Affirmations Thanks to the Chemistry Faculty and Staff at WSU for their ceaseless diligent work. We likewise recognize .


50 views
Uploaded on:
Category: Medical / Health
Description
End Group Analysis of Poly(Cyclohexene Oxide) from Photoinitiated Cationic Polymerization using the Tris(2,2,2-trifluoroethyl )phosphite / Iodonium System Steven A. Klankowski* and Thomas W. Nalli Chemistry Department, Winona State University, Winona, Minnesota 55987-5838. Abstract
Transcripts
Slide 1

End Group Analysis of Poly(Cyclohexene Oxide) from Photoinitiated Cationic Polymerization utilizing the Tris(2,2,2-trifluoroethyl )phosphite/Iodonium System Steven A. Klankowski* and Thomas W. Nalli Chemistry Department, Winona State University, Winona, Minnesota 55987-5838 Abstract Various trialkyl phosphites (P(OR) 3 ) have been appeared to begin cationic polymerizations of cyclohexene oxide (CHO) through a radical chain component with a diaryliodonium salt (Ar 2 I + ). Using noticeable light photolysis of phenylazoisobutyronitrile (PAIBN) as the radical start step ( eq 1), an engendering cycle spoke to by conditions 2-4 has been proposed. Phenyl radicals ( Ar  ) assault the phosphite to deliver the underlying phosphoranyl radicals ( eq 2). These radicals perform one-electron exchanges with the iodonium salt to frame the polymerization-beginning aryltrialkoxyphosphonium salt (ArP + (OR 3 )) ( eq 3). The diaryliodine moderate (Ar 2 I  ) created in this redox step parts delivering iodoarene ( ArI ) and recovering a phenyl radical that proceeds with the chain (eq 4). The utilization of tris(2,2,2-trifluoroethyl) phosphite (TFP) ((CF 3 CH 2 O) 3 P) permits the polymerization of CHO to continue with negligible chain-exchange (eq 8-9). This is because of the decline in nucleophilicity of the phosphite, adequately decreasing its impedance with cationic polymerization. In this publication we exhibit confirm, as polymer end bunch investigation by 19 F NMR spectroscopy, that polymerization is in fact begun by alkylation of the monomer by the aryltrialkoxyphosphonium salt (eq 6) as already proposed. 4 Mechanism Proposed system of PAIBN, iodonium Salt and TFP to deliver arylphosphonium utilized as a part of polymerization. R =CH 2 CF 3 Ar = t-BuPh Radical Chain Ph-N=N-CMe 2 CN ��  Ph • +N 2 + • CMe 2 CN (1)(init) Ar • + P(OR) 3 ��  ArP • (OR) 3 (2)(prop) Ar 2 I + ArP • (OR) 3 ��  Ar 2 I • + ArP + (OR) 3 (3)(prop) Ar 2 I • ��  Ar • + ArI (4)(prop) Ar 2-I + P(OR) 3 ��  ArI + ArP + (OR) 3 (5)(net) Polymerization ArP + (OR) 3 + ��  ArP(O)(OR) 2 + R — + ( 6 ) R—+ n ��  R-(OCH 2 CH 2 ) n (7) Polymerization Chain Transfer Quantitation of End gatherings Sample 2 – After three reprecipitations, the specimen was broken down in CDCl 3 alongside a known mass of p - bromofluorobenzene as a standard. 1 H and 19 F NMR spectra were acquired and coordinated (Figures 2 and 3). Trial General . A JEOL 300 MHz ECX spectrometer was utilized for getting spectra and in reverse direct insertion (BLIP) was utilized to handle the 19 F spectra to evacuate the wide gauge unsettling influence brought on by the Teflon ( polyTFE ) coating the test. Polymer Samples. Tests 1 and 2 were gotten from a past polymerization ponder. 4 Sample 1 was gotten from a trial that utilized 0.02 M bis(4-tert-butylphenyl)iodonium hexafluorophosphate (BIH), 0.20 M TFP, and 0.02 M PAIBN as coinitiators disintegrated in CHO. This yielded a 96% change of the monomer to polyCHO with M w = 24,300 . Test 2 utilized 0.01 M BIH, 0.10 M TFP, and 0.02 M PAIBN yielding 65% transformation to polyCHO with M w = 25,400. 4 Both responses were lighted for one hour utilizing a 65-W minimized fluorescent light. Every example had been refined once by being taken up in 10 mL CHCl 3 and treated with 10 mL of CH 3 OH. The sub-atomic weights had been controlled by utilizing HPLC with Multiple Angle Laser Light Scattering indicator. Polymer Purification. The polymer was broken down a little measure of chloroform and reprecipitated by dropwise expansion of methanol. Dissolvable was tapped, the encourage was washed with methanol and after that dried under vacuum . The cleaned polymers were taken up in CDCl 3 to acquire 1 H and 19 F NMR spectra and would be recovered for further cleanings. The sums utilized for refinement are recorded in table beneath. Polymer Sample 2 with Standard BrC 6 H 4 F Proton NMR with Area Integrations H α - polyCHO p - bromo-fluorobenzene Figure 2 Polymer Sample 2 with Standard BrC 6 H 4 F Fluorine NMR with Area Integrations (in reverse straight mix) End Group Quantitation . A quantitative NMR test was readied utilizing the 3 rd reprecipitation of Sample 2 with the expansion of 2.0 μL p-bromofluoro - benzene as an interior standard. The polymer and standard were taken up in 1.0 mL of CDCl 3 and 5000-check 1 H and 19 F NMR spectra were gotten. Pinnacles were coordinated and the end gathering to polymer proportion figured utilizing the known fixations and number-normal sub-atomic weight of the polymer. NMR Results Proton and Fluorine NMR spectra were gotten after each successive purging for poly CHO tests from beforehand revealed polymerization tests. 