Subscriber access provided by University of Newcastle, Australia
Article
Telechelic Poly(Bisphenol A Carbonate) Synthesis by Glycolysis: a Response Surface Methodology Approach Thiago do Carmo Rufino, Márcia Cristina Breitkreitz, and Maria Isabel Felisberti Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b04614 • Publication Date (Web): 17 Mar 2017 Downloaded from http://pubs.acs.org on March 18, 2017
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Industrial & Engineering Chemistry Research is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 27
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Industrial & Engineering Chemistry Research
Telechelic Poly(Bisphenol A Carbonate) Synthesis by Glycolysis: a Response Surface Methodology Approach Thiago do Carmo Rufino¹, Márcia Cristina Breitkreitz¹, and Maria Isabel Felisberti¹* Institute of Chemistry, University of Campinas, Campinas, São Paulo, Brazil, ZIP 13.083-970, PO Box 6154
[email protected] Abstract Poly(bisphenol A carbonate) (PC) is the second most produced engineering polymer in the world; therefore, there are several papers describing its recycling. However, only a few employ a multivariate approach together with a solid statistics basis for proving the trends and capabilities of their methodology. In this work, we report the progress in PC glycolysis, aimed at the production of telechelic hydroxyl-terminated oligomers (PC(OH)2), with controlled molar mass. A Box-Behnken Design (BBD) was employed to evaluate the influence of temperature, ethylene glycol (EG)/PC molar ratio, and polymer solution concentration on the PC(OH)2 molar mass and on reaction yield. The EG/PC molar ratio is the most important factor affecting reaction products. PC(OH)2 yield and bisphenol A residue amount can be controlled through reaction conditions. The BBD allowed the optimization and the scale-up of the reaction, which presented a good correlation between large and small scales. Introduction
Telechelic polymers are prepolymers capable of entering into further polymerization or other chemical modification through their reactive end-groups1. Due to this characteristic, telechelic polymers have been applied in the synthesis of block copolymers, thermoplastic elastomers, surfactants, macromonomers, and polymer networks2. There are many ways to 1 ACS Paragon Plus Environment
Industrial & Engineering Chemistry Research
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
produce telechelic polymers; most of them involve catalyzed condensation or addition reactions2,3. Poly(bisphenol A carbonate) (PC) is an amorphous polycarbonate with a glass transition temperature (Tg) around 147 °C4, high mechanical resistance, transparency and refractive index (RI=1.58)5, and it can be processed by several methods. These characteristics maintain PC as the second most produced engineering polymer in the world, being widely used in industrial areas such as aeronautics, the automotive industry, buildings, medical devices, etc.6,7. Although PC is already employed in the manufacture of many goods, telechelic PC, such as PC(OH)2, would provide many new uses and/or enable the introduction of this polymer into several polymeric systems (i.e. copolymers, polymer networks). Riffle et al.8 first reported, in 1982, a synthetic route to PC(OH)2 with controlled molar mass (Mn), based on traditional reactants: bisphenol A (BPA) and phosgene. Their strategy was to block one of the hydroxyl groups of a fraction of BPA molecules, either prior to or during phosgenation, by reaction with trimethylchlorosilane, trifluoracetic anhydride, or trifluoracetic acid. Thus, polycondensation occurred between mono- and di-hydroxylated BPA, and phosgene. The control of molar mass could be achieved by controlling the amount of mono-functional BPA in the reaction media. The authors reported hydroxyl-terminated PC in a molar mass range from 3 kg/mol to 21 kg/mol.8 Sixteen years later, based on a carbonate interchanges reaction, Korn and Gagné
9
proposed PC depolymerization, using di-aryl carbonates as interchange agent, for
producing telechelic PC oligomers. The reaction was performed in tetrahydrofuran solution using diphenyl carbonate (DPC) as the depolymerization agent and potassium tert-butoxide as catalyst. Although PC depolymerization by DPC results in phenyl end-capped oligomers, DPC was chosen as a model reactant for a kinetic study. Based on that, the authors used a functionalized diaryl carbonate to produce telechelic cyanobiphenyl end-capped PC oligomers.9 However, production of hydroxyl end-capped PC has not been demonstrated by this methodology. 2 ACS Paragon Plus Environment
Page 2 of 27
Page 3 of 27
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Industrial & Engineering Chemistry Research
The consumption of PC in the period from 2012 to 2017 has been estimated to be around 4.5 Mt with forecast global increase of 4% per year7. Therefore, there have been many published works on PC recycling in the last 15 years.10 Regarding chemical methods for PC recycling11,12, the aim is usually to recover the monomer (BPA), which has been achieved by hydrolysis13–17, alcoholysis18–22, aminolysis23–26 and glycolysis27–31. The first studies on glycolysis of polymers date back to the 1980s; none has performed a multivariate approach. In this decade, some research groups were working on glycolysis of cellulose by ethylene glycol. For instance, Bouchard et al.32 reported that glycolysis could be performed with control of product molar mass. For synthetic polymers, the first glycolysis study dates to 1995, for poly(ethylene terephthalate) in the presence of bisphenol A at 190–230 °C, aimed at recovering the monomers.33 Analogously, in 2009, Kim et al.27 evaluated the noncatalyzed glycolysis of PC using ethylene glycol (EG) as both reactant and solvent in a heterogeneous medium, with focus on chemically recycling PC with maximum bisphenol A (BPA) recovery. They showed that non-catalyzed glycolysis produces three main products: BPA, p-tert-butylphenol, and ethylene carbonate; however BPA is the main product. Also, they studied the influence of temperature, time, EG/PC mass ratio, and shaking, on the BPA yield. The authors proposed a two-step depolymerization mechanism for PC: firstly, a heterogeneous step involving the diffusion of EG into the PC pellets followed by random chain scission with subsequent formation of oligomers; secondly, a homogeneous step in which solubilized oligomers undergo further glycolysis to BPA27. In preliminary studies, we tried to halt the glycolysis in a heterogeneous medium at an intermediate stage, aiming at the production of hydroxyl-terminated PC oligomers, but without success. In this case, the heterogeneous step is the slow step of the process; consequently, whatever amount of PC oligomer is solubilized in EG, it rapidly undergoes the homogeneous step 3 ACS Paragon Plus Environment
