Syntheses, Characterization and Study of Use of Manganese (III) Schiff-Base Complex as Thermal Initiation in Radical Polymerization of Styrene

The new schiff base complex: Chloro-(bis (salicylaldehyde) ethylene diiminato) aqua manganese (III) is synthesized and characterized. It is used as thermal initiation in radical polymerization of styrene at 80 c ◦ in dark without inhibition and retardation complication, and the rate of polymerization is directly proportional to the squre root of initiator concentration [I] 1/2 . gravimetry technique is used for deteremination of the rate polymerization, and viscometery is used for determination of average of polymerization. The uv-visble spectrophotometry is used to determine the rate constant of initiator decomposition (k a ). The value of the kinetic parameter ratio k p / k t1/2 (Where k p & k t are the rate constants, propagation and termination respectively).


Introduction:-Chain reaction:-
Free radical polymerizations are chain reactions.The addition of a monomer molecule to an active chain end regenerates the active site at the chain end.Hence, alarge number of monomer molecules are "consumed" for each active site introduced into the system.
In chain reaction polymerization we many recognize four distinet types of processes.
They are (1) : 1-chain initiation----a process in which highly reactive transient molecules or active centers are formed .kd Initiator 2 ki + M Where is an initiator free radical.
M is a molecule of monomer.Kd & ki is the rate constant of Initiator https://doi.org/10.30684/etj.27

+ M + M
Where R•n is the propagation free radical with a degree of polymerization n Kp is the rate constant for propagation.

3-
Chain transfer ----involving the transfer of the active site to another molecule (e.g., monomer) the molecule that has lost the active site is now "dead" from a chain-propagation point of view.The molecule that has accepted the active site can start a new chain.
+ YZ Y + Where YZ is a chain transfer agent that may be solvent, monomer, initiator or polymer molecules.

4-
Chain termination ----a reaction in wich the active chain centers are destroyed.
Where Pn is the final inactive polymer.K t is the rate constant for termination.Numerous substance decompose to free radicals when heated.
If the decomposition temperature corresponds to a convenient temperature range for polymerization.The substance may be useful as an initiator In fact, it is dependence of the initiator decomposion rate on the temperature which determines the usfulness of the compound as an initiator.Such thermal decompositions usually yield two free radicals from on initiator molecule by first -order reaction process (2).The ability of certain metal chlates to produce freeradicals when heated was first pointed out by Arnet and Mendelsohn (3) in the course of investigations on the oxidation of these compounds thus, in the case of ferric acetyl acetonate they postulated the following reaction :-

Techniques:
1-Determination of the rate of polymerization: A polymerization process was carried out in apyrex tube 15 cm in length, 1.5 cm in diameter, and 10 cm3 capacity connected to an argon gas puring system.Dissolved air was removed by bubbling (32).Styrene saturated argon gas (Puring 99.96%) for 10 minutes.The reaction tube was protected from light using aluminum foil and placed in a bath at 80 c• ± 1 c• [ General purpose stirred thermostatic baths/ circulators-Grant-GA 100,GD 100, GD120).Average rate of polymerization were measured gravimetrically by precipitation of the polymer in pure ethanol and the rate of polymerization was calculated as follow (14).
where [m]= is the initial monomer concentration.% conv.= is the percentage of conversion of monomer to polymer.t= time of reaction in second.

2-viscometery:
The namber average molecular weight of polymer (poly styrene) was generally determined viscometrically in benzene at 30 c • with aid of Mar-Houwink equation (15).
η is the intrinsic viscosity and α and k are constant for a given polymersolvent system at particular temperature.For poly Styrene (16) .

