Synthesis and characters of hyperbranched poly(vinyl acetate) by RAFT polymeraztion

Reversible addition-fragmentation chain transfer (RAFT) polymerization of VAc in the presence of ECTVA, which capable of both reversible chain transferable through a xanthate moiety and propagation via a vinyl group, led to highly branched copolymers by a method analogous to self-condensing vinyl polymerization (SCVP). The ECTVA acted as a vinyl acetate AB^∗ inimer. It was copolymerized with vinyl acetate (VAc) in ratios selected to tune the distribution and length of branches of resulting hyperbranched poly(vinyl acetate). The degree of branching increased with chain ECTVA concentration, as confirmed by NMR spectroscopy. The polymer structure was characterized via MALDI–TOF. Retention of the xanthate compound during the polymerization was evidenced by successful chain extension of a branched (PVAc) macroCTA by RAFT polymerization. The branched PVAc led to better dissolution as compared to linear PVAc, an effect attributed primarily to an increased contribution of end groups.     

Phosphonate‐terminated poly(vinyl acetate) synthesized by RAFT/MADIX polymerization

Four different xanthates containing either phosphonate or bisphosphonate moieties were synthesized with high degree of purity. These xanthates were used as chain transfer agents (CTA) in the RAFT/MADIX polymerization of vinyl acetate (VAc) to prepare end‐capped poly(VAc). The rate of VAc polymerization in the presence of these new CTAs was shown to be similar to that obtained with conventional xanthate, that is, (methyl ethoxycarbonothioyl) sulfanyl acetate. Good control of VAc polymerization was also obtained since the molecular weight increased linearly with monomer conversion for each phosphonate‐containing xanthate. Low‐PDI values were obtained, ascribed to efficient exchange during RAFT/MADIX polymerization. C_ex value was therefore calculated to about 25, based on RAFT/MADIX of VAc in the presence of rhodixan A1/VAc adduct. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis of diblock copolymers containing poly(N‐vinylcarbazole) by reversible addition‐fragmentation chain transfer polymerization

The reversible addition‐fragmentation chain transfer (RAFT) polymerization of N‐vinylcarbazole (NVK) mediated by macromolecular xanthates was used to prepare three types of block copolymers containing poly(N‐vinylcarbazole) (PVK). Using a poly(ethylene glycol) monomethyl ether based xanthate ( PEG‐X ), the RAFT polymerization of NVK proceeded in a controlled way to afford a series of PEG‐b‐PVK with different PVK chain lengths. Successive RAFT polymerization of NVK and vinyl acetate (VAc) with a small molecule xanthate ( X1 ) as the chain transfer agent was tested to prepare PVK‐b‐PVAc. Though both monomers can be homopolymerized in a controlled manner with this xanthate, only by polymerizing NVK first could give well‐defined block copolymers. The xanthate groups in the end of PVK could be removed by radical‐induced reduction using tributylstannane, and PVK‐b‐PVA was obtained by further hydrolysis of PVK‐b‐PVAc under basic conditions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Bifunctional 2‐(alkoxycarbonothioylthio)acetic acids for the synthesis of TiO2‐poly(vinyl acetate) nanocomposites via RAFT polymerization

Reversible addition‐fragmentation chain‐transfer (RAFT) polymerization has been known as a convenient method for the synthesis of polymers of designed molecular structures. Of particular interest are bifunctional or multifunctional chain‐transfer agents (CTAs) which could be employed in the development of advanced materials via RAFT polymerization. In the present study, four bifunctional 2‐(alkoxycarbonothioylthio) RAFT CTAs with ? COOH functionalities containing methoxy, ethoxy, isopropoxy, and octyloxy groups, respectively, were synthesized and characterized by FTIR and NMR spectroscopy. Polymerizations of vinyl acetate using these CTAs exhibited increased molecular weight with consumption of monomer and relatively narrow dispersities, indicative of living polymerization behavior. The effect of the concentration of 2‐(ethoxycarbonothioylthio) acetic acid on the polymerization was examined, revealing that higher concentration of CTA led to lower molecular weight and narrower dispersity. As an example of the application of the synthesized bifunctional CTAs, TiO₂‐poly(vinyl acetate) (PVAc) nanocomposites were synthesized via a one‐pot process and characterized by TGA, DSC, TEM, and affinity test, suggesting attachment of PVAc onto the nano‐TiO₂ particles. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 606–618     

