Thermoresponsive Poly(2‐oxazoline) Molecular Brushes by Living Ionic Polymerization: Kinetic Investigations of Pendant Chain Grafting and Cloud Point Modulation by Backbone and Side Chain Length Variation

Molecular brushes of poly(2‐oxazoline)s were prepared by living anionic polymerization of 2‐iso‐propenyl‐2‐oxazoline to form the backbone and subsequent living cationic ring‐opening polymerization of 2‐n‐ or 2‐iso‐propyl‐2‐oxazoline for pendant chain grafting. In situ kinetic studies indicate that the initiation efficiency and polymerization rates are independent from the number of initiator functions per initiator molecule. This was attributed to the high efficiency of oxazolinium salt and the stretched conformation of the backbone, which is caused by the electrostatic repulsion of the oxazolinium moieties along the macroinitiator. The resulting molecular brushes showed thermoresponsive properties, that is, having a defined cloud point (CP). The dependence of the CP as a function of backbone and side chain length as well as concentration was studied.     

Block copolymers derived from photoreactive 2‐oxazolines, 1. Synthesis and micellization behavior

Amphiphilic block copolymers (BCPs) were synthesized consisting of hydrophilic poly(2‐methyl‐2‐oxazoline) blocks and hydrophobic poly(2‐alkyl‐2‐oxazoline) blocks with undecyl‐, phenyl‐, and the photopolymerizable cinnamoyl‐, 4‐azidophenyl‐, and diin‐ moieties. The BCPs were prepared by living cationic ring opening polymerization of the corresponding monomers. The resulting amphiphilic block copolymers show good solubility in water depending on the ratio of hydrophilic to hydrophobic moieties inside the block copolymer as well as the formation of block copolymeric micelles as proven by dynamic light scattering experiments and electron microscopy. The size of the aggregates shows a clear dependence on the polymers molecular weight and the ratio of the hydrophilic to hydrophobic building blocks.     

Micellar Structures of Hydrophilic/Lipophilic and Hydrophilic/Fluorophilic Poly(2‐oxazoline) Diblock Copolymers in Water

Amphiphilic poly(2‐alkyl‐2‐oxazoline) diblock copolymers of 2‐methyl‐2‐oxazoline (MOx) building the hydrophilic block and either 2‐nonyl‐2‐oxazoline (NOx) for the hydrophobic or 2‐(1H,1H′,2H,2H′‐perfluorohexyl)‐2‐oxazoline (FOx) for the fluorophilic block were synthesized by sequential living cationic polymerization. The polymer amphiphiles form core/shell micelles in aqueous solution as evidenced using small‐angle neutron scattering (SANS). Whereas the diblock copolymer micelles with a hydrophobic NOx_n block are spherical, the micelles with the fluorophilic FOx_n are slightly elongated, as observed by SANS and TEM. In water, the micelles with fluorophilic and lipophilic cores do not mix, but coexist.

     

Novel Amphiphilic Styrene‐Based Block Copolymers for Induced Surface Reconstruction

This paper describes the synthesis of amphiphilic block copolymers by living radical polymerization (NMP) of new styrene‐like monomers. The polar monomers (ethylene oxide side chains and free hydroxyl‐ or amino‐groups after deprotection) were polymerized in a “protected form” to adjust the solubility of the monomers. In this way high molar mass polymers with a narrow polydispersity (around or below 1.2) were accessible. In the bulk state hydrophobic and hydrophilic domains demix. By exposing thin films of these polymers to vacuum (air) or alternatively to water or a hydrophilic surface it becomes possible to switch the surface polarity reversibly between contact angles of about 105° and 83° as a result of surface reconstruction. Through side chains of different length and with different functionalities, it was possible to adjust the glass transition temperatures to values between ?2 °C to 140 °C for the hydrophilic blocks and ?30 °C to 100 °C for the hydrophobic block. The wide range of the glass temperatures allowed it to find a block copolymer system with a slow kinetic concerning the surface reconstruction process, so that a mechanistic examination of the process by AFM was possible. It got, thereby, possible to detect the break‐up of the hydrophobic surface lamella and the upfold of the hydrophilic lamella in contact with water.

