Optical Materials 70 (2017) 25e30
Contents lists available at ScienceDirect
Optical Materials journal homepage: www.elsevier.com/locate/optmat
Effect of the different chain transfer agents on molecular weight and optical properties of poly(methyl methacrylate) € khan Demirci b, Paweł Mergo a Onur Çetinkaya a, *, Go a b
Laboratory Optical Fiber Technology, Faculty of Chemistry, Maria Curie-Skłodowska University, Lublin, 20-031, Poland Department of Polymer Chemistry, Faculty of Chemistry, Maria Curie-Skłodowska University, Lublin, 20-614, Poland
a r t i c l e i n f o
a b s t r a c t
Article history: Received 31 January 2017 Received in revised form 24 March 2017 Accepted 4 May 2017
Investigation of molecular weight and optical properties of poly(methyl metacrylate) (PMMA) polymerized in house with different chain transfer agents was studied. Isopropyl alcohol (IPA), n-butyl mercaptan (nBMC) and pentamethyl disilane (PMDS) were used as chain transfer agents. The molecular weight (Mw) of PMMA samples were measured by Ostwald viscometer. Mw of bulk polymer samples were decreased with increase the concentration of chain transfer agents (CTA). Since reactivity of used CTAs is not same, molecular weights of samples which were produced with different type of CTA but same concentration of CTA was varied. Higher concentration of n-BMC showed higher scattering. Transmission of samples could not be correlated with different concentration of CTA. Refractive index of samples was not affected by concentration of CTA nevertheless higher molecular weight of CTA showed higher refractive index. © 2017 Elsevier B.V. All rights reserved.
Keywords: Methyl methacrylate Chain transfer agent Bulk polymerization Molecular weight Transmission Optical polymers
1. Introduction Optical polymers are useful material instead of silica with many properties for short haul communications such as lower cost, larger core-diameter and, easy handling, low weight, multiplexing capabilities [1,2]. PMMA is a preferred polymer for manufacturing polymer optical fibers and for applications [3e8] with better elastic limit (10%) according to silica (1e3%) and can stand up to 30% strains [9]. Due to impurities and intrinsic absorption [10] caused by CeH bonds [11], PMMA is not favorable material according to silica in long distance applications. In polymer optical fiber technology, polymers should have proper molecular weight (Mw) for proper drawing process. Radical chain transfer reactions are suitable for controlling Mw of polymers [12]. For this purpose, mechanism and kinetic of chain transfer agents were investigated by many researchers [13e19]. Additionally, chain transfer agents have also effect on structure of polymer which causes to changes heating resistance [20]. Thiols derivatives are commonly used as a CTA due to weakness of SeH bond [21,22]. For vinyl monomers, e.g. methyl methacrylate and styrene, thiols are effective CTA [23].
* Corresponding author. E-mail address:
[email protected] (O. Çetinkaya). http://dx.doi.org/10.1016/j.optmat.2017.05.009 0925-3467/© 2017 Elsevier B.V. All rights reserved.
