) results showed the gratings produced on the surfaces of the polymer film. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 682–691, 2008     

Graft block copolymers of propargyl methacrylate and vinyl acetate via a combination of RAFT/MADIX and click chemistry: Reaction analysis

Propargyl methacrylate with its acetylene function protected with a silyl group is polymerized via the reversible addition fragmentation chain transfer (RAFT) process, using cyanoisopropyl dithiobenzoate (CPDB) as RAFT agent, and subsequently deprotected to afford a polymer backbone where each repeated unit is decorated with an acetylene functionality (1000 < M_n < 13,600 g mol⁻¹, 1.07 < PDI < 1.29). In parallel, an azide functionalized xanthate (ethoxythiocarbonylsulfanyl‐acetic acid 3‐azido‐propyl ester) was employed to prepare narrow polydisperse poly(vinyl acetate) (M_n = 850 g mol⁻¹, PDI = 1.20). The two polymers are conjugated by Huisgen 1,3‐dipolar cycloaddition to afford narrow polydisperse comb polymer (1.12 < PDI < 1.18, 3400 < M_n < 12,500 g mol⁻¹, based on linear polystyrene calibration, 4500 < M < 15,600 g mol⁻¹). The study places special emphasis on following the copper catalyzed 1,3‐dipolar cycloaddition via Fourier Transform Infrared Spectroscopy (FTIR) as well as via on‐line UV–Vis photospectrometry on several model compounds, i.e. the nonmonomer inserted azido‐xanthate RAFT/MADIX agent as well as a 2‐propargyl‐2‐bromopropionate and 3‐azidopropyl‐2‐bromopropionate model compounds. A suitable absorption band in the VIS at 666 nm (tentatively assigned to a charge transfer complex between copper(I) and the forming triazole moieties) is identified as a promising sensor for following the click reaction kinetics, thus allowing for the rapid assessment of reaction completion in an on‐line fashion. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 155–173, 2008     

Synthesis of amphiphilic multiblock and triblock copolymers of polydimethylsiloxane and poly(N,N‐dimethylacrylamide)

The synthesis and spectroscopic characterization of a new family of amphiphilic multiblock and triblock copolymers is described. The synthetic methodology rests on the preparation of telechelic multifunctional and difunctional chain transfer agents easily available in two synthetic steps from commercially available polydimethylsiloxane‐containing starting materials. Telechelic polymers thus synthesized are used as macromolecular chain transfer agents in the reversible addition fragmentation chain transfer (RAFT) polymerization of N,N‐dimethylacrylamide (DMA) enabling the synthesis of (AB)_n‐type multiblock and ABA‐type triblock copolymers of varying compositions possessing monomodal molecular weight distribution. (AB)_n multiblock copolymers [(PDMA‐b‐PDMS)_n] were prepared with between 52 and 95 wt % poly(dimethylacrylamide) with number average molecular weights (M_n) between 14,000 and 86,000 (polydispersities of 1.20–2.30). On the other hand, ABA block copolymers with DMA led to amphiphilic block copolymers (PDMA‐b‐PDMS‐b‐PDMA) with M_n values between 9000 and 44,000 (polydispersities of 1.24–1.62). © Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7033–7048, 2008     

Stimuli‐responsive cationic terpolymers by RAFT polymerization: Synthesis,characterization, and protein interaction studies

The controlled synthesis and characterization of a range of stimuli responsive cationic terpolymers containing varying amounts of N‐isopropylacrylamide (NIPAM), 3‐(methylacryloylamino)propyl trimethylammonium chloride (MAPTAC), and poly(ethylene glycol)monomethyl methacrylate (PEGMA) is presented. The terpolymers were synthesized using reversible addition‐fragmentation chain transfer (RAFT) polymerization. Compositions of the terpolymers determined using ¹H NMR were in close agreement to the theoretical values determined from the monomer feed ratios. GPC‐MALLS was used to analyze the molecular weight characteristics of the polymers, which were found to have low polydispersities (M_w/M_n 1.1–1.4). The phase transitions were studied as a function of PEGMA and NIPAM content using temperature controlled ¹H NMR and turbidity measurements (UV‐Vis). The relationship between thermal stability and the comonomer ratio of the polymers was measured using thermogravimetric analysis (TGA). Protein interaction studies were performed to determine the suitability of the polymers for biological applications. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4021–4029, 2008     

Well‐defined amphiphilic graft copolymer consisting of hydrophilic poly(acrylic acid) backbone and hydrophobic poly(vinyl acetate) side chains

A series of well‐defined amphiphilic graft copolymers containing hydrophilic poly(acrylic acid) (PAA) backbone and hydrophobic poly(vinyl acetate) (PVAc) side chains were synthesized via sequential reversible addition‐fragmentation chain transfer (RAFT) polymerization followed by selective hydrolysis of poly(tert‐butyl acrylate) backbone. A new Br‐containing acrylate monomer, tert‐butyl 2‐((2‐bromopropanoyloxy)methyl) acrylate, was first prepared, which can be polymerized via RAFT in a controlled way to obtain a well‐defined homopolymer with narrow molecular weight distribution (M_w/M_n = 1.08). This homopolymer was transformed into xanthate‐functionalized macromolecular chain transfer agent by reacting with o‐ethyl xanthic acid potassium salt. Grafting‐from strategy was employed to synthesize PtBA‐g‐PVAc well‐defined graft copolymers with narrow molecular weight distributions (M_w/M_n < 1.40) via RAFT of vinyl acetate using macromolecular chain transfer agent. The final PAA‐g‐PVAc amphiphilic graft copolymers were obtained by selective acidic hydrolysis of PtBA backbone in acidic environment without affecting the side chains. The critical micelle concentrations in aqueous media were determined by fluorescence probe technique. The micelle morphologies were found to be spheres. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6032–6043, 2009