Synthesis,characterization, and ring opening polymerization of poly(1,4‐cyclohexylenedimethylene terephthalate) cyclic oligomers

Cyclic oligomers of poly(1,4‐cyclohexylenedimethylene terephthalate) (PCT) were prepared by reaction of 1,4‐cyclohexanedimethanol (CHDM) with terephthaloyl chloride under diluted conditions and separated from the linear products by silica gel column at a yield of 23.7 wt %. Cyclic dimer, trimer, tetramer, pentamer, and hexamer were further separated by high performance liquid chromatography, and found to constitute 98% of the cyclics mixtures. The structures of PCT cyclics were confirmed by means of mass spectrometry, Fourier transform infrared, and ¹H NMR analysis. A series of experiments were carried out to study the effects of catalysts and cis/trans configuration of isomers of CHDM on the yield of cyclic oligomers. Ring opening polymerization of the cyclic oligomers was carried out by heating the sample mixtures at 310 °C for 30 min in the presence of antimony oxide. Polymerization was confirmed by inherent viscosity changes and infrared spectra of the resulting polyesters. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1828–1833, 2000     

Oligomer formation in the emulsifier‐free emulsion polymerization of styrene

The formation of oligomers in emulsifier‐free emulsion polymerization of styrene was characterized by means of gel permeation chromatography and surface tension measurements. GPC analysis showed incessant oligomer formation throughout the emulsion polymerization process. Oligomers spanned a molecular weight range of 200–1,500, have an M̄_w of 800–900, an M̄_n of 600–800 and a polydispersity index of 1.3. On average, the oligomers contain 4 to 6 styrene units. UV detection could not be utilized to acquire the weight ratio of oligomers to polymers without correction. Combination was the major mode of termination of free radicals in the aqueous phase, but disproportionation was not negligible: for every three‐combination reactions there was about 1 disproportionation. Surface tension measurements showed that oligomers minimized the surface tension of the latex at about 50 min reaction to only 30 mN/m. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1323–1336, 2000     

Synthesis of fluoro‐substituted silole‐containing conjugated materials

2,5‐Dihydroxyboryl‐1,1‐dimethyl‐3,4‐bis(3‐fluorophenyl)‐silole ( 2a ) was prepared in 40% overall yield by reaction between 3‐fluorophenyl‐acetylene and dichlorodimethylsilane to yield bis[2(3‐fluorophenyl)ethynyl]dimethylsilane ( 1a ), which subsequently undergoes a reductive cyclization reaction using an excess of lithium naphthalenide. The fluoro substituted silole was applied as a co‐monomer in the Suzuki polycondensation reaction with 2,7‐dibromo‐9,9‐dioctyl‐fluorene. An oligomer ( 3a ) with a degree of polymerization of 6 was prepared and compared with an oligomer without fluoro substitution on the silole ( 3b ), with a degree of polymerization of 4. The new oligomers were spin coated onto glass slides and showed weak green photoluminescence (PL) in the solid state. Cyclic voltammetry, visible absorption spectroscopy, and density functional theory calculations showed that the fluoro substituents were sufficiently electron withdrawing to lower both the highest occupied molecular orbital and the lowest unoccupied molecular orbital in the oligomer. Two further alternating co‐oligomers were prepared from 2,5‐dihydroxyboryl‐1,1‐dimethyl‐3,4‐bis(phenyl)‐silole ( 2b ) and 1,3‐dibromo‐5‐fluoro‐benzene ( 4a ) or 1,3‐dibromobenzene ( 4b ). These oligomers both had degrees of polymerization of 8 and showed green PL in the solid state. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5116–5125, 2009     

Curing chemistry of phenylethynyl‐terminated imide oligomers: Synthesis of 13C‐labeled oligomers and solid‐state NMR studies

