Block-polystyrene Diblock Copolymer Research Articles

Silver Nanocrystal Array with Precise Control via Star-like Copolymer Nanoreactors.

Silver nanocrystal arrays had attracted much attention due to the unique plasmonic effect of their ordered nanostructure and the synergy among adjacent nanocrystals. Conventional preparation methods had several limitations, such as high cost, harsh preparation conditions, and complicated influencing factors, which could not be employed to fabricate the nanocrystal arrays in highly controlled fashion. To solve these issues, we reported ordered arrays of different Ag nanocrystals with precise control prepared by utilizing amphiphilic star-like poly(4-vinylpyridine)-block-polystyrene diblock copolymers as nanoreactors synthesized by sequential atom transfer radical polymerization. Moreover, this unimolecular nanoreactor method based on star-like copolymers with stable and predesigned nanostructures was proved to be a universal approach to prepare other nanocrystal arrays. This strategy had low cost, simple process flow, wide applicability, and structural stability that could fabricate nanocrystal array with precise control and continuously prepare more complex nanostructure units in a large scale to meet different functions and applications.

Synthesis of Poly(methacrylic acid)-block-Polystyrene Diblock Copolymers at High Solid Contents via RAFT Emulsion Polymerization.

The combination of polymerization–induced self-assembly (PISA) and reversible–addition fragmentation chain transfer (RAFT) emulsion polymerization offers a powerful technique to synthesize diblock copolymers and polymeric nanoparticles in a controlled manner. The RAFT emulsion diblock copolymerization of styrene and methacrylic acid (MAA) by using a trithiocarbonate as surfactant and RAFT agent was investigated. The Z-group of the RAFT agent was modified with a propyl-, butyl- and dodecyl- sidechain, increasing the hydrophobicity of the RAFT agent to offer well-controlled polymerization of poly(methacrylic acid)-block-polystyrene (PMAA-b-PS) diblock copolymers at high solid contents between 30–50 wt% in water. The kinetic data of the PMAA homopolymerization with the three different RAFT agents for various solvents was investigated as well as the RAFT emulsion polymerization of the diblock copolymers in pure water. While the polymerization of PMAA-b-PS with a propyl terminus as a Z-group suffered from slow polymerization rates at solid contents above 30 wt%, the polymerization with a dodecyl sidechain as a Z-group led to full conversion within 2 h, narrow molar mass distributions and all that at a remarkable solid content of up to 50 wt%.

General Route to Colloidal Nanocrystal Clusters with Precise Hierarchical Control via Star-like Nanoreactors.

A colloidal nanocrystal cluster (CNC) is a hierarchical nanostructure formed by clustering several nanocrystals into one nano-ensemble, which may exhibit unique optical or catalytic properties different from individual nanocrystals owing to the mutual interactions among neighboring component nanocrystals. However, there is still no universal synthetic route that could be applicable to diverse material compositions with precisely controlled hierarchical structures (i.e., nanocrystal number density, component nanocrystal size, and overall diameter of the CNC) up to now. Herein, a general and novel synthetic strategy was reported for crafting a wide range of inorganic CNCs (i.e., noble metal, semiconductor, and metal oxide) via utilizing amphiphilic star-like poly(4-vinylpyridine)-block-polystyrene diblock copolymers as nanoreactors prepared by sequential atom transfer radical polymerization. The hierarchical structure of rationally designed CNCs could be readily tailored by varying the P4VP molecular weight of star-like nanoreactors and the parameter optimization during the CNC preparation process, which was inaccessible by conventional synthetic methods.

Influence of Charge Fraction on the Phase Behavior of Symmetric Single-Ion Conducting Diblock Copolymers.

A series of symmetric poly[(oligo(ethylene glycol) methyl ether methacrylate-co-oligo(ethylene glycol) propyl sodium sulfonate methacrylate)]-block-polystyrene (PsOEGMA-PS) diblock copolymers were synthesized as a model system to probe the effect of charge fraction on the phase behavior of charged-neutral single-ion conducting diblock copolymers. Small-angle X-ray scattering (SAXS) experiments showed that increasing the charge fraction does not alter the ordered phase morphology (lamellar) but increases the order-disorder transition temperature (TODT) significantly. Additionally, the effective Flory-Huggins interaction parameter (χeff) was found to increase linearly with the charge fraction, similar to the case of conventional salt-doped diblock copolymers. This indicates that the effect of counterion solvation, attributed to the significant mismatch between the dielectric constant of each block, provides the dominant effect in tuning the phase behavior of this charged diblock copolymer. We therefore infer that electrostatic cohesion (local charge ordering induced by Coulombic interactions), which is predicted to suppress microphase separation and lead to asymmetric phase diagrams, only plays a minor role in this model system.

