TECHNICAL FIELD OF THE INVENTION

The present invention relates to a process of in-situ synthesizing polymethacrylimide (PMI) foam and its strengthened composite derivatives thereof with nanosized materials such as particles, and the polymer foam synthesized in this manner.

STATE OF THE ART

Polymer foams and composite materials thereof have various areas of usage in applications such as thermal insulation, packaging and mechanical support. However, conventional foams and composites thereof have limited mechanical, thermal, and electrical properties.

PMI foams, which are also known as structural foams with high performance and PMI foams strengthened with additives as nanosized materials have the application area in advanced structures such as sandwich composites. These lightweight PMI-cored sandwich composites are the structures having high mechanical properties that can gain multifunctionality such as electrical conductivity and high thermal resistance with nanomaterial additives. For advanced applications, multi-functional, high performing structural foams have various applications. Moreover, PMI foam has uniform cell size distribution and low density providing long life, strength, and thermal stability. Sandwich composites have areas of use in aeronautics, defense, aerospace applications, structural materials, and/or thermal insulation applications for transportation vehicles.

The production of PMI foams without additives are carried out with synthesis steps that requires long time. Multi-step synthesizing and foaming allow for obtaining products that feature cellular distribution characteristics with regular and uniform sizes as well as thermal endurance. Mechanical properties of PMI foams are developed with different additives such as flame retardant, antistatic, antioxidant, lubricant, paint, light stabilizer, etc.

EP356714 Document discloses a method of preparing PMI rigid foam containing 0.1 - 10% by weight of electrically conductive particles, in particular conductive carbon. Accordingly, a methacrylic acid-methacrylonitrile copolymer prepared by heating that contains accelerator and conductive particles is suitable for use as an interlayer material in lamination for aircraft production and similar applications for fast-flowing gases. Cross-linked polymer that forms foam, in particular PMI foam, comprises 30- 70% (meth)acrylic acid by weight, 30-60% methacrylonitrile by weight, methacrylic diester of a diol with an 0.01 -15 molar weight of at least 250 g/mol, 0.01 -15% foaming agent by weight, and 0.01 -2% polymerization initiator by weight as the weight ratio of the components.

BRIEF DESCRIPTION OF THE INVENTION

The object of the present invention is to shorten the synthesizing time in the polymethacrylimide foam production process.

The present invention, for the purpose of achieving the aforementioned object, is a PMI foam synthesis process that comprises the following steps; uniformly mixing a reactant that contains 30-80% methacrylic acid by weight, and 20-70% acrylonitrile by weight, and 1 -3% acrylamide by weight, or a mixture of derivatives thereof, as a weight ratio of the components, and the components that contain a polymerization initiator, a nucleating agent and a foaming agent in a mixing vessel such that it forms a reaction mixture; obtaining a crosslinked foamable pre-polymerization product by means of exposing the reaction mixture to light arriving from a UV source, and obtaining a copolymer PMI block by means of performing the polymerization reaction of the prepolymerization product in a container at 20-80°C, and subsequently, obtaining foam with a temperature of 100-260 °C. Performing pre-polymerization with a UV light allows for a well-controlled process. Additionally, the pre-polymerization was completed in a surprisingly short time compared to the current situation. The total synthesis process, which takes long hours to obtain commonly utilized commercial products of polymer foam, has been reduced to 12-48 hours by means of reducing the step of pre- polymerization to 1 -5 minutes. In addition, the energy consumption was seriously reduced compared to the thermal initiators. In a possible embodiment, it is possible to add 0.5-30% conventional additives to the reaction mixture. In a preferred embodiment, the container is a glass mold, and the pre-polymerization product is poured into the glass mold, and the polymerization reaction is carried out in a bath that contains liquid (water, oil, etc.), or in a furnace.

A preferred embodiment of the present invention comprises the process step of adjusting the pre-polymerization time for a maximum of 10 minutes, preferably 1 -5 minutes. After this period, it provides cell structure formation under 700 pm, and allows for obtaining a final product with improved mechanical properties and electrical conductivity.

In a preferred embodiment of the present invention, the polymerization initiator comprises 0,01 -2% azobisisobutyronitrile (AIBN), or benzoyl peroxide (BPO) by weight. Preferably, the foaming agent comprises at a rate between 1 -5% 1 -amyl alcohol or butanol by weight.

A preferred embodiment of the present invention comprises the process step of adding nanosized materials that are selected from the group including (carbon nanotube) CNT, graphene, (nanosilica) NS, (nanorubber) NR, (boron nitride nanotube) BNNT to the pre-polymerization product. These additions improve the values of thermal insulation and electrical conductivity by means of improving the mechanical properties of the polymer foam product.

A preferred embodiment of the present invention comprises the process step of adding at a rate between 0.1 -3% distilled water by weight to the reaction product.

In a preferred embodiment of the present invention, the mold, in which the pre- polymerization product is molded is a closed glass mold. Thus, polymer is synthesized in-situ. Preferably, the glass mold is kept in a water bath at a constant temperature of 20-80°C for at least 12-48 hours. This duration is sufficient to complete the polymerization. In a preferred embodiment of the present invention, the process step of foaming is adjusted as 1 -8 hours. Said process may be carried out in a furnace by using a closed or open mold, or in a device that can provide homogeneous temperature distribution.

A preferred embodiment of the present invention is a polymer foam obtained by means of the process steps of the PMI foam production method described above. In a preferred embodiment of the present invention, the polymer foam weight is adjusted between 40-140 kg/m ³ . This low density allows for achieving a more uniform pore size distribution.

