Thermo-Induced Formation of Unimolecular and Multimolecular Micelles from Novel Double Hydrophilic Multiblock Copolymers of N,N-Dimethylacrylamide and N-Isopropylacrylamide

Abstract

Two novel double hydrophilic multiblock copolymers of N,N-dimethylacrylamide and N-isopropylacrylamide, m-PDMAp-PNIPAMq, with varying degrees of polymerization (DPs) for PDMA and PNIPAM sequences (p and q) were synthesized via consecutive reversible addition-fragmentation chain transfer (RAFT) polymerizations using polytrithiocarbonate (1) as the chain transfer agent (Scheme 1), where PDMA is poly(N,N-dimethylacrylamide) and PNIPAM is poly(N-isopropylacrylamide). The DPs of PDMA and PNIPAM sequences were determined by 1H NMR, and the block numbers, i.e., number of PDMAp-PNIPAMq sequences (n), were obtained by comparing the molecular weights of multiblock copolymers to that of cleaved products as determined by gel permeation chromatography (GPC). m-PDMA42-PNIPAM37 and m-PDMA105-PNIPAM106 multiblock copolymers possess number-average molecular weights (Mn) of 4.62x10(4) and 9.53x10(4), respectively, and the polydispersities (Mw/Mn) are typically around 1.5. Block numbers of the obtained multiblock copolymers are ca. 4, which are considerably lower than the numbers of trithiocarbonate moieties per chain of 1 (approximately 20) and m-PDMAp precursors (approximately 6-7). PDMA homopolymer is water soluble to 100 degrees C, while PNIPAM has been well known to exhibit a lower critical solution temperature (LCST) at ca. 32 degrees C. In aqueous solution, m-PDMA42-PNIPAM37 and m-PDMA105-PNIPAM106 multiblock copolymers molecularly dissolve at room temperature, and their thermo-induced collapse and aggregation properties were characterized in detail by a combination of optical transmittance, fluorescence probe measurements, laser light scattering (LLS), and micro-differential scanning calorimetry (micro-DSC). It was found that chain lengths of PDMA and PNIPAM sequences exert dramatic effects on their aggregation behavior. m-PDMA105-PNIPAM106 multiblock copolymer behaves as protein-like polymers and exhibits intramolecular collapse upon heating, forming unimolecular flower-like micelles above the thermal phase transition temperature. On the other hand, m-PDMA42-PNIPAM37 multiblock copolymer exhibits collapse and intermolecular aggregation, forming associated multimolecular micelles at elevated temperatures. The intriguing aggregation behavior of this novel type of double hydrophilic multiblock copolymers argues well for their potential applications in many fields such as biomaterials and biomedicines.

Living Radical Polymerization by the RAFT Process - A Second Update

“…It was reported that aminolysis of PNIPAM trithiocarbonate proceeds quantitatively to the thiol when conducted in the presence of a [370] MMA Ph (28) AIBN [173] MMA Ph (28) 393 [173] MMA C 10 H 7 (42) AIBN B [194] 416 Ph (25) ACVA C [164,474] DMAPMAM Ph (25) AIBN [168] NIPAM C 2 H 5 S (185) 394 [368] NIPAM C 2 H 5 S (189) 394 [374] NIPAM C 12 H 25 S (139) AIBN [324] NIPAM S(PDMAM-b-PNIPAM) (398) AIBN [475] DMAM S(PDMAM) (398) AIBN [475] NAM/NAS C 12 H 25 S (115) AIBN [299] St Ph (24) AIBN [133] St C 4 H 9 S (160) AIBN D [473] St Ph (50) 395 [476] St S(PSt) (398) AIBN [475] VAc small amount of a phosphine reducing agent (TCEP). [371,372] Two groups have compared aminolysis with borohydride reduction for PSt dithiobenzoate.…”

“…St [504,505] St-b-tBA [505] 398 [475] S S S Ph n Ph St [475] DMA [475] DMA-b-NIPAM [475] 399 [475] N [376] A See footnote A of Table 3. B See footnote B of Table 3.…”

Polymerizing Nonfluorescent Monomers without Incorporating any Fluorescent Agent Produces Strong Fluorescent Polymers

“…[ 4 , 14-16 ] The RAFT agent employed in our study is poly(trithiocarbonate), and it was synthesized via a polycondensation of O -xylylene dibromide with trithiocarbonic anions ( Figure 1 A) according to earlier studies. [17][18][19] The O -xylylene dibromide is nonfl uorescent (Figure 1 A), as is PTTC (Figure 1 A) and NIPAM monomer. Generally, polymerization of nonfl uorescent monomer mediated by nonfl uorescent RAFT agent produces only a nonfl uorescent polymer.…”

Multiblock Copolymers of Styrene and Butyl Acrylate via Polytrithiocarbonate-Mediated RAFT Polymerization

“…When the RAFT agent possesses g functional groups, ideally polymers with 2g + 1 alternating segments are prepared. In addition, RAFT polymerization with polytrithiocarbonates has already been used to prepare segmented copolymers composed of poly(N,N-dimethylacrylamide) (DMA) and poly(N-isopropylacrylamide) (NIPAM) [31], of polystyrene and poly(4-tert-butylstyrene) [32] and of a random DMA-NIPAM copolymer and poly(4-vinylpyridine) [33]. It has been shown that this strategy can also be carried out preparing the polytrithiocarbonates in situ by employing cyclic trithiocarbonates in the first polymerization [34,35].…”