Cationic polymerizations of substituted 2-methylene-1,3-dioxocyclic acetals, 2-methylene-1,3-dithiolane and copolymerization of 2-methylene-1,3-dithiolane with 4-(t-butyl)-2-methylene-1,3-dioxolane1

Carbon black-supported sulfuric acid or BF₃·Et₂O-initiated polymerizations of 2-methylene-4,4,5,5-tetramethyl-1,3-dioxolane (1), 2-methylene-4-phenyl-1,3-dioxolane (2), and 2-methylene-4-isopropyl-5,5-dimethyl-1,3-dioxane (3) were performed. 1,2-Vinyl addition homopolymers of 1–3 were produced using carbon black-supported H₂SO₄ initiation at temperatures from 0°C to 60°C whereas both ring-opened and 1,2-vinyl structural units were present in the polymers using BF₃·Et₂O as an initiator. Cationic polymerizations of 2-methylene-1,3-dithiolane (4) and copolymerization of 4 with 2-methylene-4-(t-butyl)-1,3-dioxolane (5) were initiated with either carbon black-sulfuric acid or BF₃·Et₂O. Insoluble 1,2-vinyl addition homopolymers of 4 were obtained upon initiation with the supported acid or BF₃·Et₂O. A soluble copolymer of 2-methylene-1,3-dithiolane (4) and 4-(t-butyl)-2-methylene-1,3-dioxolane (5) was obtained upon BF₃·Et₂O initiation. This copolymer is composed of three structural units: a ring-opened dithioester unit, a 1,2-vinyl-polymerized 1,3-dithiolane unit, and a 1,2-vinyl polymerized 4-(t-butyl)-1,3-dioxolane unit. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2823–2840, 1999     

Relative thermodynamic stabilities of 2-substituted 4-methylene-1,3-dioxolanes and 4-methyl-1,3-dioxoles

The relative thermodynamic stabilities of 24 pairs of carbon-carbon double-bondexo-endo isomeric 2-substituted 4-methylene-1,3-dioxolanes (a) and 4-methyl-1,3-dioxoles (b) have been determined by base-catalyzed chemical equilibration in DMSO solution. In all cases, theendo isomer (b) is the favored species at thermodynamic equilibrium. A single alkyl substitutent on C-2 gives only a negligible contribution to the relative stability of the isomeric forms, but the presence of two alkyl groups on C-2 increases the relative stability of theendo isomer by 2–3 kL mol^–1. A still higher effect in favor of theendo isomer is produced by introduction of a single alkoxy group on C-2; this effect is further slightly accentuated by 2,2-dialkoxy substitution at C-2. The origin of the favorable effect of 2-alkoxy substitution on the relative stability of theendo isomer is not clear, but it seems to arise from an unexpected stability of theendo isomer rather than from an enhanced destabilization of theexo form.     

Cationic copolymerization of 2-methylene-5,5-dimethyl-1,3-dioxane with 2-methylene-1,3-dioxolane and 2-methylene-1,3-dioxane

Copolymers of the cyclic ketene acetals, 2-methylene-5,5-dimethyl-1,3-dioxane, 3 , (M₁) with 2-methylene-1,3-dioxolane, 4 , (M₂) or 2-methylene-1,3-dioxane, 5 , (M₂), were synthesized by cationic copolymerization. An experimental method was designed to study the reactivity of these very reactive and extremely acid sensitive cyclic ketene acetal monomers. The reactivity ratios, calculated using a computer program based on a nonlinear minimization algorithm, were r₁ = 6.36 and r₂ = 1.25 for the copolymerization of 3 with 4 , and r₁ = 1.56 and r₂ = 1.42 for the copolymerization of 3 with 5. FTIR and ¹H-NMR spectra when combined with the values of r₁ and r₂ showed that these copolymers were formed by a cationic 1,2-polymerization (ring-retained) route. Furthermore the tendency existed to form very short blocks of M₁ or M₂ within the copolymers. Cationic copolymerization of cyclic ketene acetals have the potential to be used for synthesis of novel polymers. © 1996 John Wiley & Sons, Inc.     

