Stereoregular Brush Polymers and Graft Copolymers by Chiral Zirconocene-Mediated Coordination Polymerization of P3HT Macromers

Two poly(3-hexylthiophene) (P3HT) macromers containing a donor polymer with a polymerizable methacrylate (MA) end group, P3HT-CH2-MA and P3HT-(CH2)2-MA, have been synthesized, and P3HT-(CH2)2-MA has been successfully homopolymerized and copolymerized with methyl methacrylate (MMA) into stereoregular brush polymers and graft copolymers, respectively, using chiral ansa-zirconocene catalysts. Macromer P3HT-CH2-MA is too sterically hindered to polymerize by the current Zr catalysts, but macromer P3HT-(CH2)2-MA is readily polymerizable via either homopolymerization or copolymerization with MMA in a stereospecific fashion with both C2-ligated zirconocenium catalyst 1 and Cs-ligated zirconocenium catalyst 2. Thus, highly isotactic (with mm% ≥ 92%) and syndiotactic (with rr% ≥ 93%) brush polymers, it-PMA-g-P3HT and st-PMA-g-P3HT, as well as well-defined stereoregular graft copolymers with different grafted P3HT densities, it-P(M)MA-g-P3HT and st-P(M)MA-g-P3HT, have been synthesized using this controlled coordination-addition polymerization system under ambient conditions. These stereoregular brush polymers and graft copolymers exhibit both thermal (glass and melting) transitions with Tg and Tm values corresponding to transitions within the stereoregular P(M)MA and crystalline P3HT domains. Acceptor molecules such as C60 can be effectively encapsulated inside the helical cavity of st-P(M)MA-g-P3HT to form a unique supramolecular helical crystalline complex, thus offering a novel strategy to control the donor/acceptor solar cell domain morphology.


Introduction
Poly(3-hexylthiophene) (P3HT) is an important conjugated donor polymer in the field of polymer electronic devices, such as organic field-effect transistors [1][2][3][4][5][6][7] and organic/polymeric photovoltaic (OPV) solar cells [8][9][10][11][12][13], thanks to its well-balanced all-around properties in terms of solution solubility, chemical stability, and charge mobility. These OPV devices are typically based on a bulk heterojunction fabricated from a blend of a donor (typically a conjugated polymer such as P3HT) and an acceptor (typically a fullerene such as C 60 and its derivatives). Intense research and development on both new materials and new device architectures has resulted in gradually improved power conversion

General Information
All synthesis and manipulations with air-and moisture-sensitive chemicals and reagents were performed using standard Schlenk techniques on a dual-manifold Schlenk line or in an inert gas (Ar or N 2 )-filled glovebox. NMR spectra were recorded on a Varian Inova 400 MHz or 500 MHz spectrometer (Varian, Palo Alto, CA, USA). Benzene-d 6 and toluene-d 8 were dried over sodium/potassium alloy and vacuum-distilled or filtered. Chemical shifts were referenced to residual undeuterated solvent resonances and are reported as parts per million relative to SiMe 4 . HPLC-grade organic solvents were first saturated with nitrogen during filling of the 20 L solvent reservoirs and then dried by passage through activated alumina (for Et 2 O, THF, and CH 2 Cl 2 ) followed by passage through Q-5 supported copper catalyst (for toluene and hexanes) stainless steel columns.
Polymer weight-average molecular weights (M w ) and molecular weight distributions or dispersities (Đ = M w /M n ) were measured by gel permeation chromatography (GPC) analyses carried out at 40 • C and a flow rate of 1.0 mL/min, with DMF as the eluent on a Waters University 1500 GPC instrument (Waters, Milford, MA, USA), equipped with one PLgel 5 µm guard and three PLgel 5 µm mixed-C columns (Polymer Laboratories; linear range of M W = 200-2,000,000). The instrument was calibrated with 10 PMMA standards, and chromatograms were processed with Waters Empower software (version 2002, Waters, Milford, MA, USA). Glass transition temperatures (T g ) and melting-transition temperatures (T m ) of the polymers were measured by differential scanning calorimetry (DSC) on a Q20 DSC, TA Instruments, New Castle, DE, USA. Samples were first heated until 250 • C at 10 • C·min −1 , cooled to 25 • C at 10 • C·min −1 , and then reheated again at 10 • C·min −1 to 250 • C. All T g and T m values were obtained from the second heating scan, after removing the thermal history. The tacticity of the polymers was analyzed by 1 H and 13 C-NMR based on that of PMMA. The macromer samples were analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF MS); the experiment was performed on a Ultraflex MALDI-TOF mass spectrometer (Bruker Daltonics, Billerica, MA, USA) operated in positive ion, reflector mode using a Nd: YAG laser at 355 nm and 25 kV accelerating voltage. External calibration was done using a peptide calibration mixture (4-6 peptides) on a spot adjacent to the sample. The raw data were processed in the FlexAnalysis software (version 2.4, Bruker Daltonics).