Controlled pseudo-living radical polymerization studies were done by Korolev et al. and Zaremskii et al. to obtain monodisperse polymers but because of reversible inhibition the polymerization rate is low [24,25]. For producing polymer with narrow molecular weight distribution, Semchikov et al. used polyfunctional silicon hydrides to solve problem [26]. Instead of mercaptans which are well-known CTA, Bulgakova et al. used organohydrodisilanes which are more effective [27,28]. In another study of Bulgakova et al., they employed silicon hydrides as CTA and compared the reactivity of silicon hydrides for Mw of styrene and methyl methacrylate [29]. As a conclusion of this study, the reactivity of organosilicon hydrides is related with chemical structure of CTA and the activity of monomer. Okay et al. employed IPA as chain transfer agent to control the average number of segments in a network chain. As concentration of IPA is increased, the chain length of the primary chains is decreased and they indicated that the average number of segments in a network chain is highly related with IPA concentration [30]. Investigation of the effects on optical properties of PMMA bulk polymer samples to use in optical fibers technology was presented. Different concentration of three CTAs were employed to fabricate proper bulk polymer samples. It was aimed to analyze optical properties of PMMA polymer samples depending on polymer structure which is affected by different structured CTAs. In literature, effect of chain transfer agents on optical properties of
26
O. Çetinkaya et al. / Optical Materials 70 (2017) 25e30
polymers was not compared. For this purpose, molecular weight, transmission and refractive index of bulk samples were measured and also scattering which was done by green laser was observed. 2. Materials and methods Methyl methacrylate (MMA, 99%, Aldrich) was used as monomer after purification via vacuum distillation method. Benzoyl peroxide (BPO, 75%, Aldrich) was purified and employed as initiator. Isopropyl alcohol (IPA, 99.9%, Fluka) and n-butyl mercaptan (nBMC, 99% Signa-Aldrich), Pentamethyldisilane (PMDS, 97%, Aldrich) were selected as CTA and only PMDS was purified with silica column (Silica gel 60, 70e230 mesh, Merck). The purity of PMDS was measured by gas chromatography (GC, Shimadzu GC2010) and it was found 98.3%. In all studies for measuring Mw, chloroform (98.5%, POCH Basic) was employed as solvent without any purification. 3. Experimental 3.1. Polymerization The monomer (MMA), initiator (BPO, 0.4%) and CTA (IPA, nBMC or PMDS) were mixed in glass test tube and thermal bulk polymerization was carried out (Fig. 1). In order to demonstrate effect of purification both purified and non-purified PMDS were used. 3.2. Characterization 3.2.1. Molecular weights Molecular weights of PMMA samples with different chain transfer agents were measured by Ostwald viscometer in chloroform at 30 C. The Mw of PMMA samples were calculated by following formula, [31].
½h ¼ 4:9 105 M0:8 w
(1)
and 1.6 cm length and optically polished from both front side to use in transmission and refractive index measurements and observing of scattering. Optical transmission measurements were done between 340 and 1100 nm wavelengths. Scattering studies were made by green laser (534 nm wavelength). In refractive index measurement Abbe refractometer (measurement accuracy ±0.0001) was used. 4. Results and discussion 4.1. Effect of chain transfer agent on molecular weight One of the purpose in this study is producing polymer for optical fiber technology. Commercially available PMMA which is used for fabricating optical fiber is around 100,000e150,000 g/mol. Therefore, Mw of bulk polymer samples should be in this range and concentration of CTA should be low as far as possible for avoiding impurities. CTAs which arrange polymer chains during polymerization control the Mw. There is a relative inversely between concentration of chain transfer agent and Mw of polymer. (Fig. 2). Due to different reactivity of varied CTAs, it is caused to have different Mw of polymer samples which were produced with same concentration of CTA [17,32]. According to molecular weight results, optimum CTA is n-BMC to produce polymer which is in desired Mw range with lower concentration of CTA (Fig. 2(b)). It can be considered that optical loss due to compounds besides PMMA in polymer structure was minimized. PMDS is also suitable CTA in this range. In Fig. 2(a), minimum Mw of polymer sample which was produce with IPA was reached to above of commercial PMMA and concentration of CTA was not increased due to avoid from optical loss. In comparison of purified and non-purified PMDS, in Fig. 2(a) and (b), it can be seen clearly that purified PMDS has better slope than non-purified PMDS. Impurities could cause inhomogeneous polymerization. Homogeneous polymerization is highly important to have proper polymer for optical fibre technology.
where h is viscosity of solution of PMMA sample in chloroform and Mw is molecular weight of PMMA sample.
4.2. Optical results
3.2.2. Optical properties Bulk PMMA samples were cut as cylindrical with 1 cm radius
In scattering studies, green laser (534 nm) was used to observe the effect of chain transfer agent on scattering behavior. Intensity of
Fig. 1. Reaction of polymerization of MMA with CTAs.
