3 lines
5.1 KiB
JSON
3 lines
5.1 KiB
JSON
{
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"protocol": "The study aims to characterize the kinetics of thermoplastic polyurethane (TPU) polymerization in situ using Raman spectroscopy. Specifically, the focus is on acquiring conversion versus time data from an uncatalyzed polyester-based TPU formulation. The data obtained through Raman spectroscopy will be compared with kinetics parameters from differential scanning calorimetry (DSC) experiments.The synthesis of hydrophilic polymers involves the use of a hydroxyl terminated poly(butylene adipate) (PBA) oligomer with a number average molecular weight of approximately 2000 g/mol as the soft segment. The hard segments are derived from 4,4'-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BDO), with MDI being supplied by Bayer and BDO supplied by ARCO chemical company.In preparation for TPU synthesis, PBA was melted and dried under a vacuum at 100°C for a minimum of 4h while BDO was dried over type 3A molecular sieves at room temperature for at least 2 weeks prior to synthesis. MDI was used as received but stored under a vacuum at 0°C until required for synthesis. The TPU was synthesized with a stoichiometric ratio of hydroxyl to isocyanate functionality at unity, using equimolar quantities of PBA and BDO. The TPU contained 76.84% PBA, 3.536% BDO, and 19.62% MDI by mass. The polymerization was performed using a 'one-shot' process, where dewatered PBA (heated to 100°C), BDO (at room temperature), and MDI (at room temperature) were gravimetrically metered into a 500ml polypropylene beaker and vigorously hand mixed for 15s. Upon thorough mixing of all TPU reactants, samples were removed and prepared for immediate kinetic analysis.To synthesize hydrophilic polymers with functional groups, prepare a TPU reactant mixture and place it between fused quartz cover slips to form samples approximately 1.0 mm in thickness. Use a hot stage preheated to isothermal polymerization temperatures of 100, 120, 140, and 160°C. Align the sample with the focused Raman laser beam and measure the kinetics of polymerization using a Kaiser Optical Systems Series 5000 Holoprobe Raman spectrometer equipped with a 785 nm GaAlAs diode laser. Conduct measurements with a 30-second exposure time every 30 seconds for a total duration of 60 minutes. Process all Raman spectra with chemometric techniques using Grams/386 software for quantitative analysis, including baseline subtraction and normalization using an internal standard related to the MDI aromatic ring breathing/stretching modes.TPU reactant mixture samples were carefully weighed to 10±2 mg and sealed in aluminum hermetic pans and lids. Samples were placed into a DSC preheated to a specific isothermal temperature. Heat flow resulting from the exothermic TPU polymerization reaction was measured as a function of time for 60 minutes. After isothermal polymerization, samples were quenched to 0°C at a cooling rate of -100°C/min and subjected to a temperature scan from 0 to 200°C at a heating rate of 20°C/min. Isothermal polymerization temperatures of 100, 120, 140, and 160°C were used to evaluate all kinetic parameters.The synthesis of hydrophilic polymers with functional groups involves the following steps: 1. Prepare a reactant mixture that includes diisocyanates, such as MDI, and polyols at a ratio conducive to urethane formation. 2. Conduct polymerization at a controlled temperature of 120°C. 3. Monitor the reaction progress using Raman spectroscopy by measuring the peak intensities of characteristic functional groups at specific Raman shifts, particularly focusing on isocyanate and urethane bands. 4. Record Raman spectra at time intervals, specifically at 1 minute, 30 minutes, and 12 hours to observe changes in band intensities. 5. Utilize the peak height of the MDI band at 1530 cm-1 as an indicator of unreacted isocyanate groups for quantitative analysis of polymer conversion. 6. Calculate the conversion of the polymer using the formula α(t) = (I0 - I(t)) / I0, where I(t) denotes the peak height at time t and I0 represents the peak height at zero conversion.The synthesis of hydrophilic polymers involves following a step growth polyaddition reaction. Initially, the isocyanate (NCO) functional groups in the TPU reactant mixture are prepared and mixed. The temperature of the reaction is monitored, and the enthalpic heat of reaction is calculated using a differential scanning calorimetry (DSC) to determine the conversion over time. The enthalpic heat lost during sample preparation and loading is considered to ensure accurate measurement. The initial conditions of the reaction are set, ensuring a homogeneous mixture, and the polymerization progresses under controlled heating conditions. The heat capacity is calculated as a linear function of temperature to yield the necessary thermal data during polymerization. Maximum temperature rise correlates with the conversion of the reaction and is combined with heat flow measurements from attenuated total reflectance (ATR) experiments to derive the overall reaction heat. This process allows for the quantitative assessment of conversion as a function of both time and temperature during the synthesis of hydrophilic polymers with functional groups."
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