Copolymerization behavior of direct polycondensation of AB2 and AB monomers that forms hyperbranched aromatic polyamide copolymers

The copolymerization behavior of the one‐step direct polycondensation of 3,5‐bis‐(4‐aminophenoxy)benzoic acid (AB₂ monomer) and 3‐(4‐aminophenoxy)benzoic acid (AB monomer) was investigated by IR and ¹³C NMR measurements. IR measurements revealed that the content of the AB₂ units in the polymer was higher in the early stages of polymerization. ¹³C NMR spectra of the polymers indicated that the number of dendritic units increased slowly with increasing reaction time. The stepwise copolymerization of the AB₂ and AB monomers was also carried out, and the structure was analyzed by ¹³C NMR measurements. Copolymer synthesized stepwise by adding AB₂ monomer first (polymer II ) had more dendritic units and less terminal units as compared with the one‐step copolymer (polymer I ). Copolymer synthesized stepwise by adding AB monomer first gave a resulting copolymer (polymer III ) composed of long AB chains. The solubility of the stepwise copolymers was low, and the inherent viscosity was high in comparison with the one‐step copolymer as a result of the difference in architecture of the copolymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3304–3310, 2001     

Hyperbranched poly(ether–urea)s using AB2‐type blocked isocyanate monomer and azide monomer: Synthesis,characterization, reactive end functionalization,and copolymerization with AB monomer

3,5‐bis(4‐aminophenoxy)phenyl phenylcarbamate—a novel AB₂‐type blocked isocyanate monomer and 3,5‐bis{ethyleneoxy(4‐aminophenoxy)}phenyl carbonyl azide—a novel AB₂‐type azide monomer were synthesized in high yield. Step‐growth polymerization of these monomers were found to give a first example of hyperbranched poly (aryl‐ether‐urea) and poly(aryl‐alkyl‐ether‐urea). Molecular weights (M_w) of the polymer were found to vary from 1,858 to 52,432 depending upon the monomer and experimental conditions used. The polydispersity indexes were relatively narrow due to the controlled regeneration of isocyanate functional groups for the polymerization reaction. The degree of branching (DB) was determined using ¹H‐NMR spectroscopy and the values ranged from 87 to 54%. All the polymers underwent two‐stage decomposition and were stable up to 300 °C. Functionalized end‐capping of poly(aryl‐ether‐urea) using phenylchloroformate and di‐t‐butyl dicarbonate (Boc)₂O changed the thermal properties and solubility of the polymers. Copolymerization of AB₂‐type blocked isocyante monomer with functionally similar AB monomer were also carried out. The molecular weights of copolymers were found to be in the order of 6 × 10⁵ with narrow dispersity. It was found that the T_g's of poly(aryl‐alkyl‐ether‐urea)s were significantly less (46–49 °C) compared to poly(aryl‐ether‐urea)s. Moreover the former showed melting transition at 154 °C, which was not observed in the latter case. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2959–2977, 2007     

Synthesis and characterization of hyperbranched aromatic polyamide copolymers prepared from AB2 and AB monomers

A series of hyperbranched aromatic polyamide copolymers has been prepared and characterized from direct polycondensation of AB₂ and AB monomers. Structure of the monomers and the molar ratio of AB₂/AB showed strong influence on the properties of resulting copolymers. A small amount of AB₂ branching unit improved markedly the solubility of the resulting copolymer. Mark-Houwink parameters of the copolymers were essentially independent of the mole ratio of the monomers. The physical and mechanical properties of resulting copolymers were influenced not only by the mole ratio of monomers, but also by the structure of the monomers employed.     