     

Synthesis of a Poly(vinyl alcohol)‐Based Graft Copolymer Having Poly(ε‐caprolactone) Side Chains by Solution Polymerization

Poly(vinyl alcohol)‐graft‐poly(ε‐caprolactone) (PVA‐g‐PCL) was synthesized by ring‐opening polymerization of ε‐caprolactone with poly(vinyl alcohol) in the presence of tin(II) 2‐ethylhexanoate as a catalyst in dimethyl sulfoxide. The relationship between the reaction conditions of the solution polymerization and the chemical structure of the graft copolymer was investigated. The degree of substitution (DS) and degree of polymerization (DP) of the PCL side chains were roughly controlled by varying the reaction periods and feed molar ratios of the monomer and the catalyst to the backbone. PVA‐g‐PCL with a PCL content of 97 wt.‐% (DP = 22.8, DS = 0.54) was obtained in 56 wt.‐% yield. The graft copolymer was soluble in a number of organic solvents, including toluene, tetrahydrofuran, chloroform, and acetonitrile, which are solvents of PCL. The molecular motion of the graft copolymer from ¹H NMR measurements appears to be restricted to some extent at 27–50°C, however the ¹H NMR signal intensities measured at temperatures higher than ca. 50°C reflect the actual chemical structure of the graft copolymer as determined by elemental analysis. The graft copolymer having a short PCL side chain (DP = 4.4, DS = 0.15) was amorphous. The melting temperature of a sample with relatively high PCL content (DP = 22.8, DS = 0.54) was observed at 39°C. Thermogravimetric analysis revealed that the thermal stability of PVA was improved by introducing PCL side chains. The surface free energies of the air‐side of a graft copolymer film, as calculated by Owens' equation using contact angles, were comparable to that of PCL homopolymer.     

Well-defined graft copolymers containing a poly(methacrylate) backbone and functional or block poly(vinyl ether) side chains

The anionic random copolymerization of methyl methacrylate (MMA) and 2-(1-acetoxyethoxy)ethyl methacrylate (AEEMA) was carried out using 1,1-diphenylhexyllithium (DPHL) as initiator, in the presence of LiCl ([LiCl]/[DPHL]₀ = 2), in tetrahydrofuran (THF), at –60°C. The resulting polymer, poly-(MMA-co-AEEMA), has a controlled molecular weight and a narrow molecular weight distribution (M_w/M_n = 1.05 ˜ 1.09). Without quenching, toluene, EtAlCl₂ and a functional monomer [2-acetoxyethyl vinyl ether (AcVE), 2-chloroethyl vinyl ether (ClVE) or 2-vinyloxyethyl methacrylate (VEMA)] were introduced into the above THF solution of the copolymer at 20°C. Every side chain of AEEMA unit of poly(MMA-co-AEEMA) was activated by EtAlCl₂ to induce the cationic polymerization of the functional monomer. THF, which was used as solvent in the preparation of the copolymer of MMA and AEEMA, acted as a Lewis base in the latter cationic polymerization, thus stabilizing the propagating site. By using this procedure, a controlled cationic polymerization of a functional monomer was achieved and a well-defined graft copolymer with functional side chains was obtained. Instead of a single functional monomer, the simultaneous addition of isobutyl vinyl ether (IBVE) and AcVE, ClVE or VEMA during the second step cationic polymerization process generated a graft copolymer with random copolymer side chains. Furthermore, a graft copolymer with block side chains could also be prepared by performing a block copolymerization during the second cationic grafting step by adding sequentially AcVE (ClVE or VEMA) and IBVE or vice versa. Every graft copolymer thus obtained possessed a high purity, controlled graft number and molecular weight as well as a narrow molecular weight distribution (M_w/M_n = 1.12 ˜ 1.25).     

