Encapsulation and release by star‐shaped block copolymers as unimolecular nanocontainers

A five‐arm star‐shaped poly(ethylene oxide) (PEO) with terminal bromide groups was used as a macroinitiator for the atom transfer radical polymerization of tert‐butyl acrylate (tBA), resulting in five‐arm star‐shaped poly(ethylene oxide)‐block‐poly(tert‐butyl acrylate) block copolymers. The polymerization proceeded in a controlled way using a copper(I)bromide/pentamethyl diethylenetriamine catalytic system in acetonitrile as solvent. The hydrolysis of the tBA blocks of the amphiphilic star‐shaped PEO‐b‐PtBA block copolymer resulted in dihydrophilic star structures. The encapsulation of the star‐block copolymers and their release properties in acid environment have been followed by UV‐spectroscopy and color changes, using the dye methyl orange as a hydrophilic guest molecule. Characterization of the structures has been done by ¹H NMR, size exclusion chromatography, MALDI‐TOF, and differential scanning calorimetry. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 650–660, 2008     

Synthesis and photoresponsive behavior of azobenzene‐containing side‐chain liquid crystalline diblock polymers with polypeptide block

Well‐defined azobenzene‐containing side‐chain liquid crystalline diblock copolymers composed of poly[6‐(4‐methoxy‐azobenzene‐4′‐oxy) hexyl methacrylate] (PMMAZO) and poly(γ‐benzyl‐L ‐glutamate) (PBLG) were synthesized by click reaction from alkyne‐ and azide‐functionalized homopolymers. The alkyne‐terminated PMMAZO homopolymers were synthesized by copper‐mediated atom transfer radical polymerization with a bromine‐containing alkyne bifunctional initiator, and the azido‐terminated PBLG homopolymers were synthesized by ring‐opening polymerization of γ‐benzyl‐L ‐glutamate‐N‐carboxyanhydride in DMF at room temperature using an amine‐containing azide initiator. The thermotropic phase behavior of PMMAZO‐b‐PBLG diblock copolymers in bulk were investigated using differential scanning calorimetry and polarized light microscopy. The PMMAZO‐b‐PBLG diblock copolymers exhibited a smectic phase and a nematic phase when the weight fraction of PMMAZO block was more than 50%. Photoisomerization behavior of PMMAZO‐b‐PBLG diblock copolymers and the corresponding PMMAZO homopolymers in solid film and in solution were investigated using UV–vis. In solution, trans–cis isomerization of diblock copolymers was slower than that of the corresponding PMMAZO homopolymers. These results may provide guidelines for the design of effective photoresponsive anisotropic materials. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Synthesis,characterization and photoinduction of optical anisotropy in liquid crystalline diblock azo‐copolymers

Diblock copolymers with polymethyl methacrylate and side chain liquid crystalline (LC) azopolymethacrylate blocks were synthesized by atom transfer radical polymerization (ATRP). The azobenzene content in these copolymers ranges from 52 to 7 wt %. For an azo content down to 20% they exhibit a LC behavior similar to that of the azo homopolymers. Thin films of these copolymers were characterized by transmission electron microscopy (TEM). A lamellar nanostructure was observed for azo content down to 20 wt %, while no structure is observed for the copolymer with a 7% azo content. The optical anisotropy induced in these films by illumination with linearly polarized 488 nm light was studied and the results compared with those of the azo homopolymer and of a random copolymer with a similar composition. The formation of azo aggregates inside the azo blocks is strongly reduced in going from the homopolymer to the copolymers. Photoinduced azo orientation perpendicular to the 488 nm light polarization was found in all the polymers. The orientational order parameter is very similar in the homopolymer and in the block copolymers with an azo content down to 20 wt %, while it is much lower in the random copolymer and in the 7 wt %. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1899–1910, 2007     

