Liquid crystalline main chain polymers with a poly(p‐phenylene‐terephthalate) backbone: 7. Thermal expansion of oriented films of the polyester with dodecyloxy side chains

Abstract

The linear thermal expansion coefficients of oriented films of poly(p‐phenylene‐2,5‐didodecyloxy‐terephthalate) in the three structures B, A, and Lf are reported. The results are interpreted in terms of a molecular laminate model in which the rigid main‐chain layers are separated by the aliphatic side chains. In a film oriented unidirectionally the rigid mainchain layers provide a negative contribution to the thermal expansion coefficient, while the side chains supply a positive contribution. Therefore, the resulting expansion coefficient α depends on the details of the main‐ and side‐chain packing and low‐temperature values between α = +0.3 × 10−5 K−1 (A and Lf and α = −1.2 × 10−5 K−1 (B) are found in highly oriented films. Measurements on undrawn films are in accordance with the molecular laminate model. © 1994 John Wiley & Sons, Inc.

Advanced Thermal Characterization of Fractionated Natural Organic Matter

“…The lower temperature transitions may be associated with either noncooperative, local mobility in the side chain (γ transition), or cooperative side chain mobility associated with β transitions, both of which occur below the main chain or α transitions. Synthetic macromolecules, such as poly(oxymethylene) (Bershtein et al, 2002), poly(phenylene‐terephthalate) (Buijs and Damman, 1994), and PMMA (Ma et al, 1995; DeLapp and LeBoeuf, 2004), exhibit γ, β, or α transitions in which the γ and β transitions occur at much lower temperatures than the glass transition. Multiple transitions measured with DSC at −160, −35, −50, and −120°C have previously been attributed to γ, β, β, and α transitions, respectively (Buijs and Damman, 1994).…”

“…Ongoing work on well‐characterized synthetic macromolecules has been especially useful in revealing the effects of structure and composition on T g , T m , α, and C p (Qu et al, 2001; Zhao et al, 2002). Of note are observations of multiple thermal transitions (Buijs and Damman, 1994; Bershtein et al, 2002) or a broadening of the T g (Alves et al, 2002; Bhat et al, 2002) within some synthetic macromolecules. Bershtein et al (2002) attributed multiple thermal transition behaviors to either (i) the heterogeneous nature of the macromolecule in which “soft” polymeric regions are confined in a rigid geometry, or (ii) covalent anchoring of segments or strong interaction with a rigid structural constituent that increases the T g Increased energy input in the form of heat resulted in a series of sequential segmental motions represented first by mobility of side‐chain functional groups (noncooperative β relaxation), followed by cooperative, main‐chain motions (α relaxation or glass transition) at higher temperatures.…”

Thermal Analysis of Whole Soils and Sediment

“…Finally, it is possible for the existence of β‐ and α‐transitions, where β‐transitions represent the mobilization of side functional groups, and α‐transitions (or glass transitions) represent movement of entire macromolecule backbones. Synthetic macromolecules such as poly(phenylene‐terephthalate) (Buijs and Damman, 1994) and PMMA (Ma et al, 1995; DeLapp et al, 2004), exhibit β‐ and α‐transitions in which the β‐transitions generally occur at much lower temperatures, and possess lower Δ C p , than the α‐transition. While the dual transitions observed in the Elliot loam may be representative of this phenomenon, the pattern of a lower Δ C p associated with the higher temperature transition is counter to what is expected for β‐ and α‐transitions.…”

Effect of the Linking Structure of Nonlinear Optical Side Groups on the Phase Behavior of an Aromatic Polyester Backbone

“…Recent advances in the nanostructure science and technology have directed much attention to the properties of molecules confined sterically within dimensions ranging 1 to 50 nm and opened up numerous possibilities for developing new materials with unique properties heretofore unfeasible. An effective way to generate bulk materials with nanoscale microstructure is based on the use of hairy‐rod polymers 1–8. Rigid rod‐like polymers with flexible side chains represent a special class whose phase behavior differs distinctively from that observed in flexible polymers.…”