(Diisopropylamido) bis (methylcyclopentadienyl) lanthanides as single-component initiators for polymerization of methyl methacrylate

It was first found that (diisopropylamido)bis(methylcyclopentadienyl)lanthanides (MeC₅H₄)₂LnN(i-Pr)₂(THF) (Ln = Yb ( 1 ), Er ( 2 ), Y ( 3 )) exhibit extremely high catalytic activity in the polymerization of methyl methacrylate. The reactions can be carried out over a quite broad range of polymerization temperatures from -78 to 40°C. The catalytic activity of the complexes increases with an increase of ionic radii of the metal elements, i.e. Y > Er > Yb. The results of GPC (gel permeation chromatography) indicate that the number-average molecular weights (M_n) of polymers obtained exceed 100 × 10³ and the molecular weight distribution (M_w/M_n) becomes broad with the increase of temperature. Furthermore highly syndiotactic PMMA (87.7%) can be obtained by lowering the reaction temperature to −78°C. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1593–1597, 1998     

Synthesis and characterization of new polyamides derived from 1,6-bis[4-(4-aminophenoxy)phenyl]diamantane

A series of new polyamides 3 were synthesized by direct polycondensation of the 1,6-bis[4-(4-aminophenoxy)phenyl]diamantane (1) with various dicarboxylic acids. The polyamides had inherent viscosities of 0.45–1.90 dL/g and number-average molecular weights (M_n) of 24,000–110,000. Dynamic mechanical analysis (DMA) reveals that polymers 3 have two relaxations on the temperature scale between −100 and 400°C. Their α relaxations occurred at high temperatures, ranging from 338 to 389°C. Moreover, these polymers remained quite stable at high temperatures and maintained good mechanical properties (G′ = ca. 10⁸ Pa) up to temperatures close to the main transition markedly exceeding 350°C. Due to the bulky diamantane elements and the flexible ether segments, the polymers 3 were amorphous and soluble in a number of organic solvents such as pyridine, N-methyl-2-pyrrolidone (NMP), and N,N-dimethylacetamide (DMAc). The polyamides 3 have tensile strengths of 56.7–90.2 MPa, elongation to breakage values of 7.5–27.7%, and initial moduli of 1.8–2.1 GPa. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2185–2192, 1998     

Synthesis and properties of a novel perfluorononenyloxy group containing polyarylates

A series of novel perfluorononenyloxy group containing polyarylates were synthesized by a high-temperature solution condensation of 5-(perfluorononenyloxy)-isophthaloyl chloride ( II ) with various aromatic diols in o-dichlorobenzene. All the polyarylates were amorphous and readily soluble in many organic solvents such as o-chlorophenol, o-dichlorobenzene, chloroform, and polar aprotic solvents at room temperature or on heating. Transparent, tough, and flexible films of these polymers could be cast from the o-chlorophenol solutions. The polymers having inherent viscosity of 0.61–1.63 dL/g were obtained in quantitative yields. These polymers were thermally quite stable. The glass transition temperatures of these polyarylates were in the range of 219–242°C by DSC and 224–251°C by DMA, and the 10% weight loss temperatures in nitrogen and air were above 415 and 397°C, respectively. Moreover, these polymers maintained good mechanical properties (G′ ∼ 10⁸ Pa) up to 220°C and had lower moisture absorption than common polyarylates. The dielectric constants of these polymers ranged from 3.23 to 3.75. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 645–653, 1998     

Synthesis and characterization of aromatic poly(ether ketone)s containing cyclotriphosphazene units

Bis(4-oxybenzoic acid) tetrakis(phenoxy) cyclotriphosphazene (IUPAC name: 4-[4-(carboxyphenoxy)-2,4,6,6-tetraphenoxy-1,3,5,2λ⁵,4λ⁵,6λ⁵-triazatriphosphinin-2-yl]oxy-benzoic acid) was synthesized and direct polycondensed with diphenylether or 1,4-diphenoxybenzene in Eaton's reagent at the temperature range of 80–120°C for 3 hours to give aromatic poly(ether ketone)s. Polycondensations at 120°C gave polymer of high molecular weight. Incorporation of cyclotriphosphazene groups in the aromatic poly(ether ketone) backbone greatly enhanced the solubility of these polymers in common organic polar solvents. Thermal stabilities by TGA for two polymer samples of polymer series ranged from 390 to 354°C in nitrogen at 10% weight loss and glass transition temperatures (T_g) ranged from 81.4 to 89.6°C by DSC. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1227–1232, 1998     

