Modification of Novel phenol-formaldehyde Resins By Esterification……

: This work involves the preparation of three phenol-formaldehyde resins that have pendant 1-cyclopentene-1,1-dicarboxylimidyl.The target compounds produce by condensation of N-(hydroxyl phenyl)-1-cyclo pentene-1,1-dicarboxylimidyl with formaldehyde under conditions similar to those in Novolac preparation. The prepared resins were modified by esterification of phenolic hydroxyl groups in the prepared resins via treatment with benzoyl, acryloyl, methacryloyl and cinnamoyl chlorides respectively in the presence of triethylamine. The synthesis compounds were characterized by FTIR and U.V spectral data and determined softening points of crystalline solid resins, intrinsic viscosities of soluble resins.


Introduction:
Phenol-formaldehyde resins are the oldest commercial synthetic polymers, first introduced around (111) years ago (1,1) .Since the discovery of phenol-formaldehyde resin in 1011 many attempts have been carried by several workers to incorporate structural modifications  .
Phenolic resins are the most important thermosetting resins which are used in a wide variety of applications include varnishes, adhesives, laminates, casting, binders and surface coatings industries due to their high performance properties namely; high mechanical and chemical resistance, strong adherence and good absorptivity of fillers (8)(9)(10)(11) .
Modifications were performed through using of aldehydes other than formaldehyde or by using different phenols to obtain new resins having new properties.
Phenolic resins were converted into a hard three dimensional crosslinked network through modification.The primary requirement for high-temperature performance necessitates the selection of polyfunctional phenolic resins and curing agents are capable of creating high crosslink densities (11,11) .
In the work three phenol-formaldehyde resins were prepared by poly condensation of N-(hydroxylphenyl) 1-cyclo pentene-1,1-dicarboxylimidyl with formaldehyde under conditions similar to those in Novolac preparation.

Experimental:
Chemicals used in this work are supplied from Sigma Aldrich and Fluka companies and are used without further purification.
Melting points were determined on Gallen Kamp capillary melting point apparatus and were uncorrected.IR spectra were recorded on a Shimadzu FTIR8111., U.V. spectra were recorded on Shimadzu UV-VIS recorder spectrophotometer UV-161.C.H.N. analyses were determined by Perkin-Elmer 111 element analyzer.Softening points were determined on Thermal Microscope Reichert Thermover, SP1, 161., Intrinsic Viscosities were determined with automatic viscometer at 11C using acetone as a solvent.
Table (1) lists melting points, percent yields and major IR absorptions of the prepared acids.1-Preparation of N-(hydroxyl phenyl)1-cyclopentene-1,1dicarboxylimidyl The titled compounds were prepared according to literature procedures (16,11) using fusion technique.The prepared imides were purified by recrystallization from cyclohexane.Melting points, percent yields and major IR absorptions of the prepared imides are listed in Table (1).
The dropping funnel was charged with (181 ml) of concentrated sulphuric acid and (181 ml) of distilled water.
The acid was added dropwise with stirring then the mixture was refluxed for (3 hrs) at (111 1 C) with continuous stirring.
The resulted mixture was added to excess water to precipitate the polymer, then the resulted precipitate was filtered and washed with petroleum ether.The produced polymer was purified by dissolving in DMF followed by reprecipitation with excess water.

Modification of
Finally obtained pure polymer was dried in an oven at (11-11) 1 C for (11 hrs).Table (3) lists percent conversions, softening points, colors, intrinsic viscosities and table (1) lists U.V absorptions and major IR absorptions of the prepared polymers.

1-Esterification of The Prepared Phenol-Formaldehyde Resins to The Corresponding Benzoates
The titled compounds were prepared according to literature procedures (11) with minor modifications: In a suitable round bottomed flask fitted with a dropping funnel was dissolved (1811mole) of the prepared resin (1-cyclo pentene-1,1-dicarboxylimidyl phenol-formaldehyde) resin in (11 ml) of DMF.To the resulted solution (1811mole) of triethylamine was added followed by dropwise addition of (1811mole) of benzoyl chloride with stirring and cooling, then stirring was continued for another (8 hrs).
The filtrate was evaporated under reduced pressure and the residue was extracted with water and chloroform.
The organic layer was dried and the solvent was evaporated to yield a thick oil which was purified by passing its chloroform solution through a Florisil column or by recrystallization from cyclohexane.Table (1) and ( 1) lists percent yields, softening points, intrinsic viscosities, colors, U.V. absorptions and major IR absorptions of the prepared N-(hydroxyl phenyl)1cyclo pentene-1,1-dicarboxylimidyl benzoyloxy phenyl-formaldehyde resins.

