GB2541415A

GB2541415A - 3-methylene-2-pyrrolidone based polymers

Info

Publication number: GB2541415A
Application number: GB1514660.8A
Authority: GB
Inventors: Klumperman Lubertus; Pfukwa Rueben; Marie Heyns Ingrid
Original assignee: Stellenbosch University
Current assignee: Stellenbosch University
Priority date: 2015-08-18
Filing date: 2015-08-18
Publication date: 2017-02-22
Also published as: WO2017029630A1; ZA201801160B; GB201514660D0

Abstract

A 3-methylene-2-pyrrolidone based polymer of formula (I) Wherein R1 and R2 are monomers that are polymerisable by radical polymerisation, such as unsubstituted and substituted styrene, N-vinyl pyrrolidone, 1-(hydroxymethyl)-3-methylenepyrrolidone (3M2P-OH), ethylene glycol, acrylonitrile, maleic anhydride, maleimide, tulipalin A, vinyl esters, viny chloride, vinyl bromide; i and k are selected from 0-100; j is 1-100; and n is selected from 1-1000, and when n < 10, then j is >10. Also disclosed is a process for the preparation of the polymer; a biocompatible polymer system comprising the polymer; and a composite material comprising the polymer.

Description

3-METHYLENE-2-PYRROLIDONE BASED POLYMERS FIELD OF THE INVENTION

This invention relates to 3-methylene-2-pyrrolidone based polymers and to methods of preparing these polymers.

BACKGROUND TO THE INVENTION

Tulipalin A, an a-methylene-y-lactone compound, also known as a-methylene-y-butyrolactone, is present in Tulipa Gesneriana L. and protects this tulip species against fungal infection.

The lactone has an exo-cyclic methylene group, which is conjugated with a carbonyl group to give this monomer the ability to alkylate thiol groups in cells and terminate cellular processes. The exo-cyclic double bond also allows for chain growth polymerisation of the monomer, where unsaturated monomer units add to an active site (radical or ion), to form a polymeric compound, poly(tulipalin A).

Tulipalin A and poly(tulipalin A)

Tulipalin A also has uses in polymer producing industries such as those producing thermoplastics and coatings (Damude, Flint, Prabhu and Wang; A biological method for the production of alpha-methylene-gamma-butyrolactone and its intermediates; United States patent application US20030170653). However, poly(tulipalin A) suffers from poor ductility or brittleness which limits its use in tough films. Furthermore, poly(tulipalin A) is a hydrophobic polymer, which is beneficial for some applications, but which make the polymer unsuitable for applications where water-solubility is necessary. 5-Methyl-3-methylenepyrrolidone (A) and 1-methyl-3-methylenepyrrolidone (B), shown below, are derivatives of the lactam analogue of Tulipalin A.

5-Methyl-3-methylenepyrrolidone (A) and 1 -methyl-3-methylenepyrrolidone (B)

Both these monomers have been shown to undergo radical polymerisation (Ueda et al. J. Polym. Sci. Polym.: Chem. Ed. 1983, 21, 1139; Van Beylen and Samyn, Makromol. Chem. 1990, 191, 2485). However, the polymer of compound (A), poly(A), is poorly characterized in terms of its solubility properties and its physical properties. Poly(A) is more hydrophilic than the polymer of compound (B), poly(B), and fairly soluble in organic solvents. The glass transition temperature (Tg) of poly(A) is estimated to be less than that of poly(B), which has a Tg of 169 °C (Ishizone et al. Macromol. Symp. 2013, 323, 86). Poly(B) shows depolymerisation above 330 °C and is a semi-crystalline material (Ueda et al. J. Polym. Sci., Part B: Polym. Phys. 1983, 20, 1139). Poly(B) is water-soluble and also soluble in methanol, dichloromethane (DCM) and polar aprotic solvents at room temperature (similar solubility behavior to that of poly(N-vinylpyrrolidone) (PVP).

There is thus a need for new biocompatible, water-soluble polymers which have good thermal stability.

SUMMARY OF THE INVENTION

In accordance with a first aspect of this invention there is provided a polymer of Formula (I)

wherein Ri and R2 are selected from monomers that are polymerisable by radical polymerisation techniques; and i and k are independently selected from integers 0 to 100; j is independently selected from integers 1 to 100; and n is independently selected from integers 1 to 1000, and when n is < 10, then j is > 10.

