TY - JOUR
T1 - Probing the Relationship between Molecular Structures, Thermal Transitions, and Morphology in Polymer Semiconductors Using a Woven Glass-Mesh-Based DMTA Technique
AU - Sharma, Anirudh
AU - Pan, Xun
AU - Bjuggren, Jonas M.
AU - Gedefaw, Desta
AU - Xu, Xiaofeng
AU - Kroon, Renee
AU - Wang, Ergang
AU - Campbell, Jonathan A.
AU - Lewis, David A.
AU - Andersson, Mats R.
PY - 2019/9/10
Y1 - 2019/9/10
N2 - The glass transition temperature (Tg) of polymers is an important parameter that determines the kinetics of molecular organization of polymeric chains. Understanding the Tg of conjugated polymers is critical in achieving a thermally stable and optimum morphology in polymer:polymer or polymer:small molecule blends in organic electronics. In this study, we have used the woven glass-mesh-based method of dynamic mechanical thermal analysis (DMTA) to evaluate the Tg of polymer semiconductors, which is generally not easy to detect using conventional techniques such as differential scanning calorimetry (DSC). More importantly, we establish the relationship between the thermal transitions and the molecular structure of polymer semiconductors. For conjugated polymers with rigid conjugated backbones and large alkyl side chains, we report the presence of separate thermal transitions corresponding to the polymer backbone as well as transitions related to side chains, with the latter being the most prominent. By systematically comparing polymer side chains, molecular weight, and backbone structure, the origin of the Tg and a sub-Tg transitions have been successfully correlated to the polymer structures. The antiplastization effect of additives has also been used to further prove the origin of the different transitions. Thermal transitions of a range of high performing polymers applied in organic photovoltaics, including TQ1, PTNT, PTB7, PTB7-Th, and N2200, have been systematically studied in this work. According to the measurements, some of these polymers have a very small amorphous part, changing the way the morphology should be described for these materials. We infer that the main phase in these polymers consists of hairy aggregates, with a few π-stacked rigid polymer chains forming the aggregates.
AB - The glass transition temperature (Tg) of polymers is an important parameter that determines the kinetics of molecular organization of polymeric chains. Understanding the Tg of conjugated polymers is critical in achieving a thermally stable and optimum morphology in polymer:polymer or polymer:small molecule blends in organic electronics. In this study, we have used the woven glass-mesh-based method of dynamic mechanical thermal analysis (DMTA) to evaluate the Tg of polymer semiconductors, which is generally not easy to detect using conventional techniques such as differential scanning calorimetry (DSC). More importantly, we establish the relationship between the thermal transitions and the molecular structure of polymer semiconductors. For conjugated polymers with rigid conjugated backbones and large alkyl side chains, we report the presence of separate thermal transitions corresponding to the polymer backbone as well as transitions related to side chains, with the latter being the most prominent. By systematically comparing polymer side chains, molecular weight, and backbone structure, the origin of the Tg and a sub-Tg transitions have been successfully correlated to the polymer structures. The antiplastization effect of additives has also been used to further prove the origin of the different transitions. Thermal transitions of a range of high performing polymers applied in organic photovoltaics, including TQ1, PTNT, PTB7, PTB7-Th, and N2200, have been systematically studied in this work. According to the measurements, some of these polymers have a very small amorphous part, changing the way the morphology should be described for these materials. We infer that the main phase in these polymers consists of hairy aggregates, with a few π-stacked rigid polymer chains forming the aggregates.
KW - glass transition temperature
KW - polymeric chains
KW - organic electronics
UR - http://www.scopus.com/inward/record.url?scp=85072833774&partnerID=8YFLogxK
UR - http://purl.org/au-research/grants/ARC/DP170102467
U2 - 10.1021/acs.chemmater.9b01213
DO - 10.1021/acs.chemmater.9b01213
M3 - Article
AN - SCOPUS:85072833774
SN - 0897-4756
VL - 31
SP - 6740
EP - 6749
JO - Chemistry of Materials
JF - Chemistry of Materials
IS - 17
ER -