Synthesis of P3HT with H/Br Chain-Ends, H-P3HT-Br
Literature procedures [36] were modified to prepare the H/Br end-capped P3HT. 2,5-Dibromo-3-hexylthiophene (1.5 g, 4.6 mmol), t-BuMgCl (4.41 mmol) and THF (9 mL) were added to a 100 mL Schlenk flask and the mixture was stirred at room temperature for 20 h. The obtained yellow solution was transferred to 100 mL Schlenk flask which contained Ni(dppp)Cl 2 (40.5 mg in Polymers 2017, 9,139 4 of 15 20 mL THF) using cannula and the resulting mixture was stirred for 12 min. The polymerization was stopped by addition of 5 mL of 5.0 M HCl. After precipitation in methanol, the polymer was filtered into a Soxhlet thimble and extracted with methanol and hexanes overnight to wash away the residual monomer and low molecular weight impurities. The purified polymer was obtained in 70% yield by redissolution in CHCl 3 and precipitation in methanol. 1 H-NMR spectrum of P3HT with H/Br chain-ends (H-P3HT-Br) is shown in Figure 1. Except the characteristic peaks of the P3HT main chain, the chain ends can also be observed at 6.7 and 2. 8  stopped by addition of 5 mL of 5.0 M HCl. After precipitation in methanol, the polymer was filtered into a Soxhlet thimble and extracted with methanol and hexanes overnight to wash away the residual monomer and low molecular weight impurities. The purified polymer was obtained in 70% yield by redissolution in CHCl3 and precipitation in methanol. 1 H-NMR spectrum of P3HT with H/Br chain-ends (H-P3HT-Br) is shown in Figure 1. Except the characteristic peaks of the P3HT main chain, the chain ends can also be observed at 6.7 and 2.8 ppm, attributed to the proton of the chain end's double bond and the protons adjacent to the thiophene ring. The number-average molecular weight (Mn) can be calculated according to the following formula: Mn(NMR) = (2I2.80ppm/I2.60ppm) × 166 + 167 + 246. Accordingly, the MW of H-P3HT-Br was calculated to be approximately 5000 and 3500 g/mol for the samples prepared by using the monomer/Ni ratio of 62/1 and 26/1, respectively.
P3HT-vinyl (0.25 g) and 15 mL THF were added to a 100 mL dried Schlenk flask and the mixture was heated to 60 °C with stirring until P3HT-vinyl was dissolved. 9-BBN (0.5 M in THF, 3.5 mL) was added via syringe and the solution was allowed to stir at 60 °C until the double bond signals (via 1 H-NMR monitoring) completely disappeared. This process usually needed 30 h to reach a full conversion. After that, 6 M (1 mL) NaOH was added and the mixture was stirred for 15 min. After cooling to room temperature, 3 mL H2O2 (30%) was added, and the mixture was heated to 45 °C and reacted for another 24 h. Following precipitation in water-methanol mixture, filtration, washing and dried, the pure P3HT-(CH2)2-OH was obtained in 92.7% yield. 1  P3HT-(CH2)2-OH (0.25 g) and 15 mL THF were added to a 100 mL dried Schlenk flask and the mixture was heated to 40 °C until P3HT-(CH2)2-OH was dissolved. Triethylamine (3 mL) and methacryloyl chloride (2 mL) were then introduced and stirred at 40 °C for 24 h prior to precipitation in methanol. The resulting final product P3HT-(CH2)2-MA was filtered, washed and dried in vacuo

Synthesis of Macromer P3HT-(CH 2 ) 2 -MA
H-P3HT-Br (0.52 g) was thoroughly dried overnight and transferred to a 250 mL Schlenk flask in a glovebox. Then Pd(dba) 3 (20 mg), tri(t-butyl)phosphine (180 mg), tri-n-butyl(vinyl) tin (0.475 g) and THF (20 mL) were introduced. The flask was sealed, taken out of the glovebox, interfaced to a Schlenk line, and stirred at 55 • C overnight. After that, the reaction mixture was poured into methanol, filtered, and washed with methanol several times. The obtained crude product was dissolved in CHCl 3 , filtered with Kieselguhr to remove the Pd catalyst and then precipitated in methanol. The resulted P3HT-vinyl polymer was dried under vacuum at room temperature to a constant weight (yield: 95%). 