Propylene Radical Copolymerization

Unlike ethylene, which is quite active in radical poly- and co-polymerization, the next member of the olefinic row–propylene (Pr)–is much less efficient in such reactions. Thermodynami-cally, the polymerization of Pr is permitted as is evidenced by reactions with Ziegler-Natta catalysts (The free energy change δG for the conversion of liquid Pr into amorphous poly-Pr at 25°C is -12.2 kcal/mol [1].), but the strong chain transfer activity of the Pr-monomer prevents formation of high molecular weight polymers via radical mechanism. Pr easily gives up H″ atoms with the formation of inactive and probably resonance stabilized allyl radicals CH₂[sbnd]CH[sbnd]CH₂ .(The high resonance stabilization of the Pr-radi-cal 'CH₂ CH[dbnd]CH₂, formed after separation of the H″ atom, should not be confused with a very low resonance stabilization of the Pr-radical 'CH₂ [sbnd]CH[sbnd]CH₃, formed after opening of the double bond. The Q–e scheme deals with the second type of radical and Pr is characterized by a low resonance factor, Q_pr 0.002.) As a result, Pr radical homopolymerization gives low-molecular weight polymer (even at a pressure of 15,000 atm the molecular weight of poly-Pr is only ～3000 [2, 3]).     

SYNTHESIS AND CHARACTERISATION OF DIORGANOANTIMONY(III) COMPLEXES OF THIOSEMICARBAZONES

Abstract

The interaction of the sodium salts of thiosemicarbazones with diphenylantimony chloride in 1:1 molar ratio in benzene solution lead to the formation of derivatives, Ph₂Sb[SC(NH₂)NN: C(R)R′] where R = H; R′ [dbnd] C₆H₅, CH₃OC₆H₄, C₆H₅CH[dbnd]CH, and R′ [dbnd] CH₃; R′[dbnd]C₆H₅, CH₃OC₆H₄, C₆H₄CH₃, respectively. The resulting complexes have been characterised on the basis of elemental analyses and molecular weight determination. The mode of bonding of the ligands with the metal atom has been proposed on the basis of I.R., ¹H and ¹³C NMR studies. All these ligands are found to behave as monofunctional bidentate moiety in these complexes.     

Synthesis of the Insect Sex Pheromone of Achroia Grisella via the Novel Synthon, 1-Tetrahydro-Pyranyloxy Dodec 11-Yne

We report the preparation of 1-tetrahydro-pyranyloxy dodec 11-yne(1), from castor oil, with an overall yield of 9.6%, and illustrate its use with the novel and practical synthesis of 1-oxo octadec (z) 11-ene(2), the insect sex pheromone of Achroia grisella, a species of wax moth, which are specific enemies of bees¹. Parenthetically, it has been found that 1 is a good precursor to the surprisingly large number of pheromones that have the structural unit, [sbnd]CH[dbnd]CH[sbnd](CH₂)₉CHXY².     

SYNTHESIS AND NMR CHARACTERIZATION OF P-VINYL SUBSTITUTED PHOSPHAZENE PRECURSORS1

Abstract

The reactions of either PhPCl₂ or PCl₃ with (Me₃Si)₂NLi followed by H₂C[dbnd]CHMgBr were used to prepare the new P-vinyl substituted [bis(trimethylsilyl)amino]phosphines, (Me₃Si)₂NP(R)CH[dbnd]CH₂ [1: R=Ph, 2: CH[dbnd]CH₂, 3: R=Me, and 4: R=N(SiMe₃)₂]. Oxidative bromination of phosphines 3–1 afforded the P-bromo-P-vinyl-N-(trimethylsilyl)phosphoranimines, Me₃SiN[dbnd]P(CH[dbnd]CH₂)(R)Br [5: R=Ph, 6: R=CH[dbnd]CH₂, 7: R=Me], which, upon treatment with CF₃CH₂OH/Et₃N, were subsequently converted to the P-trifluoroethoxy derivatives, Me₃SiN[dbnd]P(CH[dbnd]CH₂)(R)OCH₂CF₃ [8: R=Ph, 9: R=CH[dbnd]CH₂, 10: R=Me]. Compounds 1–10, which are of interest as potential precursors to P-vinyl substituted poly(phosphazenes), were fully characterized by elemental analyses (except for the thermally unstable P-Br derivatives 5–7) and NMR spectroscopy (¹H, ¹³C, and ³¹P) including complete analysis of the vinylic proton splitting patterns via HOM2DJ experiments.     

