WO2014011603A1

WO2014011603A1 - Block copolymers and their composites with inorganic nanoparticles, and methods of making and using same

Info

Publication number: WO2014011603A1
Application number: PCT/US2013/049671
Authority: WO
Inventors: Kui Xu; Christopher K. Ober; Nam-ho YOU
Original assignee: Cornell University
Priority date: 2012-07-09
Filing date: 2013-07-09
Publication date: 2014-01-16
Also published as: TW201404821A

Abstract

Block copolymers, block copolymer and inorganic nanoparticle composite materials and devices including such composite materials. The block copolymers have polar functional groups that can facilitate the dispersion of inorganic nanoparticles in composite materials. The nanoparticles can be used in devices such as optical/microelectronic sensors, transistors, memory storage devices, and photovoltaic devices.

Description

BLOCK COPOLYMERS AND THEIR COMPOSITES WITH INORGANIC NANOPARTICLES, AND METHODS OF MAKING AND USING SAME

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application No.

61/669,385, filed on July 9, 2012, the disclosure of which is incorporated herein by reference.

FIELD OF THE DISCLOSURE

[0002] The instant disclosure generally relates to block copolymer composites. More particularly the disclosure relates to block copolymer/inorganic material composites. BACKGROUND OF THE DISCLOSURE

[0003] Nano-scale filler materials for polymer composite materials are favored because their remarkable efficiency of a given property, i.e., less amount of additive is needed to achieve a desired property, due to their large surface area-to-volume ratio.

Furthermore, nano-sized filler materials provide the possibility to modify certain properties without significantly affecting others, e.g., mechanical reinforcement while maintaining optical transparency.

BRIEF SUMMARY OF THE DISCLOSURE

[0004] In an aspect, the present disclosure provides a composite material comprising a copolymer comprising one or more polymer blocks having one or more polar functional groups (e.g., carboxylic acid group(s), hydroxyl group(s), and combinations thereof) and inorganic nanoparticles. For example, the polymer blocks have 1, 2, or 3 polar functional groups. Examples of suitable polymer blocks having one or more polar functional groups include of poly(4-carboxystyrene), poly(4-hydroxystyrene), poly(2-hydroxy ethyl acrylate), poly(2-carboxyethyl acrylate), poly(2-methoxyethyl acrylate), and poly(acrylic acid), and combinations thereof. For example, the one or more polymer blocks having one or more polar functional groups have a PDI of 1.05 to 1.40.

[0005] In an embodiment, the polar functional groups are surrogate polar functional groups. Examples of suitable surrogate polar functional groups include cyano groups, chloromethyl groups, tert-butyl ester groups, and combinations thereof.

[0006] In an embodiment, the composite material further comprises one or more polymer blocks having one or more non-polar functional groups (e.g., hydrogen substituents, halogen substituents, and combinations thereof). In an embodiment, one or more of the non- polar functional groups is a fluorinated group. In an embodiment, all of non-polar functional groups on the polymer block(s) having one or more non-polar functional groups are fluorinated groups. Examples of suitable polymer blocks having one or more non-polar functional groups include polystyrene blocks, poly(4-fluorostyrene) blocks, poly(2,4- difluorostyrene) blocks, poly(pentafluorostyrene) blocks, and combinations thereof. For example, the one or more polymer blocks having one or more non-polar functional groups have a PDI of 1.05 to 1.45.

[0007] The inorganic nanoparticles can be metal oxide nanoparticles or non-metal oxide nanoparticles, or combinations thereof. Examples of suitable metal oxide nanoparticles include titanium dioxide nanoparticles, zirconium dioxide nanoparticles, hafnium dioxide nanoparticles, aluminum dioxide nanoparticles, zinc oxide nanoparticles, and combinations thereof. An example of suitable non-metal oxide nanoparticles are silicon dioxide nanoparticles.

[0008] In an aspect, the present disclosure provides devices comprising the composite material. For example, devices such as optical/microelectronic sensors, transistors, memory storage devices, and photovoltaic devices can comprise the composite material.

