Ambient temperature ATRP of benzyl methacrylate as a tool for the synthesis of block copolymers with styrene

The rapid atom transfer radical polymerization (ATRP) of benzyl methacrylate (BnMA) at ambient temperature was used to synthesize block copolymers with styrene as the second monomer. Various block copolymers such as AB diblock, BAB symmetric and asymmetric triblock, and ABABA pentablock copolymers were synthesized in which the polymerization of one of the blocks namely BnMA was performed at ambient temperature. It is demonstrated that the block copolymerization can be performed in a controlled manner, regardless of the sequence of monomer addition via halogen exchange technique. Using this reaction condition, the composition (ratio) of one block (here BnMA) can be varied from 1 to 100. It is further demonstrated that in the multiblock copolymer syntheses involving styrene and benzyl methacrylate, it is better to start from the PS macroinitiator compared with PBnMA macroinitiator. The polymers synthesized are relatively narrow dispersed (<1.5). It is identified that the ATRP of BnMA is limited to certain molecular weights of the PS macroinitiator. Additionally, a preliminary report about the synthesis of the block copolymer of BnMA‐methyl methacrylate (MMA), both at ambient temperature, is demonstrated. Subsequent deprotection of the benzyl group using Pd/C? H₂ results in methacrylic acid (MAA)–methyl methacrylate (MAA–MMA) amphiphilic block copolymer. GPC, IR, and NMR are used to characterize the synthesized polymers. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2848–2861, 2006     

Controlled radical polymerization of anthracene‐containing methacrylate copolymers for stimuli‐responsive materials

Novel reversible networks utilizing photodimerization of crosslinkable anthracene groups and thermal dissociation were investigated. Reversible addition‐fragmentation chain transfer polymerization yielded well‐defined copolymers with 9‐anthrylmethyl methacrylate (AMMA) and other alkyl methacrylates such as methyl methacrylate (MMA) and 2‐ethylhexyl methacrylate (EHMA) having different AMMA compositions. Well‐controlled block copolymerization of AMMA and alkyl methacrylates was also successfully accomplished using a trithiocarbonate‐terminated poly(alkyl methacrylate) macro‐chain transfer agent. The anthracene‐containing copolymers showed reversibility via crosslinking based on photodimerization with ultraviolet irradiation and subsequent thermal dissociation. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2302–2311     

Free‐radical polymerization of methyl methacrylate with a tetrafunctional peroxide initiator

This study examined the use of a new tetrafunctional peroxide initiator in the bulk free‐radical polymerization of methyl methacrylate. The objective was to investigate the effect of using a multifunctional initiator through an examination of the rates of polymerization and the polymer properties. The molecular weights and radii of gyration were obtained with a size exclusion chromatograph equipped with an online multi‐angle laser light scattering detector. The performance of the tetrafunctional initiator was compared to that of a monofunctional counterpart [tert‐butylperoxy 2‐ethylhexyl carbonate (TBEC)]. The results showed that the new tetrafunctional peroxide initiator produced a faster rate of polymerization than TBEC at an equivalent concentration but also generated a polymer of a lower molecular weight. This trend was the opposite of what was observed in a previous study with styrene. When TBEC was used at a concentration four times that of the new tetrafunctional peroxide initiator, both produced equal rates of polymerization and similar molecular weights. The degree of branching was also investigated with radius‐of‐gyration plots. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5647–5661, 2004     

Reverse atom transfer radical polymerization of butyl methacrylate in a miniemulsion stabilized with a cationic surfactant

The miniemulsion reverse atom transfer radical polymerization of butyl methacrylate was carried out with cetyltrimethylammonium bromide (CTAB) as the sole surfactant. The polymerizations were initiated with 2,2′‐azobis[2‐(2‐imidazolin‐2‐yl)propane] dihydrochloride and mediated with copper(II) bromide/tris[2‐di(2‐ethylhexyl acrylate)aminoethyl]amine. The living character was demonstrated by the linear increase in the number‐average molecular weight with conversion and the decreasing polydispersity index with conversion. The polymerizations were conducted at 90 °C with 1 wt % CTAB with respect to the monomer and produced a coagulum‐free latex with a mean particle diameter of 155 nm. The resulting latexes exhibited good shelf‐life stability. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1628–1634, 2006     