The radical polymerisation techniques include reversible deactivation radical polymerisation (RDRP) techniques.

Further features provide for Ri and/or R2 to be selected from the following monomers: substituted and unsubstituted styrene, /V-vinyl pyrrolidone, 1-(hydroxymethyl)-3-methylenepyrrolidone (3M2P-OH), ethylene glycol, acrylonitrile, acrylic acid and its ester and amide derivatives, methacrylic acid and its ester and amide derivatives, maleic anhydride, maleimide and its /V-substituted derivatives, tulipalin-A, vinyl esters, vinyl chloride, vinyl bromide, 2-vinyl pyridine, 3-vinyl pyridine, 4-vinyl pyridine, 5-methyl-3-methylenepyrrolidone, 1-methyl-3-methylenepyrrolidone, and /V-vinylcaprolactam.

Still further features of the present invention provide for: a) the substituted styrene derivatives to be selected from p-chloromethylstyrene, p-methoxystyrene, p-methylstyrene and alpha-methylstyrene; and/or b) for the ester and amide derivatives of acrylic acid and methacrylic acid to be selected from methyl (meth)acrylate, butyl (meth)acrylate, 2-hydroxy-ethyl (meth)acrylate, glycidyl (meth)acrylate, (meth)acrylamide, /V-methyl (meth)acrylamide and /V-isopropyl (meth)acrylamide; and/or c) for the /V-substituted derivatives of maleimide to be selected from /V-methylmaleimide and N-phenylmaleimide; and/or d) for the vinyl esters to be selected from vinyl acetate and vinyl pivalate.

Yet further features of the present invention provide for: a) i and k to be zero (0), in which case the polymer is the homopolymer of 3-methylenepyrrolidone (3M2P); or b) for i to be zero (0) and k to be >10 and for n = 1, in which case the polymer is a diblock copolymer; or c) for i to be > 10 and k to be zero (0) and for n = 1, in which case the polymer is also a diblock copolymer; or d) for i and k to be >10 and for n = 1, in which case the polymer is a triblock copolymer; or e) for i, j and k to be selected from integers 1 to 5 when n is 50 to 1000, in which case the polymer is a statistical copolymer; or f) for i, j and k to be selected from integers 10 to 50 when n is 1 to 3, in which case the polymer is a multiblock copolymer.

Further features of the present invention provide for the polymer of Formula (I) to be: a) a block copolymer, for the block copolymer to be an A-B diblock copolymer, b) an A-B-A triblock copolymer, c) an A-B-C triblock copolymer, or d) an (A-B)n multiblock copolymer; wherein the AB block copolymer is for example an amphiphilic co-polymer with a hydrophobic segment and hydrophilic segment and for the hydrophilic segment to be a polymer containing 3M2P and for the hydrophobic segment to be selected from Ri and/or R2; for the individual blocks of the block copolymers to be statistical copolymers themselves.

In one embodiment, the polymer of Formula (I) may be a block copolymer of Formula (II), where R1 is not 3M2P and in which instance k = 0,

(II)

In another embodiment, the polymer of Formula (I) is a homopolymer of Formula (III), in which instance both i and k = 0,

(III) .

In accordance with a second aspect of the invention there is provided a process for the preparation of a polymer of Formula (I) as defined above, which includes using reversible deactivation radical polymerisation (RDRP) such as atom transfer radical polymerisation (ATRP), single electron transfer living radical polymerisation (SET-LRP), nitroxide mediated polymerisation (NMP) and reversible-addition fragmentation chain-transfer (RAFT); and preparation by conventional radical polymerisation, all of which can be conducted in the form of a bulk polymerisation, solution polymerisation, emulsion polymerisation, dispersion polymerisation or suspension polymerisation.

In accordance with a third aspect of the invention there is provided a biocompatible polymer system comprising a polymer of any one of Formulae (I) to (III), which are suitable for use in direct contact with living organisms; a polymeric drug delivery system comprising the biocompatible polymer system such as micelles, vesicles or nanospheres; and a scaffold for tissue engineering comprising the biocompatible polymer system.

