Chapter 9
Reversible Deactivation Radical Polymerization: Materials and Applications Downloaded from pubs.acs.org by UNIV OF ROCHESTER on 10/14/18. For personal use only.
Direct Hydrophilic Modification of Polymer Surfaces via Surface-Initiated ATRP Yuji Higaki,1,2,3 Motoyasu Kobayashi,3 and Atsushi Takahara*,1,2,3 1Institute
for Materials Chemistry and Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan 2WPI I2CNER, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan 3JST, ERATO Takahara Soft Interfaces Project, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan *E-mail:
[email protected].
Various hydrophilic modification approaches for solid polymer articles have been proposed. However, most methods scarcely ensure the long-term stability of the hydrophilicity due to the surface reorganization. The direct surface modification of polymer fibers and films by surface-initiated atom transfer radical polymerization (SI-ATRP) of charged monomers was investigated to achieve the stable surface modification of polymer articles. 2-(Methacryloyloxy)ethyl phosphorylcholine (MPC) was polymerized in the presence of compression molded sheets of bromo-functionalized polyethylene or polypropylene macroinitiators under mild conditions to provide a superhydrophilic PMPC-grafted surface layer. The PMPC-grafted polyolefin sheets showed excellent wettability and oil-detachment behavior in water. The PMPC-grafted PP sheets retained a water contact angle of less than 10° for over three years in air. A facile surface modification procedure for electrospun poly(butylene terephthalate) (PBT) fibers by SI-ATRP was proposed. ATRP initiators were introduced on the surface of the PBT fibers through aminolysis and subsequent chemical vapor adsorption. Poly[3-(N-2-methacryloyloxyethylN,N-dimethyl)ammonatopropanesulfonate)] (PMAPS) was grafted to the PBT fibers via SI-ATRP without altering the fiber geometry. After modification with © 2018 American Chemical Society
zwitterionic poly(sulfobetaine) brushes, the surface became superhydrophilic. The surface properties were thermally stable due to the high melting temperature of the PBT crystallites, and were maintained for a prolonged period.
Introduction The surface modification of polymer fibers and molded articles are required to adjust the surface properties such as wetting, lubrication, anti-fouling, adhesion, scratch-resistance, and tactile impression, depending on the applications. Both the surface geometry and chemical composition are associated with surface performance (1–4). The corona discharge and plasma treatments have been applied for the enhancement of surface wettability and paintability because of the easy and high-speed processing (5–8). Carbonyl, hydroxy and carboxylate groups are introduced to the polymer surface through oxidation. These polar groups facilitate liquid wetting and adhesive forces due to the high surface free energy. However, the surface properties are lost in a short period because the thermally active chains migrate, and the low surface free energy components are segregated to the outermost surface to reduce the interfacial energy. The polar groups migrate into the bulk instead of disappearing from the outermost surface. Because of the spontaneous segregation of the hydrophobic components to the outermost surface, additives are not valid for the hydrophilic modification of the polymer products. Therefore, the development of stable long-term surface modification procedures has been required for a long time. Grafting of high molecular weight polymer chains on polymer articles is a promising approach to achieve long-life hydrophilic surface modifications (9–13). Typically, polymer chain grafting approaches are classified as “grafting-to” and “grafting-from” (14–16). Polymer chain grafting by the attachment of polymer chains that are able to bind to the substrates is referred to as the “grafting-to” approach, whereas polymer chain grafting by polymerization of monomers from the substrate surface is referred to as the “grafting-from” approach. The “grafting-from” approach is favorable for the production of thick polymer grafting layers because the polymer chains propagate from the initiating sites on the substrates without steric hinderance of pre-existing bulky chains. Photo-induced free radical polymerizations have been applied to the direct polymer chain grafting by the “grafting-from” process. Ultraviolet (UV) light radiation and γ-ray radiation are commonly used as light sources (8, 12). Recently, controlled radical polymerization, such as atom transfer radical polymerization (ATRP), have been applied to the “grafting-from” process to achieve the production of markedly high-graft-density polymeric brushes because of the controlled chain growth in the ATRP. The surface-initiated ATRP (SI-ATRP) has been applied to the direct surface modification of polymer fibers and molded articles. The surface properties can be controlled by tuning the chemical structure of the grafting polymer chains. Charged polymer brushes, including polyelectrolyte brushes and zwitterionic polymer brushes, exhibit outstanding hydrophilicity. Especially, the zwitterionic 158
