Polymer having a trithiocarbonate moiety in the main chain: Application to reversible addition–fragmentation chain transfer controlled thermal and photoinduced monomer insertion polymerizations

A polymer having a trithiocarbonate moiety in its main chain was synthesized with a cyclic, five‐membered dithiocarbonate as a building block. The trithiocarbonate in the polymer acted as a reversible addition–fragmentation chain transfer reagent to mediate a controlled insertion polymerization of styrene into the polymer main chain, giving the corresponding sequence‐ordered polymer having a well‐defined polystyrene segment in the main chain. During the polymerization, the polystyrene segment in the main chain gained its molecular weight, which maintained a linear relationship with the conversion of styrene. The insertion polymerization of styrene was induced not only thermally but also by ultraviolet irradiation. This photoinduced polymerization was well controlled by the trithiocarbonate moiety to give the corresponding polymer, whose structure was virtually the same as that obtained by the thermal polymerization. © 2006 Wiley Periodicals, Inc. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6324–6331, 2006     

Multiblock poly(4‐vinylpyridine) and its copolymer prepared with cyclic trithiocarbonate as a reversible addition–fragmentation transfer agent

The polymerization of 4‐vinylpyridine was conducted in the presence of a cyclic trithiocarbonate (4,7‐diphenyl‐[1,3]dithiepane‐2‐thione) as a reversible addition–fragmentation transfer (RAFT) polymerization agent, and a multiblock polymer with narrow‐polydispersity blocks was prepared. Two kinds of multiblock copolymers of styrene and 4‐vinylpyridine, that is, (ABA)_n multi‐triblock copolymers with polystyrene or poly(4‐vinylpyridine) as the outer blocks, were prepared with multiblock polystyrene or poly(4‐vinylpyridine) as a macro‐RAFT agent, respectively. GPC data for the original polymers and polymers cleaved by amine demonstrated the successful synthesis of amphiphilic multiblock copolymers of styrene and 4‐vinylpyridine via two‐step polymerization. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2617–2623, 2007     

Synthesis and characterization of fluorescence end‐labeled polystyrene via reversible addition‐fragmentation chain transfer (RAFT) polymerization

Fluorescence end‐labeled polystyrene (PS) with heteroaromatic carbazole or indole group were prepared conveniently via reversible addition‐fragmentation chain transfer (RAFT) polymerization using dithiocarbamates, ethyl 2‐(9H‐carbazole‐9‐carbonothioylthio)propanoate (ECCP) and benzyl 2‐phenyl‐1H‐indole‐1‐carbodithioate (BPIC) as RAFT agents. The end functionality of obtained PS with different molecular weights was high. The steady‐state and the time‐resolved fluorescence techniques had been used to study the fluorescence behaviors of obtained end‐labeled PS. The fluorescence of dithiocarbamates resulting PS in solid powder cannot be monitored; however, they exhibited structured absorptions and emissions in solvent DMF and the fluorescence lifetimes of PS had no obvious change with molecular weights increasing. These observations suggested that the polymer chains were possibly stretched adequately in DMF, that is, the fluorescence end group was exposed into solvent molecules and little quenching of excited state occurred upon incorporation into polymer chain. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6198–6205, 2008     

Synthesis of ω‐sulfonated polystyrene via reversible addition fragmentation chain transfer polymerization and postpolymerization modification

The synthesis of chain‐end sulfonated polystyrene [PS (ω‐sulfonated PS)] by reversible addition fragmentation chain transfer (RAFT) polymerization followed by postpolymerization modification was investigated by two methods. In the first method, the polymer was converted to a thiol‐terminated polymer by aminolysis. This polymer was then sulfonated by oxidation of the thiol end‐group with m‐chloroperoxybenzoic acid (m‐CPBA) to produce a sulfonic acid end‐group. In the second method, the RAFT‐polymerized polymer was directly sulfonated by oxidation with m‐CPBA. After purification by column chromatography, ω‐sulfonated PS was obtained by both methods with greater than 95% end‐group functionality as measured by titration. The sulfonic acid end‐group could be neutralized with various ammonium or imidazolium counter ions through acid–base or ionic metathesis reactions. The effect of the ionic end‐groups on the glass transition temperature of the PS was found to be consistent with what is known for PS ionomers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Facile and Efficient One‐Pot Transformation of RAFT Polymer End Groups via a Mild Aminolysis/Michael Addition Sequence