STEREOSELECTIVE SYNTHESIS OF MONOFLUORO-OLEFINS FROM DIISOPROPYL (CARBOETHOXYFLUORO-METHYL)PHOSPHONATE

Abstract

Treatment of ethyl oxalyl chloride or methyl oxalyl chloride with lithium diisopropyl(carboethoxyfluoromethyl)phosphonate[(i-PrO)₂P(O)CFCO₂Et]^?Li⁺ 2 followed by in siru nucle-ophilic addition with methylmagnesium iodide or vinyl magnesium bromide affords with exclusive E-stereoselectivity formation of diethyl-2-fluoro-3-methyl fumarate (CH₃)(C0₂Et)C[dbnd]CFCO₂Et 4 or 75% of the E-isomer of a-fluoro-P-vinyl-a,P-unsaturated diester (E,Z)-(CH₂[dbnd]CH)(CO₂C₂H₅)C[dbnd]CFCO₂Et 5, respectively. However, direct reaction of ethyl pyruvate with 2 gives the fluoro-olefin (CH₃)(CO₂Et)C[dbnd]CFCO₂Et 4 with 79% E-stere-oselectivity. The E/Zratio of (CH₂[dbnd]CH)(CO₂Et)C[dbnd]CFCO₂Et 5 depends on the HMFT or DMPU cosolvents present in the reaction mixture.     

Synthesis of End-Reactive Polymers with Controlled Molecular Weight by Metalloporphyrin Catalyst

α, β, γ δ-Tetraphenylporphinatoaluminum carboxylate (TPPA10COR) and phenoxide (TPPA10Ar) bring about the polymerization of β-lactone and epoxide to give polymers with controlled chain length having a carboxylic ester or phenoxy group at the end of each polymer molecule. Acrylate (TPPA10COCH=CH2) and p-vinylphenoxide (TPPA1-OC₆H₄,CH[dbnd]CH₂ (p)) as initiator give polyester or polyether macromer with narrow molecular weight distribution.     

Structural irregularities in poly(vinyl alcohol)

Poly(vinyl alcohols) derived from the product of polymerization of vinyl acetate in methanol have been characterized by various physical and chemical methods before and after NaIO₄ cleavage. The 220-MHz ¹H-NMR spectra confirm the reliability of NaIO₄ titrimetry for estimating 1,2-glycol content and help explain the tendency for viscometry to grossly underestimate the 1,2-glycol content for low molecular weight polymers. The spectra and related chemical evidence indicate that the major endgroups are HOCH₂CH₂? and CH₃CH(OH)CH(OH)CH₂? . ß-Hydroxyethyl groups also occur as short chain branches, mainly attached to α carbon atoms in the normal head-to-tail polymer chain sequence. The concentrations of the branch and endgroups depend on polymerization conditions and help explain polymerization “solvent” effects on physical properties.     

REACTION DES ENOLATES MASQUES DE SILICIUM ISSUS WESTERS DE TRIMETHYLSILYLE AVEC LES DERIVES CARBONYLES α,β-INSATURES

Abstract

Bis(trimethylsilyl) ketene acetals RCH[dbnd]C[OSi(CH₃)₃]₂ 1 add to PhCH[dbnd]CH[sbnd]COR¹ 2 in the presence of catalytic amounts (10%) of TiCl₄ leading, in good to excellent yields to the corresponding β-hydroxy or δ-ketoacids. Under kinetic control, the regioselectivity of the reaction markedly depends on the nature of R and R¹. Mixtures of 1,2 and 1,4 products are formed in some of the cases; in others, solely Michael or aldol adducts are obtained. On the contrary, the stereoselectivity, which ranges from zero to moderate, is slightly influenced by R and R¹.

It is also shown that trimethylsilyl ester of α-trimethylacetic acid (CH₃)₃SiCH₂CO₂Si(CH₃)₃ 5 add to 2 in the presence of TBAF (10%) in THF.     

