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Bis-açilfosfin oksit fotobaşlatıcısı ile serbest radikal polimerizasyonu üzerinden blok kopolimer sentezi

The Block copolymerization over free radical polymerization using bis-acylphosphine oxide

  1. Tez No: 75177
  2. Yazar: EROL DANİEL GÜNERSEL
  3. Danışmanlar: PROF. DR. YUSUF YAĞCI
  4. Tez Türü: Yüksek Lisans
  5. Konular: Kimya, Chemistry
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 1998
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Kimya Ana Bilim Dalı
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 84

Özet

ÖZET Değişik yapılara sahip açilfosfin oksit türevlerinin serbest radikal fotopolimerizasyonlarda başlatıcı olarak görev alabildikleri bilinmektedir. Bu açilfosfin oksit bileşikleri ışığa maruz bırakıldıklarında oc-yarılması vererek serbest radikalleri meydana getirirler. Oluşan bu serbest radikallerden fosfin radikali, karbonil radikalinden daha etkindir ve monomer ile reaksiyona girerek fotopolimerizasyonu başlatır. Çalışmamızda bis(2,4,6-trimetil-benzoin)-benzil-fosfin oksit ( BAPO ) fotobaşlatıcısı kullanılarak, stiren ve metil metakrilat monomerler ile blok kopolimerler sentezlenerek incelendi. Bu amaçla önce stiren monomeri içerisine BAPO ilave edilerek 420 nm'de aydınlatıldı. Elde edilen pre-polimer, metil metakrilat monomerine ilave edildi ve 380 nm'de aydınlatıldı. Bu fotopolimerizasyon sonrasında bir blok kopolimer sentezlendi. Açilfosfin oksit ile gerçekleştirilen serbest radikal polimerizasyon yöntemi, kaplama ve taş basma alanlarında büyük bir yer tutmaktadır. Özellikle kaplama sanayinde, titandioksit gibi dolgu maddeler kullanıldığı zaman açilfosfin oksit'ler tercih edilirler. Çünkü onlar dolgu maddelerinin ışığı absorblamadıkları dalga boylarındaki ( 380 nm ve üzerinde ) ışığı absorblarlar. Bu, açilfosfin oksitlerin özellikle kaplama endüstrisinde aranılan birer fotobaşlatıcı yapmaktadır.

Özet (Çeviri)