4‐(Phenylethynyl‐α,β‐¹³C)phthalic anhydride (PEPA) and ¹³C‐labeled phenylethynyl‐terminated imide (PETI) oligomers were synthesized, and solid‐state ¹³C nuclear magnetic resonance (NMR) spectroscopy was used to determine the structure of cured oligomers. Solid‐state ¹³C NMR spectra were collected before and after thermal curing. Using solid‐state ¹³C NMR difference spectroscopy, several cure products were identified. The observed ¹³C NMR resonances were assigned to four different classes of cure products: aromatics, products from backbone addition (substituted stilbenes and tetraphenylethanes), polyenes, and cyclobutadiene cyclodimers. The effects of postcuring and oligomer chain length on the structure of the cured resins were examined. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3486–3497, 2000     

Synthesis of phenylquinoxaline oligomers containing pendant electron‐donating and electron‐withdrawing groups

A series of extended 6‐substituted quinoxaline AB monomer mixtures, 2‐(4‐fluorophenyl)‐3‐[4‐(4‐hydroxyphenoxy)phenyl]‐6‐substituted quinoxaline and 3‐(4‐fluorophenyl)‐2‐[4‐(4‐hydroxyphenoxy)phenyl]‐6‐substituted quinoxaline, were prepared and polymerized to afford phenylquinoxaline oligomers. High‐molecular‐weight polymers could not be obtained because of the formation of cyclic oligomers. On the basis of matrix‐assisted laser desorption/ionization time‐of‐flight analysis and molecular modeling results, the formation of a cyclic dimer could be a favorable process resulting in low‐molecular‐weight oligomers. They were completely soluble and amorphous, with glass‐transition temperatures varying from 165 to 266 °C, and they had thermooxidative stability, with samples displaying 5% weight loss temperatures of 419–511 °C in nitrogen. The thermal properties of the monomers and resultant polymers dramatically depended on the polarity of the substituents. The monomers and resultant oligomers displayed high fluorescence in tetrahydrofuran solutions and N‐methyl‐2‐pyrrolidinone solutions, respectively. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6465–6479, 2005     

Near‐monodisperse,catalytically active,imidazole‐containing homooligomers: Synthesis by group transfer polymerization and solution characterization

Oligomers covering degrees of polymerization up to 23 of 2‐(1‐imidazolyl)ethyl methacrylate (ImEMA) were synthesized by group transfer polymerization (GTP) in propylene carbonate and tetrahydrofuran (THF). While GTP proceeds smoothly in propylene carbonate, polymerization in THF is accompanied by oligomer precipitation. The molecular weights (MWs) and molecular weight distributions (MWDs) of the oligomers were obtained by gel permeation chromatography (GPC) using acidic aqueous sodium nitrate as the eluent. Good control over the MW and small polydispersity indices (PDIs) were measured for the oligomers prepared in propylene carbonate but not in THF. The oligomers were evaluated for their ability to hydrolyze 4‐nitrophenyl acetate in aqueous solution. The hydrolytic activity increased with oligomer MW. The oligomer concentration‐ and substrate concentration‐dependencies of the initial hydrolysis rate were both found to be approximately first order. The hydrolytic activity increased with an increase in pH, manifesting the enhanced nucleophilicity and pronounced hydrophobicity of the unprotonated form of the repeating units. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1501–1512, 1999     

Photophysical characteristics of soluble oligo(p‐phenylenevinylene)–fullerene dyad

The fact that C₆₀ is a good acceptor has stimulated interest in covalently linked complexes, including polymers and oligomers. Photoinduced charge transfer in these systems has great potential for use in photovoltaic devices. In this study, an alternating conjugated oligomer of alkylated carbazole and dialkoxyl‐substituted phenylene, with pendant C₆₀ moieties, (PPV‐AFCAR) was prepared and characterized. The excited‐state properties of PPV–AFCAR were investigated with steady‐state spectroscopy and lifetime measurements. After photoexcitation, photoinduced energy transfer from the oligomer chain to the pendant moiety occurred in great proportion, but a charge‐separation process did not. Whether the energy‐transfer process was measurable or not depended on the system temperature. At 77 K, a quantum yield of more than 50% for energy transfer was found by the fitting of a linear combination of the excitation spectra of the precursor oligomer, the alternating conjugated oligomer of alkylated carbazole and dialkoxyl‐substituted phenylene PPV–ACAR, and the absorption spectra of C₆₀. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3981–3988, 2001     