Synthesis of polyacetals with various main‐chain structures by the self‐polyaddition of vinyl ethers with a hydroxyl function

To establish the optimum conditions for obtaining high molecular weight polyacetals by the self‐polyaddition of vinyl ethers with a hydroxyl group, we performed the polymerization of 4‐hydroxybutyl vinyl ether (CH₂?CH? O? CH₂CH₂CH₂CH₂? OH) with various acidic catalysts [p‐toluene sulfonic acid monohydrate, p‐toluene sulfonic anhydride (TSAA), pyridinium p‐toluene sulfonate, HCl, and BF₃OEt₂] in different solvents (tetrahydrofuran and toluene) at 0 °C. All the polymerizations proceeded exclusively via the polyaddition mechanism to give polyacetals of the structure [? CH(CH₃)? O? CH₂CH₂CH₂CH₂? O? ]_n quantitatively. The reaction with TSAA in tetrahydrofuran led to the highest molecular weight polymers (number‐average molecular weight = 110,000, weight‐average molecular weight/number‐average molecular weight = 1.59). 2‐Hydroxyethyl vinyl ether, diethylene glycol monovinyl ether, cyclohexane dimethanol monovinyl ether, and tricyclodecane dimethanol monovinyl ether were also employed as monomers, and polyacetals with various main‐chain structures were obtained. This structural variety of the main chain changed the glass‐transition temperature of the polyacetals from approximately ?70 °C to room temperature. These polyacetals were thermally stable but exhibited smooth degradation with a treatment of aqueous acid to give the corresponding diol compounds in quantitative yields. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4053–4064, 2002     

REACTIONS OF A PHOSPHORANIMINE ANION WITH SOME ORGANIC ELECTROPHILES

Abstract

The reactions of a variety of electrophiles with the N-silyl-P-trifluoroethoxyphosphoranimine anion Me₃Sin°P(Me)(OCH₂CF₃)CH^? ₂ (1a), prepared by the deprotonation of the dimethyl precursor Me₃SiN[dbnd]P(OCH₂CF₃)Me₂ (1) with n-BuLi in Et₂O at-78°C, were studied. Thus, treatment of 1a with alkyl halides, ethyl chloroformate, or bromine afforded the new N-silylphosphoranimine derivatives Me₃SiN[dbnd]P(Me)(OCH₂CF₃)CH₂R [2: R = Me, 3: R = CH₂Ph, 4: R = CH[sbnd]CH₂, 5: R = C(O)OEt, and 6: R = Br]. In another series, when 1a was allowed to react with various carbonyl compounds, 1,2-addition of the anion to the carbonyl group was observed. Quenching with Me₃SiCl gave the O-silylated products Me₃SiN[dbnd]P(Me)(OCH₂CF₃)CH₂°C(OSiMe₃)R¹R² [7: R ¹ = R ² = Me; 8: R ¹ = Me, R ² = Ph; 9: R¹ = Me, R ² = CH[sbnd]CH₂; and 10: R ¹ = H, R ² = Ph]. Compounds 2–10 were obtained as distillable, thermally stable liquids and were characterized by NMR spectroscopy (¹H, ¹³C, and ³¹P) and elemental analysis.     

Characterization of five [C4H7O]+ Ion structures. Fragmentation of the 2-pentanone molecular ion

The [C₄H₇0]⁺ ions [CH₂?CH? C(?OH)CH₃]⁺ (1), [CH₃CH?CH? C(?OH)H]⁺ (2), [CH₂?C(CH₃)C(?OH)H]⁺ (3), [Ch₃CH₂CH₂C?O]⁺ (4) and [(CH₃)₂CHC?O]⁺ (5) have been characterized by their collision-induced dissociation (CID) mass spectra and charge stripping mass spectra. The ions 1–3 were prepared by gas phase protonation of the relevant carbonyl compounds while 4 and 5 were prepared by dissociative electron impact ionization of the appropriate carbonyl compounds. Only 2 and 3 give similar spectra and are difficult to distinguish from each other; the remaining ions can be readily characterized by either their CID mass spectra or their charge stripping mass spectra. The 2-pentanone molecular ion fragments by loss of the C(1) methyl and the C(5) methyl in the ratio 60:40 for metastable ions; at higher internal energies loss of the C(1) methyl becomes more favoured. Metastable ion characteristics, CID mass spectra and charge stripping mass spectra all show that loss of the C(1) methyl leads to formation of the acyl ion 4, while loss of the C(5) methyl leads to formation of protonated vinyl methyl ketone (1). These results are in agreement with the previously proposed potential energy diagram for the [C₅H₁₀O]⁺˙ system.     