ABA and BAB Triblock Copolymers Based on 2‐Methyl‐2‐oxazoline and 2‐n‐Propyl‐2‐oxazoline: Synthesis and Thermoresponsive Behavior in Water

Inspired by the well‐known amphiphilic block copolymer platform known as Pluronics or poloxamers, a small library of ABA and BAB triblock copolymers comprising hydrophilic 2‐methyl‐2‐oxazoline (A) and thermoresponsive 2‐n‐propyl‐2‐oxazoline (B) is synthesized. These novel copolymers exhibit temperature‐induced self‐assembly in aqueous solution. The formation and size of aggregates depend on the polymer structure, temperature, and concentration. The BAB copolymers tend to agglomerate in water, with the cloud point temperature depending on the length of poly(2‐n‐propyl‐2‐oxazoline) chain. On the other hand, ABA copolymers form smaller aggregates with hydrodynamic radius from 25 to 150 nm. The dependence of viscosity and viscoelastic properties on the temperature is also studied. While several Pluronic block copolymers are known to form thermoreversible hydrogels in the concentration range 20–30 wt%, thermogelation is not observed for any of the investigated poly(2‐oxazoline)s at the investigated temperature range from 10 to 50 °C.

     

Direct Insertion Mass Spectrometric Analysis of Thermal Degradation of Poly(2‐alkyl‐2‐oxazoline)

Direct pyrolysis mass spectrometry is applied to investigate the thermal behavior of poly(2‐isopropyl‐2‐oxazoline) (PIPOX, a thermoresponsive polymer) and poly[2‐(3‐butenyl)‐2‐oxazoline] (PBOX, a “clickable” polymer). It is found that the thermal degradation of PIPOX is started by a loss of side chains. At slightly higher temperatures the degradation of the polymer backbone occurs by random chain scission processes. In the case of PBOX, vinyl polymerization of the side chains produces chains with variable thermal stabilities. The number of repeating units of the polymer has almost no effect on the thermal behavior of PIPOX, but significantly affects both thermal stability and degradation product distribution of PBOX.     

Block Copolymers of Methyl Vinyl Ether and Isobutyl Vinyl Ether With Thermo‐Adjustable Amphiphilic Properties

The thermo‐adjustable hydrophilic/hydrophobic properties of AB, ABA and BAB block copolymers in which A is poly(methyl vinyl ether) (PMVE) and B is poly(isobutyl vinyl ether) (PIBVE) have been investigated. The block copolymers were prepared by “living” cationic polymerization using sequential addition of monomers. The polymerizations were carried out with the system acetal/trimethylsilyl iodide as initiator and ZnI₂ as activator. The initiating system based on diethoxyethane leads to AB block copolymers whereas the initiating system based on tetramethoxypropane leads to ABA or BAB triblock copolymers. Well‐defined block copolymers of different composition with controlled molecular weights up to approx. 10 000 have been prepared. When IBVE is added to living PMVE, PIBVE‐blocks form only in the presence of an additional amount of ZnI₂, which is attributed to the fact that part of the ZnI₂ is inactive because of complex formation with PMVE. At room temperature, the combination of hydrophilic (PMVE) and hydrophobic (PIBVE) segments provides the copolymers with surfactant properties. Above the lower critical solution temperature (LCST) of PMVE, situated around 36 °C, the PMVE‐blocks become hydrophobic and the amphiphilic nature of the block copolymers is lost. The corresponding changes in hydrophilic/hydrophobic balance have been evaluated by investigation of the emulsifying properties of the block copolymers for water/decane mixtures as a function of the temperature. Below the LCST, the block copolymers have emulsifying properties similar to or better than those of the commercial PEO‐PPO block copolymers (Pluronic®). Either oil‐in‐water or water‐in‐oil emulsions can be obtained, depending on the polymer architecture and the water/decane volume ratio. The emulsifying properties are strongly reduced or completely lost above 40 °C. Emulsions obtained with a PMVE₃₆‐b‐PIBVE₅₄ block copolymer for a water/decane (v/v) ratio of 85/15 remained stable for more than six months.

50/50 and a 85/15 water/decane w/o emulsion (15 g/l) with the PMVE₃₆‐b‐PIBVE₅₄ block copolymer at 20 °C.     