[0009] In an aspect, the present disclosure provides a block copolymer comprising one or more polymer blocks having one or more polar functional groups. For example, the polymer blocks have 1, 2, or 3 polar functional groups. Examples of suitable polymer blocks having one or more polar functional groups include of poly(4-carboxystyrene) blocks, poly(4- hydroxystyrene) blocks, poly(2-hydroxyethyl acrylate) blocks, poly(2-carboxyethyl acrylate) blocks, poly(2-methoxyethyl acrylate) blocks, poly(acrylic acid) blocks, and combinations thereof. For example, the one or more polymer blocks having one or more polar functional groups have a PDI of 1.05 to 1.40.

[0010] In an embodiment, the polar functional groups are surrogate polar functional groups. Examples of suitable surrogate polar functional groups include cyano groups, chloromethyl groups, tert-butyl ester groups, and combinations thereof.

[0011] In an embodiment, the block copolymer further comprises one or more polymer blocks having one or more non-polar functional groups (e.g., hydrogen substituents, halogen substituents, and combinations thereof). In an embodiment, one or more of the non- polar functional groups is a fluorinated group. In an embodiment, all of non-polar functional groups on the polymer block(s) having one or more non-polar functional groups are fluorinated groups. Examples of suitable polymer blocks having one or more non-polar functional groups include polystyrene blocks, poly(4-fluorostyrene) blocks, poly(2,4- difluorostyrene) blocks, poly(pentafluorostyrene) blocks, and combinations thereof. For example, the one or more polymer blocks having one or more non-polar functional groups have a PDI of 1.05 to 1.45.

BRIEF DESCRIPTION OF THE FIGURES

[0012] Figure 1.

[0013] Figure 2.

[0014] Figure 3.

d_s.

[0015] Figure 4. Representative IR spectra of PS-fr-PCS (a) and PS-fr-PVBA(b).

[0016] Figure 5. Representative TGA curves of PS-fr-PCS and PS-fr-PVBA (under nitrogen atmosphere, 10 °C/min).

[0017] Figure 6. Representative DSC curves of PS-fr-PCS and PS-fr-PVBA (under a nitrogen atmosphere, 10 °C/min).

[0018] Figure 7. Representative UV-Vis spectra of BCP and composite films.

[0019] Figure 8. An example of a synthetic route of PFS-^-(PHEA-ran-PCEA).

[0020] Figure 9. Representative ^]H NMR spectrum of PFS-^-(PHEA-ran-PCEA).

[0021] Figure 10. Representative AFM images of Si0₂ nano-particle/PFS-^-(PHEA- co-PCEA) composite ((a) height image, (b) phase image), and AFM images of Ti0₂ nano- particle/PFS-^-(PHEA-co-PCEA) composite ((c) height image, (d) phase image).

DETAILED DESCRIPTION OF THE DISCLOSURE

[0022] The present disclosure provides block copolymers and composite materials comprising such copolymers. Also provided are uses of the copolymers and composites comprising the copolymers. For example, the copolymers and composites can be used in devices.

[0023] In an aspect, the present disclosure provides block copolymers. The copolymers have one or more blocks having a plurality of polar functional groups. Examples of polar functional groups include alcohols, amines, carboxylic acids, and esters (e.g., hydroxy/carboxy substituted esters). The copolymer can have a plurality of different functional groups (e.g., a combination of alcohol groups and carboxylic acid groups). The polar functional groups can be provided by reaction (e.g., hydrolysis) of a copolymer to provide the copolymer having polar functional groups. In various embodiments, the copolymer has 1, 2, or 3 blocks, where at least one of the blocks has one or more polar functional groups. The block copolymers can be random copolymers. Depending on the polymerization methods used, the copolymers can have a variety of structures and/or end groups.