Simple route for synthesis of H‐shaped copolymers

The H‐shaped copolymers, [poly(L ‐lactide)]₂polystyrene [poly(L ‐lactide)]₂, [(PLLA)₂PSt(PLLA)₂] have been synthesized by combination of atom transfer radical polymerization (ATRP) with cationic ring‐opening polymerization (CROP). The first step of the synthesis is ATRP of St using α,α′‐dibromo‐p‐xylene/CuBr/2,2′‐bipyridine as initiating system, and then the PSt with two bromine groups at both chain ends (Br–PSt–Br) were transformed to four terminal hydroxyl groups via the reaction of Br–PSt–Br with diethanolamine in N,N‐dimethylformamide. The H‐shaped copolymers were produced by CROP of LLA, using PSt with four terminal hydroxyl groups as macroinitiator and Sn(Oct)₂ as catalyst. The copolymers obtained were characterized by ¹H NMR spectroscopy and gel permeation chromatography. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2794–2801, 2006     

Synthesis of a novel liquid crystal rod–coil star block copolymer consisting of poly(methyl methacrylate) and poly{2,5‐bis[(4‐methoxy‐phenyl)oxycarbonyl] styrene} via atom transfer radical polymerization

A bromine capped star‐shaped poly(methyl methacrylate) (S‐PMMA‐Br) was synthesized with CuBr/sparteine/PT‐Br as a catalyst and initiator to polymerize methyl methacrylate (MMA) according to atom transfer radical polymerization (ATRP). Then, with S‐PMMA‐Br as a macroinitiator, a series of new liquid crystal rod–coil star block copolymers with different molecular weights and low polydispersity were obtained by this method. The block architecture {coil‐conformation of the MMA segment and rigid‐rod conformation of 2,5‐bis[(4‐methoxyphenyl)oxycarbonyl] styrene segment} of the four‐armed rod–coil star block copolymers were characterized by ¹H NMR. The liquid‐crystalline behavior of these copolymers was studied by differential scanning calorimetry and polarized optical microscopy. We found that the liquid‐crystalline behavior depends on the molecular weight of the rigid segment; only the four‐armed rod–coil star block copolymers with each arm's M_n,_GPC of the rigid block beyond 0.91 × 10⁴ g/mol could form liquid‐crystalline phases above the glass‐transition temperature of the rigid block. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 733–741, 2005     

Synthesis and properties of comb polymers with semirigid mesogen‐jacketed polymers as side chains

A series of novel comb polymers, poly{2,5‐bis[(4‐methoxyphenyl)oxycarbonyl]styrene}‐g‐polystyrene (PMPCS‐g‐PS), with mesogen‐jacketed rigid side chains were synthesized by the “grafting onto” method from α‐yne‐terminated PMPCS (side chain) and poly(vinylbenzyl azide) (backbone) by Cu(I)‐catalyzed 1,3‐dipolar cycloaddition click reaction. The α‐yne‐terminated PMPCS was synthesized by Cu(I)‐catalyzed atom transfer radical polymerization initiated by a yne‐functional initiator. Poly(vinylbenzyl azide) was prepared by polymerizing vinylbenzyl chloride using nitroxide mediated radical polymerization to obtain poly(vinylbenzyl chloride) as the precursor which was then converted to the azide derivative. The chemical structure and architectures of PMPCS comb polymers were confirmed by ¹H NMR, gel permeation chromatography, and multiangle laser light scattering. Both surface morphologies and solution behaviors were investigated. Surface morphologies of PMPCS combs on different surfaces were investigated by scanning probe microscopy. PMPCS combs showed different aggregation morphologies when depositing on silicon wafers with/without chemical modification. The PMPCS comb polymers transferred to polymer‐modified silicon wafers using the Langmuir‐Blodgett technique showed a worm‐like chain conformation. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis of a novel hybrid liquid‐crystalline rod–coil diblock copolymer

