Organoboronium amphiphilic block copolymers

A new class of amphiphilic organometallic block copolymers with cationic organoboron pendant groups was developed. Selective replacement of one of the bromine substitutents on each boryl group of the block copolymer PSBBr₂‐b‐PS with an organometallic reagent ArM (ArM = 2,4,6‐trimethylphenyl copper, 4‐t‐butylphenyltrimethyl tin) followed by treatment with 2,2′‐bipyridine gave the novel block copolymers [ 3Ar ](Br)_n as light yellow solid materials that show good stability in air and moisture and high solubility in most organic solvents. Their structure and composition were confirmed by multinuclear NMR, GPC, and elemental analysis. Highly regular micellar aggregates form in block‐selective solvents (e.g., MeOH, toluene) as demonstrated by ¹H NMR, dynamic light scattering, and transmission electron microscopy. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6612–6618, 2009     

Morphological transitions in aggregates of thermosensitive poly(ethylene oxide)‐b‐poly(N‐isopropylacrylamide) block copolymers prepared via RAFT polymerization

Double hydrophilic poly(ethylene oxide)‐b‐poly(N‐isopropylacrylamide) (PEO‐b‐PNIPAM) block copolymers were synthesized via reversible addition‐fragmentation chain transfer (RAFT) polymerization, using a PEO‐based chain transfer agent (PEO‐CTA). The molecular structures of the copolymers were designed to be asymmetric with a short PEO block and long PNIPAM blocks. Temperature‐induced aggregation behavior of the block copolymers in dilute aqueous solutions was systematically investigated by a combination of static and dynamic light scattering. The effects of copolymer composition, concentration (C_p), and heating rate on the size, aggregation number, and morphology of the aggregates formed at temperatures above the LCST were studied. In slow heating processes, the aggregates formed by the copolymer having the longest PNIPAM block, were found to have the same morphology (spherical “crew‐cut” micelles) within the full range of C_p. Nevertheless, for the copolymer having the shortest PNIPAM block, the morphology of the aggregates showed a great dependence on C_p. Elongation of the aggregates from spherical to ellipsoidal or even cylindrical was observed. Moreover, vesicles were observed at the highest C_p investigated. Fast heating leads to different characteristics of the aggregates, including lower sizes and aggregation numbers, higher densities, and different morphologies. Thermodynamic and kinetic mechanisms were proposed to interpret these observations, including the competition between PNIPAM intrachain collapse and interchain aggregation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4099–4110, 2009     

Organizing thermodynamic data obtained from multicomponent polymer electrolytes: Salt‐containing polymer blends and block copolymers

The objective of this review is to organize literature data on the thermodynamic properties of salt‐containing polystyrene/poly(ethylene oxide) (PS/PEO) blends and polystyrene‐b‐poly(ethylene oxide) (SEO) diblock copolymers. These systems are of interest due to their potential to serve as electrolytes in all‐solid rechargeable lithium batteries. Mean‐field theories, developed for pure polymer blends and block copolymers, are used to describe phenomenon seen in salt‐containing systems. An effective Flory–Huggins interaction parameter, χ_eff , that increases linearly with salt concentration is used to describe the effect of salt addition for both blends and block copolymers. Segregation strength, χ_effN , where N is the chain length of the homopolymers or block copolymers, is used to map phase behavior of salty systems as a function of composition. Domain spacing of salt‐containing block copolymers is normalized to account for the effect of copolymer composition using an expression obtained in the weak segregation limit. The phase behavior of salty blends, salty block copolymers, and domain spacings of the latter systems, are presented as a function of chain length, composition and salt concentration on universal plots. While the proposed framework has limitations, the universal plots should serve as a starting point for organizing data from other salt‐containing polymer mixtures. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1177–1187     

Synthesis and self‐assembly of thermotropic block copolymer with long alkyl tethered cage silsesquioxane in the side chain

