Effect of Cross-Link Density on Photoplasticity of Epoxide Networks Containing Allylic Dithioether Moieties

Abstract

A new diepoxide monomer (ADTDE) containing an allylic dithioether moiety has been synthesized to extend the suite of monomers that form networks exhibiting radical-mediated photoplasticity. These cross-linked polymers show permanent shape change under load and stress relax only when under the stimulus of visible or UV radiation. The Lewis base-catalyzed reaction of the epoxide groups in ADTDE with tri-and tetrafunctional thiols was monitored by differential scanning calorimetry and infrared spectroscopy. These curing systems were found to be more efficient than anionic, cationic, or anhydride polymerizations. The dynamic mechanical thermal analysis of ADTDE with the tetrathiol showed that the network was rubbery at room temperature which is considered ideal for the demonstration of photoplasticity. The photoinduced creep behavior was shown to be controlled by the presence of active free radicals in the matrixon cessation of irradiation, the creep was terminated. The stress relaxation of the stretched network specimens during UV irradiation was studied and was found to be similar to that shown previously for thiol− vinyl ether networks. As expected, the cross-link density of networks prepared from ADTDE with the trithiol was lower than that formed with the tetrathiol and this was found to have a significant influence on the rate and extent of photoplasticity observed the less highly cross-linked ADTDE/trithiol system exhibited more rapid and more extensive photoplasticity since it contained fewer network strands.

Thiol‐epoxy “click” chemistry: Application in preparation and postpolymerization modification of polymers

“…The dual‐chemistry tool box was further expanded by Cook and coworkers. They presented a sophisticated concept of producing photoplastic materials by incorporating allylic dithioether functionalities into a thiol‐epoxy generated network . Continuing with the concept of using thiol‐epoxy chemistry along with other efficient reactions, a recent study has shown that thiol‐ene‐epoxy formulations can be cured with light and the curing process can be carried out in two distinct steps allowing for modulation of the material properties .…”

Self-Sensing Nanocomposites for Structural Applications: Choice Criteria

“…The crosslinking density can be described by Equation (1) [ 38 ] where R is the universal gas constant (8.314 J K −1 mol −1 ); T is equal to T g +50 K, E ′ is the storage modulus at temperature of T g + 50 K. The crosslinking density can be expressed as Mc , which is the molecular weight between entanglements or crosslink sites. The value of the storage modulus in the rubbery plateau region is inversely proportional to the chain length between entanglements, M c , and is given by Equation (2) [ 38 , 39 ]: …”

“…where R is the universal gas constant (8.314 J K −1 mol −1 ); T is equal to T g +50 K, E is the storage modulus at temperature of T g + 50 K. The crosslinking density can be expressed as Mc, which is the molecular weight between entanglements or crosslink sites. The value of the storage modulus in the rubbery plateau region is inversely proportional to the chain length between entanglements, M c , and is given by Equation (2) [38,39]: Table 3 shows the values of E at the temperature T g + 50 • K for the two systems. For the TGMDA sample a value of E approximately three times higher than the sample DGEBA is detected, most likely due to the higher crosslinking sites, determined by the higher functionality number.…”

Synthesis of novel trithiocarbonate and allyl sulfide containing monomers

“…5,6 By incorporating AFT moieties throughout polymer networks, radical generation triggers the bond exchange process. Despite these potential benets, there have been only a few instances where AFT monomers have been endcapped 5,25 with functional groups that enable them to be incorporated into networks via polymerization reactions.…”