Effect of molecular weight on spherulitic growth rate of poly(ϵ‐caprolactone) and poly(ϵ‐caprolactone)‐b‐poly(ethylene glycol)

The spherulitic growth rates of a series poly (ϵ‐caprolactone) homopolymers and poly(ϵ‐caprolactone)‐ b ‐ poly(ethylene glycol) (PCL‐ b ‐PEG) block copolymers with different molecular weights but narrow polydispersity were studied. The results show that for both PCL homopolymers and PCL‐ b ‐PEG block copolymers, the spherulitic growth rate first increases with molecular weight and reaches a maximum, then decreases as molecular weight increases. Crystallization temperature has greater influence on the spherulitic growth rate of polymers with higher molecular weight. Hoffman–Lauritzen theory was used to analyze spherulitic growth kinetics and the free energy of the folding surface ( σ e ) was derived. It is found that the values of σ e decrease with molecular weight at low molecular weight level and become constant for high molecular weight polymers. The chemically linked PEG block does not change the values of σ e significantly.