In accordance with a fourth aspect of the invention there is provided a composite material comprising a polymer of any one of Formulae (I) to (III) for use in the thermoplastic and coatings industries to form materials such as paints, detergents, protective coatings, decorative coatings, structural materials, and functional materials.

BRIEF DESCRIPTION OF THE FIGURES

The invention will now be described, by way of example only, with reference to the accompanying figures in which:

Figure 1 is a presaturation 1H NMR spectrum in D2O of (A) 3M2P monomer, (B) poly(3M2P);

Figure 2 shows a thermogravimetric analysis (TGA) thermogram and corresponding weight derivative of the decomposition of poly(3M2P); and

Figure 3 is a differential scanning calorimetry (DSC) thermogram of a second heating cycle of poly(3M2P).

DETAILED DESCRIPTION OF THE INVENTION

Throughout the specification and claims unless the contents requires otherwise the word ‘comprise’ or variations such as ‘comprises’ or ‘comprising’ are to be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

There have been no previous reports published which indicate the polymerisation of a 3-methylene-2-pyrrolidone (3M2P) monomer, and it has surprisingly found that 3M2P can be homopolymerised and copolymerised with other radically polymerisable monomers to produce novel polymers with useful properties. A polymer of Formula (I) comprising the monomer 3M2P which has been homopolymerised to form a homopolymer, or copolymerised with monomer Ri and/or R2 to form diblock or triblock copolymers and statistical copolymers, as well as methods of preparing these polymers are described herein. For example, a diblock copolymer of Formula (II) or a homopolymer of Formula (III) may be formed.

In Formula (I), in one embodiment of the invention, i and k are small numbers, i.e. 0,1,2,3,4 or 5, and j = 1, 2 ,3, 4 or 5; and n > 5, and preferably n > 100, for example, i, j and k are selected from integers 1 to 5 and n is 50 to 1000. In another embodiment of the invention, i, j and k are relatively large numbers, i.e. 10 to 50, and n is a small number i.e. 1 to 3, most preferred n = 1.

Formula (I) includes homopolymers of 3M2P (i.e. where i and k = 0, as depicted in Formula (III)) and statistical copolymers of 3M2P with one or more comonomers (i.e. wherein R1 and/or R2 differ from 3M2P).

Block copolymers, where one block is comprised of 3M2P and the other block or blocks are comprised of a different comonomers R1 or R2 can be depicted as A-B diblock copolymers (where one of i or k = 0), A-B-A triblock copolymers, A-B-C triblock copolymers and (A-B)n multiblock copolymers and individual blocks of the block copolymers can be statistical copolymers themselves.

The polymer of Formula (I) may be prepared using reversible deactivation radical polymerisation (RDRP), such as single electron transfer living radical polymerisation (SET-LRP) and reversible-addition fragmentation chain-transfer (RAFT). In the case of a homopolymer (i.e. when i and k = 0), the homopolymer may also be prepared by using a radical homopolymerisation, for example, in dimethyl sulfoxide (DMSO) with azobisisobutyronitrile (AIBN) as an initiator. SET-LRP can be performed using Cu° wire as a copper catalyst, MeeTREN (tris[2-dimethylamino)ethyl]amine) as a ligand, and a bromo-ester (like 1,2-dihydroxypropane-3-oxy-2-bromo-2-methylpropionyl), as an initiator in a polar solvent (such as DMSO or water). RAFT-mediated polymerization can be performed using a trithiocarbonate, such as 2-hydroxyethyl 2-(butylthiocarbonothioylthio)-2-methylpropanoate or a hydroxyl-terminated C(CH3)2COOEt analogue as a RAFT agent, and AIBN or potassium persulfate (KPS) as an initiator, in a polar solvent such as DMSO or water, respectively. The RAFT-mediated polymerization is typically carried out at temperatures between 25 °C and 100 °C, more preferably at temperatures between 50 °C and 80 °C and most preferably at temperatures between 60 °C and 75 °C. The RAFT-mediated polymerization is preferably carried out at atmospheric pressure, and the duration of the polymerization process is preferably between 1 hour and 48 hours, more preferably between 2 hours and 36 hours and most preferably between 6 hours and 24 hours.

