Synthesis of graft copolymers. Part I. Synthesis of macroinitiators

Thermal polymeric initiators, having pendant 1,2-bis(trimethylsilyloxy)tetraphenylethane (or benzopinacolate) groups along the chain, have been prepared. First, the reactivity ratios of 4-vinylbenzophenone (4VBP) and 4-methacryloyloxybenzophenone (MOB) copolymers with styrene or methylmethacrylate were determined. Then the randomly containing 4VBP or MOB copolymers were transformed into polymeric initiators by duplication reaction of the attached benzophenone. Polymerization of MMA or St initiated by the resulting copolymers having pendant benzopinacolate groups was carried out yielding PMMA-g-PS and PS-g-PMMA. © 1995 John Wiley & Sons, Inc.     

Cationic ring-opening polymerization of 2-phenyl-1,3,6,2-trioxaphosphocane

Summary The ring-opening polymerization of 2-phenyl-1,3,-6,2-trioxaphosphocane (4), an eight-membered cyclic phosphonite, has been investigated. Cationic initiators of PhCH₂-Cl and MeOTf gave polymers, whereas anionic and radical initiators did not yield polymer. The structure of polymer was examined by IR, ¹H, ³¹P, and ³¹C NMR spectroscopy of polymers and elemental analysis as well as the alkaline hydrolysis products. The polymer consisted of two different units, i.e., the major part is the normal phosphinate structure 5 and the minor part is the isomerized unit 6 in 7% with PhCH₂Cl initiation and in 34% with MeOTf initiator. The difference in nature of propagating species from these two initiators are discussed in connection with their reactivities.On leave from the Institute of Chemistry, Academia Sinica, Beijing, China     

Wool graft copolymers initiated by azobisisobutyronitrile

Grafting of methyl methacrylate onto wool fibers using azobisisobutyronitrile as initiator has been investigated under a variety of conditions. Increasing the monomer concentration caused a significant increase in the graft yields. The same holds good for initiator concentration and reaction time, but to a lower degree. The grafting reaction was favorably influenced considerably by the nature of solvent used; it follows the order methanol > dimethylformamide > benzene. For practical significance, a mixture of water:methanol:DMF (75:24:1) was found to be the most effective medium for grafting. Presence of lithium chloride in the polymerization system favors grafting during the later stages of reaction, whereas presence of ceric sulfate was effective for higher grafting in the initial stages of reaction. Reduction of wool prior to grafting enhanced its ability to grafting; the latter increases in proportion to the thiol content. The opposite holds true for acetylation. Alkali solubility measurements reveal that an interaction between wool and methyl methacrylate in presence of AIBN took place.     

Cationic ring-opening polymerization of 2-substituted-2-oxazolines initiated by carbon black surface

Summary Carbon blacks were found capable of initiating the ringopening polymerization of 2-substituted-2-oxazolines at relativery high temperatures. The activation energy of the polymerization of 2-methyl-2-oxazoline was estimated to be 13.4 kcal/mol. Carbon black lost the initiating activity of the polymerization upon the blocking of carboxyl groups on the surface by the treatment with potassium hydroxide or diazomethane. Therefore, it was concluded that carboxyl groups on carbon black play an important role in the initiation of the polymerization. Furthermore, it was found that during the polymerization, poly(N-acylethyleneimine) was grafted onto carbon black by the termination of growing polymer chain with the surface.     