5-Molar conductivity measure-ement
Copenhagen-CDM83 was used.6-Flam atomic absorption appar-atus shimadzu-760G was used.7-Ion selective electrode orian/ metohm-686-Titroprocessor was used.Results and Discussion:-1-Characterization: The ligand and its complex ws characterized by IR spectroscopy, molar conductivity measurement, flame atomic absorption apparatus and Ion selective electrode all characterization data in Table(1),(2),(3) and figure (1).In the IR spectra of the free ligand and it's complex rc=N shifted to a lower wave number by ca.15 cm-1 upon coordination.
In addition, the disappearance of the OH band of the free ligand in the Maganese (III) complex indicates that the OH group has become deprotonated and bonded to the metal ion as-0(17-18),Anew bands appeard at 462.9, 441.7, 351 and 505.3 wich cold be attributed to the M-O19, M-N20 , M-Cl21,M-H2O..mol - ) and the square root of the Schiff base complex concentration not line.itindicates that the chelate complex weak electrolet in solution so the chlor atom inner sphere coordinate (33) .On the basis of these result it can concluded that in the complex the Schiff base is coordinated to manganese atom as hexadente.Therefore we suggest that the structure of complex.The rate of polymerization of about 0.7*10 -6 mol.l -1.s -1 for styrene in the absence of the chelate complex.Figure (2) shows that the average rate polymerization was estimate from eq.( 1), proportional to the square root of the chelate concentration at constant monomer conc.(8.7 mol.l -1 ) and temperature, the straight line in fig( 2) corresponds to the relation( 9) (31) . [][] (2), relation (10) and fig.
(3) the striate lines pass through the origin which indicate the polymerization process in this system is simple and does not involve inhibition or retardation or any other comp-lected side reactions (22) (23) .The slope of the logarithmic plot of the relation between rate of polymerization and initiator conc.(fig.4) is found 0.5 this confirms the free radical nature of the present initiating system (23).The kinetic parameter ratio kp/kt 1/2 was determined using the relation (9).the result in the table (2).the mean value of kp/kt 1/2 in table (2) equals to 3.9 *10 -4 mol -1/2 .l 3/2 .s -1/2 and is good agreement with the literature value of unretarded free radical polymerization styrene (24,25,26).The value of kp/kt 1/2 is characteristic for a given monomer at certain temp.and it does not depend on the type of initiator or mechanism of initiation.From the value of kp/kt 1/2 one can know whether the polymerization.Involves some complications, such as inhabitation, retardation….etc(32).(fig.5) is the relation between the specific viscosity to the conc.Of polymer solution in gm/.dl plotting of ήsp/c and conc.By applying equations( 5), (3) was used to determine the molecular weight of polymer (27).It was found 3*10 6 mol.gm -1 .Measurement of the number average degree of poly.The absorption between (400-600)nm is broad and low intensity may be attributed to d-d electron transition [ligand field transition],the absorption range between ( 300-400)nm which present charge transfer transition were due to electron transition between molecular orbitals located near the metal and the molecular orbital located near the ligand inrespect to that the oxidation state of Mn(III) (28) (29).The absorption range between (280-350)nm represent ligand spectra which occur as a result of electron transition between the ligand molecular orbital PDF created with pdfFactory Pro trial version www.pdffactory.comOn heating of the initiator solution in styrene at 80 c• the absorption spectrum changes as shown in (fig.9) and ultimately becomes indisting-uishable from that of manganese chelate in styrene (fig.7).
The isosebestic points appeared at 355nm indicate that the overall chemical changes are relatively simple it is also noticed that ther is alittle increase in the absorption intensity in the range between (300-600) nm during the heating process.This very broad low intensity peaks may be attributed to d-d electronic transitions for Mn(III) complex.
