WO2016137410A1

WO2016137410A1 - Method for preparing a molecularly imprinted polymeric system via radiation-induced raft polymerization

Info

Publication number: WO2016137410A1
Application number: PCT/TR2015/000068
Authority: WO
Inventors: Meshude AKBULUT SOYLEMEZ; Murat Barsbay; Olgun Guven
Original assignee: Akbulut Soylemez Meshude; Murat Barsbay; Olgun Guven
Priority date: 2015-02-24
Filing date: 2015-02-24
Publication date: 2016-09-01

Abstract

Present invention relates to a process for the preparation of molecularly imprinted polymer grafted onto the porous support material by gamma-initiated RAFT polymerization. Said gamma-initiated RAFT polymerization comprises dipping porous support material into a solution comprising a functional monomer, a crosslinking agent, a RAFT agent and a template molecule and polymerization of said solution under gamma irradiation.

Description

METHOD FOR PREPARING A MOLECULARLY IMPRINTED POLYMERIC SYSTEM VIA RADIATION-INDUCED RAFT POLYMERIZATION

Technical Field

Present invention relates to a process for the preparation of molecularly imprinted polymer grafted onto the porous support material via gamma-initiated RAFT polymerization. Said gamma-initiated RAFT polymerization comprises dipping porous support material into a solution comprising a functional monomer, a crosslinking agent, a RAFT agent and a template molecule and polymerization of said solution under gamma irradiation. Prior Art

Molecular imprinting is a useful tool for preparation of tailor made materials for specific recognition and separation of a wide range of template molecules such as drugs (Sellergren, 1994; Fischer et al., 1991), herbicides (Piletsky et al., 1995), carbohydrates (Kriz and Mosbach, 1995), amino acids (Kempe and Mosbach, 1994), proteins (Haupt, 2003), ions (Ren et al., 2008). This method basically includes polymerization of functional monomers around a certain template molecule in the presence of crosslinking agent. Removal of the template molecule leaves behind complementary binding sites in terms of size, shape and functionality in the polymeric network. These binding sites provide selectively specific recognition of the template molecule.

Molecular imprinting can be categorized due to interactions between functional monomer and template molecule as covaient and non-covalent imprinting. In covalent imprinting molecular interactions between functional monomer and template molecule are based on reversible covalent bonds such as acetals, ketals, Schiff bases, disulfide bonds, coordination bonds (Martin-Esteban, 2001). This method provides more homogeneous binding sites due to clear stoichiometry between template and functional monomer. However, there are some disadvantages of covalent imprinting. The main disadvantage is difficulty of this method. It practically cannot be used for every kind of template molecules. The removal of template molecule from final product is slowly and needs some chemical reaction steps. Non-covalent imprinting is easier than covalent one and it facilitates to imprint a wide range of template molecules, however this method causes heterogeneous binding sites (Umpleby et al., 2000; 2001) due to non-clear stoichiometric ratio between functional monomers and template molecule.

It is possible to design the shape of final product of molecular imprinting using different methods such as precipitation polymerization, sol-gel process, grafting of various surfaces like beads, filter membranes, fibres and fabrics. Traditional methods used for the preparation of molecularly imprinted polymers (MIPs) generally provide high affinity and selectivity. In order to improve capacity, accessibility and mass transfer for the target molecule traditional methods can be combined with novel controlled/living radical polymerization (CRP) techniques such as reversible addition-fragmentation chain transfer (RAFT) polymerization method. Among the CRP methods, reversible addition fragmentation chain transfer (RAFT) polymerization is of particular interest as a very wide range of (functional) monomers can be polymerized in a controlled manner under non- demanding reaction conditions (e.g., tolerance to oxygen and low temperatures) via this technique. Thiocarbonylthio compounds are used as chain transfer agents (CTA) during RAFT polymerization. RAFT technique is also is most successfully applied method among other CRP methods to grow well-controlled brushes from polymer surfaces to alter the surface properties of base materials in conjunction with radiation-induced grafting method (Barsbay and Guven 2009; 2013; Han and Pan 2006; Hua et al. 2005). The general mechanism of RAFT polymerization as proposed by the CSIRO group is shown in Scheme 1 :