The polymers of Formulae (I), (II) and (III) are suitable for use in polymeric drug delivery systems such as micelles, vesicles and nanospheres or in a suitable form for medication

The polymers of Formulae (I), (II) and (III) are also suitable in other industrial applications, such as in the thermoplastic and coatings industries to create composite materials e.g. paints, detergents, protective coatings, decorative coatings, structural materials, and functional materials

The invention will now be described in more detail with reference to the following non-limiting Examples. The invention is not intended to be limited to these Examples and it will be appreciated that numerous other examples and modifications fall within the scope of the present invention.

Materials and Methods - Preparation of 3-methylene-2-pyrrolidone-based copolymers

Monomer synthesis

3-Methy?ene-2-pyrfolidine (3M2Pi

The monomer 3M2P, which forms a repeat unit in polymers of Formulae (I) - (III), can be prepared via a number of synthetic approaches as such known in the art of organic chemistry. In one example, one can dehydrate the 3-(hydroxymethyl) lactam precursor (Klutchko and Hoefle, J. Org. Chem. 1981, 24, 104-109). Alternatively one can condense the corresponding phosphorous ylide with paraformaldehyde, to form the requisite 3M2P (Fotiadu et al. Tetrahedron Lett. 1999, 40, 867-870). With the latter approach, one can also access N-(hydroxymethyl)-3-methylene 2-pyrrolidone (3M2P-OH), a potential comonomer, by simply using a large excess of paraformaldehyde.

Polymer synthesis

Polymerisation commences upon the application of conditions under which radicals are generated, such as the addition of a suitable initiator system, and the subsequent application of heat. Figure 1 shows presaturation 1H NMR spectra in D2O of (A): the 3M2P monomer, and of (B): poly(3M2P). The disappearance of the methylene peaks of 3M2P monomer (labelled 6a and 6b) in the poly(3M2P) and the broadening of peaks around 2.0 and 3.5 ppm in the 1H NMR spectrum are indicative of polymer formation.

Example 1 A reaction vessel was charged with 3M2P (100 mg, 1.03 mmol), AIBN (2.54 g, 0.015 mmol) as initiator, and 1.0 mL DMSO added. The mixture was then purged with an inert gas. The vessel was then immersed for 24 hours in an oil bath that was preheated to and kept at 75 °C. When the polymerisation was stopped after 24 h, the polymer was isolated by precipitating from acetone and yielded a white powder. Poly(3M2P) was dialyzed against water for ~5 days using SnakeSkin® with a molecular weight cut-off of 3 500 g/mol (in order to remove any unreacted monomer or other water-soluble impurity), replacing the water every 12 h. For 1H NMR spectroscopy analysis refer to Figure 1. From SEC; number-average molar mass (Mn) = 52 335 g/mol, weight-average molar mass (Mw) = 97 137 and molar mass dispersity (£>) = 1.86.

Example 2 A reaction vessel was charged with 3M2P (60 mg, 0.62 mmol) as well as with 3M2P-OH (40 mg, 0.31 mmol) as a co-monomer. AIBN (2.93 mg, 0.018 mmol) was added as an initiator and in 1.0 mL DMSO. The mixture was then purged with an inert gas. The vessel was then immersed into an oil bath, preheated to 75 °C, for 24 h. The reaction was stopped by opening the flask to air, and cooling. From SEC: Mn = 715 g/mol, Mw = 1 932 and D = 2.70.

Example 3 A reaction vessel was charged with 3M2P (50 mg, 0.51 mmol) and N,N-dimethylaminoethyl methacrylate (DMAEMA) (81 mg, 0.52 mmol) as a co-monomer. AIBN (1.7 mg, 0.010 mmol) was added as an initiator in 1.0 ml_ DMF and the mixture was then purged with an inert gas. The vessel was then immersed in an oil bath, preheated to 75 °C, for 24 h. The reaction was stopped by opening the flask to air, and cooling. The polymer was isolated by precipitating from cooled diethyl ether. From SEC; Mn = 15 753 g/mol, Mw = 28 110 and D = 1.78. Calculated mol ratio of the copolymer from 1H NMR spectroscopy, P(DMAEMA) : P(3M2P), (61 % : 39 %).