1  P3HT-vinyl (0.25 g) and 15 mL THF were added to a 100 mL dried Schlenk flask and the mixture was heated to 60 • C with stirring until P3HT-vinyl was dissolved. 9-BBN (0.5 M in THF, 3.5 mL) was added via syringe and the solution was allowed to stir at 60 • C until the double bond signals (via 1 H-NMR monitoring) completely disappeared. This process usually needed 30 h to reach a full conversion. After that, 6 M (1 mL) NaOH was added and the mixture was stirred for 15 min. After cooling to room temperature, 3 mL H 2 O 2 (30%) was added, and the mixture was heated to 45 • C and reacted for another 24 h. Following precipitation in water-methanol mixture, filtration, washing and dried, the pure P3HT-(CH 2 ) 2 -OH was obtained in 92.7% yield. 1  P3HT-(CH 2 ) 2 -OH (0.25 g) and 15 mL THF were added to a 100 mL dried Schlenk flask and the mixture was heated to 40 • C until P3HT-(CH 2 ) 2 -OH was dissolved. Triethylamine (3 mL) and methacryloyl chloride (2 mL) were then introduced and stirred at 40 • C for 24 h prior to precipitation in methanol. The resulting final product P3HT-(CH 2 ) 2 -MA was filtered, washed and dried in vacuo at room temperature to a constant weight (yield: 97.1%). 1  P3HT-CH 2 -OH (0.5 g) and 30 mL THF were added to a 100 mL dried Schlenk flask and the mixture was heated to 40 • C until P3HT-CH 2 -OH was dissolved. Triethylamine (6 mL) and methacryloyl chloride (4 mL) were then introduced and the resulting mixture was stirred at 40 • C for 24 h prior to precipitation in methanol. The resulting product P3HT-CH 2 -MA was filtered, washed and dried in vacuo at room temperature to a constant weight (yield: 95.3%). 1

General Polymerization Procedures
Polymerizations were performed in 20 mL oven-dried glass reactors inside a glovebox. For homopolymerizations, a Zr pre-catalyst was premixed with an equimolar amount of activator [Ph 3 C][B(C 6 F 5 ) 4 ] in toluene for ca. 10 min to generate the corresponding activated cationic species. The polymerization was started by rapid addition of a macromer (P3HT-(CH 2 ) 2 -MA or P3HT-CH 2 -MA) solution in toluene. After the prescribed time, the polymerization was immediately quenched by pouring the reaction solution into 5% HCl-acidified methanol. The polymer was collected by filtering, washing several times with methanol, and drying in a vacuum oven at 50 • C to a constant weight. For copolymerizations, a Zr pre-catalyst was premixed with an equimolar amount of activator [Ph 3 C][B(C 6 F 5 ) 4 ]. The polymerization was started by rapidly adding the solution of macromer and comonomer MMA in toluene. After a prescribed time, the polymerization was immediately quenched by pouring the reaction solution into 5% HCl-acidified methanol. The crude polymer precipitated from methanol was dissolved in DMF to separate the P(M)MA-g-P3HT copolymer (soluble) and unpolymerized P3HT-MA (insoluble). The DMF-soluble polymer was then precipitated in methanol, filtered, washed several times with methanol, and dried in a vacuum oven at 50 • C to a constant weight.

Encapsulation of Acceptor C 60 by st-P(M)MA-g-P3HT
Syndiotactic graft copolymer st-P(M)MA-g-P3HT (10 mg) was dissolved in a toluene solution of C 60 (2 mg/mL, 1 mL) at 110 • C. After the solution was slowly cooled to room temperature (ca. 20 • C) without disturbance, the solution gradually gelled. The obtained soft gel was centrifuged for 10 min Polymers 2017, 9, 139 6 of 15 and the supernatant containing unencapsulated C 60 was removed from the gel by careful decantation. The condensed gel was then washed with toluene and the solvent was removed by decantation after centrifugation. This procedure was repeated several times until no purple color of C 60 retained. The solvent of complex gel was evaporated under vacuum at 50 • C to a constant weight.

