Phase Transition Behavior of Unimolecular Micelles with Thermoresponsive Poly(<i>N</i>-isopropylacrylamide) Coronas

Luo, Shi-Zhong; Xu, Jian; Zhu, Zhiyuan; Wu, Chi; Liu, Shiyong

doi:10.1021/jp061055b

Cited by 128 publications

(136 citation statements)

References 81 publications

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“…46 Theoretical prediction suggests that strong interchain interactions are present in the brush and cause a broadening of the transition of polymer chains. Our previous works 48,64 and several experimental results [68][69][70][71][72][73][74][75] have already confirmed this prediction. As we know, when PNIPAM chains are attached by one end to a flat substrate or curved interface with sufficient density, referred to as a polymer brush, they are crowned and forced to stretch away from the surface to avoid overlapping.…”

Section: Thermoresponsivity Of Unimolecular Polymeric Micellessupporting

confidence: 58%

“…Figure 10 shows also that, when the temperature is close to LCST of PNIPAM, /R g S//R h S decreases dramatically with increasing temperature because of the chain collapsing of PNIPAM. In our previous work, 48 PNIPAM brush, densely grafted at the surface of the hydrophobic hyperbranched H40 core, exhibits double thermal phase transition behavior. The collapsing of the PNIPAM brush occurs at lower temperatures (below 30 1C) and is ascribed to the fact that it is attached to a hydrophobic core.…”

Section: Thermoresponsivity Of Unimolecular Polymeric Micellesmentioning

confidence: 90%

“…Recently, we have synthesized unimolecular micelles with PNIPAM shell grafting from a hydrophobic fourth-generation hyperbranched polymester H40, and demonstrated their special phase transition behavior. 48 Up to now, water-soluble hyperbranched poly(glycidol) (HPG) has been used widely to prepare amphiphilic molecular nanocapsules because it is highly biocompatible and without evident animal toxicity, which could encapsulate polar guests from water. 34,[49][50][51][52][53][54][55][56][57][58][59][60] Peng et al 50 have obtained star-hyperbranched block copolymers of HPG-b-polystyrene using atom transfer radical polymerization; these have good structural formation for ionic conductivity.…”

Section: Introductionmentioning

confidence: 99%

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Synthesis of thermoresponsive unimolecular polymeric micelles with a hydrophilic hyperbranched poly(glycidol) core

Luo

Zhang

et al. 2010

Polym J

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This paper describes the reversible phase transition behavior of a thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) shell at the surface of a hydrophilic core. Reversible addition-fragmentation transfer (RAFT) polymerization of N-isopropylacrylamide was conducted using a hydrophilic hyperbranched poly(glycidol) (HPG)-based macroRAFT agent. At lower temperatures (o30 1C), the resultant multiarm star block copolymer (HPG-PNIPAM) exists as unimolecular micelles, with hydrophilic HPG as the core and a densely grafted PNIPAM brush as the shell. In laser light scattering (LLS) studies, the concentration used for HPG-PNIPAM is 5Â10 À6 g ml À1 , to avoid any possible aggregation between dendritic unimolecular micelles above the lower critical solution temperature (B32 1C) of PNIPAM. What we observe for the phase transition of HPG-PNIPAM involves only unimolecular process. A combination of dynamic and static LLS studies of HPG-PNIPAM in aqueous solution reveals a reversible phase transition on heating and cooling.

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Section: Thermoresponsivity Of Unimolecular Polymeric Micellessupporting

confidence: 58%

Section: Thermoresponsivity Of Unimolecular Polymeric Micellesmentioning

confidence: 90%

Section: Introductionmentioning

confidence: 99%

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Synthesis of thermoresponsive unimolecular polymeric micelles with a hydrophilic hyperbranched poly(glycidol) core

Luo

Zhang

et al. 2010

Polym J

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“…First, the high local chain density of PNIPAM chains within the micellar corona can lead to lower T c , and the same phenomenon has been observed for PNIPAM brush grafted at the surface gold 67 and silica nanoparticles 68 and at the periphery of hyperbranched polymers. 69 Second, hydrophilic PNIPAM segments are covalently attached to the surface of hydrophobic PCL core, and this will also lead to the decrease in T c . Previously, it has been well-established that when NIPAM was copolymerized with hydrophilic or hydrophobic monomers, its phase transition temperature will concomitantly increase or decrease.…”

Section: Micellization Of (C-pnipam)-b-pcl In Aqueous Solutionmentioning

confidence: 99%

Synthesis of Amphiphilic Tadpole-Shaped Linear-Cyclic Diblock Copolymers via Ring-Opening Polymerization Directly Initiating from Cyclic Precursors and Their Application as Drug Nanocarriers

