Synthesis of New Linear Polymers Containing Thiocarbonyl Groups: Polyaddition of Dicarbothioic Acid to Diolefins

Polymer Journal, Vol. 26, No. 1, pp 49-59 (1994) Synthesis of New Linear Polymers Containing Thiocarbonyl Groups: Polyaddition of Dicarbothioic Acid to Diolefins Eiichi KOBAYASHI,* Kazuyoshi TENDO, Masato KATO, and Sadahito AoSHIMA Department of Industrial Chemistry, Faculty of Science and Technology, Science University of Tokyo, Noda, Chiba 278, Japan (Received May 24, 1993) ABSTRACT: The polyaddition of 1,4-benzenedicarbothioic acid to 1,4-divinylbenzene or 1,4-diisopropenylbenzene was carried out at 70°C in toluene under a nitrogen atmosphere by radical mode such as by addition of AIBN or UV irradiation. Both diolefin compounds gave polymers in a 90% yield. The polymer obtained from I ,4-diisopropenylbenzene was soluble in chloroform, and the molecular weight of the polymer (Mw) was 40000. On the other hand, the polymer obtained from 1,4-divinylbenzene was partly soluble in conventional organic solvents, possibly due to a cross linkage formation by a pendant vinyl group. The model addition reaction of thiobenzoic acid to styrene gave a by-product ca. 8% being the I : 2 adduct with respect to thiobenzoic acid and styrene. Alkali hydrolysis of both polymers was investigated to confirm the cross linkage structures in the polymers. KEY WORDS Polyaddition / Polythioester / Addition Reaction/ Hydrolysis / 1,4-Benzenedicarbothioic Acid / 1,4-Divinylbenzene / 1,4-Diisopropenylbenzene / Thiobenzoic Acid/ Styrene/ oc-Methylstyrene / Addition reactions of carbothioic acids to (nb 8 = 1.81) and exhibited the reversible phase olefins occur easily and are used to prepare transition by heat mode. various thioesters or polythioesters. For CH2=CH-<Q)--CH=CH2 + HS-<Q)--SH R or UV example, Ipatieff et al. 1 and Crouch et al. 2 synthesized thioesters by radical addition reaction of thioacetic acid to olefins. Marvel et (1) al. reported the syntheses of various polyThe authors synthesized new saturated thioesters by radical polya_ddition of dicarbothioic acids to diolefins. 3 polymers containing the thioester bond instead Recently, the authors investigated the radical of the thioether bond. The introduction of polyaddition of 1,4-benzenedithiol to 1,4- carbonyl groups to the poly(thioethers) may divinylbenzene (DVB) as shown in eq 1. 4 •5 It increase intermolecular interactions between took place readily in solution under UV polymers. By variation of the intermolecular irradiation or in the presence of a radical interactions, thermal properties, and liquid initiator such as AIBN. The obtained polymer crystalline properties of the poly( thioethers) had a linear structure with high molecular may be improved. Thus, 1,4-benzenedicarweight (Mw=3OOO0-10OOOO). Interestingly, bothioic acid (BDTC) was polymerized with the polymer had a high refractive index DVB or 1,4-diisopropenylbenzene (DIPB) to * To whom all correspondence should be addressed. 49 E. KOBAYASHI obtain new saturated polymers as shown in eq 2. The addition reaction of thiobenzoic acid (TBA) to styrene (St) or c,:-methylstyrene (MSt) was also investigated as a model of the polyaddition of BDTC to DVB or DIPB. In addition, the hydrolysis of the obtained polymers was investigated in order to make clear their structures. f;l f;l CH 2 =C-<Q)--C=CH 2 + HSC-{5\r-SH R 11'~ 0 0 R R fCH,CHUCHCH,scucst- 0'08 n R=H,CH3 (2) EXPERIMENTAL Reagents The authors applied the synthetic method of TBA 6 to the preparation of 1,4-benzenedicarbothioic