Grafting of Poly(2‐Oxazoline) Side Chains from Polyester Containing Oxazoline Units and Their Blends with Water Soluble Vinyl Polymers

Ternary polycondensation of thiomalic acid (TMA), adipic acid (ADA), and 1,5‐pentanediol (PD) at 80 °C proceeds to give polyester having pendent mercapto groups. After the mercapto groups are consumed quantitatively by a Michael addition with 2‐isopropenyl‐2‐oxazoline (IPOx) to create an initiation point for grafting, successive additions of methyl triflate (MeOTf) and 2‐oxazoline allow ring‐opening polymerization of 2‐oxazoline from the IPOx unit to give a graft copolymer with a M_n of 2.2 × 10⁴ ‐ 3.7 × 10⁴ and an molecular dispersity index (M_w/M_n = 1.9–2.6). The synthesized polyester‐based graft copolymer is water‐soluble and forms transparent blend films with poly(vinyl alcohol) (PVA) and poly(N‐isopropy acrylamide) (PNIPAM) using solvent cast methods. Differential scanning calorimetry measurements show that blends with PVA (<30% of the graft copolymer) show a single T_gs over the whole composition range. All scans for the blends with PNIPAM have a single T_gs that is between those of the parent polymers indicating that the graft copolymer shows excellent miscibility with PNIPAM, although the parent polyester, poly(TMA‐alt‐PD)‐co‐poly (ADA‐alt‐PD) does not exhibit such miscibility.     

Amphiphilic Polyoxazoline‐block‐Polypeptoid Copolymers by Sequential One‐Pot Ring‐Opening Polymerizations

Amphiphilic block copolymers possess great potential as biomaterials in drug delivery and gene therapy. Herein, pseudopeptidic‐type diblock copolymer of poly(2‐oxazoline)‐block‐polypeptoid (POx‐b‐POI) is presented and synthesized. Poly[2‐(3‐butenyl)‐2‐oxazoline]‐block‐poly(sarcosine) (PBuOx‐b‐PSar) comprising hydrophobic POx segment bearing alkenyl side chain and hydrophilic POI segment of N‐methyl glycine, viz., sarcosine, is prepared by ring‐opening polymerization (ROP) through a one‐pot and three‐step route. Diphenyl phosphate initiates ROP of BuOx, and then the living chain end of PBuOx is quenched by ammonia to obtain PBuOx‐ammonium phosphate in situ, the active ammonium group initiates ROP of sarcosine N‐carboxy anhydride. PBuOx‐b‐PSar with controlled molecular weights (4.7–10.8 kg mol⁻¹) and narrow dispersities (Ð _M 1.15–1.21) are characterized by ¹H NMR, ¹³C NMR, and size‐exclusion chromatography. Dynamic light scattering and transmission electron microscopy analysis reveal that PBuOx‐b‐PSar self‐assembles into nanostructures of average diameter D _H of 37–109 nm in aqueous solution. 3‐(4,5‐Dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide test demonstrates the cytocompatibility (relative cell viability > 80%) of the PBuOx‐b‐PSar. In view of the self‐assembly and biocompatibility, the readily prepared diblock copolymers may hopefully be used in biomedical applications.

     

Microstructure Induced Rigidity of Polysiloxane Yielding Hierarchical Self‐Assembly of Alkyl Side Chains

The influence of a backbone microstructure on the side chain crystallization of a comb‐like polymer is analyzed systematically using a tailor‐made random versus block siloxane copolymer system. While the side alkyl chains of the random siloxane undergo a stepwise order–disorder (OD) transition to form well‐ordered orthorhombic structure at low temperature, the packing structure of the alkyl chains pertaining to the block siloxane maintains their original hexagonal lattice up to a temperature of as low as 173 K. The unit lattice ordering of side alkyl chains in the random siloxane polymer is also accompanied by a major restructuring of the backbone conformation ultimately losing out long range ordered structure in the solid state. The OD transitions of side alkyl chains and their dynamic relationship with the backbone conformation are established unambiguously by a combination of temperature dependent small‐angle X‐ray and wide‐angle X‐ray scattering techniques. The observed conformational variations in random versus block polymers are explicitly discussed in terms of molecular chain mobility and theory of macromolecular chain conformation.     

