A Versatile Synthetic Route to Macromonomers via RAFT Polymerization

Abstract

We describe a facile route to prepare functional macromonomers using reversible additionfragmentation chain transfer (RAFT) polymerization. This was demonstrated in the synthesis of R-functionalized norbornenyl, vinyl, and cinnamyl macromonomers using functional chain transfer agents bearing these end groups. Various homopolymer macromonomers of well-controlled molecular weights were synthesized with nearquantitative incorporation of the end group functionality. The use of norbornenyl and vinyl CTA's resulted in a highly quantitative polymerization of styrene and methyl methacrylate (MMA) monomers yielding well-defined linear macromonomers. On the other hand, monomers with a lower reactivity such as methyl acrylate (MA) exhibited a broader polydispersity. The cinnamyl-functionalized telechelics proved the most challenging due to a competitive chain transfer between the cinnamyl group and the RAFT CTA at higher conversions. To demonstrate utilization of the macromonomer functionality, we synthesized the poly(norbornene-g-PMMA) copolymer based on the ring-opening metathesis polymerization (ROMP) of the norbornenyl-functionalized PMMA macromonomer. The main advantage of this new approach should be in the ability to prepare a variety of macromonomer structures utilizing the mild and tolerant conditions of RAFT polymerization.

Low Molecular Weight pDMAEMA-block-pHEMA Block-Copolymers Synthesized via RAFT-Polymerization: Potential Non-Viral Gene Delivery Agents?

“…The N/P ratios of 10, 15 and 20 used for transfection experiments showed complete retardation of pDNA (data not shown). No differences were observed concerning the complexation efficiency of homo pDMAEMA 115 compared to its diblock derivatives with 6 and 57 pHEMA units, and compared to pDMAEMA 105 -block-pHEMA 24 . Copolymer pDMAEMA 151 -block-pHEMA 91 performed similarly as pDMAEMA 115 , but showed more complete retardation at N/P 1.…”

“…The copolymers with the same cationic block length of 115 units released DNA upon addition of the same heparin amount of 0.46 international units (IU). The copolymers pDMAEMA 151 -block-pHEMA 91 , pDMAEMA 105 -block-pHEMA 24 as well as pDMAEMA 115 -derivatives appeared to be more resistant to competition with heparin than PEI 25k at 0.46 IU heparin, whereas pDMAEMA 151 -block-pHEMA 91 had a less pronounced fluorescent band in lane 4 (0.46 IU). The random copolymers and pDMAEMA 97 -block-pHEMA 11 were even more resistant to the presence of heparin releasing DNA only at higher concentrations of 0.93 IU.…”

“…Copolymer pDMAEMA 97 -block-pHEMA 11 performed similarly to pDMAEMA 151 -blockpHEMA 91 . Yet, the random copolymers and pDMAEMA 97 -block-pHEMA 24 were able to retard DNA at N/P 1 already, outreaching PEI 25k in its complexation properties. Based on the obtained gel electrophoresis data, all tested low molecular pDMAEMA-pHEMA constructs showed good pDNA-complexation even at low N/P ratios.…”

“…The marginal differences of DNA-retardation at N/P 1 may be evidence of the impact of the polymer structure on interactions with pDNA. One of these slight differences can be seen in Figure 3(C), where pDMAEMA 97 -block-pHEMA 24 shows a better complexation of DNA than pDMAEMA 97 -block-pHEMA 11 at N/P ratio 1. The efficient complexation ability of the 15.3 kDa polycationic part of diblock copolymer pDMAEMA 97 -pHEMA 24 was unexpected, as a 11.1 kDa homo-pDMAEMA was reported by Jiang et al to be a poor complexer [15].…”

“…The random copolymers and pDMAEMA 97 -block-pHEMA 11 were even more resistant to the presence of heparin releasing DNA only at higher concentrations of 0.93 IU. The highest resistance to competitive polyanions was observed in case of pDMAEMA 97 -block-pHEMA 24 , where 1.87 IU of heparin was needed to release DNA from the complex. Taken together, the most stable complexes were obtained using random copolymers and short chain diblock copolymers with only 97 pDMAEMA units.…”