O. Çetinkaya et al. / Optical Materials 70 (2017) 25e30
27
Fig. 2. Molecular weights of polymer sample with different concentration of CTAs (a: IPA, b: n-BMC, c: Purified PMDS and d: non-purified PMDS).
scattered light was observed in all direction of the samples without any difference. Therefore these result were predicted as Rayleigh scattering. In Fig. 3 it is illustrated that scattering is decreased gradually by decreasing the concentration of n-BMC. This result is related with amount of CeS bonds in the polymer structure. CeS bonds are very strong in scattering as explained by Sheppard [33]. As seen in Fig. 4, only the highest concentration of IPA has higher scattering than other samples. Although there is no big difference
between concentration of IPA (1.2% and 1%), there is a big change in scattering (Fig. 4(a)). It can be correlated with polymerization process. Samples produced with purified PMDS showed lower scattering than n-BMC samples with lower concentration of CTA (Fig. 5). It can be also seen the effect of purification of PMDS in Figs. 5 and 6. Impurities in PMDS caused improper polymerization for optical fibre technology. Between 320 and 1100 nm wavelengths, transmission of
Fig. 3. Laser scattering of PMMA bulk samples produced by n-BMC (a:0.2%, b: 0.15%, c:0.1%, d: 0.05%, e:0.025%).
28
O. Çetinkaya et al. / Optical Materials 70 (2017) 25e30
Fig. 4. Laser scattering of PMMA bulk samples produced by IPA (a:1.2%, b:1%, c:0.4%, d:0.2%, e:0.075%, f:0.05%).
Fig. 5. Laser scattering of PMMA bulk samples produced by purified PMDS (a:0.8%, 0.7%, 0.6%).
structure also enlarges, refractive index is increased. Mw of CTA are 60.1, 90.18 and 132.35 g/mol for IPA, n-BMC and PMDS respectively. 5. Conclusion
Fig. 6. Laser scattering of PMMA bulk samples produced by non-purified PMDS (a:0.8%, 0.6%).
polymer samples was measured (Fig. 7). According to results, concentration of CTAs has no regular effect on transmission. Transmission was affected by different CTAs randomly since CTAs have different activities during polymerization. As seen in Fig. 7(a) and (b), some spectra (i.e. nBMC: 0.05%, IPA 0.075%) show much lower transmission than others. This could happen due to uncontrolled error which affects polymerization process leading to inhomogeneity of polymer chains. But averagely samples have 90% transmission which is acceptable for polymer optical fibers technology. In Table 1 the result of refractive index of bulk polymer samples were given. As changing the concentration of CTA, there is no variation of refractive index. But different CTA affects refractive index slightly. It can be explained by Mw of CTA. Since molecular
Different type of CTAs was employed to produce PMMA bulk samples and to investigate the effect on their Mw, optical transmission, refractive index and scattering. Same concentration of different CTAs caused to have varied Mw of polymer samples due to their different reactivity during polymerization. By comparison with commercial PMMA for drawing optical fiber, IPA is not suitable CTA due to higher Mw. n-BMC and PMDS are proper CTAs in order to fabricate polymer with desired Mw. Scattering is related with concentration of CTA but only for n-BMC since it has SeC bonds which have strong effect on scattering. For other CTAs, it can be considered that they have no effect on scattering. Further studies can be done with higher concentration of CTAs to see the effect on scattering but it will decrease the Mw and affect drawing process. There is no significant effect of CTA in transmission results for samples which were produced with different concentration of a CTA. The main reason of this result is predicted because of unexpected polymerization process error. There is no effect of CTA on refractive by changing the concentration of CTA but different type of CTAs changes the refractive index because of having different Mw which means also different molecular size. As a consequence of these results, it can be suggested that polymer produced by purified PMDS is useful among other CTAs used in this study for producing
O. Çetinkaya et al. / Optical Materials 70 (2017) 25e30
29
Fig. 7. Transmission of polymer samples with different type and concentration of CTAs (a: n-BMC, b: IPA and c: Purified PMDS).
