End-linked networks of poly(tetrahydrofuran) (PTHF) having a narrow molecular weight distribution were prepared by living cationic polymerization of PTHF followed by a crosslink reaction with pentaerythritol tetrakis(3-mercaptopropionate). It was found that the PTHF network was capable of crystallization even in the presence of crosslinks. The rate of isothermal crystallization at 20°C was of the order of days. The crystallization kinetics of the networks in a film form at 20°C was studied by monitoring the ageing time dependence of the mechanical and thermal properties, and infra-red absorption (i.r.) spectra. The mechanical behaviour was typical of that of elastomers in the induction and/or early stage of crystallization (~ 300 min). However, it changed gradually to that of semicrystalline polymers at the late stage (~ 5670min). The Avrami exponent was estimated by two methods, i.e. time evolution of the characteristic i.r. absorption band (i.r. method) and of the enthalpy of fusion (differential scanning calorimetry) (d.s.c.) method. The exponents were 2.2 by the i.r. method and 2.4 by the d.s.c, method. Morphological studies on the aged films revealed the presence of spherulites of the order of 50 to t00#m, which were much larger than those for prepolymers (25 to 50 #m). The effects of crosslinks on the crystallization kinetics and morphology as well as on the mechanical properties are discussed.
Посилання на статтю:
Isothermal crystallization of end-linked poly(tetrahydrofuran) networks / Mitsuhiro Shibayama*, Hiroshi Takahashi, Hideki Yamaguchi,Shinichi Sakurai and Shunji Nomura // Polymer. – 1994. – Vol 35. – P. 2944-2951.