Organization of poly(2-ethyl-2-oxazoline)-block-poly(2-phenyl-2-oxazoline) copolymers in water solution

Diblock copolymers were prepared from 2-ethyl-2-oxazoline and 2-phenyl-2-oxazoline via living cationic polymerization using sequential addition of the monomers. Copolymer assemblies in aqueous solutions and on surface were studied with respect to changes in the hydrophilic-hydrophobic balance induced by increasing the length of the hydrophobic poly(2-phenyl-2-oxazoline) segment while the hydrophilic poly(2-ethyl-2-oxazoline) chain was kept constant with an average of 60 monomer units. The copolymer with a short segment of four 2-phenyl-2-oxazoline units assembled into highly hydrated aggregates that decreased twice in size after drying. Their structure was destroyed and network morphologies were formed upon spin-coating. The increase of the length of the hydrophobic segment resulted in aggregates that dissociated to micelle-sized particles when subjected to mechanical shear by spin-coating or filtering. These observations imply that the aggregates are multi-core structures originating from the assembly of primarily formed micelles. The copolymer self-assembly was evidenced by a combination of techniques: DLS, SLS, AFM and SEM.     

Synthesis of block copolymers from PDMS macroinitiators

The synthesis of polystyrene‐b‐polydimethylsiloxane‐b‐polystyrene (PSt‐b‐PDMS‐b‐PSt) copolymers is described. Commercially available difunctional PDMS containing vinylsilyl terminal species was reacted with hydrogen bromide resulting in the PDMS macroinitiators. The terminal alkyl bromide groups were then used as initiators for atom transfer radical polymerization (ATRP) to produce block copolymers. Using this technique, triblock copolymers consisting of a PDMS centre block and polystyrene terminal blocks were synthesized. ATRP of St from those macroinitiators showed linear increases in M_n with conversion, demonstrating the effectiveness of ATRP to synthesize a variety of inorganic/organic polymer hybrids. Copyright © 2004 Society of Chemical Industry     

Synthesis of comb-shaped copolymers by combination of reversible addition-fragmentation chain transfer polymerization and cationic ring-opening polymerization

Comb-shaped graft copolymers with poly(methyl acrylate) as a handle were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization and ring-opening polymerization (ROP) techniques in three steps. First, copolymers of poly(styrene-co-chloromethyl styrene), poly(St-co-CMS), were prepared by RAFT copolymerization of St and CMS using 1-(ethoxycarbonyl)prop-1-yl dithiobenzoate (EPDTB) as RAFT agent. Second, the polymerization of MA using poly(St-co-CMS)-SC(S)Ph as macromolecular chain transfer agent produced block copolymer poly(St-co-CMS)-b-PMA. Third, cationic ring-opening polymerization of THF was performed using poly(St-co-CMS)-b-PMA/AgClO₄ as initiating system to produce comb-shaped copolymers. The structures of the poly(St-co-CMS), poly(St-co-CMS)-b-PMA and final comb-shaped copolymers were characterized by ¹H NMR spectroscopy and gel permeation chromatography (GPC).     

Multifunctional ATRP macroinitiators for the synthesis of graft copolymers

Multifunctional ATRP macroinitiators, polystyrene with 1-(2-bromopropionyloxy)ethyl or 1-(2-bromoisobutyryloxy)ethyl groups in the benzene rings and poly[4-methylstyrene-co-4-(bromomethyl)styrene], were synthesized. All the functionalized polymers were characterized by IR, ¹H and ¹³C NMR spectroscopy and by size exclusion chromatography.     

Cationic ring-opening polymerization of 2-phenyl-1,2-oxaphospholane (deoxophostone)

Summary The ring-opening polymerization of deoxophostone 5, a five-membered cyclic phosphinite, has been studied. Some cationic initiators gave polymer whereas anionic and radical initiators as well as metal chloride (Lewis acid) catalysts did not yield polymer. The polymer consisted of a phosphine oxide repeating unit 6. The polymerization proceeded via the Arbuzov-type reaction. The reduction of polymer 6 with a HSiCl₃/Et₃N system gave polyphosphine 7.     