Thermotropic liquid‐crystalline poly(oxadiazole)s with poly(methylene) spacers: Preparation and extraordinary odd–even effect

A novel synthetic procedure for the preparation of poly(oxadiazole)s was developed with nucleophilic substitution of α,ω-alkanediols with oxadiazole-activated bisfluoride. Seven poly(oxadiazole)s were successfully prepared by the solution polymerization of 2,5-bis(4-fluorophenyl)-1,3,4-oxadiazole and various α,ω-alkanediols [HO (CH₂)_n OH, n = 5–10 or 12] in diphenyl sulfone at temperature greater than 230 °C with K₂CO₃ as a catalyst. The reduced viscosities of the poly(oxadiazole)s were 0.14–0.51 dL/g, and the decomposition temperatures were greater than 350 °C and decreased from 436 to 379 °C with increasing spacer length (n). Corresponding model compounds, consisting of two terminal mesogenic 2,5-bisphenyl-1,3,4-oxadiazole units and central poly(methylene) spacers, were also prepared for comparison. Both the polymers and model compounds exhibited an extraordinary odd–even effect: odd ones showed higher transition temperatures (melting and clearing temperatures). With differential scanning calorimetry, polarized optical microscopy (POM), and X-ray diffraction, we found that the nematic mesophase was the only texture in the melts except for the polymers with longer methylene units (n = 9), in which smectic mesophases were observed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 293–301, 2002     

Dynamic light scattering studies of atactic and syndiotactic poly(methyl methacrylate)s in dilute theta solution

The present article considers the coil‐to‐globule transition behavior of atactic and syndiotactic poly(methyl methacrylates), (PMMA) in their theta solvent, n‐butyl chloride (nBuCl). Changes in Rh in these polymers with temperature in dilute theta solutions were investigated by dynamic light scattering. The hydrodynamic size of atactic PMMA (a‐PMMA‐1) in nBuCl (M_w: 2.55 × 10⁶ g/mol) decreases to 61% of that in the unperturbed state at 13.0°C. Atactic PMMA (a‐PMMA‐2) with higher molecular weight (M_w: 3.3 × 10⁶ g/mol) shows higher contraction in the same theta solvent (α_η = R_h(T)/R_h (θ) = 0.44) at a lower temperature, 7.25°C. Although syndiotactic PMMA (s‐PMMA) has lower molecular weight than that of atactic samples (M_w: 1.2 × 10⁶), a comparable chain collapse was observed (α_η = 0.63) at 9.0°C. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2253–2260, 1999     

Synthesis and polymerization of N‐(4‐tetrahydropyranyl‐oxyphenyl)maleimide

N‐(4‐Tetrahydropyranyl‐oxy‐phenyl)maleimide (THPMI) was prepared and polymerized by radical or anionic initiators. THPMI could be polymerized by 2,2′‐azobis(isobutyronitrile) (AIBN) and potassium tert‐butoxide. Radical polymers (poly(THPMI)r) were obtained in 15–50% yields for AIBN in THF at 65°C after 2–5 h. The yield of anionic polymers (poly(THPMI)a) obtained from potassium tert‐butoxide in THF at 0°C after 20 h was 91%. The molecular weights of poly(THPMI)r and poly(THPMI)a were M_n = 2750–3300 (M_w/M_n = 1.2–3.3) and M_n = 11300 (M_w/M_n = 6.0), respectively. The difference in molecular weights of the polymers was due to the differences in the termination mechanism of polymerization and the solubility of these polymers in THF. The thermal decomposition temperatures were 205 and 365°C. The first decomposition step was based on elimination of the tetrahydropyranyl group from the poly(THPMI). Positive image patterns were obtained by chemical amplification of positive photoresist composed of poly(THPMI) and 4‐morpholinophenyl diazonium trifluoromethanesulfonate used as an acid generator. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 341–347, 1999     

Crosslinkable fluorinated poly(arylene ethers) bearing phenyl ethynyl moiety for low-loss polymer optical waveguide devices

