Synthesis and characterization of some new oligoazoperoxyester initiators based on polyethyleneglycolos

Synthesis and Characterization of Some New Oligoazoperoxyester Initiators Based on Polyethyleneglycols Synopsis In this work, some new polyethylene glycol azoperoxy esters, designated as PAPE-400, PAPE-600, PAPE-1500 and PAPE-3000 were prepared by the condensation reaction of polyethylene glycol azoesters, terephtaloyl chloride and t-BuOOH. Polyazoester were also obtained by polyethylene glycols(PEG) having average moleculare weight of 400, 600, 1500 and 3000 with azobisisobutyro nitrile according to Heitz et al. These initiators were thermally decomposed in the presence of styreno. (S) at 60°C in order to obtain active PEG-PS block copolymers having peroxy terminal groups. Thermally decomposing of these active block copolymers at 80 C in the presence of methyl methacrylate (MMA) gives PS-PEG-PMMA block copolymers with high yields. INDR0DUCTI0N Azoperoxidic initiators can be prepared by the capping reaction of a dihydroperoxide, diisocyanate and a polyazoester in two step(Hazer, 1985) or the condensation reaction of azoblscyanopentanoyl chloride(ACPC) and ahydroper- oxide(Shaikh and 0th.,1980;Piirma and Chou, 1979;Hazer, Submit ted for pubJ. ^Because of the differant thermal stabilities of the azo and peroxide groups, bock copolymer synthesis can be carried out in two separate stage of polymerization. In the other side, since the incorporation of polyet- her segments into the backbone of a rigid polymer can have a very positive effect on the flexibility of the polymer, PS-PEG,- PVC-PEG block copolymers were prepared by using polyethylene glycols containing scissile azo units orperoxycarbamate groups(Walz and Other, 1977; Ueda and Nagai, 1986; Laverty and Gardlund, 1977; Tobolsky and Rembaum, 1984; Baysal and Other, 197&In this work, some new macroazoperoxy esters were prepared in order to obtaine multiblock copoly mers containing polyether segments with average molecular weight of 400, 600, 1500 and 3000. EXPERIMENTAL Materials Polyethyleneglycol azoesters, designating as PAE-400, PAE-600, PAE-İ500 and PAE-3000, were synthesized from PEG- 400, PEG-600, PEG-1500 and PEG-3000 with azobisisobutyronit- rile(AIBN) according to Heitz et al(Walz and Other, 1977). Triethyl amine, terephtaloyl chloride were supplied from Fluka AG and used any further purification. t-Butyl hydroperoxide was purified by distillation technique at low pressure at 25°C. The first fraction was discarded since it consisted of water, di-tert-butyl peroxide and small amount of t-butyl hydroperoxide. The remaining part in the distillation flask was dried on anhy drous Na2S0,. Its purity was better than 95.6%. Styrene, methyl mathacrylate, dichloroethane, pethroleum ether, benzene, chloroform were supllied from Merck AG and. distilled before use in a routine manner. Perkin Elmer IR-177, Varian NMR-T 60 A, Ubbelohde Viscosimeter, a laboratory type of Cryoscopy equipment were used in the characterization of the products. Synthesis of Macroazoperoxyesters(PAPE-400, 600, 1500 and 3000) In a typical preparation, 16.75 g (17 mmol) PAE-400, 5. 5 ml (40 mmol) triethyl amine and 50 ml of dichloroethane were stirred, by cooling with a mixture of ice and NaCl, into a three necked round bottom flask, equipped with a thermome ter, a reflux condenser with a calcium chloride drying tube and a dropping funnel charged with a solution of 7.5 g(37 -V--mmol) terephtaloyl chloride in 50 ml of dichloroethane. This acid chloride solution was added stepwise so that the temperature of the reaction system did not exceed 5°C. Then the mixture was continuously stirred for a night at room temperature. In the second step of the reaction, a solution of 8.05 g (85 mmol) t-butyl hydroperoxide and 11.0 ml (80 mmol) triethy] amine and 25 ml dichloroethane was added stepwise to the solution of polyazoester having acid chloride terminal groups so as to the temperature of the reaction system did not exceed 5 C. Then the mixture was continuously stirred for several hours at room temperature for a night. Triethyl amine-HCl salt, formed as by product, was filtered off and the reaction mixture was poured into 0.1M HC1. In case of PAPE-1500 and 3000, since they were soluble in the 0.1M HC1, the yields were low. Organic layer was dried on anhydrous Na^SOi. After the solvent was evaporated in a rotary evaporator at 40°C, the product was dried under vacuum at room temperature. PAPE-400 was a viscouse pale yellow liquid, PAPE-600 and 1500 were soft, pale yellow solid and PAPE-3000 was a white solid. Molecular weight determinations of the products were made by cryoscopic method by means of measurements of the freezing point depression of their benzene solutions by using a laboratory equipment. Peroxygen analysis were made by standart iodometric methods. PAPE-400, PAPE-600, PAPE-1500 and PAPE-3000 were analyzed by IR spectroscopy(in NaCl windows), and a strong absorbance at 1710 cm was observed in each of them indi cating polyester formation. Decomposition of the Macroazoperoxyesters The decomposition studies of the macroazoperoxyesters in benzene solutions(10 %) were carried out in evacuated and sealed glass tubes at 60 C for 3.5 hours. After - Vi-decomposition product was dried under vacuum, molecular weight determination and peroxygen analysis of the decom position product were carried out. Polymerization Procedures A glass tube was charged with given amount of an initiator (PAPE or active polymer) and a monomer(S or MMA) and was sealed after evacuation with freeze thaw technique. The tube was then kept at 60°C or 80°C in an oil bath for given times. Then the reaction mixture was taken out and poured into an excess amount of methanol. The polymers were filtered off and dried under vacuum at 40 C. PS Analysis in Block Copolymers For the PS analysis in block copolymers, the phenyl peak at 1600 cm of IR spectrum of the products was choosen as standart peak. A calibration curve was first obtained a CHC13 solutions of pure PS (0.1 g* 0.2 g, 0.3 g, and 0.4 g in 5 ml of CHC1-). Then the absorbances of the solutions of the samples (0. 4 g±Ti 5 ml of CHC13) were measured at the same wave number. And finally; polystyrene amounts in the block copolymer samples were calculated by using calibration curve. All the IR measurements were taken in 0.1 mm NaCl cells. RESULTS AND DISCUSSION Synthesis of Macroazoperoxy Esters Tablo I shows the results of the synthesis of macro azoperoxy esters. The yields are high. In case of PAPE-3000, and 1500, because of their solubility in water, the yields are low. The reaction pathways can be shown as follows: -VI-O CH, OH, : o I 3 o o HO^CH2CH20^nC-Ç-N =N-C - C {OCI^CH^OH +Cl-C-U^)Vc- ;h. (PEG) ""3 Polyazoester (PAE) I CH. Cl (PEG) 0 0 0 î terephtaloly chloride +(C2H5)3N (C2H5)3N.HC1 C1-C-/Q/" C-0-PAE-O-C /(3-C-C +(CH3)3C00H +(C2H5)3N r-(C2H5)3)N.HCl 0 0 0 (CH3)3COO(W^\c-0-PAE-0-C-