(I) Initiation | «

( ) (3) m («i1v} s r>„» ^onom* »^f. P o_n*₊₁ H » . Monome »r, Pi .

k₉

<*¾>

Steps I, III and V are initiation, propagation and termination steps common to all free radical polymerization systems. The termination reactions in Step V are still essentially present and therefore must be included in the reaction scheme although they are reduced by the RAFT system. Steps II and IV specifically apply to RAFT polymerization. Step II shows the initial fragmentation of the chain transfer agent (CTA), i.e. RAFT agent, (1) and the resulting equilibria between the CTA, the radical intermediate species (2) and the macro-CTA (3). The radical generated in this step (R ), as a result of macro-CTA formation, acts as an additional initiator species and will propagate new polymer chains. The main reaction equilibrium, Step IV, is established between the macro-radical intermediate species (4) and the alternating active and dormant propagating polymer chains, i.e. chains capped with a thiocarbonylthto end-group, once all initial CTAs become macro-CTAs. The equilibrium in step IV undergoes rapid exchange between the dormant and active chains such that all propagating chains grow at approximately the same rate, thus providing low polydispersity polymers and, by adjusting the monomer and CTA concentrations, polymers with predetermined molecular weights. Brief Description of the Invention Present invention relates to a process for the preparation of molecularly imprinted polymer grafted onto the porous support material via gamma-initiated RAFT polymerization. Said gamma-initiated RAFT polymerization comprises dipping porous support material into a solution comprising a functional monomer, a crosslinking agent, a RAFT agent and a template molecule and said solution is polymerized under gamma irradiation.

Object of the Invention The object of the invention is to provide a novel method for the synthesis of MIP with better binding capacities compared to those prepared by traditional methods.

The object of the invention is to control and improve the binding capacity of MIP grafts on a porous support material fabric.

Description of the Drawings

Figure 1 shows FTIR-ATR spectra of PE/PP non-woven fabric before grafting (a) and after grafting of MIPs by RAFT (b) and by conventional (c) methods.

Figure 2 shows X-ray photoelectron spectroscopy (XPS) survey scan of

polyethylene/polypropylene (PE/PP) non-woven fabric.

Figure 3 shows XPS survey scan of control polymer, which was prepared in the absence of atrazine and RAFT agent.

Figure 4 shows XPS survey scan of MIP grafted non-woven fabric by conventional method Figure 5 shows XPS survey scan of MIP produced according to a RAFT-mediated process of the present invention

Figure 6 shows C 1s spectra of pristine PE/PP non-woven fabric. Figure 7 shows C 1s spectra of control polymer, which was prepared in the absence of atrazine and RAFT agent.

Figure 8 shows C 1s spectra of MIP grafted non-woven fabric by conventional method

Figure 9 shows C 1s spectra of MIP produced according to a RAFT-mediated process of the present invention.

Figure 10 shows SEM images of non-woven fabrics before (a) and after grafting of MIPs by conventional method (b) and RAFT (c).

Figure 11 shows the effect of the [M]/[RAFT] ratio on degree of grafting and radius of free volume holes in the networks prepared by grafting of MIPs onto PE/PP non-woven fabrics ([M] is the concentration of monomer and [RAFT] is the concentration of RAFT agent).

Figure 12 shows atrazine uptake for MIP (atrazine imprinted polymer) and NIP (non- imprinted polymer which prepared in the absence of atrazine) prepared by RAFT mediated and conventional grafting methods. Detailed Description of the Invention

Porous support material according to this invention is preferably selected from the group of polyethylene/polypropylene nonwoven fabrics, other nonwoven fabrics such as PET, cotton, cellulose, or synthetic polymeric membranes, PP membranes, hallow nano-tubes, track attach membranes and inorganic materials like Ti0₂.