Example 4

An example of a RDRP of 3M2P, with the process mediated by a thiocarbonylthio chain transfer agent, is given below:

Firstly, a suitable chain transfer agent, 2-hydroxyethyl 2-(((butylthio)carbonothioyl)thio)-2-methylpropanoate, was prepared in two steps, by first preparing 2-(((butylthio)carbonothioyl)thio)-2-methylpropanoic acid (Jia et al. J. Am. Chem. Soc. 2014, 136, 5824-5827) and then coupling it with ethylene glycol, via a Steiglich coupling, with a protocol adapted from the same publication, to give the requisite RAFT agent. 1H NMR of this RAFT agent (300 MHz, CDCh) δ: 4.18 (m, 2H, -O-CFU), 3.74 (m, 2H, -CFU-OH), 3.29 (t, J = 7.4 Hz, 2H, -S-CH2), 1.65 (s, 6H, -CH(CH3)2), 1.62 (m, 2H, -S-CH^CFU), 1.37 (m, 2H, -CHs-CFb), 0.86 (t, J = 7.3 Hz, 3H, -CH3-CH2). A reaction vessel was charged with 3M2P (110 mg, 1.13 mmol), the abovementioned RAFT agent (1.65 mg, 0.006 mmol), AIBN (0.18 mg, 0.001 mmol) as initiator, and 1.0 ml_ DMSO. The mixture was then purged with an inert gas. The vessel was then immersed into an oil bath, preheated to 75 °C, for 24 h. The reaction was stopped by opening the vessel to air. The polymer was isolated by precipitating from acetone. From SEC: Mn = 14 822 g/mol, Mw = 20 057 g/mol, and B = 1.35. Calculated number average molecular weight from chain-ends on 1H NMR spectroscopy, Mn = 13 853 g/mol.

Example 5

An example of a metal catalysed RDRP process of 3M2P, via the SET-LRP technique is given below: A reaction vessel was charged with 3M2P (0.10 g, 1.03 mmol), Cu°wire wrapped around the stirring bar, and 1,2-dihydroxypropane-3-oxy-2-bromo-2-methylpropionyl (2.47 mg, 0.10 mmol) as initiator, in 1.0 ml_ DMSO. The reaction mixture was thoroughly degassed via several freeze-pump-thaw cycles, and the vessel was back filled with argon. The ligand, MeeTREN (1.19 mg, 1.4 pl_, 0.01 mmol), was then added to the reaction mixture, through a septum, using a purged syringe. The reaction vessel was placed in a pre-heated oil bath at 50 °C. After 24 h at 50 °C, the vessel was opened and exposed to air, the reaction mixture was diluted with DMSO, and then filtered through a column of basic aluminium oxide to remove copper, whereafter the polymer was precipitated from acetone, and isolated as a white powder. From SEC: Mn=11 176g/mol, Mw = 12 936 g/mol, and £)=1.16. Calculated number average molecular weight from chain-ends on 1H NMR spectroscopy: Mn = 8 009 g/mol.

Example 6

An example of a RDRP of 3M2P, with the process mediated by alkoxyamines, is given below: A reaction vessel was charged with 3M2P (0.11 g, 1.13 mmol), BlocBuilder® (Hlalele et al. Macromolecules 2011, 44, 6683-6690) (4.20 mg, 0.01 mmol), and 0.8 ml_ DMSO. The mixture was purged with an inert gas, and the vessel was then immersed into an oil bath, preheated to 110 °C, for 12 h. The polymer was isolated by precipitating from acetone. From SEC: Mn = 6 151 g/mol, Mw = 10 152 g/mol, and D = 1.65.

Example 7

An example of a block copolymer consisting of methyl methacrylate and 3M2P, with the process being mediated by the SET-LRP technique, is given below: A reaction vessel was charged with methyl methacrylate (2.0 g, 19.98 mmol), Cu° wire wrapped around the stirring bar, and ethyl 2-bromoisobutyrate (40.1 mg, 30.2 μΙ_, 0.21 mmol) as initiator, in 3.0 ml_ DMF. The reaction mixture was thoroughly degassed via several freeze-pump-thaw cycles, and the vessel was back filled with argon. The ligand, MeeTREN (23.7 mg, 27.5 μΙ_, 0.10 mmol), was then added to the reaction mixture through a septum, using a purged syringe. Subsequently, the polymerisation vessel was placed in a heated oil bath at 50 °C. After 24 h, the vessel was opened and exposed to air, the reaction mixture was diluted with DMF, and then filtered through a column of basic aluminium oxide to remove copper, where after the polymer was precipitated from methanol, and isolated as a white powder. From SEC: Mn = 20 208 g/mol, Mw = 26 510 g/mol, and £)= 1.31.