Thermotropic POSS‐containing poly(methacrylate) with long alkyl chain tethered polyhedral oligomeric silsesquioxane (POSS) in the side chain and the block copolymers (PMMA‐b‐PMAC11POSS) were developed by through living anionic polymerization. The resulting polymers indicated a phase transition temperature at 112 °C from spherocrystal to isotropic phase. The POSS‐containing polymer segments tended to form matrix of microphase‐separated nanostructures in the bulk even in the very low volume fraction, for instance, PMMA cylindrical nanostructure was obtained by PMMA₁₇₅‐b‐PMAC11POSS₁₁ (?_PMAC11POSS = 0.44). The control of thin film morphology was carried out by not only solvent annealing, but also thermal annealing, resulting in the formation of well‐ordered dot‐ and fingerprint‐type nanostructures. This is the first report in a series of POSS‐containing block polymers that are capable for thermal annealing to generate well‐ordered microphase‐separated nanostructures in thin films. The novel thermotropic POSS‐containing block copolymer offers a promising material for block copolymer lithography. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Supramolecular complexes of poly(3‐Hexylthiophene)‐block (and random)‐poly[3‐(2‐(6‐carboxyhexyl)methyl)thiophene] copolymers with perylene bisimide

Block and random copolymers of poly(3‐hexylthiophene) and poly[3‐(2‐(6‐carboxyhexyl)methyl)thiophene] with side‐chain carboxylic functionality ((P3HT‐b‐P3COOH) and (P3HT‐r‐P3COOH) were developed by Grignard Metathesis (GRIM) polymerization. The carboxylic functionality was introduced in the side chain via the oxazoline route. Both the block and random polythiophene copolymers were complexed with pyridine functionalized perylene bisimide to obtain supramolecular block and random polymer complexes. The complex formation in both systems was confirmed by ¹H NMR, WXRD and SAXS studies. An expansion of d spacing upon complex formation was observed in both the block and random copolymer, which could be traced by WXRD. Hole and electron mobilities measured for the supramolecular complexes indicated values which were higher by an order of magnitude for the supramolecular block complex (μ_h ≈ 2.9 × 10⁻⁴ cm²/Vs; μ_e ≈ 3.1 × 10⁻⁶ cm²/Vs) as compared to the random (μ_h ≈ 1.4 × 10⁻⁵ cm²/Vs; μ_e ≈ 4.7 × 10⁻⁷ cm²/Vs) copolymer. These results are indicative of the higher degree of disorder prevailing in the films of random copolymer system compared to the block copolymer. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1574–1583     

Amphiphilic diblock,triblock, and star block copolymers by living radical polymerization: Synthesis and aggregation behavior

Copper(I)‐mediated living radical polymerization was used to synthesize amphiphilic block copolymers of poly(n‐butyl methacrylate) [P(n‐BMA)] and poly[(2‐dimethylamino)ethyl methacrylate] (PDMAEMA). Functionalized bromo P(n‐BMA) macroinitiators were prepared from monofunctional, difunctional, and trifunctional initiators: 2‐bromo‐2‐methylpropionic acid 4‐methoxyphenyl ester, 1,4‐(2′‐bromo‐2′‐methyl‐propionate)benzene, and 1,3,5‐(2′‐bromo‐2′‐methylpropionato)benzene. The living nature of the polymerizations involved was investigated in each case, leading to narrow‐polydispersity polymers for which the number‐average molecular weight increased fairly linearly with time with good first‐order kinetics in the monomer. These macroinitiators were subsequently used for the polymerization of (2‐dimethylamino)ethyl methacrylate to obtain well‐defined [P(n‐BMA)_x‐b‐PDMAEMA_y]_z diblock (15,900; polydispersity index = 1.60), triblock (23,200; polydispersity index = 1.24), and star block copolymers (50,700; polydispersity index = 1.46). Amphiphilic block copolymers contained between 60 and 80 mol % hydrophilic PDMAEMA blocks to solubilize them in water. The polymers were quaternized with methyl iodide to render them even more hydrophilic. The aggregation behavior of these copolymers was investigated with fluorescence spectroscopy and dynamic light scattering. For blocks of similar comonomer compositions, the apparent critical aggregation concentration (cac = 3.22–7.13 × 10^?3 g L^?1) and the aggregate size (ca. 65 nm) were both dependent on the copolymer architecture. However, for the same copolymer structure, increasing the hydrophilic PDMAEMA block length had little effect on the cac but resulted in a change in the aggregate size. © 2002 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 439–450, 2002; DOI 10.1002/pola.10122     

