Synthesis and characterization of photocrosslinkable biodegradable polymers derived from 4-hydroxycinnamic acid

A novel series of photocrosslinkable biodegradable polymers was prepared by a high-temperature solution polycondensation from a dichloride of 4,4'-(adipoyldioxy)dicinnamic acid (CAC) and alkane diols,of various methylene lengths (HO(CH2)(n)OH; n = 6-10) or poly(ethylene glycol)s (PEG) of various molecular weights ((M) over bar = 200-8 300). The CAC was synthesized by the condensation of adipoyl chloride and 4-hydroxycinnamic acid. The chemical structures and properties of these polymers were characterized by elemental analysis, ultraviolet-visible spectroscopy (UV-VIS), Fourier transform infrared spectroscopy (FT-IR), H-1 NMR spectroscopy, differential scanning calorimertry (DSC), and thermogravimetry (TG). All polymers had a high molecular weight and good solubility in organic solvents. DSC showed that T-m values of CACn (134-180degreesC) were much higher than those of CACEm (25-56degreesC). The CACE200 degraded very rapidly in the buffer solutions (pH 7.2) of Ps. Cepacia or Rh. delemar lipase at 37 degreesC, while CACn resisted the hydrolysis by these lipases during the test period. Them ultraviolet light irradiation (lambda greater than or equal to 280 nm) caused the photocrosslinking reaction by an intermolecular dimerization at ambient temperature without a photosensitizer, as examined by UV-VIS, FT-IR spectroscopy, and gel formation. The gels prepared from CACEm (m approximate to 1000) were swollen in water and showed characteristic properties of a hydrogel. The irradiation time and the molecular weight of PEGs controlled the degree of swelling of these hydrogels. The CACE8 300 gel irradiated for 20 min showed the largest degree of swelling of 10.5.