Synthesis and Characterization of Polyvinyl Alkyl Ester and Polyvinyl Alcohol Homopolymers and Blends of Polyvinyl Alkyl Esters Dr. Ronald P. D’Amelia, Joseph Mancuso, and Masashi W. Kimura
Chemistry Department, Hofstra University, Hempstead, NY 11549-0151 Introduction
Experimental
Results
Polymers are macromolecules comprised of recurrent covalently bonded structural units known as repeating units. Polyvinyl alkyl esters (PVAe) are a class of macromolecules commonly used for manufacturing commercial products including adhesives, chewing gum bases, industrial coatings, paint thickeners, plasticizers, and textile finishes; they possess a side-chain ester (pendant group) that increases in molar mass and hydrophobicity while its structural polarity decreases as the number of carbons in the carboxylic acid increases. The figure below showcases a repeating unit for the PVAe’s we will be synthesizing:
Synthesis of PVAe from PVOH by Esterification
Table 2: General Properties of PVAc
Weighed approximately 5-grams of PVOH (Mw 13,000-23,000) into a 250-mL round-bottom flask with a condenser, thermometer, and dropping funnel attached; to this, 25-mL of anhydride (acetic, propionic, butyric, or hexanoic) was added via the dropping funnel. The solution was refluxed for around 3.5-4 hours at different temperatures depending on the anhydride (125°C for acetic, 140°C for propionic, 150°C for butyric, and 250°C for hexanoic). After reflux, the product was precipitated from solution using 1M sodium hydroxide until it had a neutral pH. After precipitation, the aqueous solution was replaced with 1M sodium tert-butoxide and left alone for a few to several days to neutralize any remaining acid remaining within the product. Afterwards, the aqueous solution was decanted and the product was placed in a vacuum oven at 50°C for a day. Then, the product was dissolved in acetone and reprecipitated using 200-mL of water to get rid of any remaining acid. Finally, the acetone-water solution was decanted and the product was dried in the vacuum oven at the same temperature and duration. The product was then weighed.
Differential Scanning Calorimetry (DSC) Each sample was placed on a volatile aluminum pan and pressed to seal them; each were analyzed with a Perkin Elmer Pyris 1 Differential Scanning Calorimeter using nitrogen as the purge gas flowing at 20-mL/min. The glass transition temperature (Tg) was determined using the Pyris DSC software package. Indium metal was used to calibrate the DSC’s temperature and enthalpy measurements.
Fourier Transform Infrared Spectroscopy (FTIR)
Where n and r are the number of repeating and methylene (-CH2-) units, respectively. When r equals zero, the resulting PVAe is polyvinyl acetate (PVAc), the precursor for making polyvinyl alcohol (PVOH), the single largest volume water-soluble, non-toxic, biodegradable, and biocompatible polymer in the world. By increasing the value of r, the methylene and side-chain length, the pendant group mass and hydrophobicity increases as a result. To synthesize PVAe’s, PVOH of a known molecular weight will be esterified with a series of acid anhydrides; these products will also be made into blends. PVOH will be obtained via an alcoholysis/saponification-hydrolysis reaction using PVAc of different molecular weights. The figure below shows the general reaction scheme for this project:
All PVAc, PVOH, and PVAe samples were analyzed using a Brucker FTIR spectrometer with a Platinum® attenuated total internal reflectance (ATR) quick snap module with a diamond crystal. The Alpha-P unit had a Michelson Interferometer with a SiC globar as the IR source, the time dependence of the IR intensity was measured with a pyroelectric DTGS detector. The data analysis was done using the Bruker OPUS® software version 7.0.122. Each sample was analyzed by simply pressing the sample between the anvil and diamond crystal, with each measurement represents the average spectrum after 16 scans and at a resolution of four wavenumber.