acid (BDTC) (eq 3). In a suspension of 12.3 g (0.22 mol) of sodium hyc1cu~ Cl _NaSOH > NaSC fc5'r·SNa U 0 0 in Et H 11 O \_\:::'.ft O _!L,. HSC~·SH II O I\ 0 (3) drosulfide (Nacalai Tesque Inc.) dried over cone. sulfuric acid in 80 ml of anhydrous ethanol (Nacalai Tesque Inc.), a solution of 10.2 g (0.05 mol) of terephthalyl chloride (Tokyo Chemical Industry Co.) in 100ml of anhydrous diethyl ether was added dropwise with stirring at 0-5°C under a nitrogen atmosphere. The reaction mixture was stirred at room temperature for 3 h to complete the reaction. 100 ml of water were added in the reaction mixture to dissolve the product. The aqueous layer was washed five times with 50 ml of diethyl ether to remove a trace amount of by-product, ethyl ester, and then 50 ml of 6N hydrochloric acid were added to the aqueous layer on an ice bath. The precipitate was recovered by filtration and washed with water until the pH was approx50 et al. imately 7. It was dried over anhydrous calcium chloride in vacuo at room temperature for about 12 h. The product was purified by sublimation at 100°C under 0.1--0.05 mmHg. BDTC was obtained in a 96% yield as a yellow solid, mp 127.5-127.7°C (lit. 7 127.0127.50C). DVB was provided by Hokko Chemical Co. DIPB (Mitsui Petrochemical Co.), TBA (Tokyo Chemical Industry Co.), MSt (Nacalai Tesque Inc.), and St (Wako Pure Chemical Industries) obtained commercially were purified twice by vacuum distillation under a nitrogen atmosphere before use. Benzene and toluene (Nacalai Tesque Inc.) as reaction solvents were distilled over calcium hydride. 2,2'-Azobisisobutyronitrile (AIBN, Wako Pure Chemical Industries) was used as received. A nitrogen gas was purified as shown in the literature. 8 For hydrolysis, tetrahydrofuran (THF, Nacalai Tesque Inc.), ethanol (Amakasu Chemical Industries), hydrochloric acid (Nacalai Tesque Inc.), chloroform (Nacalai Tesque Inc.), and ion-exchaged water were distilled to exclude oxygen under a nitrogen atmosphere before use. And powdery sodium hydroxide (Koso Chemical Industries) was heated at 150 °C in vacuo for 3 h to degas before use. Sodium tetrahydroborate (Kishida Chemical Co.) was used as received. Polyaddition Polyaddition was carried out in the presence of AIBN or with UV irradiation in toluene at 70°C under a nitrogen atmosphere as described in the previous papers. 4 •5 A typical example was as follows: in a pyrex tube equipped with a three-way stopcock, an equimolar amount of BDTC and DVB (1.1 mmol, each) in toluene (13 ml, 1.2 x 10 - 1 mol) was charged by a medical syringe under a nitrogen atmosphere. The polymerization was initiated at 70°C by the addition of AIBN (2.2 x 10- 2 mi:nol) in toluene or with UV irradiation using a 450 W high pressure mercury lamp (Ushio Co.). The polymerization was terminated by pouring the Polym. J., Vol. 26, No. I, 1994 Synthesis of New Linear Polymers Containing Thiocarbonyl Groups polymerization mixture into a large amount of methanol, then the polymer precipitated was recovered by a centrifugation. After washing out residual monomers with methanol, the polymer was dried in vacuo at room temperature for 12 hover anhydrous calcium chloride. Model Addition Reaction The addition reaction of TBA (1.0 mo11- 1 ) to St (1.0moll- 1 ) or MSt (l.0moll- 1 ) as a model of the polyaddition was carried out at 70°C in benzene by the addition of a benzene solution of AIBN (1.0 x 10- 2 or 5.0 x 10- 2 mol 1- 1 ) under a nitrogen atmosphere similarly as below (see Figure captions for the reacti (...truncated)