Secondly, the resulting PMMA macro-initiator was coupled with 3M2P. A reaction vessel was charged with the PMMA macro-initiator (0.2 g, 0.01 mmol), 3M2P (115.50 mg, 1.19 mmol) and were dissolved in 1 ml_ DMF. The reaction mixture was thoroughly degassed via several freeze-pump-thaw cycles, and the vessel was back filled with argon. The ligand, MeeTREN (0.52 mg, 0.60 μΙ_, 0.002 mmol), was then added to the reaction mixture, through a septum, using a purged syringe. Subsequently, the polymerisation vessel was placed in a heated oil bath at 50 °C for 24 h. After 24 h, the block copolymer was precipitated into isopropanol and filtered to yield a white powder. From SEC: Mn = 22 481 g/mol, Mw = 28 606 g/mol, and D = 1.27. Based on the increase in molar mass, the ratio of PMMA block to P(3M2P) block is around 10:1.

Example 8

An example of a block copolymer consisting of DMAEMA and 3M2P, with the process mediated by RAFT, is given below: A reaction vessel was charged with DMAEMA (1.0 g, 6.36 mmol), AIBN (8.0 mg, 0.05 mmol) as an initiator, and cumyl dithiobenzoate (68 mg, 0.25 mmol) as the RAFT agent, in 3.0 ml_ DMF. The RAFT agent was prepared as described in literature (Le, Moad, Rizzardo, Thang: Polymerisation with living characteristics, 1998, WO 9801478). The mixture was purged with an inert gas, whereafter the vessel was placed in a heated oil bath at 75 °C for 12h. The reaction was stopped by opening the flask to air, and cooling. The polymer was isolated by precipitating from cooled petroleum ether. From SEC, Mn = 5 142 g/mol, Mw = 6 152 g/mol and B = 1.19. Calculated number average molecular weight from chain-ends on 1H NMR spectroscopy: Mn = 6 866 g/mol.

Secondly, the resulting PDMAEMA macro-RAFT agent was coupled with 3M2P. A reaction vessel was charged with PDMAEMA macro-RAFT agent (40 mg, 0.01 mmol), 3M2P (0.1 g, 1.03 mmol), AIBN (0.3 mg, 0.02 mmol) were dissolved in 1.0 ml_ DMF. The mixture was purged with an inert gas. The mixture was then immersed in a heated oil bath at 75 °C for 24h. The reaction was stopped by opening the flask to air, and cooling. The polymer was isolated by precipitating from cooled diethyl ether. From SEC: Mn = 13 239 g/mol, Mw = 15 884 g/mol and D = 1.20. Calculated mol ratio of the block copolymer from 1H NMR spectroscopy, P(DMAEMA) block : P(3M2P) block, (36 % : 64 %).

Polymer properties

In order to obtain an impression of the newly synthesised poly(3M2P) and the possible applications thereof, different properties thereof were investigated.

Example 9

Thermogravimetric analysis (TGA) on the poly(3M2P) prepared in Example 1 was performed to give an indication of the polymer’s thermal stability. The thermogram is shown in Figure 2.

The maximum weight loss rate occurs at approximately 400 °C, indicating thermal stability up to this temperature, with the main thermal decomposition occurring between 400-500 °C. The homopolymer of 3M2P is remarkably thermally stable. The onset of ~20 % weight loss prior to 110 °C is caused by water loss, due to the hygroscopic nature of poly(3M2P).

Differential scanning calorimetry (DSC) thermograms give thermal properties such as the glass transition temperature (Tg), as well as melting and crystallization temperatures. The glass transition is shown for poly(3M2P) in Figure 3, indicating a Tg of ~ 285 °C. The high glass transition temperature is indicative of the lactam ring’s structural rigidity and due to the presence of favourable hydrogen bonding interactions by the amide linkages in poly(3M2P).

Furthermore, no melting peak was observed in the heating cycle as well as no crystallization peak in the cooling cycle and it was therefore concluded that poly(3M2P) is an amorphous polymer.

