Determination of Average Molecular Weight of Polycarbonateby Reactive Py-GC in the Presence of Organic Alkali

Significance of the Topic

Determining the average molecular weight of polycarbonate is essential for assessing material properties such as mechanical strength thermal stability and processability. Reactive pyrolysis GC in presence of organic alkali offers fast and direct measurement of end group concentrations enabling accurate number average molecular weight estimation.

Objectives and Study Overview

The primary goal was to estimate the number average molecular weight of a commercial polycarbonate sample prepared by solvent method. Reactive Py GC using a tetramethylammonium hydroxide reagent was employed to cleave polymer chains and generate diagnostic fragments for quantitative analysis.

Methodology

About 50 micrograms of freezer milled polycarbonate were mixed with 1 microliter of 25 weight percent TMAH in methanol. The mixture was subjected to pyrolysis at 400 degrees Celsius using a double shot pyrolyzer coupled to a gas chromatograph. The resulting pyrolysate was separated on a polydimethylsiloxane column and detected by flame ionization.

Instrumentation Used

• Double shot pyrolyzer
• Gas chromatograph with FID detector
• Polydimethylsiloxane column 25 meters length 0.25 millimeter inner diameter 0.25 micrometer film thickness
• Carrier gas helium flow 50 milliliters per minute column flow 1.3 milliliters per minute

Key Results and Discussion

The pyrogram displayed two main peaks ptert butylanisole from chain end groups and the dimethyl ether of bisphenol A from the polymer backbone. Peak intensities IA and IB were corrected by respective effective carbon numbers ECN of 10.2 and 15.4. Using the known monomer unit mass and end group mass and applying the ratio of corrected peak areas allowed calculation of degree of polymerization and number average molecular weight which agreed with expected values for the synthetic sample.

Benefits and Practical Applications

• Rapid assessment of polymer molecular weight without extensive sample preparation
• Provides direct measure of end group concentration for quality control
• Applicable to various synthetic polymers and copolymers
• Enables monitoring of polymerization processes and batch consistency

Future Trends and Applications

Integration of reactive Py GC with mass spectrometry detectors will allow more detailed structural analysis and identification of minor end groups. Advances in automation and software will support high throughput polymer characterization. Extension of the methodology to biodegradable polyesters and emerging copolymers can broaden its industrial relevance.

Conclusion

Reactive pyrolysis GC in the presence of TMAH provides a reliable and efficient method for determining the number average molecular weight of polycarbonate by quantifying end group derived fragments. This technique enhances quality control workflows and offers potential for wider polymer analysis applications.

References

• Ito Y Ogasawara H Ishida Y Ohtani H Tsuge S Polymer Journal 1996 28 1090 1095