BF3·OEt2-initiated polymerization of 2-methylene-1,3-dioxepanes

BF₃·OEt₂-initiated polymerizations of 2-methylene-1,3-dioxepane gave polymers composed of both ring-retained and ring-opened structures. The ring-opening content increased with an increase in polymerization temperature. Poly(4,7-dimethyl-2-methylene-1,3-dioxepane) propagated slower during BF₃·OEt₂-initiated polymerization and had a lower ring-opened content than poly(2-methylene-1,3-dioxepane). The type of acid initiator used also affected the amount of ring opening observed. Stronger acids gave less ring opening. Attempted BF₃·OEt₂-initiated copolymerizations of these seven-membered ring cyclic ketene acetals with isobutyl vinyl ether at room temperature resulted in formation of the two homopolymers. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 873–881, 1998     

Polymerization of 2-(chlorinated methyl)-4-methylene-1,3-dioxolanes

The polymerizations of the novel 2-(chlorinated methyl)-4-methylene-1,3-dioxolanes derived from mono-, di-, and trichloroacetaldehyde were investigated. Poly-2-trichloromethyl-4-methylene-1,3-dioxolane was of particular interest because of its high hydrolytic stability and nonflammability. The monomers could be polymerized with cationic catalysts via the methylene functions without cleavage of the dioxolane rings. This selectivity was due to the acetal-stabilizing negative substituents and to the use of Lewis acid complexes of low reactivity as catalysts. In contrast to previously reported poly-4-methylene-1,3-dioxolanes, the title polymers were high-melting colorless solids of good to excellent fire resistance.     

Cationic ring-opening polymerizations of cyclic ketene acetals initiated by acids at high temperatures

Three unsubstituted cyclic ketene acetals (CKAs), 2-methylene-1,3-dioxolane, 1a , 2-methylene-1,3-dioxane, 2a , and 2-methylene-1,3-dioxepane, 3a , undergo exclusive 1,2-addition polymerization at low temperatures, and only poly(CKAs) are obtained. At higher temperatures, ring-opening polymerization (ROP) can be dominant, and polymers with a mixture of ester units and cyclic ketal units are obtained. When the temperature is raised closer to the ceiling temperature (T_c) of the 1,2-addition propagation reaction, 1,2-addition polymerization becomes reversible and ring-opened units are introduced to the polymer. The ceiling temperature of 1,2-addition polymerization varies with the ring size of the CKAs (lowest for 3a , highest for 2a ). At temperatures below 138°C, 2-methylene-1,3-dioxane, 2a , underwent 1,2-addition polymerization. Insoluble poly(2-methylene-1,3-dioxane) 100% 1,2-addition was obtained. At above 150°C, a soluble polymer was obtained containing a mixture of ring-opened ester units and 1,2-addition cyclic ketal units. 2-Methylene-1,3-dioxolane, 1a , polymerized only by the 1,2-addition route at temperatures below 30°C. At 67–80°C, an insoluble polymer was obtained, which contained mostly 1,2-addition units but small amounts of ester units were detected. At 133°C, a soluble polymer was obtained containing a substantial fraction of ring-opened ester units together with 1,2-addition cyclic ketal units. 2-Methylene-1,3-dioxepane, 3a , underwent partial ROP even at 20°C to give a soluble polymer containing ring-opened ester units and 1,2-addition cyclic ketal units. At −20°C, 3a gave an insoluble polymer with 1,2-addition units exclusively. Several catalysts were able to initiate the ROP of 1a, 2a , and 3a , including RuCl₂(PPh₃)₃, BF₃, TiCl₄, H₂SO₄, H₂SO₄ supported on carbon, (CH₃)₂CHCOOH, and CH₃COOH. The initiation by Lewis acids or protonic acids probably occurs through an initial protonation. The propagation step of the ROP proceeds via an S_N2 mechanism. The chain transfer and termination rates become faster at high temperatures, and this may be the primary reason for the low molecular weights (M_n ≤ 10³) observed for all ring-opening polymers. The effects of temperature, monomer and initiator concentration, water content, and polymerization time on the polymer structure have been investigated during the Ru(PPh₃)₃Cl₂-initiated polymerization of 2a . High monomer concentrations ([M]/[ln]) increase the molecular weight and decreased the amount of ring-opening. Higher initiator concentrations (Ru(PPh₃)₃Cl₂) and longer reaction times increase molecular weight in high temperature reactions. Successful copolymerization of 2a with hexamethylcyclotrisiloxane was initiated by BF₃OEt₂. The copolymer obtained displayed a broad molecular weight distribution; M̄_n = 6,490, M̄_w = 15,100, M̄_z = 44,900. This polymer had about 47 mol % of ( Me₂SiO ) units, 35 mol % of ring-opened units, and 18 mol % 1,2-addition units of 2a . © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3655–3671, 1997     

Preparation and radical ring-opening polymerization of 2-substituted-4-methylene-1,3-dioxolanes

