Microwave irradiation poly copolymers

The conventional free radical copolymerization of 3-pinene and MMA or St, initiated by AIBN, yielded copolymers with Mw of about 11 600 and 25 400, respectively and MWD of 1.5 and 1.7, respectively [56]. When 2,3,4,5,6-pentafluorostyrene (PFS) was used as comonomer, and benzoyl peroxide as the initiator, a PFS-rich copolymer incorporating isolated isomerized 3-pinene units distributed between poly(PFS) segments was obtained [57]. This feature is related to the low reactivity of the 3-pinene free radicalar towards its monomer, that is to a reactivity ratio close to zero. These PFS-[3-pinene copol5miers were shown to combine the typical high water contact angles of perflourinated polymers (hydrophobicity) with the optical activity of polyOPESf) [57]. A recently published study indicated that the radical random copolymerization of both a- and 3-pinene with styrene under microwave irradiation yields materials with Mn values considerably higher than those obtained under conventional conditions, but still with very low conversions [18]. 

In turn, the homopolymers prepared under microwave conditions were employed as macro-chain-transfer agents (macroCTAs) for subsequent block copolymerization. The polymerization of the second monomer was also achieved via microwave irradiation, which allowed significantly accelerated access to block copolymers with with low PDI and unimodal molecular weight distributions. For instance, when poly(N, N-dimethylacrylamide) (PDMA, Af n = 6300 g mol", ... 

A catalyst free microwave-assisted polymerization was reported for the preparation of poly(e-caprolactone)-block-poly(ethylene glycol)- block-poly(e-caprolac-tone) copolymers (Yu and Liu, 2005). The resulting monomer conversion and the molecular weight of the polymers could be adjusted by changes in the microwave irradiation time, microwave power and length and amount of added poly(ethylene glycol). 

Homopolymers and block copolymers of vinyl esters were also synthesized under microwave irradiation by RAFT/macromolecular design via interchange of xanthates polymerization without any significant inhibition or retardation, which is often observed imder conventional heating conditions. Poly(vinyl acetate) (PVAc) with molecular weights of 1000-10,000 g/mol was prepared in less than 15 min under microwave irradiation at an apparent temperature of 70 °C in the presence of the commercially available chain transfer agent ethylxanthogen acetic acid (Roy and Sumerlin, 2011). 

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