2011

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We report on the facile synthesis of well-defined amphiphilic and thermoresponsive tadpole-shaped linear-cyclic diblock copolymers via ring-opening polymerization (ROP) directly initiating from cyclic precursors, their self-assembling behavior in aqueous solution, and the application of micellar assemblies as controlled release drug nanocarriers. Starting from a trifunctional core molecule containing alkynyl, hydroxyl, and bromine moieties, alkynyl-(OH)-Br, macrocyclic poly(N-isopropylacrylamide) (c-PNIPAM) bearing a single hydroxyl functionality was prepared by atom transfer radical polymerization (ATRP), the subsequent end group transformation into azide functionality, and finally the intramacromolecular ring closure reaction via click chemistry. The target amphiphilic tadpoleshaped linear-cyclic diblock copolymer, (c-PNIPAM)-b-PCL, was then synthesized via the ROP of ε-caprolactone (CL) by directly initiating from the cyclic precursor. In aqueous solution at 20°C, (c-PNIPAM)-b-PCL self-assembles into spherical micelles consisting of hydrophobic PCL cores and well-solvated coronas of cyclic PNIPAM segments. For comparison, linear diblock copolymer with comparable molecular weight and composition, (l-PNIPAM)-b-PCL, was also synthesized. It was found that the thermoresponsive coronas of micelles self-assembled from (c-PNIPAM)-b-PCL exhibit thermoinduced collapse and aggregation at a lower critical thermal phase transition temperature (T c ) compared with those of (l-PNIPAM)-b-PCL. Temperature-dependent drug release profiles from the two types of micelles of (c-PNIPAM)-b-PCL and (l-PNIPAM)-b-PCL loaded with doxorubicin (Dox) were measured, and the underlying mechanism for the observed difference in releasing properties was proposed. Moreover, MTT assays revealed that micelles of (c-PNIPAM)-b-PCL are almost noncytotoxic up to a concentration of 1.0 g/L, whereas at the same polymer concentration, micelles loaded with Dox lead to ∼60% cell death. Overall, chain topologies of thermoresponsive block copolymers, that is, (c-PNIPAM)-b-PCL versus (l-PNIPAM)-b-PCL, play considerable effects on the self-assembling and thermal phase transition properties and their functions as controlled release drug nanocarriers. ' INTRODUCTIONIn the past decades, enduring attention has been paid to explore the intrinsic correlation between the chain topology of block copolymers and their physical properties, self-assembling behavior in selective solvents or in bulk states, and the associated functional applications. 1-3 It has been well-established that the topological structures and chemical composition of nonlinearshaped block copolymers can exhibit dramatic effects on the solution properties and self-assembling morphologies as compared with their linear counterpart. [4][5][6][7][8][9] It is worthy of noting that the developments of a variety of controlled radical polymerization techniques 10 such as atom transfer radical polymerization (ATRP), 11-13 reversible addition-fragmentation chain transfer (RAFT) polymerization, [14][...

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“…With synthetic polymers, one can study polymers that are very long (N is ca. 10 5 or longer), and this allows one to monitor reversible and irreversible associations that occur at very low concentrations [73][74][75][76][77]. These probes become difficult to use at low concentrations for studying polypeptides of biologically relevant lengths.…”

Section: Unresolved Issues In the Study Of Aggregation-prone Idpsmentioning

confidence: 99%

A polymer physics perspective on driving forces and mechanisms for protein aggregation

Pappu

Wang

Vitalis

et al. 2008

Archives of Biochemistry and Biophysics

156

172

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Protein aggregation is a commonly occurring problem in biology. Cells have evolved stress-response mechanisms to cope with problems posed by protein aggregation. Yet, these quality control mechanisms are overwhelmed by chronic aggregation-related stress and the resultant consequences of aggregation become toxic to cells. As a result, a variety of systemic and neurodegenerative diseases are associated with various aspects of protein aggregation and rational approaches to either inhibit aggregation or manipulate the pathways to aggregation might lead to an alleviation of disease phenotypes. To develop such approaches, one needs a rigorous and quantitative understanding of protein aggregation. Much work has been done in this area. However, several unanswered questions linger, and these pertain primarily to the actual mechanism of aggregation as well as to the types of intermolecular associations and intramolecular fluctuations realized at low protein concentrations. It has been suggested that the concepts underlying protein aggregation are similar to those used to describe the aggregation of synthetic polymers. Following this suggestion, the relevant concepts of polymer aggregation are introduced. The focus is on explaining the driving forces for polymer aggregation and how these driving forces vary with chain length and solution conditions. It is widely accepted that protein aggregation is a nucleation-dependent process. This view is based mainly on the presence of long times for the accumulation of aggregates and the elimination of these lag times with "seeds". In this sense, protein aggregation is viewed as being analogous to the aggregation of colloidal particles. The theories for polymer aggregation reviewed in this work suggest an alternative mechanism for the origin of long lag times in protein aggregation. The proposed mechanism derives from the recognition that polymers have unique dynamics that distinguish them from other aggregation-prone systems such as colloidal particles.

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Phase Transition Behavior of Unimolecular Micelles with Thermoresponsive Poly(N-isopropylacrylamide) Coronas

Cited by 128 publications

References 81 publications

Synthesis of thermoresponsive unimolecular polymeric micelles with a hydrophilic hyperbranched poly(glycidol) core

Synthesis of thermoresponsive unimolecular polymeric micelles with a hydrophilic hyperbranched poly(glycidol) core

Synthesis of Amphiphilic Tadpole-Shaped Linear-Cyclic Diblock Copolymers via Ring-Opening Polymerization Directly Initiating from Cyclic Precursors and Their Application as Drug Nanocarriers

A polymer physics perspective on driving forces and mechanisms for protein aggregation

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