Double Ring-opening Polymerization Research Articles

Synthesis of High-Molecular-Weight Poly(ether-alt-ester) by Selective Double Ring-Opening Polymerization of Spiroorthoesters

Synthesis of High-Molecular-Weight Poly(ether-<i>alt</i>-ester) by Selective Double Ring-Opening Polymerization of Spiroorthoesters

Ring-Opening Isomerization Based on the 3-Connecting Node: Formation of a 0-D M2L3 Cage, 1-D Loop-and-Chain, and 2-D (6, 3) Network

Two semirigid ditopic ligands, 1,4-bis(benzimidazol-1-ylmethyl)-2,3,5,6-tetramethylbenzene (L1) and 1,3-bis(benzimidazol-1-ylmethyl)-2,4,6-trimethylbenzene (L2), reacted with Ag+ salts to result in two series of complexes, namely [Ag2(L1)2](CF3SO3)2 (1-R), [Ag2(L1)3](CF3SO3)2 (1-C), {[Ag2(L1)3](CF3SO3)2·CH3CN}n (1-P), and [Ag2(L2)2](ClO4)2·1.5CH3CN (2-R), {[Ag3(L2)2](ClO4)3}n (2-P). All complexes have been structurally characterized by single-crystal X-ray diffraction with the phase purity of bulk samples attested by powder X-ray diffraction (PXRD). Four types of structures are formed: (1) a discrete M2L2 ring with two Ag+ ions and two cis-L ligands comprising a molecular rectangle (1-R and 2-R), (2) a discrete M2L3 cage with two Ag+ ions and three cis-L ligands comprising a trigonal cage (1-C), (3) a one-dimensional [M2L3]n loop-and-chain with 3-connecting Ag+ ions bridged by both cis- and trans-L ligands (1-P), and (4) a two-dimensional [M2L3]n network of (6,3) topology with 3-connecting Ag+ ions bridged by trans-L ligands (2-P). The M2L3 cage 2-C was not obtained as a solid-state complex but observable in solution by ESI mass spectrometry. The complexes 1-C, 1-P and 2-C, 2-P contain comparable 3-connecting M2L3 building blocks, constituting two pairs of ring-opening isomers corresponding to single ring-opening (1-C to 1-P) and double ring-opening (2-C to 2-P) polymerization processes via cis-L to trans-L ligand conformation change, respectively. Investigations on solution behaviors by 1H NMR and ESI-MS and structural conversions monitored by PXRD disclose that the thermodynamically favored M2L2 ring can be converted to a thermodynamically disfavored M2L3 cage in solution through an L addition mechanism, which causes crystallization of isomeric structures of an M2L3 cage or [M2L3]n polymer due to ring-opening isomerization. Formation of an M2L3 cage or [M2L3]n polymer is influenced by kinetic or thermodynamic effects as well as the solubility-product constant (Ksp), implying predictable syntheses by controlling the crystallization conditions.

Flame retardance and shrinkage reduction of polystyrene modified with acrylate-containing phosphorus and crosslinkable spiro-orthoester moieties

Styrene was radically copolymerized with a spiro-orthoester with an acrylate group (SOE-AC), and terpolymerized with SOE-AC and diethyl(methacryloyloxymethyl)phosphonate (DEMMP). This was done for several different feed ratios, to obtain polymers with spiro-orthoester moieties in the side chain. These polymers were then crosslinked with ytterbium triflate, as cationic initiator, via the double ring-opening polymerization. The thermal stability and fire retardant properties of these materials were evaluated by TGA and LOI. The DEMMP-containing polymers give materials which were significantly more flame retardant than the nonphosphorus-containing materials, as indicated by the LOI measurements. The volume changes measured upon crosslinking of the polymers were evaluated by density measurements with a gas pycnometer. In all the cases, expansion was observed. This indicates that SOE-AC is an effective monomer for crosslinkable polymers without volume changes.

