Influence of Systematic Incorporation of Conjugation-Break Spacers into Semi-Random Polymers on Mechanical and Electronic Properties

Abstract

An extensive family of semi-random polymers was prepared via Stille polycondensation with varying contents of alkyl spacers incorporated into the polymer backbone to serve as a break in conjugation. This family was investigated to determine the effect of alkyl spacer length and percent incorporation on the optical, electronic, and mechanical properties. The optical bandgap was found to steadily increase from 1.53 to 1.70 eV as the amount of spacer was increased from 10 mol percent to 40 mol percent while the length of the spacer had little to no effect. In space charge limited current (SCLC) carrier mobility measurements, hole mobility was found to decrease as the amount of spacer increased but was found to steadily increase as the length of the spacer was increased from 6 to 10 carbons. Mechanical properties were observed by film-on-elastomer and film-on-water measurements, with low elastic moduli and high ductility attributed both to the break in conjugation as well as the semi-random structure of the polymer backbone. Measurements of the mechanical properties using the buckling method revealed elastic moduli between 0.14 and 1.3 GPa, and several polymers, when bonded to an elastomeric substrate, could be stretched beyond 80% strain. These polymers were further tested as free-standing films by obtaining a pull test on the surface of water, where we obtained tensile moduli between 0.13 and 0.75 GPa. These results indicate that semi-random polymers with conjugation-break spacers are promising candidates for further study in flexible electronics.

Backbone flexibility on conjugated polymer's crystallization behavior and thin film mechanical stability

“…[16][17][18] Recently, another approach, insertion of conjugation break spacers (CBS) into the backbone, has drawn increasing interests. 19 There are two major routes to incorporate CBS, one is through random copolymerization where the CBS unit is statistically distributed along the backbone; [20][21][22][23][24][25][26][27][28][29] the other, is engineering CBS into each repeating unit and blend the polymer with a fully conjugated counterpart. [30][31][32][33] Martens et al first investigated the hole transport in poly(pphenylene vinylene) derivatives using the former route in 2000.…”

“…29 However, despite the great stretchability, the charge mobility is unsatisfactory with the order of 10 À6 ~10 À4 cm 2 V À1 S À1 . 28,29 Mei and coworkers investigated the influence of CBS using the later route, that is, complementary semiconducting polymer blends (c-SPBs), 30,31 and showed its ability to retain charge transport characteristics and present tunable mechanical moduli when such polymers are blended with a fully conjugated counterpart. The alkyl CBS was inserted into each monomer with DPP conjugation core to produce a fully flexible polymer, acting as the matrix, and then blended with the fully conjugated counterpart, which is pictured as a tie chain molecule interconnecting π-crystalline aggregates for interchain charge transport.…”

Improved Mechanical Durability of High‐Performance OPVs Using Semi‐Interpenetrating Networks

“…[11] One approach to improve the mechanical properties is to engineer the molecular structure of conjugated polymers to improve flexibility. [18][19][20] For example, the incorporation of conjugation-break spacers on the backbone of polymers was shown to enhance mechanical robustness of polymer film. [19,20] Another approach is to fabricate OPVs based on blends of polymeric semiconductors, which are more mechanically robust than active layer blends containing a small molecular organic semiconductor.…”

“…[18][19][20] For example, the incorporation of conjugation-break spacers on the backbone of polymers was shown to enhance mechanical robustness of polymer film. [19,20] Another approach is to fabricate OPVs based on blends of polymeric semiconductors, which are more mechanically robust than active layer blends containing a small molecular organic semiconductor. [21] These strategies and other advances in the design of mechanically flexible organic electronic materials and devices are discussed in recent reviews.…”

Allylamine PECVD Modification of PDMS as Simple Method to Obtain Conductive Flexible Polypyrrole Thin Films

“…Extended π electron delocalization present in CPs backbone allows charge transportation but provides rigidity to polymeric chains. This phenomenon causes CPs to be insoluble in most organic solvents and to have low adaptability to substrates, decreasing mechanical deformability and robustness [18,19]. All of the above dramatically limits the implementation of conducting polymers, especially in flexible applications.…”