Crosslinkable fluorinated poly(arylene ethers) (FPAE-Fn-PEP) with high transparency and high thermal stability have been investigated for low-loss optical waveguide materials. FPAE-Fn-PEP bearing phenyl ethynyl moiety at the polymer chain end were synthesized by the reaction of 4,4′-(hexafluoro-isopropylidene)diphenol with an excess decafluorobiphenyl, followed by the reaction of 4-phenyl ethynyl phenol. The M_ns and M_w/M_ns of the polymers determined by GPC with polystyrene standard were in the range of 6200 to 19,400 and 1.4 to 2.04, respectively. The resulting polymers were thermally crosslinked at 320°C for 2 h. The cured polymers show good chemical resistance and high thermal stability up to 510°C under nitrogen. The refractive indices of their films were controlled between 1.495 and 1.530 at 1.55 μm by adjusting molecular weight. A single-mode channel waveguide made of FPAE-F20-PEP was fabricated by conventional photolithography and O₂ reactive ion etching (RIE). The propagation loss of the channel waveguide was measured and found to be less than 0.2 dB/cm at 1.55 μm. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2881–2887, 1998     

Crosslinking of polyimides via spirodilactone unit in polymer backbone

A new approach for the crosslinking of polyimides via the lactamization of spirodilactone unit in polyimide backbone was studied by two means: model reaction and the comparison of the properties of the polyimide precursors to those of the crosslinking polymers. Polyimides 4 and 5 were soluble in N,N′dimethylacetamide (DMAc), dimethylformamide (DMF), dimethylsulfoxide (DMSO), N′-methylpyrrolidone (NMP), and other common organic solvents, whereas their corresponding crosslinking polymers were insoluble in these solvents. The glass transition temperatures for polyimide 5 and its crosslinking polymer were 262°C and 291°C, whereas those for polyimide 4 and its crosslinking polymer were 265°C and 360°C. The weight-loss rate of the crosslinking polymers was apparently slower than that of the precursors when the temperature was > 400°C. The 10% weight-loss temperature for the polyimides 4 and 5 was < 500°C, whereas that for the crosslinking polymers was close to or above 600°C. The results indicate that this type of crosslinking polymer has good thermal properties. The temperature for the formation of lactam was above 180°C. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3680–3686, 1999     

Living/controlled cationic cyclopolymerization of divinyl ether with a cyclic acetal moiety: Synthesis of poly(vinyl ether)s with high glass transition temperature based on incorporation of cyclized main chain and cyclic side chains

Cationic cyclopolymerization of 2‐methyl‐5,5‐bis(vinyloxymethyl)‐1,3‐dioxane ( 1 ), a divinyl ether with a cyclic acetal group, was investigated with the HCl/ZnCl₂ initiating system in toluene and methylene chloride at ?30 °C. The reaction proceeded quantitatively to give gel‐free, soluble polymers in organic solvents. The number‐average molecular weight (M_n) of the polymers increased in direct proportion to monomer conversion, and further increased on addition of a fresh monomer feed to the almost completely polymerized reaction mixture, indicating that the polymerization proceeded in living/controlled manner. The contents of the unreacted vinyl groups in the produced soluble polymers were less than ～3 mol %, and therefore, the degree of cyclization was determined to be ～97%. In contrast, the pendant cyclic acetal groups remained intact in the polymers under the present cationic polymerization conditions. These facts show that cyclopolymerization of 1 almost exclusively occurred and the poly(vinyl ether)s with the cyclized repeating units and cyclic pendant acetal rings were obtained. Glass transition temperature (T_g) and thermal decomposition temperature (T_d) of poly( 1 ) (M_n = 7870, M_w/M_n = 1.57) were found to be 166 and 338 °C, respectively, indicating that poly( 1 ) had high T_g and high thermal stability. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 952–958, 2010     

Poly(phenyl methacrylate) and poly(1‐naphthyl methacrylate) prepared in microemulsions

