Katyonik ve initer polimerizasyon yöntemleri ile blok kopolimer sentezi

Abstract

Bu çalışmada, katycmik polimerizasyan ile trif enilmetil (tritil) uç gruplu palimer sentez edilerek, elde edilen fonk siyonlu polimerin initer özelliğinden faydalanılarak blok kopolimer sentez edilmiştir. Bu amaçla, trif enilmetil tet- raflorobarat. (TPM"1", Tr ) varlığında buiil vinileter ( BVE) polimerleşmesi incelenmiştir. Tritil grubunun polimerin ucunda bulunması yani polimerin tritil katyonu ile başlatıl ması için bu grubun, hidrojen abstraksiyonu yapmasının en gellenmesi gerekmektedir. Bu nedenle Goethals tarafından trifilik asit ile başlatılmış BVE polimerizasyonunda kulla nılmış olan tetrahidrotiof en (THT) kullanılmıştır. Böylece THT ile TPM 'm denge halinde sülfonyum tuzu oluşturması sağ lanarak BVE'in katyonik polimerleşmesi gerçekleştirilmiş ve tritil uç. gruplu palimer elde edilmiştir. Tritil grubu nun, ısısal alarak gerçekleştirilen radikal polimerizasyan- larda initer özellik göstermesinden faydalanılarak, metilme- takrilat (MMA) varlığında blak kopolimer sentezi gerçekleş tirilmiştir. Tritil uç gruplu polimer ve blak kapalimerler İR, UV NMR ve GPC yöntemleri kullanılarak karakterize edildi.

Polymerization of butylvinylether was carried out by using triphenylmethyl (trityl) cation initiated polymerization was prevented by addition tetra hydrothiophene to the polymerization system. Trityl terminated polymers served as thermal "INITERS" for polymerization of vinyl monomers which proceeded via a quasi-living radical mechanism. This procedure makes it passible to prepare black copolymers. There have been several classical methods for the preparetian af black copolymers, which generally involve the successive polymerization of two or more monomers by the same mechanism. Transformation reactions extend the range of passible monomer combinations in block copolymer. This approach allows polymers produced by one type of polymerization to be terminally functionalized by groups capable of initiating a different mode of polymerization. It have been reported the synthesis of block copolymers by cationic and radical, anionic and radical, condensation and radical, redox and thermal radical, and thermal radi cal and photochemical radical polymerization routes. The iniferter method, for the preparation of block copolymers, has been extensively explored during the last decade, primarily by Otsu et al. In this concept, iniferters (initiator-transfer agent-Terminator) were used to design the structure of polymer chain ends in radical polymerization. Several organic disulfides and phenylazotriphenylmethane were found to serve as photo and thermal iniferters, respectively. Polymers, obtained by using iniferters, still have iniferter function capable of initiating the polymerization of T another monomer yielding block copolymers. Polymerization of butylvinylether was carried out by using trityl cation initiated polymerization was prevented by addition tetrahydrothiophene to the polymerization system. Trityl terminated polybutylvinylether (Tr-PBVE), obtained this way, mas subsequently used to initiate the radical polymerization of me thyme thacryl.ate (MMA) via initer (initiator-terminator) mechanism. HUE mere polymerized in the presence of Tr BF, and thiolane as catianic initiator and carbocation stabilizer, respectively, yielding polymers uiith trityl end groups as depicted belaui. * -S.Tİ r+BF 3=fc Tr-$ TrBR -30 oc O * CHj==CHOR Tr-İCHz-ÇHVcHj-CH-^J b£ OR n OR E Tr- £ CHj-CHX-CHf-CH Bf^" + L^J^ V OR/n OR CH3OH Tr XcHrCH^-CHi-CH-OCHa + The introduction of trityl groups into PBVE was supported by H-NMR. As can be seen form Figure 1, (Fig. 1-a and Fig. 1-b) aromatic protons appear in the 7.2 ppm region, in addition to peaks at 3.5 ppm for CH-0 and 0-CH.2 and 0.9-1,9 ppm for ÇH--CH-D and alkyl protons, respectively. The UV spectrum of the polymer possesses an absorption band at around the 262 nm region (Figure 2), indicating attachment of trityl end groups. In addition, GPC analysis no contamination by physically entrained Tr BF7 in the polymers. VI 5 4 3 2 S (ppm) O Figure 1: 1H-NHR Spectra of (a) Tr+BF~ and (b) Tr-PBVE * Thiolane The polymer obtained has a trityl moiety at one end. Trityl terminated polybutylvinylether (Tr-PBVE) was used as a thermal initer in the polymerization of MMA as depicted belou. vix 200 260 A (nm) 350 Figure 2: UV-VIS Spectra of (a) Triphenylmethane CH?C1" (3.9x10~*M) and (b) Tr-PBVE in CHgCL^ (D.6 g/1). in Ph 'h Ph- ç - CH - CH**"****"*"* 1 U Ph-, Ph I c. +. Ph CH - CH OMOWMMdMlXIKM» II I CH,= ÇH Ph Ph - C - ÇH - CH2**WWWW*WWWCH - CH İr Blok copolymer Î OOaMWHIIWMWMM Vlll The plot af mal wt change af the polymers ( AMn = Mn,. -Mn ) against the conversion is shown in Figure 3. Here, Mn,. and Mn denote mal ut af the polymer recorded after variaSs polymerization times and of the prepolymer, respectively. 5 10 Conversion, % Figure 3: Polymerization of MMA uith Tr-PBVE at B0DC, (MMA)=9.36 mal/lt, (Tr-PBVE) =1 00 g/lt (Mn=17900), AMn=Mn. -Mn I a As can be seen, Mn of the polymers increased linearly uith conversation, uhich indicates that this polymerization proceeds via a quasi-living radical mechanism in a menner propoced by Otsu et al. Figure k shows the GPC traces recorded uith polymer isolated at various reaction times in bulk polymerization of MMA uith Tr-PBVE. The GPC trace of Tr-PBVE shoued unimodal mol ut distribution, that is, a neu peak, due to higher mol ut polymer, appeared and shifted to the higher mol ut side uith time. In relation to this, the peak for lauer ut polymer decreased and that of higher mol ut polymer increased. IX 30.0 Elution timz (min) Figure k: GPC Traces for PMMA Polymerized in Bulk With Tr-PBVE at Each Time. The solubility of black copolymers depends on the segment lenght of the each sequences. Block copolymers with sort segment of monomer shows similar solubility properties of the homopolymer of the long segment. In conclusion, these results indicate that the combina-" tion of cationic polymerization and the initer technique can be applied to produce a block copolymer.