Triple hydrogen‐bonding block copolymers via RAFT polymerization: Synthesis,vesicle formation,and molecule‐recognition behavior

Reversible addition fragmentation chain transfer polymerization afforded triple hydrogen‐bonding block copolymers (PBA‐b‐PDAD) with well‐controlled molecular weight and molecular weight distributions (1.2–1.4). The complexation via specific hydrogen bonding between these block copolymers in CHCl₃ provided an unprecedented approach for the formation of spherical vesicles. Atomic force microscopy and dynamic light‐scattering measurements revealed that the resultant polymeric vesicles were about 100 nm in radius. Triple hydrogen‐bonding interactions between maleimide and PBA‐b‐PDAD resulted in the dissociation of these spherical vesicles, facilitating the guest molecule recognition. The hydrogen‐bonding interaction between maleimide and the PBA‐b‐PDAD was further confirmed by ¹H NMR and FTIR spectra. These results indicated that these vesicles of triple hydrogen‐bonding block copolymer could be a potential new vehicle for molecular recognition. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1633–1638     

Synthesis of amphiphilic block copolymers bearing stable nitroxyl radicals

We present here the synthesis of two kinds of amphiphilic block copolymers, a diblock copolymer MPEG‐b‐PTAm and a triblock copolymer MPEG‐b‐PLA‐b‐PTAm, which can self‐assemble into micelles with nitroxyl radicals‐containing PTAm segment in the core. The structure of the block copolymers was characterized by ¹H NMR and GPC. Dynamic laser light scattering and transmission electron microscopy were used to study the micellar behavior of the two block copolymers in aqueous solution. The micelles carrying nitroxyl radicals in the core can generate electron paramagnetic resonance, which is stable for a period of time up to 8 min even in the presence of reducing reagent such as ascorbic acid. The enhanced stability against the reducing agent was ascribed to the inaccessibility of the nitroxyl radical core placed in the interior of the micelles. Combined with the biocompatibility, these micelles were promising to be used as the EPR probes for bioimaging in vivo. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Synthesis,micelle formation,and bulk properties of poly(ethylene glycol)‐b‐poly(pentafluorostyrene)‐g‐polyhedral oligomeric silsesquioxane amphiphilic hybrid copolymers

The synthesis, micelle formation, and bulk properties of semifluorinated amphiphilic poly(ethylene glycol)‐b‐poly(pentafluorostyrene)‐g‐cubic polyhedral oligomeric silsesquioxane (PEG‐b‐PPFS‐g‐POSS) hybrid copolymers is reported. The synthesis of amphiphilic PEG‐b‐PPFS block copolymers are achieved using atom transfer radical polymerization (ATRP) at 100 °C in trifluorotoluene using modified poly(ethylene glycol) as a macroinitiator. Subsequently, a proportion of the reactive para‐F functionality on the pentafluorostyrene units was replaced with aminopropylisobutyl POSS through aromatic nucleophilic substitution reactions. The products were fully characterized by ¹H‐NMR and GPC. The products, PEG‐b‐PPFS and PEG‐b‐PPFS‐g‐POSS, were subsequently self‐assembled in aqueous solutions to form micellar structures. The critical micelle concentrations (cmc) were estimated using two different techniques: fluorescence spectroscopy and dynamic light scattering (DLS). The cmc was found to decrease concomitantly with the number of POSS particles grafted per copolymer chain. The hydrodynamic particle sizes (R_h) of the micelles, calculated from DLS data, increase as the number of POSS molecules grafted per copolymer chain increases. For example, R_h increased from ～60 nm for PEG‐b‐PPFS to ～80 nm for PEG‐b‐PPFS‐g‐POSS25 (25 is the average number of POSS particles grafted copolymer chain). Static light scattering (SLS) data confirm that the formation of larger micelles by higher POSS containing copolymers results from higher aggregation numbers (N_agg), caused by increased hydrophobicity. The R_g/R_h values, where R_g is the radius of gyration calculated from SLS data, are consistent with a spherical particle model having a core‐shell structure. Thermal characterization by differential scanning calorimetry (DSC) reveals that the grafted POSS acts as a plasticizer; the glass transition temperature (T_g) of the PPFS block in the copolymer decreases significantly with increasing POSS content. Finally, the rhombohedral crystal structure of POSS in PEG‐b‐PPFS‐g‐POSS was verified by wide angle X‐ray diffraction measurements. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 152–163, 2010     