A series of novel rod–coil diblock copolymers on the basis of mesogen‐jacketed liquid‐crystalline polymer were successfully prepared by atom transfer radical polymerization from the flexible polydimethylsiloxane (PDMS) macroinitiator. The hybrid diblock copolymers, poly{2,5‐bis[(4‐methoxyphenyl)oxycarbonyl]styrene}‐block‐polydimethylsiloxane, had number‐average molecular weights (M_n's) ranging from 9500 to 30,900 and relatively narrow polydispersities (≤1.34). The polymerization proceeded with first‐order kinetics. Data from differential scanning calorimetry validated the microphase separation of the diblock copolymers. All block copolymers exhibited thermotropic liquid‐crystalline behavior except for the one with M_n being 9500. Four liquid‐crystalline diblock copolymers with PDMS weight fractions of more than 18% had two distinctive glass‐transition temperatures. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1799–1806, 2003     

Incorporation of poly(2‐acrylamido‐2‐methyl‐N‐propanesulfonic acid) segments into block and brush copolymers by ATRP

2‐Acrylamido‐2‐methyl‐N‐propanesulfonic acid (AMPSA) was successfully polymerized via atom transfer radical polymerization (ATRP) using a copper chloride/2,2′‐bipyridine (bpy) catalyst complex after in situ neutralization of the acidic proton in AMPSA with tri(n‐butyl)amine (TBA). A 5 mol % excess of TBA was required to completely neutralize the acid and prevent protonation of the bpy ligand, as well as to avoid side reactions caused by large excess of TBA. The use of activators generated by electron transfer (AGET) ATRP with ascorbic acid as reducing agent resulted in both increased conversion of the AMPSA monomer during polymerization (up to 50% with a 0.8 [ascorbic acid]/[Cu(II)] ratio) and much shorter polymerization times (<30 min). Block copolymers and molecular brushes containing AMPSA side chains were prepared using this method, and the solution and surface behavior of these materials were investigated. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5386–5396, 2009     

Fluorinated star‐shaped block copolymers: Synthesis and optical properties

Tetrakis(4‐(1‐bromoethyl)phenyl)silane is synthesized and utilized to initiate the atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) to generate bromo‐terminated four‐armed PMMA macroinitiators, which further initiate the ATRP of methylacryloyloxyl‐2‐hydroxypropyl perfluorooctanoate (FGOA) to create fluorinated star‐shaped block copolymers PMMA‐b‐poly(FGOA)s with fluorine content ranging from 0 to 31.7 wt %. The polymerizations are well controlled with the polydispersity indices <1.30. The polymers readily dissolve in common organic solvents and show good film‐formation. Compared with the nonfluorinated sample, the fluorinated films exhibit significantly increased water contact angles owing to the enrichment of fluorine on the surface. The enhanced hydrophobicity is advantageous for the optical stability when the devices work under a moist environment. Moreover, the films possess high thermo‐optic coefficients, tunable refractive indices, and extremely low birefringence coefficients because of the presence of bulky and rigid tetraphenylsilane core and star‐shaped topological structure, showing potential application in optical waveguide devices. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1969–1977     

Synthesis and characterization of liquid‐crystalline block copolymers with cyanoterphenyl moieties by atom transfer radical polymerization

A series of new mesomorphic block copolymers composedofdifferentmacroinitiators, including poly(ethylene oxide), polystyrene, and poly(ethylene oxide)‐b‐polystyrene,and polymethacrylate with a pendent cyanoterphenyl group were synthesized through atom transfer radical polymerization. The number‐average molecular weights of the three diblock copolymers, determined by gel permeation chromatography, were 10,254, 9,772, and 15,632 g mol^?1, and their polydispersity indices were 1.17, 1.28, and 1.34. The mesomorphic and optical properties of all the block copolymers were investigated, and they possessed a smectic A phase with mesophasic ranges wider than 100 °C. Moreover, X‐ray diffraction patterns provided evidence of the smectic A phase and the corresponding interdigitated packing of all the polymers. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4593–4602, 2006     

Tuning amphiphilicity/temperature‐induced self‐assembly and in‐situ disulfide crosslinking of reduction‐responsive block copolymers