polymer brushes show superior anti-fouling and lubrication capabilities under wet conditions. In this paper, hydrophilic surface modifications of polyolefins and aromatic polyesters through SI-ATRP approaches are reviewed (Scheme 1). Poly[2-(methacryloyloxy)ethyl phosphorylcholine] (PMPC) was grafted to compression molded sheets of bromo-functionalized polyolefins via SI-ATRP (Scheme 1(a)) (17, 18). The anti-fouling capability and lubrication effect were demonstrated. Electrospun poly(butylene terephthalate) (PBT) fibers were modified with ATRP initiating groups through aminolysis and subsequent chemical vapor adsorption (Scheme 1(b)) (19). Poly[3-(N-2methacryloyloxyethyl-N,N-dimethyl)ammonatopropanesulfonate)] (PMAPS) was grafted to the PBT fibers via SI-ATRP without altering the fiber geometry. The hydrophilicity was maintained after thermal annealing because of the high melting temperature of the PBT crystallites. Those surface properties provided by zwitterionic polymer grafting through SI-ATRP were retained for a prolonged period.
Scheme 1. Polymer Brush Grafting by SI-ATRP onto the (a) Br-Containing Polyolefin Sheets (PP-MI) and (b) PBT Electrospun Fibers
Direct Surface Modification of Polyolefin Sheets Polyolefins are the most widely used commercial polymers (20). Their mechanical strength, toughness, and chemical stability can be tuned by their tacticity, molecular weight and branching structure; therefore, a variety of products have been produced. However, surface modification is difficult because of the rapid surface rearrangement by the migration of thermally active amorphous polyolefin chains. Effective surface modification procedures have been explored in both chemical and physical treatments (5, 7, 10). Klok et al. proposed a unique approach to produce polymer brushes on polyolefine substrates. The procedure involves direct introduction of bromo-initiators through photobromination and subsequent surface-initiated polymerization. They demonstrated the non-biofouling capability of poly(oligo-ethylene glycol) methacrylate brushes, and adhesion and spreading of endothelial cells on the polymer brushes that is further modified with RGD-containing peptide (21, 22). 159
Unique polyolefins consisting of α-olefins and ω-hydroxy-α-olefins were developed by Mitsui Chemicals (Tokyo, Japan) by using their original metallocene polymerization catalysts (23). The comonomer ratio can be tuned precisely without sacrificing the regioregularity. The polyolefin macroinitiators for ATRP were produced by converting the hydroxy groups into an alkyl halide (17). The compression molded sheets of Br-containing isotactic polypropylene macroinitiator (PP-MI) or Br-containing polyethylene macroinitiator (PE-MI) were employed as substrates for the direct grafting of PMPC brushes through SI-ATRP (Scheme 1a) (17, 18). The bromine atoms in 2-bromo-isobutyl groups exist at the outermost surface of the PP-MI sheets, as shown in the XPS spectrum. PMPC-grafted PP (PMPCg-PP) sheets showed XPS signals assigned to N1s, P2s, and P2p, which indicates PMPC chain grafting. The transmission electron microscopy (TEM) image of a cross section of the PMPC-g-PP sheets also verified the PMPC brush layer. The PMPC-g-PP sheet was microtomed to provide ultrathin cross-sectional films, then the films were stained by exposure to RuO4 vapor (Figure 1). The PMPC bush layer was clearly observed, and the thickness was 40-50 nm. The lamellar structure that is typically observed in isotactic PP was observed in the bulk. The well-stained amorphous PP phase exhibited below the PMPC layer. The ATRP would initiate from the amorphous top layer with 2-bromo-isobutyl groups that are excluded from the PP lamellar crystals. The crystalline PP in the bulk is hardly swollen with methanol, while the amorphous surface region is slightly swollen to allow the ATRP reaction. Therefore, PMPC grafting is limited to the surface, and the surface geometry was maintained during