[0024] A variety of blocks having polar functional groups can be used. Each block can have one or more polar functional groups. For example, the block has 1, 2, or 3 different functional groups. Examples of such blocks include substituted polystyrene blocks, such as poly(4-carboxystyrene) and poly(4-hydroxystyrene), substituted polyacrylate blocks, such as poly(2-hydroxyethyl acrylate), poly(2-carboxyethyl acrylate), and poly(2-methoxyethyl acrylate), and poly(acrylic acid). The block can be a random copolymer of two monomers having polar functional groups (or groups that can be reacted to form polar functional groups). These blocks can have a wide range of molecular weight and polydispersity. For example, the block has a molecular weight of 5,000 g/mol to 50,000 g/mol, including all integer g/mol values and ranges therebetween, with a polydispersity index (PDI) of 1.05 to 1.40, including all values to 0.01 and ranges therebetween.

[0025] The block copolymer can comprise a block having a surrogate polar functional group that can be hydrolyzed after formation of the copolymer to provide a polar functional group on the copolymer. In an embodiment, the polar functional group is a surrogate functional group. The surrogate polar functional group is a functional group (e.g., cyano group, chloromethyl group, and ieri-butyl ester group) that can be reacted (e.g., hydrolyzed) to form polar functional groups. Examples of such blocks include poly(4-cyanostyrene), poly(4-chloromethyl styrene), and poly(ieri-butyl acrylate).

[0026] A variety of other blocks (i.e., blocks not having polar functional groups) can be used. These blocks can be fluorinated blocks. The fluorinated blocks can have a range of fluorine content. For example, the blocks can be from single fluorine substituent containing blocks to perflourinated blocks. Examples of such other blocks include polystyrene, poly(4- fluorostyrene), poly(2,4-difluorostyrene), and poly(pentafluorostyrene). These blocks can have a wide range of molecular weight and polydispersity. For example, the block has a molecular weight of 5,000 g/mol to 40,000 g/mol, including all integer g/mol values and ranges therebetween, with a polydispersity index (PDI) of 1.05 to 1.45, including all values to 0.01 and ranges therebetween. [0027] The block copolymers can be made by methods known in the art. For example, the copolymers can be made by living anionic polymerization, reversible addition fragmentation chain transfer (RAFT), atom transfer radical polymerization (ATR), or nitroxide mediated radical polymerization.

[0028] In an aspect, the present disclosure provides composite materials comprising the block copolymers and inorganic nanoparticles. The composite materials can have a high refractive index, n. For example, the composite material can have a refractive index of 1.46 to 1.67, including all values to 0.01 and ranges therebetween.

[0029] The inorganic nanoparticles can be metal oxide nanoparticles or non-metal oxide nanoparticles. Mixtures of nanoparticles can be used. For example, the metal oxide nanoparticles are titanium dioxide nanoparticles, zirconium dioxide nanoparticles, hafnium dioxide nanoparticles, aluminum dioxide nanoparticles, zinc oxide nanoparticles, or mixtures thereof. For example, the non-metal oxide nanoparticles are silicon dioxide nanoparticles.

[0030] The nanoparticles can be from 1 to 20 nm, including all integer nm values and ranges therebetween, in size (e.g., a longest dimension such as a diameter). For example, if the nanoparticles are below 20 nm in diameter the film can exhibit desirable optical properties (e.g., be optically transparent). The composite can comprise a mixture of nanoparticles having different composition.

[0031] The nanoparticles can have a high refractive index. For example, the nanoparticles have a refractive index of 1.54 to 2.17, including all values to 0.01 and ranges therebetween.

[0032] The composite can have a range of nanoparticle loading. The loading can be selected such that the composite has desirable properties (e.g., optical properties, mechanical properties, electronic properties, magnetic properties, etc.). The nanoparticle loading can be from 0 to 80 , including all integer % values and ranges therebetween.

[0033] The composite materials are provided by contacting a copolymer and a plurality of the nanoparticles. For example, the block copolymer and nanoparticles can be contacted in solvent (or mixture of solvents).

[0034] The materials exhibit desirable dispersion of the nanoparticles. The materials do not exhibit aggregation. Without intending to be bound be any particular theory, it is considered the polar functional groups interact with the surface of the nanoparticles to inhibit aggregation of the nanoparticles. [0035] In an aspect, the present disclosure provides a thin film comprising a composite material disclosed herein. It is desirable the film have high transmittance in the optical wavelength range (e.g., be optically transparent).

