An Ultrastable Polymeric Glass: Amorphous Fluoropolymer with Extreme Fictive Temperature Reduction by Vacuum Pyrolysis

Abstract

Vacuum pyrolysis deposition (VPD) has been used to create an ultrastable polymer glass having a fictive temperature T f of as much as 57 K below the nominal glass transition temperature of the thermally rejuvenated polymer. Amorphous fluoropolymer films 300 to 700 nm thick were created by VPD followed by characterization of the thermal response using rapid-scanning chip calorimetry. The deposition was performed for substrates held at temperatures from 30.0 °C (303.2 K) to 116.7 °C (389.9 K) corresponding to approximately 0.75 to 0.97 times the limiting fictive temperature T f ′ ≈ T g of the same material determined by cooling then heating at 600 K/s. Consistent with literature observations for small molecules that are vapor deposited in similar conditions relative to the material T g, large enthalpy overshoots are observed, typical of both highly aged and ultrastable glasses. The 57 K reduction in T f for the VPD polymers is greater than prior reports for physical vapor deposition of small molecules to form ultrastable glasses as well as greater than the T f reductions seen in ambers from 20 million to over 200 million years of age. The potential of using such materials to investigate systems extremely deep into the glassy condition is discussed.

Glass Transition Phenomenon for Conjugated Polymers

“…However, the sample preparation is time consuming since it requires the stacking of several hundred layers of ultrathin film in order to meet the mass requirement . With the new developments of the nanocalorimetry, including flash DSC and AC‐chip calorimetry (We note here that the modulated DSC and the AC‐chip calorimetry are considered as dynamic measurements of T g ), which has the mass requirement of nanogram, measuring the T g of sub‐100 nm a single layer of polymer ultrathin film with DSC becomes possible and has drawn increasing attention …”

Testing the paradigm of an ideal glass transition: Dynamics of an ultrastable polymeric glass

“…The technique allows the synthesis of “extremely aged glasses” in a relatively short laboratory time scale ( 4 , 6 ). The stable glasses reported in prior works have generally been produced using low–molecular weight organic materials ( 4 , 6 , 7 ) that are hard to handle in addition to being made in small quantities, thus limiting the measurements that can be made with them. Recently, we have shown that the vapor deposition technique can be extended to amorphous fluoropolymers, and we were able to produce a stable polymeric glass having extremely high kinetic stability, i.e., a very low fictive temperature relative to the glass transition temperature ( 7 ).…”

“…In that work, an amorphous Teflon was pyrolyzed in vacuum to produce an ultrastable polymeric glass. The postulated mechanism was that the polymeric chains were cleaved upon pyrolysis and they repolymerized onto the substrate during the vacuum pyrolysis deposition (VPD) process ( 7 ). This ultrastable Teflon film showed very low T f values depending on the deposition substrate temperature.…”

Exploiting physical vapor deposition for morphological control in semi‐crystalline polymer films

“…The scission of polymer chains may occur by random degradation or a depolymerization mechanism, producing low‐molecular weight fragments that are undesirable for producing a uniform film structure . Despite these challenges, new literature is emerging in which in situ polymerization is incorporated into thermal evaporation processes to make polymer films or the creation of low‐energy polymer glasses …”

“…[47] Despite these challenges, new literature is emerging in which in situ polymerization is incorporated into thermal evaporation processes to make polymer films [76,77] or the creation of low-energy polymer glasses. [78]…”