A Mechanistic and Kinetic Study of the Photoinitiated Cationic Double Ring-Opening Polymerization of 2-Methylene-7-phenyl-1,4,6,9-tetraoxa-spiro[4.4]nonane

Efficient photopolymerization of a potentially expandable monomer is of practical importance for a variety of polymeric applications demanding dimensional stability, particularly if the polymerization process is well controlled based on a detailed investigation of the reaction. In the current study, photoinitiated polymerization kinetics of 2-methylene-7-phenyl-1,4,6,9-tetraoxaspiro[4.4]nonane (MPN) either with cationic initiation alone or with combined cationic/free radical initiation was examined using real-time FT-IR. A proposed mechanism based on the simplified propagation steps of the cationic double ring-opening polymerization of MPN was confirmed by both computer modeling and NMR spectroscopic analysis of resulting polymers as well as the experimentally observed apparent activation energy. According to this mechanism, alpha-position attack is the predominant mode for the second ring opening during cationic polymerization of MPN. Further, cationic photopolymerization was performed along with a free radical co-initiator or with exposure to moisture to get an improved understanding of the complex cationic double ring-opening polymerization. As a result, free radical-promoted cationic polymerization helps increase the polymerization rate of MPN while even a trace amount of moisture was found to significantly impact both the reaction kinetics and the polymerization course.

Preparation of Asymmetric Spiro Orthocarbonates via Cyclic Thionocarbonates.

The development of monomers that show no shrinkage in volume upon polymerization is highly desirable in the field of materials such as dental fillings, high-strength composites, precision castings, and adhesives. 1 Volume shrinkage during polymerization results from the conversion of van der Waals distances between monomers to covalent bond lengths. Since the van der Waals distance separates monomer molecules approximately three times greater than a covalent bond does, the formation of new covalent bonds upon polymerization is destined to produce the substantial amount of volume contraction. A hopeful approach to prevent this shrinkage could be attained by using monomers that polymerize via the double ring-opening process, which results in two bonds breaking for each new bond formation. Since the double ring-opening polymerization was reported in 1972, 2 various monomers based on spiro orthoester (SOE), 3 bicyclo orthoester (BOE), 4 polycyclic ketal lactone (PKL), 5 cyclic ether, 6 spiroketal, 7 and spiro orthocarbonate (SOC) skeletons 8 have been developed to show the expansion in volume upon polymerization. Among them, spiro orthocarbonates (SOCs) are the most widely investigated monomers because they show the biggest volume expansion. Moreover SOCs containing exo-methylene groups undergo the ring-opening polymerization not only with cationic initiators 9 but also with radical initiators. 10 Asymmetric SOCs possessing one exo-methylene group are more favorable than symmetric SOCs, because the extra exomethylene group remained in the polymer from symmetric monomers affords the crosslinking reaction that causes the volume shrinkage. 11 Recently, N,S- 12 and S,S-analogs 13 of

Preparation of Asymmetric Spiro Orthocarbonates via Cyclic Thionocarbonates

The development of monomers that show no shrinkage in volume upon polymerization is highly desirable in the field of materials such as dental fillings, high-strength composites, precision castings, and adhesives. 1 Volume shrinkage during polymerization results from the conversion of van der Waals distances between monomers to covalent bond lengths. Since the van der Waals distance separates monomer molecules approximately three times greater than a covalent bond does, the formation of new covalent bonds upon polymerization is destined to produce the substantial amount of volume contraction. A hopeful approach to prevent this shrinkage could be attained by using monomers that polymerize via the double ring-opening process, which results in two bonds breaking for each new bond formation. Since the double ring-opening polymerization was reported in 1972, 2 various monomers based on spiro orthoester (SOE), 3 bicyclo orthoester (BOE), 4 polycyclic ketal lactone (PKL), 5 cyclic ether, 6 spiroketal, 7 and spiro orthocarbonate (SOC) skeletons 8 have been developed to show the expansion in volume upon polymerization. Among them, spiro orthocarbonates (SOCs) are the most widely investigated monomers because they show the biggest volume expansion. Moreover SOCs containing exo-methylene groups undergo the ring-opening polymerization not only with cationic initiators 9 but also with radical initiators. 10 Asymmetric SOCs possessing one exo-methylene group are more favorable than symmetric SOCs, because the extra exomethylene group remained in the polymer from symmetric monomers affords the crosslinking reaction that causes the volume shrinkage. 11 Recently, N,S- 12 and S,S-analogs 13 of

