Controlled synthesis of thermoresponsive polymer via RAFT polymerization of an acrylamide containing l-proline moiety

Reversible addition–fragmentation chain transfer (RAFT) polymerization of N-acryloyl-l-proline methyl ester (A-Pro-OMe) was investigated in order to find suitable conditions to achieve controlled synthesis of amino acid-based polymers with pre-determined molecular weight, narrow polydispersity, well-defined chain end structure, and characteristic thermoresponsive property. The effect of various parameters, such as chain transfer agent (CTA)/initiator ratio, solvent, and temperature, on RAFT polymerization of A-Pro-OMe was examined using benzyl dithiobenzoate as a CTA. Chain-end structure of the resulting poly(A-Pro-OMe) was confirmed by ¹H NMR analysis, MALDI-TOF mass spectroscopy, and chain extension experiment. Thermally induced phase separation behaviors of poly(A-Pro-OMe)s prepared by RAFT and conventional free radical polymerizations were also studied in aqueous solution.     

One-step synthesis of poly(2-oxazoline)-based amphiphilic block copolymers using a dual initiator for RAFT polymerization and CROP

A range of poly(2-oxazoline) (POx)-based amphiphilic block copolymers were synthesized using 4-cyano-4-(dodecylthiocarbonothioylthio)pentyl-4-methylbenzenesulfonate (CDPS) as a dual initiator for reversible addition-fragmentation chain transfer (RAFT) polymerization and cationic ring-opening polymerization (CROP) in a one-step procedure. Methyl (meth)acrylate, butyl (meth)acrylate, tert-butyl (meth)acrylate, and N-isopropylacrylamide were polymerized for the hydrophobic block, and 2-methyl-2-oxazoline and 2-ethyl-2-oxazoline were used as the hydrophilic block. RAFT polymerization and CROP proceeded independently in a controlled manner and resulted in amphiphilic block copolymers with a narrow molecular weight distribution. CDPS was found to be a useful dual initiator for the one-step synthesis of POx-based amphiphilic block copolymers via a combination of RAFT polymerization and CROP.     

可逆加成-断裂链转移聚合制备聚氯乙烯-b-聚乙二醇-b-聚氯乙烯共聚物

合成了含黄原酸酯端基的聚乙二醇（X-PEG-X）大分子链转移剂,并以其为可逆加成-断裂链转移试剂调控氯乙烯（VC）溶液和悬浮聚合,合成聚氯乙烯-b-聚乙二醇-b-聚氯乙烯（PVC-b-PEG-b-PVC）三嵌段共聚物。X-PEG-X调控VC溶液聚合得到的共聚物的分子量随聚合时间增加而增大,分子量分布指数小于1.65。X-PEG-X具有水/油两相分配和可显著降低水/油界面张力的特性,以X-PEG-X为链转移剂和分散剂,通过自稳定悬浮聚合也可合成PVC-b-PEG-b-PVC共聚物,共聚物颗粒无皮膜结构,分子量随聚合时间增加而增大;由于VC悬浮聚合具有聚合物富相和单体富相两相聚合特性,共聚物分子量分布指数略大于溶液聚合共聚物。通过乙酸乙烯酯（VAc）扩链反应进一步证实了PVC-b-PEG-b-PVC的“活性”,并合成PVAc-b-PVC-b-PEG-b-PVC-b-PVAc共聚物。水接触角测试表明PVC-b-PEG-b-PVC的亲水性优于PVC。     

Controlled synthesis of sulfonated block copolymers having thermoresponsive property by RAFT polymerization of vinyl sulfonate esters