Exploring the activities of vanadium,niobium, and tantalum PNP pincer complexes in the hydrogenation of phenyl-substituted CN,CN, CC,CC, and CO functional groups

The structures and stability of the designed PNP pincer amido M(NO)₂(PNP) and amino ^HM(NO)₂(PN^HP) complexes [M = V, Nb, and Ta, PNP = N(CH₂CH₂P(isopropyl)₂)₂, PN^HP = HN(CH₂CH₂P(isopropyl)₂)₂] and their hydrogenation mechanisms for phenyl-substituted unsaturated functional groups have been explored at the B3PW91 level of density functional theory. Under H₂ environment, these conjugated complexes can form equilibrium and fulfill the criteria of metal–ligand cooperated bifunctional hydrogenation catalysts. For the hydrogenation of Ph-CN, Ph-CHNH, Ph-CHNH-Ph, Ph-CHNCH₂Ph, Ph-CCH, Ph-CHCH₂, Ph-CHO, and Ph-COCH₃, the reaction prefers either a two-step or one-step mechanism for the hydridic MH and protonic NH transfer. These results clearly show that the V, Nb, and Ta complexes are promising catalysts for the hydrogenation reactions, and these provide experimental challenges.     

REACTION OF SCHIFF BASE OF THIOHYDRAZIDES WITH P(NR2)3

Abstract

Three pathways were observed in the reactions of Schiff bases of Thiohydrazides with P(NR₂)₃. (a) MeS-R₂N exchange: MeS-C([dbnd]S)-NHN[dbnd]CHPh (1) reacted with P(NR₂)₃ led to new Schiff bases, R₂N-C([dbnd]S)-NHN[dbnd]CH = Ph (2). (b) Cleavage of C[dbnd]S bond and the formation of P[dbnd]S bond: H₂N-C([dbnd]S)-NHN[dbnd]CH = Ph (3) reacted with P(NR₂)₃ gave rise to the thiophosphoric amide. (Et₂N)₂P([dbnd]S)-NH-CH = N-N[dbnd]CH-Ph (4). (c) Formation of thiadiazole and triazole: Schiff bases 2a and H₂N(MeS)C = N-N[dbnd]CH-Ph (6) reacted with P(NR₂)₃ respectively and produced 5-dimethylamino-2-phenyl-2,3-(2H)-1,3,4-thiadiazole (5) and 5-methylthio-2-phenyl-2,3-(2H)-1,3,4-triazole (7).     

Well phase separated segmented copolymers via acyclic diene metathesis (ADMET) polymerization

Segmented oligomers consisting of polyoctenylene hard segments and unsaturated polytetrahydrofuran soft segments were prepared using acyclic diene metathesis (ADMET) copolymerization techniques. These are the first such segmented materials prepared via metathesis chemistry. Two different molecular weight α,ω-poly(tetrahydrofuran)diene soft segment monomers of the structure [CH₂CH(CH₂)₄[O(CH₂)₄]-_nO(CH₂)₄CHCH₂] (1) were synthesized by the cationic living polymerization of tetrahydrofuran (THF). Trifluoromethanesulfonic anhydride, (CF₃SO₂)₂O (triflic anhydride) (2), was employed as the initiator, followed by in situ bis-functionalization with 5-hexen-1-ol, [CH₂=CH(CH₂)₄OH] (3), to yield soft segment dienes with vinyl end groups. The functionality of these soft segment monomers was approximately 1.9. These telechelic monomers possessed sufficient functionality to be homopolymerized or copolymerized with 1,9-decadiene (4) to generate well phase separated, segmented oligomers exhibiting hard segment/soft segment thermal behavior. The segmented copolymers were characterized by ¹H-NMR, ¹³C-NMR, and IR spectroscopy, elemental analysis, and TGA and DSC analysis. Average molecular weights were determined by gel permeation chromatography (GPC) and end-group analysis. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 3441–3449, 1997     

Untersuchungen zum elektronischen Einfluß von Organoliganden. XIII. Synthese und Charakterisierung von 2-funktionalisierten Vinylrhodoximen

