FIELD OF THE INVENTION

The present invention refers to a process for production of di-trimethylolpropane oxetane (Di- TMPO), wherein trimethylolpropane oxetane, dimethyl carbonate and a catalyst (base) are reacted in an aqueous solution.

BACKGROUND OF THE INVENTION

In recent years, photoinitiated cationic polymerization, also called cationic UV curing, has become an important technique for the application and cure of coatings and adhesives because of its high throughputs, low energy required, and the lack of need for polluting solvents. Many different types of monomers and oligomers, including vinyl ethers and epoxide compounds, have been used in the photoinitiated cationic polymerization. In particular, the photopolymerization of epoxy compounds gives coatings with high thermal capability, excellent adhesion and good chemical resistance. However, commercially available epoxy monomers undergo photoinitiated cationic polymerization at rather slow rates. Another class of cyclic ethers are oxetanes, that have shown to be more reactive than epoxides in photoinitiated cationic ring-opening polymerizations.

Di-functional oxetanes are particularly reactive and also contribute with a viscosity reduction of the resin. Di-Trimethylolpropane oxetane, or 3,3’-[oxybis(methylene)]bis[3-ethyl]-oxetane, (Di- TMPO) is a difunctional oxetane used in cationic curable resin compositions. This kind of resins is particularly useful for coatings on challenging materials like glass, metal and plastics, in printing inks, optical lenses and for 3D printing applications.

Sasaki and Crivello have disclosed a process for synthesis of di-trimethylolpropane oxetane, in which di-trimethylolpropane was trans-esterified with dimethyl or diethyl carbonate to a carbonate intermediate, which was subsequently pyrolyzed to the desired dioxetane (Sasaki and Crivello (1992) The Synthesis, Characterization, and Photoinitiated Cationic Polymerization of Difunctional Oxetanes, Journal of Macromolecular Science - Pure and Applied Chemistry, 29:10, 915-930). However, the process by Sasaki and Crivello is complicated as a viscous polymer melt is easily formed, and this requires heating before the process can be continued. Another drawback is the high amount of potassium carbonate that is required in the process.

Japanese patent no. 3931448 discloses another process where di-trimethylolpropane oxetane is produced by dichlorination of trimethylolpropane and subsequent cyclization and coupling. This process is however not satisfactory from an environmental point, as it requires handling of halogen compounds and produces waste products that are toxic both to living organisms and to the environment.

The present invention has revealed a process for production of di-trimethylolpropane oxetane that has several benefits compared to the processes previously described. The present invention discloses a straightforward, one-pot process that is halogen-free and more economically beneficial than previously disclosed processes.

DETAILED DESCRIPTION OF THE INVENTION

The process for production of di-trimethylolpropane oxetane according to the present invention is conveniently performed in one reaction vessel, in a stepwise procedure according to the below protocol:

(a) Adding trimethylolpropane oxetane and catalyst into a reactor, applying vacuum pressure, heating the reaction solution to 90-100°C and keeping the vacuum until the water has been completely removed.

(b) Adding dimethyl carbonate under atmospheric pressure and a temperature of 90-100°C and allowing stable reflux conditions to form.

(c) Distilling off the methanol : dimethyl carbonate azeotrope under atmospheric pressure and a temperature of 90-140°C, to drive the transesterification forward.

(d) Distilling off residual methanol : dimethyl carbonate at a reduced pressure of 0-160 mbar and a temperature of 90-120°C.

(e) Optionally adding extra trimethylolpropane-oxetane to the reaction solution.

(f) Heating the reaction mixture to 185-220°C under atmospheric, inert conditions and keeping the temperature at 185-220°C to allow the pyrolyzation of di-trimethylolpropane oxetane carbonate to di- trimethylolpropane oxetane.

(g) Cooling down the reaction mixture

(h) Purifying the di-trimethylolpropane oxetane using a conventional purification method, for example fractional distillation.

In the first step (a), trimethylolpropane oxetane and catalyst (base) are added to the reactor, vacuum is applied and the reaction solution is heated to about 90-100°C. In the scope of the present invention, vacuum is considered to be a pressure of 0-30 mbar. A stable vacuum is kept until the water has been completely removed.

According to one embodiment of the present invention, said catalyst is selected from the group consisting of potassium hydroxide, potassium carbonate and potassium tert-butoxide. According to a preferred embodiment of the present invention, said catalyst is potassium hydroxide.

The catalyst is added in a concentration of 0.5-1.5 % by weight.

Dimethyl carbonate is then added at atmospheric conditions and stable reflux conditions are allowed to form (step (b)).

According to one embodiment of the present invention the molar ratio dimethyl carbonate : trimethylolpropane oxetane is 0.6-0.8 : 1.