Example 10

An investigation of poly(3M2P)’s solubility was performed in a wide variety of solvents. Poly(3M2P), prepared in Example 1, is poorly soluble in most organic solvents. However, the polymer is readily soluble in water. Curiously, although it can be polymerised in solvents such as DMF, acetonitrile, DMAc, NMP, and dioxane, upon isolation of the polymer it was not possible to re-dissolve the polymer again in the same solvents.

Table 1: Solubility of polv(3M2P) in various solvents

S - soluble, Is - insoluble, Ps - partially soluble upon heating and sonication.

Example 11

The water-solubility of poly(3M2P) makes it an attractive polymer especially when applications are extended to the biomedical field. However, biomedical polymers require interaction with cells without any undesirable effects and thus should be non-toxic to biological systems. Investigation of the biocompatibility of poly(3M2P) and its copolymers towards cells gives this new polymer a broader scope of possible applications.

Biocompatibility is dependent on various aspects such as chemical properties, cytotoxicity, mutagenic and allergenic effects etc. Biocompatibility testing is divided in three categories; primary (level I), secondary (level II) and preclinical (level III). Level I can either be performed in vitro or in vivo. Cytotoxicity testing is generally performed on primary cultures or permanent cell lines.

In vitro cytotoxicity studies of different concentrations of poly(3M2P), prepared in Example 1 (1 mg/mL, 1 pg/mL and 1 ng/mL), were investigated against cultured GT1-7 (hypothalamic mouse cell lines).

Poly(3M2P) was dissolved in Dulbecco’s modified eagle medium (DMEM) containing 1 % penicillin/streptomycin and 10 % fetal calf serum, and added to GT1-7 cell cultures. A control (media and cells) and a positive control (media and cells treated with ethanol) were used as references. Subsequently, the samples were kept at 37 °C for 4 h, where after the cells were stained with fluorescent markers, Hoechst 33342 dye and propidium iodide, respectively. The fluorescent markers are either permeable or impermeable to the cell membrane, dependent on the cell viability. Fluorescence and light transmission micrographs were obtained and cell viability was determined.

Positively charged Hoechst 33342 dye, which is blue, binds to the minor grooves in the DNA double helix and is also permeable to healthy cell membranes. It is mainly used to stain cell structures for cell morphology studies. It can however also indicate apoptotic cell death. Propidium iodide, which is red, binds and stains DNA molecules and is impermeable to healthy cell membranes. Propidium iodide is used as a counterstain to Hoechst 33342 dye, as it is permeable to the membrane of dead cells and indicates necrotic cell death.

Fluorescence and light transmission micrographs of polymer-cell solutions which were stained with Hoechst 33342 dye and propidium iodide were taken. An overlay of Hoechst 33342 dyed and propidium iodide stained micrographs was also observed.

In control micrographs, cell membranes were permeable to the blue Hoechst 33342 dye .

In micrographs of the polymer-cell solutions with concentrations of 1 mg/mL and 1 pg/mL of poly(3M2P) present in the solution, a similar behaviour as the control was observed. The Hoechst 33342 dye stained the cells blue and the cells were healthy as no propidium iodide stain, penetrated the cell membrane, i.e. no red coloured cells were observed, indicating that the cells were in fact still healthy, with no indication of cell death.

On the contrary, in positive control cells which were treated with ethanol to visualize cell death, micrographs showed definitive propidium iodide penetrating the cell membrane with the cells staining red stain and indicating cell death. An overlay micrograph of the positive control showed a pink colour, as a result of the overlay of the red and blue stains.

In vitro experiments thus demonstrated that poly(3M2P) showed no cytotoxicity, confirming the biocompatibility of the polymer. This aspect broadens the scope of possible applications of poly(3M2P) and its copolymers, and can be compared to other biocompatible, water-soluble, non-ionic polymers such as PVP, PEG, poly(acrylamide), etc.