In a preferred embodiment of the present invention, the polymer foam pore size is adjusted between 50-700 pm. Preferably, the polymer foam compressive strength was adjusted between 0.7-8 MPa varied with the density, and the electrical conductivity thereof was adjusted greater than 10’ ³ S/cm if it is functionalized with conductive additives.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 illustrates the schematic view of a representative embodiment of the PMI production method according to present invention.

Figure 2 illustrates the flow diagram of PMI and CNT/PMI foam synthesizing method.

Figure 3 illustrates the graph that indicates the specific compressive strength and cell diameter values of pure PMI foams that are obtained with different component (methacrylic acid, acrylonitrile, and acrylamide) percentages of a, b, and c samples.

Figure 4 illustrates the optical and scanning electron microscope (SEM) images of pure PMI foams that are obtained with different component (methacrylic acid, acrylonitrile and acrylamide) percentages of a, b, and c samples.

Figure 5 illustrates the IR spectrum of pure PMI foams and commercial PMI foam that are obtained with different component (methacrylic acid, acrylonitrile and acrylamide) percentages of a, b, and c samples. Figure 6 illustrates an example of pure PMI foam obtained by the method of the present invention.

Figure 7 illustrates the in-situ synthesized CNT/PMI foam.

DETAILED DESCRIPTION OF THE INVENTION

In the detailed description provided herein, the present invention is described only to provide a better understanding of the subject matter by exemplary references and without constituting any limiting effect.

Figure 1 schematically illustrates a representative embodiment of the PMI production method of the present invention. It starts with obtaining a reaction mixture (4) by completely mixing the components containing 40% acrylonitrile by weight, 60% methacrylic acid by weight, 1 % acrylamide by weight with the 0,5% group of containing conventional additives of 2% 1 -amyl alcohol by weight, 0,3% AIBN by weight, 1 ,5% pure water by weight as liquid components (1 ) and solid components (2) in a mixing vessel (3). In the next step, the reaction mixture starts pre-polymerization by subjecting it to radiation at a UV source (6) for 1 minute in a photo-initiation unit (5). The prepolymerization product (8) that is obtained by starting the crosslinking of the reaction mixture (4) is poured into a closed mold (1 1 ) having a glass plate (9) that is sealed with a gasket (7), and it is placed in the polymerization unit (12) in a water bath adjusted at 50°C for 12-48 hours. The polymerization process is completed by means of this process, and the copolymer block (13) completes its formation as shaped in the mold (11 ). The primary casting (13), in which it is formed by the polymer product that is transported to the heat treatment unit (14) in a furnace structure is subjected to heat treatment at 180-200°C for 1 hour, thereby, obtaining PMI foam (15). Closed mold (11 ) production allows for easy shaping and obtaining closed-cell rigid foam that can expand up to three times that of the copolymer block (13). The flexibility of the copolymer block (13) with high temperature allows for obtaining high-strength PMI foam (15) by expanding as a result of allowing gas movements with its reduced rigidity. The pre-polymerization of the reaction mixture (4) takes only a few minutes, and it is possible to complete the shortened polymerization in a total of 48 hours. Figure 2 illustrates the process steps of PMI synthesis including PMI and CNT. The MAA/AN/AM initiator (A) is exposed to UV light by applying photo initiation thereon. Thus, prepolymer (B) is obtained after the reaction. Subsequently, either nanosized materials embedded polymer (C) is firstly obtained by the polymerization process by closed molding with the addition of such as nanoparticles, and then PMI foam with nanoparticle (C1 ) is obtained by heat treatment, or by converting the prepolymer (B) directly into polymer (D) by means of polymerization in a closed mold, the PMI foam (D1 ) product is obtained after heat treatment.

Figure 3 illustrates comparative specific compressive strengths and cell sizes of pure PMI foams that are obtained under different conditions (a, b, c). While there is 1 % urea and 1 .5% pure water by weight in the A synthesis, there is 2% urea, 1 .5% pure water in the B synthesis, and 1% urea and 3% pure water in the C synthesis. Other components are the same in all syntheses. In addition, optical and SEM images of a, b, c PMI foams obtained by the method of the present invention are presented in Figure 4. Each product has internal structures with uniform walls and a similar diameter distribution. Figure 5 presents the IR spectrum relating to a, b, c samples of commercial and synthesized PMI foams. The IR spectrum of a, b, and c syntheses and commercial (IG-51 ) PMI foams that are prepared with varying component ratios are given. Figure 6 illustrates pure and CNT-containing PMI copolymer and foam samples obtained by the method of the present invention. Figure 4 is the views of the optical and SEM images of pure PMI foams that are obtained with different component (methacrylic acid, acrylonitrile, and acrylamide) percentages of a, b, and c samples. Figure 5 illustrates the IR spectrum of pure PMI foams and commercial PMI foam that are obtained with different component (methacrylic acid, acrylonitrile and acrylamide) percentages of a, b, and c samples. Figure 6 illustrates the pure PMI foam sample obtained by the method of the present invention as pure and CNT reinforced PMI a) copolymer blocks, and b) foams. Figure 7, on the other hand, illustrates the samples of in-situ synthesized CNT/PMI foam. REFERENCE NUMERALS

1 Liquid components 12 Polymerization Unit

2 Solid Components 13 Primer Casting

3 Mixing Vessel 14 Heat Treatment Unit

4 Reaction Mixture 15 PMI Foam

5 Photo-initiation Unit A MAA/AN/AM Initiator

6 UV Source B Prepolymer

7 Gasket C Nanoparticle Embedded Polymer

8 Pre-polymerization Product C1 PMI Foam with Nanosized Material

9 Glass Plate D Polymer

11 Mold D1 PMI Foam