Gel Permeation Chromatography (GPC) The PVAc samples were dissolved by placing some of each into a 15x45-mm VWR clear screw thread vial and added to them was 4.0-mL of tetrahydrofuran (THF) using a 4-mL transfer pipette. The vial was sealed with a Waters PTFE white Septum and a Wheaton black plastic cap with an open top. The vials of solutions were placed in a vial carousel of the Waters 717plus Autosampler and inserted into the unit. The GPC unit itself was constructed using the following components: 1-L solvent bottle, Viscotek DG 700 Degasser, Solvent Delivery System (Waters 510 HPLC Pump), Waters 717plus Autosampler, Waters Styragel Gel Permeation Columns HR 3;4;5, Viscotek RALLS Detector Model 600, Viscotek Dual Detector consisting of a Differential Refractometer (RI) and a Viscometer Model 250, and a Viscotek Data Manager DM 400. The GPC measurements were analyzed using Viscotek TriSEC 3.0 GPC software installed on a computer.
Intrinsic Viscosity Using a calibrated Cannon-Ubbelohde low shear semi-micro dilution viscometer (size 50), viscometry measurements were conducted on the samples with no kinetic energy corrections on the measured data. The temperature was controlled using a Cannon Model M-1 Constant Temperature Bath connected to a Haake A81 cooling unit, which helped to maintain the water-bath constantly at 25.0°C ± 0.1°C. Around 1.5-grams of each sample was dissolved in 50-mL of solvent (acetone for PVAc and PVAe’s, water for PVOH) and filtered through a Hypo Interchangeable Syringe with a Whatman 25mm polytetrafluoroethylene (PTFE) filter. At least three readings were taken using a stopwatch accurate to 0.2 seconds. The intrinsic viscosities were determined by extrapolating to zero concentration on a plot of reduced specific viscosity (viscosity number) vs. concentration in g/dl.
Nuclear Magnetic Resonance (NMR) The proton NMR spectra were obtained using a 400 MHz JEOL model ECS-400 NMR spectrometer. The PVAe’s and PVOH’s were dissolved in deuterated chloroform and deuterium oxide, respectively. The JEOL Delta NMR control and process software version 5.0.2 (Windows) were used to analyze individual spectrum. Each sample was ran as a 16 scan single pulse, 1D proton NMR with a 0.25 Hz resolution and a relaxation time of 5 seconds.
Research Goals 1. To synthesize different PVAe’s with the same number of repeating units, n, but with increasing side-chain length, r. 2. To synthesize polyvinyl alcohol (PVOH) via alcoholysis/saponification-hydrolysis. 3. To analyze the physical effects and properties of changing PVAe’s side-chain sizes and structures.
Experimental Chemical Samples Used and Descriptions The PVAc samples were purchased from Union Carbide / DOW Chemical Corp and produced using solution-free radical polymerization; these samples were identified as GB-11, GB-30, GB-50, and GB-75; they are food-grade gum resins with appearances ranging from a transparent gel to white pellets. The PVOH sample, which was 98% hydrolyzed with a molecular weight of 13,000-23,000, was obtained from Sigma-Aldrich and manufactured from alcoholysis of PVAc; it consisted of small, sand-sized, light-yellow particles. Mallinckrodt’s potassium hydroxide (87% pure) and anhydrous methanol (99.8% pure) from Spectrum were used for synthesizing PVOH from PVAc. Sigma-Aldrich supplied acetic anhydride (99% pure), propionic anhydride (99% pure), butyric anhydride (98% pure), and hexanoic anhydride (97% pure) used in esterifying PVOH into PVAe’s.
Synthesis of PVOH from PVAc by Alcoholysis/SaponificationHydrolysis Weighed approximately 3-grams of PVAc (GB-11, -30, -50, or -75) into a 250-mL roundbottom flask with a condenser, thermometer, and dropping funnel attached; to this, 75-mL of anhydrous methanol was added through the dropping funnel and refluxed at approximately (65-70°C) until the PVAc was completely dissolved. Afterwards, a solution of approximately 2-grams potassium hydroxide and 25-mL of anhydrous methanol was added. After refluxing for an hour, the PVOH was gathered using a Bucher funnel. The PVOH was washed with two 25-mL potions of anhydrous methanol and left to dry overnight before weighing.