SUMMARY The block copolymerization over free radikal polymerization using bis- acylphosphin oxWe Block copolymers have become increasingly important in recent decades. The reason for this importance is due to the fact that their special chemical structure yields unusual physical properties, especially as far as solid state properties are concerned. Block copolymers are applied in various fields: they are used as surfactants, adhesives, fibres, thermoplastics an thermoplastic elastomers. A number of methods for the preparation of block copolymers have been developed so far. Living polymerization is an elegant method for the controlled synthesis of block copolymers. However, this technique requires extraordinary high purity and is limited to ionically polymerizable monomers. The synthesis of block copolymers by a radical reaction is less sensitive towards impurities present in the reaction mixture and is applicable to a great number of monomers. Bifunctional initiators play significant role regarding block copolymer synthesis by radical mechanism. Free radical block copolymerization has been performed by means of low molecular initiators containing two labile groups of different thermal reactivity or with photochemical and thermal activities. Low molecular weight azo benzoin initiators of the following structure were successfully used as photo and thermally functional initiators. OR O CH3 -C- (CHj)- O-C-CCH^-N: 2An -1 2 R = H,n = 0 R = -OCH3,n=l (i) viuThermal polymerization of styrene by means of azo benzoin initiators produced benzoin terminated polystyrene. This polymer was in a second reaction step photolyzed in the presence of methyl methacrylate monomer yielding corresponding block copolymer. Acylphosphine oxides and acylphosphonates with different structures have been used as photoinitiators for free-radical initiated photopolymerization Long wavelength absorption characteristics make these compounds particularly useful for the polymerization of TİO2 pigmented formulations containing acrylate or styrene type monomers and of glass fiber reinforced polyester laminates with reduced transparency Extensive investigations on the photochemistry of acylphosphine oxides revealed that they undergo a-cleavage with fairly high quantum yields. hv (ü) Furthermore it was found that the phosphonyl radicals formed are highly reactive towards vinyl monomers This paper reports our results on the use of bis acylphoshine oxide (BAPO) of the following structure for block copolymer synthesis. As it will be shown below, the absorption of the BAPO at 420 and of the mono acyl phosphine oxide at 380 nm makes this compound bifunctional photoinitiator when photolysed sequentially. CH3 CH3 OOO y - s^ ch3- a j^^-c-ZO/0113 CH3 (Hi) IXFigure.i. shows the absorption spectra of BAPO and a typical monoacylphosphine oxide, namely 2,4,6-trimethoxy-benzoyl-diphenyl phospine oxide (TMDPO). 1.60- 1.20- 0.80 0.40- 0.00 r~» 1 1 » 200 250 300 350 400 Figure.i. The Absorbtion spectra of BAPO an TMBPO. 450 nm BAPO shows a tail absorption band in the visible range (370-430 nm) due to the additional chromophoric effect of the second carbonyl group. Photoinitiated polymerization of styrene (St) was carried out at X=420 nm. Table.i. Photoinitiation of BAPO with styrene at X = 420 nm. As shown in Table.i., conversion to polystyrene increased with the irradiation time. By irradiating selectively at 420 nm with the aid of a monochromator, BAPO undergoes a-scission to yield benzoyl and a-benzoyl phosphonyl radicals. Polymerization is expected to be initiated mainly by phosphonyl radicals since bimolecular rate constant of the reaction of the phosphonyl radicals with St monomer is two orders of magnitude is higher than that of the benzoyl radicals.(k^jhos+st = 4.5 x 107 1 mol s“1, kbenz+st = 2 x 105 1 mol s”1). The polymers are, therefore, expected to have monoacylphosphine oxide terminal groups ( scheme iv) ch3 ca o°9 > - ^ O CH, Notable, absorption band at 420 nm decreased by the irridation time ( Figure.ii. ) 0.16 0.00 300 34° 380 Figure.ii. Absorption band of PSt-BAFU depending on tune 420 nm a) 30 min. b) 60 min. c) 90 min. d) 120 min. xiThese polymers were subsequently used in block copolymerizationby taking advantage of terminal photoactive groups. For this purpose polystyrene were irradiated at 380 nm in the presence of methyl methacrylate. Block copolymers are expected to form according to the following reaction: O O.I I' ^“u C- P- CH2- CH2- W »CH: ? r - oru - UPİ2TT^¥Twr ÛÛ CH2=i ;=ch COOCH3 ”ww**wCH- CH- P- CH2- CH2* C=0 ' ' OCH, Û6 (v) The results of photoinitiated block copolymerization are presented in table, ii. It is evident that molecular weights were increased by blok copolymerization at each case. Moreover, The concentration of the polymer containing monoacylphosphine oxide effected the polymerization rate significantly. Table.ii.Photoinitiated block copolymerization of Polystyrene-BAPO with MMA at X = 380 nm. The formation of block copolymer was evidenced by spectral analysis. ^-NMR spectra of a typical block copolymer is shown in Figure.iii.. Characteristic aromaticprotons of polystyrene at 6.4 - 7.6 ppm and methoxy protons of Xllpolymethyl methacrylate at 3.5 ppm indicates succesful block copolymerization. Moreover, molecular weight of the block copolymers were shifted to shorter elution volumes. As can be seen from Figure i.v. there is no contamination of the corresponding homopolymer at high elution volume. Both spectral and GPC analysis clearly indicates the formation of block copolymer. xm< er LU 14.0 12.0 10.0 8.0 6.0 4.0 PPM 2.0 0.0 Scheme üi.: The 'H-NMR spectra of a typical block copolymer. XIVs e.2 %-» 3 3 s o o o o 9 6 N O O O o" S H I T+0TX AM 1ÖNDIS Scheme iv. : The GPC results of a homopolymer and a block copolymer. xv

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