the polymerization process. The PMPC-g-PP sheets exhibited hydrophilicity. The water droplets were spread on the surface, while the oil droplets and air bubbles were repelled from the sheets in aqueous solutions (Figure 2). The PMPC-g-PP sheets maintained surface hydrophilicity over three years when stored under ambient conditions, demonstrating the long-term stability of the hydrophilic performance. PMPC is known as an outstanding bio-compatible polymer, so that PMPC modification is valid for biomaterial applications (24, 25). Medical devices are usually required to be sterilized before use. Sterilization is typically conducted by exposing the materials to steam at 388 K for 30 min or autoclaving the materials at 394 K for 15 min; therefore, the PMPC brush chains need to stay at the surface after the sterilization treatment. The thermal stability of the PMPC-g-PP sheets was validated by subjecting the sample to thermal annealing under vacuum at 373 K or 398 K. The PMPC-g-PP sheets retained hydrophilicity after annealing at 373 K. The melting temperature of the PP-MI was determined by differential scanning calorimetric (DSC) measurements to be 413 K. The glass transition temperature (Tg) of the PP-MI could not be clearly observed by DSC, but the Tg of isotactic PP is in the range of 267–272 K, which is much below the annealing temperature. The PMPC brush thickness is much thicker than the inter lamellar thickness, so that the thermally active amorphous PP chains are supposed to stay inside due to the network with the thermally stable PP crystalline phase. Namely, the surface rearrangement will be unfavorable because the thickness of the amorphous layer between the lamellae is less than the thickness of the grafted PMPC brushes. 160
Figure 1. TEM image of a cross section of the PMPC-g-PP sheets. The sample was stained with RuO4. Reproduced with permission from ref. (18). Copyright 2013, The Royal Society of Chemistry.
Meanwhile, the hydrophilicity was drastically reduced after annealing at 393 K. The migration of PMPC and segregation of PP to the outermost surface were suggested by XPS analysis. Because the melting temperature near the surface is lower than bulk because of the reduced-crystallite size and crystal imperfections, surface reorganization was induced, even though the annealing temperature was below the bulk melting temperature of PP-MI. The hydrophilicity was partially recovered by soaking the sheets in hot water at 363 K for 60 min. The segregation of the PMPC chains to the outermost surface was indicated by XPS analysis. Although the PMPC brushes at the vicinity of surface are spontaneously exposed to the water interface to reduce the interfacial free energy, the hydrophilicity was not completely recovered because of the temperature was far below Tg of the PP chains. The PMPC-g-PP sheets showed a significant reduction in the friction coefficient to 0.1-0.2 in a humid atmosphere or in water (26). The friction coefficient depends on the sliding velocity, viscosity of the lubricant, and the normal pressure, and is associated with the well-known classic tribology theory “Stribeck curve” (27). At a low sliding velocity, the sliding probe and surface exhibit a strong interaction to provide a large friction coefficient, the so-called boundary lubrication. The friction coefficient reduces with increasing sliding velocity, the so-called mixed lubrication. Grafting of the PMPC brushes results in a lowering of the friction coefficient in the full friction velocity range. The hydrodynamic lubrication layer formation assisted by polyelectrolyte brushes was directly demonstrated by double-spacer-layer ultrathin-film interferometry (28). The PMPC-g-PP sheets showed anti-fouling behavior against fibroblast cells. NIH3T3 fibroblast cells were resuspended in an RPMI1640 medium supplemented with 10% fetal bovine serum (FBS) for 24 hours. The NIH3T3 fibroblast (1 × 106 161
cells) were seeded onto the PP-MI, PMPC-g-PP sheets and polystyrene well (as the control) and incubated at 310 K with 5% CO2. The attached cells after 24 hours of incubation were observed with a phase contrast microscope (Figure 3). Although the cells substantially adhered to the polystyrene well, the pristine PP-MI sheets kept away the cell adhesion. The anti-fouling capability was enhanced by grafting the PMPC brushes, and the adhered cells were hardly observed.
Figure 2. Side view of the liquid droplets and air bubbles on the PMPC-g-PP sheets at 298 K. Reproduced with permission from ref. (18). Copyright 2013, The Royal Society of Chemistry.
