Dimethacrylate monomers

Continuous porous polymer rods have been prepared by an in situ polymerization within the confines of a chromatographic column. The column is filled with glycidyl methacrylate and ethylene dimethacrylate monomer mixtures, cyclo-hexanol and dodecanol diluents, and AIBN initiator. They are then purged with nitrogen, stopped, and closed with a silicon rubber septum. The polymerization is allowed to proceed for 6 hr at 70°C with the column acting as a mold (47). 

Dimethacrylate monomers were polymerized by free radical chain reactions to yield crosslinked networks which have dental applications. These networks may resemble ones formed by stepwise polymerization reactions, in having a microstructure in which crosslinked particles are embedded in a much more lightly crosslinked matrix. Consistently, polydimethacrylates were found to have very low values of Tg by reference to changes in modulus of elasticity determined by dynamic mechanical analysis. 

Coupling of GTP living polymers with halide-terminating agents to form star polymers has been achieved [Hertler, 1996 Webster and Sogah, 1989]. Star polymers are also synthesized by using polyfunctional initiators or by copolymerization with dimethacrylate monomers. 

The majority of resins are composed of two dimethacrylate monomers, 2,2 -bis [4(2-hydroxy-3-methacryloyloxypropyloxy)phenyl] propane (Bis-GMA) and triethylene glycol dimethacrylate (TEGDMA) [22-28]. Typically, TEGDMA or other methacrylate monomers are added as viscosity modifiers to Bis-GMA to make the solution less viscous and more appropriate for clinical use. These diluents also allow for better distribution of the components during manufacture of these composite systems. Another common monomer used to make dental composites, especially those manufactured in Europe, is urethane dimethacrylate [24,29, 30], Ethoxy bisphenol A dimethacrylate is another modification of the Bis-GMA monomer that can be used to make a more hydrophobic polymer that would better withstand the wet oral environment. Other diluents include low viscosity diacrylates and dimethacrylates. Table 1 lists some of these monomers [31-37]. 

Chiral induction was observed in the cyclopolymerization of optically active dimethacrylate monomer 42 [88], Free-radical polymerization of 42 proceeds via a cycliza-tion mechanism, and the resulting polymer can be converted to PMMA. The PMMA exhibits optical activity ([ct]405 -4.3°) and the tacticity of the polymer (mm/mr/rr =12/49 / 39) is different from that of free-radical polymerization products of MMA. Free-radical polymerization of vinyl ethers with a chiral binaphthyl structure also involved chiral induction [91,92]. Optically active PMMA was also synthesized through the polymerization of methacrylic acid complexed with chitosan and conversion of the resulting polymer into methyl ester [93,94]. 

Janssen et al. [144] focused their work on ozonization of polyvinyl lactam, grafting with hydrophilic methacrylic monomers for applications in the field of contact lenses and other products used in the medical domain. The most studied polymer remains the poly-N-vinyl pyrrolidone which is ozonized either in solid state or in aqueous solution. This activation step leads to three hydroperoxides per chain but also to chain scissions. The resulting product is formulated with different mixtures of methacrylic and dimethacrylic monomers to graft them onto activated polymer by UV initiation. Using dimethacrylic monomers lead to perfect cross-linked polymers presenting excellent resistance to solvents. Unfortunately, the mechanisms of action of ozone onto polyvinyl lactams do not seem to have been studied in detail. 

Dimethacrylate monomers and polymethacrylate monomers must be discussed separately from other methacrylates because of their ability to cross-link under normal free-radical polymerization conditions. Even at very low conversion, less than 1%, they produce completely cross-linked polymers that cannot be solvent-swollen and are insoluble. CCT agents reduce molecular weight and thereby move the gelation point to a much higher degree of conversion, though CCT cannot prevent gelation completely.320... 

Hyperbranched polymers were synthesized by direct free-radical polymerization of ethylene glycol dimethacrylate monomer in the presence of a CCT catalyst. The free-radical homopolymerization of divinyl monomers is thought to selectively yield trimer 96,32i 322 though previous work on oligomer distributions would indicate that this is unlikely. 