Results and Discussion
3.1. Synthesis of Macromers P3HT-(CH 2 ) 2 -MA and P3HT-CH 2 -MA Two polymerizable P3HT-methacrylate macromers, P3HT-(CH 2 ) 2 -MA and P3HT-CH 2 -MA, were synthesized following the routes outlined in Scheme 1b,c, starting from P3HT with H/Br chain-ends, H-P3HT-Br. This starting oligomeric material was prepared using the known quasi-living Grignard metathesis polymerization of 2,5-dibromo-3-hexylthiophene, which was first treated with t BuMgCl and followed by addition of initiator Ni(dppp)Cl 2 (Scheme 1a) [36]. The formation of H-P3HT-Br was verified by 1 H-NMR (Figure 1), from which the molecular weight (MW) was calculated to be approximately 5000 and 3500 g/mol for the samples prepared by using the monomer/Ni ratio of 62/1 and 26/1, respectively. MALDI-TOF MS ( Figure 2) also showed the presence of a small amount of P3HT with Br/Br chain-ends, but no H/H "dead" chain-ends.

Synthesis of Macromers P3HT-(CH2)2-MA and P3HT-CH2-MA
Two polymerizable P3HT-methacrylate macromers, P3HT-(CH2)2-MA and P3HT-CH2-MA, were synthesized following the routes outlined in Scheme 1b,c, starting from P3HT with H/Br chain-ends, H-P3HT-Br. This starting oligomeric material was prepared using the known quasi-living Grignard metathesis polymerization of 2,5-dibromo-3-hexylthiophene, which was first treated with t BuMgCl and followed by addition of initiator Ni(dppp)Cl2 (Scheme 1a) [36]. The formation of H-P3HT-Br was verified by 1 H-NMR (Figure 1), from which the molecular weight (MW) was calculated to be approximately 5000 and 3500 g/mol for the samples prepared by using the monomer/Ni ratio of 62/1 and 26/1, respectively. MALDI-TOF MS (Figure 2) also showed the presence of a small amount of P3HT with Br/Br chain-ends, but no H/H "dead" chain-ends.    Next, two different types of effective end-functionalization reactions were carried out utilizing the active bromide end group on the thiophene ring. First, the Stille coupling reaction of H-P3HT-Br with n Bu3Sn(CH=CH2) in the presence of Pd2(dba)2 as the catalyst led to the vinyl end-functionalized H-P3HT-(CH=CH2) in 95% isolated yield, which was subsequently converted into hydroxyl end-functionalized H-P3HT-(CH2CH2OH) in 93% isolated yield via hydroboration-oxidation reaction with 9-BBN/NaOH/H2O2. In the final step, the acylation of this hydroxyl end-functionalized P3HT intermediate with methacryloyl chloride in the presence of Et3N afforded macromer P3HT-(CH2)2-MA in 97% isolated yield (Scheme 1b). It is worth noting that a small amount of the P3HT with doubly functionalized chain ends also formed during the process (due to the initial presence of Br-P3HT-Br) was readily removed after a simple purification procedure involving washing with methanol. The entire course of the reaction and the formation of the isolated intermediates were monitored and confirmed by 1 H-NMR. For example, Figure 3 Figure 4). Thus, the slope corresponds to the mass of the P3HT monomer, whereas the intercept is the sum of the masses for the chain-end groups, H/MA. Through the same synthetic procedure, P3HT-(CH2)2-MA with Mn ~5000 g/mol) was also synthesized.