Phenyl methacrylate and 1‐naphthyl methacrylate were polymerized in microemulsions using stearyltrimethylammonium chloride, cetyltrimethylammonium bromide, and a mixture of nonionic Triton surfactants to form latexes that were 20–30 nm in diameter. A temperature of 70 °C was needed to obtain polymers using thermal initiation. The tacticities of poly(phenyl methacrylate) (PPhMA) (55% rr) and poly(1‐naphthyl methacrylate) (P‐1‐NM) (47% rr) were the same as those of the polymers prepared in toluene solutions. The weight average molecular weights were 1 × 10⁶ and 5 × 10⁵ g/mol for PPhMA and P‐1‐NM prepared in microemulsions with very broad distributions. PPhMA samples from microemulsions and solution had the same T_g = 127 °C. P‐1‐NM from microemulsions had T_g = 145–147 °C compared with T_g = 142 °C for P‐1‐NM from solution. The molecular weights and the glass‐transition temperatures of both PPhMA and P‐1‐NM from microemulsions are substantially higher than any previously reported. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 519–524, 2001     

Various silicon‐containing polymers with Si(H)?CC units

Nine new kinds of thermosetting polymers with the Si(H)? C?C unit were synthesized by dehydrogenative polycondensation reactions between hydrosilanes and diethynyl compounds in the presence of a magnesia catalyst. Phenylsilane, silane, vinylsilane, and n‐octylsilane were used as the hydrosilanes, and 1,3‐diethynylbenzene, 1,4‐diethynylbenzene, 4,4′‐diethynyldiphenyl ether, and 1,3‐diethynyl‐1,1,3,3‐tetramethyldisiloxane were used as the diethynyl compounds. All the polymers were thermosetting, highly heat‐resistant, easily soluble in a solvent, and moldable. In particular, ? Si(R)H? C?C? C₆H₄? C?C? (R = H or CH?CH₂) showed high thermal stability; the temperature of 5% weight loss was greater than 800 °C, and the residue at 1000 °C was over 90%. The thermal stabilities of the polymers were attributed to the crosslinking reaction of the Si? H and C?C bonds. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2658–2669, 2001     

Controlled free radical ring-opening polymerization and chain extension of the “living” polymer

Free radical ring-opening polymerization of 2-methylene-1,3-dioxepane (MDP) in the presence of 2,2,6,6-tetramethyl-1-piperidinyloxy free radical (TEMPO) has been achieved to afford a chain polyester (PMDP) with di-t-butyl peroxide (DTBP) as an initiator at 125°C. The polydispersity of the polymers decreases as the concentration of TEMPO is increased. At high TEMPO concentrations, the polydispersity as low as 1.2 was obtained, which is below the theoretical lower limit for a conventional free radical polymerization. A linear relationship between the number-average molecular weight (M_n) and the monomer conversion was observed with the best-fit line passing very close to the origin of the M_n-conversion plot. The isolated and purified TEMPO-capped PMDP polymers have been employed to prepare chain extended polymers upon addition of more MDP monomer. These results are suggestive of the “living” polymerization process. A possible polymerization mechanism might involve thermal homolysis of the TEMPO-PMDP bonds followed by the addition of the monomers. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 761–771, 1998     

Crystallization kinetics of a thermotropic liquid crystalline polyimide derived from 1,3-bis[4-(4′-aminophenoxy) cumyl] benzene

We have studied the nonisothermal and isothermal crystallization kinetics of an aromatic thermotropic liquid crystalline polyimide synthesized from 1,2,4,5-benzenetetracarboxylic dianhydride (PMDA) and 1,3-bis[4-(4′-aminophenoxy) cumyl] benzene (BACB) by means of differential scanning calorimetry (DSC). Polarized light microscopy (PLM) and wide-angle X-ray diffraction (WAXD) results confirm that this polyimide exhibits a smectic texture. Nonisothermal crystallization showed two strong and one weak exothermic peaks during cooling. The phase transition from isotropic melt to liquid crystalline state is extremely fast which completes in several seconds. The mesophase transition has a small Avrami parameter, n, of approximate 1. The isothermal crystallization of 253–258°C has been examined. The average value n is about 2.6 and the temperature-dependent rate constant k changes about two orders of magnitude in the crystallization temperature range of 6°C. The slope of ln k versus 1/(T_cΔT) is calculated to be −2.4 × 10⁵, which suggests nucleation control, via primary and/or secondary nucleation for the crystallization process. During the annealing process, a new phase (slow transition) is induced, which grows gradually with annealing time. At lower annealing temperatures (220–230°C), the slow transition process seems not to be influenced by the crystals formed during cooling process and its Avrami parameter n is ca. 0.3–0.4. However, the slow transition was hindered by the crystals formed during cooling process when annealed at higher temperature (230–240°C). © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1679–1694, 1998     