Most chemically activated denture resins and filling materials employ the BP-DMPT or BP-N,N-bis(2-hydroxyethyl)-2-toluidine (DHEPT) system. Use of DHEPT increases the setting time somewhat. Methacrylate or dimethacrylate monomers using this accelerator have improved storage stability ( ) and thus will not gel prematurely even on exposure to elevated temperatures. 

Their concentration in the cured resin is considerably higher for dimethacrylate monomers than for those with a single methacrylate group in the molecule. Infrared reflectance measurements indicate that the residual methacrylate group in commercial dental composites with dimethacrylate ingredients ranges from 30 to 48 percent. 

Reactivity of the accelerator employed is dependent on the monomer used in the respective formulation. Whereas compositions containing DEAPAA cure bis-phenol A dimethacrylate monomer formulations fastest, those containing p-(dialkylamino)phenethanol result in the more rapid polymerization of methyl methacrylate monomer-polymer slurries (39). Addition of Bronsted acids (40) to similar systems increases the polymerization rate but, as has been discussed above, reduces storage stability. 

The chemical system studied was that of the network forming copol-ymerlzatlon of methyl methacrylate (Aldrich) with small amounts of ethylene glycol dimethacrylate (Monomer Polymer Laboratories). 

Representative shear bond strength ranges for the bonding agents discussed in the foregoing are listed in Table 5, and the structural representations and universally used abbreviations for the principal methacrylate and dimethacrylate monomers are found in Tables 6 and 7. Detailed characterization techniques for methacrylates and derived polymers have been described by Ruyter and 0ysaed [62]. 

Table 7 Structures and Abbreviations of Representative Dimethacrylate Monomers... 

Polymers can also be used to manufacture lenses and screens for projection television systems. These are most conveniently made from PMMA, or combinations of glass and PMMA, to counteract the high thermal expansion of the polymer. The use of ultraviolet curable coatings for lens replication and protective layers is widespread, and these systems are based on diacrylate or dimethacrylate monomers mixed with photoinitiators such as... 

The concept behind this approach is that when equal volumes of pastes are mixed, benzoyl peroxide is introduced to the tertiary amine and free radicals are generated. These free radicals promote polymerization of dimethacrylate monomers and cause the composite to harden. There are still a few commercial composite resins supplied as two-paste systems, but their number is dwindling and this technology is fast becoming obsolete in developed countries [8],... 

Composite resin pastes generally set by free radical polymerization, a process which is a chain reaction that involves opening of the terminal carbon-carbon double bonds in the dimethacrylate monomers [21]. There are three steps in the overall process, beginning with initiation, followed by propagation and termination. 

Dimethacrylate monomers employed in dental resin composites. 

With added fillers - typically 70 wt% for early materials - the dimethacrylate monomers form very viscous pseudoplastic pastes (Watts et al., 1980). The manipulation of these materials was very technique-sensitive. Thorough mixing of the two pastes was essential, yet this was difficult to ensure, given that both pastes were of the same color. 

PEG-10 bisphenol A dimethacrylate monomer, adhesion improving fibers Propylene glycol methacrylate monomer, adhesion improving radiation-curable inks... 

PEG-10 bisphenol A dimethacrylate monomer, hexafluoropropylene epoxide polymers... 

Pig. 5. Dimethacrylate monomers/reactive diluents. EGDMA (R = CH2CH2) DEGDMA (R = CH2CH2OCH2CH2) TEGDMA (R = CH2CH2OCH2CH2OCH2CH2). 

Gerasimov, T.G. and Snavely, D.L., Vibrational overtone spectroscopy of ethylene glycol diacrylate and ethylene glycol dimethacrylate, monomer and polymer, App/. Spectrosc., 56(2), 212-216, 2002. Snavely, D.L. and Angevine, C., Near-infrared spectrum of polybutadiene, J, Polym. ScL Part A, 34, 1669-1673, 1996. 

Gerasimov, T.G and D.L. Suavely, Vibrational Overtone Spectroscopy of Ethylene Glycol Diacrylate and Ethylene Glycol Dimethacrylate, Monomer and Polymer. Appl. Spectrosc., 2002. 56 212-216. 

SR-708 is a metallic dimethacrylate monomer developed to assist adhesion to metals and plastics in peroxide cure applications. SR-708 features hot tear strength. Usage levels of 4-10% are recommended. 

---