Summary: The trithiocarbonate end groups of polymers prepared by RAFT polymerization are converted into colorless and stable thioethers in a one‐pot process that combines aminolysis of the trithiocarbonate functions and Michael addition of the resulting thiols to α, β‐unsaturated carbonyl derivatives. This post polymerization procedure, which is carried out under mild conditions to near quantitative conversion, is described in the case of a telechelic poly(N‐isopropylacrylamide) sample bearing isobutylsulfanylthiocarbonylsulfanyl end groups. The chemical composition, purity, and molar masses of the modified polymers are assessed by GPC, ¹H NMR spectroscopy and UV‐vis spectroscopy, which together demonstrate the efficiency of the method and confirm that the molecular weight and polydispersity of the precursor RAFT polymer are not affected by the treatment.

The facile, one pot synthesis combines the reactions of trithiocarbonate aminolysis and Michael addition of a thiol to an α, β‐unsaturated ester to transform the labile, colored thiocarbonylthio moiety into a stable, colorless thioether.     

Functional and tuneable amino acid polymers prepared by RAFT polymerization

We report the application of reversible addition‐fragmentation chain transfer polymerization using a novel chain transfer agent toward the synthesis of a variety of copolymers containing proline‐derived monomeric units. This methodology enables ready access to a number of polymeric species with narrow molecular weight distributions, reliable functional unit incorporations, and high conversions. The methodology is also a facile approach to novel copolymeric species incorporating amino acids, which possess unique material properties and the potential for further organocatalytic application. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009     

Synthesis of enantiopure homo and copolymers by raft polymerization and investigation of their enantioselective lipase‐catalyzed esterification

Homo and copolymers were synthesized from enantionpure (R)‐ and (S)‐1‐(4‐vinylphenyl)ethanol by reversible addition‐fragmentation chain transfer polymerization. The polymerization conditions were optimized resulting in dioxane as the preferred reaction solvent. First‐order polymerization kinetics and well‐defined enantiopure homopolymers with low dispersities were obtained. In agreement with their enantiomeric composition, the (R) and (S)‐polymers gave opposite optical rotation of light. Polymer analogous esterification of the chiral hydroxy groups catalyzed by enantioselective Candida antarctica Lipase B was strongly (R)‐selective. Esterification on the homopolymer and copolymers could be achieved to a maximum of around 50 %. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Accelerated Combinatorial High Throughput Star Polymer Synthesis via a Rapid One‐Pot Sequential Aqueous RAFT (rosa‐RAFT) Polymerization Scheme

Advanced polymerization methodologies, such as reversible addition‐fragmentation transfer (RAFT), allow unprecedented control over star polymer composition, topology, and functionality. However, using RAFT to produce high throughput (HTP) combinatorial star polymer libraries remains, to date, impracticable due to several technical limitations. Herein, the methodology “rapid one‐pot sequential aqueous RAFT” or “rosa‐RAFT,” in which well‐defined homo‐, copolymer, and mikto‐arm star polymers can be prepared in very low to medium reaction volumes (50 µL to 2 mL) via an “arm‐first” approach in air within minutes, is reported. Due to the high conversion of a variety of acrylamide/acrylate monomers achieved during each successive short reaction step (each taking 3 min), the requirement for intermediary purification is avoided, drastically facilitating and accelerating the star synthesis process. The presented methodology enables RAFT to be applied to HTP polymeric bio/nanomaterials discovery pipelines, in which hundreds of complex polymeric formulations can be rapidly produced, screened, and scaled up for assessment in a wide range of applications.