Substituent Effect on the Cationic Monomer-Isomerization Polymerization of (Cyclic Imide)-Substituted Oxetanes with Two Different Ring-Opening Routes

This study reports the effect of substituent on the cationic monomer-isomerization ring-opening polymerization of 3-(R 1 -methyl)-substituted 3-R 2 -oxetanes (1), in which R 1 is phthalimide, maleimide, succinimide, or glutarimide and R 2 is ethyl, benzyl, phenyl, or isopropyl. The acid-catalyzed polymerization of 1 gave polyacetal (3) or polyether (4), together with an isomeric bicyclic acetal (2). The isomerization of 1 to 2 took place prior to polymerization. Subsequently the polymerization of 2 occured by either single or double ring opening depending on temperature. The polymerization mechanism is discussed in detail based on the coordination of 1 to Lewis acid and the substituent effect on the polymerization manner. In the double ring-opening polymerization of 2 at 130°c, a carbon-carbon double bond of the lactam ring was indispensable for stabilizing the carboxonium-propagating end. Therefore, 2 carrying a saturated lactam ring did not polymerize in such a manner. Phenyl-substitued oxetane phthalimide was unique in undergoing an unusual cyclodimerization at 130°C, primarily because of the high susceptibility of the neophyl-type carbon skeleton to a cation transfer. On the other hand, most 2 brought about the single ring-opening polymerization below room temperature, regardless of the lactam substituent and the R 2 group. This polymerization was an equilibrium polymerization through a bicyclic oxonium-propragating end, and the thermodynamic parameters of polymerization were determined. Thus, 3 was transformed into 4 in one pot, by a combination of the depolymerization of 3 and the repolymerization of 2 above the ceiling temperature. From the structure analysis of 2 it was inferred that the single ring-opening polymerizability arises from dipole-dipole repulsion between the parallel standing lone pairs of two acetalic oxygen atoms in a nearly symmetric bicycle. There fore, 2 having a somewhat twisted bicyle showed no single ring-opening polymerizability.

Synthesis and Cationic Polymerization of 2-Phenyl-1,6-dioxaspiro[4.6]undecane. A Novel Expandable Monomer Undergoing Cationic Double Ring-Opening Polymerization

Synthesis and Cationic Polymerization of 2-Phenyl-1,6-dioxaspiro[4.6]undecane. A Novel Expandable Monomer Undergoing Cationic Double Ring-Opening Polymerization

Synthesis, cationic polymerization and curing reaction with epoxy resin of 3,9-di(p-methoxybenzyl)-1,5,7,11-tetra-oxaspiro(5,5)undecane

A new spiro ortho carbonate, 3,9-di(p-methoxybenzyl)-1,5,7,11-tetra-oxaspiro(5,5)undecane was prepared by the reaction of 2-methoxybenzyl-1,3-propanediol with di(n-butyl)tin oxide, following with carbon disulfide. Its cationic polymerization was carried out in dichloromethane using BF3-OEt2 as catalyst. The [1H], [13C]NMR and IR data as well as elementary analysis of the polymers obtained indicated that it underwent double ring-opening polymerization. The polymerization mechanism is discussed. The curing reaction of bisphenol A type epoxy resin in the presence of the monomer and a curing agent was investigated. DSC measurements were used to follow the curing process. In the case of boron trifluoride-o-phenylenediamine (BF3-OPDA) as curing agent, two peaks were found on the DSC curves, one of which was attributed to the polymerization of the epoxy group, and the other to the copolymerization of the monomer with the isolated epoxy groups or homopolymerization. However, when BF3-H2NEt was used as curing agent, only one peak was present. IR measurement of the modified epoxy resin with various weight ratios of epoxy resin/monomer was performed in the presence of BF3-H2NEt as curing agent. The results demonstrate that the conversion of epoxy group increases as the content of monomer increases. The curing process and the structure of the epoxy resin network are discussed. © 2000 Society of Chemical Industry

