Squaraine DYES based photocatalysts for preparation of polymers

Abstract

The present invention relates to photocatalysts of formula I for controlled radical polymerization including photoinduced electron transfer-reversible addition-fragmentation chain transfer PET-RAFT polymerization. The present invention also discloses a process of preparation of polymers including copolymers, block copolymers, homopolymers and / or related polymers / copolymers where two or more monomers are reacted in presence of said a squaraine dye based photocatalyst of formula I, chain transfer agent (CTA), and light source, and optionally in presence of a catalyst activator in both batch and flow modes. The process of the present invention significantly reduces the induction period in the photocatalyzed controlled radical polymerization and also affords shorter reaction time of photocatalyzed controlled radical polymerization.

Description

[0001] P_W0100777

[0002] SQUARAINE DYES BASED PHOTOCATALYSTS FOR PREPARATION OF POLYMERS

[0003] FIELD OF THE INVENTION

[0004] The present invention relates to organic photocatalysts. Specifically, the present invention relates to an organic photocatalyst of formula I based on squaraine dye moiety, and a process of preparation thereof. Additionally, the present invention relates to a process of preparation of polymers using said organic photocatalyst of formula I via controlled radical polymerization technique such as photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization.

[0005] BACKGROUND OF THE INVENTION

[0006] Synthesis of functional polymers has been an important research goal in the polymer science and industry related thereto. There is a continuing effort in polymer chemistry to develop polymers that exhibit macro functionality or to develop new functional polymers that possess specific chemical reactivity. These developments would extend the level of control available to material engineers in processing polymers and using polymers as building blocks in, or components for, subsequent material forming reactions, such as copolymerization, chain extension and crosslinking reactions, and interaction with substrates, including dispersed solids. To be commercially useful, it is preferred that the reactants utilized are readily available, low-cost monomers and produce materials which are reactive during separate operations or during fabrication, for example, by reaction injection molding, compounding or alloying, and other processes to form coatings, fibers, films, composite structures or bulk articles, with modifiable and controllable desirable properties.

[0007] Controlled radical polymerization (CRP) process, also referred to as reversible-deactivation radical polymerization (RDRP), grants the ability to regulate molecular weight, dispersity (£)), composition, architecture, and end-group fidelity of vinyl polymers. Currently, numerous CRP techniques are available, atom transfer radical polymerization (ATRP), nitroxide- mediated polymerization (NMP), and reversible addition-fragmentation chain-transfer (RAFT) polymerization. Importantly, polymers synthesized by CRP find use as emulsifiers, dispersants, electrolytes, rheology, and surface modifiers and are applied in commercial products related to home care, beauty, health, paint, energy, and electronics. Among these, the ATRP and RAFT polymerizations remain the most widely studied methods however conventional RAFT technique requires high temperature conditions which is not P_W0100777 preferable. To overcome this limitation, photoinduced electron transfer-reversible additionfragmentation chain transfer (PET-RAFT) polymerization technique is known in the art which uses visible light at ambient temperature conditions, in order to synthesize functional polymers of the controlled molecular weight.

[0008] The PET-RAFT processes are conventionally carried out with different photocatalysts e.g. transition metal complexes such as [Ru(II)(bpy)3], [Ir(ppy)3], and ZnTPP, which possess remarkable attributes, including strong light absorption capabilities, extended excited state lifetimes, and remarkable stability. However, these complexes require higher reaction time, multiple steps, and also remain in the final product polymer, hence, are not desirable for high end / biomedical applications. Also, these transition metal complexes suffer from certain limitations, including their relatively high cost, potential toxicity, which may hamper their widespread adoption and contamination. There are very few examples of organic dye molecules as photocatalysts known in the art for PET-RAFT polymerization e.g. naturally derived photocatalysts such as bacteriochlorophyll a & chlorophyll a, and aggregation- induced emission luminogen (refer, Xu, J. et al., J. Am. Chem. Soc., 2016, 138 (9), pages 3094-3106; and Li, Z. et al., Macromolecules, 2022, 55, 7, pages 2904-2910) and synthetic dyes such as Eosin Y and 4,7-di-(2-thienyl)-2,l,3- benzothiadiazole (DTBT). However, these reported organic dyes are also not preferable due to tedious and time-consuming process steps. Alternative to said metal complexes and dyes, organo-photocatalysts have emerged as a promising alternative to their metallic counterparts, as they offer several advantages, such as lower costs, widespread availability and reduced toxicity. The article Squaraines as NearInfrared. Photocatalysts for Organic Reaction, Sellet et. al., Chem. Commun., 2022,58, 13759-13762, documents the research done on squaraine derivatives as new organic nearinfrared photocatalysts. However, the document is focused on near infrared wavelengths of > 750nm, that have lower energy to promote organic transformation. The document does not directly address the problems of shorter wavelengths during photocatalysis which lead to selectivity issues, formation of by-products and also have reduced penetration into the medium that can affect the scalability of the reaction. Furthermore, the process requires stringent conditions and parameters.

[0009] In other disclosures such as in W02000058405A2 and in “ Recent advances on squaraine- based photoinitiators of polymerization, Giacoletto et.al, European Polymer Journal 150 (2021) 110427, squaraine dyes have been explored for applications such as optical detection and imaging, and photo initiators but not as a photocatalyst for polymerization. Recently, the field of photopolymerization has undergone a renaissance with the development of P_W0100777 photocatalytic systems enabling the content of photoinitiators in the photocurable resins to be drastically reduced, allowing the polymerization speed to increase and higher conversion yields.

[0010] Photopolymerization may be induced by a photoinitiator (PI) or a Photo Initiating System (PIS) which, under irradiation, generates active species initiating the polymerization according to a radical or a cationic mechanism. Meanwhile a photocatalyst must have at least one photosensitive function, a chromophore, to absorb the light (photons) and consequently to convert the light to active species (such as radical and cations) and thereby initiating a polymerization reaction. Three properties of photocatalysts, i.e. light absorption, redox potentials and long lifetime of excited states, are decisive for the efficiency of the photopolymerization process. Also, such complete conversion using reported organic photocatalysts requires long time ranging from 12-60 h accompanied with induction period of several hours.

