ANewMethod for Synthesis of Poly ( 2 , 6-dimethyl-1 , 4-phenylene oxide ) and Poly ( 2 , 6-diphenyl-1 , 4-phenyl oxide )

e polymerization of two monomers 2,6-dimethylphenol and 2,6-diphenylphenol was carried out by an oxidative route in the presence of Cu(I) as a catalyst and amine complex as a solvent assisted by microwave heating. e synthesized polymers were characterized by NMR spectroscopy, differential scanning calorimetry (DSC), and gel permeation chromatography (GPC). It was observed that this process of polymerization gives high yield (98wt%) of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and poly(2,6-diphenyl-1,4-phenylene oxide) (PPPO)with amolarmass of 1180 (MMnn), 1400 (MMww) and 28000 (MMnn), 46500 (MMww) gm/mol, respectively. A negligible amount of diphenoquinone was also observed and its dispersity was rather moderate, 1.17 and 1.68, respectively.


Introduction
Microwave-assisted reaction was introduced in 1986 [1].Comparing with conventional heating, it requires lesser time with higher yield.It was attributed to dielectric heating [2] and to specify the microwave effect by others [3].However, the main advantage of microwave reaction is to maintain a uniform temperature throughout the reaction period, as a result of internal heating by irradiation [4].
An atom transfer radical polymerization (ATRP) was introduced in 1995, which allows an efficient polymerization with well-de�ned molar masses and narrow dispersity of polymers produced.Microwave-assisted ATRP has been successfully used for polymerization of vinylic or acrylic monomers such as styrene [5][6][7], methyl methacrylate [6][7][8], vinyl acetate, acrylonitrile, and n-octyl acrylate [9].In ATRP, an organic halide (RX) is used to initiate a transition-metal compound in its lower oxidation state along with an electrondonating compound for catalyzing polymerization [10].
An oxidative polymerization of 2,6-dimethylphenol was discovered in 1956 [11,12], leading to the formation of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO).Polymerization occurred at room temperature using an amine complex of copper (I) salt as a catalyst in the presence of oxygen (Scheme 1).A high molar mass linear PPO was formed along with a small amount of diphenoquinone [13].In this investigation it was observed that the length of the polymer chain depended on the amine type used, its molar ratio, and polarity of the solvent.According to Hasy works [14] in a similar reaction, it was noted that the diphenoquinone became its major product at a high temperature.
In this work PPO and PPPO were synthesized for the �rst time by oxidative polymerization using the Cu(I) in amine complex as catalyst, heating by microwave.100 mL round bottom �ask at room temperature.en, 0.5 gm (4.3 mmol) of TMEDA and 0.03 gm (0.27 mmol) of BC were added simultaneously.e mixture was sonicated for 2 minutes at room temperature and transferred to a Pyrex tube of 100 mL.e monomer was added to the reaction mixture aer one minute.e tube was �tted with re�ux and transferred to the microwave.e reaction was performed at 100 Watt for 3 min then at 300 Watt for 6 min.e polymer was cooled, treated 10 times with 10 mL of HCl/methanol (10 wt %), and then isolated in excess methanol.e polymers synthesized were puri�ed by repeated dissolution in THF and precipitation in n-heptane, then isolated by �ltration, and dried to a constant weight at 40 ∘ C in a vacuum oven for 5 days.Contrarily to PPO which has a white yellow color, the PPPO was light red.

Experimental
2.3.Characterization. 13C and 1 H NMR spectra of the PPO and PPPO in deuterated chloroform were recorded with a JEOL ECLIPSE 400 spectrometer, using tetramethylsilane (TMS) as an internal standard.e glass transition temperature (Tg) of PPO and PPPO was measured with a DSC (Shimadzu DSC 60), previously calibrated with indium.e samples were heated from 30 to 240 ∘ C at a heating rate of 20 ∘ C min −1 .e dispersity of PPO and PPPO was determined at 30 ∘ C with a Viscotek Complete Tetra Detector Platform and GPCMax front-end chromatography setup equipped with 2 × 1-MBMMW column by using standard polystyrene and tetrahydrofuran (THF) as a solvent.

Results and Discussion
A viscous solution appeared immediately aer adding the monomer to the reaction mixture and viscosity was increased during the reaction.Under the same condition, a maximum of 98 wt % conversion was obtained for PPO and PPPO aer 3 min of the reaction time with a negligible amount of diphenoquinone.From the results of the molar mass of these two polymers, it was observed that the PPPO was relatively more active than PPO.e structures of the two polymers were con�rmed by 1 H and 13 C NMR techniques.e 1 H NMR spectra of PPO and PPPO are illustrated in Figure 1.It shows two sets of peaks.In the spectra of PPO, a triplet centered at 2.11 ppm was observed which can be assigned to the methyl protons, and one multiplet centered at 6.46 ppm was also seen, which can be attributed to the aromatic protons.e spectra of PPPO in Figure 1 show the presence of one large multiplet between 7.04 and 7.70 ppm assigned to 10 protons of the two substituted phenyl and another between 6.87 and 7.04 ppm attributed to the 2 protons of the phenylene of the backbone.e absence of any peak between 4 and 5 ppm clearly indicates the disappearance of hydroxyl groups, which supports the formation of the polymer.
e 13 C NMR spectra of PPO and PPPO are gathered in Figure 2. e spectra of PPO show a peak at 16.88 ppm that can be assigned to the methyl carbons.Furthermore there are four sets of carbon peaks attributed to the phenyl at 154.62, 145.50, 134.2, and 114.59 ppm assigned to the carbons C 1 , C 4 , the symmetric lateral C 2 +C 6 and C 3 +C 5 , respectively.Concerning the PPPO, the presence of one large multiplet between 128 and 130 ppm was assigned to the 12 carbons (C 2 , C 3 , C 5 , and C 7 ).e peaks at 156.2, 143, 136.2, and 137.8 ppm were attributed to C 1 , C 4 , C 6 , and C 5 , respectively.e multiplet between 116.5 and 118.2 ppm was assigned to the two carbons C 8 .e average molar mass,   and   of the isolated PPO are 1180 and 1400 gm/mol, respectively, and those of PPPO are 28000 and 46500 gm/mol, respectively, as shown in the Chromatograms of Figure 3. eir dispersity is rather moderate 1.17 and 1.68 respectively.As can be noticed, PPPO is unexpectedly obtained with the highest molar mass; PPO has two methyl groups and would rather polymerize to a lower molar mass with a tendency towards a monodisperse polymer.e DSC thermograms of PPO and PPPO plotted together in Figure 4 show a Tg at 210 ∘ C and 90 ∘ C, respectively.

Conclusion
From these results, it can be concluded that the polymerization of 2,6-dimethyl-phenol and 2,6-diphenylphenol assisted by microwave led to the formation of poly(2,6-dimethyl-1,4-phenylene oxide) and poly(2,6-diphenyl-1,4-phenylene oxide), respectively.Heating by the microwave technique resulted in a high conversion to polymers aer only 3 min and allowed obtaining moderate molar masses.From these data it was also noted that the poly(2.6-diphenyl-1,4-phenyleneoxide) was relatively more active than poly (2,6-dimethyl-1,4phenylene oxide) due to the    substitute group, which increases the radical stability by resonance effect.

F 1 : 1 H
NMR spectra of PPO and PPPO.

F 2 :
13 C NMR spectra of PPO and PPPO.