WO2023182941A2

WO2023182941A2 - A polymerizable composition, a three-dimensional printed article and methods of preparing the same

Info

Publication number: WO2023182941A2
Application number: PCT/SG2023/050194
Authority: WO
Inventors: Fuke Wang; Yi Ting Chong; Baiqun CHEN; Lin Guo
Original assignee: Agency For Science, Technology And Research; Star3D Material Development Company (Singapore) Pte Ltd
Priority date: 2022-03-24
Filing date: 2023-03-23
Publication date: 2023-09-28
Also published as: WO2023182941A3

Abstract

There is provided a polymerizable composition comprising at least one monomer of a thermoplastic polymer and at least one monomer of thermosetting resin. There is also provided a three-dimensional printed article comprising a plurality of thermoplastic structures embedded within a thermosetting resin, wherein the thermoplastic structures are comprised of monomers of a thermoplastic polymer. There is also provided a method of making the composition and a method of forming a three-dimensional printed article using the composition.

Description

A Polymerizable Composition, A Three-Dimensional Printed Article and Methods of Preparing the Same

Cross-Reference To Related Application

This application makes reference to and claims the benefit of priority of Singapore application number 10202203029P, filed on 24 March 2022, the contents of which is hereby incorporated by reference in its entirety for all purposes.

Technical Field

The present invention relates generally to a polymerizable composition and a method of forming the polymerizable composition. The present invention also relates generally to a method of forming a three-dimensional printed article and a three-dimensional printed article.

Background Art

The global dental implant market size was valued at USD 3.6 billion in 2020 and is expected to expand at a compound annual growth rate (CAGR) of 11.0% from 2021 to 2028 (Report from Global Market Insight). Increasing applications of dental implants in various therapeutic areas along with increasing demand for prosthetics are some of the key factors expected to boost the market growth. The primary goal in implant placement is to achieve and maintain an intimate bone-to-implant connection, which is also known as dental osseointegration. Dental implant aims to fix an alloplastic material (the implant) in bone with the ability to withstand occlusal forces.

For dental implants, metals had been used widely for their biomechanical characteristics, surface finishing characteristics and machining characteristics. Nowadays, metals like Co-Cr, stainless steel and gold are outdated in the dental implant industry but are still used to make some of the dental implant components like abutment or abutment screws; while currently available metals used for dental implants are titanium and zirconium that have high passivity and resistance to chemicals. Metal implants has few drawbacks such as unaesthetic in the frontal area.

To overcome the drawback of dental metal implants, ceramic implants are being developed. Zirconia is the most popular ceramic for dental inserts as it demonstrates least particle discharge and is thought to be dormant in the body. Zirconia has a tooth like shading, great mechanical properties and subsequently great biocompatibility. The utilization of zirconia inserts maintains a strategic distance from the drawback of metal implants and acquiesces to the demand of numerous patients seeking alternatives to metal inserts. Zirconia is also believed to maintain excellent oral health, specifically gum health and crack sturdiness. However, the most significant disadvantage of zirconia dental implants is that the material does not do well in low-temperature or humid environments. When exposed for long periods to cold temperatures, zirconia slowly changes form and loses durability. In addition, zirconia requires that a patient heals without applying any pressure to the affected area, which can be difficult or impossible to achieve in some circumstances.

Subsequently, a variety of polymers have been developed as dental implant materials. Examples of polymers include polymethylmethacrylate, polytetrafluoroethylene, polyethylene, polysulfone, or polyurethane. Today, polymeric materials are constrained to the assembling of shock retaining segments joined into the superstructures bolstered by inserts, whereby the inserts are made from an extensive variety of biomaterials. As such, the choice of an adept biomaterial is important as proper determination of biomaterials impacts clinical achievement and life span of inserts.

Recently, with the fast development of digital technologies, numerous clinical reports have demonstrated the benefits of digital technology in the diagnosis, treatment and fabrication of implant- supported dental prostheses. Digital diagnostic impressions, virtual planning, computer- guided implant surgery and custom abutments, fabricated using Computer-Aided Design/Computer-Aided Manufacturing (CAD/CAM), can be used to plan and complete implant placement and implant supported dental prostheses. Particularly, with the improvements in 3D printing technology such as increased precision, high-resolution imaging, and state of the art 3D printers, 3D printing has now become a mainstream technique used across different fields today. The rise of 3D printing in dentistry has been parallel with CAD advancements and enhanced imaging techniques like cone beam computed tomography (CBCT) and magnetic resonance imaging (MRI) to plan and print dental and maxillofacial prosthesis to restore and replace lost structures. Nowadays, modern CAD software is available, which uses intricate algorithmic designs and artificial intelligence to aid in modelling any object or tissue and reproducing it exactly as the clinician desires. There has been an increase in the use of 3D printing for various dental applications and more and more dentists utilize digital scanning, 3D printing manufacturing to provide patient- specific custom-made prosthesis and restorations. This can be directly reflected from the rapid growing market. The dental 3D printing market is projected to reach USD 6.5 billion by 2025 from USD 1.8 billion in 2020, at a CAGR of 28.8%. The dental 3D printing medical devices market is primarily driven by factors such as the high incidence of dental caries and other dental diseases, rising demand for cosmetic dentistry, the growing adoption of dental 3D printers in hospitals and clinics, and rapid growth in the geriatric population (report from Market and Markets).

Various materials can be used for dental 3D printing such as metal, photopolymer, and ceramic. However, photopolymer printing materials accounts for the largest market in dental 3D printing with market share of 58.0% in 2016. The popular use of photopolymers comes from the ability of photopolymer to be compatible for construction of a wide variety of dental models and is cost effective. The choice of the photopolymers or composites for modem dentistry requires balancing a large number of requirements but the excellent mechanical property is the most critical factor. Silicate cements was the early attempt in traditional dental treatment, but its solubility problems limited further development and application. In 1950s, unfilled acrylic resin based on methyl methacrylate was developed and the acrylic -based materials have since retained a prominent position in restorative and prosthetic dentistry. In 1962, the bisphenol glycidyl methacrylate (Bis- GMA) monomer with improved physical and mechanical properties of acrylic resins was developed. In the early 1970s, the use of the photopolymer composites was proposed and developed. Various fillers with different types and sizes have been used to develop a wide array of resin composites with respect to ease of polishability and strength. The addition of fillers helps to reduce the volume of polymeric matrix and thus lower polymerization shrinkage. It also helps to reduce the overall coefficient of thermal expansion of the resin composite.