The second type of the end-functionalization reaction began with the Vilsmeier-Haack formylation [37], followed by reduction and acylation (Scheme 1c). Thus, formylation of H-P3HT-Br with POCl3 led to H-P3HT-CHO in 93% isolated yield; subsequent reduction with NaBH4 afforded the corresponding H-P3HT-CH2OH in 96% isolated yield, which was acylated to the final macromer P3HT-CH2-MA in 95% isolated yield, after purification by removing any doubly functionalized P3HT possibly formed. 1  Next, two different types of effective end-functionalization reactions were carried out utilizing the active bromide end group on the thiophene ring. First, the Stille coupling reaction of H-P3HT-Br with n Bu 3 Sn(CH=CH 2 ) in the presence of Pd 2 (dba) 2 as the catalyst led to the vinyl end-functionalized H-P3HT-(CH=CH 2 ) in 95% isolated yield, which was subsequently converted into hydroxyl end-functionalized H-P3HT-(CH 2 CH 2 OH) in 93% isolated yield via hydroboration-oxidation reaction with 9-BBN/NaOH/H 2 O 2 . In the final step, the acylation of this hydroxyl end-functionalized P3HT intermediate with methacryloyl chloride in the presence of Et 3 N afforded macromer P3HT-(CH 2 ) 2 -MA in 97% isolated yield (Scheme 1b). It is worth noting that a small amount of the P3HT with doubly functionalized chain ends also formed during the process (due to the initial presence of Br-P3HT-Br) was readily removed after a simple purification procedure involving washing with methanol. The entire course of the reaction and the formation of the isolated intermediates were monitored and confirmed by 1 H-NMR. For example, Figure 3 depicts the spectrum of the final macromer P3HT-(CH 2 ) 2 -MA, clearly showing the resonances for the two vinylidene protons >C=CH 2 at δ 6.17 and 5.60 ppm (labeled as protons 1) and for the -OCH 2 CH 2 -group at δ 4.34 and 3.13 ppm (labeled as protons 2 and 3, respectively). The calculated M n by 1 H-NMR was~3500 g/mol. The formation of the exclusive H/MA chain-end groups and the M n were further confirmed by MALDI-TOF MS (Figure 4), which displays only one series of molecular mass ion peaks to show the presence of only one type of chain ends. A plot of m/z values vs. the number of P3HT repeat units yields a straight line with a slope of 166.3 and an intercept of 113.3 ( Figure 4). Thus, the slope corresponds to the mass of the P3HT monomer, whereas the intercept is the sum of the masses for the chain-end groups, H/MA. Through the same synthetic procedure, P3HT-(CH 2 ) 2 -MA with M ñ 5000 g/mol) was also synthesized.
The second type of the end-functionalization reaction began with the Vilsmeier-Haack formylation [37], followed by reduction and acylation (Scheme 1c). Thus, formylation of H-P3HT-Br with POCl 3 led to H-P3HT-CHO in 93% isolated yield; subsequent reduction with NaBH 4 afforded the corresponding H-P3HT-CH 2 OH in 96% isolated yield, which was acylated to the final macromer P3HT-CH 2 -MA in 95% isolated yield, after purification by removing any doubly functionalized P3HT possibly formed. 1

Homopolymerization of P3HT-MA Macromers and Theirs Copolymerization with MMA
To examine the polymerizability of the two P3HT-MA macromers, C 2 -ligated precatalysts Zr-1 and C s -ligated Zr-2, which upon activation with [Ph 3 C][B(C 6 F 5 ) 4 ] generates the corresponding cationic catalysts Zr-1 + [B(C 6 F 5 ) 4 ] − and Zr-2 + [B(C 6 F 5 ) 4 ] − (Scheme 2) [31][32][33], were employed for the polymerization study. The results of their homopolymerization and copolymerization with MMA are summarized in Table 1. With C 2 -ligated catalyst Zr-1 + [B(C 6 F 5 ) 4 ] − , macromer P3HT-(CH 2 ) 2 -MA was successfully homopolymerized to the corresponding isotactic polymer in 92% yield (run 1). The resulting polymer has an isotactic poly(methacrylate) backbone and a P3HT side chain on every methacrylate repeat unit, thus a densely grafted polymer, or a brush polymer, it-PMA-g-P3HT, which displayed both glass transition temperature (T g ) and melting-transition temperature (T m ) endothermic peaks on the DSC curve characteristic of the isotactic poly(methacrylate) and crystalline P3HT domains, respectively (vide infra). Likewise, macromer P3HT-(CH 2 ) 2 -MA was also successfully polymerized by C s -ligated catalyst Zr-2 + [B(C 6 F 5 ) 4 ] − to the corresponding syndiotactic brush polymer in 96% yield (run 4). The resulting densely grafted polymer st-PMA-g-P3HT exhibited also both the T g and T m values corresponding to the syndiotactic poly(methacrylate) and crystalline P3HT domains, respectively (vide infra). In sharp contrast, macromer P3HT-CH 2 -MA was not polymerizable by either C 2 -or C s -ligated catalysts, even after extended times (up to 12 h), attributable to the sterically hindered ester group of the macromer with only one carbon linkage between the P3HT chain and the MA moiety, which presumably hinders the coordination of this bulkier monomer to the cationic Zr center, the step essential for initiation of this coordination-addition polymerization.
