Hyperbranched polymers from divinylbenzene and 1,3-diisopropenylbenzene through anionic self-condensing vinyl polymerization

Hyperbranched polymers were synthesized using anionic self-condensing vinyl polymerization (ASCVP) by forming ‘inimer’ (initiator within a monomer) in situ from divinylbenzene (DVB) and 1,3-diisopropenylbenzene (DIPB) using anionic initiators in THF at −40 °C. The reaction of equimolar amounts of DVB and nBuLi results in the formation of hyperbranched poly(divinylbenzene) through self-condensing vinyl polymerization (SCVP). The hyperbranched polymers were invariably contaminated with small amount of gel (<15%). No gelation was observed when using DIBP with anionic initiators. The presence of monomer-polymer equilibrium in the SCVP of DIPB restricts the growth of hyperbranched poly(DIPB). The inimer synthesized from DIPB at 35 °C undergoes intermolecular self-condensation to different extent depending on the nature of anionic initiator at −40 °C. The molecular weight of the hyperbranched polymers was higher when DPHLi was used as initiator. A small amount of styrene ([styrene]/[Li⁺]=1) was used to promote the chain growth by inducing cross-over reaction with styrene, and subsequent reaction of styryl anion with isopropenyl groups of inimer/hyperbranched oligomer. The hyperbranched polymers were soluble in organic solvents and exhibited broad molecular weight distribution (2<M_w/M_n<17).     

Synthesis and characterization of hyperbranched polymers via Cp2TiCl-catalyzed self-condensing vinyl polymerization using glycidyl methacrylate as inimer

Hyperbranched polymers were produced using glycidyl methacrylate (GMA)/Cp₂TiCl₂/Zn as self-condensing vinyl polymerization (SCVP) system. The polymerization is firstly initiated by the epoxide radical ring opening catalyzed by Cp₂Ti(III)Cl generated in situ via the reaction of Cp₂TiCl₂ with Zn. By optimizing the molar ratio of the SCVP inimer (GMA) to the mediator (Cp₂Ti(III)Cl), the active propagation chains are reversibly transformed to the dormant species and the cross-linking does not occur until a higher level of monomer conversion (ca. 80%). We detail this facile one-step polymerization technique to prepare highly branched polymers with a multiplicity of particular end reactive functionalities including Ti alkoxide, hydroxyl and vinyl functional groups, which differs from most previously reported SCVP systems.     

Effect of feed rate on structure of hyperbranched polymers formed by stepwise addition of AB2 monomers into multifunctional cores

Hyperbranched polymers generated from the copolymerization of AB₂-type monomers slowly added into trifunctional C₃ cores under various feed rates were investigated by a kinetic model. The dependences of average molecular weight, polydispersity, degree of branching (DB), and number of structural units of the hyperbranched polymers on the feed rate were calculated by a generating function method. It was found that the final PDI can be attained below 1.5 by a slow addition with the parameter of feed rate, φ, less than 1. While the AB₂ monomers fed quickly, the system with a lower content of the C₃ cores results in a broader molecular weight distribution. A high DB, about 0.66, can be achieved by addition of a small amount of C₃ cores at φ lower than 10.     

Synthesis of hyperbranched polymers via a facile self-condensing vinyl polymerization system - Glycidyl methacrylate/Cp2TiCl2/Zn

A facile self-condensing vinyl polymerization (SCVP) system, the combination of glycidyl methacrylate, Cp₂TiCl₂ and Zn, has been firstly used to prepare novel hyperbranched polymers, consisting of vinyl polymers as the backbone, and cyclic ester polymers (poly(?-caprolactone) or poly(l-lactide)) as the side chains. The polymerizations are initiated by the epoxide radical ring-opening catalyzed by Cp₂Ti(III)Cl which is generated in situ via the reaction of Cp₂TiCl₂ with Zn. The key to success is that the polymerizations can proceed concurrently via two dissimilar chemistries possessing the opposite active initiating species, including ring-opening polymerization (ROP) and controlled/living radical polymerization (CRP). We have demonstrated that this facile one-step polymerization technique can be applied successfully to prepare highly branched polymers with a multiplicity of end reactive functionalities including Ti alkoxide, hydroxyl and vinyl functional groups.     