Although the use of Bis-GMA and composites leads to high strength and hardness, the resulting mechanical performance is still not good enough for dental implant products development, particularly in the flexural strength. The flexural strength of most Bis-GMA resin is in the range of 80 to 100 MPa, which is not tough enough for dental implant as high flexural strength is essential for stress-bearing restorations, when high pressure/stress is exerted on the material or restoration. High flexural strength also affects the thickness of the restoration walls as a high-strength material can be produced with a low wall thickness. This means that a material with high flexural strength and high fracture toughness allows for very thin restorations to be made and is therefore well suited for minimally invasive treatment options. Therefore, for the development of printable material for dental implant products such as implant crown and abutment, printable resin with high flexural strength of more than 150 MPa is highly sought after and in high demand by the market.

Various methods have been employed to enhance the toughness of the thermosetting resins. Toughness modification of epoxy resins by rubber elastomer had been demonstrated as being effective but it generally led to remarkable decrease of mechanical properties and thermal stability. Addition of liquid crystals polymers to the thermosetting resins showed a worthy toughness effect and made the composite material possess both high orientation of the liquid crystal and three- dimensional network structure. However, thermotropic liquid crystal polymers have a relatively high melting point, which increases the difficulty of processing. The most popular strategy is to use nanoparticles as it has been confirmed that nanoparticles could transfer the external force to the surroundings and induce microcracks in the thermosetting matrix hence achieving purposeful toughening. However, most nanoparticles are prone to agglomeration during the modification process and thus affect the mechanical properties.

Thermoplastic materials have also been proposed to enhance the toughness because thermoplastic materials have both good toughness and high modulus, but most thermoplastic materials suffer from problems such as miscibility and phase separation.

Therefore, there is a need to overcome or ameliorate the problems as discussed above by providing a polymerizable composition, that can be used in dental applications. There is also provided a three-dimensional article that can be used as a dental product and methods of producing the polymerizable composition and the three-dimensional article.

Summary

In one aspect, the present disclosure refers to a polymerizable composition comprising at least one monomer of a thermoplastic polymer and at least one monomer of thermosetting resin.

Advantageously, as the monomer of the thermoplastic polymer may have a different hydrophobicity as compared to that of the thermosetting resin, this hydrophobicity difference allows for phase separation to assist in the formation of the structures when the polymerizable composition polymerizes.

In another aspect, the present disclosure refers to a method of preparing a polymerizable composition comprising the steps of (a) mixing at least one monomer of a thermoplastic polymer and at least one monomer of a thermosetting resin, and (b) optionally mixing an initiator to the mixture of step (a).

In another aspect, the present disclosure relates to a method of forming a three-dimensional printed article comprising the steps of: (a) printing a polymerizable composition comprising at least one monomer of a thermoplastic polymer, at least one monomer of a thermosetting resin and an initiator via three-dimensional printing to form a three-dimensional printed article; and (b) curing the printed article, wherein the printing step (a) is before or simultaneous with the curing step (b). In another aspect, there is provided a three-dimensional printed article comprising a plurality of thermoplastic structures embedded within a thermosetting resin, wherein the thermoplastic structures are comprised of monomers of a thermoplastic polymer.

Advantageously, thermoplastic structures are formed in situ during polymerization of the polymerizable composition when forming the three-dimensional printed article. The in situ formed thermoplastic structures can help to stabilize micro-crack growth by enhancing the extent of the energy dissipated during fracture and therefore play an important role in managing crack initiation and extrinsic deformation mechanisms.

Further advantageously, the in situ formed thermoplastic structures can change the failure mode from brittle fracture to a quasi-stable one.

Definitions

As used herein, the term “thermoplastic”, when used in the context of this disclosure, refers to a class of polymers that can be softened through heating.

The term “thermosetting”, when used in the context of this disclosure refers to a class of polymers that irreversibly becomes rigid when heated.

The term “photo-polymerization”, when used in the context of this disclosure, refers to a process initiated by light irradiation and through which a polymer is formed.

The term “photo-initiator”, when used in the context of this disclosure, refers to a substance which, when subjected to light irradiation, is able to generate a reactive species and trigger a chemical transformation.

The term “light irradiation”, when used in the context of this disclosure, refers to a sample resin subjected to the irradiation of an electromagnetic wave such as radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays. More typically, it refers to the fact that the sample is subjected to the irradiation of visible light or ultraviolet radiation. Visible light typically refers to an electromagnetic radiation having a wavelength comprised from 400 to 800 nm. Ultraviolet (UV) radiation typically refers to an electromagnetic radiation having a wavelength comprised from 10 nm to 400 nm.

The term “thermo-initiator”, when used in the context of this disclosure, refers to a substance, which when subjected to heat, is able to generate a reactive species and trigger a chemical transformation.

The term “structure”, when used in the context of this disclosure, refers to tubes, rods, cylinders, wafers, disks, sheets, plates, planes, cones, ellipsoids, polymeric fibers, and other such objects. When the structure has at least one characteristic dimension less than about 500 microns, the structure is termed as a “nanostructure”.

The term “brittle fracture”, when used in the context of this disclosure, refers to an unstable failure process in polymers, defined by a sudden catastrophic crack propagation that is initiated from a microscale defect, such as a void, inclusion, or discontinuity, when the material is under excessive stress.

The term “quasi-stable”, when used in the context of this disclosure, refers to a polymer that is stable for a period of time under excessive stress levels.

Unless specified otherwise, the terms “comprising” and “comprise”, and grammatical variants thereof, are intended to represent “open” or “inclusive” language such that they include recited elements but also permit inclusion of additional, unrecited elements.

Additionally, the terms and expressions employed herein have been used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments and optional features, modification and variation of the inventions embodied therein herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention.