New poly(ethylene oxide)‐based block copolymers (ssBCs) with a random copolymer block consisting of a reduction‐responsive disulfide‐labeled methacrylate (HMssEt) and a thermoresponsive di(ethylene glycol)‐containing methacrylate (MEO₂MA) units were synthesized. The ratio of HMssEt/MEO₂MA units in the random P(MEO₂MA‐co‐HMssEt) copolymer block enables the characteristics of well‐defined ssBCs to be amphiphilic or thermoresponsive and double hydrophilic. Their amphiphilicity or temperature‐induced self‐assembly results in nanoaggregates with hydrophobic cores having different densities of pendant disulfide linkages. The effect of disulfide crosslinking density on morphological variation of disulfide‐crosslinked nanogels is investigated. In response to reductive reactions, the partial cleavage of pendant disulfide linkages in the hydrophobic cores converts the physically associated aggregates to disulfide‐crosslinked nanogels. The occurrence of in‐situ disulfide crosslinks provides colloidal stability upon dilution. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2057–2067     

Amphiphilic star‐block copolymers based on a hyperbranched core: Synthesis and supramolecular self‐assembly

Novel amphiphilic star‐block copolymers, star poly(caprolactone)‐block‐poly[(2‐dimethylamino)ethyl methacrylate] and poly(caprolactone)‐block‐poly(methacrylic acid), with hyperbranched poly(2‐hydroxyethyl methacrylate) (PHEMA–OH) as a core moiety were synthesized and characterized. The star‐block copolymers were prepared by a combination of ring‐opening polymerization and atom transfer radical polymerization (ATRP). First, hyperbranched PHEMA–OH with 18 hydroxyl end groups on average was used as an initiator for the ring‐opening polymerization of ε‐caprolactone to produce PHEMA–PCL star homopolymers [PHEMA = poly(2‐hydroxyethyl methacrylate); PCL = poly(caprolactone)]. Next, the hydroxyl end groups of PHEMA–PCL were converted to 2‐bromoesters, and this gave rise to macroinitiator PHEMA–PCL–Br for ATRP. Then, 2‐dimethylaminoethyl methacrylate or tert‐butyl methacrylate was polymerized from the macroinitiators, and this afforded the star‐block copolymers PHEMA–PCL–PDMA [PDMA = poly(2‐dimethylaminoethyl methacrylate)] and PHEMA–PCL–PtBMA [PtBMA = poly(tert‐butyl methacrylate)]. Characterization by gel permeation chromatography and nuclear magnetic resonance confirmed the expected molecular structure. The hydrolysis of tert‐butyl ester groups of the poly(tert‐butyl methacrylate) blocks gave the star‐block copolymer PHEMA–PCL–PMAA [PMAA = poly(methacrylic acid)]. These amphiphilic star‐block copolymers could self‐assemble into spherical micelles, as characterized by dynamic light scattering and transmission electron microscopy. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6534–6544, 2005     

Modular synthesis of ABC type block copolymers by “click” chemistry

Heterotelechelic polystyrene (PS), poly(tert‐butyl acrylate) (PtBA), and poly (methyl acrylate) (PMA), containing both azide and triisopropylsilyl (TIPS) protected acetylene end groups, were prepared in good control (M_w/M_n ≤ 1.24) by atom transfer radical polymerization (ATRP). The end groups were independently applied in two successive “click” reactions, that is: first the azide termini were functionalized and, after deprotection, the acetylene moieties were utilized for a second conjugation step. As a proof of concept, PS was consecutively functionalized with propargyl alcohol and azidoacetic acid, as confirmed by MALDI‐ToF MS. In addition, the same methodology was employed to modularly build up an ABC type triblock terpolymer. Size exclusion chromatography measurements demonstrated first coupling of PtBA to PS and, after the deprotection of the acetylene functionality on PS, connection of PMA, yielding a PMA‐b‐PS‐b‐PtBA triblock terpolymer. The reactions were driven to completion using a slight excess of azide functionalized polymers. Reduction of the residual azide groups into amines allowed easy removal of this excess of polymer by column chromatography. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2913–2924, 2007     