Bioinspired All‐Polyester Diblock Copolymers Made from Poly(pentadecalactone) and Poly(2‐(2‐hydroxyethoxy)benzoate): Synthesis and Polymer Film Properties

The bioinspired diblock copolymers poly(pentadecalactone)‐block‐poly(2‐(2‐hydroxyethoxy)benzoate) (PPDL‐block‐P2HEB) are synthesized from pentadecalactone and dihydro‐5H‐1,4‐benzodioxepin‐5‐one (2,3‐DHB). No transesterification between the blocks is observed. In a sequential approach, PPDL obtained by ring‐opening polymerization (ROP) is used to initiate 2,3‐DHB. Here, the molar mass M_n of the P2HEB block is limited. In a modular approach, end‐functionalized PPDL and P2HEB are obtained separately by ROP with functional initiators, and connected by 1,3‐dipolar Huisgen reaction (“click‐chemistry”). Block copolymer compositions from 85:15 mass percent to 28:72 mass percent (PPDL:P2HEB) are synthesized, with M_n of from about 30 000–50 000 g mol^?1. The structure of the block copolymer is confirmed by proton NMR, Fourier‐transform infrared spectroscopy, and gel permeation chromatography. Morphological studies by atomic force microscopy (AFM) further confirms the block copolymer structure, while quantitative nanomechanical AFM measurements reveal that the Derjaguin–Muller–Toporov moduli of the block copolymers range between 17.2 ± 1.8 and 62.3 ± 5.7 MPa, i.e., between the values of the parent P2HEB and PPDL homopolymers (7.6 ± 1.4 and 801 ± 42 MPa, respectively). Differential scanning calorimetry shows that the thermal properties of the homopolymers are retained by each of the copolymer blocks (melting temperature 90 °C, glass transition temperature 36 °C).     

Direct Pyrolysis ‐ Mass Spectrometry Analysis of Thermal Degradation of Thio‐Click‐Modified Poly(2‐oxazoline)

Poly(2‐(3‐butenyl)‐2‐oxazoline)s (PBOX) with glucose‐S‐butyl (Glc) and perfluoroalkyl‐S‐butyl (F) side chains (three samples: Glc/F = 100/0, 0/100, and 88/12) are synthesized by ring‐opening polymerization of 2‐butenyl‐2‐oxazoline and thiol‐ene click photochemistry, and their thermal properties are analyzed by direct‐pyrolysis mass spectrometry. Significant changes in the thermal stability and thermal‐degradation products are observed depending on the structure of the side chain. The thermal degradation of PBOX‐Glc and PBOX‐F homopolymers starts with loss of side chains at relatively low temperatures and successive cleavage along the side and main chains follows. The stability of the glucose units of the PBOX‐Glc/F copolymer is significantly increased by the presence of perfluoroalkyl groups, attributable to OH···F hydrogen bonding interactions during pyrolysis.

     

Novel Olefin Block Copolymer,Polypropene‐block‐poly(methylene‐1,3‐cyclopentane‐co‐propene), Synthesized from Propene and 1,5‐Hexadiene by a Modified Stopped‐Flow Method

A block copolymer of propene and 1,5‐hexadiene, polypropene‐block‐poly(methylene‐1,3‐cyclopentane‐co‐propene) (PP‐b‐(PMCP‐co‐PP)), was synthesized using a modified stopped‐flow polymerization method with an MgCl₂‐supported Ziegler catalyst. Regarding the basic characteristics of the PP‐b‐(PMCP‐co‐PP), the block formation was investigated in detail. The obtained block copolymer showed a unimodal GPC curve without any peak in the low molecular weight region. It was also clear that the molecular weight of each part could be controlled by changing the polymerization time (from about 0.1 to 0.2 s). Furthermore, the elution pattern by temperature‐rising elution fractionation clearly showed that the block copolymer eluted in each temperature region between 20°C to 120°C was mainly composed of a unified component. Even after extraction with boiling heptane, the ¹³C NMR spectra of the block copolymer showed that the signals from PMCP‐co‐PP remained unchanged, but disappeared in the blend of polypropene and PMCP‐co‐PP. The differential scanning calorimetry results and optical microscopic observations indicated not only the formation of a block copolymer having a chemical linkage between polypropene and PMCP‐co‐PP, but also the regulation of the crystalline distribution in the block copolymer by changing the composition of each block part.     

