A series of poly(butylene succinate‐co‐butylene 2‐methyl succinate)s were prepared through variations in the molar fraction of succinic acid to 2‐methyl succinic acid, and the effects of methyl substitution on the shear‐induced crystallization, nonisothermal crystallization behavior, dynamic rheological properties, crystal morphology, and mechanical properties were investigated. Introducing 2‐methyl succinic units reduced the melting temperature and crystallization temperature; this indicated that the substituted units retarded crystallization of the polymer. The Avrami exponents, estimated by modified Avrami plots, ranged from 2.1 to 3.5 and were a little diminished by the substitution. The substitution also reduced the rate of crystallization under shear. However, the effect was diminished with an increasing shear rate because most polymer chains were more regularly arranged at higher shear rates. Dynamic experiments in the solid state revealed that the peak on a plot of the loss tangent against the temperature became sharper at higher contents of the substituted unit, and the peak temperature, the glass‐transition temperature, was reduced as the content of 2‐methyl succinic acid increased. Wide‐angle X‐ray diffraction patterns showed that there was little effect of the 2‐methyl succinic acid unit on the crystal morphology. The toughness of the polymer was abruptly increased up to 350% at the expense of the tensile modulus. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1759–1766, 2004

ABSTRACT:The molecular weight (MW) of polycaprolactone (PCL) component had a profound effect on the ester interchange reactions during melt blending with poly(ethylene terephthalate) (PET). Utilization of lower MW of PCL component gave rise to higher degree of ester interchange reactions, and it could reduce mixing time required for generating a copolyester. The thermal properties and crystalline structure of resultant copolyesters were depended on the degree of ester interchange reactions by varying MW of PCL. It converted the morphology of copolyesters to a continuous single phase, suggesting formation of more random copolyester. Further, the substitution of PCL with low MW (M w : 1250) as third component in melt blends of PET and PCL with high MW(M w : 80000) led to higher degree of ester interchange reactions as well.KEY WORDS Poly(ethylene terephthalate) / Polycaprolactone / Melt Blending / Ester Interchange Reactions / Molecular Weight / The ester interchange reactions commonly occur in melt blending of different kinds of polyesters, which produces first the block copolyesters from immiscible blends and finally microstructure becomes randomized. [1][2][3][4] The physicochemical properties of produced copolyesters are closely related to their structural characteristics such as sequence length and randomness, which influenced by the degree of ester interchange reactions. Therefore, the control of ester interchange reactions in polyester blends may be technical key for their industrial applications.On the other hand, the copolyesters consisted of amorphous aliphatic ester unit and high melting crystalline ester unit are expected to find their applications for functional materials. Among them, poly(ethylene terephthalate/caprolactone) [P(ET/CL)] copolyester has been early focused on the biodegradable polymeric materials required for desirable mechanical and thermal properties. 5-10 It has recently attracted much interest for elastomeric materials. 11, 12 Thus, the elastic fiber spun from P(ET/CL) copolyesters is used as plastic and mechanical energy-absorbing device in seat belt assembly.However, it is difficult to obtain the copolyester by melt blending of poly(ethylene terephthalate) (PET) and polycaprolactone (PCL) because of the poor thermal stability of PCL. In order to prevent the thermal degradation of PCL component during melt blending, the mixing procedure must be accomplished within a short time. However, this frequently raises the problem of immiscibility between PET and PCL because of the lack of ester interchange reactions.As well known, ester interchange reactions during melt blending includes alcoholysis, acidolysis, and direct transesterification. 4,[13][14][15] The degree of ester interchange reactions is more seriously dependent on alcoholysis than acidolysis and direct transesterification because the former reaction is kinetically faster than the latter reactions. Recently, it is reconfirmed the fact that the importance of the role of alcoholysis by hydroxyl end group via the control of mole...

A series of poly(ethylene terephthalate/polycaprolactone) (PET/PCL) copolyesters were prepared by adding PCL with a weight‐average molecular weight of 40,000 to the PET oligomer during polycondensation, and the composition and physical properties of the copolymers were investigated. In the case of copolyesters containing caprolactone (CL) units less than 26 mol %, the melting and crystallization temperatures were decreased with increasing CL content. They exhibited wide‐angle X‐ray diffraction (WAXD) patterns similar to PET. However, the variation of d‐spacing on the WAXD pattern suggested that a small amount of CL could be included into the crystal of ethylene (ET) because of strong hydrogen bonding between crystallizable ET blocks. In the copolyesters containing CL components higher than 38 mol %, they exhibited thermal behavior and WAXD patterns typical of amorphous random copolymers. The copolyester composition has a decisive effect on the rheological properties. The copolyesters with CL contents higher than 38 mol % exhibited a viscosity behavior similar to Bingham fluid, although the copolyesters with CL contents lower than 26 mol % exhibited a Newtonian flow behavior similar to PET. In addition, the value of the loss tangent of the copolyester melts notably decreased with an increasing CL content, and the bulk exhibited rubberlike behavior. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2552–2560, 2002

The physical properties and gelation behavior of polyacrylonitrile (PAN) solutions were investigated in mixed solvents of N,N‐dimethylformamide (DMF) and dimethylsulfoxide (DMSO). For the individual solubility parameters, DMSO had the polar term closer to PAN than DMF. Small‐angle X‐ray scattering profiles and Fourier transform infrared spectra of 20 wt% PAN solutions confirmed that the internal structure and intermolecular complexes between nitrile groups were broken up by the DMSO molecules. The slope of Cole–Cole plot, a measure of the solution heterogeneity, increased with the mole fraction of DMSO (XDMSO) via three distinct zones. The homogenization was particularly noticeable in Zone 1 (0.0 < XDMSO < 0.4) and Zone 3 (0.7 < XDMSO < 1.0). The Huggins constant and UV‐visible absorption at 268 nm of dilute solutions decreased sharply above XDMSO of 0.7 in Zone 3. This indicated a marked increase of PAN solubility by dissociating the intramolecular complexes between nitrile groups. In Zone 1, the storage modulus of 20 wt% PAN solutions decreased but loss modulus remained almost constant with XDMSO at lower frequency below 1 rad s−1, indicating the weakening of the true entanglement points of the intermolecular complexes. The mechanism indicated that the intermolecular complexes between nitrile groups were dissociated by DMSO earlier than the intramolecular ones. © 2017 Society of Chemical Industry