Butadiene–isoprene copolymerization with V(acac)3‐MAO. Crystalline and amorphous trans‐1,4 copolymers

Butadiene‐isoprene copolymerization with the system V(acac)₃‐MAO was examined. Crystalline or amorphous copolymers were obtained depending on isoprene content. Both butadiene and isoprene units exhibit a trans‐1,4 structure and are statistically distributed along the polymer chain. Polymer microstructure, comonomer composition, and distribution along the polymer chain were determined by ¹³C and ¹H NMR analysis. The thermal and X‐ray behaviors of the copolymers were also investigated and compared with results from solid‐state ¹³C NMR experiments. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4635–4646, 2007     

Inclusion complexes of α‐cyclodextrin and (AB)n block copolymers

Cyclodextrins thread onto polymer chains to form inclusion complexes, especially when the polymer is hydrophobic relative to the solvent. Selective threading might occur when the polymer architecture contains both hydrophobic and hydrophilic segments. α‐Cyclodextrin formed crystalline inclusion complexes with (AB)_n microblock copolymers, where the A block was a linear alkyl segment containing a single double bond and the B block was an exact length segment of poly(ethylene oxide). The complexes were isolated and characterized by solution and solid‐state NMR, X‐ray diffraction, differential scanning calorimetry, and thermogravimetric analysis. Each method confirmed complex formation and showed that the physical properties of the complexes were distinct from those of its individual components. The X‐ray data were consistent with known inclusion complexes having a channel or column crystal structure. The stoichiometry of the complex formation, 2.3 α‐cyclodextrin rings per polymer repeat unit, was determined by NMR analysis of the complexes and from an analysis of the inclusion complex yields. The data suggest that the inclusion complex stoichiometry is defined by the increasing insolubility of the polymer–cyclodextrin complex. Solid‐state NMR data were consistent with a preference for threading onto hydrophobic segments of the (AB)_n polymer. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2731–2739, 2001     

Facile synthesis and characterization of hyperbranched poly(ether amide)s generated from Michael addition polymerization of in situ created AB2 monomers

A new straightforward strategy for synthesis of novel hyperbranched poly (ether amide)s from readily available monomers has been developed. By optimizing the reaction conditions, the AB₂‐type monomers were formed dominantly during the initial reaction stage. Without any purification, the AB₂ intermediate was subjected to further polymerization in the presence (or absence) of an initiator, to prepare the hyperbranched polymer‐bearing multihydroxyl end‐groups. The influence of monomer, initiator, and solvent on polymerization and the molecular weight (MW) of the resultant polymers was studied thoroughly. The MALDI–TOF MS of the polymers indicated that the polymerization proceeded in the proposed way. Analyses of ¹H NMR and ¹³C NMR spectra revealed the branched structures of the polymers obtained. These polymers exhibit high‐moderate MWs and broad MW distributions determined by gel permeation chromatography (GPC) in combination with triple detectors, including refractive index, light scattering, and viscosity detectors. In addition, the examination of the solution behavior of these polymers showed that the values of intrinsic viscosity [η] and the Mark–Houwink exponent α were remarkably lower compared with their linear analogs, because of their branched nature. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4309–4321, 2007     

Synthesis and properties of hyperbranched polyurethanes,hyperbranched polyurethane copolymers with and without ether and ester groups using blocked isocyanate monomers

Starting from 3,5‐diamino benzoic acid, 2‐hydroxy propyl[3,5‐bis{(benzoxycarbonyl)imino}]benzyl ether, an AB₂‐type blocked isocyanate monomer with flexible ether group, and 2‐hydroxy propyl[3,5‐bis{(benzoxycarbonyl)imino}]benzoate, an AB₂‐type blocked isocyanate monomer with ester group, were synthesized for the first time. Using the same starting compound, 3,5‐bis{(benzoxycarbonyl)imino}benzylalcohol, an AB₂‐type blocked isocyanate monomer, was synthesized through a highly efficient short‐cut route. Step‐growth polymerization of these monomers at individually optimized experimental conditions results in the formation of hyperbranched polyurethanes with and without ether and ester groups. Copolymerizations of these monomers with functionally similar AB monomers were also carried out. The molecular weights of the polymers were determined using GPC and the values (M_w) were found to vary from 1.5 × 10⁴ to 1.2 × 10⁶. While hyperbranched polyurethanes having no ether or ester group were found to be thermally stable up to 217 °C, hyperbranched poly(ether–urethane)s and poly(ester–urethane)s were found to be thermally stable up to 245 and 300 °C, respectively. Glass transition temperature (T_g) of polyurethane was reduced significantly when introducing ether groups into the polymer chain, whereas T_g was not observed even up to 250 °C in the case of poly(ester–urethane). Hyperbranched polyurethanes derived from all the three different AB₂ monomers were soluble in highly polar solvents and the copolymers showed improved solubility. Polyethylene glycol monomethyl ether of molecular weight 550 and decanol were used as end‐capping groups, which were seen to affect the thermal, solution, and solubility properties of polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3877–3893, 2007     