Functionai monomer according to this invention is preferably methacryfic acid (MAA). Acrylic acid, metacrylamide and N-vinyl imidazole are the possible functional monomers for synthesis of molecularly imprinted polymers.

Crosslinking agent according to this invention is preferably ethylene glycol dimethacrylate (EGDMA). EGDMA is the most used crosslinking agent but it is possible to use other crosslinking agent like divinyl benzene and trimethylolpropane trimethacrylate (TRIM) in order to prepare molecularly imprinted polymers. Template molecule according to this invention is preferably any different molecule suitable for this purpose, preferably an herbicide or a pesticide. Preferred template molecule according to this invention is preferably atrazine, metribuzine, simazine, desmetryn, fenuron and iso-proturon.

RAFT agent according to this invention is preferably 2-phenyl-2-propyl benzodithioate. Other agents such as 2-Cyano-2-propyl benzodithioate, 4-Cyanopentanoic acid dithiobenzoate, Carboxymethyl dithiobenzoate, and 1-cyanoethyl 2-pyrolidone-1- carbodithioate can also be used as the RAFT agent.

In an exemplary embodiment, monomer is selected as methacrylic acid (MAA) and crosslinking agent is selected as ethylene glycol dimethacrylate (EGDMA). Template molecule is selected as atrazine. 2-phenyl-2-propyl benzodithioate was employed as the RAFT agent in different amounts. Methacrylic acid (MAA) was grafted onto PE/PP nonwoven fabrics using γ-rays for the generation of radicals. 2-phenyl-2-propyl benzodithioate was employed as the chain transfer agent (CTA), i.e. RAFT agent. MAA/atrazine ratio was determined as 2/1 and ethylene glycol dimethacrylate (EGDMA) was used as crosslinker in dimethyl formamide (DMF). Non-imprinted polymers (NIPs) were also synthesized in the absence of atrazine. The synthesized MIPs were characterized by ATR-FTIR, XPS and positron annihilation lifetime spectroscopy (PALS). It was seen that RAFT polymerization could be successfully utilized in conjunction with radiation-induced grafting technique for the preparation of well-defined MIPs. The MIPs synthesized by RAFT method presented a better binding capacity (up to 40 %) compared to those prepared by conventional method where no RAFT agent was employed.

PE/PP non-woven fabric is a porous material consisting of two components; a PP core and a PE shell. Non-woven fabrics were cut into 0.6 cm diameter samples and then washed with methanol and water. After drying, the non-woven fabrics were dipped into a solution that included functional monomer MAA, crosslinking agent EGDMA, RAFT agent and template molecule atrazine in DMF. After waiting 30 min, the solutions were purged with nitrogen for 5 min and then placed into a Co-60 gamma cell (Gammacell 220 Nordion, Canada) in which the radiation dose was 0.263 kGym. Irradiation was conducted at room temperature. After polymerization/grafting, MIPs grafted onto the PE/PP non- woven fabrics were washed using a mixture of methanohacetic acid:water (0.9:0.1 :1 by volume) in order to remove the template molecule.

Following polymers are used in the experiments:

- PE/PP non-woven fabric-Control polymer (NIP) which was prepared by grafting monomer onto non-woven fabric in the absence of atrazine and RAFT agent according to the process of the present invention given below

- MIP produced by a conventional grafting method

- MIP by a process according to the process of the present invention given below.

Control polymers (NIP) were prepared using the same procedure in the absence of both template molecule and RAFT agent. The degree of grafting was calculated using the following equation:

Wf ~ Wi

Degree of Grafting (wt. %) = ~~— x 100

where Wj is the weight of the PE/PP non-woven fabric and W_f is the weight of the MIP grafted non-woven fabric.