2-Methyl-2-phenyl-4-methylene-1,3-dioxolane ( IIa ), 2-ethyl-2-phenyl-4-methylene-1,3-dioxolane ( IIb ), 2-phenyl-2-(n-propyl)-4-methylene-1,3-dioxolane ( IIc ), 2-phenyl-2-(i-propyl)-4-methylene-1,3-dioxolane ( IId ), 2-(n-heptyl)-2-phenyl-4-methylene-1,3-dioxolane ( IIe ), 2-methyl-2-(2-naphthyl)-4-methylene-1,3-dioxolane ( IIf ), and 2,2-diphenyl-4-methylene-1,3-dioxolane ( IIg ) were prepared and polymerized in the presence of a radical initiator. IIa–IIf were found to undergo vinyl polymerization with ring-opening reaction accompanying the elimination of ketone groups in bulk. IIg was found to undergo the quantitative ring-opening reaction accompanying the elimination of benzophenone in solution to obtain polyketone without any side reaction.     

Novel photoinitiated cationic copolymerizations of 4-methylene-2-phenyl-1,3-dioxolane

Photoinitiated polymerization of 4-methylene-2-phenyl-1,3-dioxolane ( 1 ) was carried out using either tris (4-methylphenyl) sulfonium hexafluoroantimonate or 4-decyloxyphenyl phenyliodonium hexafluoroantimonate as initiators. ¹H-NMR analyses confirmed exclusive ring-opening while DSC and SEC were used to determine the glass transition temperatures (T_gs) and molecular weights, respectively. Photoinitiated cationic copolymerizations of 1 were investigated with several acyclic and cyclic monomers. Copolymerization of 1 with vinyl ethers and a spiroorthoester resulted in copolymers whose thermal properties were dependent on comonomer ratios. Copolymers of 1 and dihydrofuran or dihydropyran afforded soluble polymers with T_gs significantly higher than the homopolymer of 1 . © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2207–2219, 1997     

Investigation of homopolymerization rate of perfluoro-4,5-substituted-2-methylene-1,3-dioxolane derivatives and properties of the polymers

Five perfluoro-4,5-substituted-2-methylene-1,3-dioxolane monomers were synthesized. These monomers were found to readily polymerized by a free radical initiator in bulk and/or in solutions. Homopolymerization rates were determined using in situ ¹⁹F NMR measurements and found to be 0.25 to 1.66 × 10⁻⁴ mol L⁻¹ s⁻¹ in 1,1,2-trichlorotrifluoroethane at 41 °C using the perfluorodibenzoyl peroxide as an initiator. The rates depend on the substituents on the 4 and 5 positions of the dioxolane. The purified polymers were thermally stable (up to 350 °C). They show low refractive indexes (1.33-1.36 at 532 nm). They are transparent from UV to near IR region and have high glass transition temperatures (100-170 °C).     

Cationic 1,2-vinyl addition polymerization of cyclic ketene acetals initiated by conventional acids

Pure 1,2-addition polymers, poly(2-methylene-1,3-dioxolane), 1b , poly(2-methylene-1,3-dioxane), 2b , and poly(2-methylene-5,5-dimethyl-1,3-dioxane), 3b , were prepared using the cationic initiators H₂SO₄, TiCl₄, BF₃, and also Ru(PPh₃)₃Cl₂. Small ester carbonyl bands in the IR spectra of 1b and 2b were observed when the polymerizations were performed at 80°C ( 1b ) and both 67 and 138°C ( 2b ) using Ru(PPh₃)₃Cl₂. The poly(cyclic ketene acetals) were stable if they were not exposed to acid and water. They were quite thermally stable and did not decompose until 290°C ( 1b ), 240°C ( 2b ), and 294°C ( 3b ). Different chemical shifts for axial and equatorial H and CH₃ on the ketal rings were found in the ¹H NMR spectrum of 3b at room temperature. High molecular weight 3b (M̄_n = 8.68 × 10⁴, M̄_w = 1.31 × 10⁵, M̄_z = 1.57 × 10⁵) was obtained upon cationic initiation by H₂SO₄. Poly(2-methylene-1,3-dioxane), 2b , underwent partial hydrolysis when Ru(PPh₃)₃Cl₂ and water were present in the polymer. The hydrolyzed products were 1,3-propanediol and a polymer containing both poly(2-methylene-1,3-dioxane) and polyketene units. The percentages of these two units in the hydrolyzed polymer were about 32% polyketene and 68% poly(2-methylene-1,3-dioxane). No crosslinked or aromatic structures were observed in the hydrolyzed products. The molecular weight of hydrolyzed polymer was M̄_n = 5740, M̄_w = 7260, and M̄_z = 9060. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3707–3716, 1997     