Synthesis of multiblock hyperbranched‐linear poly(ether sulfone) copolymers

Hyperbranched poly(ether sulfone) was prepared in the presence of an oligomeric linear poly(ether sulfone) to generate multiblock hyperbranched‐linear (LxHB) copolymers. The LxHB copolymers were prepared in a two‐step, one‐pot synthesis by first polymerizing AB monomer to generate a linear block of a desired molecular weight followed by addition of the AB₂ monomer in a large excess (19:1, AB₂:AB) to generate the hyperbranched block. NMR integration analysis indicates that AB₂:AB ratio is independent of the reaction time. Because the molecular weight still increases with reaction time, these results suggest that polymer growth continues after consumption of monomer by condensation into a multiblock architecture. The LxHB poly(ether sulfone)s have better thermal stability (10% mass loss > 343 vs. 317 °C) and lower T_g (200 vs. > 250 °C) than the hyperbranched homopolymer, higher T_g than the linear homopolymer (<154 °C), while little difference in the solubility character was observed between the two polymers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4785–4793, 2008     

Hyperbranched aryl polycarbonates derived from A2B monomers versus AB2 monomers

Hyperbranched aryl polycarbonates were prepared via the polymerizations of A₂B and AB₂ monomers, which involved the condensation of chloroformate (A) functionalities with tert‐butyldimethylsilyl‐protected phenols (B), facilitated by reactions with silver fluoride. The polymerization of the A₂B monomer gave hyperbranched polycarbonates bearing fluoroformate chain ends, which were hydrolyzed to phenolic chain‐end moieties and further elaborated to tert‐butyldimethylsilyl ether groups. The polymerization of the AB₂ monomer gave tert‐butyldimethylsilyl ether‐terminated hyperbranched polycarbonates. The polymerizations were conducted at 23–70 °C in 20% acetonitrile/tetrahydrofuran in the presence of a stoichiometric excess of silver fluoride for 20–40 h to afford hyperbranched polycarbonates with weight‐average molecular weights exceeding 100,000 Da and polydispersity indices of typically 2–3. The degrees of branching were determined by a reductive degradation procedure followed by high‐performance liquid chromatography. Alternatively, the degrees of branching were measurable by solution‐state ¹H NMR analyses and agreed with the statistical 50% branching expected for the polymerization of A₂B and AB₂ monomers not experiencing constructive or destructive electronic effects on the reactivity of the multiple functional groups. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 823–835, 2002; DOI 10.1002/pola.10167     

Polymeric ruthenium bipyridine complexes: New potential materials for polymer solar cells

Methyl methacrylate‐containing bipyridine monomers were synthesized with a hydoxy‐functionalized bipyridine. The 4′‐methyl group of the 2,2′‐bipyridine was used to introduce hydoxy‐functionalized alkyl spacers of two different lengths. Two, different synthetic routes were applied for the preparation of the hydoxy‐functionalized bipyridine via a bromo‐(C₇ spacer) or a silylated‐(C₃ spacer) intermediate. A copolymer of poly(methyl methacrylate) with bipyridine units in the side chains was prepared by free‐radical copolymerization and characterized with ¹H NMR, ultraviolet–visible, and IR spectroscopy as well as gel permeation chromatography. The bipyridine units of the copolymer were reacted with ruthenium bipyridine precursors. The resulting graft copolymers displayed promising photophysical and electrochemical properties, opening interesting perspectives for applications in the field of solar‐cell devices. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 374–385, 2004     

Unimolecular micelles and reverse micelles based on hyperbranched polyethers—Comparative study of AB2 + A‐R and A2 + B3 + A‐R type strategies