As can be seen in Figure 7, a transesterification reaction will now take place between two trimethylolpropane oxetane molecules and one dimethyl carbonate molecule, forming the intermediate product bis-trimethylolpropane carbonate. In this reaction, methanol is formed. Methanol forms an azeotrope with dimethyl carbonate. In the next step (c), the reaction solution is heated to 90-140°C to distill off the methanol : dimethyl carbonate azeotrope. This will drive the transesterification reaction forward. In step (d), a pressure of 0-160 mbar and a temperature of 90- 120°C is applied, to distill off any residual methanol : dimethyl carbonate.

In order for the next reaction step to take place, it is important that there is enough trimethylolpropane oxetane available; so that trimethylolpropane oxetane can react with bis- trimethylolpropane carbonate in a pyrolysis reaction and form di-trimethylolpropane oxetane and trimethylolpropane oxetane (see Figure 1).

Figure 1. In some cases it may be necessary to add additional trimethylolpropane oxetane in the optional step (e) in order for the pyrolysis reaction to get started. Adding additional trimethylolpropane oxetane will speed up the pyrolysis reaction. However, as the reaction becomes faster the risk for formation of biproducts also increases, so the reaction time needs to be balanced against the yield and amount of biproducts formed.

The temperature is then raised to 185-220°C in step (f) and kept there long enough to allow the conversion of di-trimethylolpropane oxetane carbonate to di-trimethylolpropane oxetane in a pyrolysis reaction.

According to a preferred embodiment of the present invention the temperature in step (f) is 190- 210°C.

The reaction mixture is then cooled down in step (g). The reaction mixture should be cooled down to a temperature that is suitable for performing the next step, the purification step (h).

The di-trimethylolpropane oxetane is finally purified using a conventional purification method, such as fractional distillation (step (h)).

If fractional distillation is used as purification method in step (h), this can be either a non-ballasted distillation or a ballasted distillation.

According to one embodiment of the invention the distillation is performed utilizing a ballast and at vacuum at pressure in the range 0 - 40 mBar, preferably 0- 30 mBar. The ballast chosen shall have a boiling point in the range 130 - 170°C at 1.5 mBar.

According to one embodiment of the present invention, the distillation in step (h) is a ballasted distillation wherein trimethylolpropane is added to the reaction residue at a weight ratio of approximately 3:2, residue : trimethylolpropane.

According to one embodiment of the present invention, the solution is neutralized with an acid after the distillation step. This will make it easier to reuse the trimethylolpropane used in the ballasted distillation. The present invention is illustrated in the below Embodiment Example, which is to be construed as merely illustrative and not limiting in any way.

EMBODIMENT EXAMPLE

Synthesis of Di-trimethylolyroyane oxetane

Recipe for the synthesis:

The synthesis was carried out in a 20 L jacketed glass reactor equipped with a pitched blade impeller, Heidolph overhead stirrer and PTFE-baffle for mixing, a 2 L dropping funnel for manual feed of DMC, a Julabo Presto W50 circulator for temperature control, nitrogen feed below surface for inerting and sampling device in the same tube, reflux divider with temperature sensor and total condenser above, Vacuubrand PC 3010 NT Vario membrane pump, Radleys AVA-software and datahubs.

Distillation experiments were performed with a reflux column setup packed with approx. 1,0 m of Sulzer structured mesh packing and a 2 L boiling flask. The setup was controlled via NI CompactRIO, a Lab View-program, and following peripherals were used: a vacuubrand PC 3010 NT Vario membrane pump, a Huber CC-205B circulator for condenser temperature management and an IKA overhead stirrer with anchor impeller.

Analyses for purposes of reaction following were done on a GC-FID with helium as carrier gas, a HP-1 column, 30 m, ID 0,32 mm and film thickness 0,25 pm. Samples were prepared by diluting ~5 pl in 1,5 ml CAN. Analyses were non-calibrated. Trimethylolpropane oxetane and potassium hydroxide were added to the reactor. Vacuum was applied and the temperature was raised to 100°C. Vacuum and temperature were kept for 2,5 hours to allow the water to evaporate. Dimethyl carbonate was added under atmospheric conditions and a stable reflux equilibrium was allowed to form during 5 hours. The methanol : dimethyl carbonate azeotrope was distilled off under atmospheric conditions by gradually raising the temperature to 135°C during 3 hours. To distill off the residual methanol : dimethyl carbonate, a pressure of about 80 mbar was applied and the temperature was set to 100°C and then allowed to raise again to about 110°C. A stable vacuum was allowed to form during 7,5 hours.

The temperature was raised to 210°C during 5 hours, under atmospheric, inert conditions. The pyrolysis reaction was cut off by cooling once the IPC GC-FID analysis showed near-complete conversion after 30 hours.

Di-trimethylolpropane oxetane was purified from the reaction solution by fractional distillation.

Results

The yield of di-trimethylolpropane oxetane, calculated against consumed trimethylolpropane oxetane, was approximately 33% by weight.