Controlled radical double ring-opening polymerization of 2-methylene-1,4,6-trioxaspiro[4,4]nonane

Controlled radical double ring-opening polymerization of 2-methylene-1,4,6-trioxaspiro[4,4]nonane (MTN) has been achieved with tert-butyl perbenzoate (TBPB) as initiator in the presence of 2,2,6,6-tetramethyl-1-piperidinyloxy free radical (TEMPO) at 125 °C. The molecular weight polydispersity of the polymers is obviously lower than that of polymers obtained by conventional procedures. As the [TEMPO]/[TBPB] molar ratio increased, the polydispersity decreased and a polydisperty as low as 1.2 was obtained at high TEMPO concentration. With the conversion of the monomer increasing, the molecular weight of the polymers turned higher and a linear relationship between the Mw and the monomer conversion was observed. The monomer conversion, however, did not exceed 30 %. © 2000 Society of Chemical Industry

The double ring-opening polymerization of sulfur containing spiro orthocarbonates

The polymerization of new sulfur containing spiro orthocarbonates with the ability to undergo double ring-opening is reported. Various initiators were used in the cationic polymerization study, and the polymer structure determined. The polymerization is proposed to occur via a controlled tandem double ring-opening mechanism.

Monomer-Isomerization Polymerization of 3-Methyl-3-(phthalimidomethyl)oxetane with Two Different Ring-Opening Courses

The cationic polymerization of 3-methyl-3-(phthalimidomethyl)oxetane (1) afforded two kinds of polymers. One was a polyacetal, i.e., poly{oxy(8,9-benzo-4-methyl-7-oxo-2,6-oxazabicycio[4,3]nona-8-ene-1,4-diyl)methylene (3), produced at 50 °C and below, and the other was a polyether, i.e., poly[oxy-(2-methyl-2-phthalimidomethyltrimethylene)] (4), produced at 80 °C and above. This new polymerization with the two ring-opening courses was accompanied by the monomer-isomerization process of 1 to give 5,6-benzo-1-methyl-8,11,3-dioxazatricyclo[5.2.2.0 3,7 ]undeca-5-en-4-on (2). The cyclic acetal 2, therefore, functioned as the real monomer, and either single or double ring-opening polymerization took place to give 3 or 4, respectively, depending on the reaction temperature. The strain of 2 for ring-opening is discussed on the basis of the result of X-ray structure analysis. The single ring-opening process of 2 was an equilibrium polymerization having the standard enthalpy and entropy changes in dichloromethane equal to -15.8 kJ mol -1 and -46.0 J mol -1 K -1 , respectively, and the ceiling temperature (T c ) equal to 70.1 °C for 1 mol L -1 solution. The critical temperature, where the structure of the product polymer changed, was related to a T c calculated for the conditions employed (59. 1 °C for polymerization in 0.83 mol L -1 dichloromethane solution). Therefore, 3 was successfully transformed to 4 with a thermal latent catalyst at a higher temperature than the T c through the ring-closure depolymerization of 3 to 2 followed by the repolymerization of 2 in the double ring-opening manner. When 1 was polymerized in a temperature step-down mode, a block copolymer with the 3-4 sequence was prepared from the single monomer. Moreover, 1 was copolymerized with a nonisomerizable oxetane, accompanying the monomer isomerization of 1.