Claims

CLAIMS:

1. A polymer of Formula (I)

wherein Ri and R2 are selected from monomers that are polymerisable by radical polymerisation techniques; and i and k are independently selected from integers 0 to 100; j is independently selected from integers 1 to 100; and n is independently selected from integers 1 to 1000, and when n is < 10, then j is > 10,
2. The polymer as claimed in claim 1, wherein the radical polymerisation techniques are reversible deactivation radical polymerisation (RDRP) techniques.
3. The polymer as claimed in either one of claims 1 or 2, wherein R1 and/or R2 are selected from the following monomers: unsubstituted and substituted styrene, N-vinyl pyrrolidone, 1-(hydroxymethyl)-3-methylenepyrrolidone (3M2P-OH), ethylene glycol, acrylonitrile, acrylic acid and its ester and amide derivatives and methacrylic acid and its ester and amide derivatives, maleic anhydride, maleimide and its /V-substituted derivatives, tulipalin-A, vinyl esters, vinyl chloride, vinyl bromide, 2-vinyl pyridine, 3-vinyl pyridine, 4-vinyl pyridine, 5-methyl-3-methylenepyrrolidone, 1-methyl-3-methylenepyrrolidone and N-vinylcaprolactam.
4. The polymer as claimed in claim 3, wherein: a) the substituted styrene are selected from p-chloromethylstyrene, p-methoxystyrene, p-methylstyrene and alpha-methylstyrene; and/or b) the ester and amide derivatives of acrylic acid and methacrylic acid are selected from methyl (meth)acrylate, butyl (meth)acrylate, 2-hydroxy-ethyl (meth)acrylate, glycidyl (meth)acrylate, (meth)acrylamide, A/-methyl (meth)acrylamide and /V-isopropyl (meth)acrylamide; and/or c) the /V-substituted derivatives of maleimide are selected from /V-methylmaleimide and /V-phenylmaleimide; and/or d) the vinyl esters are selected from vinyl acetate and vinyl pivalate.
5. The polymer as claimed in any one of claims 1 to 4, wherein: a) i and k = zero (0), in which case the polymer is the homopolymer of 3-methylene-2-pyrrolidone (3M2P); or b) i = zero (0) and k >10 and n = 1, in which case the polymer is a diblock copolymer; or c) i > 10 and k = zero (0) and n = 1, in which case the polymer is also a diblock copolymer; or d) i and k >10 and n = 1, in which case the polymer is a triblock copolymer; or e) i, j and k are selected from integers 1 to 5 when n is 50 to 1000, in which case the polymer is a statistical copolymer; or f) i, j and k are selected from integers 10 to 50 when n is 1 to 3, in which case the polymer is a multiblock copolymer.
6. The polymer as claimed in any one of claims 1 to 5, in the form of a block copolymer selected from an A-B diblock copolymer, or an A-B-A triblock copolymer, or an A-B-C triblock copolymer or an (A-B)n multiblock copolymer, wherein one block is comprised of a comonomer Ri or R2.
7. The polymer as claimed in claim 6, wherein the A-B diblock copolymer is a block copolymer of Formula (II) where R1 is not 3M2P and in which instance k = 0,
8. The polymer as claimed in claim 7, wherein the A-B diblock copolymer is an amphiphilic copolymer with a hydrophobic segment containing 3M2P and a hydrophilic segment containing Ri.
9. The polymer as claimed in any one of claims 6 to 8, wherein the individual blocks of the block copolymers are statistical copolymers themselves.
10. The polymer as claimed in either one of claims 1 or 2, which is a homopolymer having Formula (III), in which instance both i and k = 0,
11. A process for the preparation of a polymer of Formula (I) using reversible deactivation radical polymerisation (RDRP) selected from atom transfer radical polymerisation (ATRP), single electron transfer living radical polymerisation (SET-LRP), nitroxide mediated polymerisation (NMP) or reversible-addition fragmentation chain-transfer (RAFT).
12. A process for the preparation of a polymer of Formula (I) using conventional radical polymerisation conducted in the form of bulk polymerisation, solution polymerisation, emulsion polymerisation, dispersion polymerisation or suspension polymerisation.
13. A biocompatible polymer system comprising a polymer of Formula (I) for use in direct contact with living organisms selected from a scaffold for tissue engineering or a polymeric drug delivery system, comprising micelles, vesicles or nanospheres.
14. A composite material comprising a polymer of Formula (I) for use in thermoplastic and coatings industries to form materials selected from paints, detergents, protective coatings, decorative coatings, structural materials, and functional materials.