Owing to the overlap between the 1 H-NMR resonances of the hexyl group of P3HT and those of the methyl triads (mm, mr and rr appeared at δ 1.20, 1.02 and 0.82 ppm) of the poly(methacrylate) of the homopolymers, we were unable to obtain the accurate tacticity values of these homopolymers, although it was estimated to be at least >90%. However, this issue was addressed through our study of copolymerizations with MMA. First, the copolymerization of P3HT-(CH 2 ) 2 -MA with MMA was investigated by C 2 -ligated Zr-1 + [B(C 6 F 5 ) 4 ] − with two different MMA/macromer ratios; the relatively high 383/1 MMA/macromer ratio run afforded a high M w isotactic graft copolymer it-P(M)MA-g-P3HT with M w = 132 kg/mol, Ð = 1.25, and isotacticity mm% = 92% (run 2). Again, the thermal transitions are consistent with the isotactic poly(methacrylate) and crystalline P3HT domains (vide infra). As expected, the graft density is relatively low, with only 4.3 mol % P3HT incorporation. The graft density can be increased by decreasing the MMA/macromer ratio (or increasing the macromer in the feed); thus isotactic graft copolymer with 13.2 mol % P3HT was produced with a MMA/macromer ratio of 38/1 (run 3). This feed ratio change also enhanced the isotacticity of the graft copolymer slightly to 94%, while the T g and T m values were essentially the same (run 3 vs. 2). Figure 5 depicts the 1 H-NMR spectrum of it-P(M)MA-g-P3HT, showing that the characteristic peaks of the PMMA main chain and P3HT side chain appeared simultaneously after the copolymerization, while the peaks at 5.60 and 6.17 ppm due to the double bond of the MA end disappeared (see the inset with 7× intensity enhancement). GPC traces of the above two graft copolymers showed unimodal molecular weight distributions with low Ð values from 1.14-1.25 ( Figure 6). In short, these results demonstrated the copolymerization proceeded successfully to form the well-defined isotactic graft copolymer.
Polymers 2017, 9, 139 9 of 15 methacrylate repeat unit, thus a densely grafted polymer, or a brush polymer, it-PMA-g-P3HT, which displayed both glass transition temperature (Tg) and melting-transition temperature (Tm) endothermic peaks on the DSC curve characteristic of the isotactic poly(methacrylate) and crystalline P3HT domains, respectively (vide infra). Likewise, macromer P3HT-(CH2)2-MA was also successfully polymerized by Cs-ligated catalyst Zr-2 + [B(C6F5)4] − to the corresponding syndiotactic brush polymer in 96% yield (run 4). The resulting densely grafted polymer st-PMA-g-P3HT exhibited also both the Tg and Tm values corresponding to the syndiotactic poly(methacrylate) and crystalline P3HT domains, respectively (vide infra). In sharp contrast, macromer P3HT-CH2-MA was not polymerizable by either C2-or Cs-ligated catalysts, even after extended times (up to 12 h), attributable to the sterically hindered ester group of the macromer with only one carbon linkage between the P3HT chain and the MA moiety, which presumably hinders the coordination of this bulkier monomer to the cationic Zr center, the step essential for initiation of this coordination-addition polymerization.