[0011] Thus, there is a need to develop new organic photocatalysts in order to improve controlled radical polymerization processes for preparing functionalized materials / polymers, and those which work efficiently over the entire visible spectrum, possess negligible or lesser (e.g. less than 1 hour) induction period with a shorter polymerization time.

[0012] OBJECTIVES OF THE INVENTION

[0013] An object of the present invention is to provide photocatalysts for controlled radical polymerization.

[0014] Another object of the present invention is to provide a process of preparation of functionalized materials / polymers using an organic photocatalyst via controlled radical polymerization.

[0015] It is yet another object of the present invention to provide for a combination of the photocatalyst with a chain transfer agent for controlled radical polymerization of monomers to obtain functionalized materials / polymers.

[0016] Another object of the present invention is to provide organic photocatalysts, which can significantly reduce or eliminate the induction period in the controlled radical polymerization as compared to the reported photocatalysts.

[0017] Another object of the present invention is to provide photocatalysts to catalyze PET-RAFT polymerization reactions under visible light.

[0018] SUMMARY OF THE INVENTION

[0019] In an aspect, the present invention relates to a process of preparing polymers, comprising a P_W0100777 step of: reacting one or more monomers in presence of a photocatalyst of formula I wherein:

[0020] R1 is selected from H, C1-C8 alkyl and C4-C6 aryl;

[0021] R2 is selected from O or C(CN)2;

[0022] R3 is selected from

[0023] R4, R5, R7, R8 and R9 are independently selected from H, C1-C6 alkyl and C1-C12 alkoxy; and

[0024] R6 is selected from H, C1-C6 alkyl, -COOH, -SO3H, -PO3H, hydroxyl, C4-C8 aryl and Cl- C12 alkoxy; a chain transfer agent (CTA) and a solvent in the presence of a light source.

[0025] In an embodiment the process of preparing polymers utilizes the photocatalysts as per Formula I of the present invention such as

[0026] In an embodiment the present invention provides for a combination of the photocatalyst of Formula 1 with a chain transfer agent (CTA) for controlled radical polymerization of monomers to obtain polymers.

[0027] In an embodiment the process of preparing polymers comprises the monomers, chain transfer P_W0100777 agent and the photocatalyst in a ratio of the amounts in the range of 20-1000: 1: 0.015-0.030.

[0028] In another aspect the process of preparing polymers is controlled radical polymerization.

[0029] In yet another aspect the process of preparing polymers is PET-RAFT polymerization reactions under visible region of the spectrum.

[0030] BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 displays schematic 2D representation of photo flow reactor setup for polymerization under blue, green or red light (continuous flow mode).

[0032] Figure 2 displays schematic 3D representation of the flow reactor setup of reaction chamber for polymerization under blue, green or red light (continuous flow mode).

[0033] Figure 3 shows A) Normalized absorption spectra of ASQH (black) and ASQMe (red) in CH2CI2; and B) Normalized fluorescence emissionspectra of ASQH (black) and ASQMe (red) in CH2CI2.

[0034] Figure 4 shows the fluorescence spectra and Stem- Volmer plot for the fluorescence quenching of photo-excited catalyst ASQH by CTA.

[0035] Figure 5 shows the fluorescence spectra and Stem- Volmer plot for the fluorescence quenching of catalyst ASQMe by CTA.

[0036] Figure 6a and 6b shows the cyclic voltammograms of catalysts ASQH and ASQMe, INSQ and Cis-INSQ.

[0037] Figure 7 shows the absorption spectra of catalysts of the present invention at various concentrations (left), Beer-Lambert plots (right) of catalysts ASQH and ASQMe in DMSO solutions (quartz cuvette of 1.0 cm path length).

[0038] Figure 8 displays thekinetics plot of PET-RAFT polymerization by using ASQH as photocatalysts in DMSO with CPADB as thiocarbonyl compound, where (A) covers homopolymers (with ratio of M: CTA: Photocatalyst is 50: 1:0.022), and DP is calculated by1H NMR; and (B) covers PMMA homopolymer (with ratio of M: CTA: PC is 200: 1:0.022). Figure 9 shows the effect of catalyst loading and temporal control in the polymerization process, where A) shows influence of catalyst ASQH on monomer conversion (M: CTA: Photocatalyst = 50: 1:0 to 0.09); and B) shows the plot of DP vs. time (h) for the conversion of MMA in the shining (“ON”) and dark (“OFF”) of blue light (M: CTA: Photocatalyst = 50: 1:0.022). P_W0100777

[0039] Figure 10 shows the GPC chromatograms of (A) homopolymers synthesized in the presence of ASQH; (B) homopolymers synthesized in the presence of ASQMe;(C) PFMA synthesized by using ASQH and ASQMe; D) Block copolymers; E) Random copolymers; F) PMMA by flow technique with targeted Mn 20000 g / mol at different flow rates; and G) PMMA by flow technique with targeted Mn 5000 g / mol at different flow rates.

[0040] Figure 11 shows quenching of the self-aggregation of photocatalysts with use of ratio of components MMA: CTA: ASQH:Et3N = 50:1:0.022: 0 to 100 eq.;where (A) shows absorption spectroscopy of self-aggregation vs triethyl amine; (B) shows degree of polymerization vs addition of triethyl amine; (C) shows quenching of the self-aggregations of ZnTPP by using the TEA; (D) shows quenching of the self-aggregations of Eosin Y by using the TEA;(E) shows quenching of the self-aggregations of ASQMe by using the TEA;(F) shows quenching of the self-aggregations of Nile Red by using the TEA; and (G) shows quenching of the selfaggregations of Fluorescein by using the TEA. This figure confirms that there is no selfaggregation considering the broad absorption peak of ASQH and ASQMe in presence of catalyst activator.

