Synthesis and micellization of thermoresponsive galactose‐based diblock copolymers

Thermoresponsive double hydrophilic diblock copolymers poly(2‐(2′‐methoxyethoxy)ethyl methacrylate‐co‐oligo(ethylene glycol) methacrylate)‐b‐poly(6‐O‐methacryloyl‐D ‐galactopyranose) (P(MEO₂MA‐co‐OEGMA)‐b‐PMAGP) with various compositions and molecular weights were obtained by deprotection of amphiphilic diblock copolymers P(MEO₂MA‐co‐OEGMA)‐b‐poly(6‐O‐methacryloyl‐1,2:3,4‐di‐O‐isopropylidene‐D ‐galactopyranose) (P(MEO₂MA‐co‐OEGMA)‐b‐PMAlpGP), which were prepared via reversible addition‐fragmentation chain transfer (RAFT) polymerization using P(MEO₂MA‐co‐OEGMA) as macro‐RAFT agent. Dynamic light scattering and UV–vis studies showed that the micelles self‐assembled from P(MEO₂MA‐co‐OEGMA)‐b‐PMAlpGP were thermoresponsive. A hydrophobic dye Nile Red could be encapsulated by block copolymers P(MEO₂MA‐co‐OEGMA)‐b‐PMAGP upon micellization and released upon dissociation of the formed micelles under different temperatures. The galactose functional groups in the PMAGP block have specific interaction with HepG2 cells, and P(MEO₂MA‐co‐OEGMA)‐b‐PMAGP has potential applications in hepatoma‐targeting drug delivery and biodetection. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and characterization of water‐soluble gold nanoparticles stabilized by comb‐shaped copolymers

The water‐soluble gold nanoparticles stabilized by well‐defined comb‐shaped copolymers have been synthesized successfully. The hybrid nanoparticles consist of gold core and poly[poly(ethylene oxide) methyl ether acrylate]‐block‐poly(N‐isopropylacrylamide) [P(A‐MPEO)‐block‐PNIPAM] shell. The water‐soluble comb‐shaped copolymers, P(A‐MPEO)‐block‐PNIPAM with PNIPAM as a handle, were successfully synthesized via a macromonomer technique using reversible addition fragmentation chain transfer (RAFT) polymerization method. The terminal dithioester group of the comb‐shaped copolymer was reduced to a thiol end group forming SH‐terminated copolymers, P(A‐MPEO)‐block‐PNIPAM‐SH. Successively they were used to stabilize gold nanoparticles by the “grafting‐to” approach. The hybrid nanoparticles were characterized by TEM, UV–vis, and HRTEM. Because of the thermosensitive property of PNIPAM in aqueous solution, the comblike copolymer‐tethered gold nanoparticles show a sharp and reversible phase transition at 30 °C in aqueous solution, which was determined by microdifferential scanning calorimetry. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 341–352, 2008     

Synthesis and characterization of hyperbranched amphiphilic block copolymers prepared via self‐condensing RAFT polymerization

Four families of hyperbranched amphiphilic block copolymers of styrene (Sty, less polar monomer) and 2‐vinylpyridine (2VPy, one of the two more polar monomers) or 4‐vinylpyridine (4VPy, the other polar monomer) were prepared via self‐condensing vinyl reversible addition‐fragmentation chain transfer polymerization (SCVP‐RAFT). Two families contained 4VPy as the more polar monomer, one of which possessing a Sty‐b‐4VPy architecture, and the other possessing the reverse block architecture. The other two families bore 2VPy as the more polar monomer and had either a 2VPy‐b‐Sty or a Sty‐b‐2VPy architecture. Characterization of the hyperbranched block copolymers in terms of their molecular weights and compositions indicated better control when the VPy monomers were polymerized first. Control over the molecular weights of the hyperbranched copolymers was also confirmed with the aminolysis of the dithioester moiety at the branching points to produce linear polymers with number‐average molecular weights slightly greater than the theoretically expected ones, due to recombination of the resulting thiol‐terminated linear polymers. The amphiphilicity of the hyperbranched copolymers led to their self‐assembly in selective solvents, which was probed using atomic force microscopy and dynamic light scattering, which indicated the formation of large spherical micelles of uniform diameter. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1310–1319     