[0036] The thin films can be formed by solution-based deposition processes. It is desirable the copolymers can form composite materials having the solubility necessary for such deposition processes. Individual solvents or mixtures of solvents can be used to form the thin films. The films can be deposited by methods known in the art. For example, a thin film can be formed by spin coating a solution comprising a copolymer and a plurality of nanoparticles.

[0037] In an aspect, the present disclosure provides devices comprising the copolymers or composite materials disclosed herein. Examples of such devices include optical/microelectronic sensors, transistors, memory storage devices, and photovoltaic devices. The devices can be made using methods known in the art.

[0038] The following examples are presented to illustrate the present disclosure. They are not intended to limiting in any manner.

EXAMPLE 1

[0039] This example provides synthesis and characterization of block copolymers and composites.

[0040] Synthesis and Characterization of PS-&-PVBA and Composites. The synthesis of PS-&-PVBA involves the preparation of a precursor block copolymer polystyrene-^- poly(4-cyanstyrene) (PS-&-PCS) via living anionic polymerization and subsequent hydrolysis of cyanate groups to obtain carboxylic acid groups. Figure 1 shows the synthetic route of PS- b-FCS and PS-&-PVBA. Anion polymerizations were carried out in 10-fold excess of LiCl and 4-fold excess of 1,1-diphenylethylene (DPE) against sec-BuLi. PS-&-PCS with total molecular weight of 14K were obtained with narrow polydispersity indices. Relative molecular weights measured by size exclusion chromatography (SEC) were calibrated against PS linear standard as shown in Figure 2.

[0041] The chemical structure and composition of obtained block copolymers were also characterized by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (NMR). The ^]H-NMR spectrum of PS-&-PCS and PS-&-PVBA is shown in Figure 3. The signal from 6.0 to 7.5 ppm was assigned to aromatic protons of PS and PCS. The signal from 12.5 ppm was assigned to hydroxyl group after hydrolysis. The FT-IR spectrum of PS-&-PVBA (Figure 4) shows a peak at 3380 cm^"1, which indicates the presence of the COOH group after hydrolysis. The disappearance of a peak at 2200 cm^"1 indicates complete removal of the cyano groups during hydrolysis. Analysis of the FT-IR and NMR spectra confirmed the desired all structures of diblock copolymers PS-&-PCS and PS-&-PVBA.

[0042] The thermal properties of the block copolymers was characterized by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The TGA curves measured in nitrogen and the DSC curves are presented in Figure 5 and Figure 6, respectively. The BCP exhibits good thermal stability without significant weight loss up to approximately 300 °C in nitrogen. The glass transition temperatures (T_g) of the Pis estimated by DSC (Figure 6). The BCPs show T_gs ranging from 164-215 °C.

[0043] An effective method to develop high-n polymers is to combine the high-n inorganic nanoparticles such as Ti0₂ (anatase, n = 2.45; rutile, n = 2.70), Zr0₂ (n = 2.10), amorphous silicon (n = 4.23), PbS (n = 4.20), or ZnS (n = 2.36) with an organic polymer matrix in order to develop an organic-inorganic nanocomposite system. When the sizes of the high-n nanoparticles are below 50 nm, the nanocomposite films are often optically transparent. The Ti0₂ nanoparticles used in this work are a nontoxic, thermal and environmentally stable nanoparticle, Ti0₂ is widely used in many high-tech fields. As expected, the BCP film showed the good optical transparency in the UV and visible area and refractive index (1.476 at 581nm) as shown in Table 1 ; thus, it was adopted to be combined with titania nanoparticles. The homogeneous and transparent nanocomposite film had a refractive index in the range of 1.476- 1.577 nm while maintaining high optical transparency.

[0044] Table 1. Optical properties of Block Copolymer and nanocomposite films via

Anionic Polymerization

[0045] The present BCP and BCP-Ti02 nanocomposite films exhibits good transparency above 400 nm, as shown in the UV-Vis spectra in Figure 7. The BCP films show the cutoff wavelengths at about 260 nm.

