Aktive edilmiş monomer polimerizasyonu ile fotoaktif polimer sentezi /
Yazar: YEŞİM HEPUZER
Danışman: PROF.DR. YUSUF YAĞCI
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü
Derece: Yüksek Lisans, 1995
Konu: Kimya = Chemistry
Dizin: Fotoaktivite = Photoactivity ; Polimerler = Polymers ; Polimerleşme = Polymerization ; Sentez = Synthesis

Özet:
ÖZET Bu çalışmada, epiklorhidrin (ECH) aktive edilmiş monomer mekanizması (AM) ile sırasıyla benzoin (B) ve alfa-metilol benzoin metil eter (MBME) varlığında polimerleştirilmiştir. Spektroskopik çalışmalar, bu yöntemle elde edilen polimerlerin benzoin uç gruplar içerdiğini göstermiştir. AM mekanizması ile hazırlanan poliepiklorhidrin (MBME-PECH), metilmetakrilat'ın (MMA) serbest radikal polimerizasyonunda başlatıcı olarak kullamlmıştır. Deneysel olarak, fotoaktif poliepiklorhidrin'in etkinliği, aydınlatma süresi ve monomer konsantrasyonunun polimerizasyon hızına etkileri incelenmiştir. Elde edilen sonuçlar, metilmetakrilat ve epiklorhidrin'in blok kopolimerlerinin önemli ölçüde homopolimetilmetakrilat ile birlikte oluştuğunu göstermiştir. Benzer şekilde, fotoaktif PECH (B-PECH ve MBME-PECH), sikloheksenoksit'in (CHO), N-Etoksi-2 Metil Piridinyum Hekzaflorafosfat tuzu (EMP+) varlığında yükseltgenmiş katyonik polimerizasyonunda başlatıcı olarak kullanılmıştır. Bu metod, UV ışık ile elektron veren polimerik radikallerin oluşumunu ve bu radikallerin piridinyum tuzu varlığında katyona yükseltgenmelerini içermektedir. vı

Abstract:
Epichlorohydrin (ECH) was polymerized by an activated monomer mechanism (AM) in the presence of benzoin (B) and a-methylol benzoin methyether (MBME), respectively. Spectroscopic studies showed that polymers obtained via this initiation method contained benzoin terminal groups. Benzoin and derivatives are frequently used as photoinitiators for vinyl polymerization. Upon irradiation, these compounds undergo a-cleavage yielding benzoyl and substituted benzyl radicals. II.. O OR II I Ph-C-C-Ph k R' = H, alkyl, substituted alkyl R" = H, alkyl, substituted alkyl Both radicals are capable of initiating vinyl polymerization. However, they may exhibit different reactivities and roles if the radical and monomer concentrations are varied. Monomer structure also influences the reactivity. The attachment of structurally related benzoin and its derivatives to the polymer main and side chains would afford a convenient procedure for block and graft copolymer formation, respectively. It has been shown that oxiranes can be polymerized in the presence of hydroxyl containing compounds by the activated monomer (AM) mechanism. The propagation in these systems can be represented by the following reaction; R-OH + H-O: R-O OH + H VIIBy its nature, this process may be adapted so that hydroxy group containing functional molecules, monomers and polymers are used as initiators to yield telechelic, macromonomer and block copolymers, respectively. We have synthesized block copolymers by combination of AM and free radical polymerization mechanism. In the present work, the following benzoin type photo initiators were used in the AM polymerization of epichlorohydrin (ECH) to produce polymers with terminal photoactive groups. O H II I Ph-C-C-Ph OH (B) O OMe II I Ph-C-C-Ph I CH2OH (MB ME) Benzoin (B) and a-methylol-benzoin methylether (MBME) were used as initiators of AM polymerization of ECH catalysed with BF3 THF complex. H o:.CH2CI + H-O:,CH2CI + h-o:.ci-uci OH II I Ph-C-C-OH I Ph O H CH2CI HI I l Ph-C-C-0-CH-CH2-OH + I Ph HT H-6: CH2CI O H CH2CI IMI2 Pb-C-C-O-f CH-CH2-04- H I Ph n PECH VIII30 35 elution volume 25 30 elution volume 35 40 Figure 1. Gel permeation