Synthesis and characterization of side-chain liquid-crystalline poly(ether ester)s havingp-substituted biphenyl mesogenic side groups

Several novel mesogenic spiro-orthoester monomers such as 1,6,10-trioxaspiro[4,5]decanes 4, containing biphenyl mesogens at the C-8 positions of the five- and six-membered spirocyclic ring, through the alkylene spacers of different lengths were prepared by condensation reaction of the corresponding biphenyl mesogenic 1,3-propanediol 3 with 2,2-diethoxytetrahydrofuran, with 50–75% yields. Through cationic double ring-opening polymerization, carried out with boron trifluoride etherate as an initiator (5 mol % vs. monomer) in bulk at 150°C, spiro-orthoester monomers 4 afforded a novel class of side-chain thermotropic LC polymers with a poly(ether ester) as the main chain 8. The liquid-crystalline properties of the spiro-orthoester monomers and the resulting polymers were examined by differential scanning calorimetry and optical polarized microscopy. Biphase separation was observed in the side-chain liquid-crystalline poly(ether ester)s upon annealing in the broad isotropic region. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2439–2455, 1998

Sulfur Analog of Spirocyclic Orthocarbonate Capable of Undergoing Tandem Double Ring-Opening Polymerization: Synthesis, Structure, and Cationic Polymerization of Dibenzo[3,4;10,11]-1,6,8,13-tetrathiaspiro[6.6]tridecane, Property of the Polymer, and Volume Change on Polymerization

The sulfur analog of spiroorthocarbonate (SOC) capable of undergoing tandem double ring-opening polymerization (dibenzo[3,4;10,11]-1,6,8,13-tetrathiaspiro[6.6]tridecane, 4) was synthesized, and its polymerization behavior was studied. Some properties of the polymers obtained and the volume change on polymerization of 4 were also examined. The synthesis of 4 was performed by the acid-catalyzed ester-exchange reaction of tetrakis(methylthio)methane with o-xylenedithiol and was obtained in 98% yield. The structure of 4 was determined by the spectral and elemental analysis data. Cationic polymerization of 4 with latent thermal initiator benzyl tetrahydrothiophenium hexafluoroantimonate in nitrobenzene proceeded efficiently at more than 150 °C to give the corresponding poly(thioethertrithiocarbonate) 5. The polymer structure was determined by the spectral data and further confirmed by the structures of the decomposition products formed by the reductive cleavage of the trithiocarbonate bond of with LiA1H 4 . The mechanism of the polymerization was postulated from the results obtained. Thermal properties of such as T g and T m were examined and compared with those of its oxygen analog (13). The volume change was studied in the polymerizations of4 and its oxygen analog (2), during which 5.2 and 6.7% volume expansions were observed, respectively.

Controlled free radical double ring-opening polymerization of 8,9-benzo-2-methylene-1,4,6-trioxaspiro[4,4]nonane

Abstract The first controlled free radical double ring-opening polymerization of 8,9-benzo-2-methylene-1,4,6-trioxaspiro[4,4]nonane has been achieved with tert-butyl perbenzoate as initiator in the presence of 2,2,6,6-tetramethyl-1-piperidinyloxy free radical (TEMPO) at 125 °C. Polydispersity of the polymer is significantly lower than that by the conventional radical polymerization and decreases as the concentration of TEMPO is increased. The molecular weight increases linearly with the monomer conversion.

Synthesis and Photoinitiated Cationic Polymerization of 2-Methylene-7-phenyl-1,4,6,9-tetraoxaspiro[4.4]nonane

Synthesis of the asymmetrically substituted 2-methylene-7-phenyl-1,4,6,9-tetraoxaspiro[4.4]nonane monomer in four steps and its polymerization are described. The spiromonomer is liquid at room temperature. Photoinitiated cationic polymerization of 2-methylene-7-phenyl-1,4,6,9-tetraoxaspiro[4.4]nonane at ambient temperature in bulk was investigated, using a cationic photoinitiator system based on (η5-2,4-cyclopentadiene-1-yl)[1,2,3,4,5,6-η](1-(methylethyl)benzene)iron(I) hexafluorophosphate (Irgacure 261). Upon irradiation, within 10 min quantitative double ring-opening polymerization to a structurally well-defined poly(alkylene−carbonate−ketone) with molecular weight average Mw of 27.000 (GPC) occurred. No elimination, vinylidene polymerization, or single ring-opening polymerization was detected, as commonly observed in the case of free-radical initiation of similar spiroorthocarbonates, spiroorthoesters, or methylenedioxolanes were detected. Despite quantitative double ring opening, no volume expansion occurred during polymerization. A volume shrinkage of 4.1% was found. General structural prerequisites for expanding and pseudoexpanding monomer systems are discussed.

