L-menthol-based xanthate mediator for RAFT polymerization of vinyl acetate

Abstract

A xanthate RAFT agent 2-isopropyl-5-methylcyclohexyl 2-(ethoxycarbonothioyl)thio) propanoate has been synthesized via the reactions of L-menthol with 2-bromo-propionyl bromide in THF in the presence of triethylamine leading to the formation of 2-isopropyl-5-methylcyclohexyl 2-bromopropanoate followed by its reaction with potassium-O-ethyl xanthate in ethanol at room temperature and characterized by ¹H, ¹³C NMR and FTIR. RAFT polymerization of vinyl acetate (VAc) using it has resulted in the formation of well-defined polyVAc in controlled manner. This is evidenced by (i) the observation of the pseudo first order kinetics upto ∼90% conversion, (ii) linear increment of molecular weight (unimodal GPC chromatogram) of the polymer keeping its PDI low with the progress of the reaction upto ∼90% conversion, (iii) the linear increment of the molecular weight of the polymers with low PDI on increasing monomer loading, (iv) chain-end analysis of the polymer using ¹H NMR confirming the presence of the RAFT agent fragment at the polymer chain-ends, and (v) successful homo- and hetero-chain extension with VAc and NVP, respectively. L-Menthyl-capped polyvinyl acetate has shown higher (i) light transmission properties of its dichloromethane solution at ∼277 nm, (ii) thermal stability, and (iii) glass transition temperature in comparison to its non-L-Menthyl-capped homolog.

Synthesis and characterization of L-menthol-based xanthate RAFT agent 2-isopropyl-5-methylcyclohexyl 2-(ethoxycarbonothioyl)thio) propanoate and its successful use for controlled bulk polymerization of vinyl acetate in the presence of azobis-isobutyronitrile (AIBN) at 70^oC have been explored.

Keywords:

• L-Menthol-based RAFT agents
• vinyl acetate
• RAFT polymerization
• chain-extension
• optical and thermal properties

Acknowledgments

BR acknowledges the financial support from DBT (Govt. of India) through grant no. BT/PR889/NNT/28/570/2011 and the Council of Science and Industrial Research, Government of India, through Grant no. 02(0002)/11/EMR-II. SV gratefully acknowledges the financial support from Banaras Hindu University through UGC-CRET-fellowship.

Additional information

Funding

The financial support from DBT (Govt. of India) through grant no. BT/PR889/NNT/28/570/2011 and the Council of Science and Industrial Research, Government of India, through Grant no. 02(0002)/11/EMR-II. SV; Banaras Hindu University through UGC-CRET-fellowship.