Copolymerization Parameters of 2-( N-Phthalimido ) ethyl Methacrylate with Different Vinyl Monomers

2-(N-phthalimido)ethyl methacrylate was prepared by the reaction of methacrylic acid with N(2-hydroxyethyl)phthalimide in presence of N,N’-dicyclohexylcarbodiimide. The monomer reactivity ratios for copolymerization reactions of 2-(N-phthalimido)ethyl methacrylate with methyl acrylate, ethyl acrylate, butyl acrylate and styrene, respectively, in solution with azobisisobutyronitrile (AIBN) as initiator, were estimated by nitrogen analysis. The structure of the copolymers was investigated by IR spectroscopy. The Q and e values for 2-(N-phthalimido)ethyl methacrylate were calculated. Some of the synthesized polymers were tested for their antimicrobial activity against bacteria and fungi.


INTRODUCTION
Copolymerization is one of the most important means to improve the performance of polymers.Since polymers are generally immiscible due to adverse entropy effects, copolymerization offers a convenient method of incorporating different monomers in polymer chain.The difficulties associated with the synthesis of copolymers are the wide variation in the reactivity ratios of the monomers 1,2 .Reactivity ratios are among the most important parameters for the composition equation of copolymers, which can offer information such as the relative reactivity of monomer pairs and help estimate the copolymer composition 3 .To calculate the polymerization rate or polymer productivity and copolymer composition, monomer reactivity ratios must be known.The method which is used most often nowadays for estimating monomer reactivity ratios is to perform a low conversion copolymerization at various initial monomers feed compositions.Subsequently, the copolymer composition is determined for each reaction 4 .Reactivity ratio values may be evaluated by various procedures [5][6][7][8] .
Aromatic polyimides have become an important class of polymers that have a wide range of application as high performance materials in the aerospace and industries electronics because of high thermal stability [9][10][11][12][13] .Aromatic polyimide having phthalimide pendent group into the polymer are found to possess excellent heat resistance, transparency and enhances the solubility and thermal stability of polymer 14,15 .
Phthalimide and its derivatives are very important compounds.They used in the synthesis of antimicrobial activity, antiandrogens and other agents for treating tumour necrosis factor.Certain phthalimide derivatives are used as herbicides and for reducing bacterial contamination 16 .Copolymers containing the phthalimide derivatives have been used as optical brightening agents 17 .N-Substituted phthalimide copolymers may be used as activated drug binding materials 18 .

Materials
Methyl acrylate, ethyl acrylate, butyl acrylate and styrene were BDH (England) products.Phthalic anhydride and N,N-dicyclohexylcarbodiimide (DCCI) were from Aldrich Co.. Methacrylic acid and the free radical initiator, azobisisobutyronitril (AIBN), were from E. Merck, Darmstadt.All the solvents were of reagent grade and were purified by distillation before use.

Synthesis 1-Preparation of N-(2-hydroxyethyl) phthalimide (NHEP)
Phthalic anhydride (0.1 Mol) was taken in a two-necked flask fitted with a reflux condenser and a nitrogen inlet, and dissolved in 50 ml of DMF, 0.1 mol of ethanolamine was added dropwise to it.The reaction was moderately exothermic hence cooled in an ice bath.The contents were stirred with magnetic stirrer and heated in an oil bath to 130°C in nitrogen atmosphere for 3 h.Excess DMF was removed by vacuum distillation and the contents were poured into water.The precipitated product, NHEP, was filtered off and recrystallised using ethanol as a solvent.The yield was 75% and m.p. was 125-127°C.(Lit.126) 25

Homopolymerization
Solution (10%) of the monomer in DMF was treated with azobisisobutyronitrile (AIBN) (1mol%).After purging with deoxygenated nitrogen, the reaction mixture was allowed to stand at 60 o C for 6h.The polymer was obtained by reprecipitation in methanol and were collected by filtration, washed dried and weighted.The yield was 80%.

Copolymerization reactions
Copolymers of 2-(N-phthalimido)ethyl methacrylate (PEMA) with methyl acrylate, ethyl acrylate, butyl acrylate and styrene were studied for different mole fractions in the feed.The reaction time was restricted to give conversion less than 10% in order to obtained polymer samples with homogeneous composition.
The copolymers were obtained by solution polymerization method in presence of azobisisobutronitrile (AIBN) as a free radical initiator.Thus the pre-determined amounts of the comonomers were placed in glass tubes, and diluted with dimethyl formamide so that the total monomer composition was about (1.5mol/l).Polymerization was commenced by adding AIBN (1mol%).The tubes were flushed with oxygenfree nitrogen for 10 minutes, capped and thermostated at 65 0 C for 1-3h, depending on the comonomer pairs and composition.All copolymers were obtained by reprecipitation from methanol, except EA reprecipitation from 50% methanol and 50% distilled water and all washed several times, dried and weighed.The composition of copolymers was determined from nitrogen analysis.
1 HNMR spectra were recorded on a Varian Gemini 200 MHz spectrophotometer, Cairo University.The chemical shift (δ) are given downfield relative to tetramethylsilian (TMS) as the internal standard.The elemental analysis were also carried out in Microanalytical center, Cairo University.The antibacterial and antifungal activities were carried out at the Regional Centre for Mycology, and Biotechnology at Microanalyticl Center, Cairo University.