Thermoresponsive hyperbranched polymers via In Situ RAFT copolymerization of peg‐based monomethacrylate and dimethacrylate monomers

Here we report the preparation of PEG‐based thermoresponsive hyperbranched polymers via a facile in situ reversible addition‐fragmentation chain transfer (RAFT) copolymerization using bis(thiobenzoyl) disulphide to form 2‐cyanoprop‐2‐yl dithiobenzoate in situ. This novel one‐pot in situ RAFT approach was studied firstly using methyl methacrylate (MMA) monomer, then was used to prepare thermoresponsive hyperbranched polymers by copolymerization of poly(ethylene glycol) methyl ether methacrylate (PEGMEMA, M_n = 475), poly(propylene glycol) methacrylate (PPGMA, M_n = 375) and up to 30 % of ethylene glycol dimethacrylate (EGDMA) as the branching agent. The resultant PEGMEMA‐PPGMA‐EGDMA copolymers from in situ RAFT were characterized by Gel Permeation Chromatography (GPC) and ¹H‐NMR analysis. The results confirmed the copolymers with multiple methacrylate groups and hyperbranched structure as well as RAFT functional residues. These water‐soluble copolymers with tailored compositions demonstrated tuneable lower critical solution temperature (LCST) from 22 °C to 32 °C. The phase transition temperature can be further altered by post functionalization via aminolysis of RAFT agent residues in polymer chains. Moreover, it was demonstrated by rheological studies and particle size measurements that these copolymers can form either micro‐ or macro photocrosslinked gels at suitable concentrations due to the presence of multiple methacrylate groups. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3751–3761     

New associative EHEC‐g‐PAam copolymers: Their syntheses,characterization, and rheological behavior

The syntheses and rheological behavior of ethyl hydroxyethyl cellulose (EHEC)‐based graft‐copolymers were studied. Copolymers were prepared by grafting EHEC with acrylamide (Aam) via reversible addition fragmentation chain transfer (RAFT) polymerization. Hydroxyl groups of EHEC were esterified with a carboxylic acid functional chain transfer agent (CTA) to prepare EHEC‐macroCTAs with different degrees of substitution. EHEC‐macroCTAs were characterized by ATR‐FTIR, ¹³C NMR, and SEC, and elemental analysis was used to quantify the degree of CTA substitution. EHEC‐macroCTAs with different degrees of substitution were copolymerized with acrylamide by “grafting from” technique. Formation of new cellulose‐based copolymers was comprehensively confirmed by ¹H NMR, ATR‐FTIR, and SEC measurements. Further, the associations of EHEC‐g‐PAam copolymers in water were studied at various concentrations and temperatures by means of UV–vis spectroscopy, fluorescence spectroscopy, and rheological measurements. The results indicate that copolymers have both intra and intermolecular association in water depending on the amount of grafts. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1869–1879, 2009     

NMR investigation of effect of dissolved salts on the thermoresponsive behavior of oligo(ethylene glycol)‐methacrylate‐based polymers

The synthesis of thermo‐ and ionic‐responsive copolymers based on polyethylene glycol methyl ether methacrylate (OEGMA) and 2,2,2‐trifluoroethyl acrylate (TFEA) via reversible addition‐fragmentation chain transfer polymerization is described. Reactivity ratios for the copolymerization of OEGMA and TFEA are r_OEGMA = 2.46 and r_TFEA = 0.22, indicating that OEGMA is incorporated more rapidly than TFEA monomers. The copolymers are thermosensitive and exhibit volume phase transitions (lower critical solution behavior) at temperature, which depend on copolymer composition and the presence of added salts in the aqueous solutions. It was found that the copolymers exhibited LCST transitions at temperatures below 353 K only in salt solutions. ¹H NMR measurements indicated that motion of the protons located in and near the hydrophobic main chain are more sensitive to temperature than protons in the hydrophilic OEGMA side chains. The hydrophilic side chains remain largely hydrated; however, the presence of two distinct conformations of the terminal groups of the side chains was confirmed. The influence of OEGMA side chain length, copolymer composition, and salt type on aggregation behavior and dynamics was examined in detail. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2375–2385     