[0041] ABBREVIATIONS:

[0042] ASQH: Catalyst of formula I or catalyst 1: (Z)-3-oxo-4-(phenyliminio)-2-(((Z)-l,3,3- trimethylindolin-2-ylidene)methyl)cyclobut- 1 -en- 1 -olate.

[0043] ASQMe: Catalyst of formula I or catalyst 2: (Z)-4-(methyl(phenyl)iminio)-3-oxo-2-(((Z)- 1 ,3 ,3 -trimethylindolin-2-ylidene)methyl)cy clobut- 1 -en- 1 -olate.

[0044] Cis-INSQ: Catalyst of formula I or catalyst 3: (Z)-3-(dicyanomethylene)-4-((l,3,3-trimethyl- 3H-indol-l-ium-2-yl)methylene)-2-(((E)-l,3,3-trimethylindolin-2-ylidene)methyl)cyclobut- 1-en-l -olate.

[0045] TEA: Triethyl amine.

[0046] ZnTPP: Zinc tetraphenylporphyrin.

[0047] MMA: methyl methacrylate.

[0048] PMMA: Poly (methyl methacrylate).

[0049] FMA: furfuryl methacrylate.

[0050] PFMA: Poly(Furfuryl methacrylate).

[0051] Macro-RAFT agent: chain transfer agent (CTA).

[0052] GMA: Glycidyl methacrylate.

[0053] PGMA: Poly(glycidyl methacrylate).

[0054] HMA: Hexyl methacrylate. P_W0100777

[0055] PHMA: Poly (hexyl methacrylate).

[0056] HEMA: Hydroxy ethylmethacrylate.

[0057] PHEMA: Poly(hydroxyethylmethacrylate).

[0058] DEAEMA: Diethylaminoethyl methacrylate.

[0059] PDEAEMA: Poly (diethylaminoethyl methacrylate).

[0060] HBA: Hydroxybutyl Acrylate.

[0061] PHBA: Poly(hydroxybutyl Acrylate).

[0062] AMMA: Anthrylmethyl methacrylate.

[0063] PAMMA: Poly(anthrylmethyl methacrylate).

[0064] NIPAM: N-Isopropylacrylamide.

[0065] PNIPAM: Poly (N-Isopropylacrylamide) .

[0066] MBL :a- Methylene -y-Butyrolactone.

[0067] PMBL: Poly (a-Methylene-y-Butyrolactone).

[0068] DPAEMA: Diisopropyl amino ethyl methacrylate.

[0069] PDPAEMA: Poly (Diisopropyl amino ethyl methacrylate).

[0070] TBAEMA: Tert-butyl aminoethyl methacrylate.

[0071] PTBAEMA: Poly (tert-butyl aminoethyl methacrylate).

[0072] DMAEMA: Dimethyl amino ethyl methacrylate.

[0073] PDMAEMA: Poly (Dimethyl amino ethyl methacrylate).

[0074] TMAEMA.C1: Trimethyl amino ethyl methacrylate chloride.

[0075] PTMAEMA.C1: Poly (Trimethyl amino ethyl methacrylate chloride).

[0076] AEMA.HCL: Amino ethyl methacrylate hydrochloric acid.

[0077] PAEMA.HCL: Poly (amino ethyl methacrylate hydrochloric acid).

[0078] BSTP: 3-[[(Benzylthio)carbonothioyl]thio]propionic Acid

[0079] CDB: Cumyl Dithiobenzoate

[0080] CDTPA: 4-Cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid

[0081] CPADB: 4-Cyano-4-(phenylcarbonothioylthio)pentanoic acid

[0082] DBTC: dibenzyl trithiocarbonate

[0083] DDMAT: 2-(Dodecylthiocarbonothioylthio)-2-methylpropionic acid

[0084] DETAILED DESCRIPTION OF THE INVENTION

[0085] The term “homopolymer” is a polymer that has the same monomer unit in the chain. The term “copolymer” is a polymer that has the different monomer units in the chain. The term “block copolymer” is a polymer that is made up of blocks of different polymerized monomers. For P_W0100777 example, polystyrene-b-poly(methyl methacrylate) or PS-b-PMMA (where b = block) is usually made by first polymerizing styrene, and then subsequently polymerizing methyl methacrylate (MMA) from the reactive end of the polystyrene chains.

[0086] The term “random co-polymer” is a type of polymer made of multiple types of monomer units arranged together in a random manner.

[0087] The term “functionalized materials” relate to polymers with controlled molecular weight, low dispersity, defined architectures, and end-group fidelity. These macromolecules have unique properties or uses that are determined by the presence of chemical functional groups dissimilar to those of the backbone chains. Functionalized materials include polymers with narrow molecular weight distributions, such that they enable the synthesis of specialized structured polymers including block copolymers, random copolymers, homopolymers, star shaped polymers, hyperbranched polymers, graft polymers, and bottlebrush polymers.

[0088] The term “polymers” or “functionalized polymers” include polymers such as but not limited to block copolymers, random copolymers, homopolymers, star shaped polymers, hyperbranched polymers, graft polymers, and bottlebrush polymers.

[0089] The term “photocatalyst” refers to materials that convert light energy into chemical energy by absorbing photons. Commonly, photocatalysis is a process that involves the absorption of light by a catalyst to initiate and boosting up chemical reactions

[0090] The term “induction time” is the initial slow phase of a chemical reaction which later accelerates. Induction periods are often observed with radical reactions, but they may also occur in other systems.

[0091] The term “chain transfer agents” are moieties that react with a growing polymer radical, causing the growing chain to terminate while creating a new reactive species capable of initiating polymerization. Chain transfer agents are useful for controlling the molecular weights of polymers, for reducing gelation when polymerizations and copolymerization involving diene monomers are conducted, and for preparing polymers and copolymers with useful chemical functionality at their chain ends.