Industrial & Engineering Chemistry Research
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
and results in the production of BPA only – even at temperatures lower (140–180 °C) and reaction times lower (90–180 min) than those studied by Kim et al.27. Thus, this two-step heterogeneous glycolysis is very efficient at obtaining BPA from PC residues, but is not suitable for producing telechelic oligomers. Design of experiment (DOE) is a technique that allows the study of different experimental factors simultaneously, and the identification of interactions between them, in order to quantify their influence on one or more properties of interest to multivariate models34. These models relate experimental factors to the properties of interest (named responses) by Multiple Linear Regression (MLR) and allow the building of Response Surface graphs. To build these models with high order coefficients (e.g. quadratic and cubic) a three level design, such as a 3³ factorial design, is necessary. However, this type of design requires a number of experiments beyond those necessary to calculate these coefficients. Box and Behnken have demonstrated that it is possible to obtain the same conclusions from a reduced number of experiments35. Thus, a BoxBehnken design is characterized by a three-level combination of experimental factors, in which experiments are not performed at extreme conditions of each combination of factors, but rather at a position along the edges, as shown in Figure 1. It also allows the building of second order models and, additionally, it is possible to estimate higher order model coefficients if nonsignificant coefficients are removed.
4 ACS Paragon Plus Environment
Page 4 of 27
Page 5 of 27
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Industrial & Engineering Chemistry Research
. Figure 1. Box-Behhken design for three factors, represented by dark spheres. The whole set of experiments (3³) is obtained when considering both dark and light spheres.
The best approach to verify the predictive capability of the built models is Analysis of Variance (ANOVA), in which F tests are performed to test Regression Significance and Model Lack of Fit. Regression is considered significant if the Regression Mean Square (MQR) is statistically greater than the Residual Mean Squares (MQr) and indicates that the variation of experimental factors indeed causes a significant change in the studied property of interest and, therefore, it is not due to a random variation. Furthermore, the model is considered a good fit to the experimental data if the Lack of Fit Mean Square (MQLOF) is equal to Pure Error Mean Square (MQPE).36 In this work we present a systematic study on the glycolysis of PC by ethylene glycol (EG) in solution with N,N dimethylacetamide (DMAc), with no addition of catalyst, aiming at the production of hydroxyl end-capped PC oligomers, denoted herein as PC(OH)2. A BoxBehnken design was employed to derive empirical models to predict and to correlate PC(OH)2 properties with the synthesis parameters, such as temperature, solution concentration and EG/PC molar ratio, on the responses molar mass (Mr), molar mass dispersity (ĐM), PC(OH)2 yield (%), 5 ACS Paragon Plus Environment
Industrial & Engineering Chemistry Research
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
and BPA residue (%). From this study, it was possible to optimize PC(OH)2 production and scale up from 1.0 g to 1.0 kg, to confirm the consistency of the methodology. Our results also open perspectives for studies in chemical recycling with the production of telechelic PC oligomers, which present wide potential for application to polymer synthesis.2 Experimental
Pellets of PC (Mn = 15 kg/mol, ĐM = 3.2, both determined by Gel Permeation Chromatography - GPC) supplied by GVS were used in the Box-Behnken design to study the influence of reaction conditions on PC(OH)2 properties. For the scale-up study, Lexan® (Mn = 13 kg/mol, ĐM = 3.3, both determined by GPC), supplied by Sabic, was used. Ethylene glycol (EG) (PA–Synth), N,N-dimethylacetamide (DMAc) (PA–Vetec), chloroform (PA–Synth), and ethanol were used as reactant and solvents for precipitation/purification of glycolysis products.
Box-Behnken Design A Box-Behnken design was used to study the effects of temperature (Factor T, levels studied: 140, 150, and 160 °C), of PC concentration in DMAc solution (Factor C, levels studied: 20, 30 and 40 wt%), and of EG/PC molar ratio (Factor R, levels studied: 4:1, 8:1, and 16:1) on the characteristics of the glycolysis products. Three replicates were included at the center point (T = 150 °C; C = 30%; R=8:1). It is important to point out that the center point was dislocated for the factor R, which was -0.333 instead of 0.0. We were interested in evaluating the effect of half (4:1) and double (16:1) amount of EG over the glycolysis. The statistical treatment was carried out accordingly. The evaluated responses were relative molar mass (Mr), molar mass dispersity (ĐM), PC(OH)2 yield (%), and BPA residue (%) – Table 1. The PC glycolysis was carried out to obtain PC(OH)2 with low molar mass and dispersity (Mr ≈ 2.5 kg/mol, ĐM < 1.5), high PC(OH)2 6 ACS Paragon Plus Environment
Page 6 of 27
Page 7 of 27
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Industrial & Engineering Chemistry Research
yield (>50%) and low BPA residue (