As used in this application, the singular form “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise.

As used herein, the term “about”, in the context of concentrations of components of the formulations, typically means +/- 5% of the stated value, more typically +/- 4% of the stated value, more typically +/- 3% of the stated value, more typically, +/- 2% of the stated value, even more typically +/- 1% of the stated value, and even more typically +/- 0.5% of the stated value.

Throughout this disclosure, certain embodiments may be disclosed in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosed ranges. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range. Certain embodiments may also be described broadly and generically herein. Each of the narrower species and sub-generic groupings falling within the generic disclosure also form part of the disclosure. This includes the generic description of the embodiments with a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein.

Other embodiments are within the following claims and non- limiting examples. In addition, where features or aspects of the invention are described in terms of Markush groups, those skilled in the art will recognize that the invention is also thereby described in terms of any individual member or subgroup of members of the Markush group.

Detailed Disclosure of Optional Embodiments

Exemplary, non-limiting embodiments of a polymerizable composition will now be disclosed. The polymerizable composition comprises at least one monomer of a thermoplastic polymer and at least one monomer of thermosetting resin.

The monomer of the thermoplastic polymer may polymerize and form self-assembling thermoplastic structures in situ when the polymerizable composition undergoes polymerization.

The monomer of the thermoplastic polymer may be selected from a thermal-polymerizable monomer or a photo-polymerizable monomer.

The monomer of the thermoplastic polymer may be selected from monomers that can form phase separation with the thermosetting matrix.

The thermoplastic polymer may be derived from the monomer(s) as defined herein as side chains of a polymer backbone or may comprise the monomer(s) as defined herein as part of a polymer backbone, whereby the polymer backbone comprises a polyacrylate, a polymethacrylate, a polyvinyl, an epoxy backbone or a combination thereof. The polymer backbone of the thermoplastic polymer may be a polyacrylate or a polymethacrylate backbone.

The thermoplastic polymer may be a co-polymer derived from at least two of the monomers as defined herein. The thermoplastic polymer may be a co-polymer derived from a hydrophobic monomer and a hydrophilic monomer.

When polymerized (or formed), the thermoplastic polymer may be derived from repeat units of a hydrophobic monomer or a hydrophilic monomer, whereby the hydrophobic monomer or hydrophilic monomer is selected from the list of monomers as defined herein as appropriate. The monomer of the thermoplastic polymer may have a different hydrophobicity as compared to that of the thermosetting resin. Advantageously, this hydrophobicity difference between the thermosetting resin and the thermoplastic polymer is required for phase separation to assist in the formation of the structures.

The repeat units of the thermoplastic polymer may be derived from both hydrophobic and hydrophilic monomers, which has the ability of self-assembly in the thermosetting resin. Before photo-polymerization, the monomers of the thermoplastic polymer and the thermosetting resin are miscible, forming a homogenous solution. Accordingly, the monomers of the thermoplastic polymer may be hydrophilic monomers before photo -polymerization. When the photopolymerization is initiated, as the chain length of the thermoplastic polymer increases, the polarity of the thermoplastic polymer region decreases (hydrophobic) while the polarity of the mixture containing the thermosetting resin remains high (hydrophilic). Therefore, the difference in polarity between the thermoplastic polymer and the thermosetting resin leads to the spontaneous phase separation of the thermoplastic oligomer/polymer from thermosetting resin and subsequently lead to the self-assembly of the thermoplastic polymer to form a structure (such as a macro/nano structure) that function as a toughening element for the resulting composition. During selfassembly, the structures may be formed occupying the least surface area.

The monomer of the thermoplastic polymer may be selected from the group consisting of methyl acrylate, ethyl acrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, 2-ethylhexyl methacrylate, 2-ethylhexyl vinyl ether, benzyl acrylate, acrylic acid, acrylic amine, (hydroxyethyl)methacrylate, 2-hydroxyethyl methacrylate, allyl cyclohexanepropionate, ethylene glycol phenyl ether acrylate, ethylene glycol phenyl ether methacrylate, benzyl methacrylate, 2- hydroxyethyl acrylate, butyl acrylate, sec-Butyl acrylate, tert-Butyl acrylate, butyl glydicyl ether, butyl methacrylate, 2-cyanoethyl acrylate, glycerol monomethacrylate, cyclohexyl acrylate, isobutyl acrylate, isobutyl vinyl ether, isopropyl acrylate, 2-methoxyethyl acrylate, methyl glycidyl ether, methyl vinyl ether, dimethylaminoethyl methacrylate, dodecyl acrylate, dodecyl methacrylate, dodecyl vinyl ether, 2-ethoxyethyl acrylate, ethylene malonate, 2-ethylhexyl vinyl ether, ethyl vinyl ether, hexadecyl methacrylate, hexyl acrylate, hexyl methacrylate, propyl vinyl ether, 2,2,2-trifluoroethyl acrylate, vinyl propionate, butyl glycidyl ether, l,2-epoxy-3- phenoxypropane, glycidyl 2-methylphenyl ether, benzyl glycidyl ether, glycidyl benzyl ether, glycidyl methyl ether, glycidol, 2,3 -epoxy- 1-(1 -ethoxy ethoxy )propane, 3,4-epoxy-2-phenyl-l,l,l- trifluoro-2-butanol, mixtures and combinations thereof. The monomers of the thermoplastic polymer may be 2-hydroxyethyl acrylate and acrylic amine.

As an example, when 2-hydroxyethyl acrylate and acrylic amine are used as the monomers of the thermoplastic polymer, acrylic amine may form the major thermoplastic monomer while 2- hydroxyethyl acrylate may assist in reducing the viscosity of the thermosetting resin. Before photo- polymerization, the hydrophilic 2-hydroxyethyl acrylate and acrylic amine may form a homogenous solution with the hydrophilic urethane acrylate oligomers (thermosetting resin). During photo-polymerization, the acrylic amine polymer has a reduced polarity and increased hydrophobicity. The difference in polarity between the acrylic amine polymer and the urethane acrylate oligomers leads to the spontaneous phase separation. Accordingly, self-assembly of the acrylic amine polymer leads to the formation of the thermoplastic structure.