     

Influence of the chemical structure of dithiocarbamates with different N‐groups on the reversible addition–fragmentation chain transfer polymerization of styrene

Polymerizations of styrene with azobisisobutyronitrile initiation or thermal initiation have been performed in the presence of dithiocarbamates with different N‐groups, that is, benzyl 4,5‐diphenyl‐1H‐imidazole‐1‐carbodithioate ( 2a ), benzyl 1H‐1,2,4‐triazole‐1‐carbodithioate ( 2b ), benzyl indole‐1‐carbodithioate ( 2c ), benzyl 2‐phenyl‐indole‐1‐carbodithioate ( 2d ), benzyl phenothiazine‐10‐carbodithioate ( 2e ), benzyl 9H‐carbazole‐9‐carbodithioate ( 2f ), and benzyl dibenzo[b,f]azepine‐5‐carbodithioate ( 2g ). The results show that the structure of the N‐group of dithiocarbamates has significant effects on the activity of dithiocarbamates for the polymerization of styrene. 2a , 2b , 2c , 2d , and 2f are effective reversible addition–fragmentation chain transfer (RAFT) agents for the RAFT polymerization of styrene, and the polymerizations have good living characteristics. However, in the cases of 2e and 2g , the obtained polymers have uncontrolled molecular weights and broad molecular weight distributions. The polymerization rate is markedly influenced by the conjugation structure of the N‐group of the dithiocarbamate, and the polymerization rate of 2b is greater than that of 2a . For 2b , the rate of polymerization seems independent of the RAFT agent concentration. However, a significant retardation in the rate of polymerization can be observed in the case of 2c . 2d is more effective than 2c , and the substitution group of phenyl on this dithiocarbamate has obvious effects on the effectiveness of the controlled polymerization of styrene. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4849–4856, 2005     

Synthesis of arborescent (Dendritic) polystyrenes via controlled inimer‐type reversible addition‐fragmentation chain transfer polymerization

The reversible addition‐fragmentation chain transfer (RAFT) copolymerization of styrene and 4‐vinylbenzyl dithiobenzoate, a RAFT‐based inimer (initiator‐monomer), is described. Controlled polymerization was achieved in bulk conditions using thermal initiation at 110 °C to give arborescent polystyrene (arbPSt). The number‐average molecular weights of the polymers increased linearly with conversion and were much higher than theoretically calculated for a linear polymerization, reaching M_n = 364,000 g/mol with M_w/M_n = 2.65. Branching analysis by NMR showed an average of 3.5 branches per chain. SEC data, which were similar to those measured in arborescent polyisobutylene, supported the architectural analysis. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7621–7627, 2008     

Synthesis and swelling behavior of comb‐type grafted hydrogels by reversible addition–fragmentation chain transfer polymerization

The comb‐type grafted hydrogels poly(N‐isopropylacrylamide)‐g‐poly(N‐isopropylacrylamide) (PNIPAM‐g‐PNIPAM) and poly(acrylic acid)‐g‐poly(N‐isopropylacrylamide) (PAAc‐g‐PNIPAM) were prepared by reversible addition–fragmentation chain transfer polymerization. A macromolecular chain‐transfer agent was prepared first. Then, hydrogels were obtained by a reaction with a comonomer (N‐isopropylacrylamide or acrylic acid) in the presence of N,N‐methylenebisacrylamide as a crosslinker. The equilibrium swelling ratios and the swelling and deswelling kinetics of PNIPAM‐g‐PNIPAM were measured. The effects of the chain length and amount on the swelling behavior were investigated. The deswelling mechanism was illustrated. Meanwhile, the PAAc‐g‐PNIPAM hydrogel was used to confirm the versatility of this novel method. It was prepared in an alcoholic medium, whereas hydrogen‐bonding complexes formed in 1,4‐dioxane, which was chosen as the reaction medium for the PNIPAM‐g‐PNIPAM hydrogel. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2615–2624, 2005     

Synthesis of chiral micelles and nanoparticles from amino acid based monomers using RAFT polymerization

Homopolymers of ^tbutyl acrylate (P^tBuA) and a monosubstituted acrylamide (PAM) having an amino acid moiety in the side chain, N‐acryloyl‐(L )‐phenylalanine methyl ester 1 , have been synthesized by Reversible Addition‐Fragmentation Chain Transfer (RAFT) polymerization. Diblock copolymers of these homopolymers were also synthesized by chain extending P^tBuA with monomer 1 and after modification, using simple acid deprotection chemistries of the acrylate block to afford a poly (acrylic acid) block, an optically active amphiphilic diblock copolymer was isolated. The optically active amphiphilic diblock copolymers, which contain chiral amino acid moieties within the hydrophobic segment, were then self‐assembled to afford spherical micelles which were subsequently crosslinked throughout the shell layer to afford robust chiral nanoparticles. The hydrodynamic diameters (D_h) of the block copolymer micelles and nanoparticles were measured by dynamic light scattering (DLS) and the dimensions of the nanoparticles were determined using tapping‐mode atomic force microscopy (AFM) and transmission electron microscopy (TEM). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3690–3702, 2008     