Preparation of hyperbranched copolymers of maleimide inimer and styrene by ATRP

Novel hyperbranched copolymers were prepared by the atom transfer radical copolymerization of N-(4-α-bromobutyryloxy phenyl) maleimide (BBPMI) with styrene in 1-methyl-2-pyrrolidone (NMP) using the complex of CuBr/2,2′-bipyridine as catalyst. The copolymerization behavior was investigated by comparison of the conversion of double bond of BBPMI determined by ¹H NMR with that of styrene. The hyperbranched structure of resulting copolymers was verified by gel permeation chromatography (GPC) coupled with multi-angle laser light scattering (MALLS). The influences of dosage of catalyst and monomer ratio on the polymerization rate and structure of the resulting polymers were also investigated. The glass transition temperature of the resulting hyperbranched copolymer increases with increasing mole fraction of BBPMI, f_BBPMI. The resulting copolymers exhibit improved solubility in organic solvents; however, they show lower thermal stabilities than their linear analogues.     

Statistical properties for the self-condensing vinyl polymerization in presence of multifunctional core initiators

The self-condensing vinyl polymerization system consisting of inimers and multifunctional core initiators is studied by the principle of statistical mechanics. From viewpoints of functional groups and polymers, two types of canonical partition functions are constructed and further are proved to be consistent with each other. In this way, the explicit expressions of equilibrium free energy and law of mass action concerning the polymerization are obtained, and then the equilibrium size distribution functions of hyperbranched polymers are given. With the help of the size distribution functions, the k-th mean square radii of gyration of hyperbranched polymers with and without a core are derived, respectively. In order to investigate the effect of core initiators on the statistical properties of the system, the number and functionality of core initiators have been explicitly taken into account, and the variations of relevant physical quantities against the conversion of vinyl groups under various conditions are presented. It is shown that the presence of core initiator results in a significant influence on average properties of the system, which can be explained from the competition between polymers with and those without a core initiator in their growth process.     

Synthesis and characterization of hyperbranched azobenzene-containing polymers via self-condensing atom transfer radical polymerization and copolymerization

We report on the synthesis of an azobenzene-containing inimer 6-{4-[4-(2-(2-bromoisobutyryloxy)hexyloxy)phenylazo]phenoxy}hexyl methacrylate (I) and used it to prepare hyperbranched homopolymer and copolymers by self-condensing vinyl polymerization (SCVP) and copolymerization (SCVCP) with its precursor 6-{4-[4-(6-hydroxyhexyloxy)phenylazo]phenoxy}hexyl methacrylate (M) using atom transfer radical polymerization (ATRP). Depending on the comonomer ratio, γ=[M]₀/[I]₀, branched polymethacrylates with number-average weights between 8000 and 20,000 and degree of branching (DB) between 0.08 and 0.49 were obtained by SCVCP, as evidenced by GPC and ¹H NMR analysis. In addition, the photochemical properties of the polymers were also studied by UV-vis spectra and found the structure of polymers affect obviously the trans-cis isomerization properties of the branched polymers.     