Synthesis and characterization of double hydrophilic block copolymers containing semi-rigid and flexible segments

3-Methyl-(E)-stilbene (3MSti) and 4-(diethylamino)-(E)-stilbene (DEASti) monomers are synthesized and polymerized separately with maleic anhydride (MAn) in a strictly alternating fashion using reversible addition-fragmentation chain transfer (RAFT) polymerization techniques. The optimal RAFT chain transfer agents (CTAs) for each copolymerization affect the reaction kinetics and CTA compatibilities. Psuedo-first order polymerization kinetics are demonstrated for the synthesis of poly((3-methyl-(E)-stilbene)-alt-maleic anhydride) (3MSti-alt-MAn) with a thiocarbonylthio CTA (methyl 2-(dodecylthiocarbonothioylthio)−2-methylpropionate, TTCMe). In contrast, a dithioester CTA (cumyl dithiobenzoate, CDB) controls the synthesis of poly((4-(diethylamino)-(E)-stilbene)-alt-maleic anhydride) (DEASti-alt-MAn) with pseudo-first order polymerization kinetics. DEASti-alt-MAn is chain extended with 4-acryloylmorpholine (ACMO) to synthesize diblock copolymers and subsequently converted to a double hydrophilic polyampholyte block copolymers (poly((4-(diethylamino)-(E)-stilbene)-alt-maleic acid))-b-acryloylmorpholine) (DEASti-alt-MA)-b-ACMO) via acid hydrolysis. The isoelectric point and dissociation behavior of these maleic acid-containing copolymers are determined using ζ-potential and acid–base titrations, respectively. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 219–227     

Thermoresponsive fluorescent water‐soluble copolymers containing BODIPY dye: Inhibition of H‐aggregation of the BODIPY units in their copolymers by LCST

Novel water‐soluble copolymers containing 4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) dyes were synthesized by reversible addition‐fragmentation chain transfer (RAFT) polymerization. The copolymers with both number‐average molecular weight between 5.0 × 10³ and 5.8 × 10³ and narrow molecular weight distribution (M_w/M_n < 1.19) were obtained by the copolymerization of (2‐dimethylamino)ethyl methacrylate (DMAEMA) and BODIPY‐based methyl methacrylate ( 1 ) with 2,2′‐azobis(isobutyronitrile) (AIBN) as an initiator in the presence of cumyl dithiobenzoate (CDB) as a chain transfer agent (CTA). The structures of the resulting copolymers were characterized by ¹H, ¹³C, and ¹¹B NMR spectroscopies, and the comonomer compositions were good consistent with the feed ratio. Characteristic optical properties of the obtained copolymers were investigated by UV‐vis and PL spectroscopic methods. The copolymers composed of [DMAEMA]: [1] = 98.0:2.0 and 99.4:1.4 led to thermoresponsive polymers having phase separation temperatures at 32 °C and 40 °C, respectively, depending on the compositions of hydrophilic/hydrophobic balances. Further, the effective reversible decrease/increase of the emission intensity of the copolymers led to the reversible formation/inhibition of the H‐aggregation between two BODIPY planes in the copolymers on heating and cooling across the border of LCST. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 627–634, 2010     

Synthesis and characterization of well‐defined optically active methacrylic diblock copolymers