chromatograms of the reaction mixture (with MBME as initiator) at different conversions. (a) [ECH] added/ [ MBME ]Q =5, (b) [ECH] added/ [MflME]0= 25. Figure 2. Gel permeation chromatogram of the isolated and purified (by washing with methanol) product of the polymerization (with MBME as initiator) by UV and RI dedection. IXIn both cases reaction was carried out by slow addition of ECH to the solution of B or MBME in methylene chloride, in the presence of the catalyst. At these conditions, both initiators were consumed at the early stages of the reaction, as evidenced by the decrease of corresponding signals in GPC chromatograms of the reaction mixtures at different conversions (Fig.l). After termination of the polymerization the products (viscous liquids) were extracted with methanol in order to remove the possibly present traces of unreacted initiators. The GPC curve for purified products is shown in Fig.2. The products were analysed by :H-NMR and UV spectroscopy. In the UV analysis (Fig.3), the spectra of initiators were recorded as reference. In the UV spectrum of BME-PEÇH, absorption band at 340 nm (e=2.05 x 102 mol-1 1 cm"1) corresponding to n-*n* appears together with a much stronger absorption with a maximum at 250 nm. Int the spectrum of B-PECH only the slight shoulder is observed at 340 nm and the extinction coefficient measured at 340 nm is considerably lower (e=0,93 x 102 mol-1 1 cm"1). These values were consequently used to calculate the content of aromatic end groups in polymers. 300 350 A(nm) 300 350 A(nm) Figure 3. UV absorption spectra of methylene choride solutions containing (a) B (6.6 x 10"4 mol l"1), (b) B-PECH (1.33 g l'1) (c) MBME (2.3 x 10'3 mol 1'') and (d) MBME-PECH (2.03 g l"1)-hot, -oı -o 4- (pewl _J^jf^\_jJJjhj^j !. S; SO 7J 78 74 7} tew) O-hrO s İSO") Figure 4 : ^-NMR spectrum of polyepichlorohydin (poly-ECH) prepared with benzoin (B) as initiator a- expanded region of aromatic end-groups absorption b- expanded region of absorption of aromatic groups in initiator (benzoin) In ^-NMR spectra (Fig.4) the group of signals at 3.5-3.8 ppm, corresponding to CH2, CH and CH2C1 groups of the PECH chain appears, together with signals in the range of 7.2-7.5 ppm, corresponding to aromatic protons in benzoin moiety (end group). Additionally, for the products prepared with MBME as initiator (BME-PECH), the singlet at 3.36 ppm appears. As this signal is absent in the spectra of polymers prepared with B as initiator (B-PECH), it was assigned to CII3O group in the incorporated MBME moiety (Fig.4). XIThese polymers were used as photoinitiators for free radical polymerization and promoted cationic polymerization. In the former case, MMA was used as free radical polymerizable monomer. Experimently, effect of photoactive PECH, photolysis time and monomer concentration on the rate of polymerization was investigated. The obtained results, reviewed that block copolymers of ECH and MMA are radically formed together with some homopolymers formation. Homopolymer formation may be due to the unsuitable selective irradiation conditions and the fact that low molar mass benzoil radicals. Similarly, photoactive PECH is used to initiate cationic polymerization of CHO via electron transfer process. This method pertains to the generation of polymeric electron donor radicals upon UV irradiation and subsequent oxidation of these radicals by pridinium salts. The general mechanism is detected below. OCH3 l Ph-C- + I ÇH2 CH2C! CH20[CHCH20]-H N PR OEt OCH3 I 3 + C-Ph I + ÇH2 ÇH2CI CH20[CHCH2cg-H I OEt I OEt OEt OCH3 PECH****0 + PF« I Ph OCH3 PEChh-C-O^v/' * c> *o o OCB ! PECH*«C I Ph b PECH-b-PCHO XII