Core‐shell type hyperbranched polymers that are capable of forming unimolecular micelles and reverse micelles in aqueous and hydrocarbon medium, respectively, were synthesized via two approaches, namely AB₂ + A‐R and A₂ + B₃ + A‐R type copolymerizations. In case of micelle‐forming polymers, an AB₂ monomer carrying a decamethylene spacer was used along with heptaethylene glycol monomethyl ether (HPEG) as the A‐R type comonomer. One the other hand, for the preparation of reverse micelle‐forming polymers, an AB₂ monomer containing an oligo(oxyethylene) spacer was used along with cetyl alcohol as the A‐R type comonomer. The former was readily soluble in water while the latter was soluble in hydrocarbon solvents like hexane. NMR spectral studies confirmed that both the approaches generated highly branched structures wherein about 65–70% of the terminal B groups were capped by the A‐R comonomer. Dye‐uptake measurements revealed that the polymers prepared via the AB₂ + A‐R approach exhibited a significantly larger uptake compared with those prepared via the A₂ + B₃ + A‐R approach. This suggests that the AB₂ + A‐R approach generates hyperbranched polymers with better defined core‐shell topology when compared with polymers prepared via the A₂ + B₃ + A‐R approach, which is in accordance with previous studies that suggest that A₂ + B₃ approach yields polymers with significantly lower branching levels and consequently less compact structures. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 80–91, 2009     

Synthesis and characterization of alkylated N‐vinylformamide monomers and their polymers

N‐alkyl‐N‐vinylformamide monomers (alkyl: n‐butyl, hexyl, decyl, and dodecyl) are synthesized in two steps: first, preparation of N‐vinylformamide potassium salt by the reaction of N‐vinylformamide (NVF) with potassium t‐butoxide, then reaction with alkyl bromide. All four monomers are liquid and are characterized by IR, ¹H NMR, ¹³C NMR, and mass spectra. They exist as rotomers in solution and a 2D NOE experiment on the N‐hexyl containing polymer shows the E isomer to be favored. The polymerizability of the four monomers is from good to fair, depending upon the length of alkyl chain on the N‐atom‐‐the longer the chain length, the lower lower the polymerizability of monomer. The hydrolysis of poly(N‐hexyl‐N‐vinylformamide) and poly(N‐dodecyl‐N‐vinylformamide) under acidic and basic conditions was examined. Studies show that hydrolytic cleavage of formyl groups of poly (N‐alkylated‐N‐vinylformamide) depends on the hydrophobicity of the alkyl substituent on the N‐atom under acidic conditions; both polymers were hydrolyzed to only a minor extent under alkaline conditions. The N‐alkylated monomers can copolymerize with NVF and demonstrate amphiphilic properties. The copolymers demonstrate a critical aggregation concentration above which they can solubilize a water insoluble dye; the N‐hexyl containing copolymer stabilizes a castor oil‐in‐water emulsion. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4994–5004, 2004     

Ethylene/hindered phenol substituted norbornene copolymers: Synthesis and NMR structural determination

A new family of ethylene‐based copolymers with controlled amounts of a norbornene comonomer (N_ArOH) bearing a stabilizing antioxidant functionality (2,6‐di‐tert‐butyl phenol) was prepared. Due to unavoidable exo/endo equilibrium operative in N_ArOH comonomer, a complete and detailed NMR assignment of the structure of the prepared ethylene/N_ArOH copolymers was carried out for the determination of the exo/endo ratio inside the polymer. These novel functionalized comonomers can be considered suitable starting material for preparing ethylene‐based copolymers, with tunable comonomer content, as non‐releasing macromolecular antioxidant additives for specific application in safe food and/or drug packaging © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Microstructure analysis and thermal property of copolymers made of glycolide and ϵ‐caprolactone by stannous octoate

