Synthesis of Poly(Tetramethylene Ether) Glycol Containing Ester Linkages Derived from Castor Oil and Properties of Recyclable Polyurethanes Prepared Therefrom

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Ricinoleic acid derived from castor oil was utilized for the preparation of ester linkages-containing poly(tetramethylene ether) [or poly(tetrahydrofuran)] glycol {HO-CH[(CH2)5CH3]CH2CH=CH(CH2)7-C(=O)O-[(CH2)4O]n-1-(CH2)4-OC(=O)-(CH2)7-CH=CH-CH2CH[(CH2)5CH3]-OH; PTHF-RA-OH}. This polyol was reacted with two-fold amount of 4,4’-diphenylmethane diisocyanate followed by the chain-extension reaction with1,4-butanediol to give a new polyurethane with degradable ester moieties. The obtained polyurethane (PTHF-RA-BD-PU) exhibited similar thermal and mechanical properties to those of the polyurethane (PTHF-BD-PU) prepared from poly(tetramethylene ether) [or poly(tetrahydrofuran)] glycol (PTHF-OH). The treatment of PTHF-RA-BD-PU with potassium hydroxide in tetrahydrofuran/ethanol (9/1 v/v) solvent in the presence of a small amount of water caused hydrolysis reaction of the recinolate ester linkages to give the mixture of PTHF-OH and the urethane oligomers capped with recinoleic acid moieties.The extraction of PTHF-OH with methylene chloride from the mixture resulted in the recovery of PTHF-OH in over 90% yield based on the poly(tetrahydrofuran) segments of PTHF-RA-BD-PU. Enzymatic degradation of PTHF-RA-BD-PU was carried out with lipase as a catalyst. Both of the heterogeneous reaction with film specimens in water using phosphate buffer solution (pH 7.4) at 37 oC and the homogeneous reaction in N,N-dimethylformamide at 45 oC caused the decrease in the molecular weight of PTHF-RA-BD-PU. This is probably due to the lipase-catalyzed hydrolysis of the recinolate ester groups of PTHF-RA-BD-PU.