Ultrasonically initiated emulsion polymerization of methyl methacrylate

The ultrasonically initiated emulsion polymerization of methyl methacrylate (MMA) was investigated. Experimental results show that sodium dodecyl sulfonate (SDS) surfactant plays a very important role in obtaining a high polymer yield, because in the absence of SDS, monomer conversion is near zero. Thus, the surfactant serves as an initiator and as interfacial modifier in this system (MMA/H₂O), and the monomer conversion increases significantly with increasing SDS concentration. An increase in the reactor temperature also leads to an increase in the monomer conversion. An appropriate increase in the N₂ purging rate also leads to higher conversion. The conversion of MMA decreases with increasing monomer concentration because of the higher viscosity of the system. With the experimental results, optimized reaction conditions were obtained. Accordingly, a high monomer conversion of about 67% and a high molecular weight of several millions can be obtained in a period of about 30 min. Furthermore, transmission electron micrographs show that the latex particles prepared are nanosized, indicating a promising technique for preparing nanoscale latex particles with a small amount of surfactant. In conclusion, a promising technique for ultrasonically initiated emulsion polymerization has been successfully performed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3356–3364, 2001     

Synthesis and monomer reactivity ratios of methyl methacrylate and 2‐vinyl‐4,4′‐dimethylazlactone copolymers

We report the monomer reactivity ratios for copolymers of methyl methacrylate (MMA) and a reactive monomer, 2‐vinyl‐4,4′‐dimethylazlactone (VDMA), using the Fineman–Ross, inverted Fineman–Ross, Kelen–Tudos, extended Kelen–Tudos, and Tidwell–Mortimer methods at low and high polymer conversions. Copolymers were obtained by radical polymerization initiated by 2,2′‐azobisisobutyronitrile in methyl ethyl ketone solutions and were analyzed by NMR, gas chromatography (GC), and gel permeation chromatography. ¹H NMR analysis was used to determine the molar fractions of MMA and VDMA in the copolymers at both low and high conversions. GC analysis determined the molar fractions of the monomers at conversions of less than 27% and greater than 65% for the low‐ and high‐conversion copolymers, respectively. The reactivity ratios indicated a tendency toward random copolymerization, with a higher rate of consumption of VDMA at high conversions. For both low‐ and high‐conversion copolymers, the molecular weights increased with increasing molar fractions of VDMA, and this was consistent with the faster consumption of VDMA (compared with that of MMA). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3027–3037, 2003     

Reverse atom transfer radical polymerization of methyl methacrylate in room‐temperature ionic liquids

The reverse atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) was successfully carried out in 1‐butyl‐3‐methylimidazolium hexafluorophosphate with 2,2′‐azobisisobutyronitrile/CuCl₂/bipyridine as the initiating system, which had been reported as not able to promote a controlled process of MMA in bulk. The living nature of the polymerization was confirmed by kinetic studies, end‐group analysis, chain extension, and block copolymerization results. The polydispersity of the polymer obtained was quite narrow, with a weight‐average molecular weight/number‐average molecular weight ratio of less than 1.2. In comparison with other reverse ATRPs in bulk or conventional solvents, a much smaller amount of the catalyst was used. After a relatively easy removal of the polymer and residue monomer, the ionic liquid and catalytic system could be reused without further treatment. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 143–151, 2003     