Studies on the Electronic Influence of Organoligands. XIII. Synthesis and Characterization of 2-Functionalized Vinyl Rhodoximes 2-Functionalized vinyl rhodoximes [Rh(dmgH)₂ (PPh₃)cis/trans-CH = CHZ] ([Rh]? CH = CHZ) ) ( 1 ) can be prepared with a wide variation of the substituent Z (cis: OEt ( 1 a ), OPh ( 1 b ), Cl ( 1 c ), Me ( 1 j ), Ph ( 1 k ), SMe ( 1 l ), SPh ( 1 m ); trans: SPh ( 1 d ), Me ( 1 e ), Ph ( 1 f ), CMe₃ ( 1 g ), SiMe₃ ( 1 h )) by oxidative addition of XCH = CHZ and/or by nucleophilic addition of HC?CZ and Me₃SiC?CZ, respectively, to [Rh]^?. 1 a is converted to [Rh]? CH₂CHO ( 2 ) already in a weakly acid medium. 1 l is isomerized to trans-[Rh]? CH = CHSMe ( 1 n ) in the presence of acids. The complexes 1 are characterized by microanalysis and by ¹H, ¹³C and ³¹P NMR spectroscopy. The magnitude of the coupling constants ¹J(¹⁰³Rh, ³¹P) reveals only a small effect of Z on the (NMR) trans influence of the vinyl ligands CH = CHZ. The molecular structures of cis-[Rh]? CH = CHSPh ( 1 m ) and trans-[Rh]? CH = CHSPh ( 1 d ) show a distorted octahedral coordination of Rh with a mutual trans position of triphenyl-phosphine and the 2-phenylmercaptovinyl ligands. Van der Waals interactions exist between the sulfur and the equatorial dimethylglyoximato ligands in the cis complex 1 m .     

CARBODIPHOSPHAN (2.4.6-tBu3C6H2[sbnd]P[dbnd]2)C: REAKTION MIT ELEKTROPHILEN

Abstract

The reaction of Ar[sbnd]P[dbnd]C[dbnd]P[sbnd]Ar (Ar=2.4.6-^tBu₃C₆H₂) with electrophiles (H⁺, S₈) proceeds at the phosphorus atom with subsequent cyclisation of an o-^tbutyl group.     

Structures and stabilities of [C3H3O]+ ions in the gas phase: A molecular orbital study

The relative energies of 11 [C₃H₃O]⁺ ions are calculated by different molecular orbital methods (MINDO/3, MNDO, ab initio with 3-21G and 4-31G* basis set and configuration interaction). The four most stable structures are: a ([CH₂?CH? CO]⁺), b c ([CH?C? CHOH]⁺) and d ([CH₂?C?COH]⁺); their relative energies at the CI/4-31G*//3-21G level are 0, 117, 171 and 218 kJ mol^?1, respectively. The isomerizations c→[CH?CH? CHO]⁺→[CH₂?C? CHO]⁺→ a and dissociations into [C₂H₃]⁺+CO and [HCO]⁺+C₂H₂ are explored. The calculated potential energy profile reveals that the energy-determining step is the 1,3-H migration c→[CH?CH? CHO]⁺. This explains the value of unity of the branching ratio and the spread of kinetic energy released for the two dissociation channels.     

1‐Silacyclopent‐2‐enes and 1‐silacyclohex‐2‐enes bearing functionally substituted silyl groups in 2‐positions. Novel electron‐deficient Si?H?B bridges

The reactions of alkyn‐1‐yl(vinyl)silanes R₂Si[C?C‐Si(H)Me₂]CH?CH₂ [R = Me (1a), Ph (1b)], Me₂Si[C?C‐Si(Br)Me₂]CH?CH₂ (2a), and of alkyn‐1‐yl(allyl)silanes R₂Si[C?C‐Si(H)Me₂]CH₂CH?CH₂ (R = Me (3a), R = Ph (3b)] with 9‐borabicyclo[3.3.1]nonane in a 1:1 ratio afford in high yield the 1‐silacyclopent‐2‐ene derivatives 4a, b and 5a, and the 1‐silacyclohex‐2‐ene derivatives 6a, b, respectively, all of which bear a functionally substituted silyl group in 2‐position and the boryl group in 3‐position. This is the result of selective intermolecular 1,2‐hydroboration of the vinyl or allyl group, followed by intramolecular 1,1‐organoboration of the alkynyl group. In the cases of 4a, b, potential electron‐deficient Si? H? B bridges are absent or extremely weak, whereas in 6a,b the existence of Si? H? B bridges is evident from the NMR spectroscopic data (¹H, ¹¹B, ¹³C and ²⁹Si NMR). The molecular structure of 4b was determined by X‐ray analysis. Copyright © 2005 John Wiley & Sons, Ltd.     