4 The examples were cleaned by rehashed reprecipitation from CHCl 3 by dropwise methanol expansion. Test 1 – After three reprecipitations the example was immaculate as affirmed by no further change in the 19 F NMR range (Figure 1). Foundation Photoinitiated, cationic polymerization is of incredible significance in the improvement of particular curing polymer frameworks. 1 The utilization of trialkoxyphosphites have been appeared to be great co-initiators for diaryliodonium salt-incited photoinitiation of cationic polymerizations. In any case, the choice of the alkyl bunches upon the phosphite was found to straightforwardly influence the rate of polymerization because of its adjustment in nucleophilicity. 2,3 If the phosphite is excessively nucleophilic, photopolymerization is likewise moderate and gives low atomic weight polymers. This is expected to the nucleophilic phosphite repressing polymerization and achieving chain exchange by contending with the epoxy monomer for cationic destinations (eq 8 and 9). 2,3,4 Tris(2,2,2-trifluoroethyl)phosphite (TFP) was found to have a diminished nucleophilicity, yet at the same time fit for take part in the radical–chain science. 5 In late outcomes, illumination with a modest bright light gave great yields (65-95%) of polyCHO with sub-atomic weights in the scope of 20,000 to 25,400 in as meager as one hour of light time. 4 If the proposed component is taken after, the polymer chain ought to incorporate trifluoroethyl end bunches topping the polymer ( eq 6). Along these lines, examination of the end-bunches on the polymer chains ought to give prove important to affirm the proposed system. p - bromo-fluorobenzene CF 3 CH 2 - CHO Conclusions After three progressive reprecipitations, the polymer was found to have great immaculateness and still show F-19 (- 75.1 ppm ) tops that must be ascribed to trifluoroethoxy endgroups on polymer, not pollutions. Expansion of p - bromofluorobenzene took into account simple reconciliation of fluorine and hydrogen tops to discover normal sub-atomic number and include of endgroups present polymer. End aggregate examination demonstrated that 1 out of 5.3 polymer chains contains the trifluoroethyl gather. These outcomes demonstrate that alkylation of the monomer by the aryltrialkoxy phosphonium salt (eq 6) is a key component venture in the polymerization as proposed by our gathering already. Figure 3 Results and Discussion The watched multiplet at - 75.1 ppm is reliable with the concoction move for –OCH 2 CF 3 bunches (writing values 6 are in the scope of - 73 to - 78 ppm ) Thus we ascribe this multiplet to the trifluoroethoxy polymer endgroups. A quantitative trial was directed on Sample 2 utilizing p - bromofluorobenzene as an inward standard (2.0 µL; 3:1 mole proportion of standard to polymer. ) The outcomes in Figure 3 demonstrate a 1.0:6.2 incorporation proportion of polymeric F to standard F implying that the refined polymer has one –OCH 2 CF 3 endgroup for about each five polymer chains. (This expect the MW of the material did not change accordingly of decontamination.) The proton NMR (Figure 2) demonstrates a 1:68 coordination proportion of the standard compound hydrogens to monomer hydrogens, giving a computed weight of polymer to be 0.121 g, (5.1% mistake), therefore approving the estimation of the additional standard. Beginning Polymer 1 st Reprecipitation References Tasdelen , M.A.; Yagci, Y.; Kumbaraci , V.; and so forth. Macromolecules 2008 , 41, 295-297 Muneer , R.; Nalli, T. W.; Macromolecules 1998 , 31, 7976-7979 Nalli, T. W . ; Stanek , L. G. Modified works of Papers , 219th National Meeting of the ACS, San Francisco, CA, March 2000; ORGN 405. Nalli, T.W.; Stanek , L.G.; Steidler , R. H.; and so forth. Trialkyl Phosphites and Onium Salts as Co-initiators in an Efficient System for Visible-Light-Induced Cationic Polymerization. Introduced at the ACS 235 th National Meeting, New Orleans, LA, Spring 2008, ORGN 125 Kampmeier, J. A,; Nalli. T. W. J . Organization. Chem. 1993 ,58,943-949. Everett , T.S. in Chemistry of Organic Fluorine Compounds II ; ACS, Washington, DC.1995 . pp 1037-1086. 2 nd Reprecipitation 3 rd Reprecipitation Acknowledgments Thanks to the Chemistry Faculty and Staff at WSU for their constant diligent work . We likewise recognize the National Science Foundation, CCLI Grant #0126470 (JEOL NMR ). Figure 1

Recommended
View more...