Anionic ring-opening alternating copolymerization of a bicyclic bis(.gamma.-lactone) with an epoxide: a novel ring-opening polymerization of a monomer containing a .gamma.-lactone structure

Anionic ring-opening polymerization of 2,8-dioxa-1-methylbicyclo[3.3.0]octane-3,7-dione (1b) was carried out. 1b had no homopolymerizability but copolymerized with glycidyl phenyl ether (2) to selectively give the corresponding alternating copolymer. IR, 1 H NMR, and 13 C NMR spectra and products of the alkine hydrolysis of the obtained polymer strongly suggested an alternating copolymer structure consisting of two successive units derived from 1b and 2. The unit from 1b was a linear diester, probably formed by a successive double ring-opening polymerization with isomerization. The 1:1 copolymer composition was not changed by varying the monomer feed ratio in the range between 20:80 and 80:20

Efficient ring-opening polymerization of a .gamma.-butyrolactone derivative. First anionic double ring-opening polymerization

Anionic double ring opening polymerization of 4p,5p-diphenyl-1,3-dihydro-3-oxo-spiro[benzo[c]furane-1:2p-1,3-dioxolane] was found to yield the polyester [COPhCOOCHPhCHPhO] n with molecular weight M n in the 6500-10000 range and narrow molecular weight distribution (M w /M n = 1.13-1.59)

Synthesis and evaluation of new oxaspiro monomers for double ring-opening polymerization.

Polymerization with expansion in volume can be achieved with spiro orthocarbonate monomers through a double ring-opening process wherein two bonds are cleaved for each new bond formed. The resulting expansion can be applied to counter the polymerization shrinkage associated with the conventional methacrylate monomers used in dental composites and thereby provide formulations with drastically reduced degrees of shrinkage. New monomers have been prepared that exhibit enhanced reactivities and ring-opening efficiencies compared with earlier free-radical-polymerizable oxaspiro compounds. In dental composite formulations, the monofunctional oxaspiro monomers provided DTS values equivalent to those of the controls under certain curing conditions; however, only modest reductions in polymerization shrinkage were observed. 2,3-Bis(methylene) spiro orthocarbonate monomers with a conjugated diene structure were also synthesized and evaluated. These novel monomers appear to offer significant potential for future development of free-radical ring-opening polymerization. While visible-light-cured formulations of the bis(methylene) compounds with methacrylate comonomers did not yield acceptable composite materials in this initial attempt, the high reactivity and the ability to form rigid, cross-linked polymers make this type of monomer worthy of continued investigation. These properties may allow the bis(methylene) oxaspiro monomers to be used alone or in concert with other ring-opening monomers for special applications.

Polymerization chemistry of the family of cyclic imino ethers

Characteristics of the polymerization mechanisms of the family of cyclic imino ethers are described. The variety of the mechanism of propagation has been systematized on the basis of the nature of propagating species, i.e., cationic or electrophilic covalent (dipole) species. In the polymerizations of 2-alkyl cyclic imino ethers (5- and 6-membered), propagation mechanism via one of these two different species has been established, which is dependent upon the relative nucleophilic reactivities of the monomer and the counter anion derived from initiator. The polymerization of cyclic pseudoureas having a cyclic amine substituent at 2-position proceeds in two different ways. Ionic propagation leads to the single isomerization/ring-opening polymerization involving only the cyclic imino ether ring. On the other hand, covalent propagation gives rise to the double isomerization ring-opening polymerization involving the two rings of cyclic imino ether and cyclic amine. Polymerization of 5-membered cyclic iminocarbonate with a sulfonate initiator proceeds through the isomerization/ring-opening of 2-oxazoline ring. The same monomer was isomerized to the corresponding cyclic urethane when it was treated with benzyl bromide.