A new, simple, and cost‐effective approach toward the development of well‐defined optically active diblock copolymers based on methacrylate monomers is described for the first time. Starting from the low‐cost optically active (S)‐(?)‐2‐methyl‐1‐butanol, a new optically active methacrylic monomer, namely, (S)‐(+)‐2‐methyl‐1‐butyl methacrylate [(S)‐(+)‐MBuMA], was synthesized. Reversible addition fragmentation chain transfer polymerization was then used for preparing well‐defined poly[(S)‐(+)‐MBuMA] homopolymers and water‐soluble diblock copolymers based on [(S)‐(+)‐MBuMA] and the hydrophilic and ionizable monomer 2‐(dimethyl amino)ethyl methacrylate (DMAEMA). The respective homopolymers and diblock copolymers were characterized in terms of their molecular weights, polydispersity indices, and compositions by size exclusion chromatography and ¹H NMR spectroscopy. Polarimetry measurements were used to determine the specific optical rotations of these systems. The structural and compositional characteristics of micellar nanostructures possessing an optically active core generated by p((S)‐(+)‐MBuMA)‐b‐p(DMAEMA) chains characterized by predetermined molecular characteristics may be easily tuned to match biological constructs. Consequently, the aggregation behavior of the p[(S)‐(+)‐MBuMA]‐b‐p[DMAEMA] diblock copolymers was investigated in aqueous media by means of dynamic light scattering and atomic force microscopy, which revealed the formation of micelles in neutral and acidified aqueous solutions. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis and characterization of block copolymers containing poly(di(ethylene glycol) 2‐ethylhexyl ether acrylate) by reversible addition–fragmentation chain transfer polymerization

Reversible addition–fragmentation chain transfer (RAFT) polymerization has emerged as one of the important living radical polymerization techniques. Herein, we report the polymerization of di(ethylene glycol) 2‐ethylhexyl ether acrylate (DEHEA), a commercially‐available monomer consisting of an amphiphilic side chain, via RAFT by using bis(2‐propionic acid) trithiocarbonate as the chain transfer agent (CTA) and AIBN as the radical initiator, at 70 °C. The kinetics of DEHEA polymerization was also evaluated. Synthesis of well‐defined ABA triblock copolymers consisting of poly(tert‐butyl acrylate) (PtBA) or poly(octadecyl acrylate) (PODA) middle blocks were prepared from a PDEHEA macroCTA. By starting from a PtBA macroCTA, a BAB triblock copolymer with PDEHEA as the middle block was also readily prepared. These amphiphilic block copolymers with PDEHEA segments bearing unique amphiphilic side chains could potentially be used as the precursor components for construction of self‐assembled nanostructures. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5420–5430, 2007     

Flocculation‐resistant multimolecular micelles with thermoresponsive corona from dendritic heteroarm star copolymers

In this article, we report the self‐assembly of flocculation‐resistant multimolecular micelles with thermoresponsive corona from novel dendritic heteroarm star copolymers. The micelles have a core‐shell‐corona structure at room temperature according to pyrene probe fluorescence spectrometry, proton nuclear magnetic resonance (¹H NMR), transmission electron microscopy, and dynamic light scattering measurements. Increasing the temperature above the lower critical solution temperature (LCST), the micelles show high flocculation‐resistant ability resulting from a structure transition from core‐shell‐corona to core‐shell confirmed by a quantitative variable temperature ¹H NMR analysis method using potassium hydrogen phthalate as an external standard. A big volume change of the micelles is observed during the LCST transition. The drug loading and temperature‐dependent release properties of the micelles are also investigated by using coumarin 102 as a model drug, which displays a rapid drug release at a temperature above the LCST. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Double thermoresponsive block–random copolymers with adjustable phase transition temperatures: From block‐like to gradient‐like behavior

Stimuli‐responsive block–random copolymers are very useful “smart” materials as their switching behavior can be tuned by simply adjusting the composition of the random copolymer block. Because of that, we synthesized double thermoresponsive poly(N‐acryloylpyrrolidine)‐block‐poly(N‐acryloylpiperidine‐co‐N‐acryloylpyrrolidine) (PAPy‐b‐P(APi‐co‐APy)) copolymers via reversible addition fragmentation chain transfer (RAFT) polymerization and investigated their temperature‐induced self‐assembly in aqueous solution. By varying the APi/APy ratio in the random copolymer block, its phase transition temperature (PTT₁) can indeed be precisely adjusted while the temperature‐induced collapse upon heating leads to a fully reversible well‐defined micellization. By making the two blocks compositionally similar to more than 60%, the polymers' mechanistic thermoresponsiveness can furthermore be changed from block‐like to rather gradient‐like behavior. This means the micellization onset at PTT₁ and the corona collapse at the PTT of the more hydrophilic pure PAPy block (PTT₂) overlap resulting in one single broad transition. This work thus contributes to the detailed understanding of design, synthesis and mechanistic behavior of tailored “on‐demand” switchable materials. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 399–411     