Ordered mesoporous CoO/CeO2 heterostructures with highly crystallized walls and enhanced peroxidase-like bioactivity

With increasing requirements of replacing the high-cost and unstable natural enzymes, the rational design of highly efficient inorganic mimetic enzymes (nanozymes), as one of the most important bioactive materials, has attracted more and more attention in recent years. In our work, using the solvent evaporation induced co-assembly strategy with high-molecular weight poly(ethylene oxide)-block-polystyrene (PEO-b-PS) diblock copolymer as the template and two metal salts as the co-precursors in one-pot system, we synthesized ordered mesoporous heteroatom-doped CeO2 with high surface area, bimodal pore sizes and highly crystallized walls. The composite materials were then constructed as the mimetic enzymes to investigate their peroxidase-like catalytic performance and detect H2O2 and glucose as bioactive materials in diverse systems including complex biological samples. It was demonstrated that mesoporous 5%CoO/CeO2 catalyst was the best peroxidase mimic, following the typical Michaelis–Menten kinetics and exhibiting the excellent peroxidase-like catalytic performance toward 3,3′,5,5′-tetramethylbenzidine (TMB) with comparable Km and Vm values to horseradish peroxidase (HRP) enzyme. A highly sensitive and selective colorimetric assay was developed to detect H2O2 and glucose with detection limits of 0.88 and 19.6μM, respectively. The promising catalytic behavior of mesoporous 5%CoO/CeO2 as the peroxidase-like bioactive catalyst could be ascribed to its interconnected large mesopores, rich exposed surface defects and oxygen vacancies introduced by the heterojunction interface of ultrasmall CeO2 and CoO nanocrystals within pore walls.

The effect of reaction-induced micro-phase separation of block copolymer on curing kinetics of epoxy thermosets

The curing kinetics of epoxy system modified with Poly(e-caprolactone)-block-Polystyrene (PCL-b-PS) diblock copolymer was investigated by differential scanning calorimetry(DSC). PCL-b-PS was synthesized Via the combination of ROP and ATRP, then incorporated into epoxy to access the nanostructured thermosets. The results of TEM, SAXS and DSC demonstrated the occurrence of Reaction-induced Micro-phase Separation. Kinetic studies showed that the PCL-b-PS block copolymer delayed the curing reactions of epoxy system. The occurrence of Reaction-induced Micro-phase Separation had no significant effect on the total heat of reaction ∆H and the total activation energy, but resulted in a higher activation energy at the beginning of curing. The increase in activation energy at the initial stage of curing was related to the size and distribution of the dispersed phase. It is expected that the investigation of cure kinetics of EP/PCL-b-PS could provide more theoretical basis for the preparation of block copolymer modified epoxy resin.

Polymer/metal segmental Janus nanoparticles

Polymer/metal composite segmental Janus nanoparticles (NPs) are synthesized by sequential growth against poly(4-vinylpyridine) (P4VP) crosslinked cP4VP-PS Janus NPs. A Janus cluster of poly(4-vinylpyridine)-block-polystyrene (P4VP-b-PS) diblock copolymer is self-organized after absorption onto a silica patchy sphere via hydrogen bonding. Selective crosslinking of P4VP leads to the formation of robust cP4VP-PS Janus NPs. Within the cP4VP domain, functional species such as metals are preferentially grown by in situ reduction. Other thiol-capped polymers, for example, thiol-capped poly(N-isopropylacrylamide) (PNIPAM-SH), can be conjugated onto the opposite side to form polymer/metal triple segmental Janus NPs. The hyperthermia effect of Au NP of PNIPAM-Au@cP4VP-PS by near infrared (NIR) irradiation can trigger a fast transition from amphiphilic to hydrophobic of the Janus NPs at low surrounding temperature. De-stabilization of the emulsion is NIR triggered although the system temperature is below LCST (~32℃).