Bioinspired All‐Polyester Diblock Copolymers Made from Poly(pentadecalactone) and Poly(3‐hydroxycinnamate): Synthesis and Polymer Film Properties

A bioinspired diblock copolymer is synthesized from pentadecalactone and 3‐hydroxy cinnamic acid. Poly(pentadecalactone) (PPDL) with a molar mass of up to 43 000 g mol^?1 is obtained by ring‐opening polymerization initiated by propargyl alcohol. Poly(3‐hydroxycinnamate) (P3HCA) is obtained by polycondensation and end‐functionalized with 3‐azido propanol. The two functionalized homopolymers are connected via 1,3‐dipolar Huisgen addition to yield the block copolymer PPDL‐triazole‐P3HCA. The structure of the block copolymer is confirmed by proton NMR, FTIR spectroscopy and GPC. By analyzing the morphology of polymer films made from the homopolymers, from a 1:1 homopolymer blend, and from the PPDL‐triazole‐P3HCA block copolymer, clearly distinct micro‐ and nanostructures are revealed. Quantitative nanomechanical measurements reveal that the block copolymer PPDL‐triazole‐P3HCA has a DMT modulus of 22.3 ± 2.7 MPa, which is lower than that of the PPDL homopolymer (801 ± 42 MPa), yet significantly higher than that of the P3HCA homopolymer (1.77 ± 0.63 MPa). Thermal analytics show that the melting point of PPDL‐triazole‐P3HCA is similar to PPDL (89–90 °C), while it has a glass transition temperature similar to P3HCA (123–124 °C). Thus, the semicrystalline, potentially degradable all‐polyester block copolymer PPDL‐triazole‐P3HCA combines the thermal properties of either homopolymer, and has an intermediate elastic modulus.     

Allylthioketone Mediating Radical Polymerization of Styrene

By combination of high trapping radical efficiency of thioketone with resonance of allylic radicals, a novel mediated agent, 1,3,3‐triphenylprop‐2‐ene‐1‐thione (TPPT) is successfully synthesized. The results of studying TPPT‐mediated radical polymerization of styrene (St) respectively at 70 °C and 100 °C reveal that at 70 °C, the monomer conversion is very low (less than 5%), the molecular weights do not change obviously with the monomer conversion, and their molecular weights are also low. However, the polymerization at 100 °C displays first‐order kinetics and a linear increase of the molecular weight with conversion. Several methods are used to study polymerization mechanisms and the results are interesting. The TPPT can efficiently capture the growing PS radicals to form PS‐TPPT radicals, this highly stable radical can be cross‐terminated by the primary radical R? (or the growing PS radicals) to form PS‐TPPT‐R (or PS‐TPPT‐PS), but this termination reaction is irreversible, and the dormant PS‐TPPT‐PS chains cannot be cleaved to regenerate the propagating radicals in the polymerization at 70 °C. However, the growing PS radical can be regenerated from the dormant chains at 100 °C, and the factors influencing the polymerization of St are studied.     

Synthesis of a Novel Chitin Derivative Having Oligo(ε‐caprolactone) Side Chains in Aqueous Reaction Media

A chitin‐based graft copolymer, chitin‐graft‐oligo(ε‐caprolactone) ( 2 ), was synthesized via ring‐opening graft polymerization of (ε‐caprolactone (ε‐CL) to ca. 50% partially deacetylated chitin 1 catalyzed by tin(II) 2‐ethylhexanoate in the presence of water as a swelling agent. The graft copolymer with ca. 40 wt.‐% poly(ε‐CL) content was obtained by the reaction using the catalyst of 0.17 mol‐% and water of 130 mol‐%, respectively, to the ε‐CL monomer at 100°C for 20 h. The chemical structure of 2 was characterized by IR, ¹H and ¹³C NMR spectroscopies. The poly(ε‐CL) contents by IR were in accordance with those determined by ¹H NMR analysis. T₁ measurements of an aqueous solution of 2 suggested that the molecular motion of the hydrophobic poly(ε‐CL) side chains is restricted to some extent. On the other hand, it was demonstrated by ¹³C CP/MAS NMR that the mobility of the chitin skeleton of 2 in the solid‐state is higher than that of the partially deacetylated chitin. X‐ray diffraction diagrams showed that 2 is amorphous, indicating that the crystallinity due to the chitin main chain was reduced by introducing the oligo(ε‐CL) side chains.     