Synthesis of poly(n‐butyl acrylate) containing multiblocks with a narrow molecular weight distribution using cyclic trithiocarbonates

The polymerization of n‐butyl acrylate in the presence of two cyclic trithiocarbonates (CTTCs) and the synthesis of multiblock poly(n‐butyl acrylate) have been investigated. The CTTCs not only can be stepwise incorporated into the polymer chain via reversible addition–fragmentation chain transfer (RAFT) but also can be polymerized into polytrithiocarbonate, which functions as a macro‐RAFT agent in turn. Through two kinds of mechanisms, multiblock poly(n‐butyl acrylate) containing narrow‐polydispersity blocks can be prepared. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6600–6606, 2006     

Macromolecular design via reversible addition–fragmentation chain transfer (RAFT)/xanthates (MADIX) polymerization

Among the living radical polymerization techniques, reversible addition–fragmentation chain transfer (RAFT) and macromolecular design via the interchange of xanthates (MADIX) polymerizations appear to be the most versatile processes in terms of the reaction conditions, the variety of monomers for which polymerization can be controlled, tolerance to functionalities, and the range of polymeric architectures that can be produced. This review highlights the progress made in RAFT/MADIX polymerization since the first report in 1998. It addresses, in turn, the mechanism and kinetics of the process, examines the various components of the system, including the synthesis paths of the thiocarbonyl‐thio compounds used as chain‐transfer agents, and the conditions of polymerization, and gives an account of the wide range of monomers that have been successfully polymerized to date, as well as the various polymeric architectures that have been produced. In the last section, this review describes the future challenges that the process will face and shows its opening to a wider scientific community as a synthetic tool for the production of functional macromolecules and materials. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43:5347–5393, 2005     

Synthesis of polymer with defined fluorescent end groups via reversible addition fragmentation transfer polymerization for characterizing the conformations of polymer chains in solutions

A new type of chain transfer agent used in reversible addition fragmentation chain transfer (RAFT) polymerization named 9‐anthracenylmethyl (4‐cyano‐4‐(N‐carbazylcarbodithioate) pentanoate) (ACCP) was synthesized with a total yield over 75% by the incorporation of both fluorescent donor and acceptor chromophores. Polymerization of heterotelechelic α,ω end‐labeled dye‐functionalized polystyrene (PS), poly(methyl methacrylate) (PMMA), and poly(n‐butyl methacrylate) (PBMA) with adjustable molecular weights and narrow polydispersity could be conducted by a one‐pot procedure through RAFT polymerization with this bischromophore chain transfer agent. The polymerizations demonstrated “living” controlled characteristics. By taking advantage of the characteristic fluorescence resonance energy transfer (FRET) response between the polymer chain terminals, the variation of chain dimensions in solution from the dilute region to the semidilute region can be monitored by changes in the ratio of the fluorescence intensities of the carbazolyl group to the anthryl group, which lends itself to potential applications in characterizing chain dimensions in solutions for thermodynamic or dynamic studies. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2413–2420     

Synthesis and characterization of double hydrophilic block copolymers containing semi-rigid and flexible segments