The amount of the at least one monomer of the thermoplastic polymer may be in the range of about 5 wt% to about 70 wt%, about 10 wt% to about 70 wt%, about 20 wt% to about 70 wt%, about 40 wt% to about 70 wt%, about 60 wt% to about 70 wt%, about 5 wt% to about 60 wt%, about 5 wt% to about 40 wt%, about 5 wt% to about 20 wt%, about 5 wt% to about 10 wt%, about 5 wt% to about 15 wt%, about 15 wt% to about 50 wt%, or about 50 wt% to about 70 wt%, based on the weight of the polymerizable composition.

The monomer of the thermosetting resin may be a (meth) aery late/epoxy resin with two or more coupling groups.

The monomer of the thermosetting resin may be selected from an acrylate/epoxy monomer and/or an oligomer selected from the group consisting of bisphenol A dimethacrylate (Bis-DMA), bisphenol A diglycidyl ether methacrylate (Bis-GMA), ethoxylated bisphenol-A dimethacrylate (Bis-EMA), tricyclo[5.2.1.02,6]decanedimethanol diacrylate, bisphenol A glycerolate diacrylate, bisphenol A ethoxylate diacrylate, bisphenol A ethoxylate dimethacrylate (oligo), bisphenol F ethoxylate diacrylate (oligo), bis(4-hydroxyphenyl)dimethylmethane diglycidyl ether, polyisocyanate acrylate, urethane acrylate oligomers, branched hexa-functional aliphatic urethane acrylate, DER332, bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, di(trimethylolpropane) tetraacrylate, pentaerythritol triacrylate, l,3,5-triacryloylhexahydro-l,3,5- triazine, trimethylolpropane propoxylate triacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, di(trimethylolpropane)tetraacrylate, pentaerythritol tetraacrylate, , vinyl T- structure polymers, methacryloxypropyl T-structure Siloxanes, methacryl polyhedral oligomeric silsesquioxane cage mixture, methacrylethyl polyhedral oligomeric silsesquioxane, Trimethylolpropane triglycidyl ether, Tris(4-hydroxyphenyl)methane triglycidyl ether, monophenyl functional tris(epoxy terminated poly dimethylsiloxane), epoxycyclohexyl polyhedral oligomeric silsesquioxane cage mixture, triglycidyllsobutyl polyhedral oligomeric silsesquioxane, glycidyl polyhedral oligomeric silsesquioxane cage, mixtures or combinations thereof. The monomer of the thermosetting resin may be urethane acrylate oligomers. The thermosetting resin may further comprise a diluent resin selected from the group consisting of ethyl acetate and 1,6-hexanediol diacrylate, phenylglycidyl ether, butylglycidyl ether, allylgylcidyl ether, butanediol diglycidyl ether, and combinations thereof. The optional diluent resin may be used to decrease the viscosity of certain resins that have a large viscosity. The decreased viscosity of the resin may facilitate kinetic molecular movement and self-assembly of the thermosetting resin. The formation of the structures can be achieved through optimization of the light intensity, applied shear force during assembly and viscosity of the thermosetting resin. The amount of the monomer of the thermosetting resin may be in the range of about 30 wt% to about 95 wt%, about 45 wt% to about 95 wt%, about 60 wt% to about 95 wt%, about 75 wt% to about 95 wt%, about 85 wt% to about 95 wt%, about 30 wt% to about 80 wt%, about 30 wt% to about 65 wt%, about 30 wt% to about 50 wt% or about 30 wt% to about 40 wt%, based on the weight of the polymerizable composition.

The polymerizable composition may further comprise an initiator to initiate polymerization of the polymerizable composition. The initiator may be a thermo-initiator or a photo-initiator. Advantageously, photo-curing or photo -polymerization can be used as the polymerization technique which allows the application in lithography-based 3D printing.

The thermo-initiators may be selected from the group consisting of 2,2’-azobis(isobutyronitrile), 2,2’-azobis(methylbutyronitrile), 2,2’-azobis(2,4-dimethylvaleronitrile), 4,4-azobis(4- cyanovaleric acid), dimethyl 2,2’-azobis(2-methylpropionate), 2,2’-azobis(2-amidinopropane) dihydrochloride, 2,2’-azobis[2-(2-imidazolin-2-yl)-propane] dihydrochloride, tert-butyl hydroperoxide, cumene hydroperoxide, di-tert-butyl peroxide, dicumyl peroxide, benzoyl peroxide, dicyandiamide, cyclohexyl tosylate, diphenyl(methyl)sulfonium tetrafluoroborate, benzyl(4-hydroxyphenyl)-methylsulfonium hexafluoroantimonate, (4-hydroxyphenyl)methyl-(2- methylbenzyl)sulfonium hexafluoroantimonate, ammonium persulfate, potassium persulfate, sodium persulfate, mixtures and combinations thereof.

The thermo-initiators may be used either singly or in the form of a mixture of two or more members. The amount of thermo-initiators used may be in the range of about 1 wt% to about 10 wt%, about 2 wt% to about 10 wt%, about 4 wt% to about 10 wt%, about 8 wt% to about 10 wt%, about 1 wt% to about 8 wt%, about 1 wt% to about 6 wt%, about 1 wt% to about 5 wt%, about 1 wt% to about 3 wt%, or about 1 wt% to about 2 wt%, based on the weight of the polymerizable composition.