Synthesis and characterization of graft copolymers with poly(epichlorohydrin-co-ethylene oxide) as backbone by combination of ring-opening polymerization with living anionic polymerization

Series of graft copolymers with [Poly(epichlorohydrin-co-ethylene oxide)] [Poly(ECH-co-EO)] as backbone and polystyrene (PS), poly(isoprene) (PI) or their block copolymers as side chains were successfully synthesized by combination of ring-opening polymerization (ROP) with living anionic polymerization. The Poly(ECH-co-EO) with high molecular weight (M_n = 3.3 × 10⁴ g/mol) and low polydispersity index (PDI = 1.34) was firstly synthesized by ring-ROP using ethylene glycol potassium as initiator and triisobutylaluminium (i-Bu₃Al) as activator. Subsequently, by “grafting onto” strategy, the graft copolymers Poly(ECH-co-EO)-g-PI, Poly(ECH-co-EO)-g-PS and Poly(ECH-co-EO)-g-(PI-b-PS) were obtained using the coupling reaction between living PI⁻Li⁺, PS⁻Li⁺ or PS-b-PI⁻Li⁺ species capped with or without 1,1-diphenylethylene (DPE) agent and chloromethyl groups on poly(ECH-co-EO). By model experiment, the addition of DPE agent was confirmed to have an important effect on the grafting efficiency at room temperature. Finally, the target graft copolymers and intermediates were characterized by SEC, ¹H NMR, MALLS and FTIR in detail, and thermal behaviours of the graft copolymers were also investigated by DSC measurement.     

Synthesis of biopolymer-grafted nanodiamond by ring-opening polymerization

We have developed an efficient and biological method for the covalent functionalization of nanodiamond (ND) biopolymers. ND-grafted-poly(l-lactic acid) (ND-g-PLLA) and ND-grafted-poly(ε-caprolactone) (ND-g-PCL) were prepared by surface-initiated ring-opening polymerization. After homogenization of the surface by mixed acids and thionyl chlorides, the surface of ND was modified with 1,6-hexanediol to possess hydroxyl groups, which could be used as coinitiators to polymerize l-lactide or ε-caprolactone to yield ND grafted with bio-polyesters. The FT-IR, Raman and NMR spectra revealed that the polyester chains were covalently attached to the ND and the weight gains as a result of the functionalized ND particles were determined by TGA analysis. The ND-g-PLLA and ND-g-PCL were both well dispersed in the organic solvents and the average diameters were measured. The TEM images demonstrate that the dispersion of pristine ND has been significantly improved after modification of ND with PLLA or PCL.     

新型环境友好材料聚乳酸合成工艺研究

以工业乳酸为原料,采用开环聚合法对聚乳酸合成工艺进行系统研究,对传统工艺中的催化剂及投加方式作了改进。在丙交酯合成工艺中,采用ZnO/La2O3作催化剂并分2次顺序加入,明显提高了丙交酯的产率(达52%);在丙交酯开环聚合工艺中,采用辛酸亚锡甲苯溶液作催化剂,在反应温度为130—180℃,反应时间8h,体系真空度控制在0.098MPa的条件下,制备出聚乳酸的分子质量达到2.4×104g/mol,优于文献报道。     

Synthesis of latex particles by ring-opening metathesis polymerization

This paper reviews the recent discoveries that were achieved by our group in the field of particle synthesis via ring-opening metathesis polymerization (ROMP). Both polynorbornene and polybutadiene-based particles were prepared by the respective ROMP of norbornene and cyclooctadiene initiated by (PCy₃)₂Cl₂RuCHPh using several methods of polymerization in dispersed media, such as dispersion, suspension and miniemulsion. Depending upon the process implemented, particles size was found to range from 300 nm to 20 μm.     

Synthesis of amphiphilic copolymers by ATRP initiated with a bifunctional initiator containing trichloromethyl groups

Bifunctional polystyrene macroinitiators, having various molecular weights, were prepared by atom transfer radical polymerization (ATRP), initiated with bifunctional initiator 1,3-bis{1-methyl-1[(2,2,2-trichloroethoxy) carbonylamino]ethyl}benzene in conjunction with CuCl catalyst and polyamine ligands. These macroinitiators were subsequently used for ATRP of tert-butyl acrylate (t-BuA), giving BAB triblocks poly[(t-BuA)-b-(Sty)-b-(t-BuA)] as precursors of amphiphilic copolymers. Both the polymerization steps proceeded as controlled processes with linear semi-logarithmic conversion plots and lengths of the blocks following theoretical predictions. Hydrolysis of outer poly(t-BuA) blocks led to triblock copolymers with the central polystyrene block and outer blocks of poly(acrylic acid), the molecular weights of which ranged from ca. 5 × 10³ to almost 1 × 10⁵ Da.     

