Joachim E. Klee

Monomers for low shrinking composites, 2. Synthesis of branched methacrylates and their application in dental composites

A novel family of branched methacrylates was prepared by Michael addition reaction of various di- and polyamines with ethylene glycol acrylate methacrylate. Molecular masses of the resulting branched methacrylates were varied between 900 to 1 800 g/mol. Such branched methacrylates exhibit very low viscosity (50 to 500 mPa.s) and a low volume shrinkage (ΔV = 1.5 to 6.0%) during photoinitiated cure. Dental composites with volume shrinkage of 1.0% were based upon blends of branched methacrylates and Bis-GMA. In contrast to conventional reactive diluents, branched methacrylates give simultaneous improvement of low volume shrinkage and low viscosity.

Branched macromonomers and their application in dental composites. Monomers for low‐shrinking composites, 3

Branched macromonomers were synthesized by esterification of epoxy-carboxylic acid macromonomers with long aliphatic monocarboxylic acids. The molar masses of the resulting branched epoxy-carboxylic acid macromonomers varied between 1200 and 1700 g mol 1 . Such branched macromonomers composed of aliphatic dicarboxylic acids in the main chain exhibit a very low viscosity (20 to 45 Pa s) and a relatively low volumetric shrinkage (AV = 2.3 to 3.4%) during photoinitiated cure. Dental composites with a volumetric shrinkage of 1.0% were based on the blends of these branched macromonomers. Due to the flexible structure of the macromonomers a relatively low mechanical stiffness of the composites was found.

Acrylate‐Terminated Macromonomers by Michael Addition

A series of diacrylate macromonomers bearing alkoxysilyl units was prepared by convenient Michael addition of aminopropyl methyl diethoxysilane to 1,2-ethylene glycol diacrylate (EGDA), p-phenylene di-acrylate (PDA) and 1,4-cyclohexanediol diacrylate (CHDA). The resulting macromonomers have been characterized in detail by NMR spectroscopy, vapor pressure osmometry (VPO) measurements and fast-atom bombardment mass spectroscopy (FAB-MS). Average molecular weights Mn ranged between 530 and 1300 g . mol -1 (VPO). FAB-MS and size exclusion chromatography (SEC) showed the formation of a homologous macromonomer series. Viscosities of the liquid monomers are relatively low, ranging from 0.082 to 8.30 Pa . s. This renders these compounds interesting as reactive diluents in dental composite formulations. Upon polymerization of the macromonomers, low volumetric shrinkage occured, which was in the range of ΔV=2.4 and 3.9 vol-% at high conversion. Crosslinking was monitored by photo-differential scanning calorimetry (photo-DSC). Furthermore, composites were prepared by mixing 2,2-bis-[p-(2-hydroxy-3-methacryloxypropoxy)-phenyl]propane (Bis-GMA) with the new macromonomers, initiator and glass filler. The composites showed compressive strengths up to 244 MPa, flexural strengths from 22 to 42 MPa and Youngs moduli between 870 and 3070 MPa. The composite materials exhibited low volume shrinkage of commercially available composites.

High-molecular weight diepoxide-dicarboxylic acid addition polymers

SummaryThe addition polymerization of 2,2-bis[4-(2,3-epoxypropoxy)phenyl] propane (DGEBA) and dicarboxylic acid results in high molecular weight addition polymers (Mn 8000–13000). Their molecular weight distribution is rather broad (Mw/Mn=11,6) due to side reactions such as transesterification and formation of ether linkages. Due to the incorporation of the aliphatic dicarboxylic acid moieties in the polymer backbone, the addition polymers show relatively low glass transition temperatures ranging from 26 to 45 °C.

Uncrosslinked epoxide-amine addition polymers, 45. Linear addition polymerization of 2,2-bis[4-(2,3-epoxypropoxy)-phenyl]propane and arylamines in highly concentrated solutions†

In highly concentrated solutions (40 to 70 wt.-%) such as in chlorobenzene (CB) or 2-methoxyethanol (ME) the addition polymerization of 2.2-bis[4-(2,3-epoxypropoxy)phenyl]propan (DGEBA) and disecondary diamines leads to high molecular weight linear addition polymers. The broad molecular weight distribution (M w /M n = 4 to 17) is caused by the formation of cyclic oligomers. After precipitation in acetone, M w /M n values of 2.8 to 3.4 were obtained which indicate a regular linear step-growth polymerization. Differential scanning calorimetry (DSC) investigations show that CB retards the addition polymerization, whereas ME exhibits an acceleration of the polymerization. The suggested kinetic model describes the reaction behavior over the whole range of polymerization by one parameter set only. In order to find the optimum parameters, the set of differential equations was solved numerically by multivariate non-linear regression. An excellent agreement between calculated and experimental curves was found.