Figure 3. Phase contrast images of the NIH3T3 fibroblast cells adhered on a (a) polystyrene sheet, (b) PP-MI sheet, and (c) PMPC-g-PP sheets. 162
The surface properties depend on the grafting polymer chains. Polycations with positively charged quaternary ammonium groups show antibacterial properties. A poly(methacrylate) with quaternary ammonium groups, poly(2-(methacryloyloxy)ethyltrimethylammonium chloride) (PMTAC), was grafted on the PP sheets by SI-ATRP process, then the anti-bacterial properties were examined. The PMTAC brushes were prepared on the PP-MI sheets by dipping the PP-MI sheet in MTAC/methanol solution at 60°C in the presence of a CuBr/ligand complex and a free initiator to provide PMTAC grafted PP (PMTAC-g-PP) sheets. The anti-bacterial property of the PMTAC-g-PP sheets was assessed by means of Escherichia coli NBRC 3972 and Staphylococcus aureussubsp aureus NBRC 12732. The number of bacteria just after inoculating onto the sheet and after incubating for 24 hours at 35°C are shown in Table 1. Pristine polyethylene (PE) sheets without any modifications were used as the control sample. The both bacteria were propagated vigorously on the naked PE sheets, indicating the activity of the bacteria in the assay. Meanwhile, the PMTAC-g-PP sheets got rid of the both bacteria, and the alive bacteria was hardly observed after 24 hours incubation. Consequently, the effective anti-bacterial property of the PMTAC-g-PP sheets was demonstrated.
Table 1. Anti-bacterial Assays on the PMTAC-g-PP and PE Sheets. Reproduced with permission from ref. (17). Copyright 2009, Springer Nature. Bacteria Escherichia coli NBRC 3972 Staphylococcus aureussubsp aureus NBRC 12732
Incubation time
Sheet
The number of alive bacteria
0 h
PE
2.1 × 105
24 h
PE PMTAC-g-PP
1.0 × 107 30
0 h
PE
2.2 × 105
24 h
PE PMTAC-g-PP
1.2 × 106 < 10
Direct Surface Modification of Polyester Electrospun Fibers Polyesters are general semicrystalline thermoplastics that are widely used for the production of fibers, sheets, and injection molding products. PBT exhibits rapid crystallization rate, high thermal stability, enhanced mechanical performance, and good moldability (29). A surface modification procedure for poly(ethylene terephthalate) (PET) films by means of 3-aminopropyltriethoxysilane (APTES) was reported by McCarthy et al. (30) APTES reacts with PET via aminolysis of the primary amine head group and esters in PET without a significant degradation in the bulk PET by soaking the PET films into a solution of APTES. The bulky triethoxysilyl group can limit the 163
aminolysis in the outermost surface. The subsequent hydrolysis of the ethoxysilyl groups produces silanol groups. Genzer et al. reported polymer brush grafting on electrospun PET fibers via SI-ATRP by using of the abovementioned surface modification procedure (31). We proposed the surface modification of electrospun PBT fibers by a multistep surface modification consisting of aminolysis by APTES, hydrolysis, condensation of (2-bromo-2-methyl)-propionyloxyhexyltriethoxysilane (BHE) using a chemical vapor adsorption (CVA) process, and SI-ATRP of a zwitterionic 3-(N-2-methacryloyloxyethyl-N,N-dimethyl)ammonatopropanesulfonate (Scheme 1b) (19). The electrospun PBT fibers were prepared from an 8.0 wt% 1,1,1,3,3,3-hexafluoro-2-propanol solution of PBT onto a plate collector (Figure 4a). Uniform fiber mats were obtained without significant orientation. The average fiber diameter was 2 μm. Ethoxysilyl groups were introduced by soaking the as-spun PBT fiber mats in an APTES toluene solution. The amorphous PBT chains at the surface were modified with APTES by aminolysis, whereas the reaction was limited to the surface because of the bulkiness of the ethoxysilyl groups and unreactive PBT crystals in the bulk. The hydrolysis by hydrochloric acid yields silanol groups on the fiber surface, and BHE was attached to the silanol groups by using a CVA process instead of solution processes. The CVA process achieves a homogeneous surface modification because the vapor accesses the depth of the fiber mats, whereas a solution process often suffers from the limited wetting of the inside of the fiber network. Because the melting temperature of PBT is Tm = 472 K, the high temperature vapor processing at 433 K was used for surface modification without serious deformation to the microfiber morphology. The BHE-modified PBT fibers exhibited almost identical morphology with the as-spun PBT fibers (Figure 4b).