Physical and chemical properties of MIPs grafted onto PE/PP non-woven fabrics were evaluated using different methods such as attenuated total reflectance Fourier transform infra-red spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The size and size distribution of free volume holes in MIPs and NIPs were analyzed using positron annihilation lifetime spectroscopy (PALS).

Atrazine binding ability of MIP grafted PE/PP non-woven fabrics were tested in an aqueous medium. The amount of atrazine before and after binding was determined using the HPLC system, which includes a Water 1525 binary pump system and a Waters 2487 Dual Wavelength Absorbance UV-Vis detector set at 236 nm (the mobile phase was 40 % methanol solution and the column was Symmetry, C18, 5μηι, 4.60 χ 150 mm, Waters). All the analyses were repeated thrice. The differences between non-woven fabric and MIP grafted non-woven fabric were evaluated by ATR-FTIR (Figure 1). FTIR spectra were recorded in attenuated total reflexion (ATR) mode using a Thermo Nicolet iS10 model spectrometer. Spectra were obtained by cumulating 32 scans with a 4 cm^'1 resolution. As shown in Figure 1 , the grafting process causes the appearance of new peaks, such as stretching of carbonyl groups (1725 cm^"1) and C-0 (1140-1250 cm^"1), because of the formation of poly (methacrylic acid-co-ethylene glycol dimethacrylate) matrices onto fabrics. C-H sp³ stretching (2914-2844 cm^'1) and bending (1469 and 1369 cm^'1) peaks are common for both samples.

In order to evaluate the surface modifications of fabrics and analyze the chemical composition of modified surfaces, X-ray photoelectron spectroscopy (XPS) experiments were carried out. X-ray photoelectron experiments were conducted using a Thermo spectrometer with a mono-chromatized Al K a X-ray source. Survey and region scans were recorded with 30 eV and 200 eV pass energy, respectively. All samples were analyzed at a take-off angle of 90 °. Surface elemental composition was determined using a X-ray spot size of 400 μιτι and binding energy varied between 0-1000 eV. Figures 2-9 represent the XPS spectra of non-woven fabrics before and after grafting of MIPs and NIPs. In addition to the C 1s peak, an O 1s peak was observed on a survey scan of bare PE/PP non-woven fabric. The presence of small oxygen content can be attributed to an increase in the bounded oxygen amount on carbon atoms in the PE sheath of PE/PP non- woven fabric an air medium.

The main difference between MIP and NIP grafted fabric is the appearance of a nitrogen peak in the survey scan due to the presence of the template molecule, atrazine. Detailed analysis of the C 1 s spectra indicates a new peak for the C-N bond with a binding energy of 286.98 eV for both samples prepared by grafting of MIPs using conventional and RAFT polymerization methods (Figure 9). In addition to this new peak there is one more peak in the spectrum of RAFT-mediated grafted MIPs onto fabrics which coming from C-S bond with 286.5 eV binding energy due to the presence of RAFT agent.

SEM images were evaluated to observe surface modifications due to MIP grafting onto PE/PP non-woven fabrics (Figure 10). SEM images of samples were taken using FEI Quanta 200FEG at different magnifications. As can be seen by comparing Figure 9b and Figure 9c, RAFT method provides a decrease in the formation of crosslinked species between fibres of non-woven fabrics. This causes homogeneity in the grafting of MIP layers by RAFT method which further provides a better binding capacity for RAFT compared to conventional method.

In order to investigate the size of the cavities in the MIP network Positron annihilation lifetime spectroscopy (PALS) experiments were carried out. The positron source, a droplet

22

of NaCI from a carrier-free neutral solution (activity: 55 Ci), was dried between two DuPont Kapton® foils. The source was placed between two identically dried MIP or NIP grafted non-woven fabrics in a typical 'sandwich' configuration. The lifetime spectra were obtained by using a conventional ORTEC fast - fast coincidence system with a time resolution of approximately 248 ps. The measurements were conducted in air at room temperature. The spectra were recorded at every 2.8 h. Thereafter, for each type of sample, ten spectra were summed together resulting in a statistical representation of 2.36x107counts. The obtained spectra were evaluated by using LT designed to analysis of Positron Annihilation Lifetime Spectra (PALS).

