Water-responsive interpenetrating polymer network, preparation method and use thereof

Abstract

A water-responsive interpenetrating polymer network, a preparation method and use thereof are provided. The water-responsive interpenetrating polymer network comprises an interpenetrating polymer network formed by a cholesteric liquid crystal polymer and a polyionic liquid; wherein the cholesteric liquid crystal polymer is formed by polymerization of a liquid crystal mixture; and the polyionic liquid contains a hydrophilic group or is a hydrophilic salt. The interpenetrating polymer network is water responsive without needs of activation with an alkaline solution, which simplifies the preparation process, and has stable water responsiveness performance after prolonged and/or repeated exposure to water. The water-responsive interpenetrating polymer network can be used to prepare light reflective coatings and reflective devices, and has higher commercial value.

Claims

1. A water-responsive interpenetrating polymer network, comprising a cholesteric liquid crystal polymer and a polyionic liquid; wherein the cholesteric liquid crystal polymer is a polymerized liquid crystal mixture; and the polyionic liquid is a hydrophilic salt; wherein the polyionic liquid is derived from the following polymerizable salt: ##STR00030## wherein, R.sub.1, R.sub.2 are each independently selected from the group consisting of hydrogen, a C1 to C10 alkyl group, a halogen group, and a C1 to C10 alkoxyl group, R.sub.3 is selected from a C1 to C10 alkylene group, R.sub.4, R.sub.5 are independently selected from the group consisting of hydrogen, and C1 to C10 alkyl group.

2. The water-responsive interpenetrating polymer network according to claim 1, wherein R.sub.1 is selected from hydrogen or methyl, R.sub.2 is selected from hydrogen or methyl, R.sub.3 is selected from C1 to C6 alkylene, R.sub.4, R.sub.5 are each independently selected from one of hydrogen, methyl and ethyl.

3. The water-responsive interpenetrating polymer network according to claim 1, wherein the polymerized liquid crystal mixture is derived from polymerizable liquid crystal monomers, a chiral dopant and a photoinitiator.

4. The water-responsive interpenetrating polymer network according to claim 3, wherein the polymerized liquid crystal mixture further comprises a surfactant.

5. A method of preparing the water-responsive interpenetrating polymer network comprising the steps of: mixing a polymerizable cholesteric liquid crystal mixture and a pore-forming agent, performing polymerization, and then removing the pore-forming agent; and adding a polymerizable salt, and performing polymerization again, wherein the polymerizable salt is as follows: ##STR00031## wherein, R.sub.1, R.sub.2 are each independently selected from the group consisting of hydrogen, a C1 to C10 alkyl group, a halogen group, and a C1 to C10 alkoxyl group, R.sub.3 is selected from a C1 to C10 alkylene group, R.sub.4, R.sub.5 are independently selected from the group consisting of hydrogen, and C1 to C10 alkyl group.

6. The method of preparing the water-responsive interpenetrating polymer network according to claim 5, wherein the pore-forming agent is a non-photopolymerizable liquid crystal monomer.

7. The method of preparing the water-responsive interpenetrating polymer network according to claim 5, wherein after the polymerizable cholesteric liquid crystal mixture and the pore-forming agent are mixed, they are coated onto a substrate prior to polymerization.

8. The method of preparing the water-responsive interpenetrating polymer network according to claim 7, wherein the pore-forming agent is removed by heating evaporation or washing with a solvent.

9. The method of preparing the water-responsive interpenetrating polymer network according to claim 7, wherein the substrate is coated with an alignment layer.

10. A method of using the water-responsive interpenetrating polymer network according to claim 1, comprising the step of applying the water-responsive interpenetrating polymer network in intelligent infrared reflectors, water-responsive color patterns, sensors, imaging and anti-counterfeiting measures.

11. A light reflective coating, comprising the water-responsive interpenetrating polymer network of claim 1.

12. A reflective device, comprising the water-responsive light reflective coating of claim 11.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a test result diagram of the water responsiveness stability of an interpenetrating polymer network in the Comparative Example 1.

(2) FIG. 2 is a test result diagram of the water responsiveness stability of an interpenetrating polymer network in Example 1.

DETAILED DESCRIPTION

(3) The concept and the resulting technical effects of the present disclosure will be clearly and sufficiently described in conjunction with the examples below in order to facilitate fully understanding the objectives, technical features and effects of the present disclosure. Apparently, examples or embodiments described herein are only some of rather than all of the examples or embodiments of the present disclosure, and those examples or embodiments which may be obtained by those skilled in the art without creative work based on the examples or embodiments herein are intended to be included in the scope of protection of the present disclosure.

(4) In the following examples, the nematic liquid crystal monomer HCM-002 was purchased from Jiangsu Hecheng New Material Co., Ltd., with the structure:

(5) ##STR00023##
the chiral dopant HCM-006 was purchased from Jiangsu Hecheng New Material Co., Ltd., with the structure:

(6) ##STR00024##
the non-polymerizable liquid crystal unit 5CB was purchased from Jiangsu Creative Electronic Chemmicals with the structure:

(7) ##STR00025##
the structure of the photoinitiator was:

(8) ##STR00026##
and the structure of the surfactant was:

(9) ##STR00027##

EXAMPLE 1

(10) A mixture was obtained by mixing 48.6 parts by mass of nematic liquid crystal monomer HCM-002, 6.8 parts by mass of chiral dopant HCM-006, 2 parts by mass of photoinitiator, 2 parts by mass of surfactant, and 40.6 parts by mass of non-polymerizable liquid crystal unit 5CB. The mixture was coated onto a methacrylate-functionalized glass substrate using knife coating, and the molecules was oriented by shear force. After coating, ultraviolet irradiation was conducted immediately, and the oriented coating was photopolymerized under a nitrogen atmosphere, wherein the non-polymerizable liquid crystal unit 5CB was present as a pore-forming agent. Then 5 CB was removed by heating at 140° C. for 10 min to obtain a cholesteric polymer coating.

