Polymerization of Cyclic Monomers. 5. Synthesis and radical polymerization of 4-methylene-3,5-dioxabicyclo[5.1.0]octane

Abstract

Cyclic monomers, such as spiro orthocarbonates or spiro orthoesters, can show a near zero volume shrinkage or sometimes expansion in volume during their ring-opening polymerization. Therefore, they are of interest in the fields of precision casting, dental fillings, or adhesives [2]. 2-Methylene-1,3-dioxepane derivatives are known as monomers which polymerize radically with almost quantitative ring-opening in the presence of di-tert-butyl peroxide (DTBP) at 120 "C and with radical photoinitiators at room temperature [3-51, respectively. In this context, we showed [5] that bicyclic 2-methylene-1,3-dioxepanes primarily undergo a radical ring-opening polymerization, while their cationic photopolymerization is mainly a vinyl polymerization. Previously, we reported about the synthesis and polymerization of unsaturated spiro orthocarbonates [6] and vinylcyclopropanes [ 1,7].The ring-opening behaviour of cyclic monomers can be influenced by fusing them with a strained ring. Therefore, the present paper describes the synthesis of 4-methylene-3,5dioxabicyclo[5.1 .O]octane (2) and the radical and cationic polymerization of 2 and of 2-methylene-1,3-dioxepane (MDE) as a model compound.The monomer 2 was prepared by dehydrobromination of bromomethyl dioxepane 1 with potassium tert-butoxide with 63% yield. Compound 1 can be obtained by acetalization of (2)-1,2-bis(hydroxymethyl)cyclopropane with bromoacetaldehyde diethyl acetal in the presence of p-toluenesulfonic acid (PTSA) with 77% yield. The synthesized bicyclic monomer2 is a colourless liquid compound which is only stable under exclusion of moisture or acid compounds.The characterization of the new bicyclic monomer 2 was carried out by 'H NMR, I3C NMR, IR spectroscopy and elemental analyses. The formation of the cyclopropane ring is supported by the presence of the peaks assignable to CH2 or CH of the cyclopropane ring at 6= 0.67-1.47 ppm in the lH NMR spectrum. The chemical shift of the singulett of the methylene protons is at 3.51 ppm, whereas the signal arising from the carbon atom 4 is at about 6 = 165.27 ppm.The radical polymerization of 2 and MDE was carried out in the presence of DtBPO at 120 "C. In case of MDE, highly viscous polymerizates with number-average molecular weights of 7700 or 9150 g/mol were obtained. Contrary to this, the radical bulk polymerization of 2 yielded crosslinked polymers (Tab. 1). Tab. 1 Bulk polymerization of 4-Methylen-3S-dioxabicyclo[5.l.0]octane (2) and MDE in the presence of DtB-PO at 120 "C, polymerization time 16 h Monomer [DtBPO] Conversion Mn (mol-%) (%) (dmol) MDE 2.5 83.9 7700 MDE 1 .0 76.2 9150 2 2.5 54.0 insoluble product 2 1 .0 42.3 insoluble productThe spectroscopic characterization of the obtained polymers clearly shows that during the radical polymerization of the bicyclic monomers 2 and of MDE, respectively, opening of the ketene acetal ring has taken place. For example, the IR spectra of both poly[2] and poly [MDE] show a strong C=O absorption at 1734 cm-'. Moreover, the 13C NMR specta of poly[MDE] also confirms the poly...

Radical Ring-Opening Polymerization: Scope, Limitations, and Application to (Bio)Degradable Materials

“…IR spectroscopy proved the complete ring-opening of the dioxepane moiety. According to Zeuner and co-workers 199 the cross-linking reactions explaining…”

“…IR spectroscopy proved the complete ring-opening of the dioxepane moiety. According to Zeuner and co-workers, 199 the crosslinking reactions explaining the insoluble character of the polymer might imply hydrogen abstraction from tertiary C−H of both the monomer and the polymer (after ring-opening). In addition, after opening of the main ring, the cyclopropane probably underwent a β-scission reaction giving rise to an easily accessible CC double bond.…”

New calix[4]arenedimethacrylate derivatives for dental composites

“…Calixarenes are cyclic oligomers of para ‐ tert ‐butylphenol and formaldehyde 8, 9. Calixarenemethacrylates are known in polymer chemistry,10 and some of them have been employed and patent‐registered in dental materials11–13 leading to a lower polymerization shrinkage in comparison to conventional linear dimethacrylates 14–18. However, the solubility of simple calixarenemethacrylates in monomer matrices is a problem.…”

Photoinitiated Cationic Polymerization of Substituted Vinylcyclopropanes

“…In some cases authors tried to polymerize monomers with two rings combined in a bicyclic structure which both should be opened during the polymerization (see ref. [1][2][3][4][5] ). Because of the ring strain a cyclopropane structure should be easily opened and, thus, also investigations were made on vinyl substituted cyclopropanes (see ref.…”

“…Therefore, it was of interest to investigate the cationic photopolymerization of a monomer which forms a cation without oxygen in the neighbourhood of the positive charge. We synthesized 1-cyclopropyl-l-phenyl-ethylene l, l-cyclopropyl-l-(p-methoxyphenyl)ethylene 2 and l-cyclopropyll-(p-fluorophenyl)ethylene 3 and polymerized the monomers in the presence of (Z 5 -2,4-cyclopentadiene-lyl) [1,2,3,4,5,6-Z](l-(methylethyl)benzene)iron(I) hexafluorophosphate (Irgacure 261, I-1) and ditolyliodonium hexafluorophosphate (I-2) as cationic photoinitiators. For comparison also a conventional cationic polymerization using BF 3 OEt 2 as initiator has been carried out ( Figure 2).…”