As it can be seen in Figure 11 , while the degree of grafting increases, the size of the binding sites shows a decrease with the increasing the ratio of monomer concentration to RAFT agent. This causes a better separation and binding capacity since the size of the cavities is getting smaller enough to control the specific binding of MIPs.

As seen in Figure 12, a better binding capacity up to around 40% was obtained with RAFT mediated grafting due to the surface homogeneity of graft layers onto PE/PP non-woven fabrics. The atrazine uptake for MIP synthesized by RAFT method was observed to be 160 μΐτιοΙ atrazine/g polymer whereas this value was just 112 μηΊθΙ/g for conventional method. By employing the RAFT method better binding capacity was obtained for a selected template molecule, i.e. atrazine.

Method of the present invention is developed in order to control and improve binding capacity of MIP grafts onto a porous support material. It was seen that RAFT polymerization is successfully utilizable in conjunction with radiation-induced grafting technique for the preparation of well-defined MIPs onto porous materials, e.g. PE/PP non- woven fabrics. The MIPs synthesized by RAFT method according to present invention presents better binding capacities compared to those prepared by traditional method. it is possible to use final product of this process in order to remove herbicides from water resources or enrichment of samples before possible chromatographic or spectroscopic applications like HPLC and GC-MS via preparing SPE cartridge using atrazine imprinted polymers grafted PE/PP non-woven fabrics.

Claims

1. A process for the preparation of molecularly imprinted polymer grafted onto the porous support material characterized by gamma-initiated RAFT polymerization which comprises dipping porous support material into a solution comprising a functional monomer, a crosslinking agent, a RAFT agent and a template molecule, and polymerization of said solution under gamma irradiation.

2. The process according to claim 1 characterized in that said process comprises removing the template molecule after gamma irradiation of said solution.

3. The process according to claim 1 characterized in that said solution comprises dimethyl formamide.

4. The process according to claim 1 wherein said porous support material is a nonwoven fabric, cotton, cellulose, synthetic polymeric membrane, polypropylene membrane, hallow nano-tube, track attach membrane and inorganic material like titanium dioxide.

5. The process according to claim 4 wherein said nonwoven fabric is a polyethylene/polypropylene fabric.

6. The process according to claim 4 wherein said nonwoven fabric is polyethylene terephthalate.

7. The process according to claim 1 wherein said functional monomer is selected from methacrylic acid, acrylic acid, metacrylamide and N-vinyl imidazole.

8. The process according to claim 1 wherein said crosslinking agent is selected from ethylene glycol dimethacrylate, divinyl benzene or trimethylolpropane trimethacrylate.

9. The process according to claim 1 wherein said template molecule is an herbicide or a pesticide.

10. The process according to claim 1 wherein said template molecule is selected from atrazine, metribuzine, simazine, desmetryn, fenuron or iso-proturon.

11. The process according to claim 1 wherein said template molecule is atrazine.

12. The process according to claim 1 wherein said RAFT agent is selected from 2- phenyl-2-propyl benzodithioate, 2-cyano-2-propyl benzodithioate, 4- cyanopentanoic acid dithiobenzoate, carboxymethyl dithiobenzoate, or 1- cyanoethyl 2-pyrolidone-1-carbodithioate.

13. The process according to claim 1 wherein the ratio of functional monomer to template molecule is 2/1.

14. Moleculariy imprinted polymer grafted onto the porous support material produced by gamma-initiated RAFT polymerization which comprises dipping porous support material into a solution comprising a functional monomer, a crosslinking agent, a RAFT agent and a template molecule, and polymerization of said solution under gamma irradiation.