Synthesis of four‐armed poly(ε‐caprolactone)‐block‐poly(ethylene oxide) by diethylzinc catalyst

Biodegradable, amphiphilic, four‐armed poly(?‐caprolactone)‐block‐poly(ethylene oxide) (PCL‐b‐PEO) copolymers were synthesized by ring‐opening polymerization of ethylene oxide in the presence of four‐armed poly(?‐caprolactone) (PCL) with terminal OH groups with diethylzinc (ZnEt₂) as a catalyst. The chemical structure of PCL‐b‐PEO copolymer was confirmed by ¹H NMR and ¹³C NMR. The hydroxyl end groups of the four‐armed PCL were successfully substituted by PEO blocks in the copolymer. The monomodal profile of molecular weight distribution by gel permeation chromatography provided further evidence for the four‐armed architecture of the copolymer. Physicochemical properties of the four‐armed block copolymers differed from their starting four‐armed PCL precursor. The melting points were between those of PCL precursor and linear poly(ethylene glycol). The length of the outer PEO blocks exhibited an obvious effect on the crystallizability of the block copolymer. The degree of swelling of the four‐armed block copolymer increased with PEO length and PEO content. The micelle formation of the four‐armed block copolymer was examined by a fluorescent probe technique, and the existence of the critical micelle concentration (cmc) confirmed the amphiphilic nature of the resulting copolymer. The cmc value increased with increasing PEO length. The absolute cmc values were higher than those for linear amphiphilic block copolymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 950–959, 2004     

Temperature and pH dual stimuli responsive PCL‐b‐PNIPAAm block copolymer assemblies and the cargo release studies

A new atom transfer radical polymerization (ATRP) initiator, namely, 2‐(1‐(2‐azidoethoxy)ethoxy)ethyl 2‐bromo‐2‐methylpropanoate containing both “cleavable” acetal linkage and “clickable” azido group was synthesized. Well‐defined azido‐terminated poly(N‐isopropylacrylamide)s (PNIPAAm‐N₃)s with molecular weights and dispersity in the range 11,000–19,000 g mol^?1 and 1.20–1.28, respectively, were synthesized employing the initiator by ATRP. Acetal containing PCL‐b‐PNIPAAm block copolymer was obtained by alkyne–azide click reaction of azido‐terminated PNIPAAm‐N₃ with propargyl‐terminated PCL. Critical aggregation concentration (CAC) of PCL‐b‐PNIPAAm copolymer in aqueous solution was found to be 8.99 × 10^?6 M. Lower critical solution temperature (LCST) of PCL‐b‐PNIPAAm copolymer was found to be 32 °C which was lower than that of the precursor PNIPAAm‐N₃ (36.4 °C). The effect of dual stimuli viz . temperature and pH on size and morphology of the assemblies of PCL‐b‐PNIPAAm block copolymer revealed that the copolymer below LCST assembled in spherical micelles which subsequently transformed to unstable vesicles above the LCST. Heating these assemblies above 40 °C led to the precipitation of PCL‐b‐PNIPAAm block copolymer. Whereas, at decreased pH, micelles of PCL‐b‐PNIPAAm copolymer disintegrate due to the cleavage of acetal linkage and precipitation of hydrophobic hydroxyl‐terminated PCL. The encapsulated pyrene release kinetics from the micelles of synthesized PCL‐b‐PNIPAAm copolymer was found to be faster at higher temperature and at lower pH. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 1383–1396     