A Micelle Fusion-Aggregation Assembly Approach to Mesoporous Carbon Materials with Rich Active Sites for Ultrasensitive Ammonia Sensing.

Nanostructured carbon materials have received considerable attention due to their special physicochemical properties. Herein, ordered mesoporous carbons (OMCs) with two-dimension (2D) hexagonal mesostructure and unique buckled large mesopores have successfully been synthesized via a micelle fusion-aggregation assembly method by using poly(ethylene oxide)-block-polystyrene (PEO-b-PS) diblock copolymers as a template and resorcinol-based phenolic resin as a carbon precursor. The obtained ordered mesoporous carbons possess unique fiber-like morphology, specific surface area of 571-880 m(2)/g, pore volume of 0.54 cm(3)/g and large mesopores (up to 36.3 nm) and high density of active sites (i.e., carboxylic groups) of 0.188/nm(2). Gas sensor based on the ordered mesoporous carbons exhibits an excellent performance in sensing NH3 at a low temperature with fast response (<2 min), ultralow limit of detection (<1 ppm), and good selectivity, due to the large pore sizes, high surface area and rich active sites in the carbon pore walls.

Polymer-Templated Carbon Hybridized Nanostructured Transition Metal Oxide As Advanced Lithium-Ion Anodes

An enormous spectrum of applications of lithium-ion batteries (LIBs), particularly in electric vehicles (EVs), hybrid EVs and electric grids, invokes essential requirements on their energy storage capabilities. However, the most common commercial graphite anode material still exhibits a relatively low theoretical specific capacity of 372 mAh g-1, which cannot meet the demand of the high-energy applications noted above. To date, a wide variety of anode materials with much higher capacities have been extensively investigated. In this regard, transition metal oxides (MxOy, where M is Fe, Co, Ni, Cu, Sn, Mn, etc.) clearly stand out as the promising alternatives to graphite owing to their attractive higher theoretical capacities (＞ 600 mAh g-1), low cost, environmental friendliness and wide availability containing earth-abundant elements. To further achieve high rate capability, hybrid nanomaterials with more conductive carbonaceous materials have been constructured. The ability to create a synergistic effect of nanostructure engineering and its hybridization with conductive carbonaceous material is highly desirable for attaining high-performance lithium ion batteries (LIBs). However, it remains challenging to achieve this synergy. Here we propose a general method to create a synergistic effect of nanostructure engineering and its hybridization with conductive carbonaceous material. Star-like and bottlebrush-like poly (acrylic acid)-block-polystyrene (PAA-PS) diblock copolymer and polystyrene-block-poly(acrylic acid)-block-polystyrene (PS-PAA-PS) triblock copolymer with controlled dimensions will be synthesized through atom transfer rapid polymerization (ATRP). Through a strong coordination bonding between the metal moiety of inorganic precursors and the functional groups of PAA (-COOH), the inorganic precursors can be selectively incorporated into the space formed by the PAA block. As a result, nanostructured transition metal oxide solid nanocrystals and hollow nanocrystals can be synthesized guided by the PAA-PS and PS-PAA-PS templates, respectively. In addition, by changing the polymeric templates from star-like to bottlebrush-like structure, the transition metal oxide nanocrystals varied from isotropic (i.e. nanoparticles, hollow nanoparticles) to anisotropic (i.e. nanorods, nanotubes). The diameter of the transition metal oxide nanocrystals is determined by the dimension of the PAA part, and it could be easily changed by varying the molecular weight of PAA part in the polymeric templates. Morever, the polymeric template not only serves as an easy control over the size and shape of the inorganic nanocrystals, but also acts as carbon source when calcinated at high temperature at argon atmosphere. We demonstrated that the carbon-hybridized nanocrystals obtained by the polymer templating method would be superior anode materials for LIBs.