Precise synthesis of polymers containing functional end groups by living ring-opening metathesis polymerization (ROMP): Efficient tools for synthesis of block/graft copolymers

This article summarizes recent examples for precise synthesis of (co)polymers containing functional end groups prepared by living ring-opening metathesis polymerization (ROMP) using molybdenum, ruthenium complex catalysts. In particular, this article reviews recent examples for synthesis of amphiphilic block/graft copolymers by adopting transition metal-catalyzed living ROMP technique. Unique characteristics of the living ROMP initiated by the molybdenum alkylidene complexes (so-called Schrock type catalyst), which accomplish precise control of the block segment (hydrophilic and hydrophobic) as well as exclusive introduction of functionalities at the polymer chain end, enable us to provide the synthesis of block copolymers varying different backbones by adopting the “grafting to” or the “grafting from” approach as well as “soluble” star shape polymers with controlled manner. The “grafting through” approach (polymerization of macromonomers) by the repetitive ROMP technique offers precise control of the amphiphilic block segments.     

Synthesis of novel block copolymers containing polyhedral oligomeric silsesquioxane (POSS) pendent groups via ring-opening metathesis polymerization (ROMP)

Ring-opening metathesis copolymerization of norbornene ethyl polyhedral oligomeric silsesquioxane monomer (NBEPOSS) and 2-endo-3-exo-5-norbornene-2,3-dicaboxylic acid trimethyl ester (NBETMS) was performed using a Ru-based catalyst, RuCl₂(CHPh)(PCy₃)₂. The block copolymers poly(NBETMS-b-NBEPOSS) were then converted to poly(NBECOOH-b-NBEPOSS) by hydrolysis and precipitation. The polymers were characterized by NMR and GPC and the actual NBEPOSS contents were found in good correspondence with the theoretical values. A linear dependence of M_n on conversion and a linear dependence of ln([M₀]/[M]) on reaction time observed in the polymerization of NBETMS suggest that chain breaking reactions such as termination and chain transfer are minimal. Low PDI values and smooth GPC peak shifts during polymerization after addition of a second batch of the same monomer or a NBEPOSS monomer also reflect a living process.     

Synthesis of the model macroinitiators of free radical polymerization and their application for the preparation of block copolymers

A series of polystyrenes having low molecular weight (4600–23,100) and narrow molecular weight distribution and functionalized with a benzophenone group at one or both ends of the chain have been prepared through anionic polymerization. Then the terminal benzophenone groups have been transformed into 1,2-bis(trimethylsilyloxy)tetraphenylethane (or benzopinacolate) groups by the duplication reaction with free benzophenone in the presence of chlorotrimethylsilane and hexamethylphosphorous triamide (HMPT) or hexamethylphosphoramide (HMPA), producing model thermal macroinitiators of free radical polymerization with well-defined structure. Polymerization of MMA initiated by these macroinitiators was carried out yielding poly(styrene-b-methyl-methacrylate) (PS-b-PMMA). © 1996 John Wiley & Sons, Inc.     

Synthesis and polymerization of 2-(β-N-ethylenediphenylamine)-2-oxazoline

Summary The synthesis of 2-(-N-ethylenediphenylamine)-2-oxazoline and its living cationic polymerization in the presence of methyltosylate are described. This 2-substituted 2-oxazoline was used for the synthesis of a ABA triblock copolymer with poly(N--(N-diphenylamine)propionylethylenimine) as A block and poly(ethyleneglycoladipate) as B block.