Glycolide (GL) and ?‐caprolactone (CL) were copolymerized in bulk at relatively high temperatures using stannous octoate as a catalyst. To investigate the relationship among microstructure, thermal properties, and crystallinity, three series of copolymers prepared at various reaction temperatures, times, and comonomer feed ratios were prepared and characterized by ¹H and ¹³C NMR, DSC, and wide‐angle X‐ray diffraction (WAXD). The 600‐MHz ¹H NMR spectra provided information about not only the copolymer compositions but also about the chain microstructure. The reactivity ratios (r_G and r_C) were calculated from the monomer sequences and were 6.84 and 0.13, respectively. In terms of overall feed compositions, the sequence lengths of the glycolyl units calculated from the reactivity ratios exceeded those measured from the polymeric products. Mechanistic considerations based on reactivity ratios, monomer consumption data, and average sequence lengths are discussed. The unusual phase diagram of GL/CL copolymers implies that the copolymer melting temperature does not depend on its composition alone but rather on the nature of the sequence distribution. The DSC and WAXD measurements show a close relationship between polymer crystallinity and the nature of the polymer sequence. © 2002 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 544–554, 2002; DOI 10.1002/pola.10123     

Preparation and Morphologies of AB6¯ Block‐Graft Copolymers

Microphase‐separated structures of a series of AB₆ block‐graft copolymers were studied by TEM and SAXS. Ten copolymers with the same polystyrene (S) backbone and six polyisoprene (I) grafts on the average but with different graft chain lengths were carefully synthesized by living anionic polymerization, covering the range 0.21 ≤ ?_S ≤ 0.90, where ?_S denotes polystyrene compositions. From TEM observation of the AB₆ block‐graft copolymers, it turns out to be clear that they show four microphase‐separated structures, S‐spheres, S‐cylinders(S‐prisms), alternative lamellae, and I‐cylinders. Among them, for example, the samples with 0.54 ≤ ?_S ≤ 0.58 shows prism structures whose cross sections of the S domains are close to hexagons, not circles, due to packing frustration of grafts. Composition dependence of morphologies of the present AB₆ block‐graft copolymers reveals their phase diagram is extremely asymmetric with respect to ?_S = 0.5. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 952–960     

Synthesis and properties of polyethylene with side‐chain triphenylamines as hole‐transporting materials

The copolymerization of ethylene with triphenylamine (TPA)‐containing α‐olefin monomer 1 using a rac‐Et(Ind)₂ZrCl₂ ( EBIZr )/MAO catalytic system was investigated to prepare polyethylene with pendent TPA groups. Despite the presence of a large excess of TPA moieties, the polymerization reactions efficiently produce copolymers of high‐molecular‐weight with the comonomer incorporation up to 6.1 mol % upon varying the comonomer concentration in the feed. Inspection of the aliphatic region of the ¹³C‐NMR spectrum and the estimated copolymerization parameters (r ₁ ≈ 0 for 1 and r_E ≈ 43 for ethylene) reveal the presence of isolated comonomer units in the polymer chain. While UV–vis absorption measurements of the copolymers show an invariant absorption feature, PL spectra exhibit a slightly red‐shifted emission with increasing content of 1 in the polymer chain. All the copolymers show high thermal stability (T_d5 > 436 °C), and the electrochemical stability toward oxidation is also observed. Particularly, the copolymer displays hole‐transporting ability for the stable green emission of Alq₃ when incorporated into the hole‐transporting layer of an electroluminescence device. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5816–5825, 2008     

Hydroxyl‐ and amine‐terminated hyperbranched polyurethanes using AB2‐type azide monomers: Synthesis,characterization, fluorescence,and charge‐transfer complexation studies

