The glass transition temperature (
Polymers with low ceiling temperatures (
- NSF-PAR ID:
- 10391285
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 14
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract T g) is a key property that dictates the applicability of conjugated polymers. TheT gdemarks the transition into a brittle glassy state, making its accurate prediction for conjugated polymers crucial for the design of soft, stretchable, or flexible electronics. Here we show that a single adjustable parameter can be used to build a relationship between theT gand the molecular structure of 32 semiflexible (mostly conjugated) polymers that differ drastically in aromatic backbone and alkyl side chain chemistry. An effective mobility value,ζ , is calculated using an assigned atomic mobility value within each repeat unit. The only adjustable parameter in the calculation ofζ is the ratio of mobility between conjugated and non-conjugated atoms. We show thatζ correlates strongly to theT g, and that this simple method predicts theT gwith a root-mean-square error of 13 °C for conjugated polymers with alkyl side chains. -
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Abstract Chemical recycling to monomer (CRM) is a promising route for transitioning to a circular polymer economy. To develop new CRM systems with useful properties, it is important to understand the effects of monomer structure on polymerization/depolymerization behavior. In earlier work, this group demonstrated chemically recyclable polymers prepared by ring‐opening metathesis polymerization of
trans ‐cyclobutane fused cyclooctenes (t CBCO). Here, it is investigated how different substituents on cyclobutane impact the thermodynamics and thermal properties oft CBCO polymers. Introducing additional substituents to acis ‐diester functionalizedt CBCO is found to favor the conversion of polymerization; increased polymerization conversion is also observed when thecis ‐diester is isomerized into itstrans counterpart. The effects of these structural features on the thermal properties are also studied. These findings can provide important insights into designing next‐generation CRM polymers. -
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Abstract Organic semiconducting donor–acceptor polymers are promising candidates for stretchable electronics owing to their mechanical compliance. However, the effect of the electron‐donating thiophene group on the thermomechanical properties of conjugated polymers has not been carefully studied. Here, thin‐film mechanical properties are investigated for diketopyrrolopyrrole (DPP)‐based conjugated polymers with varying numbers of isolated thiophene moieties and sizes of fused thiophene rings in the polymer backbone. Interestingly, it is found that these thiophene units act as an antiplasticizer, where more isolated thiophene rings or bigger fused rings result in an increased glass transition temperature (
T g) of the polymer backbone, and consequently elastic modulus of the respective DPP polymers. Detailed morphological studies suggests that all samples show similar semicrystalline morphology. This antiplasticization effect also exists inpara ‐azaquinodimethane‐based conjugated polymers, indicating that this can be a general trend for various conjugated polymer systems. Using the knowledge gained above, a new DPP‐based polymer with increased alkyl side chain density through attaching alky chains to the thiophene unit is engineered. The new DPP polymer demonstrates a record lowT g, and 50% lower elastic modulus than a reference polymer without side‐chain decorated on the thiophene unit. This work provides a general design rule for making low‐T gconjugated polymers for stretchable electronics. -
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Abstract Efficient doping of polymer semiconductors is required for high conductivity and efficient thermoelectric performance. Lewis acids, e.g., B(C6F5)3, have been widely employed as dopants, but the mechanism is not fully understood. 1:1 “Wheland type” or zwitterionic complexes of B(C6F5)3are created with small conjugated molecules 3,6‐bis(5‐(7‐(5‐methylthiophen‐2‐yl)‐2,3‐dihydrothieno[3,4‐b][1,4]dioxin‐5‐yl)thiophen‐2‐yl)‐2,5‐dioctyl‐2,5‐dihydropyrrolo[3,4‐c]pyrrole‐1,4‐dione [oligo_DPP(EDOT)2] and 3,6‐bis(5''‐methyl‐[2,2':5',2''‐terthiophen]‐5‐yl)‐2,5‐dioctyl‐2,5‐dihydropyrrolo[3,4‐c]pyrrole‐1,4‐dione [oligo_DPP(Th)2]. Using a wide variety of experimental and computational approaches, the doping ability of these Wheland Complexes with B(C6F5)3are characterized for five novel diketopyrrolopyrrole‐ethylenedioxythiophene (DPP‐EDOT)‐based conjugated polymers. The electrical properties are a strong function of the specific conjugated molecule constituting the adduct, rather than acidic protons generated via hydrolysis of B(C6F5)3, serving as the oxidant. It is highly probable that certain repeat units/segments form adduct structures in
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ABSTRACT Thermomechanical properties of polymers highly depend on their glass transition temperature (
T g ). Differential scanning calorimetry (DSC) is commonly used to measureT g of polymers. However, many conjugated polymers (CPs), especially donor–acceptor CPs (D–A CPs), do not show a clear glass transition when measured by conventional DSC using simple heat and cool scan. In this work, we discuss the origin of the difficulty for measuringT g in such type of polymers. The changes in specific heat capacity (Δc p ) atT g were accurately probed for a series of CPs by DSC. The results showed a significant decrease in Δc p from flexible polymer (0.28 J g−1K−1for polystyrene) to rigid CPs (10−3J g−1K−1for a naphthalene diimide‐based D–A CP). When a conjugation breaker unit (flexible unit) is added to the D–A CPs, we observed restoration of the Δc p atT g by a factor of 10, confirming that backbone rigidity reduces the Δc p . Additionally, an increase in the crystalline fraction of the CPs further reduces Δc p . We conclude that the difficulties of determiningT g for CPs using DSC are mainly due to rigid backbone and semicrystalline nature. We also demonstrate that physical aging can be used on DSC to help locate and confirm the glass transition for D‐A CPs with weak transition signals. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys.2019 , 57, 1635–1644