The decomposition of Mn(III) complex in styrene and ethanol mixture during heating at 80 c • has been monitored spectrophotometrically, aseries of wavelength 355 nm has been selected for this purpose.thevalue of (At-A∞) decreases exponentially with the reaction time corresponding to the first order (31) chelate decomposition and consisten values for the first order rate constant (ka) were obtained.(fig.10) shows the variation of ln(At-A∞) of manganese chelate in styrene solution with time of heating at 80 c• and ka found 4.5×10 -2 s -1 when the concentration of initiator was 2.6×10 -4 mol.l -1 .the rate of thermal decomposition of chelate manganese was found 1.2×10 -5 mol.l -1 .s - according to the equation( 12 .6.7 2412-0758/University of Technology-Iraq, Baghdad, Iraq This is an open access article under the CC BY 4.0 license http://creativecommons.org/licenses/by/4.0Eng.& Tech.Journal ,Vol.27,No.6, 2009 Synthsese, Characterization and Study of Use of Manganese(III) Schiff-Base Complex as Thermal Initiation in Radical Polymerization of Styrene * Chemical Engineering Department, University of Technology/Baghdad 2-chain propagationthe addition of monomer molecules to the active chain end, accompanied by regeneration of the terminal active site.
The intrinsic viscosity of polymer solution was measured with an ostwaldu-tube viscometer.Solution were made by dissolving the polymer in a solvent (penzene) in (gm/100ml) and the flow times of polymer solution and pure solvent are t and t0 respectively.
concentration of polymer solution in g.dl -1 .3-Changes in the Absorption spectra during photochemical reaction:-The photo composition of the initiator at 355 nn ( at 25 c• ) was followed with the aid of Hitachi-u-2000 double beam spectro-photometer using the quartz uvcell of 10 mm path length the shown in Fig.(9).The change in absorbance was measured for different irradiation times at a different wave lengths.In order to PDF created with pdfFactory Pro trial version www.pdffactory.comEng.& Tech.Journal ,Vol.27,No.6, 2009 Synthsese, Characterization and Study of Use of Manganese(III) Schiff-Base Complex as Thermal Initiation in Radical Polymerization of Styrene * Chemical Engineering Department, University of Technology/Baghdadstudy the kinetics of photodecay of the initiator in certain monomer for measurements of the absorbance at infinite irradiation time (A∞ ), the solution was given prolonged irradiation for at least 10 half lives of the rate of inihiator (about 6 hours).In order to calculate the specific rate constant of the decomposition of the initiator (ka) the following equation was used(31) .Ln (a-x) =Ln a-kat ---6 Where: a= concentration of initiator before irradiation.x= the concentration of inititor after irradiation.t= time of irradiation of initiator solution.A•= Absorbance of initiator before irradiation.a-x= At-A∞ ---7 Ln(At-A∞) = Ln(A•-A∞)-kat---8 Thus aplot of Ln IAt-A∞I with versus variety irradiation time (t) gives astriaight line with slope equal to ka(s-1).
Fig.(1) shows the relation between the molar conductivity (AM) (cm 2 .ohm- 1 (salicyaldehyde) ethylene-diiminato] aqua manganese (III) was used as initiator it PDF created with pdfFactory Pro trial version www.pdffactory.comEng.& Tech.Journal ,Vol.27,No.6, 2009 Synthsese, Characterization and Study of Use of Manganese(III) Schiff-Base Complex as Thermal Initiation in Radical Polymerization of Styrene * Chemical Engineering Department, University of Technology/Baghdad was readily initiate the polymerization of styrene at 80c•.
absorption:The uv-visble absorption spectrum of manganese chelate in ethanol sol-ution and the manganese chelate in styreneethanol solution and styrene spectrum are shown in (fig6,.7,8)respetively.

Figure ( 4 )
Figure(4) Relation between logarithmic rate of polymerization at 80C o logarithmic initiator con.

* Chemical Engineering Department, University of Technology/Baghdad
PDF created with pdfFactory Pro trial version www.pdffactory.comEng.

& Tech. Journal ,Vol.27, No.6, 2009
Synthsese, Characterization and Study of Use of Manganese(III) Schiff-Base Complex as Thermal Initiation in Radical Polymerization of Styrene * Chemical Engineering Department, University of Technology/Baghdad

Table ( 3): date of rates polymerization, concentration initiator co% and rate contants at 80 c• & [8.7] mol.l-1 monomer.
Relation between rate Polymerization and square root of the chelate con. at constant monomer con.
PDF created with pdfFactory Pro trial version www.pdffactory.comEng.& Tech.Journal ,Vol.27,No.6, 2009 Synthsese, Characterization and Study of Use of Manganese(III) Schiff-Base Complex as Thermal Initiation in Radical Polymerization of Styrene * Chemical Engineering Department, University of Technology/Baghdad Figure (2)