[0092] In an aspect, the present invention relates to photocatalysts of Formula I, that significantly enhance the controlled radical polymerization reactions wherein Formula I is defined as P_W0100777 wherein:

[0093] R1 is selected from H, C1-C8 alkyl and C4-C6 aryl;

[0094] R2 is selected from

[0095] R3 is selected from R4, R5, R7, R8 and R9 are independently selected from H, C1-C6 alkyl and C1-C12 alkoxy; and R6 is selected from H, C1-C6 alkyl, -COOH, -SO3H, -PO3H, hydroxyl, C4-C8 aryl and C1-C12 alkoxy.

[0096] In an embodiment, the photocatalyst of Formula I wherein R3 is

[0097] In another embodiment, the photocatalyst of Formula I wherein R2 is

[0098] Preferably, the photocatalyst as per Formula I of the present invention is In an embodiment, the compound(s) of formula (I) are stable for about 2 years at the temperature ranging from 20-40 °C.

[0099] In an aspect the present invention relates to a process of preparing polymers comprising the steps of reacting one or more monomers in the presence of a photocatalyst of formula I P_W0100777 wherein:

[0100] R1 is selected from H, C1-C8 alkyl and C4-C6 aryl;

[0101] R2 is selected from

[0102] R3 is selected from

[0103] R4, R5, R7, R8 and R9 are independently selected from H, C1-C6 alkyl and C1-C12 alkoxy; and

[0104] R6 is selected from H, C1-C6 alkyl, -COOH, -SO3H, -P03H, hydroxyl, C4-C8 aryl and Cl- C12 alkoxy; a chain transfer agent (CTA) and a solvent in the presence of a light source.

[0105] In an embodiment, the present invention relates to a process of controlled radical polymerization which is photocatalyzed by the compounds of Formula I.

[0106] In another embodiment, the present invention also relates to a process of controlled radical polymerization for preparing polymers in the presence of a combination of the photocatalysts of Formula I and chain transfer agents. It has been surprisingly found that the combination of a photocatalyst of Formula I and a chain transfer agent in the process of preparing polymers of the present invention, reduces the induction time for the said polymerization process significantly. The induction time is at the initial stages of a polymerization reaction when the rate of active species generation (initiation) is slow, leading to a period of minimal polymerization before the dynamic equilibrium of active and dormant species is established and controlled polymerization begins. Induction time is influenced by the rate of activation of the catalyst and is a necessary phase where the initiating species are formed until the controlled, steady-state concentration of active radicals is reached. This low concentration of active radicals is crucial for minimizing termination and achieving molecular weight control Figures 4 and 5 shows that in a polymerization reaction with ASQH and ASQMe respectively, electron transfer from photocatalyst to chain transfer agent (CT A) has been successful leading P_W0100777 to fluorescence quenching thereby establishing the occurrence of catalytic activity. Still further, as reflected in Figure 6a and 6b, cyclic voltammogram quantitatively gives the energy levels of dyes and CTA, which helps to confirm the electron transfer from dye to CTA. CVs of INSQ, Cis-INSQ, ASQH and ASQMe are shown in Figure 6a and 6b.

[0107] In an embodiment, the combination of a photocatalyst of Formula I and a chain transfer agent reduces the induction time required in controlled radical polymerization reactions. Preferably, the induction time as per the process of the present invention is about a few minutes, preferably it is 0-10 minutes. More preferably, the induction time is about 5 minutes.

[0108] In an embodiment, the process of preparing polymers by controlled radical polymerization (CRP) as per the present invention comprises the step of: reacting one or more monomers in the presence of a photocatalyst of formula I wherein:

[0109] R1 is selected from H, C1-C8 alkyl and C4-C6 aryl;

[0110] R2 is selected from

[0111] R3 is selected from

[0112] R4, R5, R7, R8 and R9 are independently selected from H, C1-C6 alkyl and C1-C12 alkoxy; and

[0113] R6 is selected from H, C1-C6 alkyl, -COOH, -SO3H, -PO3H, hydroxyl, C4-C8 aryl and Cl- C12 alkoxy; a chain transfer agent (CTA) and a solvent in the presence of a light source.

[0114] In a further embodiment, the process of preparing polymers by PET-RAFT polymerization as per the present invention comprises the steps of: reacting one or more monomers in the presence of a photocatalyst of formula I P_W0100777 wherein:

[0115] R1 is selected from H, C1-C8 alkyl and C4-C6 aryl;

[0116] R2 is selected from

[0117] R3 is selected from

[0118] R4, R5, R7, R8 and R9 are independently selected from H, C1-C6 alkyl and C1-C12 alkoxy; and

[0119] R6 is selected from H, C1-C6 alkyl, -COOH, -SO3H, -PO3H, hydroxyl, C4-C8 aryl and Cl- C12 alkoxy; a chain transfer agent (CTA) and a solvent in the presence of a light source.

[0120] In a further embodiment, the photocatalysts of Formula I catalyze PET-RAFT polymerization reactions under visible light. In an embodiment, the PET-RAFT polymerization proceeds successfully under red light or blue light.

[0121] The one or more monomer as per the present invention is / are selected from but not limited to molecules of acrylates, amides and styrene. The acrylate(s) is / are selected from but not limited to methyl methacrylate, furfuryl methacrylate, glycidyl methacrylate, hexyl methacrylate, 2- hydroxyethylmethacrylate, diethylaminoethyl methacrylate, hydroxybutyl acrylate, anthrylmethyl methacrylate, N-isopropylacrylamide, N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethyl methacrylate, N,N-diisopropylaminoethyl methacrylate, Boc-phenyl alanine methacrylate and N-Boc-O-TBDMS serine methacrylate.

[0122] In an embodiment, the monomers may also be selected from the following: P_W0100777

[0123] In an embodiment the photocatalyst of formula I is selected from but not limited to catalyst 1 (ASQH), catalyst 2 (ASQMe), catalyst 3 (cis-INSQ), catalyst 4 (INSQ), the same are represented by:

[0124] ASQH ASQME cis-INSQ INSQ.