In Situ Synthesis of Thermoresponsive Polystyrene-b-poly(N-isopropylacrylamide)-b-polystyrene Nanospheres and Comparative Study of the Looped and Linear Poly(N-isopropylacrylamide)s

Well-defined triblock copolymer nanospheres of polystyrene-block-poly(N-isopropylacrylamide)-block-polystyrene (PS-b-PNIPAM-b-PS) containing a hydrophobic core of the polystyrene (PS) block and a looped corona of the thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) block were prepared by the bifunctional macro-RAFT agent mediated dispersion polymerization via polymerization-induced self-assembly. This synthesis affords the fine control on the chemical composition of the PS-b-PNIPAM-b-PS triblock copolymer and on the diameter of the triblock copolymer nanospheres. By precisely investigating the thermoresponse of the PS-b-PNIPAM-b-PS triblock copolymer nanospheres and the poly(N-isopropylacrylamide)-block-polystyrene (PNIPAM-b-PS) diblock copolymer nanospheres under the strictly similar conditions, it is found that the phase transition of the looped PNIPAM chains takes place at a lower temperature and within a narrower temperature range than that of the linear PNIPAM chains. We believe that the present...

Microphase separation of poly(tert-butyl methacrylate)-block-polystyrene diblock copolymers to form perforated lamellae

Perforated lamellar (PL) microphase structure of block copolymers in the bulk is rarely observed. Herein, formation of the PL structure from simple block copolymer, poly(tert-butyl methacrylate)-block-polystyrene (PtBMA-b-PS) prepared by reversible addition–fragmentation chain transfer (RAFT) mediated radical polymerization, is reported. The PL phase consists of alternating layers of PS and PtBMA microdomains, among which the PS layers contain ordered cylindrical domains of PtBMA. It is confirmed that the PL phase is located between the cylindrical phase and lamellar phase. In methanol, the microphase-separated sample is readily split into individual core/shell nanosheets with perforated glassy PS core. The PtBMA domains are densely attached both as the shells along PS sheets and as passages with a hexagonal pattern. The passage has a diameter of ca. 12 nm and an average periodic distance of 31 nm.

Remarkable humidity-responsive sensor based on poly (N,N-diethylaminoethyl methacrylate)-b-polystyrene block copolymers

We report on the synthesis and characterization of Poly (N,N-diethylaminoethyl methacrylate)-block-Polystyrene (PDEAEMA-b-PS) di-block copolymer. The synthesis was finished by using reversible addition-fragmentation chain transfer (RAFT) polymerization method. The investigation results of humidity sensing property of pure PDEAEMA, pure PS and PDEAEMA-b-PS di-block copolymer demonstrated that the block copolymer shown the best sensing performance. Its impedance changed more than three orders of magnitude in the range from 22% to 95% relative humidity. The hysteresis was less than 8% RH, the response and recovery time was 60 and 206s, respectively. The humidity sensing mechanism was discussed based on complex impedance plots. This work broadens the responsive scope of PDEAEMA-based materials from double-responsive (pH and temperature) to multi-responsive (pH, temperature and humidity).

Disassembly of Block Copolymer Vesicles into Nanospheres through Vesicle Mediated RAFT Polymerization

Block copolymer vesicles have aroused great interest, whereas how vesicles being formed is not well clarified. In this contribution, the vesicle mediated RAFT polymerization was performed, and the disassembly of block copolymer vesicles during the RAFT polymerization was investigated. It was found that when a solvophilic block of poly(N,N-dimethylacrylamide) (PDMA) was introduced into the vesicles of the poly[N-(4-vinylbenzyl)-N,N-diethylamine]-block-polystyrene (PVEA-b-PS) diblock copolymer, the PVEA-b-PS vesicles were gradually disassembled. With the increasing polymerization degree of the PDMA block, vesicles were first flattened to form tubules, then tubules were broken to form the jellyfish-like morphology, and last jellyfish converted into worms and worms minced into nanospheres of poly[N-(4-vinylbenzyl)-N,N-diethylamine]-block-polystyrene-block-poly(dimethylacrylamide) (PVEA-b-PS-b-PDMA). It is believed that the present vesicle mediated RAFT polymerization affords a real-time observation of vesicle disassembly, which is helpful to clarify the assembly of block copolymer vesicles.

