We present here the application of one-dimensional and two-dimensional NMR techniques to characterize the structure of methoxyl end-functionalized polystyrenes (PS). The peaks in 1H-NMR spectra corresponding to main-chain, side-chain and chain-end groups are assigned by 1H-1H gCOSY, 1H-13C gHSQC and gHMBC spectra. For the first time, the spin-lattice relaxation time (T1) of protons of the chain-ends is revealed to be affected more by polymer molecular weight (MW) than by the protons of the main-chains and the side-chains (almost independent from MW). As a result, a much higher delay time (d1) for chain-ends (d1 > 20T1) is needed for quantitative NMR measurement when using end-group estimation method to obtain the MW of PS, which is in accordance with the value estimated by GPC. An improved method for the polymer MW determination is established, by combination of different NMR techniques to distinguish the peaks, and a large d1 setting to achieve quantitative NMR analysis.

Indene-C60 bisadduct (IC60BA), which can offer a significantly higher open-circuit voltage (Voc) than monoadducts, has become the research focus as electron acceptor materials in polymer solar cells (PSCs) in recent years. However, despite its popularity, IC60BA have always been applied in PSCs as mixture of several regioisomers and the nature of this mixture has never been fully investigated and understood. Herein, for the first time, 12 major regioisomers of IC60BA were isolated and a full investigation was carried out with respect to their structure, abundance, solubility and their corresponding photovoltaic performance. The results show that the PSCs based on these regioisomeric structures present very diverse PCE and their photovoltaic performance was dramatically affected not only by the relative indene positions but also by the steric orientation of the two indene groups. Electrochemical studies further revealed that the effect of energetic disorder inside the IC60BA regioisomers on their photovoltaic performance is insignificant when applied in PSCs. However, the steric structures and solubility of the regioisomers were found to have significant impact on the morphology and bulk properties of the active layer of PSCs, which give rise to very different PCE of devices based on IC60BA regioisomers with different structures.

•A polycondensation-coupling ring-opening polymerization (PROP) method is developed.•(PBT-b-PTMO-b-PBT)n multiblock copolymers were synthesized by the PROP method.•The multiblock copolymers show better thermal stability than PTMO homopolymers.A novel polycondensation-coupling ring-opening polymerization (PROP) method is utilized to synthesize poly(butylene terephthalate)-block-poly(tetramethylene oxide) alternative multiblock copolymers (PBT-b-PTMO-b-PBT)nvia the one pot melt polymerization of cyclic oligo(butylene terephthalate)s (COBTs) and dihydroxy end-functional PTMO (macroinitiator). The proton peaks in 1H NMR spectra corresponding to each block segments, the segmental ends connecting with different blocks, and copolymer chain ends, are assigned by the 1H-1H gCOSY 2D NMR spectra, respectively. The number-average molecular weights of multiblock copolymers and each segment are revealed by an improved quantitative 1H NMR spectra. The results show the molecular weights of the multiblock copolymers increase linearly with reaction time, while the molecular weights for each block segment remain the same, following the PROP mechanism, i.e., the ring-opening polymerization of COBTs by PTMO macroinitiator to form PBT-b-PTMO-b-PBT triblock copolymers at the first stage (short and quickly), then coupling with the condensation polymerization of triblock copolymers to form (PBT-b-PTMO-b-PBT)n alternative multiblock copolymers at the second stage. The mechanism is also supported by GPC results. These multiblock copolymers show improved thermal stability compared with PTMO homopolymers.

The monomer-activating effect imposed by hydrogen bonding has been long acknowledged, however, an in-depth understanding is still lacking. In this work, for the first time, the monomer-activating effect was elucidated with 2-vinyl pyridine (2VP) as the model monomer and 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) as the hydrogen bonding donor (solvent). Strong hydrogen bonding between HFIP and 2VP was revealed by careful 1H NMR analysis and computer simulations. Upon this solid hydrogen bonding, 2VP underwent a well-controlled radical polymerization with improved control over the molecular weight in contrast to those under a non-hydrogen bonding environment. The well-controlled manner of the polymerization was ascribed to the electron induction effect of monomer molecules under hydrogen bonding interactions, i.e., the electron redistribution of the monomer's vinyl double bonds, activating the monomers. The hydrogen bonding interactions between HFIP and growing radicals or HFIP and the terminal monomer units of dormant polymeric species might also contribute to the good control. The unprecedented explanation of hydrogen bonding promoting controlled radical polymerization or a monomer-activating effect was testified for other monomers, and some reasonable discussion was made.

To achieve high refractive index polymers (HRIPs), we report here the design and synthesis of four fullerene polyesters (P1–P4), based on the conjunction effect from the high refractive index polyester backbones and pendent fullerene side chains. At sodium D line (589 nm), the refractive indices of the fullerene polyesters are all higher than 1.80, the used believed upper limitation of intrinsic organic polymers. To achieve precise pendent fullerene structure, these polyesters were synthesized via condensation polymerization by a fullerene diol with different aromatic diacyl chlorides, where the diacyl chlorides with high molar refraction increment value moiety were selected by molecular tailoring according to Lorentz–Lorenz equation. The fullerene polyesters are characterized by gel permeation chromatography (GPC), ultraviolet–visible (UV–vis) spectroscopy, and the molecular weights are obtained by a quantitative NMR technique with end-group estimation. The formation of fullerene polyesters is also proved by the 1H DOSY NMR results. These fullerene polyesters have good solubility in some common organic solvents, good thermal stability up to 320 °C, and film forming ability. All these films have good adhesion to glass sheets with relatively good hardness. Among them, the thiophene-containing fullerene polyesters (P1) has the best optical properties, with the highest refractive index value (1.86 at 589 nm), one of the highest value for intrinsic organic polymers, and the highest Abbe number (27.9).

Indene-C60 bisadduct (IC60BA), which can offer a significantly higher open-circuit voltage (Voc) than monoadducts, has become the research focus as electron acceptor materials in polymer solar cells (PSCs) in recent years. However, despite its popularity, IC60BA have always been applied in PSCs as mixture of several regioisomers and the nature of this mixture has never been fully investigated and understood. Herein, for the first time, 12 major regioisomers of IC60BA were isolated and a full investigation was carried out with respect to their structure, abundance, solubility and their corresponding photovoltaic performance. The results show that the PSCs based on these regioisomeric structures present very diverse PCE and their photovoltaic performance was dramatically affected not only by the relative indene positions but also by the steric orientation of the two indene groups. Electrochemical studies further revealed that the effect of energetic disorder inside the IC60BA regioisomers on their photovoltaic performance is insignificant when applied in PSCs. However, the steric structures and solubility of the regioisomers were found to have significant impact on the morphology and bulk properties of the active layer of PSCs, which give rise to very different PCE of devices based on IC60BA regioisomers with different structures.