[0125] Chain transfer agents are critical for effecting the chain transfer in polymerization reactions. Since chain transfer may alter the molecular weight of the polymers adversely, controlled chain transfer via chain transfer agents may be required to control the molecular wight at a desired level. The chain transfer agents in the process of the present invention are selected from but not limited to 4-cyano- 4(phenylcarbonothioylthio)pentanoic acid (CPADB), 4-cyano-4

[0126] [(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid (CDTPA), 2-menthyl-2 (tridecanethioylthio)propanoic acid), 2-phenylpropan-2-yl benzodithioate, 2-cyanoprop-2-yl-l- dithionaphthalate, 2 -butyltrithiocarbonate -propionic acid, 3- [[(Benzylthio)carbonothioyl]thio]propionic Acid (BSTP), cumyl dithiobenzoate (CDB), dibenzyl trithiocarbonate (DBTC), 2-(Dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT). P_W0100777

[0127] In an embodiment, the process of preparing polymers as per the present invention comprises reacting the monomers, chain transfer agent and the photocatalyst wherein the mole ratio of the amounts of the said monomers, chain transfer agent and the photocatalyst is in the range of 20-1000: 1: 0.015-0.030. Preferably the mole ratio is 50: 1:0.022.

[0128] Solvents serve diverse roles in the process of the present invention. They function to solubilize monomers and polymers, maintain a homogeneous mixture, facilitate heat transfer, and influence activation rate constants, which is critical in controlling polymer chain growth. The solvents for the controlled radical polymerization are selected from but not limited to DMSO, methanol, ethanol, DMF, and 1, 4-dioxanealone or in a combination thereof. Preferably the solvent is DMSO. In an embodiment for aqueous conditions DMSO:Water is in the ratio of 40:60.

[0129] The process of preparing polymers as per the present invention comprises exposing the reaction mixture to a light source. The light source is selected from but not limited to blue LED light, red LED light and green LED light. The blue LED light has a wavelength in the range of 450 and 495 nm, the green LED light has a wavelength in the range of 520 and 620nm and the red LED light has a wavelength in the range of 620 to 750 nm.

[0130] The process of preparing polymers as per the present invention optionally includes the introduction of a catalyst activator. The catalyst activator is selected from a group but not limited tertiary amine including triethyl amine, trimethyl amine, triisopropyl amine, triisobutyl amine, triisopentyl amine, and diazabicyclo[2.2.2]octane (DABCO) or 1,8- Diazabicyclo[5.4.0]undec-7-ene (DBU). Preferably, the catalyst activator is triethyl amine. The induction period when triethyl amine is used is significantly reduced to only few minutes in the present case as compared to the other reported photocatalysts which still need more than 1 h for activation. In an embodiment, quenching or suppression of aggregation of the photocatalyst is required for its activation towards polymerization. In the presence of catalyst activator such as triethylamine, for ASQH catalysed polymerization, induction period is eliminated, and reaction time is reduced.

[0131] This is reflected in Figure 11.

[0132] In another embodiment, the mole ratio of one or more monomers: CTA: catalyst of formula I: catalyst activator is in the range of 20-1000: 1:0.015-0.030:0.1-100. Preferably, the mole ratio is 1000: 1:0.015: 1

[0133] The process of preparing polymers as per the present invention is performed at a room temperature in the range of 15-30 °C in the presence light of desired wavelength in glass vial or Teflon tube. The time taken for the process of preparing polymers is in the range of 1.5 - 8 P_W0100777 hours. The said process can be performed in a batch mode and / or in a continuous flow mode. In another embodiment, the process of preparing polymers as per the present invention is done in presence or absence of oxygen.

[0134] The present invention thus provides for a process of preparing polymers by a process wherein the polymerization time is significantly shorter than the conventional processes due to the presence of photocatalysts of Formula I. The novel photocatalysts are based on squaraine dyes and have surprisingly been found to be effective as photocatalysts in controlled radical polymerization reactions. The present invention successfully leads to 100% conversion of monomers into functionalized materials / polymers with a negligible induction time.

[0135] EXAMPLES

[0136] Example 1: Example 1: Synthesis of photocatalysts of the present invention.

[0137] Required precursors for the synthesis of ASQ dyes of (ASQH, ASQMe and Cis -INS Q); precursors (compounds) 1 and 4 were synthesized by following the procedure present in the literature (ACS Appl. Energy Mater.2021, 4, 3182-3193, and ACS Appl. Mater. Interfaces 2018, 10, 1641-16551), and precursors (compounds) 2 and 5 are commercially available compounds.

[0138] 46, Cis-INSQ, 60%

[0139] Compound 1: (E)-3-hydroxy-4-((l,3,3-trimethylindolin-2-ylidene)methyl)cyclobut-3-ene- 1, 2-dione

[0140] Compound 2: N-methylaniline (R = Me) OR Aniline (R = H)

[0141] Compound 4: (E)-3-(dicyanomethylene)-4-oxo-2-((l,3,3-trimethylindolin-2- ylidene)methyl)cyclobut- 1 -en- 1 -olate P_W0100777

[0142] Compound 5: l,3,3-trimethyl-2-methyleneindoline

[0143] The compound 1 (1 equiv.) and aniline / N-methylaniline (1 equiv.) were dissolved in anhydrous anhydrous PhMe and n-butanol (1: 1, 10 mL of each) in a 50 mL round-bottom flask, charged with Dean-Stark apparatus and reflux under an inert atmosphere for 2 h. The reaction mixture was cooled and solvent were evaporated under reduced pressure. Further reaction mixture was purified by column chromatography (SiCh, 100-200 mesh, MeOH, and CH2CI2) to afford the required dye. Figure 7 enables the calculation of the molar extinction coefficient indicating the efficiency of the photocatalysts to absorb light.