Synthesis and investigation of α,ω-methacryloyl terminated epoxide-amine macromonomers

Summaryα,ω-methacryloyl-poly (epoxide-amine)-macromonomers were synthesized by reaction of bisphenol-A diglycidylether DGEBA and methacrylic acid followed by addition polymerization of unreacted expoxide groups with primary monoamines or disecondary diamines, respectively. The resultant macromonomers having Mn (vpo)-values between 530 and 2000 g/mol were analysed by IR-, 1H-NMR- and 13C-NMR-spectroscopy. HPLC and GPC analysis were used to determine the distribution of oligomers. The macromonomers are glassy or viscous liquids with Tg between 0 and 50 °C depending on the nature of the amine and polymerization degree.

Laser photolysis of polymer EDA complexes including 4,4′-diaminodiphenylmethane derivatives

Transient optical absorption spectra were obtained and photochemical transformations of aromatic amine derivatives (Am) used as electron donors in polymer EDA complexes were studied. It was shown that successive electron — proton — electron processes in (Am.CBr4) complexes are strongly influenced by whether the Am is monomer or a molecular fragment chemically incorporated into a macromolecular chain.

Development of Novel Photoinitiators as Substitutes of Camphorquinone for the LED Induced Polymerization of Methacrylates: A Bis‐Silyl Ketone

A new photoinitiator based on a bis-silylketone (BSK) structure is proposed as a novel compound leading to highly efficient initiating silyl radicals for the polymerization of methacrylates (e.g., a bisphenol A-glycidyl methacrylate/triethyleneglycol dimethacrylate blend (70%/30% w/w)) upon exposure to a blue light emitting diode and a green laser diode. The polymerization profiles are recorded by real time Fourier transform IR (FTIR) spectroscopy. Absorption, fluorescence, electron spin resonance (ESR), and steady state experiments are used to investigate the involved chemical mechanisms. Molecular orbital calculations are also carried out. Remarkably, BSK efficiently works in the presence of an iodonium salt. The overall mechanism for the initiation step is clarified. This novel class of silyl radical generating photoinitiators is really promising for the photopolymerization of methacrylates, e.g., in dental materials.

A novel photoinitiating system producing germyl radicals for the polymerization of representative methacrylate resins: Camphorquinone/R3GeH/iodonium salt

OBJECTIVES The aim of our study is to find an amine free photoinitiating system (PIS) for the polymerization of representative dental methacrylate resins. A photoinitiating system (PIS) based on camphorquinone (CQ)/triphenylgermanium hydride/diphenyl iodonium hexafluorophosphate is proposed and compared to the conventional CQ/amine couple. The polymerization monitoring of thin (∼20μm) and thick (1.4mm) samples of a bisphenol A-glycidyl methacrylate (Bis-GMA)/triethyleneglycol dimethacrylate (TEGDMA) blend (70%/30% w/w) and of a urethane dimethacrylate (UDMA) upon exposure to a commercial blue LED centered at 477nm under air or in laminate is described. Finally, the impact of the photoinitiating system composition on the final polymer color is evaluated in detail. METHODS FTIR and DSC experiments are used to record the photopolymerization profiles. ESR spectrometry and steady state photolysis are used to detect the produced radicals. Color measurements are carried out to determine the key parameters in the bleaching of the different dental formulations. RESULTS The efficiency of the newly proposed PISs for the photopolymerization of BisGMA/TEGDMA and UDMA for thin (20μm) or for thick (1.4mm) samples upon exposure to a dental blue LED under air is excellent. It is noticeably higher than that of the CQ/amine reference couple. Excellent bleaching properties are also observed under irradiation in presence of the new PISs. A good correlation is found between the sample bleaching and the amount of Ph3GeH in the formulation. The excited state processes could be established. The overall chemical mechanisms for the initiation step were also clarified.

SYNTHESIS OF DYE CONTAINING EPOXIDE-AMINE ADDITION POLYMERS AND INVESTIGATION OF THEIR THERMAL AND OPTICAL-PROPERTIES .39. UNCROSS LINKED EPOXIDE-AMINE ADDITION POLYMERS

SummaryN-alkylated epoxide-amine addition polymers as well as epoxide-amine addition polymers containing carboxylate groups are used for an ion exchange by various anionic dyes such as diamine green, crocein or cationic dyes, respectively like rodamine and malachite green. The polymer-dye salts 1 and 2 are soluble in DMF, DMF/2-methoxy ethanol and other solvents and can be cast into transparent coloured films from these solutions. The glass transition temperatures were found between 90 and 165°C (1) and between 85 and 112°C (2), respectively. The thermal decomposition of polymers 1 and 2 takes place at 300–370°C. Furthermore, non-linear optical properties (third harmonic generation) of the polymer-dye salts 1 and 2 were expected and calculated to be 10-12–10-13 esu.