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

Abstract

The spherulitic growth rates of a series poly (e-caprolactone) homopolymers and poly(e-caprolactone)-bpoly(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 (s e ) was derived. It is found that the values of s 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 s e significantly.

Crystallization of polymer chains confined in nanodomains

“…When T c,1 is close to T c,2 , two kinds of crystallization may start simultaneously to yield a cooperative morphology formation (lower route in Fig. 7) [46][47][48][49][50][51][52][53][54][55]. In PCL-b-PEO diblock copolymers, for example, the crystallizable temperature of PCL blocks is comparable to that of PEO blocks, and very unique crystalline morphologies, such as a concentric spherulite consisting of PCL cores and PEO coronas, are sometimes observed [46,47,49].…”

Competition between Structural Relaxation and Crystallization in the Glass Transition Range of Random Copolymers

“…The complex interaction between structure, molecular constitution, and configuration as well as the local molecular mobility determines the crystallization kinetics [ 12 , 13 , 14 , 15 , 16 ]. The complexity of the polymer crystallization becomes evident if the crystallinity, the crystal size, and the melting temperature are discussed as a function of the crystallization temperature [ 17 , 18 , 19 , 20 , 21 ].…”

Solubility considerations in relative block crystallization and morphology of PEO‐ b ‐PCL films

“…The cooling thermograms for 5k5k, 5k10k, 5k16.3k, and 5k24.5k PEO-b-PCL are shown in Figure 1. The first peak is assigned to PCL crystallization because of its larger weight fraction, [17][18]21,[23][24][25][26][27][28][29][30][31][32][33][34][35] and therefore the second peak (indicated by arrows) was assigned to PEO crystallization. Onset Txs were determined for both PCL and PEO using Pyris software.…”

“…These morphologies match well with other reports of PEO-b-PCL, where PEO crystallization is not obvious via POM but was identified using techniques such as FTIR, XRD, or DSC. [17][18]21,[23][24][25][26][27][28][29][30][31][32][33][34] Films cast from toluene (Figures 4b, 4f, and 4j) show little-to-no birefringence. Because there is evidence for crystallization of both blocks in the FTIR spectra (Figure 3), it was concluded that crystals in films cast from toluene were preferentially flat-on instead of edge-on.…”

“…PEO-b-PCL block copolymer crystallization has been studied extensively (see, for example, Refs. [21][22][23][24][25][26][27][28][29][30][31][32][33][34] because PEO and PCL homopolymer Tms are similar.…”