Owing to the overlap between the 1 H-NMR resonances of the hexyl group of P3HT and those of the methyl triads (mm, mr and rr appeared at δ 1.20, 1.02 and 0.82 ppm) of the poly(methacrylate) of the homopolymers, we were unable to obtain the accurate tacticity values of these homopolymers, although it was estimated to be at least >90%. However, this issue was addressed through our study of copolymerizations with MMA. First, the copolymerization of P3HT-(CH2)2-MA with MMA was investigated by C2-ligated Zr-1 + [B(C6F5)4] − with two different MMA/macromer ratios; the relatively high 383/1 MMA/macromer ratio run afforded a high Mw isotactic graft copolymer it-P(M)MA-g-P3HT with Mw = 132 kg/mol, Ð = 1.25, and isotacticity mm% = 92% (run 2). Again, the thermal transitions are consistent with the isotactic poly(methacrylate) and crystalline P3HT domains (vide infra). As expected, the graft density is relatively low, with only 4.3 mol % P3HT incorporation. The graft density can be increased by decreasing the MMA/macromer ratio (or increasing the macromer in the feed); thus isotactic graft copolymer with 13.2 mol % P3HT was produced with a MMA/macromer ratio of 38/1 (run 3). This feed ratio change also enhanced the isotacticity of the graft copolymer slightly to 94%, while the Tg and Tm values were essentially the same (run 3 vs. 2). Figure 5 depicts the 1 H-NMR spectrum of it-P(M)MA-g-P3HT, showing that the characteristic peaks of the PMMA main chain and P3HT side chain appeared simultaneously after the copolymerization, while the peaks at 5.60 and 6.17 ppm due to the double bond of the MA end disappeared (see the inset with 7× intensity enhancement). GPC traces of the above two graft copolymers showed unimodal molecular weight distributions with low Ð values from 1.14-1.25 ( Figure 6). In short, these results demonstrated the copolymerization proceeded successfully to form the well-defined isotactic graft copolymer.

Thermal Behavior of Brush Polymers and Graft Copolymers and Inclusion Complex Formation between C60 and st-P(M)MA-g-P3HT
The thermal transition temperatures of brush homopolymers and graft copolymers were measured by DSC analysis. Typical second heating scans of DSC curves are shown in

Thermal Behavior of Brush Polymers and Graft Copolymers and Inclusion Complex Formation between C 60 and st-P(M)MA-g-P3HT
The thermal transition temperatures of brush homopolymers and graft copolymers were measured by DSC analysis. Typical second heating scans of DSC curves are shown in Figures 7 and 8, displaying both T g and T m for both isotactic and syndiotactic graft homo-and copolymers. As a control, homopolymers it-PMMA, st-PMMA, and P3HT prepared by the current catalyst systems were also analyzed by DSC to show their thermal transitions: T g = 51.8 • C for it-PMMA, T g = 132 • C for st-PMMA, and T m = 222 • C for P3HT. It is clear from the DSC trace ( Figure 7) that isotactic brush polymer it-PMA-g-P3HT obtained from the homopolymerization of macromer P3HT-(CH 2 ) 2 -MA by the C 2 -ligated catalyst exhibited both thermal transitions with T g = 53.2 • C and T m = 224 • C, characteristic of the isotactic poly(methacrylate) and crystalline P3HT domains, respectively, which further demonstrated the successful homopolymerization. For graft copolymer it-P(M)MA-g-P3HT, both thermal transitions were also observed ( Figure 7). Thus, it-P(M)MA-g-P3HT with the relatively low graft density of 4.3 mol % P3HT, the T g and T m values were 51.9 • C and 217 • C, corresponding to the isotactic PMMA and crystalline P3HT domains, respectively. Increasing the graft density to 13.2 mol % P3HT kept the T g and T m values essentially unchanged.
Likewise, syndiotactic brush polymer st-PMA-g-P3HT obtained from the homopolymerization of macromer P3HT-(CH 2 ) 2 -MA by the C s -ligated catalyst also exhibited both thermal transitions with T g = 133 • C and T m = 219 • C, corresponding to the syndiotactic poly(methacrylate) and crystalline P3HT domains, respectively. For the syndiotactic graft copolymer st-P(M)MA-g-P3HT, the observed T g of 112 • C and T m of 218 • C (Figure 8) are attributed to the syndiotactic PMMA main chain and crystalline P3HT side chain domains, again indicating the successful copolymerization of P3HT-(CH 2 ) 2 -MA and MMA. Considering that st-PMMA possesses the unique ability to encapsulate fullerenes such as C60 within its large (~1 nm) helical cavity to form a peapod-like helical crystalline inclusion complex [24] we explored the possibility of syndiotactic graft copolymer st-P(M)MA-g-P3HT to form a crystalline inclusion complex with C60. Thus, the graft copolymer was dissolved in a toluene solution of C60 at 110 °C; after the solution was slowly cooled to room