Homopolymerization and copolymerization of isocyanatoethyl methacrylate

This article describes the homopolymerization of isocyanatoethyl methacrylate (IEM) and its copolymerization with methyl methacrylate (MMA) in acetonitrile in the presence of 2,2′‐azobisisobutyronitrile. The constant characteristic of IEM polymerizability (k_p²/k_te = 128 × 10^?3 L mol^?1 s^?1, where k_p is the propagation constant and k_te is the termination constant) was determined. The study of IEM reactivity toward MMA gave ratios of 0.88 and 1.20 for IEM and MMA, respectively. The physicochemical properties of the IEM homopolymer and IEM/MMA copolymers were also studied. The glass‐transition temperature of poly(isocyanatoethyl methacrylate) was found to be 47 °C. From the thermogravimetric analysis of the weight‐loss percentage corresponding to the first wave of the thermogram, it was shown that the degradation mechanism of the IEM/MMA copolymers started from the isocyanate group. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4762–4768, 2006     

Synthesis of star‐shaped copolymers with methyl methacrylate and n‐butyl methacrylate by metal‐catalyzed living radical polymerization: Block and random copolymer arms and microgel cores

Various star‐shaped copolymers of methyl methacrylate (MMA) and n‐butyl methacrylate (nBMA) were synthesized in one pot with RuCl₂(PPh₃)₃‐catalyzed living radical polymerization and subsequent polymer linking reactions with divinyl compounds. Sequential living radical polymerization of nBMA and MMA in that order and vice versa, followed by linking reactions of the living block copolymers with appropriate divinyl compounds, afforded star block copolymers consisting of AB‐ or BA‐type block copolymer arms with controlled lengths and comonomer compositions in high yields (≥90%). The lengths and compositions of each unit varied with the amount of each monomer feed. Star copolymers with random copolymer arms were prepared by the living radical random copolymerization of MMA and nBMA followed by linking reactions. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 633–641, 2002; DOI 10.1002/pola.10145     

Synthesis and characterization of poly(methyl methacrylate)/casein nanoparticles with a well‐defined core‐shell structure

Well‐defined, core‐shell poly(methyl methacrylate) (PMMA)/casein nanoparticles, ranging from 80 to 130 nm in diameter, were prepared via a direct graft copolymerization of methyl methacrylate (MMA) from casein. The polymerization was induced by a small amount of alkyl hydroperoxide (ROOH) in water at 80 °C. Free radicals on the amino groups of casein and alkoxy radicals were generated concurrently, which initiated the graft copolymerization and homopolymerization of MMA, respectively. The presence of casein micelles promoted the emulsion polymerization of the monomer and provided particle stability. The conversion and grafting efficiency of the monomer strongly depended on the type of radical initiator, ROOH concentration, casein to MMA ratio, and reaction temperature. The graft copolymers and homopolymer of PMMA were isolated and characterized with Fourier transform infrared spectroscopy and differential scanning calorimetry. The molecular weight determination of both the grafted and homopolymer of PMMA suggested that the graft copolymerization and homopolymerization of MMA proceeded at a similar rate. The transmission electron microscopic image of the nanoparticles clearly showed a well‐defined core‐shell morphology, where PMMA cores were coated with casein shells. The casein shells were further confirmed with a zeta‐potential measurement. Finally, this synthetic method allowed us to prepare PMMA/casein nanoparticles with a solid content of up to 31%. Thus, our new process is commercially viable. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3346–3353, 2003     

Reverse atom transfer radical polymerization of methyl methacrylate with a new catalytic system,FeCl3/isophthalic acid

A new catalytic system, FeCl₃/isophthalic acid, was successfully used in the reverse atom transfer radical polymerization (RATRP) of methyl methacrylate (MMA) in the presence of a conventional radical initiator, 2,2′‐azo‐bis‐isobutyrontrile. Well‐defined poly(methyl methacrylate) (PMMA) was synthesized in an N,N‐dimethylformamide solvent at 90–120 °C. The polymerization was controlled up to a molecular weight of 50,000, and the polydispersity index was 1.4. Chain extension was performed to confirm the living nature of the polymer. The kinetics of the RATRP of MMA with FeCl₃/isophthalic acid as the catalyst system was investigated. The apparent activation energy was 10.47 kcal/mol. The presence of the end chloride atom on the resulting PMMA was demonstrated by ¹H NMR spectroscopy. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 765–774, 2001     