Four vinyl sulfonate ester derivatives, methyl ethenesulfonate (MES), ethyl ethenesulfonate (EES), 2,2,2-trifluoroethyl ethenesulfonate (TFES), and 2,2,2-trichloroethyl ethenesulfonate (TCLES), which are protected forms of vinyl sulfonic acids, were polymerized by reversible addition-fragmentation chain transfer (RAFT) polymerization. Polymers having relatively narrow molecular weight distributions and pre-determined molecular weights were obtained by the polymerization of all monomers using a suitable xanthate-type chain transfer agent (CTA). The RAFT polymerizations of EES and TCLES were found to proceed in controlled fashions under suitable conditions, as confirmed by the formation of narrow polydispersity products, molecular weights controlled by the monomer/chain transfer agent ratio, and linear increases in molecular weight with conversion. Deprotection of the ethyl group of poly(EES) by LiBr in refluxing 2-butanone proceeded smoothly to give water-soluble poly(lithium vinyl sulfonate). Poly(potassium vinyl sulfonate) was also obtained by the deprotection of poly(TCLES) using potassium tert-butoxide. The syntheses of thermoresponsive block copolymers involving poly(lithium vinyl sulfonate) segments were conducted by RAFT polymerization of N-isopropylacrylamide using poly(EES) macro-CTA, followed by deprotection. The thermally-induced phase separation behavior and assembled structures of the block copolymers were also studied in aqueous solution.     

One-pot synthesis of poly(N-vinylcaprolactam)-based biocompatible block copolymers using a dual initiator for ROP and RAFT polymerization

Thermosensitive, biocompatible poly(ε-caprolactone)-b-poly(N-vinylcaprolactam) (PCL-b-PVCL), poly(δ-valerolactone)-b-PVCL, and poly(trimethylene carbonate)-b-PVCL block copolymers were synthesized at 30 °C using a hydroxyl-functionalized xanthate reversible addition-fragmentation chain transfer (RAFT) agent, 2-hydroxyethyl 2-(ethoxycarbonothioylthio)propanoate (HECP), as a dual initiator for ring-opening polymerization (ROP) and RAFT polymerization in a one-pot procedure. The hydrophobic blocks were first synthesized by the ROP of cyclic monomers using diphenyl phosphate (DPP) as a catalyst and the RAFT polymerization of the PVCL block was followed by adding N-vinylcaprolactam (VCL) and 2,2′-azobis(4-methoxy-2,4-dimethyl valeronitrile) (V-70) as an initiator to the reaction mixture. This novel one-pot process is convenient and powerful method for the synthesis of the PVCL-based biocompatible block copolymers. The lower critical solution temperature (LCST) of the PVCL-based biocompatible block copolymer can be readily tuned by controlling the hydrophobicity of the block copolymers. By copolymerizing a hydrophilic N-vinylpyrrolidone moiety to the PVCL blocks by RAFT copolymerization, the LCST of the copolymer was matched with the body temperature for its future biomedical applications.     

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.     

Poly(N-tert-butyl acrylamide-b-N-acryloylmorpholine) amphiphilic block copolymers via RAFT polymerization: Synthesis, purification and characterization

Amphiphilic block copolymers consisting of two poly(acrylamide) derivative blocks have been synthesized via the reversible addition fragmentation chain transfer (RAFT) polymerization process with a hydrophobic block, poly(N-tert-butyl acrylamide), poly(TBAm), and a non-ionic hydrophilic one, poly(N-acryloylmorpholine), poly(NAM). Both polymerization orders, poly(TBAm-b-NAM) and poly(NAM-b-TBAm), were compared in terms of conversion and control over molecular weights (MW). Purification of the block copolymers was carried out via several methods in order to optimize their subsequent characterization. ¹H NMR analysis resulted in an accurate determination of the second block MW whereas determination of the CMC by the pendant drop method confirmed the ability of the poly(TBAm-b-NAM) block copolymers to self-assemble into micelles in aqueous phase.     