Figure 4. SEM images of the (a) as-spun, (b) BHE-modified, (c) PMAPS-g-PBT fibers, and (d) PMAPS-g-PBT fibers after thermal annealing at 473 K for 2 hours. Reproduced with permission from ref. (19). Copyright 2015, Wiley. 164
Figure 5. Side view of the water droplets on the (a) PBT electrospun fibers, (b) PMAPS-g-PBT electrospun fibers, (c) PMAPS-g-PBT electrospun fibers after thermal annealing at 423 K for 2 hours, and (d) PMAPS-g-PBT electrospun fibers after thermal annealing at 473 K for 2 hours. Reproduced with permission from ref. (19). Copyright 2015, Wiley ATRP of MAPS was performed in the presence of the BHE-modified electrospun PBT fiber mat by using 2,2,2-trifluoroethane as a solvent. The fiber morphology was maintained and no significant thickening in the fiber diameter was observed in the scanning electron microscopy (SEM) images (Figure 4(c)). The PMAPS brush grafting was demonstrated by the drastic change in the hydrophilicity and XPS spectroscopic analysis. Because the crystalline polyesters composed of terephthalate units show a high melting temperature, the electrospun PBT fibers show heat resistance properties compared with the amorphous vinyl polymers and aliphatic polyesters. A DSC thermogram of the PMAPS grafted PBT (PMAPS-g-PBT) fibers exhibit an endothermic peak assignable to the melting temperature of the PBT crystals at 472 K. The triclinic crystalline structure in the PMAPS-g-PBT fibers was verified by X-ray diffraction measurements. The thermal stability of the surface wetting performance was demonstrated by tracking the water droplet contact angle after annealing at various temperatures (Figure 5). The water droplet was repelled and exhibits a static contact angle of 143° on the as-spun PBT fiber mats (Figure 5(a)), while the water droplet spreads completely on the PMAPS-g-PBT fibers (Figure 5(b)). The PMAPS-g-PBT fiber mats maintained its hydrophilic nature up to annealing temperatures of 453 K. The static contact angle slightly increased to 143°. However, the contact angle of the water droplets substantially increased to 128° after thermal annealing at 473 K. An XPS analysis indicated that the surface atomic composition of nitrogen and sulfur decreased after annealing at 473 K, while the fiber morphology was 165
preserved even after annealing at 473 K (Figure 4(d)). These results indicated that the large contact angle on the PMAPS-g-PBT fiber mats is attributed to the segregation of the hydrophobic PBT component or the decomposition of the PMAPS chains. Because the decomposition temperature of PMAPS was determined by thermal gravimetric analysis to be 548 K (5 wt% weight loss temperature), a surface rearrangement is more plausible. The morphological stability of the PBT electrospun fibers is attributed to the high melting temperature of the PBT component. Although the fiber morphology was preserved, the slight change in surface chemical composition caused a drastic change in the wetting behavior of the fiber mats. The hydrophilicity was maintained at room temperature over a prolonged period. The PMAPS-g-PBT fiber mats were stored in a cool dark place for 12 months, but the water droplet contact angle showed an angle below 10°, indicating the long-term stability of the hydrophilicity.
Conclusions Hydrophilic modification approaches for solid polymer articles have been proposed. However, most methods scarcely ensure the long-term stability of the hydrophilicity due to surface reorganization. The direct surface modification of polymer fibers and films by SI-ATRP of charged monomers has been investigated to achieve the stable surface modification of polymer articles. MPC was polymerized in the presence of compression molded sheets of bromo-functionalized polyethylene or polypropylene macroinitiators under mild conditions to provide a superhydrophilic PMPC-grafted surface layer. The PMPC-grafted polyolefin sheets showed excellent wettability and oil-detachment behavior in water. The PMPC-grafted PP sheets retained a water contact angle of less than 10° for over three years in air. The PMPC brushes showed anti-adhesion of fibroblast cells, while the PMTAC brushes exhibited anti-bacterial properties. A facile surface modification procedure for electrospun PBT fibers by SI-ATRP was proposed. ATRP initiators were introduced onto the surface of the PBT fibers through aminolysis and subsequent chemical vapor adsorption. PMAPS was grafted to the PBT fibers via SI-ATRP without altering the fiber geometry. After modification with the zwitterionic poly(sulfobetaine) brushes, the surface became superhydrophilic. The surface properties were thermally stable due to the high melting temperature of the PBT crystallites and were maintained for a prolonged period.