PVAc
Glass Intrinsic Mw IR Transition Viscosity from Temperature (Acetone) MALLS (°C)
Results Table 1: Elemental Analysis of PVOH and PVAe Homopolymers Percent Compositions from Elemental Analysis Theoretical Percent Compositions Polymer % Carbon % Hydrogen % Oxygen % Carbon % Hydrogen % Oxygen PVOH 52.79 9.22 37.99 54.53 9.15 36.32 PVAc 55.57 6.89 37.54 55.81 7.02 37.17 PVPr 59.93 8.73 31.34 59.98 8.05 31.96 PVBu 63.34 9.59 27.07 63.14 8.83 28.03 PVHex 67.53 10.42 22.05 67.57 9.92 22.50
Figure 1: Overlaid FTIR Spectrum of PVAe Homopolymers
Mp GPC
Mw GPC
(Mv)*
GB-75
36.6
0.373
75,000
X 43,600 61,000
85,800
79,268
GB-50
35.4
0.260
55,300
X 28,400 47,400
59,000
46,441
GB-30
34.4
0.172
28,400
X 20,800 31,800
35,400
25,180
GB-11
27.7
0.100
11,300
X
14,000
11,275
7,850
12,800
*Calculated using the Mark-Howink equation for PVAc in acetone at 25°C: [η] = 1.82X10-4 Mv675
Table 3: General Properties of PVOH after Alcoholysis/Saponification-Hydrolysis of PVAc PVOH
Theoretical Yield (g)
Percent Yield
From GB-75 From GB-50 From GB-30 From GB-11 Mw 13K23K
1.612 1.554 1.547 1.537 -
104.8 104.3 103.3 56.1 -
Intrinsic Viscosity (H2O) 0.355 0.262 0.229 0.141 0.371
(Mv)**
IR
18,878 12,657 10,602 5,695 19,973
X X X X X
**Calculated using the Mark-Howink equation for PVOH in water at 25°C: [η] = 2.0X10-4 Mv76
Table 4: General Properties of PVAe’s from Esterification of PVOH (Mw 13,000-23,000) PVAe Made
Multi Angle Laser Light Scattering (MALLS) The average molecular weights (Mw) of the PVAc samples were obtained by dissolving in THF at 25°C and using Wyatt Multi Angle Laser Light Scattering Photometry model mini DAWN containing a K5 cell. The scattering intensities were measured at three angles (45°, 90°, and 135°) using 690nm wavelength of light. The data was analyzed using Zimm plots obtained from double extrapolated plots of Kc/Rθ vs. Sin2(θ/2) + kc using Wyatt Aurora software.
Mn GPC
PVAc PVPr PVBu PVHex
Intrinsic Molecular Calc. Mw Viscosity Weight (Acetone) 0.223 0.230 0.245 -
34,438 -
Tacticity
IR
0 + ++ +++
X X X X
39,038 45,394 51,749 -
Glass Transition Temperature (°C) 35 ----
Conclusions 1. Adding more methylene units (CH2) in the side chain (pendant group), with a constant carbon backbone, increases the molecular weight and intrinsic viscosity, while decreasing the tacticity and glass transition temperature. 2. The size of the IR methylene peak (2975 cm-1) increases proportionally from PVAc to PVHex due to the addition of more methylene units in the side chain. 3. The Mv of the PVOH’s decreases proportionally from the Mv obtained from the respective PVAc samples. 4. The average PVAc molecular weights were consistent using MALLS and GPC. 5. The glass transition temperature of the PVAc standard samples increases with Mw. 6. Percent carbons, hydrogens, and oxygens from elemental analysis are consistent with the theoretical percentages of those respective elements in PVOH and PVAe homopolymers. 7. Percent carbons and hydrogens increases while percent oxygens decreases as more methylene units are added to the side chain of the PVAe homopolymers.
References • Harris, F. W. Introduction to Polymer Chemistry. Journal of Chemical Education 1981, 58 (11), 837–843. • Lipșa, R.; Tudorachi, N.; Grigoraș, A.; Vasile, C.; Grӑdinariu, P. Study on Poly(Vinyl Alcohol) Copolymers Biodegradation. Memoirs of the Scientific Sections of the Romanian Academy 2015, 38. • Nagy, D. J.; Terwilliger, D. A. Sec of Poly(Vinyl Alcohol) Using Multi-Detection Methods. International GPC Symposium 1991, 161-179.
Support We acknowledge the support from a Hofstra HCLAS Faculty Research & Development Grant as well as Kyle O’Neil, Wayne Simonetti, and Lawrence Cheng for providing data for this project. printed by
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