A readily modified polyethersulfone with amino-substituted groups: Its amphiphilic copolymer synthesis and membrane application

An amino-substituted polyethersulfone (PES) was synthesized by the polycondensation of a functional monomer bis(3-amino-4-hydroxyphenyl) sulfone with bis(4-fluorophenyl) sulfone. The amine groups incorporated into PES were employed as anchors to immobilize the chain transfer agents of reversible addition-fragmentation polymerization (RAFT). The resultant macro chain transfer agent was used to initiate the polymerization of the hydrophilic monomers N-isopropyl acrylamino (NIPAAm) and N, N-dimethylamino-2-ethyl methacrylate (DMAEMA), respectively. The gel permeation chromatography (GPC) results confirmed the successful synthesis of the amphiphilic copolymers PES-g-PNIPAAm and PES-g-PDMAEMA, and these two copolymers were perhaps the few examples of amphiphilic copolymer synthesized via a radical polymerization from PES main chains. The amino-substituted PES seemed a versatile precursor that showed a potential of functionalization via various strategies including click chemistry, atom transfer radical polymerization and RAFT polymerization. The synthesized amphiphilic copolymers were finally used as additives to improve the hydrophilicity and the filtration performances of PES membranes.     

Synthesis of thermoresponsive block and graft copolymers via the combination of living cationic polymerization and RAFT polymerization using a vinyl ether-type RAFT agent

A novel vinyl ether-type RAFT agent, benzyl 2-(vinyloxy)ethyl carbonotrithioate (BVCT) was synthesized for various block copolymers via the combination of living cationic polymerization of vinyl ethers and reversible addition−fragmentation chain transfer (RAFT) polymerization. The novel BVCT–trifluoroacetic acid adduct play an important role to produce well-defined block copolymers, which is both as a cationogen under EtAlCl₂ initiation system in the presence of ethyl acetate for living cationic polymerization and a RAFT agent for blocks by RAFT polymerization. The resulting polymer, poly(vinyl ether)s, by living cationic polymerization had a high number average α-end functionality (≥0.9) as determined by both ¹H NMR and MALDI-TOF-MS spectrometry. In addition, this poly(vinyl ether)s worked well as a macromolecular chain transfer agent for RAFT polymerization. The RAFT polymerization of radically polymerizable monomers was conducted in toluene using 2,2′-azobis(isobutyronitrile) at 70 °C. For example, a double thermoresponsive block copolymer (MOVE₆₁-b-NIPAM₁₅₀) consisting of 2-methoxyethyl vinyl ether (MOVE) and N-isopropylacrylamide (NIPAM) was prepared via the combination of living cationic polymerization and RAFT polymerization. The block copolymer reversibly formed and deformed micellar assemblies above the phase separation temperature (T_ps) of poly(NIPAM) block in water. This BVCT is not only functioned as an initiator, but also acted as a monomer. When BVCT was copolymerized with MOVE by living cationic polymerization, followed by graft copolymerization with NIPAM via RAFT polymerization, well-defined graft copolymers (MOVE_n-co-BVCT_m)-g-NIPAM_x (n = 62–73, m = 1–9, x = 19–214) were successfully obtained. However, no micelle formed in water above T_ps of poly(NIPAM) graft chain unlike the case of block copolymers.     

Controlled synthesis of vinyl-functionalized homopolymers and block copolymers by RAFT polymerization of vinyl methacrylate

Reversible addition-fragmentation chain transfer (RAFT) polymerization of an asymmetrical divinyl monomer, vinyl methacrylate (VMA), was investigated under various conditions. RAFT polymerization of VMA using a dithioester-type chain transfer agent (CTA) under suitable conditions afforded soluble polymers with a high content of pendant vinyl ester side chains in sufficient yields (>70%). The monomer concentration, the nature of the CTA, and the CTA/initiator ratio were found to affect the polymerization reaction and the structure of the resulting polymers; this behavior is attributed to the relative propensities for intermolecular propagating/cross-linking reactions and intramolecular cyclization. A kinetic study of the RAFT polymerization of VMA with the dithioester-type CTA 1 suggested that the propagation reaction of the methacryloyl group proceeded predominantly with a certain level of intramolecular cyclization during the early stage of the polymerization and intermolecular cross-linking during the final stage of the polymerization. Block copolymers with one segment featuring pendant vinyl functionality were synthesized by RAFT polymerization of VMA using poly(methyl methacrylate) as a macro-chain transfer agent (macro-CTA).     