[0046] Synthesis and Characterization of PFS-^-(PHEA-ran-PCEA) and Compositi [0047] PFS-^-(PHEA-ran-PCEA) was prepared via reversible addition fragmentation chain transfer (RAFT) technology, following the synthetic route illustrated in Figure 8. 4- Cyano-4-(phenylcarbonothioylthio)pentanoic acid was used as the chain transfer agent in the polymerization of 4-fluorostyrene, and the subsequent RAFT polymerization of a mixture of 2-carboxyethyl acrylate (CEA) and 2-hydroxyethyl acrylate (HEA) gave the second block. It is worth noting that, by manipulating the monomer feed ratio and the polymerization reaction time, the chain length and mole ratio of HEA and CEA unit in the block copolymer can be tuned. Two HEA/CEA ratios, 2.01:1 and 0.9:1 were obtained, which were accessed from the integral data of ¹H NMR spectrum. As shown in Figure 9, ¹H NMR spectrum of PFS-&- (PHEA-ran-PCEA) exhibits a characteristic signal at 6.42-7.11 ppm attributed to the aromatic protons of PFS and multiple peaks at 3.67, 4.80 and 3.97-4.42 ppm corresponding to methylene groups on the side chains of PHEA-ran-PCEA block. These clearly assigned NMR peaks provide substantial confirmation of the chemical structure of the block copolymer.

[0048] Since solution process is an important processing technique for

polymer/nanoparticle composite materials, the solubility of the block copolymer, PFS-&- (PHEA-ran-PCEA), in a variety of organic solvents were examined. Tetrahydrofuran (THF), acetone, dioxane, ethyl acetate, dimethylformamide (DMF), etc. were found to be good solvents for the PFS-^-(PHEA-ran-PCEA) block copolymers that were prepared.

[0049] Table 2. Characteristics of Si0₂ and Zr0₂ nanoparticle.

Sample Name EF-10M1 MA-ST-XS

Particle Zr0₂ Si0₂

Particle Size (DLS) 9.2 nm 7 nm

Dispersion Medium Methanol Methanol

Particle Content 10.0 wt 10.7 wt%

Appearance Clear Clear

[0050] The presence of highly polar functional groups like carboxylic acid and hydroxyl groups in the block copolymers opens opportunity for creating miscible polymer/inorganic nano-particle composite materials owing to the binding interactions of acid groups to the surface of inorganic particles such as silica, titanium oxide, etc.

Introducing nanoparticles with specific properties provides new functions and applications to the materials. Several inorganic nanoparticles including Si0₂ and Zr0₂ were investigated. These nanoparticles are well-dispersed in methanol, and their characteristics are summarized in Table 2. The particle sizes of Si0₂ and Zr0₂ are around 7 and 9.7 nm, respectively.

[0051] It is known that there is a crucial hurdle hampering the progress of all polymer/nano-particle composites, i.e. the strong tendency of nanoparticles to aggregate in polymeric matrices. The instant materials take advantage of acid/nano-particle surface binding interactions to assist the dispersion of the nano-particles in polymer matrix to address this issue. Thin films of block copolymer/nano-particle composites were prepared by spin- coating their solutions in appropriate organic solvents onto silicon wafers. The choice of solvent has been found to have significant effect on the dispersion and aggregation of the nanoparticles in the composite film. After trying many solvents, it was found THF is the best solvent for preparing Si0₂/block copolymer composite film, while the best solvent for preparing Zr0₂/block copolymer composite is acetone + DMF (4: 1 by volume). Figure lOa-b and Figure lOc-d show atomic force microscopy (AFM) images of Si0₂/PFS- ?-(PHEA-ran- PCEA) and Ti0₂/PFS- ?-(PHEA-ran-PCEA) composite films, respectively. These images show remarkably well-dispersed nano-particles in the block copolymer without seeing undesirable particle aggregation.

[0052] While the disclosure has been particularly shown and described with reference to specific embodiments (some of which are preferred embodiments), it should be understood by those having skill in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the present disclosure as disclosed herein.

Claims

WHAT IS CLAIMED IS:

1. A composite material comprising a copolymer comprising one or more polymer blocks having one or more polar functional groups and inorganic nanoparticles.