Syntheses of random PET‐co‐PTTs and some related copolyesters by entropically‐driven ring‐opening polymerizations and by melt blending: Thermal properties and crystallinity

A library of random poly(ethylene terephthalate) (PET), poly(trimethylene terephthalate) (PTT), and seven PET–PTT copolymers has been prepared in a high throughput manner by entropically‐driven ring‐opening polymerizations of the corresponding macrocyclic oligomers. The products have been investigated by differential scanning calorimetry and wide angle X‐ray diffraction. They show that the 50:50 copolymer displays a crystalline phase. The same phase can be formed by in situ transesterification when a 50:50 mixture of PET and PTT is melt blended. Poly(butylene terephthalate) (PBT)–PET and PTT–PBT 50:50 copolymers also show crystal phases. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Kinetic studies on the formation of cyclic oligomers in poly(ethylene terephthalate)

The mechanism of cyclic oligomer formation has been kinetically studied by determining the rate of the formation of cyclic oligomers during melt of poly(ethylene terephthalate) (PET) at several levels of average molecular weight, which were obtained by fractionation and did not initially contain oligomers. The experimental rate equation of cyclic oligomer formation was introduced and then compared with the rate equation derived theoretically. The close agreement between the two equations suggested that the cyclic oligomer formation takes place according to cyclodepolymerization by the action of hydroxyl end groups in PET. The relation is represented as [C] = m·[OH]₀·t^1–n, where [C] is the concentration of cyclic oligomers, [OH]₀ is the initial concentration of hydroxyl end groups, m and n are constants, and t is melting time. A method has also been developed for separating cyclic oligomers from PET using dimethylformamide (DMF) as a solvent.     

Essential role of chain ends in the nylon‐6/poly(ethylene terephthalate) exchange

A combination of NMR and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF) techniques were suitable tools for examining the exchange reactions that occur during the melt‐mixing of nylon‐6 and poly(ethylene terephthalate) (Ny6/PET) blends in the presence of p‐toluene sulfonic acid (TsOH) at 285 °C. Some researchers believe that TsOH is an efficient catalyst for the amide–ester exchange reactions in PET/Ny6 and PET/nylon‐66 blends in the molten state. Instead, we have found that TsOH is able to react in the molten state with PET, yielding PET oligomers terminated with carboxyl groups. Because the latter oligomers can quickly react with Ny6 producing a Ny6/PET copolymer, the role of TsOH in the melt‐mixing process is not that of a catalyst but of a reactant. Our study allowed the structural identification of the Ny6/PET copolyesteramide produced in the exchange as a function of melt‐mixing time. The results revealed the essential role of carboxyl end groups in the exchange reaction between Ny6 and PET and allowed a detailed mechanism for this reaction. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2778–2793, 2003     

Effects of external donors and hydrogen concentration on oligomer formation and chain end distribution in propylene polymerization with Ziegler‐Natta catalysts

The effect of type and concentration of external donor and hydrogen concentration on oligomer formation and chain end distribution were studied. Bulk polymerization of propylene was carried out with two different Ziegler‐Natta catalysts at 70 °C, one a novel self‐supported catalyst (A) and the other a conventional MgCl₂‐supported catalyst (B) with triethyl aluminum as cocatalyst. The external donors used were dicyclopentyl dimethoxy silane (DCP) and cyclohexylmethyl dimethoxy silane (CHM). The oligomer amount was shown to be strongly dependent on the molecular weight of the polymer. Catalyst A gave approximately 50 % lower oligomer content than catalyst B due to narrower molecular weight distribution in case of catalyst A. More n‐Bu‐terminated chain ends were found for catalyst A indicating more frequent 2,1 insertions. Catalyst A also gave more vinylidene‐terminated oligomers, suggesting that chain transfer to monomer, responsible for the vinylidene chain ends, was a more important chain termination mechanism for this catalyst, especially at low hydrogen concentration. Low site selectivity, due to low external donor concentration or use of a weak external donor (CHM), was also found to increase formation of vinylidene‐terminated oligomers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 351–358, 2010     