References
Table 1 Refractive index values of all samples. CTA (%)
Refractive Index IPA
n-BMC
PMDS
Non-purified PMDS
1.2 1.0 0.8 0.7 0.6 0.4 0.2 0.15 0.1 0.075 0.05 0.025
1.4911 1.4910 e e e 1.4910 1.4909 e e 1.4911 1.4910 e
e e e e e e 1,4912 1,4912 1,4913 e 1,4914 1,4913
e e 1,4915 1,4914 1,4914 e e e e e e e
e e 1,4916 1,4916 1,4916 e e e e e e e
optical fiber. These polymers have better properties in Mw and scattering results.
Acknowledgment The research leading to these results has received funding from the People Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme FP7/2007e2013/ under REA grant agreement n 608382.
[1] A.D. Alobaidani, D. Furniss, M.S. Johnson, A. Endruweit, A.B. Seddon, Optical transmission of PMMA optical fibres exposed to high intensity UVA and visible blue light, Opt. Laser Eng. 48 (2010) 575e582. [2] K. Peters, Polymer optical fiber sensorsda review, Smart Mater. Struct. 20 (2011) 13002. [3] Z. Xiong, G.D. Peng, B. Wu, P.L. Chu, Highly tunable bragg gratings in singlemode polymer optical fibers, IEEE Photonic Tech. L. 11 (1999) 3. [4] M.A. van Eijkelenborg, M.C.J. Large, A. Argyros, J. Zagari, S. Manos, N.A. Issa, I. Bassett, S. Fleming, R.C. McPhedran, C. Martijn de Sterke, N.A.P. Nicorovici, Microstructured polymer optical fibre, Opt. Express 9 (7) (2001) 319e327. [5] D.X. Yang, J. Yu, X. Tao, H. Tam, Structural and mechanical properties of polymeric optical fiber, Mater. Sci. Eng. A 364 (2004) 256e259. [6] M. Rajesh, K. Geetha, M. Sheeba, C.P.G. Vallabhan, P. Radhakrishnan, V.P.N. Nampoori, Characterization of rhodamine 6G doped polymer optical fiber by side illumination fluorescence, Opt. Eng. 45 (7) (2006) 075003 (1-4). [7] A. Stefani, K. Nielsen, H.K. Rasmussen, O. Bang, Cleaving of TOPAS and PMMA microstructured polymer optical fibers: core-shift and statistical quality optimization, Opt. Commun. 285 (2012) 1825e1833. [8] M. Latino, R. Montanini, N. Donato, G. Neri, Ethanol sensing properties of PMMA-coated fiber Bragg grating, Proced. Eng. 47 (2012) 1263e1266. [9] M.C.J. Large, J. Moran, L. Ye, The role of viscoelastic properties in strain testing using microstructured polymer optical fibres (mPOF), Meas. Sci. Technol. 20 (2009) 034014 (1-6). [10] A.N.Z. Rashed, Submarine fiber cable network systems cost planning considerations with achieved high transmission capacity and signal quality enhancement, Opt. Commun. 311 (2013) 44e54. jcik, J. Pe˛ dzisz, J. Kopec, [11] P. Mergo, M. Gil, K. Skorupski, J. Klimek, G. Wo K. Poruraj, L. Czyzewska, A. Walewski, A. Gorgol, Low loss poly(methyl methacrylate) useful in polymer optical fibers technology, Photonics Lett. Pol. 5 (4) (2013) 170e172. [12] M.O. Zink, D. Colombani, P. Chaumont, Chain transfer by additionfragmentation mechanism-9. Access to diene-functional macromonomers using 5-(substituted)- 1,3-pentadiene-type addition-fragmentation chaintransfer agents in radical polymerization, Eur. Polym. J. 33 (9) (1997)
30
O. Çetinkaya et al. / Optical Materials 70 (2017) 25e30