Facile synthesis of block copolymers from a cinnamate derivative by combination of AGET ATRP and click chemistry

An azido- and bromo-containing compound derived from naturally occurring ethyl cinnamate was used successfully to prepare block copolymers by a combination of ‘activator generated by electron transfer atom transfer radical polymerization’ (AGET ATRP) and Huisgen “click” reactions in emulsion. First, azido-end poly(methyl methacrylate) and alkyne-end polystyrene were prepared under AGET ATRP conditions, then, poly(methyl methacrylate) block polystyrene (PMMA-b-PS) diblock copolymer was formed by Huisgen 1,3-dipolar cycloaddition. Finally, polystyrene block poly(methyl methacrylate) block polystyrene (PS-b-PMMA-b-PS) triblock copolymer was synthesized via simultaneous AGET ATRP and click reactions, catalyzed by the same copper-based catalyst. The polymers were characterized by 1H nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC), which confirmed the successful synthesis of the corresponding polymers.

Block copolymer/ferroelectric nanoparticle nanocomposites

Nanocomposites composed of diblock copolymer/ferroelectric nanoparticles were formed by selectively constraining ferroelectric nanoparticles (NPs) within diblock copolymer nanodomains via judicious surface modification of ferroelectric NPs. Ferroelectric barium titanate (BaTiO3) NPs with different sizes that are permanently capped with polystyrene chains (i.e., PS-functionalized BaTiO3NPs) were first synthesized by exploiting amphiphilic unimolecular star-like poly(acrylic acid)-block-polystyrene (PAA-b-PS) diblock copolymers as nanoreactors. Subsequently, PS-functionalized BaTiO3 NPs were preferentially sequestered within PS nanocylinders in the linear cylinder-forming polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymer upon mixing the BaTiO3 NPs with PS-b-PMMA. The use of PS-b-PMMA diblock copolymers, rather than traditional homopolymers, offers the opportunity for controlling the spatial organization of PS-functionalized BaTiO3 NPs in the PS-b-PMMA/BaTiO3 NP nanocomposites. Selective solvent vapor annealing was utilized to control the nanodomain orientation in the nanocomposites. Vertically oriented PS nanocylinders containing PS-functionalized BaTiO3 NPs were yielded after exposing the PS-b-PMMA/BaTiO3 NP nanocomposite thin film to acetone vapor, which is a selective solvent for PMMA block. The dielectric properties of nanocomposites in the microwave frequency range were investigated. The molecular weight of PS-b-PMMA and the size of BaTiO3 NPs were found to exert an apparent influence on the dielectric properties of the resulting nanocomposites.

Structural evolution of low-molecular-weight poly(ethylene oxide)-block-polystyrene diblock copolymer thin film.

The structural evolution of low-molecular-weight poly(ethylene oxide)-block-polystyrene (PEO-b-PS) diblock copolymer thin film with various initial film thicknesses on silicon substrate under thermal annealing was investigated by atomic force microscopy, optical microscopy, and contact angle measurement. At film thickness below half of the interlamellar spacing of the diblock copolymer (6.2 nm), the entire silicon is covered by a polymer brush with PEO blocks anchored on the Si substrate due to the substrate-induced effect. When the film is thicker than 6.2 nm, a dense polymer brush which is equal to half of an interlamellar layer was formed on the silicon, while the excess material dewet this layer to form droplets. The droplet surface was rich with PS block and the PEO block crystallized inside the bigger droplet to form spherulite.

Original route to polylactide–polystyrene diblock copolymers containing a sulfonyl group at the junction between both blocks as precursors to functional nanoporous materials

Novel functionalized nanoporous polymeric materials could be derived from poly(D,L-lactide)-block-polystyrene (PLA-b-PS) diblock copolymers with a sulfonyl group at the junction between both blocks were synthesized by a combination of ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP) using a synthetic difunctional initiator through a three-step sequential methodology. Different ω-bromo PLA polymers with various molar masses ranging from 3640 to 11,440gmol−1 were first produced by coupling ω-hydroxy PLA precursors to a chlorosulfonyl-functionalized ATRP initiator previously prepared, thus leading to the formation of suitable macroinitiators for the subsequent ATRP polymerization of styrene. Consequently, PLA-b-PS diblock copolymers were obtained with a finely tuned PLA volume fraction (fPLA) in order to develop a microphased-separation morphology. The resulting copolymers as well as the intermediate compounds were carefully analyzed by size exclusion chromatography and 1H NMR. Upon shear flow induced by a channel die processing, oriented copolymers were generally afforded as characterized by small-angle-X-ray scattering (SAXS). Such copolymers were finally submitted to mild alkaline conditions so as to hydrolyze the sacrificial PLA block, and the presence of the sulfonic acid functionality on the pore walls of the resulting nanoporous materials was evidenced by means of a post-modification reaction consisting in the corresponding sulfonamide formation.