Synthesis of poly(2‐hydroxyethyl methacrylate) in protic media through atom transfer radical polymerization using activators generated by electron transfer

Atom transfer radical polymerization (ATRP) using activators generated by electron transfer (AGET) was investigated for the controlled polymerization of 2‐hydroxyethyl methacrylate (HEMA) in a protic solvent, a 3/2 (v/v) mixture of methyl ethyl ketone and methanol. The AGET process enabled ATRP to be started with an air‐stable Cu(II) complex that was reduced in situ by tin(II) 2‐ethylhexanoate. The reaction temperature, Cu catalysts with different ligands, and variation of the initial concentration ratio of HEMA to the initiator were examined for the synthesis of well‐controlled poly(2‐hydroxyethyl methacrylate) and a poly(methyl methacrylate)‐b‐poly(2‐hydroxyethyl methacrylate) block copolymer. The level of control in AGET ATRP was similar to that in normal ATRP in protic solvents, and this resulted in a linear increase in the molecular weight with the conversion and a narrow molecular weight distribution (weight‐average molecular weight/number‐average molecular weight < 1.3). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3787–3796, 2006     

Synthesis of poly(methyl methacrylate) in a pyridine solution by atom transfer radical polymerization

Pyridine was used as a solvent for the atom transfer radical polymerization (ATRP) of methyl methacrylate. The homopolymerizations were carried out with methyl 2‐halopropionate (MeXPr, where X was Cl or Br) as an initiator, copper halide (CuX) as a catalyst, and 2,2′‐bipyridine as a ligand from 80 to 120 °C. The mixed halogen system methyl 2‐bromopropionate/copper chloride was also used. For all the initiator systems used, the polymerization reaction showed linear first‐order rate plots, a linear increase in the number‐average molecular weight with conversion, and relatively low polydispersities. In addition, the dependence of the polymerization rate on the temperature is presented. These data are compared with those obtained in bulk, demonstrating the effectiveness of this solvent for this monomer in ATRP. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3443–3450, 2001     

Catalytic effect of dimethyl sulfoxide in the Cu(0)/tris(2‐dimethylaminoethyl)amine‐catalyzed living radical polymerization of methyl methacrylate at 0–90 °C initiated with CH3CHClI as a model compound for α,ω‐di(iodo)poly(vinyl chloride) chain ends

A variety of conditions, including catalysts [CuCl, CuI, Cu₂O, and Cu(0)], ligands [2,2′‐bipyridine (bpy), tris(2‐dimethylaminoethyl)amine (Me₆‐TREN), polyethyleneimine, and hexamethyl triethylenetetramine], initiators [CH₃CHClI, CH₂I₂, CHI₃, and F(CF₂)₈I], solvents [diphenyl ether, toluene, tetrahydrofuran, dimethyl sulfoxide (DMSO), dimethylformamide, ethylene carbonate, dimethylacetamide, and cyclohexanone], and temperatures [90, 25, and 0 °C] were studied to assess previous methods for poly(methyl methacrylate)‐b‐poly(vinyl chloride)‐b‐poly(methyl methacrylate) (PMMA‐b‐PVC‐b‐PMMA) synthesis by the living radical block copolymerization of methyl methacrylate (MMA) initiated with α,ω‐di(iodo)poly(vinyl chloride). CH₃CHClI was used as a model for α,ω‐di(iodo)poly(vinyl chloride) employed as a macroinitiator in the living radical block copolymerization of MMA. Two groups of methods evolved. The first involved CuCl/bpy or Me₆‐TREN at 90 °C, whereas the second involved Cu(0)/Me₆‐TREN in DMSO at 25 or 0 °C. Related ligands were used in both methods. The highest initiator efficiency and rate of polymerization were obtained with Cu(0)/Me₆‐TREN in DMSO at 25 °C. This demonstrated that the ultrafast block copolymerization reported previously is the most efficient with respect to the rate of polymerization and precision of the PMMA‐b‐PVC‐b‐PMMA architecture. Moreover, Cu(0)/Me₆‐TREN‐catalyzed polymerization exhibits an external first order of reaction in DMSO, and so this solvent has a catalytic effect in this living radical polymerization (LRP). This polymerization can be performed between 90 and 0 °C and provides access to controlled poly(methyl methacrylate) tacticity by LRP and block copolymerization. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1935–1947, 2005     