The photo-initiators may be selected from the group consisting of acetophenone, anisoin, anthraquinone, triarylsulfonium hexafluorophosphate salt, triarylsulfonium hexafluoroantimonate salts, 3 -methylbenzophenone, 4-hydroxybenzophenone, dibenzosuberenone, 2,2- diethoxyacetophenone, 4-Benzoylbiphenyl, 2-Benzyl-2-(dimethylamino)-4’ - morpholinobutyrophenone, benzil, benzoin, benzoin ethyl ether, bis(2,4, 6-trimethyl benzoyl)phenylphosphine oxide (IRGACURE 819), 2,4,6-trimethylbenzoyl diphenyl phosphine (TPO), 2-hydroxy-2-methyl- 1 -phenyl- 1 -propane (DAROCUR 1173), benzophenone (BP) and the like, or the following thermal-initiators include 4,4-azobis(4-cyanovaleric acid), 1,1’- azobis(cyclohexanecarbonitrile), 2,2’-azobisisobutyronitrile (AIBN), benzoyl peroxide, 1,1- bis(tert-butylperoxy)cyclohexane, tert-butyl hydroperoxide, tert-butyl peracetate, tert-butyl peroxide, cumene hydroperoxide, cyclohexanone peroxide, 2,4- pentanedione peroxide, ammonium persulfate, potassium persulfate, lithium phenyl (2,4,6-trimethylbenzoyl) phosphinate, sodium phenyl (2,4,6-trimethylbenzoyl) phosphinate, lithium bisacylphosphine oxide, sodium bisacylphosphine oxide, 2-hydroxy-l-[4-(2 -hydroxy ethoxy) phenyl] -2-methyl-l -propanone (Irgacure 2959), 1-hydroxy-cyclohexyl-phenylketone (Irgacure 184), 2-benzyl-2-dimethylamino- l-(4-morpholinophenyl)-l-butanone (Irgacure 369), 2-methyl-4'-(methylthio)-2- morpholinopropiophenone (Irgacure 907), mixtures and combinations thereof. The photo-initiator may be IGACURE 819.

The photo-initiators may be used either singly or in the form of a mixture of two or more members. The amount of photo -initiators used may be in the range of about 0.5 wt% to about 5 wt%, about 1 wt% to about 5 wt%, about 2 wt% to about 5 wt%, about 3 wt% to about 5 wt%, about 4 wt% to about 5 wt%, about 0.5 wt% to about 4 wt%, about 0.5 wt% to about 3 wt%, about 0.5 wt% to about 2 wt%, or about 0.5 wt% to about 1 wt%, based on the weight of the polymerizable composition.

Exemplary, non-limiting embodiments of a method of preparing a polymerizable composition will now be disclosed. The method comprising the steps of (a) mixing at least one monomer of a thermoplastic polymer and at least one monomer of a thermosetting resin, and (b) optionally mixing an initiator to the mixture of step (a).

The mixing step (a) and the mixing step (b) may independently be carried out under agitation for a time duration in the range of 1 to 4 hours.

The agitation in mixing step (a) may be stirring, which in turn can be mechanical stirring, hand stirring, use of a magnetic stirrer/stir bar or any combinations thereof. The agitation in mixing step (a) may be conducted for the duration in the range of about 1 hour to about 4 hours, about 1 hour to about 3 hours, about 1 hour to about 2 hours, about 1 hour to about 4 hours, about 2 hours to about 4 hours or about 3 hours to about 4 hours, or at least for a period of time until the mixture of step (a) forms a substantially clear solution. The agitation of the mixing step (b) may be stirring, which in turn can be mechanical stirring, hand stirring, use of a magnetic stirrer/stir bar or any combinations thereof. The agitation of the mixing step (b) may be conducted for the duration in the range of about 1 hour to about 4 hours, about 1 hour to about 3 hours, about 1 hour to about 2 hours, about 1 hour to about 4 hours, about 2 hours to about 4 hours or about 3 hours to about 4 hours, or at least for a period of time until the mixture of step (a) forms a substantially clear solution.

The mixing step (b) may be undertaken at room temperature (or at a temperature in the range of 28°C to 30°C).

Exemplary, non-limiting embodiments of a method of forming a three-dimensional printed article will now be disclosed. The method comprises the steps of (a) printing a polymerizable composition comprising at least one monomer of a thermoplastic polymer, at least one monomer of thermosetting resin and an initiator via three-dimensional printing to form a three-dimensional printed article; and (b) curing the printed article, wherein the printing step (a) is before or simultaneous with the curing step (b).

The printing step (a) may further comprise the step of (al) washing the printed article with a suitable solvent (such as an alcohol, for example, iso-propanol), and a step of (a2) air-drying the printed article, before the curing step (b).

The curing step (b) may comprise the step of subjecting the printed article to photo -polymerization to polymerize both the monomer(s) of the thermoplastic polymer and the monomer(s) of the thermosetting resin.

The curing step (b) may comprise the step of applying ultra-violet light irradiation to initiate photopolymerization, wherein the radiation power is applied in the range of about 2 mW/cm² to about 100 mW/cm², about 5 mW/cm² to about 100 mW/cm², about 10 mW/cm² to about 100 mW/cm², about 25 mW/cm² to about 100 mW/cm², about 50 mW/cm² to about 100 mW/cm², about 70 mW/cm² to about 100 mW/cm², about 90 mW/cm² to about 100 mW/cm², about 2 mW/cm² to about 90 mW/cm², about 2 mW/cm² to about 70 mW/cm², about 2 mW/cm² to about 50 mW/cm², about 2 mW/cm² to about 25 mW/cm² or about 5 mW/cm² to about 30 mW/cm².

The ultra-violet irradiation to initiate polymerization may be applied for a duration in the range of about 3 seconds to about 60 seconds, about 10 seconds to about 60 seconds, about 20 seconds to about 60 seconds, about 30 seconds to about 60 seconds, about 50 seconds to about 60 seconds, about 3 seconds to about 50 seconds, about 3 seconds to about 30 seconds, about 3 seconds to about 20 seconds, about 3 seconds to about 10 seconds or about 3 seconds to about 5 seconds. When photo-polymerization is used in the method, the initiator is the photo-initiator. The curing step (b) may comprise the step of subjecting the printed article to thermalpolymerization to polymerize both the monomer(s) of the thermoplastic polymer and the monomer(s) of the thermosetting resin. The thermal-polymerization may also reduce the viscosity of the thermosetting resin.

The curing step (b) may further comprise applying a temperature in the range of about 25 °C to about 90 °C, about 40 °C to about 90 °C , about 55 °C to about 90 °C, about 70 °C to about 90 °C, about 80 °C to about 90 °C, about 25 °C to about 80 °C, about 25 °C to about 65 °C , about 25°C to about 50 °C, about 25 °C to about 35 °C or about 25 °C to about 30 °C.