Synthesis of comb-shaped copolymers by combination of reversible addition-fragmentation chain transfer polymerization and cationic ring-opening polymerization

Comb-shaped graft copolymers with poly(methyl acrylate) as a handle were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization and ring-opening polymerization (ROP) techniques in three steps. First, copolymers of poly(styrene-co-chloromethyl styrene), poly(St-co-CMS), were prepared by RAFT copolymerization of St and CMS using 1-(ethoxycarbonyl)prop-1-yl dithiobenzoate (EPDTB) as RAFT agent. Second, the polymerization of MA using poly(St-co-CMS)-SC(S)Ph as macromolecular chain transfer agent produced block copolymer poly(St-co-CMS)-b-PMA. Third, cationic ring-opening polymerization of THF was performed using poly(St-co-CMS)-b-PMA/AgClO₄ as initiating system to produce comb-shaped copolymers. The structures of the poly(St-co-CMS), poly(St-co-CMS)-b-PMA and final comb-shaped copolymers were characterized by ¹H NMR spectroscopy and gel permeation chromatography (GPC).     

One-pot synthesis of poly(vinyl alcohol)-based biocompatible block copolymers using a dual initiator for ROP and RAFT polymerization

Biocompatible poly(ε-caprolactone)-b-poly(vinyl alcohol) (PCL-b-PVA), poly(δ-valerolactone)-b-PVA, and poly(trimethylene carbonate)-b-PVA block copolymers were synthesized at 30 °C using a hydroxyl-functionalized xanthate reversible addition-fragmentation chain transfer (RAFT) agent, 2-hydroxyethyl 2-(ethoxycarbonothioylthio)propanoate, as a dual initiator for ring-opening polymerization (ROP) and RAFT polymerization in a one-pot procedure. The ROP of ε-caprolactone, δ-valerolactone, and trimethylene carbonate was first performed using diphenyl phosphate as the ROP catalyst followed by the RAFT polymerization of vinyl chloroacetate after quenching the ROP with 4-dimethyamino pyridine. The resulting block copolymers were aminolyzed directly to the PVA-based biocompatible block copolymers by adding hexylamine to the reaction mixture. To the best of our knowledge, this is the most convenient method for synthesizing PVA-based biocompatible block copolymers.     

Thermoresponsive core–shell nanoparticles with cross-linked π-conjugate core based on amphiphilic block copolymers by RAFT polymerization and palladium-catalyzed coupling reactions

Well-defined amphiphilic block copolymers composed of S-vinyl sulfides and N-isopropyl acrylamide (NIPAM) were synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization. Thermoresponsive core–shell nanoparticles with cross-linked π-conjugate cores were obtained by in situ cross-linking reactions between 4-bromophenyl moieties in the block copolymers and diboronic acids or a diamine compound in the presence of a palladium catalyst following micelle formation in ethanol/H₂O or ethanol. We initially investigated RAFT polymerization of two S-vinyl sulfide derivatives, namely phenyl vinyl sulfide (PVS) and 4-bromophenyl vinyl sulfide (BPVS), using a dithiocarbamate-type chain transfer agent (CTA). Then, RAFT polymerization of NIPAM using poly(S-vinyl sulfide) macro-CTAs was conducted to synthesize the amphiphilic block copolymers. Suzuki and Buchwald-Hartwig coupling reactions were found to be effective in the preparation of core–shell nanoparticles with thermoresponsive shells and cross-linked optoelectronic cores. The resulting nanoparticles showed characteristic thermoresponsive properties, as confirmed by turbidity and dynamic light scattering measurements. Stable and uniform core cross-linked nanoparticles were successfully prepared by the in situ palladium-catalyzed coupling reactions, and the optoelectronic and thermoresponsive properties of the nanoparticles could be tuned depending on the nature of the difunctional coupling agents, reaction conditions, and comonomer composition of the block copolymers.     