Anionic polymerization of N,N‐dialkyl‐2‐methylenebut‐3‐enamide: Effect of alkyl substituents on polymerization behavior

Anionic polymerizations of three 1,3‐butadiene derivatives containing different N,N‐dialkyl amide functions, N,N‐diisopropylamide (DiPA), piperidineamide (PiA), and cis‐2,6‐dimethylpiperidineamide (DMPA) were performed under various conditions, and their polymerization behavior was compared with that of N,N‐diethylamide analogue (DEA), which was previously reported. When polymerization of DiPA was performed at ?78 °C with potassium counter ion, only trace amounts of oligomers were formed, whereas polymers with a narrow molecular weight distribution were obtained in moderate yield when DiPA was polymerized at 0 °C in the presence of LiCl. Decrease in molecular weight and broadening of molecular weight distribution were observed when polymerization was performed at a higher temperature of 20 °C, presumably because of the effect of ceiling temperature. In the case of DMPA, no polymer was formed at 0 °C and polymers with relatively broad molecular weight distributions (M_w/M_n = 1.2) were obtained at 20 °C. The polymerization rate of PiA was much faster than that of the other monomers, and poly(PiA) was obtained in high yield even at ?78 °C in 24 h. The microstructure of the resulting polymers were exclusively 1,4‐ for poly(DMPA), whereas 20–30% of the 1,2‐structure was contained in poly(DiPA) and poly(PiA). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3714–3721, 2010     

Synthesis and characterization of new AB-type poly(etherimide)s containing bisphenol moieties

A series of new AB-type poly(etherimide)s having bisphenol-type moiety was prepared by the one-pot polyimidization using triphenylphosphite(TPP) in N-methyl-2-pyrrolidone(NMP)/pyridine solution at 150°C. Complete cyclodehydration was observed in the polymerizations as well as in model reactions. Polymers were obtained with inherent viscosities in the 0.27–0.49 dL/g range. The M_n and M_w/M_n of poly[4-(1,4-phenyleneoxy-1,4-phenylenehexafluoro-isopropylidene-1,4-phenylene)oxyphthalimide] (4d) with η_inh = 0.49 dL/g were 73,400 g/mol and 1.5, respectively. Most polymers could readily be dissolved in common organic solvents such as DMAc, NMP, and m-cresol. The polymer 4d was soluble even in chloroform. These polymers had glass transition temperatures between 205 and 235°C, and 5% weight loss temperatures in the range of 511–532°C in nitrogen. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3530–3536, 1999     

Synthesis of polymers with pendant hydroxyl groups by polyaddition of bis(oxetane)s with dithiols

Addition reaction of (3-methyl-3-oxetanyl)methyl acetate (MOMA) with bis(4-mercaptophenyl) sulfide (BMPS) was examined in certain organic solvents. When the reaction of MOMA with BMPS was performed without any catalyst in hexamethylphosphoric triamide (HMPA) and N-methyl-2-pyrrolidone (NMP) at 130°C for 24 h, conversions of the corresponding adduct were 96 and 36%, respectively, which was confirmed by ¹H-NMR spectra. On the other hand, when the reaction was carried out using tetraphenylphosphonium bromide (TPPB) as a catalyst under the same conditions, conversions of the adduct were 96 and 81% in HMPA and NMP, respectively. This result shows that although the addition reaction of oxetane compound with aromatic dithiol proceeds without any catalyst in HMPA, the reaction was strongly enhanced by adding TPPB in NMP. On the basis of the above results, polyadditions of bis((3-methyl-3-oxetanyl)methyl) terephthalate (BMOT) and bis((3-ethyl-3-oxetanyl)methyl) terephthalate with BMPS were performed using TPPB as the catalyst in NMP at 130°C for 24 h. As a result, the corresponding high molecular weight polymers 1 (M_n = 22,400) and 2 (M_n = 12,800) with pendant primary hydroxyl groups were obtained in 83 and 89% yields without any gel products, respectively. Furthermore, a low molecular weight oligomer was obtained from the polyaddition of BMOT with aliphatic dithiol, bis(mercaptomethyl)benzene, under the same reaction conditions. The catalytic activity on the polyaddition of BMOT with BMPS was also examined, and it was found that thermally stable TPPB and crown ether complexes at the reaction temperature (130°C) have higher catalytic activity than tetrabutylammonium bromide and tetrabutylphosphonium bromide to produce polymer 1 with high molecular weight. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2873–2880, 1998     