The temperature in the curing step (b) may be applied for a duration in the range of about 1 hour to about 4 hours, about 1 hour to about 3 hours, about 1 hour to about 2 hours, about 1 hour to about 4 hours, about 2 hours to about 4 hours or about 3 hours to about 4 hours.

The method of producing the three-dimensional printed article may further comprise the step of (c) adding a plurality of hydroxyapatite nanoparticles to the polymerizable composition as defined herein before the printing step (a).

The hydroxyapatite nanoparticle may comprise ceramic materials selected from group 4, 13 and 14 of the periodic table of elements. The ceramic material may be silica, alumina, titania, zirconia, zirconium phosphates, or any combination thereof. The hydroxyapatite nanoparticle may comprise cellulose fibers selected from the group consisting of hemp, linen, cotton, ramie, sisa, or any combinations thereof.

Alternatively, or additionally, the nanoparticle may comprise clay selected from the group consisting of montmorillonite, bentonite, laponite, kaolinite, saponite, vermiculite or any combination thereof.

The printing step (a) may be undertaken using a Digital Light Processing (DLP) printer with slice thickness of about 50 pm, using the polymerizable composition with added hydroxyapatite nanoparticles as described herein. The printing step may also be undertaken using a Stereolithography (SLA) printer.

Exemplary, non-limiting embodiments of a three-dimensional printed article will now be disclosed. The three-dimensional printed article comprises a plurality of thermoplastic structures embedded within a thermosetting resin, wherein the thermoplastic structures are comprised of monomers of a thermoplastic polymer. The three-dimensional article may be a dental product.

The thermoplastic structures may be formed in situ in the thermosetting resin, wherein the thermoplastic structures comprise of monomers of a thermoplastic polymer. The three- dimensional printed article may be obtained from subjecting the polymerizable composition as defined herein to three-dimensional printing and curing. Advantageously, the formed thermoplastic structure can function as fillers to enhance the toughness, strength and mechanical performance.

The thermoplastic structures may be nanometer sized or micrometer sized in the form of a fiber, a rod, a sheet, a particle or a sheet-like structure.

The dimensions of the formed thermoplastic structures may be in the range of about 10 nm to about 500 pm, about 100 nm to about 500 pm, about 200 nm to about 500 pm, about 400 nm to about 500 pm, about 800 nm to about 500 pm, about 1 pm to about 500 pm, about 100 pm to about 500 pm, about 200 pm to about 500 pm, about 400 pm to about 500 pm, about 10 nm to about 400 pm, about 10 nm to about 200 pm, about 10 nm to about 100 pm, about 10 nm to about 1 pm, about 10 nm to about 800 nm, about 10 nm to about 400 nm, about 10 nm to about 200 nm, about 10 nm to about 100 nm or about 10 nm to about 50 nm. This dimension can refer to a diameter of the fiber or rod structure, the particle or refer to a length or breadth of the sheet-like structure. Depending on the dimension size, as defined above, the structure may be termed as a nanostructure.

When the three-dimensional printed article is prepared according to the method as defined above, thermoplastic structures are formed within the three-dimensional printed article, which can be regarded as being formed in situ. The formation of thermoplastic particles mainly arises from the difference in hydrophobicity of the thermoplastic and thermosetting monomers, which are further amplified upon initiation of polymerization as the polymerization process causes an increase in molecular size. The amplified difference in hydrophobicity eventually leads to a micro-level phase separation of the thermoplastic polymer from the thermosetting resin, leading to the formation of thermoplastic structures. Further, the use of co-polymers may enhance the phase separation of the thermoplastic polymer from the thermosetting resin.

The shapes of the structures are determined by the concentration of thermoplastic monomers used, wherein the structures tend to be particles when low concentrations of the thermoplastic monomers were used in the polymerizable composition (< 15 wt%); rods and wires when moderate concentrations of the thermoplastic monomers were used in the polymerizable composition (15 wt% to 50 wt%); and a three-dimensional network of fibers when high concentrations of the thermoplastic monomers were used in the polymerizable composition (> 50 wt%).

Advantageously, the in situ formed thermoplastic structures can help to stabilize micro-crack growth by enhancing the extent of the energy dissipated during fracture and therefore play an important role in managing crack initiation and extrinsic deformation mechanisms.

Further advantageously, the in situ formed thermoplastic structures can change the failure mode from brittle fracture to a quasi-stable one. In one example, the three-dimensional printed article may be a dental product printed using the polymerizable composition with added hydroxyapatite nanoparticles as prepared herein. The dental product may be an implant dental crown and abutment with good surface finishing and good accuracy. Advantageously, the dental product can be printed precisely even for structures less than 0.2 nm.

In another example, the three-dimensional printed article with thermoplastic nanostructures embedded within the thermosetting resin produced according to this disclosure, has about 40% increase in flexural strength (from 70 MPa to 101 Mpa), about a 2-fold increase in elongation (from 3-7% to about 7-15%), and a about a 2-fold increase in Young’s modulus index (from about 2508 Mpa to about 4427 Mpa) as compared to the same thermosetting resin but without the thermoplastic fibers. The thermoplastic nanostructure may be acrylic amine.

Brief Description of Drawings

The accompanying drawings illustrate a disclosed embodiment and serves to explain the principles of the disclosed embodiment. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

[Fig. 1A]

Fig. 1A shows a photograph of a dental implant crown.

[Fig. IB]

Fig. IB shows a photograph of an implant abutment.

[Fig. 2]

Fig. 2 shows SEM images of a quenched sample surface after 1 minute of photo curing (UV light: 360 nm, 15 W) from the bottom of the sample, as demonstrated in Example 2 below. The scale bar of the SEM image is 100 nm.

Examples

Non- limiting examples of the invention and a comparative example will be further described in greater detail by reference to specific examples, which should not be construed as in any way limiting the scope of the invention.