Sequence-regulated oligomers and polymers by living cationic polymerization. III. Synthesis and reactions of sequence-regulated oligomers with a polymerizable group

New sequence-regulated macromonomers ( 3 ) with a vinyl ether terminal were prepared by the HI/ZnI₂-mediated living cationic polymerization of vinyl ethers: CH₃? CH(OR¹)? CH₂CH(OR²)? C(COOEt)₂CH₂CH₂OCH?CH₂ ( 3a : R¹ = nBu, R² = CH₂CH₂OCOPh; 3b : R¹ = iOct, R² = CH₂CH₂Cl). The synthesis consisted of three consecutive steps: (i) quantitative addition of hydrogen iodide to the first vinyl ether into an adduct [CH₃? CH(OR¹)? l]; (ii) propagation of a second vinyl ether from the adduct in the presence of zinc iodide; and (iii) quenching the resulting AB-type heterodimeric living intermediate with a carbanion [^θC(COOEt)₂CH₂CH₂OCH?CH₂] carrying a vinyl ether group. The HI/ZnI₂-initiated living cationic polymerization of 3a and 3b yielded narrowly distributed polymers $\left( {\overline {DP}} _{_n } \sim 10 \right)$ consisting of a poly(vinyl ether) backbone and sequence-regulated oligomer branches. The terminal vinyl ether function of 3 was also utilized to prepare pentamers and hexamers with controlled sequence of functional vinyl ethers by selective dimerization and chain extension reactions with HI/ZnI₂. © 1993 John Wiley & Sons, Inc.     

Acyclic diene metathesis polymerization of 2,5‐dialkyl‐1,4‐divinylbenzene with molybdenum or ruthenium catalysts: Factors affecting the precise synthesis of defect‐free,high‐molecular‐weight trans‐poly(p‐phenylene vinylene)s

Factors affecting the syntheses of high‐molecular‐weight poly(2,5‐dialkyl‐1,4‐phenylene vinylene) by the acyclic diene metathesis polymerization of 2,5‐dialkyl‐1,4‐divinylbenzenes [alkyl = n‐octyl ( 2 ) and 2‐ethylhexyl ( 3 )] with a molybdenum or ruthenium catalyst were explored. The polymerizations of 2 by Mo(N‐2,6‐Me₂C₆H₃) (CHMe₂ Ph)[OCMe(CF₃)₂]₂ at 25 °C was completed with both a high initial monomer concentration and reduced pressure, affording poly(p‐phenylene vinylene)s with low polydispersity index values (number‐average molecular weight = 3.3–3.65 × 10³ by gel permeation chromatography vs polystyrene standards, weight‐average molecular weight/number‐average molecular weight = 1.1–1.2), but the polymerization of 3 was not completed under the same conditions. The synthesis of structurally regular (all‐trans), defect‐free, high‐molecular‐weight 2‐ethylhexyl substituted poly(p‐phenylene vinylene)s [poly 3 ; degree of monomer repeating unit (DP_n) = ca. 16–70 by ¹H NMR] with unimodal molecular weight distributions (number‐average molecular weight = 8.30–36.3 × 10³ by gel permeation chromatography, weight‐average molecular weight/number‐average molecular weight = 1.6–2.1) and with defined polymer chain ends (as a vinyl group, ? CH?CH₂) was achieved when Ru(CHPh)(Cl)₂(IMesH₂)(PCy₃) or Ru(CH‐2‐OⁱPr‐C₆H₄)(Cl)₂(IMesH₂) [IMesH₂ = 1,3‐bis(2,4,6‐trimethylphenyl)‐2‐imidazolidinylidene] was employed as a catalyst at 50 °C. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6166–6177, 2005