(11) Equimolar of acrylic acid and 2-(dimethylamino) ethyl methacrylate were taken to carry out the neutralization reaction to produce a polymerizable salt, the specific formation process was:

(12) ##STR00028##
The polymerizable salt generated from the reaction was placed on the above cholesteric polymer coating, immediately covered with a clean glass plate, heated to allow better and faster penetration of the polymerizable salt, and then a second UV irradiation was performed to polymerize the polymerizable salt to form a polyionic liquid and then form an interpenetrating polymer network with the cholesteric polymer.

(13) The polymerizable salt used for the formation of the polyionic liquid in this example was a carboxylate generated by the reaction of acrylic acid and 2-(dimethylamino)ethyl methacrylate. In the present disclosure, the polyionic liquid comprised, but was not limited to, a carboxylic acid based ionic liquid, a sulfonic acid based ionic liquid such as 4-vinylbenzenesulfonic acid-tetrabutyl quaternary phosphonium salt polymer (PTPSS), an amide based ionic liquid such as N-isopropyl acrylamide polymer (PNIPAM) and the like. Since the polyionic liquid had a hydrophilic group or was a hydrophilic salt, it was hygroscopic, which enabled the interpenetrating polymer network to absorb water and swell, increasing the length of the pitch of the cholesteric polymer in the interpenetrating polymer network, which in turn lead to an increase in the reflection wavelength of the interpenetrating polymer network material. Thus, water responsiveness was exhibited; meanwhile, since both positive and negative ions are part of the polyionic liquid, when they were trapped in the interpenetrating polymer network, no ions can escape from the network, thus there was no loss of the water responsiveness of the material.

COMPARATIVE EXAMPLE 1

(14) Comparative Example 1 provided a cholesteric interpenetrating polymer network, and its preparation process was the same as that of Example 1, except that acrylic acid was used in place of the polymerizable salt in Example 1 and formed an interpenetrating polymer network with cholesteric polymer, and KOH was used for activation.

EXAMPLE 2

(15) The interpenetrating polymer networks in Example 1 and Comparative Example 1 were tested for water responsiveness stability. The specific process was conducted as follows: both interpenetrating polymer networks were immersed in deionized water, and UV-Vis/IR spectroscopy was used to determine the reflection bands of both interpenetrating polymer networks in wet state after immersion for different periods of time. Results were shown in FIG. 1 and FIG. 2, in which FIG. 1 showed results of Comparative Example 1 and FIG. 2 showed results of Example 1. As shown in FIG. 1, for the activated polyacrylic acid interpenetrating polymer network in Comparative Example 1, the reflection bands had blue shifts as the immersion time increased. The reflection bands at 563 nm when immersed for 5 minutes continued to have blue shift as the immersion time extended, and arrived at the position of 436 nm when immersed for up to 7 days, which is basically the same as the position of the reflection band when dried, indicating that the positive ions continued to escape from the network and water responsiveness was disappearing gradually as the immersion time extended. It can be seen from FIG. 2 that, for the interpenetrating polymer network formed by the polyionic liquid and the cholesteric liquid crystal polymer in Example 1, the measured positions of the reflection band maintained substantially the same value as the immersion time increaseed, which was approximately at the position of 513 nm. The reflection band curves measured after immersion for 5 min and immersion for 30 min were basically the same, and the reflection band curves measured after immersion for 3 h and 1 d were basically the same, suggesting that the water responsiveness performance of the interpenetrating polymer network of the present disclosure was quite stable. Therefore, it can be concluded that, compared to conventional interpenetrating polymer networks formed from polyacrylic acid, the interpenetrating polymer network of the present disclosure was more stable in responsiveness performance after prolonged and/or repeated exposure to water.

EXAMPLE 3

(16) The mixture was obtained by mixing 48.6 parts by mass of nematic liquid crystal monomer HCM-002, 6.8 parts by mass of chiral dopant HCM-006, 2 parts by mass of photoinitiator, 2 parts by mass of surfactant, and 40.6 parts by mass of non-polymerizable liquid crystal unit 5CB. The mixture was coated onto a methacrylate-functionalized glass substrate using knife coating, and the molecules were oriented by shear force. After coating, ultraviolet irradiation was conducted immediately, and the oriented coating was photopolymerized under a nitrogen atmosphere, wherein the non-polymerizable liquid crystal unit 5CB was present as a pore-forming agent, and then heated at 140° C. for 10 min to remove 5CB to obtain a cholesteric polymer coating.

(17) Equimolar of 4-vinylbenzenesulfonic acid and tetrabutylphosphonium bromide were taken and reacted to produce a polymerizable salt, which gave a polymer of 4-vinylbenzenesulfonic acid-tetrabutyl quaternary phosphonium salt having the structural formula:

(18) ##STR00029##
The polymerizable salt generated from the reaction was placed on the above cholesteric polymer coating, immediately covered with a clean glass plate, heated to allow better and faster penetration of the polymerizable salt; and then a second UV irradiation was performed to polymerize the polymerizable salt to form a polyionic liquid and then form an interpenetrating polymer network with the cholesteric polymer. The resulted interpenetrating polymer network was tested and determined to have stable water responsiveness.