Maleation of poly(3,4‐epoxy‐1‐butene) for accelerated crosslinking in the presence of a redox catalyst

Accelerated crosslinking of novel poly(3,4‐epoxy‐1‐butene) (3,4‐PEPB) oligomers in the presence of a cobalt‐based redox catalyst was investigated. Previous studies using model compounds, 3,4‐dimethoxy‐1‐butene and 1,4‐dimethoxy‐2‐butene, suggested that maleation of hydroxyl‐terminated 3,4‐PEPB oligomers would result in more rapid crosslinking in thin films. Novel maleated oligomers offered a unique combination of both electron‐rich and electron‐poor olefinic sites, and quantitative maleation significantly increased the crosslinking rate of 3,4‐PEPB. Efficient copolymerization between terminal maleate groups and olefinic groups in the repeating unit was proposed to account for accelerated crosslinking rates. Furthermore, the addition of novel reactive diluents, such as maleic acid mono‐ethyl ester, also effectively improved the 3,4‐PEPB crosslinking rate. Sol fraction measurements as a function of coating thickness revealed that the crosslinking rate versus oxygen diffusion was less significant for the maleated oligomers because of the presence of reactive electron‐poor olefins. Sol fractions were constant for catalyst concentrations greater than 0.25–0.50 wt % (as compared with oligomer feed). This observation suggested that a redox process was not a dominant factor in determining crosslinking rates at various experimental conditions. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2789–2798, 2002     

3‐Phenylethynyl phthalimide end‐capped imide oligomers and the cured polymers

In the past decades, 4‐phenylethynyl phthalic anhydride (4‐PEPA) has been the most important endcapper used for thermoset polyimide. As the isomer of4‐PEPA, 3‐phenylethynyl phthalic anhydride (3‐PEPA) has attracted our interest. In this article, 3‐PEPA was synthesized and a comparative study with 4‐PEPA on curing temperature, curing rate, thermal and mechanical properties of oligomers and cured polymers was presented. The new phenylethynyl endcapped model compound, N‐phenyl‐3‐phenylethynyl phthalimide, was synthesized and characterized. The molecular structure of model compound was determined via single‐crystal X‐ray diffraction and the thermal curing process was investigated by Fourier transform infrared. Differential scanning calorimetry clearly showed that the model compound from 3‐PEPA had about 20 °C higher curing onset and peak temperature than the 4‐PEPA analog. This result was further proved by the dynamic rheological analysis that the temperature of minimum viscosity for oligomers end‐capped with 3‐PEPA was above 20 °C higher than that of the corresponding 4‐PEPA endcapped oligomers with the same calculated number average molecular weight. The cured polymer from 3‐PEPA displayed slightly higher thermal oxidative stability than those from 4‐PEPA by thermogravimetric analysis. The thermal curing kinetics of 3‐PEPA endcapped oligomer (OI‐5) and 4‐PEPA endcapped oligomer (OI‐6) fitted a first‐order rate law quite well and revealed a similar rate acceleration trend. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4227–4235, 2008     

Ring‐chain interactions in solutions of cyclic and linear poly(methylene) ester oligomers in p‐dioxan and chloroform

The thermodynamic behavior of ternary solutions containing one cyclic (CYC10 and CYC20) and one linear (LIN10 and LIN20) poly(methylene) ester oligomer, respectively, in p‐dioxan and chloroform were investigated through vapor‐pressure measurements. Experiments were carried out at 25, 30, 35, and 40 °C. The ring‐chain interaction parameters χ″ were evaluated using the Leonard's equation for a ternary polymer solution containing one ring polymer. Results indicated that the values of χ″ are concentration and solvent dependent, and they vary with molecular size and slightly with temperature. All χ″ values were positive for both CYC10/LIN10 and CYC20/LIN20 blends, with the higher values for the former system, indicating that both ring‐chain oligomer blends are nearly immiscible, and the difference between cyclic and linear oligomers decreases as molecular size increases. The positive χ″ agrees with differential scanning calorimetric measurements performed on ring‐chain oligomer blends that show two distinct endotherms for the blends. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1425–1433, 2002     

