Crystallization of polyethylene and polydioxanone with multiple hydrogen bonds between their terminal groups

In order to clarify the effects of multiple hydrogen bonds between chain ends on the crystal growth of polymers, we studied the growth rate of crystal G of polyethylene (PE) having amino groups and thymine units in the terminal (PE-Thym) and polydioxanone having hydroxy groups and thymine units in the terminal (PDX-Thym) from the melt as a function of the degree of supercooling ΔT by means of polarizing optical microscope, DSC and WAXS. PE-Thym and PDX-Thym have multiple hydrogen bonds between their terminals. We also prepared PE having amino and hydroxy groups in the terminal (PE-OH) and PDX having carboxy and hydroxy groups in the terminal (PDX-OH) as reference samples. Those show weak single hydrogen bond between their terminals. Number average molecular weights M_n of PE-Thym and PE-OH are almost the same (M_n = ca, 2000). M_n of PDX-Thym and PDX-OH are 3000 and 5600, respectively. G of all the samples obeyed the equation, G = G₀exp(-B/Δr). The exponent B for PE-Thym and PDX-Thym is almost the same as for PE-OH and PDX-OH. Since B is proportional to the surface free energy of the end surface of the nucleus, this indicates that the regularity of folding at the surface is also the same. On the other hand, G₀ of PE-Thym and PDX-Thym is much less than that of PE-OH and PDX-OH. We speculate that the reeling motion from the melt to the nucleus during crystal growth is suppressed due to the formation of a dynamic multiple-hydrogen-bond network between chain ends in the melt. Moreover, in order to shield the multiple hydrogen bonds in the terminal, we studied the ΔT dependence of G for PDX-Thym with added adenine. Compared to PDX-Thym without added adenine, we found that the ΔT dependence of G changed. This indicates that the influence of hydrogen bonds on crystal growth is closely related with the regime of crystal growth.