End group transformations of RAFT‐generated polymers with bismaleimides: Functional telechelics and modular block copolymers

End group activation of polymers prepared by reversible addition‐fragmentation chain transfer (RAFT) polymerization was accomplished by conversion of thiocarbonylthio end groups to thiols and subsequent reaction with excess of a bismaleimide. Poly(N‐isopropylacrylamide) (PNIPAM) was prepared by RAFT, and subsequent aminolysis led to sulfhydryl‐terminated polymers that reacted with an excess of 1,8‐bismaleimidodiethyleneglycol to yield maleimido‐terminated macromolecules. The maleimido end groups allowed near‐quantitative coupling with model low molecular weight thiols or dienes by Michael addition or Diels‐Alder reactions, respectively. Reaction of maleimide‐activated PNIPAM with another thiol‐terminated polymer proved an efficient means of preparing block copolymers by a modular coupling approach. Successful end group functionalization of the well‐defined polymers was confirmed by combination of UV–vis, FTIR, and NMR spectroscopy and gel permeation chromatography. The general strategy proved to be versatile for the preparation of functional telechelics and modular block copolymers from RAFT‐generated (co)polymers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5093–5100, 2008     

One‐pot synthesis of hyperbranched glycopolymers by RAFT polymerization

Soluble hyperbranched glycopolymers were prepared by copolymerization of glycan monomers with reversible addition‐fragmentation chain transfer polymerization (RAFT) inimers in a simple one‐pot reaction. Two novel RAFT inimers, 2‐(methacryloyloxy)ethyl 4‐cyano‐4‐(phenylcarbonothioylthio)pentanoate (MAE‐CPP) and 2‐(3‐(benzylthiocarbonothioylthio)propanoyloxy)ethyl acrylate (BCP‐EA) were synthesized and used to prepare hyperbranched glycopolymers. Two types of galactose‐based saccharide monomers, 6‐O‐methacryloyl‐1,2:3,4‐di‐O‐isopropylidene‐D ‐galactopyranose (proGal‐M) and 6‐O‐(2′‐acrylamido‐2′‐methylpropanoate)‐1,2:3,4‐di‐O‐isopropylidene‐D ‐galactopyranose (proGal‐A), containing a methacrylate and an acrylamide group, respectively, were also synthesized and polymerized under the mediation of the MAE‐CPP and BCP‐EA inimers, respectively. In addition, hyperbranched poly(proGal‐M), linear poly(proGal‐A), and hyperbranched poly(proGal‐A) were generated and their polymerization kinetics were studied and compared. An unexpected difference was observed in the kinetics between the two monomers during polymerization: the relationship between polymerization rate and concentration of inimer was totally opposite in the two monomer–inimer systems. Branching analysis was conducted by using degree of branching (DB) as the measurement parameter. As expected, a higher DB occurred with increased inimer content. Furthermore, these polymers were readily deprotected by hydrolysis in trifluoroacetic acid solution resulting in water‐soluble polymers. The resulting branched glycopolymers have potential as biomimetics of polysaccharides. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Tuning the sugar‐response of boronic acid block copolymers