Preparation and characterization of hyperbranched polymer grafted mesoporous silica nanoparticles via self-condensing atom transfer radical vinyl polymerization

Hyperbranched poly(2-((bromobutyryl)oxy)ethyl acrylate) (HPBBEA) was grafted onto the exterior surface of mesoporous silica nanoparticles (MSNs) by surface-initiated self-condensing atom transfer radical vinyl polymerization (SCATRVP). The MSNs with ATRP initiator anchored on the exterior surface (MSN-Br) were prepared by the reaction of 5,6-dihydroxyhexyl-functionalized MSNs (MSN-OH) with α-bromoisobutyryl bromide. Afterwards, MSN-Br was utilized as initiator in the SCATRVP of inimer BBEA, resulting in core-shell nanoparticles with MSN core and HPBBEA shell (MSN-g-HPBBEA). The molecular weight of HPBBEA increased with the increasing ratio of BBEA to MSN-Br. In view of the high density of bromoester groups on the surface of HPBBEA shell, MSN-HPBBEA was used to initiate the successive polymerization of (2-dimethylamino-ethylmethacrylate) (DMAEMA), forming core-shell nanoparticles MSN-g-HPBBEA-g-PDMAEMA. The resultant products were characterized by FT-IR, NMR, HRTEM and thermogravimetric analysis (TGA), etc. The pH-responsive property of MSN-g-HPBBEA-g-PDMAEMA was characterized by measuring the hydrodynamics radius at different pH values, and this core-shell nanostructure may have potential applications in biomedicine and biotechnology.     

Preparation of hyperbranched polymers through ATRP of in situ formed AB* monomer

The self‐condensing vinyl polymerization of an AB* monomer formed in situ by atom transfer radical addition from divinylbenzene (DVB) and (1‐bromoethyl)benzene (BEB) using atom transfer radical polymerization technique was studied. The catalyst concentration has a dramatic effect on polymerization. To study the polymerization mechanism and to achieve high molecular weight polymer, the polymerization was carried out in bulk with a catalyst to monomer ratio, 2,2′‐bipyridine to DVB, of 0.2 at 90°C. Proton nuclear magnetic resonance (¹H NMR) spectroscopy and size‐exclusion chromatography coupled with multiangle laser light scattering were used to analyze the polymerization aliquots and the obtained polymer. The intrinsic viscosities of the prepared polymers were also measured. Experimental results, from the comparison of the apparent molecular weights measured by size‐exclusion chromatography with the absolute values measured by multiangle laser light scattering as well as viscosity measurements, indicate the existence of hyperbranched structures in the prepared polymers. In sharp contrast to hyperbranched polymers from AB* monomer preprepared, hyperbranched ploy(divinylbenzene) prepared at equimolar amount of DVB and BEB has numerous residual pendant vinyl groups rather than only one double bond at its focal point. The hyperbranched polymers show relatively narrow molecular weight distribution (2.13–3.77) and exhibit excellent solubility in common organic solvents such as acetone. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 850–856, 2006     

Distribution function of hyperbranched polymers formed by AB2 type polycondensation with substitution effect

By kinetic model, the analytical expression of the distribution function for the hyperbranched polymers formed from AB₂ type polycondensation with substitution effect was derived. The results are compared to those for self-condensing vinyl polymerization of AB* monomers. Reaction becomes faster with the increasing reactivity of a linear B group. At any finite conversion of A group, both average degree of polymerization and dispersity increase with the increase of low rate constant, r (ratio of the reactivity of a linear B group to that of a terminal B group). However, the variation of these parameters is moderate if r>100 and they converge to respective limiting value. The average degree of polymerization and dispersity are much smaller than that of self-condensing vinyl polymerization of AB* monomers at the same conversion.     

Kinetic analysis of co-polycondensation of AB2 and AB type monomers in presence of multi-functional cores

This work theoretically deals with the kinetics of the co-polycondensation of AB₂ and AB type monomers in the presence of multi-functional cores. The analytical expressions of the molecular size distribution function and the molecular parameters of the resultant hyperbranched polymers were derived. The general expressions are applicable for the copolymerization of AB₂ and AB monomers and the polymerization of homogeneous AB₂ or AB monomers in either presence or absence of cores. The feed ratio of the core molecules (β) or the AB₂ monomers (α) to the total monomers significantly affects the molecular weight distribution and the molecular parameters of the products. The polydispersity index of the copolymerization of AB₂ and AB monomers without cores is infinite when the reaction approaches to completion, while the presence of core molecules makes it become finite. The polydispersity index decreases with decreasing α, which also decreases with increasing β. The higher the functionality of the core (f), the lower the polydispersity index is as well.     