Nitroxide-mediated photo-living radical polymerization of methyl methacrylate in solution

The photoradical polymerization of methyl methacrylate (MMA) was performed in an acetonitrile solution at room temperature using (2RS,2′RS)-azobis(4-methoxy-2,4-dimethylvaleronitrile) as the initiator, 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl as the mediator, and (4-tert-butylphenyl)diphenylsulfonium triflate as the photo-acid generator. This solution polymerization showed a non-steady-state during the very early stage followed by a steady-state. The polymerization produced oligomers with several thousand molecular weights at a very low conversion under the non-steady-state. It was confirmed that the polymerization proceeded in accordance with a living mechanism under the steady-state based on the linear correlations for both the first-order time-conversion plots and the conversion–molecular weight plots. The molecular weight distributions of the polymers obtained in the steady-state were approximately 1.8. The block copolymerization with isopropyl methacrylate ( ⁱ PMA) demonstrated that the growing polymer chain ends of the MMA prepolymer were stabilized even at a high conversion and efficiently initiated the ⁱ PMA polymerization.     

A novel route to poly(2-hydroxyethyl methacrylate) and its amphiphilic block copolymers

The vinyl of the ester group of 2-vinyloxyethyl methacrylate was first selectively reacted with acetic acid to obtain 2-[1-(acetoxy)ethoxy]ethyl methacrylate ( 2 ). This protected monomer was subjected to anionic polymerization in tetrahydrofuran at −60°C in the presence of LiCl, using 1,1-diphenylhexyllithium as initiator. The molecular weight of the polymer could thus be controlled and a narrow molecular weight distribution obtained. The protecting group, 1-(acetoxy)ethyl, could be easily eliminated (by quenching the polymerization reaction with methanol and water) to generate poly(2-hydroxyethyl methacrylate) (poly(HEMA)). Block copolymers were also prepared by the sequential anionic polymerization of MMA and 2 or styrene and 2 . They possess narrow molecular weight distributions, and controlled molecular weights and compositions. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1865–1872, 1998     

Synthesis of Block Copolymers of 2‐Ethylhexyl Methacrylate,n‐Hexyl Methacrylate and Methyl Methacrylate via Anionic Polymerization at Ambient Temperature

It still remains a concern to break through the bottlenecks of anionic polymerization of polar monomers, such as side reactions, low conversion and low temperature (–78°C). In this work, potassium tert‐butoxide (t‐BuOK) was chosen to initiate the anionic polymerization of 2‐ethylhexyl methacrylate (EHMA) in tetrahydrofuran. The conversions were above 99% at 0 or 30°C, and above 95% at 60°C without side reaction inhibitors. The high conversions implied t‐BuOK could suppress the side reactions. A series of block copolymers of EHMA, n‐hexyl methacrylate (HMA) and methyl methacrylate (MMA) were further synthesized at 0°C, and the conversions were all above 99%. The GPC and ¹H NMR results confirmed the successful synthesis of the block copolymers. The molecular size of monomer and the state of t‐BuOK (free ion pairs or aggregates) remarkably affected the polymerization rates and the molecular structures of the products. The DMA results indicated that the glass transition temperatures of PEHMA or PHMA block and PMMA block were 20°C and 60°C, respectively, which deviated from –2°C and 105°C of homopolymer, respectively, due to the partial compatibility of the blocks. This work explored a route of the anionic polymerization of polar monomers at room temperature.     