A detailed study of the pH‐ and sugar‐responsive behavior of poly(3‐acrylamidophenylboronic acid pinacol ester)‐b‐poly(N,N‐dimethylacrylamide) (PAPBAE‐b‐PDMA) block copolymers is presented. Reversible addition‐fragmentation chain transfer (RAFT) polymerization of the pinacol ester of 3‐acrylamidophenylboronic acid resulted in homopolymers with molecular weights between 12,000 and 37,000 g/mol. The resulting homopolymers were employed as macro‐chain transfer agents during the polymerization of N,N‐dimethylacrylamide (DMA). Successful chain extension and removal of the pinacol protecting groups to yield poly(3‐acrylamidophenylboronic acid)‐b‐PDMA (PAPBA‐b‐PDMA) with free boronic acid moieties resulted in pH‐ and sugar‐responsive block copolymers that were subsequently investigated for their behavior in aqueous solution. The PAPBA‐b‐PDMA block copolymers were capable of solution self‐assembly due to the PAPBA block being water‐insoluble below its pK_a. The resulting aggregates were demonstrated to solubilize and release model hydrophobic compounds, as demonstrated by fluorescence studies. Dissociation of the aggregates was induced by raising the pH above the pK_a of the boronic acid residues or by adding sugars capable of forming boronate esters. Aggregate size, dissociation kinetics, and the effect of various sugars were considered. The critical sugar concentration needed to induce aggregate dissociation was tuned by incorporation of hydrophilic DMA units within the PAPBA responsive segment to yield PDMA‐b‐poly(3‐acrylamidophenylboronic acid‐co‐DMA) block copolymers. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis of enantiopure homo and copolymers by raft polymerization and investigation of their enantioselective lipase‐catalyzed esterification

Homo and copolymers were synthesized from enantionpure (R)‐ and (S)‐1‐(4‐vinylphenyl)ethanol by reversible addition‐fragmentation chain transfer polymerization. The polymerization conditions were optimized resulting in dioxane as the preferred reaction solvent. First‐order polymerization kinetics and well‐defined enantiopure homopolymers with low dispersities were obtained. In agreement with their enantiomeric composition, the (R) and (S)‐polymers gave opposite optical rotation of light. Polymer analogous esterification of the chiral hydroxy groups catalyzed by enantioselective Candida antarctica Lipase B was strongly (R)‐selective. Esterification on the homopolymer and copolymers could be achieved to a maximum of around 50 %. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Hybrid amphiphilic block copolymers containing polyhedral oligomeric silsesquioxane: Synthesis,characterization, and self‐assembly in solutions

In this article, the amphiphilic block copolymers containing polyhedral oligomeric silsesquioxane (POSS), namely PMAPOSS‐b‐PAA and PMAPOSS‐b‐P(AA‐co‐St), were synthesized consecutively by reversible addition–fragmentation chain transfer and selective hydrolysis, and characterized by ¹H NMR, ¹³C NMR, Fourier transform infrared spectroscopy and gel permeation chromatography. In the presence of the nearly gradient styrene distribution along the hydrophilic block with a feed molar ratio of tert‐butyl acrylate (tBA) to St being 10/1, patterned core‐corona nanoparticles (NPs) were formed from the mixture of good/selective solvents (THF/water) by a simple evaporation process at room temperature. With the extending of the co‐block length, the self‐assembled NPs exhibited phase separation behavior of spheres‐dispersed, onion‐like and onion‐cluster hierarchical structures in turn. However, while a change in the feed molar ratio occurred, it resulted in the formation of typical core‐shell micelles (20/1, tBA/St) and disordered particles (5/1, tBA/St), respectively. Furthermore, the self‐assembly behavior of PMAPOSS‐b‐P(AA‐co‐St) in DMF was investigated, which showed that it could perform a mixture morphology of well‐dispersive sphere micelles and large aggregate of micelles. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis and self‐assembly of stimuli‐responsive amphiphilic block copolymers based on polyhedral oligomeric silsesquioxane

