Multistage Structural Ordering and Crystallization of Poly(trimethylene terephthalate) during Sub-T_g Stretching: Synergetic Effects of Chain Orientation and Conformational Transition

Abstract

Crystallizable glassy polymers can undergo multistage structural evolutions and form multiple types of ordered phases (e.g., mesomorphic and crystalline phases) during stretching below their glass transition temperatures (T g ). However, the structural evolution of polymers during sub-T g stretching and the associated molecular mechanisms have not been well understood. In this work, we investigated the multistage structural ordering of glassy polymers and the related mechanisms during stretching below T g by studying poly(trimethylene terephthalate) (PTT) as a model system. Roles of chain orientation and conformational transition on the multistage structural evolution of melt-quenched PTT were elucidated through a loading−unloading experiment. When stretched below T g (e.g., 25 °C), the orientation of polymer chains and the stacking of phenylene rings lead to an intermolecular ordering, which induces the generation of a smectic C-like mesomorphic phase. The orientation degree of chains in such a mesomorphic phase increases with further stretching. This highly oriented mesomorphic phase transforms into a triclinic crystalline phase when the applied stress is unloaded. Stretching at a higher temperature (e.g., 40 °C) results in the formation of a more ordered mesomorphic phase and facilitates the induced crystallization due to the enhanced chain mobility. Fourier transform infrared results demonstrated that the unloading-induced crystallization of stretched PTT is originated from the trans-gauche conformational transition.

2,2‐Bistrifluoromethyl‐4,5‐difluoro‐1,3‐dioxole‐co‐tetrafluoroethylene copolymers with different compositions: Synthesis, chain and condensed matter structures and optical properties

“…WAXD patterns of PDD‐TFE‐HC copolymers were split and fitted using PeakFit software, 34 as shown in Figure 8. The crystalline and grain size of the PDD‐TFE‐HC copolymers, the integral area of each cleavage peak and other parameters are listed in Table 5.…”

“…The microstructure of the copolymer was probed with wide‐angle X‐ray diffraction (WAXD) using Nano‐inXider (France) with an X‐ray wavelength of 0.15406 nm. Due to the presence of amorphous and crystalline phases in the copolymers with low PDD compositions, the WAXD patterns of the copolymers were split and fitted, 33,34 and the crystallinity ( x c ) of the copolymers was calculated using the optimized Equation (). where A i is the total area of the crystalline peaks, and A t is the total area of diffraction characteristic peaks.…”

The Initial Molecular Interactions in the Course of Enthalpy Relaxation and Nucleation in Polyethylene Terephthalate (PET) as Monitored by Combined Nanocalorimetry and FTIR Spectroscopy

“…Crystallization in low-molecular weight liquids and polymers is well explored by a multitude of experimental techniques delivering detailed information on atomistic and mesoscopic scales. [1,2] In contrast, knowledge concerning nucleation is sparse, especially if one asks for the initiating molecular interactions. The collaborative research center ('Sonderforschungsberiche Transregio' SFB-TRR 102, total funding period 2011-2023) with a focus on "Polymers under multiple constraints: restricted and controlled molecular order and mobility" has the long-term goal to achieve a unifying fundamental understanding of structure formation processes driven by local ordering in polymers of synthetic and biological origin.…”

Glassy Alfa-Relaxation Promotes Surprising Homo-Crystal Nucleation in the Low-Molar-Mass Enantiomeric Poly(lactic acid) Blend

“…16 The phenomenon has been confirmed in various polymers including isotactic polystyrene, 17 PET, 18,19 poly(arylether-ether-ketone), 20 PLA, 21 polybutene-1 22 and its Form II to I phase transition, 23 and stretched poly(trimethylene terephthalate). 24 Nevertheless, recently, fast-scanning DSC measurements revealed that cold crystallization becomes apparent only in the temperature region above the enthalpy relaxation peak upon heating from the glassy state of polymers. 25,26 The low-temperature crystal nucleation yields very small crystallites, challenging the conventional experimental approaches.…”