1433e1440. [13] F.R. Mayo, Chain transfer in the polymerization of styrene: the reaction of solvents with free radicals, J. Am. Chem. Soc. 65 (12) (1943) 2324e2329. [14] F.R. Mayo, R.A. Gregg, M.S. Matheson, Chain transfer in the polymerization of styrene. VI. chain transfer with styrene and benzoyl peroxide; the efficiency of initiation and the mechanism of chain termination, J. Am. Chem. Soc. 73 (1951) 41691e41700. [15] F.R. Mayo, Chain transfer in the polymerization of styrene. VIII. chain transfer with bromobenzene and mechanism of thermal initiation, J. Am. Chem. Soc. 75 (24) (1953) 6133e6141. [16] R.A. Gregg, D.M. Alderman, F.R. Mayo, Chain transfer in the polymerization of styrene. V. polymerization of styrene in the presence of mercaptans, J. Am. Chem. Soc. 70 (11) (1948) 3740e3743. [17] C. Henriquez, C. Bueno, E.A. Lissi, M.V. Encinas, Thiols as chain transfer agents in free radical polymerization in aqueous solution, Polymer 44 (2003) 5559e5561M. [18] T. Furuncuoglu, I. Ugur, I. Degirmenci, V. Aviyente, Role of chain transfer agents in free radical polymerization kinetics, Macromolecules 43 (2010) 1823e1835. [19] J. Mendoza, J.C. De la Cal, J.M. Asua, Kinetics of the styrene emulsion polymerization using n-dodecyl mercaptan as chain-transfer agent, J. Polym. Sci. A1 38 (2000) 4490e4505. [20] S.A. Zhiltsov, S.A. Bulgakova, Y.D. Semchikov, Effect of organosilicon chain transfer agents on heat resistance of vinyl polymers, Russ. J. Appl. Chem. 81 (7) (2008) 1262e1266. [21] F.G. Bordwell, X.M. Zhang, A.V. Satish, J.P. Cheng, Assessment of the importance of changes in ground-state energies on the bond dissociation enthalpies of the 0-H bonds in phenols and the S-H bonds in thiophenols, J. Am. Chem. Soc. 116 (1994) 6605e6610.
[22] P. Wardman, C. Von Sonntag, Kinetic factors that control the fate of thiyl radicals in cells, Methods Enzymol. 251 (1995) 31e45. [23] G. Moad, D.H. Solomon, The Chemistry of Free Radical Polymerization, Pergamon Press, Oxford, 1995. [24] G.V. Korolev, A.P. Marchenko, ‘Living’-chain radical polymerisation, Russ. Chem. Rev. 69 (2000) 409e434. [25] M.Y. Zaremskii, V.B. Golubev, Reversible inhibition of radical polymerization, Vysokomol. Soedin. Ser. C 43 (9) (2001) 1689e1728. [26] Y.D. Semchikov, S.A. Bulgakova, L.M. Mazanova, Use of organohydridodisilanes for controlling the molecular-weight distribution of highconversion polymers, Russ. J. Appl. Chem. 78 (7) (2005) 11661e12169. [27] S.A. Bulgakova, Y.D. Semchikov, L.M. Mazanova, V.V. Semenov, Organodisilane hydrides: a promising new class of chain-transfer agents in free-radical polymerization, Polym. Sci. B 40 (1e2) (1998) 5e7. [28] C. Walling, Free Radicals in Solution, New York, Wiley, 1957. [29] S.A. Bulgakova, L.M. Mazanova, V.V. Semenov, Y.D. Semchikov, Organosilicon hydrides in macromolecular design: reactions of chain-transfer and hydrosilylation, Eur. Polym. J. 43 (2007) 644e651. [30] O. Okay, N.K. Balimtas, H.J. Naghash, Effects of cyclization and pendant vinyl group reactivity on the swelling behavior of polyacrylamide gels, Polym. Bull. 39 (1997) 233e239. [31] Y.S. Lipatov, A.E. Nesterov, R.A. Griczenko, R.A. Veselovsky, Reference Book on Chemistry of Polymer, Naukova Dumka, Kiev, 1971. [32] S.G. Gaynor, J.S. Wang, K. Matyjaszewski, Controlled radical polymerization by degenerative transfer: effect of the structure of the transfer agent, Macromolecules 28 (1995) 8051e8056. [33] N. Sheppard, The vibrational spectra of some organic sulphur compounds and the characteristic frequencies of c-s linkages, Trans. Faraday Soc. 46 (1950) 429e439.
