A synchronization observation was carried out to investigate the growth of PEO spherulites by using a polarizing optical microscope in order to learn the phenomenon of concentric banded stripes occurred during the growth of PEO spherulites.It was found that the concentric banded stripe didn’t come into being until at least two independent PEO-spherulites met each other,the formation of the concentric banded stripes were owing to the tortuosity of the spherulite after colliding with other spherulites.
A new biodegradable PtBA-PHB-PtBA triblock copolymer was successfully synthesized by ATRP method with Br-PHB-Br as macroinitiator,tert-butyl acrylate as monomer and CuBr/PMDETA as the catalyst system.Cleavage of the tert-butyl ether groups of the PtBA-PHB-PtBA triblock copolymer was then performed via hydrolysis with trifluoroacetic acid as the catalyst in dichloromethane to afford the amphiphilic PAA-PHB-PAA triblock copolymer.The hydrolysis is successful but trace tert-butyl ether groups still remain in the backbone.The molecular weight characteristics and chain structures were conformed by GPC and NMR,respectively.Because of hydrophilic and biocompatibility,the amphiphilic triblock copolymers have potential applications in the field of drug release.
In order to investigate the property and concentration dependence of dissociation and hydrolysis of polyelectrolytes,acrylic acid-sodium acrylate copolymers with various degree of neutralization were prepared by adding calculated amounts of sodium hydroxide into the aqueous solutions of a poly(acrylic acid) sample,and the pH values of the solutions covering a wide concentration range were measured for each copolymer at 25℃.It was found that the pH values of the solutions of a copolymer with degree of neutralization of 0.96 kept constant and equaled to 9.80 as c>0.001 mol/L.For another copolymer with degree of neutralization of 0.30,the pH values of its solutions remained constant and equaled to 6.25 as c<0.001 mol/L.These two copolymers may serve as polymeric buffer reagents which couldn’t penetrate through semi-permeable membranes in the corresponding concentration regions.