Acknowledgments This work was supported by the Photon and Quantum Basic Research Coordinated Development Program of the Ministry of Education, Culture, Sports, Science and Technology, Japan. Part of this work was funded by ImPACT Program of Council for Science, Technology and Innovation (Cabinet Office, Government of Japan). This work was performed under the Cooperative Research Program of “Network Joint Research Center for Materials and Devices.” 166
References 1. 2. 3.
4. 5. 6. 7.
8.
9. 10. 11.
12.
13.
14.
15.
16.
Extrand, C. W. Origins of Wetting. Langmuir 2016, 32, 7697–7706. Callies, M.; Quéré, D. On Water Repellency. Soft Matter 2005, 1, 55–61. Yoshimitsu, Z.; Nakajima, A.; Watanabe, T.; Hashimoto, K. Effects of Surface Structure on the Hydrophobicity and Sliding Behavior of Water Droplets. Langmuir 2002, 18, 5818–5822. Öner, D.; McCarthy, T. J. Ultrahydrophobic Surfaces. Effects of Topography Length Scales on Wettability. Langmuir 2000, 16, 7777–7782. Nitschke, M. Plasma Modification of Polymer Surfaces and Plasma Polymerization; Springer: Berlin Heidelberg, 2008; pp 203−214. Desai, S. M.; Singh, R. P. Surface Modification of Polyethylene; Springer: Berlin Heidelberg, 2004; Vol. 169, pp 231−294. Holmes-Farley, S. R.; Reamey, R. H.; McCarthy, T. J.; Deutch, J.; Whitesides, G. M. Acid-Base Behavior of Carboxylic Acid Groups Covalently Attached at the Surface of Polyethylene: The Usefulness of Contact Angle in Following the Ionization of Surface Functionality. Langmuir 1985, 1, 725–740. Dargaville, T. R.; George, G. A.; Hill, D. J. T.; Whittaker, A. K. High Energy Radiation Grafting of Fluoropolymers. Prog. Polym. Sci. 2003, 28, 1355–1376. Rånby, B. Surface Modification of Polymers by Photoinitiated Graft Polymerization. Makromol. Chem., Macromol. Symp. 1992, 63, 55–67. Yang, W.; Rånby, B. Radical Living Graft Polymerization on the Surface of Polymeric Materials. Macromolecules 1996, 29, 3308–3310. Ishihara, K.; Iwasaki, Y.; Ebihara, S.; Shindo, Y.; Nakabayashi, N. Photoinduced Graft Polymerization of 2-Methacryloyloxyethyl Phosphorylcholine on Polyethylene Membrane Surface for Obtaining Blood Cell Adhesion Resistance. Colloids Surf., B 2000, 18, 325–335. Xu, F. J.; Neoh, K. G.; Kang, E. T. Bioactive Surfaces and Biomaterials via Atom Transfer Radical Polymerization. Prog. Polym. Sci. 2009, 34, 719–761. Bongiovanni, R.; Marchi, S.; Zeno, E.; Pollicino, A.; Thomas, R. R. Water Resistance Improvement of Filter Paper by a UV-grafting Modification with a Fluoromonomer. Colloids Surf., A 2013, 418, 52–59. Zoppe, J. O.; Ataman, N. C.; Mocny, P.; Wang, J.; Moraes, J.; Klok, H.-A. Surface-Initiated Controlled Radical Polymerization: State-of-the-Art, Opportunities, and Challenges in Surface and Interface Engineering with Polymer Brushes. Chem. Rev. 2017, 117, 1105–1318. Chen, W.-L.; Cordero, R.; Tran, H.; Ober, C. K. 50th Anniversary Perspective: Polymer Brushes: Novel Surfaces for Future Materials. Macromolecules 2017, 50, 4089–4113. Barbey, R.; Lavanant, L.; Paripovic, D.; Schüwer, N.; Sugnaux, C.; Tugulu, S.; Klok, H.-A. Polymer Brushes via Surface-Initiated Controlled Radical Polymerization: Synthesis, Characterization, Properties, and Applications. Chem. Rev. 2009, 109, 5437–5527. 167