Cationic copolymerization of cyclic ketene acetals: The effect of substituents on reactivity

Cationic copolymerizations of 4-methyl-2-methylene-1,3-dioxane, 2 (M₁), with 2-methylene-1,3-dioxane, 1 (M₂); of 4,4,6-trimethyl-2-methylene-1,3-dioxane, 3 (M₁), with 2-methylene-1,3-dioxane, 1 (M₂); of 4-methyl-2-methylene-1,3-dioxolane, 5 (M₁), with 2-methylene-1,3-dioxolane, 4 (M₂); and of 4,5-dimethyl-2-methylene-1,3-dioxolane, 6 (M₁), with 2-methylene-1,3-dioxolane, 4 (M₂) were conducted. The reactivity ratios for these four types of copolymerizations were r₁ = 1.73 and r₂ = 0.846; r₁ = 2.26 and r₂ = 0.310; r₁ = 1.28 and r₂ = 0.825; r₁ = 2.23 and r₂ = 0.515, respectively. The relative reactivities of these monomers towards cationic polymerization are: 3 > 2 > 1; and 6 > 5 > 4. With both five- and six-membered ring cyclic ketene acetals, the reactivity increased with increasing methyl substitution on the ring. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 861–871, 1998     

Cationic ring-opening polymerization of 2-isopropenyl-4-methylene-1,3-dioxolane

Preparation and cationic ring-opening polymerization of 2-isopropenyl-4-methylene-1,3-dioxolane ( VI ) was performed. Unsaturated cyclic acetal VI was prepared by dehydrochlorination of 2-isopropenyl-4-chloromethyl-1,3-dioxolane, which was easily obtained from methacrolein and epichlorohydrin, with sodium methoxide at ambient temperature. The cationic polymerization of VI with BF₃OEt₂ or CF₃SO₃H at ?78°C afforded only crosslinked polymers, whereas the polymerization by CH₃SO₃H gave soluble poly(keto-ether) which consisted of units VII containing an isopropenyl group in the side chain and units VIII containing a carbon-carbon double bond in the main chain. The reaction of VI with ethanethiol in the presence of protic acid was also carried out as a model reaction of the polymerization. The reaction initiated by the addition of proton to the 4-methylene group of VI , and quantitative ring-opening isomerization followed by the addition of ethanethiol afforded acyclic ketone IX and X . On the basis of the model reaction, the polymerization mechanism is also discussed. © 1993 John Wiley & Sons, Inc.     

New results of the free radical ring-opening polymerization

The reaction of 5-ring ketene-O, N-acetals with peroxides was investigated. It was shown that benzoyl peroxide adds to monomers 5a and 5b by ring opening, giving the corresponding linear diester amides 6a and 6b , respectively. The ketene-O,N-acetal 5c adds benzoyl peroxide, without ring opening, by addition to the exomethylene group, giving the cyclic-O,N-acetal diester 6c . With phthaloyl peroxide cyclic esteramides 7 and oligomeric products are formed. The chemical structures of the addition products were confirmed by NMR spectra and elemental analysis. © 1994 John Wiley & Sons, Inc.     

Ring opening during the cationic polymerization of 2-methylene-1,3-dioxepane: Cyclic ketene acetal initiation with sulfuric acid supported on carbon

The stable cyclic ketene acetal, 2-methylene-1,3-dioxepane, 7, has been polymerized cationically in pentane, CH₂Cl₂ and THF at 25°C to form a polymer which is composed of both ring-opened (40–50%) and ring-retained (50–60%) structures. Initiation was catalyzed by using H₂SO₄-supported on activated carbon black. This unique outcome differs significantly from the cationic polymerization of several other five- and six-membered ring cyclic ketene acetals which gave 100% 1,2-vinylpolymerization under these conditions. As the polymerization temperature increased in cationic polymerization of 7 the ring-opened content increased and the molecular weight of the polymers decreased in such solvents as cyclohexane, 1,2-dichloroethane, dimethoxyethane, and bis-(2-methoxyethyl) ether. The mechanism of this polymerization is discussed. This research also illustrated the ability to initiate the cationic polymerization of cyclic ketene acetals by acidified carbon black while avoiding subsequent polymer decomposition. © 1997 John Wiley & Sons, Inc.     