A novel POSS‐containing methacrylate monomer (HEMAPOSS) was fabricated by extending the side chain between polyhedral oligomeric silsesquioxane (POSS) unit and methacrylate group, which can efficiently decrease the steric hindrance in free‐radical polymerization of POSS‐methacrylate monomer. POSS‐containing homopolymers (PHEMAPOSS) with a higher degree of polymerization (DP) can be prepared using HEMAPOSS monomer via reversible addition–fragmentation chain transfer (RAFT) polymerization. PHEMAPOSS was further used as the macro‐RAFT agent to construct a series of amphiphilic POSS‐containing poly(N, N‐dimethylaminoethyl methacrylate) diblock copolymers, PHEMAPOSS‐b‐PDMAEMA. PHEMAPOSS‐b‐PDMAEMA block copolymers can self‐assemble into a plethora of morphologies ranging from irregular assembled aggregates to core‐shell spheres and further from complex spheres (pearl‐necklace‐liked structure) to large compound vesicles. The thermo‐ and pH‐responsive behaviors of the micelles were also investigated by dynamic laser scattering, UV spectroscopy, SEM, and TEM. The results reveal the reversible transition of the assembled morphologies from spherical micelles to complex micelles was realized through acid‐base control. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2669‐2683     

Unusual effect of molecular weight and concentration on thermoresponsive behaviors of well‐defined water‐soluble semirigid polymers

A series of water‐soluble semirigid thermoresponsive polymers with well‐defined molecular weights based on mesogen‐jacketed liquid crystal polymers (MJLCPs), poly[bis(N‐hydroxyisopropyl pyrrolidone) 2‐vinylterephthalate] (PHIPPVTA) have been synthesized via reversible addition fragmentation chain transfer (RAFT) polymerization. Dynamic light scattering (DLS) revealed that the novel monomer and polymers have thermoresponsive properties with cloud point in the range between 10 and 90 °C. The cloud point was increased by 56.2 °C when the polymer molecular weight increased from 0.47 × 10⁴ g mol^?1 to 3.69 × 10⁴ g mol^?1. In addition, the cloud point of PHIPPVTA was decreased by 18.8 °C with the increase of polymer concentration from 5 to 10 mg mL^?1. A slight increase (0.1–3.5 °C) of cloud point has been observed after knocking off the end‐groups of PHIPPVTA. Moreover, the cloud point of polymer increased with increasing of its molecular weight with or without the trithiocarbonate end‐groups, which showed the opposite trend comparing with other thermoresponsive polymers with flexible backbones. These polymers show a dramatic solvent isotopic effect that the cloud point in D₂O was lower than in H₂O. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Novel thermoresponsive fluorinated double‐hydrophilic poly{[N‐(2,2‐difluoroethyl)acrylamide]‐b‐[N‐(2‐fluoroethyl)acrylamide]} block copolymers

Novel thermoresponsive double‐hydrophilic fluorinated block copolymers were successfully synthesized by reversible addition‐fragmentation chain transfer (RAFT) polymerization. Poly[N‐(2,2‐difluoroethyl)acrylamide] (P2F) was synthesized via RAFT polymerization of N‐(2,2‐difluoroethyl)acrylamide (M2F) using 2‐dodecylsulfanylthiocarbonylsulfanyl‐2‐methylpropionic acid (DMP) as the chain transfer agent (CTA) and 2,2′‐azobisisobutyronitrile (AIBN) as the initiator. The resulting P2F macroCTA was further chain extended with N‐(2‐fluoroethyl)acrylamide (M1F) to yield poly{[N‐(2,2‐difluoroethyl)acrylamide]‐b‐[N‐(2‐fluoroethyl)acrylamide]} (P2F‐b‐P1F) block copolymers with different lengths of the P1F block. Molecular weight and molecular weight distribution were determined by gel permeation chromatography. The average molecular weight (M_n) of the resulting polymers ranged from 2.9 × 10⁴ to 5.8 × 10⁴ depending on the length of the P1F block. The molecular weight distribution was low (M_w/M_n = 1.11–1.19). Turbidimetry by UV‐Visble (UV‐Vis) spectroscopy, dynamic light scattering, and in situ temperature‐dependent ¹H NMR measurements demonstrated that the P2F block underwent a thermal transition from hydrophilic to hydrophobic, which in turn induced self‐assembly from unimers to aggregates. Transmission electron microscopy studies demonstrated that polymeric aggregates formed from an aqueous solution of P2F‐b‐P1F at 60 °C were disrupted by cooling down to 20 °C and regenerated by heating to 60 °C. Temperature‐triggered release of a model hydrophobic drug, coumarin 102, was also demonstrated. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013