Preparation of hyperbranched polymers by atom transfer radical polymerization

A cheap acrylic AB* monomer, 2‐(2‐chloroacetyloxy)‐isopropyl acrylate (CAIPA), was prepared from 2‐hydroxyisopropyl acrylate with chloroacetyl chloride in the presence of triethylamine. The self‐condensing vinyl polymerization by atom transfer radical polymerization (ATRP), a “living”/controlled radical polymerization, has yielded hyperbranched polymers. All the polymerization products were characterized by proton nuclear magnetic resonance spectroscopy (¹H NMR). CAIPA exhibited distinctive polymerization behavior that is similar to a classical step‐growth polymerization in the relationship of molecular weight to polymerization time, especially during the initial stage of the polymerization. However, a significant amount of monomer remained present throughout the polymerization, which is consistent with typical chain polymerization. Also, if a much longer polymerization time was used, the polymer became gel. As a result of the unequal reactivity of group A* and B*, the polymerization is different from an ideal self‐condensing vinyl polymerization: the branch structures of polymers prepared depend dramatically on the ratio of 2,2'‐bipyridyl to CAIPA. Hyperbranched polymers exhibit improved solubility in organic solvent, however, they have lower thermal stability than their linear analogs. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2114–2123, 2002     

Kinetic analysis of AB2 polycondensation in the presence of multifunctional cores with various reactivities

This work is theoretically dealt with the kinetics of polycondensation of AB₂-type monomers in the presence of multifunctional cores (C_f) with various reactivities. The analytical expressions of the molecular size distribution function and the molecular parameters of the resultant hyperbranched polymers were derived. The conversion of A groups (x), feed ratio of the core/monomer (β), functionality of the core (f), and reactivity ratio of C to B (r) significantly effect the molecular weight distribution and the molecular parameters of the products. High feed ratio, functionality and reactivity of the core can improve the molecular weight distribution and decrease the polydispersity for the resultant products. Compared with the polycondensation of equal reactivity, the effect of the core which has enough high reactivity on the polydispersity is equal to doubling the functionality of the core.     

Two-photon absorption properties of hyperbranched conjugated polymers with triphenylamine as the core

Two new hyperbranched phenylene vinylenes (HPVs) with triphenylamine as the core, 2,5-dihexyloxyl substituted phenylene vinylene as the connecting unit, and electron-donating triphenylamine or electron-deficient nitrobenzene as the different terminal groups were synthesized by modified Wittig polymerization reaction. Their one- and two-photon absorption (TPA) properties have been investigated. The two-photon absorption cross sections of the two polymers were performed by open-aperture Z-scan experiment using 120 femtosecond (fs) pulse, and their TPA cross section were determined to be 1.43 and 0.64×10⁻²⁰ cm⁴/GW per repeating unit at 800 nm, respectively. In chloroform, HPVs exhibit intense frequency up-converted fluorescence under the excitation of 120 fs pulses at 800 nm with the peaks located at 544 and 554 nm, respectively.     

Influence of reaction parameters on the synthesis of hyperbranched polymers via reversible addition fragmentation chain transfer (RAFT) polymerization

The synthesis of hyperbranched poly(methyl methacrylate) (PMMA) via reversible addition fragmentation chain transfer (RAFT) polymerization was investigated by varying the ratio chain transfer agent (CTA): monomer (methyl methacrylate, MMA): brancher (ethylene glycol dimethyl methacrylate, EGDMA): free radical initiator (AIBN) at various temperatures (50, 55, 60, 65, 70 °C). The rate of polymerization was observed to increase with temperature and concentration in brancher, whilst it was lowered by an increase in chain transfer agent concentration. The molecular weight of the samples increased with the ratios brancher: CTA and monomer: CTA. The polydispersity of the samples increase with conversion, as the level of branching increases. At fixed concentration in brancher, an increase of CTA concentration led to polymers with lower PDI. The variation of enthalpy and entropy relative to the monomer reaction were calculated, and it was observed that an increase in the brancher concentration induced an increase in both and , whilst lower CTA concentrations led to an increase in . The variation in Gibbs energy for the monomer reaction was calculated at 60 °C, and results confirmed the presence of a retardation effect when increasing CTA concentration generally observed in RAFT polymerization.     