Thermodynamics of solutions of cyclic polymethylene ester oligomers in p‐dioxane and chloroform

Differential vapor pressures were measured for mixtures of two cyclic polymethylene ester oligomers in p‐dioxane and chloroform at 25, 30, 35, and 40 °C at five different concentrations ranging from 1 to 20 wt %. The Flory–Huggins interaction parameter (χ) as well as Leonard's interaction parameter (χ′) for flexible and semiflexible rings were calculated and compared to one another. A new method for the estimation of the number of segments of a cyclic polymer is proposed that allows Leonard's equations to be applied correctly to a particular cyclic compound. Consistent differences between χ and χ′ were observed for all studied mixtures, and the differences became smaller if the cyclic oligomers were considered semiflexible. Interestingly, the enthalpic parameter (κ) deduced from values of χ and χ′ did not differ within their uncertainties. This supports the prediction that mixing cyclic polymer compared to its linear counterpart is mainly due to a molecular configurational entropy difference and that this difference should become less pronounced as the cyclic compound becomes larger. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 443–455, 2000     

Synthesis of star‐shaped polystyrenes via nitroxide‐mediated stable free‐radical polymerization

High molecular weight star‐shaped polystyrenes were prepared via the coupling of 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO) terminated polystyrene oligomers with divinylbenzene (DVB) in m‐xylene at 138 °C. The optimum ratio of the coupling solvent (m‐xylene) to divinylbenzene was determined to be 9 to 1 based on volume. Linear polystyrene oligomers (M_n = 19,300 g/mol, M_w/M_n = 1.10) were prepared in bulk styrene using benzoyl peroxide in the presence of TEMPO at approximately 130 °C under an inert atmosphere. Coupling of the TEMPO‐terminated oligomers under optimum conditions resulted in a product with a number average molecular weight exceeding 300,000 g/mol (M_w/M_n = 3.03) after 24 h, suggesting the formation of relatively well‐defined star‐shaped polymers. Additionally, the intrinsic viscosities of the star‐shaped products were lower than calculated values for linear analogs of equivalent molecular weight, which further supported the formation of a star‐shaped architecture. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 216–223, 2001     

The NSN link as electron accepting moiety for stable,solution‐processable conjugated oligomers

New conjugated oligomers, oligo(9,9‐didodecylfluorene‐bis‐sulphurdiimide), consisting of 9,9‐didodecylfluorene separated by ? N?S?N? moieties, are reported. These oligomers are stable purple solids under ambient conditions with absorption covering a broad spectral window in the UV‐vis range and a main broad peak centered at 555 nm with onset extending to 700 nm. These oligomers show an obviously longer conjugation length than its dimeric analogue, bis‐9,9‐didodecyl‐fluorene‐2‐sulfurdiimide that shows a band‐edge absorption centered at 484 nm with onset at 590 nm. The dimer and oligomers are soluble in a variety of organic solvents. Moreover, we found that the oligomer with an average repeating‐unit number of six could significantly quench the photoluminescence (PL) of poly[2‐methoxy‐5‐(2′‐ethyl‐hexyloxy)‐1,4‐phenylene vinylene] (MEH‐PPV) or poly(3‐hexylthiophene) (P3HT) in the solid state. More importantly, the composites of this oligomer with P3HT showed a nearly 10‐fold enhancement of the photocurrent, compared with that of P3HT itself. In addition, the PL of this oligomer could be quenched by the presence of phenyl‐C₆₁‐butyric acid methyl ester (PCBM) in toluene. These results suggest the presence of photoinduced charge transfer in composites of these oligomers blended with an electronic partner that either donates or accepts electrons. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and properties of novel polyimide/nylon‐6 triblock copolymers