Synthesis and self‐assembling of poly(N‐isopropylacrylamide‐block‐poly(L‐lactide)‐block‐poly(N‐isopropylacrylamide) triblock copolymers prepared by combination of ring‐opening polymerization and atom transfer radical polymerization

Novel thermo‐responsive poly(N‐isopropylacrylamide)‐block‐poly(l ‐lactide)‐block‐poly(N‐isopropylacylamide) (PNIPAAm‐b‐PLLA‐b‐PNIPAAm) triblock copolymers were successfully prepared by atom transfer radical polymerization of NIPAAm with Br‐PLLA‐Br macroinitiator, using a CuCl/tris(2‐dimethylaminoethyl) amine (Me₆TREN) complex as catalyst at 25 °C in a N,N‐dimethylformamide/water mixture. The molecular weight of the copolymers ranges from 18,000 to 38,000 g mol^?1, and the dispersity from 1.10 to 1.28. Micelles are formed by self‐assembly of copolymers in aqueous medium at room temperature, as evidenced by ¹H NMR, dynamic light scattering (DLS) and transmission electron microscopy (TEM). The critical micelle concentration determined by fluorescence spectroscopy ranges from 0.0077 to 0.016 mg mL^?1. ¹H NMR analysis in selective solvents confirmed the core‐shell structure of micelles. The copolymers exhibit a lower critical solution temperature (LCST) between 32.1 and 32.8 °C. The micelles are spherical in shape with a mean diameter between 31.4 and 83.3 nm, as determined by TEM and DLS. When the temperature is raised above the LCST, micelle size increases at high copolymer concentrations due to aggregation. In contrast, at low copolymer concentrations, decrease of micelle size is observed due to collapse of PNIPAAm chains. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3274–3283     

The influence of solution‐state conditions and stirring rate on the assembly of poly(acrylic acid)‐containing amphiphilic triblock copolymers with multi‐amines

In the effort towards making nanoscale objects and assemblies feasible for use as functional materials, it is imperative to obtain control over the fundamental architectures and essential to understand what experimental conditions cause the manifestation of specific morphologies. A number of factors are known to influence the shape during the self‐assembly of amphiphilic block copolymers in solution, including solvent composition, polymer length, hydrophobicity versus hydrophilicity, as well as the addition of additives that can interact with segments of the block copolymers. This research, focused on developing an understanding of the micellar architectures accessed by the amphiphilic triblock copolymer of acrylic acid, methyl acrylate, and styrene, PAA₈₅‐b‐PMA₄₀‐b‐PS₃₅, as a function of the stirring rate, together with other factors, when undergoing coassembly with ethylenediamine or diethylenetriamine in water/tetrahydrofuran solutions. The work demonstrates that the rate at which the polymer solution was stirred impacts the shape of the solution‐state assemblies formed by the triblock copolymer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Well‐defined diblock copolymers possessing fluorescent and metal chelating functionalities as novel macromolecular sensors for amines and metal ions

The amino‐ and metal‐ion sensing capability of a novel type of well‐defined block copolymers based on 9‐anthrylmethyl methacrylate (AnMMA; hydrophobic, fluorescent) and 2‐(acetoacetoxy)ethyl methacrylate (AEMA; hydrophobic, metal chelating) has been investigated in organic media. AEMA_x‐b‐AnMMA_y diblock copolymers were prepared for the first time using reversible addition‐fragmentation chain transfer (RAFT) polymerization. All polymers were characterized in terms of molecular weights, polydispersity indices and compositions by size exclusion chromatography and ¹H NMR spectroscopy, respectively. The glass transition (T_g) temperatures of the AEMA_x and AnMMA_x homopolymers and the AEMA_x‐b‐AnMMA_y diblock copolymers were determined using differential scanning calorimetry. These systems were evaluated toward their ability to act as effective dual chemosensors (i.e., amino‐ and metal‐ion sensors) in an organic solvent (chloroform). More precisely, the fluorescence intensity of both the AnMMA_x homopolymers and the AnMMA_x‐b‐AEMA_y diblock copolymers in solution exhibited a significant decrease in the presence of triethylamine. Moreover, the presence of iron (III) cations were also found to significantly affect the fluorescence signal of the anthracene moieties when those were combined in a block copolymer structure with the AEMA units, due to complex formation occurring between the β‐ketoester groups of the AEMA_x segment and the cations. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Syntheses,characterization, and properties of multiblock copolymers consisting of polyisobutylene and poly(L‐lactide) segments