Reversible addition‐fragmentation chain transfer polymerization of vinyl acetate under high pressure

In this work, high molecular weight polyvinyl acetate (PVAc) (M_n,GPC = 123,000 g/mol, M_w/M_n = 1.28) was synthesized by reversible addition‐fragmentation chain transfer polymerization (RAFT) under high pressure (5 kbar), using benzoyl peroxide and N,N‐dimethylaniline as initiator mediated by (S)‐2‐(ethyl propionate)‐(O‐ethyl xanthate) (X1) at 35 °C. Polymerization kinetic study with RAFT agent showed pseudo‐first order kinetics. Additionally, the polymerization rate of VAc under high pressure increased greatly than that under atmospheric pressure. The “living” feature of the resultant PVAc was confirmed by ¹H NMR spectroscopy and chain extension experiments. Well‐defined PVAc with high molecular weight and narrow molecular weight distribution can be obtained relatively fast by using RAFT polymerization at 5 kbar. © 2015 Wiley Periodicals, Inc. J. Polym. Sci. Part A: Polym. Chem. 2015 , 53, 1430–1436     

Organometallic mediated radical polymerization of vinyl acetate with Fe(acac)2

The radical polymerization of vinyl acetate (VAc) is moderated by iron(II) acetylacetonate (Fe(acac)₂) by the organometallic route (OMRP), as well as by degenerative transfer polymerization (DTP) when in the presence of excess radicals, through the formation of thermally labile organometallic Fe^III dormant species. The poly(vinyl acetate) (PVAc)‐Fe^III(acac)₂ dormant species has been isolated in the form of an oligomer and characterized by ¹H NMR, EPR, and IR methods, and then used as a single‐component initiator for the OMRP of VAc. The degree of polymerization of this isolated oligomeric species demonstrates the limited ability of Fe(acac)₂, relative to the Co(acac)₂ congener, to rapidly trap the growing PVAc radical chain. Control under OMRP conditions is improved by the presence of Lewis bases, especially PMe₂Ph. On the other hand, iron(II) phthalocyanine inhibits the radical polymerization of VAc completely. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3494–3504     

A cyclic selenium‐based reversible addition‐fragmentation chain transfer agent mediated polymerization of vinyl acetate

A cyclic selenium‐based reversible addition‐fragmentation chain transfer (RAFT) agent, 5,5‐dimethyl‐3‐phenyl‐2‐selenoxo‐1,3‐selenazolidin‐4‐one (RAFT‐Se), was synthesized and utilized in the RAFT polymerizations of vinyl acetate (VAc). Its analog, 5,5‐dimethyl‐3‐phenyl‐2‐thioxothiazolidin‐4‐one (RAFT‐S), was also used in RAFT polymerizations for comparison under identical conditions. The RAFT polymerizations of VAc with RAFT‐Se were moderately controlled evidenced by the increase of molecular weights with conversion, despite the slightly high M_w/M_n (less than 1.90), whereas the molecular weights were poorly controlled in the presence of RAFT‐S (2.00 < M_w/M_n < 2.30). Thanks to its unusual cyclic structure of RAFT‐Se, one or more RAFT‐Se species was incorporated into the resultant poly(VAc) as revealed by the results of cleavage of polymer and atomic absorption spectroscopy. Considering the biorelated functions of both poly(VAc) and Se element, this work undoubtedly provided a successful methodology of how to incorporate high content of Se into a molecular weight controlled poly(VAc). © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Solution and aqueous miniemulsion polymerization of vinyl chloride mediated by a fluorinated xanthate