RESULTS AND DISCUSSION
In the present investigation, 2-(Nphthalimido)ethyl methacrylate (PEMA) was prepared by the reaction of N-(2-hydroxyethyl) phthalimide (NHEP) with methacrylic acid in the presence of DCCI, according to the following (Scheme1): The monomer was a crystalline solid, easily soluble in most organic solvents, but sparingly soluble in aliphatic hydrocarbons, such as n-hexane and petroleum ether.The copolymerization of PEMA with MA, EA, BA and ST were studied and the reaction can be written as shown in (Scheme 2).In all systems studied, the composition of each copolymer was calculated from its nitrogen content.The structure of the copolymers was confirmed by IR spectroscopy.The IR spectrum of PEMA-ST copolymer, as example, shows peak at 3030 cm -1 is due to the C-H stretching of aromatic protons.Peaks at 2929 and 2858 cm -1 corresponding to the C-H stretching of methyl and methylene groups.The strong absorption peaks at 1770 and 1750 cm -1 are due to the ester carbonyl stretching and that at 1732 cm -1 is due to the carbonyl stretching of the phthalimido group and a strong band at 760 cm -1 due to monosubstituted benzene ring.

Scheme 2.
For the industrial preparation of any copolymers, knowledge of reactivity ratio is very essential.The reactivity ratios of PEMA with MA, EA, BA and ST were evaluated from the monomer feed ratios and the copolymer composition.
Tables (1-4) illustrate the analytical data for copolymerization reactions of PEMA with MA, EA, BA and ST.From the values of feed and copolymer composition, the monomer reactivity ratios (r 1 and r 2) for each system were evaluated using Fineman -Ross 27 and Kelen-Tudos 28 methods and the standard deviations of the results were calculated by regression analysis as given in Table The Q and e values were calculated by using the Alfrey-Price equations (29) e 1 = e 2 ± (-In r 1 r 2 ) 1/2 , The Q and e values which represent the extent of resonance stabilization and the polarity of the double bond, respectively, in a monomer and its radical are extensively tabulated by Young (30) from earlier copolymerization data.Thus, the average Q and e values for PEMA were obtained by using the monomer reactivity ratios determined for the copolymer systems and using the Q and e values for the vinyl monomers.The average Q and e values for NPEMA were found to be Q =1.4 and e = 0.51 and are in agreement with those reported in the literature (30) for the esters of methacrylic acid.

Antimicrobial activity
The antimicrobial activity of the synthesized compounds was determined in vitro using the hole plate and filter paper method 24 against a variety of bacteria and fungi.Comparative studies of our prepared compounds and standard drug were also carried out .The tested compounds were dissolved in DMSO, different concentration have been chosen (125, 250 and 500 µg/ml).The inhibition zones of microbial growth produced by different compounds were measured in millimeters at the end of an incubation period of 48h at 28 o C. DMSO alone showed no inhibition zone.The gram +ve bacteria were Staphylococcus aureus; the gram -ve bacteria were Escherichia coli and the fungi were Aspergillus flavus and Candida albicans.
Tetracyclin and Amphotericin B were used as standard for antibacterial and antifungal activity, respectively.The results are illustrated in (Table 6).

CONCLUSION
Copolymers from PEMA with MA, EA, BA and ST with different compositions were easily synthesized in DMF by free radical polymerization.The monomer reactivity ratios (r 1 and r 2) for each system were evaluated using Fineman -Ross and Kelen-Tudos methods and the values obtained are in good agreement.The r 1 r 2 value for PEMA-MA (0.15) indicates that the copolymer should have a random distribution of the monomer units, while for the PEMA-EA, PEMA-BA and PEMA-ST systems the r 1 r 2 values (2.5, 1.5 and 1.32) respectively illustrate a low tendency of monomers to alternated, and the copolymer should be composed mainly of small sequences of monomeric units of the same type.The composition curves indicates that all studied systems gave no azeotropic compositions.The average Q and e values for PEMA are in agreement with those reported in the literature for the esters of methacrylic acid.