Example 1: Preparation of Resins

All reactions were carried out in a fume hood due to the strong volatilization of the monomers and their smell. Resin 1 preparation

To a flask was added 40 g of urethane acrylate oligomers (obtained from Merck Chemicals, New York, USA), 30 g of 2-hydroxyethyl acrylate (obtained from Merck Chemicals, New York, USA) and 20 g of acrylic amine (obtained from Merck Chemicals, New York, USA). Under stirring, 0.9 g of IRGACURE 819 (obtained from Merck Chemicals, New York, USA) was added to the resulting mixture after a clear solution was obtained. The resulting mixture was further stirred at room temperature for another 2 hours until a translucent or clear solution was obtained.

Acrylic amine formed the major thermoplastic monomer while 2-hydroxyethyl acrylate assisted in reducing the viscosity of the thermosetting resin. Before photo-polymerization, the hydrophilic 2-hydroxyethyl acrylate and acrylic amine formed a homogenous solution with the hydrophilic urethane acrylate oligomers (thermosetting resin). During photo-polymerization, the acrylic amine polymer has a reduced polarity and increased hydrophobicity. The difference in polarity between the acrylic amine polymer and the urethane acrylate oligomers leads to the spontaneous phase separation. Accordingly, self-assembly of the acrylic amine polymer leads to the formation of the thermoplastic nanostructure.

Resin 2 (control resin) preparation

To a flask was added 40 g of urethane acrylate oligomers (obtained from Merck Chemicals, New York, USA), 50 g of 2-hydroxyethyl acrylate (obtained from Merck Chemicals, New York, USA). Under stirring, 0.9 g of IRGACURE 819 (obtained from Merck Chemicals, New York, USA) was added to the resulting mixture after a clear solution was obtained. The resulting mixture was further stirred at room temperature for another 2 hours until a clear solution was obtained.

Example 2: Samples 3D printing and testing

To evaluate their printability and mechanical strength, dog-shape tensile bars were printed on a DLP printer (LittleRP with build volume 60mm(X) 40mm(Y) 100mm(Z), which uses DLP projector with a resolution of 1024x768 (Brand & model: Acer P128) as light source and Creation Workshop as controlling software.) Printing was carried out with slice thickness of 50 pm. Exposure time per layer was 3 seconds. After printing, the printed part was washed thoroughly with iso-propanol, air dried and placed inside UV oven for further curing.

To evaluate their printability and potential application for dental products development, hydroxyapatite nanoparticles with sizes of 60-80 nm were added to the resin as described in Example 1. Then, both dental crown and abutment were printed on a DLP printer. Printing was carried out with slice thickness of 50 m. Exposure time per layer was 3 seconds. After printing, the printed part was washed thoroughly with iso-propanol, air dried and placed inside UV oven for another 10 minutes curing. It can be seen clearly from Fig. 1A and Fig. IB that both dental crown and abutment can be printed accurately with a good surface finishing. For abutment printing, it is also observed that structures less than 0.2 mm were printed precisely.

Example 3: Mechanical studies

The Young’s modulus and flexural strength were measured on a universal tensile machine ASTM D638-03. At least five printed samples for each resin were tested by INSTRON universal testing machine, with a loading rate of Imm/s. Results are an average of at least five specimens.

The Young’s modulus of the bulk fabricated, and 3D printed polymer structure were determined using uniaxial tensile tests according to ISO 572-2. Dumbbell specimens were machined from the polymer plates using a water-jet cutter or directly printed from a 3D printer. The tests were performed using an Instron 5584 universal testing machine, with a gauge length of 25 mm and a displacement rate of 1 mm min ¹. A minimum of five samples were tested for each formulation.

The test results for both Resin 1 and Resin 2 (control sample) were compared in Table 1.

From the results, it is clear that both the modulus and flexural strength of Resin 1 were significantly enhanced as compared to the Resin 2 (control resin). Similarly, the elongation was increased by around 2 folds.

Example 4: Mechanism studies

To confirm the thermoplastic nanostructure formation, the resin mixture as described in Example 1 was added to a glass Petri dish and then irradiated with a UV FED light from bottom with a distance of 10 cm at room temperature. Unreacted liquid resin was decanted, and the obtained polymer films was washed with IPA three times and then dried under vacuum for 8 hours before SEM analysis. As shown in Fig. 2, nano fibers with diameter of tens nanometers can be seen in the resulted polymer matrix.

Industrial Applicability The disclosed polymerizable composition and the three-dimensional printed article printed using the polymerizable composition may be used in a dental product as an implant dental crown, an abutment, brace or night guard. This is applicable to industries such as dental, cosmetics, medical and healthcare where the polymerizable composition can be used for the development of three- dimensional printable material to be used as a dental product with good surface finishing and good accuracy.

It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.