Solution and aqueous miniemulsion polymerizations of vinyl chloride (VC) mediated by (3,3,4,4,5,5,6,6,7,7,8,8,8‐tridecafluorooctyl‐2‐((ethoxycarbonothioyl)thio) propanoate) (X1) were studied. The living characters of X1‐mediated solution and miniemulsion polymerizations of VC were confirmed by polymerization kinetics. The miniemulsion polymerization exhibits higher rate than solution polymerization. Final conversions of VC in the reversible addition‐fragmentation chain transfer (RAFT) miniemulsion polymerization reach as high as 87% and are independent of X1 concentration. Initiation process of X1‐mediated RAFT miniemulsion polymerization is controlled by the diffusion–adsorption process of prime radicals. Due to the heterogeneity of polymerization environments and concentration fluctuation of RAFT agent in droplets or latex particles, PVCs prepared in RAFT miniemulsion exhibit relatively broad molecular weight distribution. Furthermore, chain extensions of living PVC (PVC‐X) with VC, vinyl acetate (VAc), and N‐vinylpyrrolidone (NVP) reveal that PVC‐X can be reinitiated and extended, further confirming the living nature of VC RAFT polymerization. PVC‐b‐PVAc diblock copolymer is successfully synthesized by the chain extension of PVC‐X in RAFT miniemulsion polymerization. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2092–2101     

Polymer-Titanium hybrids obtained by radical polymerization and Sol-Gel process

The possibility to prepare hybrids made by poly(vinyl acetate) (PVAc), poly(methyl methacrylate) (PMMA) and/or poly(ethyl acrylate) (PEtA) with TiO₂ was studied. The processes of polymer formation-radical polymerization and sol-gel process for inorganic network —were achieved simultaneously. Due to a high reactivity of titanium isopropoxide (TIP) in the sol-gel process, a complexant comonomer, allyl acetoacetate (AlAcAc), was used. Covalent bonds between polymer and inorganic chains were obtained by addition of trialkoxysilane derivates with vinyl (VTES) or methacryloyl (MPTS) groups. The presence of TIP inhibits the radical polymerization of vinyl acetate (VAc). The PVAc-TiO₂ hybrids were produced by the sol-gel process of TIP in the presence of pre-obtained PVAc. Except for VTES and MPTS, trialkoxysilane derivates with methyl (MeTES), octyl (OTES) and phenyl (PTES) groups were used. The thermal stability of hybrids is strongly affected by TiO₂ presence and by the type of trialkoxysilane derivates. The thermal stability of PVAc hybrids decreases in the presence of TiO₂ inorganic network. The glass transition temperature of polymers increases in the presence of the inorganic network.     

Controlled synthesis of pH‐responsive amphiphilic A2B2 miktoarm star block copolymer by combination of SET‐LRP and RAFT polymerization

The pH‐responsive amphiphilic A₂B₂ miktoarm star block copolymer, poly(acrylic acid)₂‐poly(vinyl acetate)₂ [(PAA)₂(PVAc)₂], with controlled molecular weight and well‐defined structure was successfully synthesized via combination of single‐electron transfer‐mediated living radical polymerization (SET‐LRP) and reversible addition‐fragmentation chain transfer (RAFT) polymerization methods. First, the precursor two‐armed poly(t‐butyl acrylate) (PtBA)₂ functionalized with two xanthate groups was prepared by SET‐LRP of t‐butyl acrylate in acetone at 25 °C using the novel tetrafunctional bromoxanthate (Xanthate₂‐Br₂) as an Iniferter (initiator‐transfer agent‐terminator) agent. The polymerization behavior showed typical LRP natures by the first‐order polymerization kinetics and the linear dependence of molecular weight of the polymer on the monomer conversion. Second, the A₂B₂ miktoarm star block copolymer (PtBA)₂(PVAc)₂ was prepared by RAFT polymerization of VAc using (PtBA‐N₃)₂(Xanthate)₂ obtained as the macro‐RAFT agent. Finally, the pH‐sensitive A₂B₂ amphiphilic miktoarm star block copolymer poly(acrylic acid)₂‐poly(vinyl acetate)₂ ((PAA)₂(PVAc)₂) was obtained by selectively cleavage of t‐butyl esters of (PtBA)₂(PVAc)₂. All the miktoarm star block copolymers were characterized by GPC, ¹H‐NMR, and FT‐IR spectra. The self‐assembly behaviors of the amphiphilic A₂B₂ miktoarm block copolymers (PAA)₂(PVAc)₂ were also investigated by transmission electron microscopy. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009     