[0144] Example 2: Synthesis of PET-RAFT polymerization in the presence of oxygen:

[0145] The polymerization process was carried out in a vial that had a rubber septum. The vial contained monomer (M), CPADB as CTA (Chain Transfer Agent) and ASQH as Photocatalyst (in a ratio of 50: 1:0.022) triethylamine used as catalyst activator. To dissolve the monomer (methyl methacrylate), DMSO was used as a solvent in a 1: 1 volume ratio with the monomer after that added few drops of triethylamine and then exposed to blue LED light (6 W, kmax = 490 nm) at room temperature. The monomer conversion and molecular weights were determined using1H NMR (CDCI3) (refer below), and ON-OFF comparison (refer, figure 9). For the kinetic study, the 0.1 mL sample was withdrawn by syringes from the reaction mixture after Ih. The monomer conversions and repeating unit (DP) i.e., degree of polymerization were analyzed by IH NMR (CDC13) (refer, figure 8). The figure 8 and 9 show that the polymerization is controlled, has minimal induction period and establishes the formation of block copolymers confirming the retention of active chain ends.

[0146] One significant advantage of PET-RAFT polymerization is the use of visible light as a stimulus to initiate and mediate the polymerization. Figure 3 shows the selection of wavelength of light used for polymerization in the present invention.

[0147] Table 1: Testing of the different photocatalysts as per the present invention for PET-RAFT polymerizations for various monomers under blue and red light in batch mode in presence of oxygen. P_W0100777

[0148] Characterization of synthesized homopolymers:

[0149] • The prepared polymer PMMA:1H NMR (CDC13) d: 7.78 (s, 2H), 3.59 (br. s., 139H), 3.29 (br. s., 60H), 2.79 (s, 11H), 2.44 (br. s., 14H), 1.79 (br. s., 67H), 0.99 (br. s., 52H), 0.80 (br. s., 81H).

[0150] • The prepared polymer PHMA:1H NMR (CDCI3) d: 7.85 (br. s., 2H), 7.51 (s, 1H), 7.35 (s, 2H), 3.93 (d, J = 5.8 Hz, 94H), 1.90 (br. s., 45H), 1.81 (br. s., 46H), 1.62 (br. s., 101H),

[0151] 1.32 (br. s., 22H), 1.26 (br. s., 47H), 1.03 (br. s., 45H), 0.67 - 0.97 (m, 224H).

[0152] • The prepared polymer PHEMA:1H NMR (METHANOL-d4) d: 7.80 (d, J = 7.6 Hz, 2H),

[0153] 7.48 (d, J = 7.6 Hz, 1H), 7.35 (d, J = 7.5 Hz, 2H), 4.78 (s, 198H), 3.96 (br. s., 160H), 3.70 (br. s., 169H), 3.17 - 3.27 (m, 27H), 1.88 (br. s., 138H), 1.03 (br. s., 96H), 0.86 (br. s., 137H).

[0154] • The prepared polymer PFMA: 1H NMR (CDCI3) d: 7.43 (s, 1H), 6.18 - 6.48 (m, 2H), 5.14 (s, 1H), 4.71 - 5.03 (m, 1H), 2.83 - 3.02 (m, 4H), 1.60 - 1.99 (m, 2H), 0.87 (br. s., 1H), 0.70 (br. s., 1H).

[0155] • The prepared polymer PEPMA: 1H NMR (CHLOROFORM-d) d: 7.01 (br. s., 1H), 6.86 (br. s., 2H), 3.66 - 3.86 (m, 51H), 3.21 (br. s., 52H), 2.68 (br. s., 163H), 1.38 (br. s., 60H),

[0156] 1.33 (br. s., 53H), 0.96 (br. s., 15H), 0.69 (br. s., 17H), 0.50 (br. s., 50H), 0.32 (br. s., 95H).

[0157] • The prepared polymer PDEA-EMA: 1H NMR (CHLOROFORM-d) d: 7.77 (br. s., 2H),

[0158] 7.49 (s, 1H), 7.29 (br. s., 2H), 3.91 (br. s., 100H), 3.16 (s, 208H), 1.85 (s, 67H), 1.72 (br. s., 46H), 0.88 - 1.17 (m, 253H), 0.80 (br. s., 101H). P_W0100777

[0159] Example 3: Synthesis of polymers via PET-RAFT polymerization in the absence of oxygen:

[0160] Polymerization process was carried out in a vial that had a rubber septum. The vial contained monomer (M), CTA, and ASQMe as Photocatalyst (in a ratio of 50: 1:0.022). To dissolve the monomer, DMSO was used as a solvent in a 1:1 volume ratio with the monomer. The reaction mixture in the vial was degassed for 30 minutes using argon and then exposed to blue / red LED light (6 W, km ax = 490 nm) at room temperature. The monomer conversion and molecular weights were determined using1H NMR (CDCL) (refer below), and GPC techniques (refer, figure 13). The representative figure for this process is covered broadly in figure 1.

[0161] Example 4: Synthesis of polymers with “ON-OFF” experiment by PET-RAFT polymerization :

[0162] The polymerization process was carried out in a vial that had a rubber septum. The vial contained monomer (M) [PHMA, PHEMA, PEPMA, PFMA], CTA (CPDB) and photocatalyst ASQH and Cis-INSQ (in a ratio of 50:1:0.022). To dissolve the monomer, DMSO was used as a solvent in a 1 : 1 volume ratio with the monomer. Vial covered with aluminum foil contains reaction solution was degassed for 30 minutes with Argon and then irradiated under a blue LED light (“On” state) or set in dark environment (“Off” state) at ambient temperature. Aliquots were withdrawn by syringes from the reaction mixture before and after irradiation, and then analyzed by1H NMR (CDCI3) (refer below), and GPC techniques (refer, figure 10). Figures 10a- 10g show controlled nature of polymerization and formation of block copolymers indicated by monomodal GPC chromatograms.