17. Matsugi, T.; Saito, J.; Kawahara, N.; Matsuo, S.; Kaneko, H.; Kashiwa, N.; Kobayashi, M.; Takahara, A. Surface Modification of Polypropylene Molded Sheets by Means of Surface-Initiated ATRP of Methacrylates. Polym. J. 2009, 41, 547–554. 18. Kobayashi, M.; Matsugi, T.; Saito, J.; Imuta, J.-i.; Kashiwa, N.; Takahara, A. Direct Modification of Polyolefin Films by Surface-Initiated Polymerization of a Phosphobetaine Monomer. Polym. Chem. 2013, 4, 731–739. 19. Higaki, Y.; Kabayama, H.; Tao, D.; Takahara, A. Surface Functionalization of Electrospun Poly (butylene terephthalate) Fibers by Surface‐Initiated Radical Polymerization. Macromol. Chem. Phys. 2015, 216, 1103–1108. 20. Kaminsky, W. Trends in Polyolefin Chemistry. Macromol. Chem. Phys. 2008, 209, 459–466. 21. Lavanant, L.; Pullin, B.; Hubbell, J. A.; Klok, H.-A. A Facile Strategy for the Modification of Polyethylene Substrates with Non-Fouling, Bioactive Poly(poly(ethylene glycol) methacrylate) Brushes. Macromol. Biosci. 2010, 10, 101–108. 22. Fortin, N.; Klok, H.-A. Glucose Monitoring Using a Polymer Brush Modified Polypropylene Hollow Fiber-based Hydraulic Flow Sensor. ACS Appl. Mater. Interfaces 2015, 7, 4631–4640. 23. Imuta, J.-i.; Toda, Y.; Kashiwa, N. New Metallocene Catalyst Having an Indenyl Group and a Fluorenyl Group for Ethylene-Polar Monomer Copolymerization. Chem. Lett. 2001, 30, 710–711. 24. Ishihara, K.; Ziats, N. P.; Tierney, B. P.; Nakabayashi, N.; Anderson, J. M. Protein Adsorption from Human Plasma is Reduced on Phospholipid Polymers. J. Biomed. Mater. Res. 1991, 25, 1397–1407. 25. Feng, W.; Zhu, S.; Ishihara, K.; Brash, J. L. Adsorption of Fibrinogen and Lysozyme on Silicon Grafted with Poly(2-methacryloyloxyethyl phosphorylcholine) via Surface-Initiated Atom Transfer Radical Polymerization. Langmuir 2005, 21, 5980–5987. 26. Kobayashi, M.; Terayama, Y.; Hosaka, N.; Kaido, M.; Suzuki, A.; Yamada, N.; Torikai, N.; Ishihara, K.; Takahara, A. Friction Behavior of High-Density Poly(2-methacryloyloxyethyl phosphorylcholine) Brush in Aqueous Media. Soft Matter 2007, 3, 740–746. 27. Luengo, G.; Israelachvili, J.; Granick, S. Generalized Effects in Confined Fluids: New Friction Map for Boundary Lubrication. Wear 1996, 200, 328–335. 28. Kobayashi, M.; Tanaka, H.; Minn, M.; Sugimura, J.; Takahara, A. Interferometry Study of Aqueous Lubrication on the Surface of Polyelectrolyte Brush. ACS Appl. Mater. Interfaces 2014, 6, 20365–20371. 29. Stein, R. S.; Misra, A. Morphological Studies on Polybutylene Terephthalate. J. Polym. Sci., Polym. Phys. Ed. 1980, 18, 327–342. 30. Fadeev, A. Y.; McCarthy, T. J. Surface Modification of Poly(ethylene terephthalate) to Prepare Surfaces with Silica-like Reactivity. Langmuir 1998, 14, 5586–5593. 31. Oezcam, A. E.; Roskov, K. E.; Spontak, R. J.; Genzer, J. Generation of Functional PET Microfibers through Surface-Initiated Polymerization. J. Mater. Chem. 2012, 22, 5855–5864. 168