Well-defined diblock copolymers of poly(tert-butyldimethylsilyl methacrylate) and poly(dimethylsiloxane) synthesized by RAFT polymerization

We report the application of reversible addition-fragmentation chain transfer (RAFT) polymerization using poly(dimethylsiloxane) (PDMS) chain transfer agents toward the synthesis of a variety of diblock copolymers containing tert-butyldimethylsilyl methacrylic (MASi) monomer units. The methodology relies on the synthesis of PDMS monofunctional chain transfer agents easily available in one synthetic step from commercially available hydroxylated PDMSs. The RAFT process enables access to polymer chains with narrow molar mass distributions and high conversions. Data from differential scanning calorimetric measurements revealed that the diblock copolymers exhibited two glass transition temperatures, corresponding to the PDMS- and PMASi-enriched phases, respectively. Copolymerizations of MASi and butyl methacrylate (BMA) within the second block led to immiscible phases with lower glass transition temperatures than PDMS-block-PMASi copolymers.     

Vesicular and micellar self‐assembly of stimuli‐responsive poly(N‐isopropyl acrylamide‐b‐9‐anthracene methyl methacrylate) amphiphilic diblock copolymers

Dually responsive amphiphilic diblock copolymers consisting of hydrophilic poly(N‐isopropyl acrylamide) [poly(NIPAAm)] and hydrophobic poly(9‐anthracene methyl methacrylate) were synthesized by reversible addition fragmentation chain‐transfer (RAFT) polymerization with 3‐(benzyl sulfanyl thiocarbonyl sulfanyl) propionic acid as a chain‐transfer agent. In the first step, the poly(NIPAAm) chain was grown to make a macro‐RAFT agent, and in the second step, the chain was extended by hydrophobic 9‐anthryl methyl methacrylate to yield amphiphilic poly(N‐isopropyl acrylamide‐b‐9‐anthracene methyl methacrylate) block copolymers. The formation of copolymers with three different hydrophobic block lengths and a fixed hydrophilic block was confirmed from their molecular weights. The self‐assembly of these copolymers was studied through the determination of the lower critical solution temperature and critical micelle concentration of the copolymers in aqueous solution. The self‐assembled block copolymers displayed vesicular morphology in the case of the small hydrophobic chain, but the morphology gradually turned into a micellar type when the hydrophobic chain length was increased. The variations in the length and chemical composition of the blocks allowed the tuning of the block copolymer responsiveness toward both the pH and temperature. The resulting self‐assembled structures underwent thermally induced and pH‐induced morphological transitions from vesicles to micelles and vice versa in aqueous solution. These dually responsive amphiphilic diblock copolymers have potential applications in the encapsulation of both hydrophobic and hydrophilic drug molecules, as evidenced from the dye encapsulation studies. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46474.     

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.     

Synthesis of N-acryloxysuccinimide copolymers by RAFT polymerization, as reactive building blocks with full control of composition and molecular weights

The reversible addition-fragmentation chain transfer (RAFT) polymerization process was used to synthesize well-defined N-acryloxysuccinimide (NAS) based copolymers, very useful reactive building blocks for various applications. Kinetic studies of RAFT copolymerization of NAS with a bi-substituted acrylamide derivative, N-acryloylmorpholine (NAM), were performed in the presence of tert-butyl dithiobenzoate (tBDB). An excellent control was reached with very high conversions (>95%), molecular weights (MW) up to 80?000 g mol⁻¹ and very narrow molecular weight distributions (MWD) (polydispersity indices, PDI<1.1), as determined by aqueous size exclusion chromatography with on-line light scattering detector (SEC/LS). In addition, the comparison of RAFT and conventional NAM/NAS free radical copolymerization indicated that the apparent reactivity ratios in RAFT are similar to the reactivity ratios determined from conventional copolymerization. An identical azeotropic composition (60/40 NAM/NAS molar ratio) was obtained providing perfectly random poly(NAM-co-NAS) copolymers with full control of composition and MW. These copolymer chains with regularly-distributed reactive functions can be integrated into more complex architectures. As an example, poly[(NAM-co-NAS)-b-NAM] block copolymers with length-varying poly(NAM) block were synthesized with a very efficient control over MW, MWD and composition.     