3-Methyl-(E)-stilbene (3MSti) and 4-(diethylamino)-(E)-stilbene (DEASti) monomers are synthesized and polymerized separately with maleic anhydride (MAn) in a strictly alternating fashion using reversible addition-fragmentation chain transfer (RAFT) polymerization techniques. The optimal RAFT chain transfer agents (CTAs) for each copolymerization affect the reaction kinetics and CTA compatibilities. Psuedo-first order polymerization kinetics are demonstrated for the synthesis of poly((3-methyl-(E)-stilbene)-alt-maleic anhydride) (3MSti-alt-MAn) with a thiocarbonylthio CTA (methyl 2-(dodecylthiocarbonothioylthio)−2-methylpropionate, TTCMe). In contrast, a dithioester CTA (cumyl dithiobenzoate, CDB) controls the synthesis of poly((4-(diethylamino)-(E)-stilbene)-alt-maleic anhydride) (DEASti-alt-MAn) with pseudo-first order polymerization kinetics. DEASti-alt-MAn is chain extended with 4-acryloylmorpholine (ACMO) to synthesize diblock copolymers and subsequently converted to a double hydrophilic polyampholyte block copolymers (poly((4-(diethylamino)-(E)-stilbene)-alt-maleic acid))-b-acryloylmorpholine) (DEASti-alt-MA)-b-ACMO) via acid hydrolysis. The isoelectric point and dissociation behavior of these maleic acid-containing copolymers are determined using ζ-potential and acid–base titrations, respectively. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 219–227     

Effect of Topology on the Properties of Poly(N-isopropylacrylamide) in Water and in Bulk

Three macrocyclic poly(N-isopropylacrylamide)s (PNIPAM) with molecular weight (MW) ranging from 6 to 19 kg/mol were synthesized by ‘click’ ring closure of the corresponding α-azido ω-propargyl telechelic linear PNIPAMs, themselves prepared by reversible addition fragmentation chain transfer (RAFT) polymerization of N-isopropylacrylamide. Differential scanning calorimetry (DSC) studies revealed that both the thermal phase separation in water and the glass transition in bulk of PNIPAM were affected by polymer topology. In aqueous solution, the cyclic polymers exhibit a higher phase separation temperature and broader phase transition range than the corresponding linear counterparts. In bulk, the cyclic polymers display a higher glass transition temperature of lesser molecular weight dependence, as compared to their linear precursors.     

Influence of small amounts of addition‐fragmentation capable monomers on polymerization‐induced shrinkage stress

The effects of the addition of small amounts of multifunctional monomers that contain functional groups capable of undergoing addition‐fragmentation during radical polymerizations are investigated. Specifically, up to 6 wt % of phenyl trithiocarbonate (TTC)‐containing diacrylate was added to conventional thiol‐multiacrylate photopolymerizations where its addition led to up to 60% reduction in polymerization‐induced shrinkage stress. The higher levels of TTC achieve the lowest stress though they also significantly depress the polymerization rate. Using up to 0.5 wt % phenyl TTC successfully reduces the stress by nearly 20%, demonstrating the effectiveness of the phenyl TTC, while minimizing the influence that the RAFT activity of the TTC unit has on the polymerization rate. When the polymerization rates of the TTC‐containing resins are increased by changing the incident light intensity, complete acrylate conversion is achieved and the stress remains up to 40% lower in the TTC‐containing resins. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1315–1321     

Synthesis and characterization of well‐defined optically active methacrylic diblock copolymers

A new, simple, and cost‐effective approach toward the development of well‐defined optically active diblock copolymers based on methacrylate monomers is described for the first time. Starting from the low‐cost optically active (S)‐(?)‐2‐methyl‐1‐butanol, a new optically active methacrylic monomer, namely, (S)‐(+)‐2‐methyl‐1‐butyl methacrylate [(S)‐(+)‐MBuMA], was synthesized. Reversible addition fragmentation chain transfer polymerization was then used for preparing well‐defined poly[(S)‐(+)‐MBuMA] homopolymers and water‐soluble diblock copolymers based on [(S)‐(+)‐MBuMA] and the hydrophilic and ionizable monomer 2‐(dimethyl amino)ethyl methacrylate (DMAEMA). The respective homopolymers and diblock copolymers were characterized in terms of their molecular weights, polydispersity indices, and compositions by size exclusion chromatography and ¹H NMR spectroscopy. Polarimetry measurements were used to determine the specific optical rotations of these systems. The structural and compositional characteristics of micellar nanostructures possessing an optically active core generated by p((S)‐(+)‐MBuMA)‐b‐p(DMAEMA) chains characterized by predetermined molecular characteristics may be easily tuned to match biological constructs. Consequently, the aggregation behavior of the p[(S)‐(+)‐MBuMA]‐b‐p[DMAEMA] diblock copolymers was investigated in aqueous media by means of dynamic light scattering and atomic force microscopy, which revealed the formation of micelles in neutral and acidified aqueous solutions. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012