Study on copolymerization behavior of 2-substituted 4-methylene-1,3-dioxolane with maleic anhydride and acrylonitrile

Copolymerizations of 4-methylene-2-styryl-1,3-dioxolane ( 1 ) and 4-methylene-2-methyl-2-styryl-1,3-dioxolane ( 2 ) with electron-deficient monomers, such as maleic anhydride (MA) and acrylonitrile (AN) were investigated. Only homopolymer of 1 was obtained from the copolymerization of 1 with MA in the presence or absence of AIBN. The copolymerization of 1 and AN with AIBN as initiator gave a copolymer consisting of three kinds of repeating units. Reaction of 2 with MA gave a crystalline product with and without AIBN present. A nine-membered ring structure is proposed for this product based on its IR, UV, proton and ¹³C-NMR spectra, as well as elemental analysis. No polymer was obtained from the copolymerization of 2 and AN with or without AIBN initiator. Based on the structures of the products obtained from the copolymerization, a number of polymerization mechanisms are proposed. © 1996 John Wiley & Sons, Inc.     

Free Radical Ring-Opening Polymerization of 4-n-Hexyl- and 4-n-Decyl-2-methylene-1,3-dioxolanes

Two alkyl-substituted cyclic ketene acetals, 4-n-hexyl-2-methylene-1,3-dioxolane (4) and 4-n-decyl-2-methylene-1,3-dioxolane (6), were shown to undergo free radical ring-opening polymerization with the introduction of an ester group into the backbone of an addition polymer. The spontaneous polymerization of 4 (presumable by an ionic mechanism) produced a polymer containing no ring-opened units; furthermore 4 and 6 could be stabilized with respect to spontaneous polymerization by the addition of small amounts of pyridine. On the other hand, the polymerization of 4 in a 50% (by weight) benzene solution at 110°C with di-tertbutyl peroxide as the catalyst gave quantitative ring opening to give a polyester containing both possible isomeric ring-opened units. Bulk polymerization of 4 at 60°C at 53% conversion gave 50% ring opening which was divided 31% to 19% between cleavage to give the intermediate secondary free radical and the intermediate primary radical. Copolymerization of 4 with equimolar quantities of styrene at 110°C gave at 56% conversion a copolymer consisting of 67% styrene units, 22% ester-containing units resulting from cleavage to form a secondary radical, 7% of the isomeric ester-containing units, and 4% nonring-opened units. Polymerization studies with monomer 6 gave results very similar to those obtained with 4.     

Synthesis of poly-ϵ-caprolactone via a free radical mechanism. Free radical ring-opening polymerization of 2-methylene-1,3-dioxepane

2-Methylene-1,3-dioxepane 6 polymerized with a quantitative ring opening to form poly-?-caprolactone via a free radical mechanism. On the other hand, 2-methylene-1,3-dioxolane (ethylene ketene acetal) 4 and 2-methylene-1,3-dioxane 5, under the same conditions, generated polymers with mixed ring-opened and nonring-opened structures. In copolymerization monomer 6 also showed a high tendency toward ring opening by which the ester functionality could be conveniently introduced into the backbone of the addition polymers.     

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     

Synthesis of novel 2-trifluoromethyl-1-methylene-3-phenylindene derivatives via carbocyclization reaction of 2-trifluoromethyl-1,1-diphenyl-1,3-enynes

Trifluoromethylated enynyl sulfones 3 were reacted with PhLi at −78 °C for 2–4 h to give 2-trifluoromethyl-1,1-diphenyl-1,3-enynes 6 in good yields. Carbocyclization reaction of 6 with 10 mol% of Pd(OAc)₂ in cosolvent of CF₃COOH and MC (4:1) at room temperature for 1 h afforded 2-trifluoromethyl-1-methylene-3-phenylindene derivatives 7 in good yields.     

Synthesis and polymerization of 2-butyl-7-methylene-1,4,6-trioxaspiro(4,4)nonane

2-Butyl-7-methylene-1,4,6-trioxaspiro(4,4)nonane ( 7 ) was prepared by the reaction of 2-(bromomethyl)-5-oxo-tetrahydrofuran with 1,2-epoxyhexane, followed by dehydrobromination. Compound 7 could be polymerized by free radical initiators to give a viscous polymer. The IR and NMR spectra of the polymers indicated that the polymer structure contained ester and ketone units in the backbone, and a cyclic acetal side chain. Compound 7 readily copolymerized with acrylonitrile in the presence and absence of radical initiators, but did not copolymerize well with styrene. Ultraviolet spectra suggest that the spontaneous polymerization proceeds via a chargetransfer complex between 7 as an electron donor and AN as an electron acceptor.