Nylon‐6‐b‐polyimide‐b‐nylon‐6 copolymers were prepared by first synthesizing a series of imide oligomers end‐capped with phenyl 4‐aminobenzoate. The oligomers were then used to activate the anionic polymerization of molten ϵ‐caprolactam. In the block copolymer syntheses, the phenyl ester groups reacted quickly with caprolactam anions at 120 °C to generate N‐acyllactam moieties, which activated the anionic polymerization. In essence, nylon‐6 chains grew from the oligomer chain ends. All of the block copolymers had higher moduli and tensile strengths than those of nylon‐6. However, their elongations at break were much lower. The thermal stability, chemical resistance, moisture resistance, and impact strength were dramatically increased by the incorporation of only 5 wt % polyimide in the block copolymers. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4247–4257, 2000     

Synthesis of thianthrene‐5,5,10,10‐tetraoxide‐containing polyimides via Yamazaki–Higashi phosphorylation method and their pervaporation properties to aromatic/nonaromatic hydrocarbon mixtures

High molecular weight polyimide was successfully prepared from thianthrene‐2,3,7,8‐tetracarboxylic acid‐5,5,10,10‐tetraoxide (TADATO‐4A) and 3,7‐diamino‐2,8(6)‐dimethyldibenzothiophene sulfone (DDBT) via the Yamazaki–Higashi phosphorylation method in the presence of triphenyl phosphite (TPP) and pyridine (Py). The obtained polyimide showed about 3–4 times larger inherent viscosity than that prepared by the conventional two‐step method in which the anhydride form (TADATO) of TADATO‐4A was used. The combination of the conventional two‐step method and Yamazaki–Higashi phosphorylation method, in which a dianhydride monomer [3,3′,4,4′‐diphenylsulfonetetracarboxylic dianhydride (DSDA)] was allowed to react with excessive DDBT to form an amine end‐capped polyamic acid oligomer and subsequently the oligomer was further polymerized with TADATO‐4A in the presence of TPP and Py, succeeded in giving the high molecular weight copolyimide, TADATO/DSDA(1/1)‐DDBT. However, both TADATO‐DDBT and TADATO/DSDA(1/1)‐DDBT showed fairly poor thermal stability due to the highly rigid structures. The pervaporation (PV) properties of the prepared polyimide membranes for benzene/cyclohexane (Bz/Cx) and benzene/n‐hexane (Bz/n‐Hx) mixtures were investigated. TADATO‐DDBT showed similar PV performance to DSDA‐DDBT at 60 °C. The sorption measurement revealed that these two kinds of polyimide membranes had a similar sorption amount, solubility selectivity, and diffusivity selectivity. The PV performance of TADATO/DSDA(1/1)‐DDBT was also found similar to DSDA‐DDBT for Bz/Cx mixture. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 895–906, 2000     

Designing of dipeptide‐based oligoconjugates as potential carrier for drug delivery. Pyroglutamil‐S‐glutamic acid bisoligo‐3‐hydroxybutyrates

In the present article, we describe the synthesis and characterization of conjugates based on pyroglutamyl‐S‐glutamic acid and bisoligo‐[R,S]‐3‐hydroxybutyrates (PyGlu‐S_‐Glu_bisOHB) using anionic ring opening polymerization of β‐butyrolactone with a dipeptide bearing two carboxylate groups as potassium salt. The results indicated that the above‐mentioned reaction is accompanied of oligomerization of β‐butyrolactone yielding (3‐hydroxybutyrates) oligomers with crotonate and carboxyl end groups. We report also the end group analysis of the synthesized conjugates using electrospray ionization tandem mass spectrometry (ESI‐MS), the latter confirmed the presence of a mixture of dipeptide conjugate with β‐butyrolactone oligomer chain and β‐butyrolactone homopolymer. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4103–4111, 2008