Novel AB₂‐type azide monomers such as 3,5‐bis(4‐methylolphenoxy)carbonyl azide (monomer 1) , 3,5‐bis(methylol)phenyl carbonyl azide (monomer 2) , 4‐(methylol phenoxy) isopthaloyl azide (monomer 3) , and 5‐(methylol) isopthaloyl azide (monomer 4) were synthesized. Melt and solution polymerization of these monomers yielded hydroxyl‐ and amine‐terminated hyperbranched polyurethanes with and without flexible ether groups. The structures of theses polymers were established using FT‐IR and NMR spectroscopy. The molecular weights (M_w) of the polymers were found to vary from 3.2 × 10³ to 5.5 × 10⁴ g/mol depending on the experimental conditions used. The thermal properties of the polymers were evaluated using TGA and DSC: the polymer obtained from monomer ( 1 ) exhibited lowest T_g and highest thermal stability and the polymer obtained from monomer ( 2 ) registered the highest T_g and lowest thermal stability. All the polymers displayed fluorescence maxima in the 425–525 nm range with relatively narrow peak widths indicating that they had pure and intense fluorescence. Also, the polymers formed charge transfer (CT) complexes with electron acceptor molecules such as 7,7,8,8‐tetracyano‐quino‐dimethane (TCNQ) and 1,1,2,2‐tetracyanoethane (TCNE) as evidenced by UV‐visible spectra. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3337–3351, 2009     

Synthesis of hyperbranched poly(ether nitrile)s by one‐step polycondensation of an AB2 monomer

Hyperbranched poly(ether nitrile)s were prepared from a novel AB₂ type monomer, 2‐chloro‐4‐(3,5‐dihydroxyphenoxy)benzonitrile, via nucleophilic aromatic substitution. Soluble and low‐viscous hyperbranched polymers with molecular weights upto 233,600 (M_w) were isolated. According to the ¹H NMR and GPC data, the unique polymerization behavior was observed, which implies that the weight average molecular weight increased after the number average molecular weight reached plateau region. Model compounds were prepared to characterize the branching structure. Spectroscopic measurements of the model compounds and the resulting polymers, such as ¹H, DEPT ¹³C NMR, and MS, strongly suggest that the ether exchange reaction and cyclization are involved in the propagation reaction. The side reactions would affect the unique polymerization behavior. The resulting polymers showed a good solubility in organic solvents similar to other hyperbranched aromatic polymers. The hydroxy‐terminated polymer was even soluble in basic water. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5835–5844, 2009     

Synthesis of end‐functionalized AB copolymers. II. Synthesis and characterization of carboxyl‐terminated poly(ethylene glycol)–poly(amino acid) block copolymers

AB block copolymers composed of hydrophilic poly(ethylene glycol) (PEG) and hydrophobic poly(amino acid) with a carboxyl group at the end of PEG were synthesized with α‐carboxylic sodium‐ω‐amino‐PEG as a macroinitiator for the ring‐opening polymerization of N‐carboxy anhydride. Characterizations by ¹H NMR, IR, and gel permeation chromatography were carried out to confirm that the diblock copolymers were formed. In aqueous media this copolymer formed self‐associated polymer micelles that have a carboxyl group on the surface. The carboxyl groups located at the outer shell of the polymeric micelle were expected to combine with ligands to target specific cell populations. The diameter of the polymer micelles was in the range of 30–80 nm. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3527–3536, 2004     

Preparation of gradient copolymers via ATRP in miniemulsion. II. Forced gradient

A series of forced gradient copolymers with different controlled distribution of monomer units along the copolymer backbone were successfully prepared by atom transfer radical polymerization in miniemulsion. The newly developed initiation technique, known as activators generated by electron transfer, was beneficial for forced gradient copolymers preparation because all polymer chains were initiated within the miniemulsion droplets and the miniemulsion remained stable throughout the entire polymerization. Various monomer pairs with different reactivity ratios were examined in this study, including n‐butyl acrylate/t‐butyl acrylate, n‐butyl methacrylate/methyl methacrylate, and n‐butyl acrylate/styrene. In each case, the added monomer diffused across the aqueous suspending medium and gradient copolymers with different forced distributions of comonomer units along the polymer backbone were obtained. The shape of the gradient along the backbone of the copolymers was influenced by the molar ratio of the monomers, the reactivity ratio of the comonomers as well as the feeding rate. The shape of the gradient was also affected by the relative hydrophobicities of the comonomers. Copolymerizations exhibited good control for all feeding rates and comonomer feeding ratios, as evidenced by narrow molecular weight distribution (M_w/M_n = 1.20–1.40) and molecular weight increasing smoothly with polymer yield, indicating high initiation efficiency. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1413–1423, 2007