Polymers from multifunctional isocyanates 14. Alternating copolymers from isocyanato alkenes: Copolymerization of 2-propenyl isocyanate with trimethylsilyl methacrylate as electron acceptor monomer

The copolymerization of 2-propenyl isocyanate ( 1 ) with trimethylsilyl methacrylate ( 2 ) has been investigated. 1 is an electron donor monomer with little tendency to undergo homopolymerization, while 2 is an electron acceptor monomer, capable of free radical homopolymerization. Polymerization to low conversion in benzene gave copolymers with preferential incorporation of 2 and a tendency towards alternating copolymers with increasing amounts of 1 in the feed (1 : 1.13 with a 9 : 1 feed ratio of monomers 1 : 2 ). The glass transition temperatures of the amorphous polymers are in the range from 100–70°C, with a T_g of poly(trimethylsilyl methacrylate) being 135°C. Desilylation occurs in the presence of water, causing an exothermal reaction above the glass transition temperature probably with formation of amides, a reaction that can be used for crosslinking. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 611–616, 1998     

Influence of tertiary diamines on the synthesis of high‐molecular‐weight poly(1,3‐cyclohexadiene)

The living synthesis of poly(1,3‐cyclohexadiene) was performed with an initiator adduct that was synthesized from a 1:2 (mol/mol) mixture of N,N,N′,N′‐tetramethylethylenediamine (TMEDA) and n‐butyllithium. This initiator, which was preformed at 65 °C, facilitated the synthesis of high‐molecular‐weight poly(1,3‐cyclohexadiene) (number‐average molecular weight = 50,000 g/mol) with a narrow molecular weight distribution (weight‐average molecular weight/number‐average molecular weight = 1.12). A plot of the kinetic chain length versus the time indicated that termination was minimized and chain transfer to the monomer was eliminated when a preformed initiator adduct was used. Chain transfer was determined to occur when the initiator was generated in situ. The polymerization was highly sensitive to both the temperature and the choice of tertiary diamine. The use of the bulky tertiary diamines sparteine and dipiperidinoethane resulted in poor polymerization control and reduced polymerization rates (7.0 × 10⁻⁵ s⁻¹) in comparison with TMEDA‐mediated polymerizations (1.5 × 10⁻⁴ s⁻¹). A series of poly(1,3‐cyclohexadiene‐block‐isoprene) diblock copolymers were synthesized to determine the molar crossover efficiency of the polymerization. Polymerizations performed at 25 °C exhibited improved molar crossover efficiencies (93%) versus polymerizations performed at 40 °C (80%). The improved crossover efficiency was attributed to the reduction of termination events at reduced polymerization temperatures. The microstructure of these polymers was determined with ¹H NMR spectroscopy, and the relationship between the molecular weight and glass‐transition temperature at an infinite molecular weight was determined for polymers containing 70% 1,2‐addition (150 °C) and 80% 1,4‐addition (138 °C). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1216–1227, 2005     

Synthesis of macrocycles by the ring‐crossover reaction of a cyclic dithioester

The ring‐crossover polymerization of cyclic dithioester 1 was performed in the presence of quaternary onium salts as catalysts at 70–150 °C for 24 h in NMP. It was found that predictable cyclic polymers with the same repeating structures as 1 were obtained with M_ns in the range between 700 and 3,500, quantitatively. It was observed that intermolecular and intramolecular thioester‐exchange reactions proceeded between cyclic monomer 1 and resulting cyclic polymers under thermodynamic control to give a lower‐molecular‐weight cyclic polymer with a lower polydispersity ratio (M_n = 2,400, M_w/M_n = 1.70). © 2006Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 680–687, 2007