Synthesis of ultrahigh molecular weight phenolic polymers by enzymatic polymerization in the presence of amphiphilic triblock copolymer in water

An enzymatic oxidative polymerization of phenols was investigated in the presence of poly(ethylene glycol) (PEG)-poly(propylene glycol) (PPG)-poly(ethylene glycol) (PEG) triblock copolymer (Pluronic) in water. The formation of micellar aggregate of phenol and Pluronic by hydrogen bonding interaction in an aqueous solution was verified by DLS measurement. The PEG content of Pluronic greatly affected the polymerization behaviors. Using Pluronic with high PEG content improved the regioselectivity of the polymerization of phenol to give the polymer mainly consisting of phenylene unit. The polymerization in the presence of Pluronic F68 (EG₇₆-PG₂₉-EG₇₆) produced the phenolic polymer with ultrahigh molecular weight (M_w > 10⁶). From other phenols, high molecular weight polymers were also obtained. In addition, the FT-IR, DSC, and XRD analyses exhibited the formation of miscible complex between the phenolic polymer and Pluronic by hydrogen bonding interaction.     

黄原酸酯调控的氯乙烯的可逆-加成断裂链转移聚合

以三种不同结构的黄原酸酯为调控剂,进行氯乙烯（VC）溶液和细乳液可逆加成-断裂链转移（RAFT）聚合,发现O-乙基黄原酸丙酸乙酯对VC聚合的调控效果良好,氯乙烯RAFT细乳液聚合速率明显大于溶液聚合,VC聚合12 h转化率大于90%,但聚氯乙烯（PVC）的分子量分布宽于溶液聚合产物。核磁共振和紫外可见吸收光谱分析证明合成的PVC具有黄原酸酯基端基结构,结构缺陷少。含黄原酸酯基PVC可进一步调控VC及醋酸乙烯酯聚合,进行扩链或得到嵌段共聚物。结合聚合动力学,说明黄原酸酯调控的氯乙烯聚合具有活性特征。     

Template polymerization of sodium vinyl sulphonate in the presence of poly(allylamine) hydrochloride

The radical polymerization in aqueous solution of sodium vinly sulphonate in the presence of poly(allylamine) hydrochloride as a template has been studied using dilatometry and the obtained polyelectrolyte complexes have been characterized by viscosimetric and thermal analysis. The time–conversion curves have shown an unusual trend characterized by a slowing down phase followed by an increase in the polymerization rate. The same trend has been observed at various reaction temperatures, and at different monomer concentrations. The results of the viscosimetric analysis have indicated that the molecular weight of the formed polymer increases by increasing the initial template concentration, the other operating conditions remaining unchanged. The mechanism of this template polymerization is discussed in this paper.     

Resins containing extractants: Morphology of polymers prepared by polymerization of vinyl monomers in the presence of uranium-selective extractants

The effect of a selective organophosphours extractant on the structure and properties of crosslinked polymers was studied. The extractant, incorporated in the polymerization mixture, affected the formation of the polymer. The uranium capacity of the resin was directly proportional to the amount of extractant. The use of scanning electron microscopy showed that the polymers are macroporous and that the porosity depends on the amounts of extractant and crosslinking agent.     

氯乙烯聚合技术研究进展

对2009年美国《化学文摘》报道的氯乙烯自由基聚合、活性自由基聚合和茂金属催化聚合方面的论文和专利进行了综述。