1-Esterification of The Prepared Phenol-Formaldehyde Resins to The
Corresponding Methacrylates The titled compounds were prepared by the same procedure used in the preparation of benzoates except the using of methacryloyl chloride instead of benzoyl chloride.Table (1) and (1) lists softening points, percent yields, colors, intrinsic viscosities, U.V. absorptions and major IR absorptions of the prepared 1-cyclopentene-1,1-dicarboxylimidyl methacryloyloxy phenylformaldehyde resins.

6-Esterification of The Prepared Phenol-Formaldehyde Resins to The Corresponding Acrylates
The titled compounds were prepared by following the same procedure used in the preparation of benzoates except the using of acryloyl chloride instead of benzoyl chloride.Table (1) and (1) lists softening points, percent yields, colors, intrinsic viscosities, U.V. absorption and major IR absorptions of the prepared 1-cyclo pentene-1,1-dicarboxylimidyl acryloyloxy phenylformaldehyde resins.The same procedure used in the preparation of benzoates was followed in the preparation of the titled compounds except using of cinnamoyl chloride instead of benzoyl chloride.Table (1) and (1) lists softening points, percent yields, colors, intrinsic viscosities, U.V. absorptions and major IR absorptions of the prepared 1-cyclopentene-1,1-dicarboxylimidyl cinnamoyloxyphenylformaldehyde resins.

Discussion and Results:
The core of this work is to introduce prepared 1-cyclo pentene-1,1dicarboxylimidyl to produce new resins with new properties.In order to perform this target must be includes preparation of three N-(hydroxyl phenyl)-1-cyclo pentene-1,1-dicarboxylamic acids by reaction of 1-cyclo pentene-1,1-dicarboxylic anhydride with o, m and p-amino phenols and prepared N-(hydroxyl phenyl)-1-cyclo pentene-1,1-dicarboxylimidyls were dehydrated from the corresponding amic acids by using fusion technique.
Poly condensation of the prepared imides with formaldehyde under conditions similar to those in Novolac preparation was performed to produce three phenol-formaldehyde resins having pendant 1-cyclopentene-1,1dicarboxylimidyls.modified of the prepared phenolic resins by esterification of phenolic hyroxyl groups via treatment of the prepared phenolic resins with different acid chlorides including benzoyl, acryloyl, methacryloyl and cinnamoyl chlorides in the presence of triethyl amine to produce the corresponding benzoate, acrylate, methacrylate and cinnamate esters.
Physical properties, U.V. and major IR absorptions of the prepared resins and cured resins via esterification are listed in Tables (1,1,3,1,1).IR spectra of the prepared (1-cyclo pentene-1,1-dicarboxylimidyl phenolformaldehyde) resins revealed a clear band in the region (3111-3381)cm -1 due to stretching vibration of phenolic OH groups but this band disappeared in IR spectra of the cured resins produced by esterification.
Thus success of esterification reaction was confirmed by disappearance of phenolic hydroxyl absorption band in IR spectra of the cured resins and appearance of two characteristic clear absorption bands in the regions (1181-1111) cm -1 and (1111-1161) cm -1 due to ester (C=O) and ester (C-O) respectively.
On the other hand U.V spectra of the modified resins showed absorptions at λmax (331-311)nm due to ( *) transitions in the conjugated system of carbonyl groups with phenyl ring in imide moiety and phenyl ring with attached benzoate, methacrylate and cinnamate groups (1) .Also these cured resins give positive results in characteristic tests for esters.It is noticeable that most of the cured resins by esterification are dark oils or low softening point  resins which are soluble in many organic solvents including (Acetone, CHCl 3 , DMSO, DMF, Dioxane , THF) but are insoluble in (methanol and benzene) and have low intrinsic viscosities ranged from (1811-1811) dL/g.All these physical properties are fitted with the expected results for introducing ester functional groups in the starting phenolic resins and at the same time these properties make the cured resins suitable for certain applications such as plasticization and adhesives.(11,11) As a final results it is clear that this work supply us through curing with several new resins having new properties in hope to serve different applications.