One-pot synthesis of poly(methacrylic acid)-b-poly(2,2,2-trifluoroethyl methacrylate) diblock copolymers via RAFT polymerization

In this work, the reversible addition-fragmentation chain transfer (RAFT) polymerization was utilized to synthesize the amphiphilic diblock copolymers of poly(methacrylic acid)-b-poly(2,2,2-trifluoroethyl methacrylate) (PMAA-b-PTFEMA) via one-pot two-step reaction protocol. The controlled radical polymerization of MAA monomer was first carried out in pure water by using 4-cyanopentanoic acid dithiobenzoate (CADB) as chain transfer agent. Subsequently, the as-synthesized PMAA homopolymers with dithiobenzoate end-groups were employed as macro-CTA and chain-extended in situ with the hydrophobic TFEMA monomer. The reactions were carried out in 1,4-dioxane/water medium. Both the polymerization of PMAA and PTFEMA blocks showed the well controllability on the molecular weighs and distributions. It was found that the amphiphilic diblock copolymers formed the stable spherical particles via the polymerization-induced self-assembly. Meanwhile, the effect of various parameters, such as the concentration ratio of TFEMA monomer over PMAA macro-CTA, the solvent condition (different ratio of 1,4-dixane/water), and the pH, on the RAFT polymerization of TFEMA monomer were investigated in detail. Their kinetic results suggested that the propagation of TFEMA monomer on the macro-CTA was performed at the particle/water interfaces. The concentration of chain transfer agents at the interfaces determined the polymerization rate. Finally, the stability of the fluorinated polymer dispersions was also evaluated in this work.     

Preparation of well‐defined block copolymer having one polystyrene segment and another poly(styrene‐alt‐maleic anhydride) segment with RAFT polymerization

Block copolymers, polystyrene‐b‐poly(styrene‐co‐maleic anhydride), have been prepared by reversible addition‐fragmentation chain transfer (RAFT) polymerization technique using three different approaches: 1‐phenylethyl phenyldithioacetate (PEPDTA) directly as RAFT agent, mediated polystyrene (PS) block as the macromolecular PS‐RAFT agent and mediated poly(styrene‐maleic anhydride) (SMA) block with alternating sequence as the macromolecular SMA‐RAFT agent. Copolymers synthesized in the one‐step method using PEPDTA as RAFT agent possess one PS block and one SMA block with gradient structure. When the macromolecular RAFT agents are employed, copolymers with one PS block and one alternating SMA block can be produced. However, block copolymers with narrow molecular weight distribution (MWD) can only be obtained using the PS‐RAFT agent. The MWD deviates considerably from the typical RAFT polymerization system when the SMA is used as the RAFT agent. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

RAFT synthesis of poly(N‐isopropylacrylamide) and poly(methacrylic acid) homopolymers and block copolymers: Kinetics and characterization

Reversible addition‐fragmentation chain transfer (RAFT) polymerization was used successfully to synthesize temperature‐responsive poly(N‐isopropylacrylamide) (PNIPAAm), poly(methacrylic acid) (PMAA), and their temperature‐responsive block copolymers. Detailed RAFT polymerization kinetics of the homopolymers was studied. PNIPAAm and PMAA homopolymerization showed living characteristics that include a linear relationship between M _n and conversion, controlled molecular weights, and relatively narrow molecular weight distribution (PDI < 1.3). Furthermore, the homopolymers can be reactivated to produce block copolymers. The RAFT agent, carboxymethyl dithiobenzoate (CMDB), proved to control molecular weight and PDI. As the RAFT agent concentration increases, molecular weight and PDI decreased. However, CMDB showed evidence of having a relatively low chain transfer constant as well as degradation during polymerization. Solution of the block copolymers in phosphate buffered saline displayed temperature reversible characteristics at a lower critical solution temperature (LCST) transition of 31°C. A 5 wt % solution of the block copolymers form thermoreversible gels by a self‐assembly mechanism above the LCST. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1191–1201, 2006