Synthesis of gold–poly(methyl methacrylate) core–shell nanoparticles by surface‐confined atom transfer radical polymerization at elevated temperature

Surface‐confined atom transfer radical polymerization was used to prepare gold nanoparticle–poly(methyl methacrylate) core–shell particles at elevated temperature. First, gold nanoparticles were prepared by the one‐pot borohydride reduction of tetrachloroaurate in the presence of 11‐mercapto‐1‐undecanol (MUD). MUD‐capped gold nanoparticles were then exchanged with 3‐mercaptopropyltrimethoxysilane (MPS) to prepare a self‐assembled monolayer (SAM) of MPS on the gold nanoparticle surfaces and subsequently hydrolyzed with hydrochloric acid. The extent of exchange of MUD with MPS was determined by NMR. The resulting crosslinked silica‐primer layer stabilized the SAM of MPS and was allowed to react with the initiator [(chloromethyl)phenylethyl] trimethoxysilane. Atom transfer radical polymerization was conducted on the Cl‐terminated gold nanoparticles with the CuCl/2,2′‐bipyridyl catalyst system at elevated temperature. The rates of polymerization with the initiator‐modified gold nanoparticles exhibited first‐order kinetics with respect to the monomer, and the number‐average molecular weight of the cleaved graft polymer increased linearly with the monomer conversion. The presence of the polymer on the gold nanoparticle surface was identified by Fourier transform infrared spectroscopy and transmission electron microscopy. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3631–3642, 2005     

Preparation of functional polymers by living anionic polymerization: Polymerization of allyl methacrylate

The anionic polymerization of allyl methacrylate was carried out in tetrahydrofuran, both in the presence and in the absence of LiCl, with a variety of initiators, at various temperatures. It was found that (1,1-diphenylhexyl)lithium and the living oligomers of methyl methacrylate and tert-butyl methacrylate are suitable initiators for the anionic polymerization of this monomer. The temperature should be below −30°C, even in the presence of LiCl, for the living polymerization to occur. When the polymerization proceeded at −60°C, in the presence of LiCl, with (1,1-diphenylhexyl)-lithium as initiator, the number-average molecular weight of the polymer was directly proportional to the monomer conversion and monodisperse poly(allyl methacrylate)s with high molecular weights were obtained. ¹H-NMR and FT-IR indicated that the α CC double bond of the monomer was selectively polymerized and that the allyl group remained unreacted. The prepared poly(allyl methacrylate) is a functional polymer since it contains a reactive CC double bond on each repeating unit. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2901–2906, 1997     

Polymerization of methyl methacrylate by metallocene imido complexes and tris(pentafluorophenyl)alane

The polymerization of methyl methacrylate (MMA) was investigated with tris(pentafluorophenyl)alane [Al(C₆F₅)₃] and four metallocene imido complexes that varied in the complex symmetry/chirality, metal, and R group in the ?NR moiety, as well as a zirconocene enolate preformed from the imido zirconocene and MMA. This study examined four aspects of MMA polymerization: the effects of the metallocene imido complex structure on the polymerization activity and polymer tacticity, the degree of polymerization control, the elementary reactions of the imido complex with Al(C₆F₅)₃ and MMA, and the polymerization kinetics and mechanism. There was no effect of the imido complex symmetry/chirality on the polymerization stereochemistry; the polymerization followed Bernoullian statistics, producing syndiotactic poly(methyl methacrylate)s with moderate (～70% [rr]) to high (～91% [rr]) syndiotacticity, depending on the polymerization temperature. Polymerization control was demonstrated by the number‐average molecular weight, which increased linearly with an increase in the monomer conversion to 100%, and the relatively small and insensitive polydispersity indices (from 1.21 to 1.17) to conversion. The reactions of the zirconocene imido complex with Al(C₆F₅)₃ and MMA produced the parent base‐free imido complex and the [2 + 4] cycloaddition product (i.e., zirconocene enolate), respectively; the latter product reacted with Al(C₆F₅)₃ to generate the active zirconocenium enolaluminate. The MMA polymerization with the metallocene imido complex and the alane proceeded via intermolecular Michael addition of the enolaluminate to the alane‐activated MMA involved in the propagation step. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3132–3142, 2003