Synthesis of amphiphilic A4B4 star‐shaped copolymers by mechanisms transformation combining with thiol‐ene reaction

Using core‐first strategy, the amphiphilic A₄B₄ star‐shaped copolymers [poly(ethylene oxide)]₄[poly(ε‐caprolactone)]₄ [(PEO)₄(PCL)₄], [poly(ethylene oxide)]₄[poly(styrene)]₄ [(PEO)₄(PS)₄], and [poly(ethylene oxide)]₄[poly(tert‐butyl acrylate)]₄ [(PEO)₄(PtBA)₄] were synthesized by mechanisms transformation combining with thiol‐ene reaction. First, using a designed multifunctional mikto‐initiator with four active hydroxyl groups and four allyl groups, the four‐armed star‐shaped polymers (PEO‐Ph)₄/(OH)₄ with four active hydroxyl groups at core position were obtained by sequential ring‐opening polymerization (ROP) of ethylene oxide monomers, capping reaction of living oxyanion with benzyl chloride, and transformation of allyl groups into hydroxyl groups by thiol‐ene reaction. Then, the A₄B₄ star‐shaped copolymers (PEO)₄(PS)₄ or (PEO)₄(PtBA)₄ were obtained by atom transfer radical polymerization (ATRP) of styrene or tert‐butyl acrylate (tBA) monomers from macroinitiator of (PEO‐Ph)₄/(Br)₄, which was obtained by esterification of (PEO‐Ph)₄/(OH)₄ with 2‐bromoisobutyryl bromide. The A₄B₄ star‐shaped copolymers (PEO)₄(PCL)₄ were also obtained by ROP of ε‐caprolactopne monomers from macroinitiator of (PEO‐Ph)₄/(OH)₄. The target copolymers and intermediates were characterized by size‐exclusion chromatography, matrix‐assisted laser desorption/ionization time‐of‐flight mass spectroscopy, and nuclear magnetic resonance in detail. This synthetic route might be a versatile one to various A_nB_n (n ≥ 3) star‐shaped copolymers with defined structure and compositions. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4572–4583     

Synthesis and characterizations of the four‐armed amphiphilic block copolymer S[poly(2,3‐dihydroxypropyl acrylate)‐block‐poly(methyl acrylate)]4

The polymers poly[(2,2‐dimethyl‐1,3‐dioxolane‐4yl) methyl acrylate] (PDMDMA) and four‐armed PDMDMA with well‐defined structures were prepared by the polymerization of (2,2‐dimethyl‐1,3‐dioxolane‐4yl) methyl acrylate (DMDMA) in the presence of an atom transfer radical polymerization (ATRP) initiator system. The successive hydrolyses of the polymers obtained produced the corresponding water‐soluble polymers poly(2,3‐dihydroxypropyl acrylate) (PDHPA) and four‐armed PDHPA. The controllable features for the ATRP of DMDMA were studied with kinetic measurements, gel permeation chromatography (GPC), and NMR data. With the macroinitiators PDMDMA–Br and four‐armed PDMDMA–Br in combination with CuBr and 2,2′‐bipyridine, the block polymerizations of methyl acrylate (MA) with PDMDMA were carried out to afford the AB diblock copolymer PDMDMA‐b‐MA and the four‐armed block copolymer S{poly[(2,2‐dimethyl‐1,3‐dioxolane‐4yl) methyl acrylate]‐block‐poly(methyl acrylate)}₄, respectively. The block copolymers were hydrolyzed in an acidic aqueous solution, and the amphiphilic diblock and four‐armed block copolymers poly(2,3‐dihydroxypropyl acrylate)‐block‐poly(methyl acrylate) were prepared successfully. The structures of these block copolymers were verified with NMR and GPC measurements. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3062–3072, 2001     

Synthesis of polystyrene–poly(tert‐butyl methacrylate)–poly(ethylene oxide) triarm star block copolymers