The syntheses of {‐poly(L ‐lactide) (PLLA)‐b‐polyisobutylene (PIB)‐}_n multiblock copolymers were accomplished for the first time by chain extension of PLLA‐b‐PIB‐b‐PLLA triblock copolymers. Well‐defined PLLA‐b‐PIB‐b‐PLLA triblock copolymers with predictable M_ns, low PDIs (1.10–1.18) and excellent blocking efficiencies were prepared by anionic ring‐opening polymerizations of L ‐lactide initiated with hydroxyallyl telechelic PIB (HO‐Allyl‐PIB‐Allyl‐OH) in toluene at 110 °C. The triblock copolymers were successfully chain extended with 4,4′‐methylenebis(phenylisocyanate) (MDI) to obtain the multiblock copolymers with good gravimetric yields of ～86 to 96%. The chain‐extended polymers were soluble in a range of common organic solvents. The block copolymers showed two glass transition temperatures in differential scanning calorimetric analysis for the PIB and PLLA blocks indicating microphase separation, which was supported by atomic force microscopy images. The as‐synthesized compression molded multiblock copolymers exhibited tensile strengths in the range of 8–24 MPa with elongations at break in the range of 2.5–400%. The static and dynamic mechanical properties showed a strong dependence on the relative PLLA content in the copolymer. The dynamic mechanical analysis also indicated microphase separation at higher PLLA compositions. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3490–3505, 2009     

Comparison of micelles formed by amphiphilic star block copolymers prepared in the presence of a nonmetallic monomer activator

In this article, we describe the synthesis of PEG‐b‐polyester star block copolymers via ring‐opening polymerization (ROP) of ester monomers initiated at the hydroxyl end group of the core poly(ethylene glycol) (PEG) using HCl Et₂O as a monomer activator. The ROP of ε‐caprolactone (CL), trimethylene carbonate (TMC), or 1,4‐dioxan‐2‐one (DO) was performed to synthesize PEG‐b‐polyester star block copolymers with one, two, four, and eight arms. The PEG‐b‐polyester star block copolymers were obtained in quantitative yield, had molecular weights close to the theoretical values calculated from the molar ratio of ester monomers to PEG, and exhibited monomodal GPC curves. The crystallinity of the PEG‐b‐polyester star block copolymers was determined by differential scanning calorimetry and X‐ray diffraction. Copolymers with a higher arm number had a higher tendency toward crystallization. The crystallinity of the PEG‐b‐polyester star block copolymers also depended on the nature of the polyester block. The CMCs of the PEG‐b‐PCL star block copolymers, determined from fluorescence measurements, increased with increasing arm number. The CMCs of the four‐arm star block copolymers with different polyester segments increased in the order 4a‐PEG‐b‐PCL < 4a‐PEG‐b‐PDO < 4a‐PEG‐b‐PLGA < 4a‐PEG‐b‐PTMC, suggesting a relationship between CMC and star block copolymer crystallinity. The partition equilibrium constant, K_v, which is an indicator of the hydrophobicity of the micelles of the PEG‐polyester star block copolymers in aqueous media, increased with decreasing arm number and increasing crystallinity. A key aspect of the present work is that we successfully prepared PEG‐b‐polyester star block copolymers by a metal‐free method. Thus, unlike copolymers synthesized by ROP using a metal as the monomer activator, our copolymers do not contain traces of metals and hence are more suitable for biomedical applications. Moreover, we confirmed that the PEG‐b‐polyester star block copolymers form micelles and hence may be potential hydrophobic drug delivery vehicles. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2084–2096, 2008     