[0163] Example 5: Synthesis of block copolymer by PET-RAFT polymerization:

[0164] The vial has monomer (HEMA), dithioester- or trithiocarbonate-terminated poly(methyl methacrylate)PMMA polymeric-CTA (Mn =3900 Da and PDI=1.2), and photocatalyst ASQH and Cis-INSQ (in a ratio of 1000: 1:0.022). To dissolve the monomer, DMSO was used as a solvent in a 1: 1.2 volume ratio with the monomer. The vial covered with aluminum foil containing reaction solution was degassed for 30 minutes with argon and then irradiated under a blue LED light (6 W, kmax= 490 nm) at room temperature. The monomer conversions and molecular weights were analyzed by1H NMR (CDCI3) (refer below), and GPC techniques (refer, figure 10). The test results of the prepared block copolymers are covered in table 4 below.

[0165] Example 6: Synthesis of random copolymer via PET-RAFT polymerization:

[0166] The polymerization was conducted in vial equipped with a rubber septum. The vial comprised of MMA and HEMA, CTA (CPDB) and photocatalyst ASQH and Cis-INSQ (in a ratio of P_W0100777

[0167] 40:40: 1:0.022). To dissolve the monomer, DMSO was used as a solvent in a 1: 1.2 volume ratio with the monomer. Vial covered with aluminum foil contains reaction solution was degassed for 30 minutes with Argon and then irradiated under a blue LED light (6 W, km ax = 490 nm) at room temperature. The monomer conversions and molecular weights were analyzed by1H NMR (CDCL) (refer below), and GPC techniques (refer, figure 10). The test results of the prepared random copolymers are covered in table 4 below. The figure lOa-g show that the polymerization is controlled, has minimal induction period and establishes the formation of block copolymers confirming the retention of active chain ends.

[0168] Table 2: Molecular weight data for block or random copolymers of methyl methacrylate (MM A) with different monomers

[0169] Characterization of functionalized materials / polymers including synthesized block or random copolymers using the claimed catalysts:

[0170] • The prepared polymer ispoly(Boc-Ph alanyl acrylate): ’ H NMR (CHLOROFORM-d) d: 7.05 (s, 2H), 7.11 (s, 3H), 5.39 (br. s., 1H), 4.40 (br. s., 1H), 4.05 - 4.30 (m, 2H), 3.98 (br. s., 2H), 3.61 (br. s., 1H), 2.87 (d, J = 10.7 Hz, 4H), 1.60 - 1.94 (m, 2H), 1.09 - 1.45 (m, 10H), 0.88 - 1.03 (m, 1H), 0.62 - 0.88 (m, 2H).

[0171] • The prepared polymer is poly(Boc-isoleucine acrylate): 1H NMR (DMSO-d6) d: 7.81 (br. s., 2H), 7.63 (br. s., 1H), 7.46 (br. s., 2H), 6.94 (br. s., 19H), 6.89 (br. s., 15H), 4.28 (br. s., 31H), 4.23 (br. s., 44H), 4.03 - 4.17 (m, 79H), 3.96 (br. s., 33H), 1.87 (br. s., 51H), 1.77

[0172] (br. s., 59H), 1.32 - 1.44 (m, 139H), 1.12 - 1.25 (m, 53H), 0.99 (br. s., 33H), 0.84 (br. s., 51H). P_W0100777

[0173] • The prepared polymer is PMMA-b-PHMA: 1H NMR (CHLOROFORM-d) d: 7.89 (br. s., 2H), 7.52 (br. s., 1H), 7.36 (br. s., 2H), 6.10 (s, 4H), 5.55 (s, 3H), 4.14 (t, J = 6.7 Hz, 8H), 3.94 (br. s., 51H), 3.59 (br. s., 74H), 1.86 - 2.14 (m, 94H), 1.81 (br. s., 61H), 1.56 - 1.70 (m, 76H), 1.29 - 1.47 (m, 223H), 1.25 (br. s., 29H), 1.02 (br. s., 56H), 0.67 - 0.97 (m, 214H).

[0174] • The prepared polymer is PMMA-b-PFMA 1H NMR (CHLOROFORM-d) d: 3.99 (br. s., 83H), 3.59 (s, 119H), 2.41 - 2.83 (m, BOH), 1.80 (s, 88H), 1.88 (s, 64H), 1.24 (br. s., 63H), 0.92 - 1.12 (m, 129H), 0.83 (br. s., 144H).

[0175] • The prepared polymer is PMMA-b-PHEMA: 1H NMR (METHANOL-d4) d: 4.04 (br. s., 240H), 3.77 (br. s., 239H), 3.64 (br. s., 8H), 3.23 - 3.38 (m, 102H), 2.64 (s, 118H), 1.95 (br. s., 114H), 1.09 (br. s., 195H), 0.93 (br. s., 104H).

[0176] • The prepared polymer is PMMA-co-PHMA: 1H NMR (CHLOROFORM-d) d: 7.89 (br. s., 2H), 7.52 (br. s., 1H), 7.36 (br. s., 2H), 6.10 (s, 4H), 5.55 (s, 3H), 4.14 (t, J = 6.7 Hz, 8H), 3.94 (br. s., 51H), 3.59 (br. s., 74H), 1.86 - 2.14 (m, 94H), 1.81 (br. s., 61H), 1.56 - 1.70 (m, 76H), 1.29 - 1.47 (m, 223H), 1.25 (br. s., 29H), 1.02 (br. s., 56H), 0.67 - 0.97 (m, 214H).

[0177] • The prepared polymer is PMMA-co-PHEMA: 1H NMR (METHANOL-d4) d: 3.90 (br. s., 80H), 3.63 (br. s., 82H), 3.47 (br. s., 119H), 3.00 - 3.19 (m, 21H), 1.79 (br. s., 134H), 1.46 (br. s., 28H), 1.14 (d, J = 5.2 Hz, 34H), 0.93 (br. s., 77H), 0.75 (br. s., 129H).