Nano‐Scale Molecular Shapes of Water‐Soluble Chitin Derivatives Having Monodisperse Poly(2‐alkyl‐2‐oxazoline) Side Chains

The molecular shapes and the sizes of structures formed by chitin derivatives with monodisperse poly(2‐alkyl‐2‐oxazoline) side chains were investigated using atomic force microscopy (AFM), cryo‐transmission electron microscopy (cryo‐TEM), and small‐angle neutron scattering (SANS) analyses. A ring structure with an outside diameter of 45–60 nm and a cross‐sectional diameter of 10–18 nm was observed in the AFM image for chitin‐graft‐poly(2‐methyl‐2‐oxazoline) 1d (DP of the side chain, 8.5; [side chain]/[glucosamine unit], 0.53). From the cryo‐TEM observation of the graft copolymer 1d in 0.5 wt.‐% D₂O solution, an average diameter of 40 nm for the particles was determined, with a narrow size distribution. SANS measurements of the 0.5 wt.‐% D₂O solution of 1d revealed that the outside diameter of the particles and the cross‐sectional diameter were 57 nm and 8 nm, respectively. The absolute weight average molecular weight of 1d was determined to be 5.4 × 10⁵ by static light scattering. From these results it was concluded that 1d can form a unimolecular ring structure in aqueous solution. However, graft copolymers with fewer side chains ( 1c ; [side chain]/[glucosamine unit], 0.30) and with more side chains ( 1e ; [side chain]/[glucosamine unit], 0.96) did not form rings but instead formed monodisperse unimolecular spherical particles of diameters of 28–36 nm by AFM. A graft copolymer 1f with relatively long side chains (DP of side chain, 19.6; [side chain]/[glucosamine unit], 1.00) was also observed as a spherical particle by AFM (diameter: 30–40 nm by AFM; 40 nm by SANS). On the other hand, an intermolecular aggregate formation (diameter of the aggregate: 36–143 nm) was observed for graft copolymers 1a and 1b having short side chains (DP of side chains, 5.6; [side chain]/[glucosamine unit], 0.35 and 0.48, respectively), with a spherical molecular particle of diameter 36 nm by the AFM analysis. Chitin‐graft‐poly(2‐ethyl‐2‐oxazoline) ( 2 ) (DP of side chains, 21.7; [side chain]/[glucosamine unit], 0.95) generated larger aggregates of diameter 100–400 nm by AFM. The complexation behavior of graft copolymer 1d with magnesium 8‐anilino‐1‐naphthalenesulfonate (ANS) and with N‐phenyl‐1‐naphthylamine (PNA) was also examined by fluorescence measurement in an aqueous solution. It was found that graft copolymer 1d complexed with both ANS and PNA, and the binding constants were calculated to be 7.5 × 10⁴ M ^?1 and 5.3 × 10⁴ M ^?1, respectively.

Chemical structure of chitin‐graft‐poly(2‐alkyl‐2‐oxazoline).     

Morphology Control of Highly Sulfonated Block Copolymers by a Simple Thermal Process

Well‐defined sulfonated block copolymers were prepared by direct thermolysis with block copolymers of n‐butyl acrylate (nBA) and neopentyl styrene sulfonated (NSS), which were synthesized by Cu‐based living radical polymerization ( <1.20). A simple thermal process for 10 min at 150 °C completely deprotected the neopentyl groups in the poly(NSS) block segment to give fully sulfonated polystyrene backbone. SAXS profile of the block copolymer with 47 wt.‐% of poly(NSS) showed lamella structure, which appeared more clearly with long ranged order after sulfonation of the block copolymer.