Thiolene polymers

Thiolactic acid Thiol chloroformates Thiolene polymers Thiols... 

Within the field of radical polymerization, special attention was recently drawn to the use of microreactors for controlled radical polymerization techniques, namely, ATRP, NMRP and RAFT. Shen and Zhu [126] have devised a column reactor packed with silica-gel-supported copper bromide-hexamethyltriethylenetetramine (HMTETA) for the continuous ATRP of homo- and block copolymers of MMA. Wu et al. [127] report the use of microfluidic chips made from thiolene polymer for continuous ATRP of... 

Several recent studies have demonstrated ATRP reactions within microfluidic devices. An initial study demonstrates the use of a thiolene polymer based reactor with rectangular microchannels (500 x 600 j,m) [86]. The device consists of two inlet channels, an active mixing chamber containing a magnetic stir bar and one outlet channel. Homopolymerization of 2-hydroxypropyl methacrylate (HPMA) by ATRP was demonstrated in this device and it was shown that the kinetics and product properties were similar to those for experiments performed in a batch reactor. This technique provides a fast way of screening various ATRP reaction conditions while using a minimum of raw materials. 

The correlation of residence time to reaction time is critical in the ability to treat the volume of the channel as a continuous gradient in molecular mass. ATRP is particularly well-suited to this type of device because the reaction can be initiated at a fixed mixing element at the head of the channel where a catalyst and initiator can be brought together. By replacing a small molecule initiator with a polymer chain capable of being reinitiated, copolymers could be prepared. This was done in the thiolene/glass devices with a poly(n-butyl methacrylate) block... 

Fig. 21 Representative microfluidic device and resulting data from ATRP on a chip a image of a microfluidic device (dimensions 25 mm x 75 mm) fabricated from UV curable thiolene resin between two glass slides b reaction data for ATRP of HPMA synthesized on a chip showing the correlation of flow rate (or residence time) to reaction time and resulting conversion of monomer (M) to polymer (ln([M]o/[M]) c comparison of number average molecular mass (M ) and poly-dispersity for -butyl acrylate prepared in a traditional round bottom flask ( Flask ) and on a chip ( CRP Chip ). (Reproduced with permission from [102])...

The addition of thiols to olefins (thiolene reaction), to form thioethers, is a well-known reaction. The process can occur by either free-radical or ionic mechanisms. The free-radical reaction can be initiated thermally via a peroxide or by UV irradiation with benzophenone. The initiation step involves the formation of a thiyl radical by hydrogen atom abstraction. Both of these species are capable of starting polymer chains (Table 2.30). 

Hoyle CE, Hensel RD, Grubb MD. Laser-initiated polymerization of a thiolene systems. J Polym Photochem. 1984 4 69-70. 

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