Claims

CLAIMS A polymerizable composition comprising at least one monomer of a thermoplastic polymer and at least one monomer of thermosetting resin. The polymerizable composition according to claim 1, wherein the monomer of the thermoplastic polymer is a thermal-polymerizable monomer or a photo-polymerizable monomer. The polymerizable composition according to claim 1 or 2, comprising at least two monomers of the thermoplastic polymer, wherein one monomer is a hydrophobic monomer and the other monomer is a hydrophilic monomer. The polymerizable composition according to any one of claims 1 to 3, wherein the monomer of the thermoplastic polymer is selected from the group consisting of methyl acrylate, ethyl acrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, 2-ethylhexyl methacrylate, 2-ethylhexyl vinyl ether, benzyl acrylate, acrylic acid, acrylic amine, (hydroxyethyl)methacrylate, 2-hydroxyethyl methacrylate, allyl cyclohexanepropionate, ethylene glycol phenyl ether acrylate, ethylene glycol phenyl ether methacrylate, benzyl methacrylate, 2-hydroxyethyl acrylate, butyl acrylate, sec-Butyl acrylate, tert-Butyl acrylate, butyl glydicyl ether, butyl methacrylate, 2-cyanoethyl acrylate, glycerol monomethacrylate, cyclohexyl acrylate, isobutyl acrylate, isobutyl vinyl ether, isopropyl acrylate, 2-methoxyethyl acrylate, methyl glycidyl ether, methyl vinyl ether, dimethylaminoethyl methacrylate, dodecyl acrylate, dodecyl methacrylate, dodecyl vinyl ether, 2-ethoxyethyl acrylate, ethylene malonate, 2-ethylhexyl vinyl ether, ethyl vinyl ether, hexadecyl methacrylate, hexyl acrylate, hexyl methacrylate, propyl vinyl ether, 2,2,2-trifluoroethyl acrylate, vinyl propionate, butyl glycidyl ether, l,2-epoxy-3- phenoxypropane, glycidyl 2-methylphenyl ether, benzyl glycidyl ether, glycidyl benzyl ether, glycidyl methyl ether, glycidol, 2,3 -epoxy- 1-(1 -ethoxy ethoxy )propane, 3,4-epoxy- 2-phenyl-l,l,l-trifluoro-2-butanol, mixtures and combinations thereof. The polymerizable composition according to claim 3 or 4, wherein the monomers of the thermoplastic polymer are 2-hydroxyethyl acrylate and acrylic amine. The polymerizable composition according to any one of claims 1 to 5, wherein the amount of the at least one monomer of the thermoplastic polymer is in the range of 5 wt% to 70 wt%, based on the weight of the polymerizable composition. The polymerizable composition according to any one of claims 1 to 6, wherein the monomer of the thermosetting resin is selected from a (meth)acrylate/epoxy resin monomer and/or an oligomer selected from the group consisting of bisphenol A dimethacrylate (Bis-DMA), bisphenol A diglycidyl ether methacrylate (Bis-GMA), ethoxylated bisphenol-A dimethacrylate (Bis-EMA), tricyclo[5.2.1.02,6]decanedimethanol diacrylate, bisphenol A glycerolate diacrylate, bisphenol A ethoxylate diacrylate, bisphenol A ethoxylate dimethacrylate (oligo), bisphenol F ethoxylate diacrylate (oligo), bis(4-hydroxyphenyl)dimethylmethane diglycidyl ether, polyisocyanate acrylate, urethane acrylate oligomers, branched hexafunctional aliphatic urethane acrylate, DER332, bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, di(trimethylolpropane) tetraacrylate, pentaerythritol triacrylate, 1,3,5- triacryloylhexahydro-l,3,5-triazine, trimethylolpropane propoxylate triacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, di(trimethylolpropane)tetraacrylate, pentaerythritol tetraacrylate, , vinyl T-structure polymers, methacryloxypropyl T-structure Siloxanes, methacryl polyhedral oligomeric silsesquioxane (POSS) cage mixture, methacrylethyl polyhedral oligomeric silsesquioxane, trimethylolpropane triglycidyl ether, tris(4- hydroxyphenyl)methane triglycidyl ether, monophenyl functional tris(epoxy terminated poly dimethylsiloxane), epoxycyclohexyl polyhedral oligomeric silsesquioxane cage mixture, triglycidyllsobutyl polyhedral oligomeric silsesquioxane, glycidyl polyhedral oligomeric silsesquioxane cage, mixtures or combinations thereof. The polymerizable composition according to any one of claims 1 to 7, wherein the monomer of the thermosetting resin is urethane acrylate oligomers. The polymerizable composition according to any one of claims 1 to 8, wherein the thermosetting resin further comprises a diluent resin selected from the group consisting of ethyl acetate and 1,6-hexanediol diacrylate, phenylglycidyl ether, butylglycidyl ether, allylgylcidyl ether, butanediol diglycidyl ether, and combinations thereof. The polymerizable composition according to any one of claims 1 to 9, wherein the amount of the monomer of the thermosetting resin is in the range of 30 wt% to 95 wt%, based on the weight of the polymerizable composition. A method of preparing a polymerizable composition comprising the steps of:

(a) mixing at least one monomer of a thermoplastic polymer and at least one monomer of a thermosetting resin, and

(b) optionally mixing an initiator to the mixture of step (a). The method of claim 11, wherein the mixing step (a) and the mixing step (b) is independently carried out under agitation for a time duration in the range of 1 to 4 hours. A method of forming a three-dimensional printed article comprising the steps of:

(a) printing a polymerizable composition comprising at least one monomer of a thermoplastic polymer, at least one monomer of a thermosetting resin and an initiator via three-dimensional printing to form a three-dimensional printed article; and

(b) curing the printed article, wherein the printing step (a) is before or simultaneous with the curing step (b). The method according to claim 13, wherein the printing step (a) comprises the steps of:

(al) washing the printed article with a suitable solvent; and

(a2) air-drying the printed article, before the curing step (b). The method according to claim 13 or 14, wherein the curing step (b) comprises the step of subjecting the printed article to photo- polymerization to polymerize both the monomer(s) of the thermoplastic polymer and the monomer(s) of the thermosetting resin. The method according to claim 15, wherein: the curing step (b) comprises the step of applying ultra-violet light irradiation to initiate the photo-polymerization, wherein the radiation power is applied in the range of 2 mW/cm² to 100 mW/cm² for a duration in the range of 3 seconds to 60 seconds. The method according to claim 13 further comprising the step of:

(c) adding a plurality of hydroxyapatite nanoparticles to the polymerizable composition before printing step (a). The method according to claim 17, wherein the hydroxyapatite nanoparticles comprise: ceramic materials selected from silica, alumina, titania, zirconia, zirconium phosphates, or any combination thereof; cellulose fibers selected from hemp, linen, cotton, ramie, sisa, or any combinations thereof; or clay selected from montmorillonite, bentonite, laponite, kaolinite, saponite, vermiculite or any combination thereof. A three-dimensional printed article comprising a plurality of thermoplastic structures embedded within a thermosetting resin, wherein the thermoplastic structures are comprised of monomers of a thermoplastic polymer. The three-dimensional printed article according to claim 19, wherein the thermoplastic structures are nanometer sized or micrometer sized in the form of a fiber, a rod, a sheet, a particle or a sheet-like structure.

21. The three-dimensional printed article according to claim 19 or 20, wherein the dimension of the thermoplastic structures is in the range of 10 nm to 500 pm.