temperature without disturbance, the solution gradually gelled. The strong evidence for successful encapsulation of C60 with the helical hollow space of st-P(M)MA-g-P3HT was provided by DSC analysis (Figure 9). For st-PMMA-g-P3HT/C60 inclusion complex, in addition to the Tg of 114 °C for the st-PMMA main chain and Tm of 194 °C for the crystalline P3HT side chain, a new Tm peak appeared at 241 °C attributed to the crystalline inclusion complex formation. As a control, isotactic graft copolymer it-P(M)MA-g-P3HT did not encapsulate C60 to form an inclusion complex, consistent with the inability of it-PMMA to encapsulate C60 [34,35]. Considering that st-PMMA possesses the unique ability to encapsulate fullerenes such as C60 within its large (~1 nm) helical cavity to form a peapod-like helical crystalline inclusion complex [24] we explored the possibility of syndiotactic graft copolymer st-P(M)MA-g-P3HT to form a crystalline inclusion complex with C60. Thus, the graft copolymer was dissolved in a toluene solution of C60 at 110 °C; after the solution was slowly cooled to room temperature without disturbance, the solution gradually gelled. The strong evidence for successful encapsulation of C60 with the helical hollow space of st-P(M)MA-g-P3HT was provided by DSC analysis (Figure 9). For st-PMMA-g-P3HT/C60 inclusion complex, in addition to the Tg of 114 °C for the st-PMMA main chain and Tm of 194 °C for the crystalline P3HT side chain, a new Tm peak appeared at 241 °C attributed to the crystalline inclusion complex formation. As a control, isotactic graft copolymer it-P(M)MA-g-P3HT did not encapsulate C60 to form an inclusion complex, consistent with the inability of it-PMMA to encapsulate C60 [34,35].  Table 1) produced by the C s -ligated catalyst. Curves for syndiotactic st-PMMA and P3HT are included for comparison.
Considering that st-PMMA possesses the unique ability to encapsulate fullerenes such as C 60 within its large (~1 nm) helical cavity to form a peapod-like helical crystalline inclusion complex [24] we explored the possibility of syndiotactic graft copolymer st-P(M)MA-g-P3HT to form a crystalline inclusion complex with C 60 . Thus, the graft copolymer was dissolved in a toluene solution of C 60 at 110 • C; after the solution was slowly cooled to room temperature without disturbance, the solution gradually gelled. The strong evidence for successful encapsulation of C 60 with the helical hollow space of st-P(M)MA-g-P3HT was provided by DSC analysis (Figure 9). For st-PMMA-g-P3HT/C 60 inclusion complex, in addition to the T g of 114 • C for the st-PMMA main chain and T m of 194 • C for the crystalline P3HT side chain, a new T m peak appeared at 241 • C attributed to the crystalline inclusion complex formation. As a control, isotactic graft copolymer it-P(M)MA-g-P3HT did not encapsulate C 60 to form an inclusion complex, consistent with the inability of it-PMMA to encapsulate C 60 [34,35].

Conclusions
In summary, we have designed and synthesized two P3HT macromers with the polymerizable methacrylate end group. Although macromer P3HT-CH 2 -MA was found to be too sterically hindered to polymerize by the current chiral ansa-zirconocene-based catalysts via the coordination-addition polymerization mechanism, macromer P3HT-(CH 2 ) 2 -MA with eased steric pressure through insertion of one more carbon to the linkage between the P3HT and MA moieties was readily homopolymerized or copolymerized with MMA in the stereospecific fashion. With the C 2 -ligated zirconocenium catalyst 1, highly isotactic brush polymer it-PMA-g-P3HT and graft copolymer it-P(M)MA-g-P3HT with mm% ≥ 92% were readily synthesized under ambient conditions. The P3HT graft density in the graft copolymer can be controlled by the initial MMA/macromer feed ratio. The synthesized isotactic brush polymer and graft copolymers displayed both thermal transitions with the T g and T m values corresponding to the isotactic P(M)MA and crystalline P3HT domains. On the other hand, the C s -ligated zirconocenium catalyst 2 produced highly syndiotactic brush polymer st-PMA-g-P3HT and graft copolymer st-P(M)MA-g-P3HT with rr% ≥ 93%. The resulting syndiotactic brush polymer and graft copolymers also showed both thermal transitions with the T g and T m values corresponding to the syndiotactic P(M)MA and crystalline P3HT domains. With successful encapsulation of the acceptor C 60 by graft copolymer st-P(M)MA-g-P3HT to construct a thermodynamically driven (via molecular recognition), unique supramolecular helical crystalline complex, these new architectures offer a novel strategy to potentially control the donor/acceptor domain morphology of critical importance to the solar conversion efficiency of OPV solar cells.