Synthesis of tertiary amine‐based pH‐responsive polymers by RAFT Polymerization

Well‐defined tertiary amine‐based pH‐responsive homopolymers and block copolymers were synthesized via reversible addition‐fragmentation chain transfer (RAFT) polymerization using 4‐cyanopentanoic acid dithiobenzoate (CPAD) as the RAFT agent for homopolymers and a poly(ethylene glycol) (PEG) macro‐RAFT agent for the block copolymers. ¹H NMR and gel permeation chromatography results confirmed the successful synthesis of these homopolymers and block copolymers. Kinetics studies indicated that the formation of both the homopolymers and the block copolymers were well defined. The pKa titration experiments suggested that the homopolymers and the related block copolymers have a similar pKa. The dynamic light scattering investigation showed that all of the block copolymers underwent a sharp transition from unimers to micelles around their pKa and the hydrodynamic diameter (D_h) was not only dependent on the molecular weight but also on the composition of the block copolymers. The polymer solution of PEG‐b‐PPPDEMA formed the largest micelle compare to the PEG‐b‐PDPAEMA and PEG‐b‐PDBAEMA with a similar molecular weight. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1010–1022     

Synthesis and morphology of polyethylene‐block‐poly(methyl methacrylate) through the combination of metallocene catalysis with living radical polymerization

Polyethylene‐block‐poly(methyl methacrylate) (PE‐b‐PMMA) was successfully synthesized through the combination of metallocene catalysis with living radical polymerization. Terminally hydroxylated polyethylene, prepared by ethylene/allyl alcohol copolymerization with a specific zirconium metallocene/methylaluminoxane/triethylaluminum catalyst system, was treated with 2‐bromoisobutyryl bromide to produce terminally esterified polyethylene (PE‐Br). With the resulting PE‐Br as an initiator for transition‐metal‐mediated living radical polymerization, methyl methacrylate polymerization was subsequently performed with CuBr or RuCl₂(PPh₃)₃ as a catalyst. Then, PE‐b‐PMMA block copolymers of different poly(methyl methacrylate) (PMMA) contents were prepared. Transmission electron microscopy of the obtained block copolymers revealed unique morphological features that depended on the content of the PMMA segment. The block copolymer possessing 75 wt % PMMA contained 50–100‐nm spherical polyethylene lamellae uniformly dispersed in the PMMA matrix. Moreover, the PE‐b‐PMMA block copolymers effectively compatibilized homopolyethylene and homo‐PMMA at a nanometer level. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3965–3973, 2003     

Polystyrene‐b‐poly(2,2,2‐trifluoroethyl acrylate)‐b‐polystyrene copolymers: Synthesis and fabrication of their hydrophobic porous films,spheres, and fibers

New block copolymers Polystyrene‐b‐poly (2,2,2‐trifluoroethyl acrylate)‐b‐Polystyrene (PS‐PTFEA‐PS) with controlled molecular weight (M_n=5000‐11000 g?mol^?1) and narrow molecular weight distribution (M_w/M_n=1.13‐1.17) were synthesized via RAFT polymerization. The molecular structure and component of PS‐PTFEA‐PS block copolymers were characterized through ¹H NMR, ¹⁹F NMR, GPC, FT‐IR and elemental analysis. The porous films of such copolymers with average pore size of 0.80‐1.34 μm and good regularity were fabricated via a static breath‐figure (BF) process. The effects of solvent, temperature, and polymer concentration on the surface morphology of such film were investigated. In addition, microstructured spheres and fibers of such block copolymers were fabricated by electrospinning process and observed by scanning electron microscopy (SEM). Furthermore, the hydrophobicity of porous films, spheres, and fibers was investigated. The porous film showed a good hydrophobicity with the water‐droplet contact angles of 129°, and the fibers showed higher hydrophobicity with the water‐droplet contact angles of 142°. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 678–685