Thermally amendable and thermally stable thin film of POSS tethered Poly(methyl methacrylate) (PMMA) synthesized by ATRP

Abstract

In this article we report the stability, dewetting suppression and scratch mending of thin film of POSS tethered PMMA hybrid material having thickness in the range of 100–300nm. The POSS–PMMA hybrid material was synthesized via thermal thiol-ene modification of allyl-POSS followed by O-acylation reaction and atom transfer radical polymerization (ATRP). The polymerization reaction was carried out using CuBr as catalyst in combination with N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA) as ligand, and POSS–Br as initiator. NMR, FT-IR, WAXD and FE-SEM analyses were used to study the structure and morphology of the hybrid materials. FE-SEM analysis showed interesting honeycomb architecture in the hybrid material. Subsequently we investigated the thermal stability and scratch mending (SM) of spin cast thin films of the synthesized POSS–PMMA hybrid material. The as cast film had a holey, Swiss cheese morphology when dispersed from a rapidly evaporating solvent THF. The film, upon thermal annealing flattened out in favor of a smooth, featureless film that did not dewet with time even upon prolonged annealing. Further, scratches made on the film surface using a scalpel were seen to mend completely upon prolonged thermal annealing at temperatures above Tg of the polymer. The film could mend repeated scratches at the same location with complete recovery of mechanical strength, which was verified by nano-indentation measurement. The mending is entirely due to wetting of the polymer film in presence of low surface energy POSS. The scratch mending was slow, but was observed during repeated mending cycles. The films also exhibited improved hydrophobicity which remains un-altered even upon repeated mending cycles indicating presence of POSS moieties in the film surface. Importantly, when scratches made on the pristine PMMA film surface using a scalpel, the film was found to be ruptured during annealing due to strong influence of the dispersion forces across the low thickness zone and consequently, the film dewetted and the scratch width gradually increased with time.