Amine-functionalized nanoporous thin films from a poly(ethylene oxide)-block-polystyrene diblock copolymer bearing a photocleavable o-nitrobenzyl carbamate junction

The synthesis of a poly(ethylene oxide)-block-polystyrene (PEO-b-PS) diblock copolymer bearing an o-nitrobenzyl carbamate junction is reported via a one-pot atom transfer radical polymerization (ATRP)–copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC). The accordingly obtained block copolymer was self-assembled into thin films showing, after solvent annealing, ordered PEO cylinders oriented normal to the film surface and embedded in a PS matrix. In the next step, the easy photocleavage of the o-nitrobenzyl carbamate junction and the subsequent removal of the PEO nanophase were demonstrated. This led to amine-functionalized nanoporous PS thin films as evidenced by the successful coupling of a fluorescent dye bearing a carboxylic acid group. The possibility to obtain fluorescent nanopores was then further exploited to pattern the films using a photolithographic mask.

Formation of nanophases in epoxy thermosets containing an organic–inorganic macrocyclic molecular brush with poly(ε-caprolactone)-block-polystyrene side chains

In this contribution, we report the synthesis of organic–inorganic macrocyclic molecular brushes with a 24-membered macrocyclic oligomeric silsesquioxane (MOSS) backbone and with poly(e-caprolactone) (PCL) (or poly(e-caprolactone)-block-polystyrene (PCL-b-PS) diblock copolymer) side chains. The macrocyclic molecular brushes were incorporated into epoxy to access the nanostructured thermosets. The nanostructures in the thermosets were investigated by means of atomic force microscopy (AFM), small angle X-ray scattering (SAXS) and dynamic mechanical thermal analysis (DMTA). It is judged that the formation of the nanophases in the thermosets containing the macrocyclic molecular brush with PCL side chains (MOSS[PCL]12) follows the self-assembly mechanism in terms of the immiscibility of the MOSS backbone with epoxy after and before the curing reaction. It was found that the spherical, vesicular and lamellar nanophases were formed in the epoxy thermosets containing the macrocyclic molecular brush with PCL-b-PS side chains (MOSS[PCL-b-PS]12). In contrast to the thermosets containing MOSS[PCL]12 the formation of the nanophases in the thermosets containing MOSS[PCL-b-PS]12 was ascribed to the self-assembly-directed reaction-induced microphase separation mechanism.

Photo-Induced Micellization of Block Copolymers

We found novel photo-induced micellizations through photolysis, photoelectron transfer, and photo-Claisen rearrangement. The photolysis-induced micellization was attained using poly(4-tert-butoxystyrene)-block-polystyrene diblock copolymer (PBSt-b-PSt). BSt-b-PSt showed no self-assembly in dichloromethane and existed as isolated copolymers. Dynamic light scattering demonstrated that the copolymer produced spherical micelles in this solvent due to irradiation with a high-pressure mercury lamp in the presence of photo-acid generators, such as bis(alkylphenyl)iodonium hexafluorophosphate, diphenyliodonium hexafluorophosphate, and triphenylsulfonium triflate. The 1H NMR analysis confirmed that PBSt-b-PSt was converted into poly(4-vinylphenol)-block-PSt by the irradiation, resulting in self-assembly into micelles. The irradiation in the presence of the photo-acid generator also induced the micellization of poly(4-pyridinemethoxymethylstyrene)-block-polystyrene diblock copolymer (PPySt-b-PSt). Micellization occurred by electron transfer from the pyridine to the photo-acid generator in their excited states and provided monodispersed spherical micelles with cores of PPySt blocks. Further, the photo-Claisen rearrangement caused the micellization of poly(4-allyloxystyrene)-block-polystyrene diblock copolymer (PASt-b-PSt). Micellization was promoted in cyclohexane at room temperature without a catalyst. During micellization, the elimination of the allyl groups competitively occurred along with the photorearrangement of the 4-allyloxystyrene units into the 3-allyl-4-hydroxystyrene units.