2. The composite material of claim 1, further comprising one or more polymer blocks

having one or more non-polar functional groups.

3. The composite material of claim 2, wherein the non-polar functional groups are selected from the group consisting of hydrogen substituents, halogen substituents, and

combinations thereof.

4. The composite material of claim 2, wherein the polymer blocks having one or more non- polar functional groups are selected from the group consisting of polystyrene, poly(4- fluorostyrene), poly(2,4-difluorostyrene), poly(pentafluorostyrene), and combinations thereof.

5. The composite material of claim 2, wherein the one or more polymer blocks having one or more non-polar functional groups have a PDI of 1.05 to 1.45.

6. The composite material of claim 1, wherein the polar functional group is selected from the group consisting of carboxylic acid group, hydroxyl group, and combinations thereof.

7. The composite material of claim 1, wherein the polymer blocks have 1, 2, or 3 polar functional groups.

8. The composite material of claim 1, wherein the one or more polymer blocks having one or more polar functional groups are selected from the group consisting of poly(4- carboxystyrene) block, poly(4-hydroxystyrene) block, poly(2-hydroxyethyl acrylate) block, poly(2-carboxyethyl acrylate) block, poly(2-methoxyethyl acrylate) block, poly(acrylic acid) block, and combinations thereof.

9. The composite material of claim 1, wherein polar functional groups are surrogate polar functional groups.

10. The composite material of claim 9, wherein the surrogate polar functional groups are cyano groups, chloromethyl groups, ieri-butyl ester groups, or a combination thereof.

11. The composite material of claim 1 , wherein the one or more polymer blocks having one or more polar functional groups have a PDI of 1.05 to 1.40.

12. The composite material of claim 1, wherein the inorganic nanoparticles are metal oxide nanoparticles or non-metal oxide nanoparticles.

13. The composite material of claim 12, wherein the metal oxide nanoparticles are selected from the group consisting of titanium dioxide nanoparticles, zirconium dioxide nanoparticles, hafnium dioxide nanoparticles, aluminum dioxide nanoparticles, zinc oxide nanoparticles, and combinations thereof.

14. The composite material of claim 13, wherein the non-metal oxide nanoparticles are

silicon dioxide nanoparticles.

15. A device comprising the composite material of claim 1.

16. A block copolymer comprising one or more polymer blocks having one or more polar functional groups.

17. The block copolymer of claim 16, wherein the one or more polymer blocks having one or more polar functional groups have a PDI of 1.05 to 1.40.

18. The block copolymer of claim 16, further comprising one or more polymer blocks having one or more non-polar functional groups.

19. The block copolymer of claim 18, wherein the one or more polymer blocks having one or more non-polar functional groups have a PDI of 1.05 to 1.45

20. The block copolymer of claim 16, wherein the polar functional group is selected from the group consisting of carboxylic acid group, hydroxyl group, and combinations thereof.

21. The block copolymer of claim 16, wherein the polymer blocks have 1, 2, or 3 polar functional groups.

22. The block copolymer of claim 16, wherein the one or more polymer blocks having one or more polar functional groups are selected from the group consisting of poly(4- carboxystyrene) block, poly(4-hydroxystyrene) block, poly(2-hydroxyethyl acrylate) block, poly(2-carboxyethyl acrylate) block, poly(2-methoxyethyl acrylate) block, poly(acrylic acid) block, and combinations thereof.

23. The block copolymer of claim 16, wherein polar functional groups are surrogate polar functional groups.

24. The block copolymer of claim 23, wherein the surrogate polar functional groups are cyano groups, chloromethyl groups, ieri-butyl ester groups, or a combination thereof.

25. The block copolymer of claim 24, wherein the non-polar functional groups are selected from the group consisting of hydrogen substituents, halogen substituents, and combinations thereof.

26. The block copolymer of claim 25, wherein the polymer blocks having one or more non- polar functional groups are selected from the group consisting of polystyrene, poly(4- fluorostyrene), poly(2,4-difluorostyrene), poly(pentafluorostyrene), and combinations thereof.