Three alternative routes, using the heterobifunctional macroinitiator technique, have been developed to obtain polystyrene–poly(tert‐butyl methacrylate)–poly(ethylene oxide) triarm star block copolymers. Only the route showing the reverse initiation of tert‐butyl methacrylate on potassium alkoxide leads to the pure star, whereas the other strategies lead to incomplete initiation because of either an increase in the side reactions, such as transesterification, or a decrease in the accessibility toward bulky catalysts. These limits are linked to the particular location of the initiating group at the junction of the two blocks of the copolymer precursor. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1745–1751, 2004     

Self‐assembly of star‐shaped polystyrene‐block‐polypeptide copolymers synthesized by the combination of atom transfer radical polymerization and ring‐opening living polymerization of α‐amino acid‐N‐carboxyanhydrides

The self‐assembling nature and phase‐transition behavior of a novel class of triarm, star‐shaped polymer–peptide block copolymers synthesized by the combination of atom transfer radical polymerization and living ring‐opening polymerization of α‐amino acid‐N‐carboxyanhydride are demonstrated. The two‐step synthesis strategy adopted here allows incorporating polypeptides into the usual synthetic polymers via an amido–amidate nickelacycle intermediate, which is used as the macroinitiator for the growth of poly(γ‐benzyl‐L ‐glutamate). The characterization data are reported from analyses using gel permeation chromatography and infrared, ¹H NMR, and ¹³C NMR spectroscopy. This synthetic scheme grants a facile way to prepare a wide range of polymer–peptide architectures with perfect microstructure control, preventing the formation of homopolypeptide contaminants. Studies regarding the supramolecular organization and phase‐transition behavior of this class of polymer‐block‐polypeptide copolymers have been accomplished with X‐ray diffraction, infrared spectroscopy, and thermal analyses. The conformational change of the peptide segment in the block copolymer has been investigated with variable‐temperature infrared spectroscopy. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2774–2783, 2006     

Synthesis and characterization of pH sensitive poly(glycidol)‐b‐poly(4‐vinylpyridine) block copolymers

Block copolymers of poly(glycidol)‐b‐poly(4‐vinylpyridine) were obtained by ATRP of 4‐vinylpyridine initiated by ω‐(2‐chloropropionyl) poly(glycidol) macroinitiators. By changing the monomer/macroinitiator ratio in the synthesis polymers with varied P4VP/PGl molar ratio were obtained. The obtained block copolymers showed pH sensitive solubility. It was found that the linkage of a hydrophilic poly(glycidol) block to a P4VP influenced the pK_a value of P4VP. DLS measurements showed the formation of fully collapsed aggregates exceeding pH 4.7. Above this pH values the collapsed P4VP core of the aggregates was stabilized by a surrounding hydrophilic poly(glycidol) corona. The size of the aggregates depended significantly upon the composition of the block copolymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1782–1794, 2009     

Synthesis of liquid crystalline–amorphous block copolymers by the combination of atom transfer and photoinduced radical polymerization mechanisms

The synthesis of ABA‐type block copolymers, involving liquid‐crystalline 6‐(4‐cyanobiphenyl‐4′‐oxy)hexyl acrylate (LC6) and styrene (St) monomer with copper‐based atom transfer radical polymerization (ATRP) and photoinduced radical polymerization (PIRP), was studied. First, photoactive α‐methylol benzoin methyl ether was esterified with 2‐bromopropionyl bromide, and it was subsequently used for ATRP of LC6 in diphenylether in conjunction with CuBr/N,N,N′,N″,N″‐pentamethyldiethylenetriamine as a catalyst. The obtained photoactive functional liquid‐crystalline polymer, poly[6‐(4‐cyanobiphenyl‐4′‐oxy)hexyl acrylate] (PLC6), was used as an initiator in PIRP of St. Similarly, photoactive polystyrenes were also synthesized and employed for the block copolymerization of LC6 in the second stage. The spectral, thermal, and optical measurements confirmed a full combination of ATRP and PIRP, which resulted in the formation of ABA‐type block copolymers with very narrow polydispersities. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1892–1903, 2003