[0178] • The prepared polymer is PMMA-co-PFMA: 1H NMR (CHLOROFORM-d) d: 7.43 (br. s., 40H), 6.27 - 6.50 (m, 77H), 5.14 (s, 8H), 4.95 (br. s., 69H), 3.57 (br. s., 86H), 1.95 (br. s., 48H), 1.79 (br. s., 78H), 0.91 (br. s., 77H), 0.75 (br. s., 116H).

[0179] Example 7: Synthesis of polymers via PET-RAFT polymerization in the absence of oxygen in red light

[0180] The polymerization process was carried out in a vial that had a rubber septum. The vial contained monomer (M= Boc-Phly- Acrylate and Boc-Iso-Acrylate), CTA, and Cis-INSQ as PC (in a ratio of 50: 1:0.022). To dissolve the monomer, DMSO was used as a solvent in a 1: 1 volume ratio with the monomer. The reaction mixture in the vial was degassed for 30 minutes using argon and then exposed to red LED light (6 W, Xmax = 690 nm) at room temperature. The monomer conversion and molecular weights were determined using1H NMR (CDCh) (refer above), and GPC techniques (refer, figure 10).

[0181] Example 8: Continuous (flow) homo polymer preparation via PET-RAFT polymerization P_W0100777

[0182] A typical procedure to synthesize PMMA homopolymers ([M]: [RAFT]: [EY]: [TEA] = 50 or 200: 1: 0.02: 1) in water (1: 1 volume of monomer), (M= MMA, CTA = CPADB, PC = ASQH) in DMSO:water (40:60) by aqueous RAFT photopolymerization was set up as follows. The solution was weighed into a vial with covered by aluminum foil and subsequently transferred to a 1 mL gastight SGE syringe that was covered by aluminum foil. A ImL tubular reactor was employed for the polymerization under illumination of blue / redlight (490 nm) with a residence time of 99 min (10uL-min-l flow rate). Monomer conversions were determined via 1H NMR and molecular weight distributions were analyzed via SEC. The reactor setup for the continuous flow mode of preparation of polymer is covered in figure 2 Table3: Synthesis of PMMA through Continuous Flow Technique

[0183] Example 9: Performance of reported organic photocatalysts under similar reaction conditions (CPADB as CTA and blue light) as for the present invention is shown in table 4.

[0184] Table 4. P_W0100777

[0185] ADVANTAGES OF THE INVENTION

[0186] • The invention provides novel photocatalysts of formula (I) for controlled radical polymerization including PET-RAFT polymerization.

[0187] • The present invention provides photocatalysts that significantly reduce or eliminate induction period in the photocatalyzed controlled radical polymerization as compared to reported Photocatalyst.

[0188] • The invention provides squaraine dye-based photocatalysts of formula I that afford shorter reaction time of photocatalyzed controlled radical polymerization as compared to reported photocatalysts.

[0189] • Polymers generated by controlled radical polymerization are used in many applications. Surface modification, commonly performed through ATRP, enables advancement in many applications which rely on tailored hydrophilicity, adhesive properties, or nanoparticle functionalization. Block copolymers for bio-applications, commonly performed through RAFT or ATRP, enable advancements in drug delivery, bio-mineralization, bio- compatibilization, and hydrogel applications. Block copolymers generated from NMP are used in pigment dispersion, memory devices, composite manufacturing, and many others.

Claims

P_W0100777We Claim:

1. A process of preparing polymers comprising the steps of: reacting one or more monomers in presence of a photocatalyst of formula I with a chain transfer agent and a solvent in the presence of a light source;wherein:R1 is selected from H, C1-C8 alkyl and C4-C6 aryl;R2 is selected from O or C(CN)2;R3 is selected fromR4, R5, R7, R8 and R9 are independently selected from H, C1-C6 alkyl and C1-C12 alkoxy; andR6 is selected from H, C1-C6 alkyl, -COOH, -SO3H, -PO3H, hydroxyl, C4-C8 aryl and Cl C12 alkoxy.

2. The process of preparing polymers as claimed in claim 1, wherein the photocatalyst is3. The process of preparing polymers as claimed in claim 1, wherein the monomers are selected from acrylates, amides, styrenes either alone or in a combination thereof.P_W01007774. The process of preparing polymers as claimed in claim 1 , wherein the chain transfer agent is selected from a group comprising 4-cyano-4(phenylcarbonothioylthio)pentanoic acid (CPADB), 4-cyano-4 [(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid (CDTPA), 2- menthyl-2 (tridecanethioylthio)propanoic acid), 2-phenylpropan-2-yl benzodithioate, 2- cyanoprop-2-yl-l-dithionaphthalate, 2-butyltrithiocarbonate -propionic acid, 3-[[(Benzylthio)carbonothioyl]thio]propionic Acid (BSTP), cumyl dithiobenzoate (CDB), dibenzyl trithiocarbonate (DBTC), 2-(Dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT).

5. The process of preparing polymers as claimed in claim 1, wherein the solvent is selected from a group comprising water, dimethyl sulfoxide methanol, ethanol, N,N-dimethyl formamide, 1, 4-dioxane either alone or in combination thereof.

6. The process of preparing polymers as claimed in claim 1, wherein the mole ratio of the amounts of the monomers, chain transfer agent and the photocatalyst is in the range of 20-1000: 1: 0.015-0.030.

7. The process of preparing polymers as claimed in claim 1, wherein the process is a controlled radical polymerization.

8. The process of preparing polymers as claimed in claim 1, wherein the process is a photoinduced electron transfer-reversible addition-fragmentation chain transfer polymerization9. The process of preparing polymers as claimed in claim 1, which optionally includes the introduction of a catalyst activator in the said process.

10. The process of preparing polymers as claimed in claim 9, wherein the catalyst activator is selected from a group comprising tertiary amine including triethyl amine, trimethyl amine, triisopropyl amine, triisobutyl amine, triisopentyl amine, and diazabicyclo[2.2.2]octane or l,8-Diazabicyclo[5.4.0]undec-7-ene.

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