Low temperature suspension polymerization of vinyl acetate using 2,2′-azobis(2,4-dimethylvaleronitrile) for the preparation of high molecular weight poly(vinyl alcohol) with high yield

 To obtain high molecular weight (HMW) poly(vinyl acetate) (PVAc) with high conversion and high linearity for a precursor of HMW poly(vinyl alcohol) (PVA), vinyl acetate (VAc) was suspension-poly-merized using a low-temperature initiator, 2,2′-azobis (2,4-dimethyl-valeronitrile) (ADMVN), and the effects of polymerization conditions on the polymerization behavior and molecular structures of PVAc and PVA prepared by saponifying PVAc were investigated. On the whole, the experimental results well corres-ponded to the theoretically predicted tendencies. Suspension polymerization was slightly inferior to bulk polymerization in increasing molecular weight of PVA. In contrast, the former was absolutely superior to the latter in increasing conversion of the polymer, which indicated that the suspension polymerization rate of VAc was faster than the bulk one. These effects could be explained by a kinetic order of ADMVN concentration calculated by initial-rate method and an activation energy difference of polymerization obtained from the Arrhenius plot. Suspension polymerization at 30 °C by adopting ADMVN proved to be successful in obtaining PVA of HMW (number-average degree of polymerization (P _n)): (4200–5800) and of high yield (ultimate conversion of VAc into PVAc: 85–95%) with diminishing heat generated during polymerization. In the case of bulk polymerization of VAc at the same conditions, maximum P _n and conversion of 5200–6200 and 20–30% was obtained, respectively. The P _n, lightness, and syndiotacticity were higher with PVA prepared from PVAc polymerized at lower temperatures. Received: 10 February 1998 Accepted: 15 April 1998     

Preparation of miktoarm star‐block copolymers PSn‐b‐PVAc4‐n via combination of ATRP and RAFT polymerization

Three tetrafunctional bromoxanthate agents (Xanthate₃‐Br, Xanthate₂‐Br₂, and Xanthate‐Br₃) were synthesized. Initiative atom transfer radical polymerizations (ATRP) of styrene (St) or reversible addition fragmentation chain transfer (RAFT) polymerizations of vinyl acetate (VAc) proceeded in a controlled manner in the presence of Xanthate₃‐Br, Xanthate₂‐Br₂, or Xanthate‐Br₃, respectively. The miktoarm star‐block copolymers containing polystyrene (PS) and poly(vinyl acetate) (PVAc) chains, PS_n‐b‐PVAc_4‐n (n = 1, 2, and 3), with controlled structures were successfully prepared by successive RAFT and ATRP chain‐extension experiments using VAc and St as the second monomers, respectively. The architecture of the miktoarm star‐block copolymers PS_n‐b‐PVAc_4‐n (n = 1, 2, and 3) were characterized by gel permeation chromatography and ¹H NMR spectra. Furthermore, the results of the cleavage of PS₃‐b‐PVAc and PVAc₂‐b‐PS₂ confirmed the structures of the obtained miktoarm star‐block copolymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Cobalt‐Mediated Radical Polymerization of Vinyl Acetate in Miniemulsion: Very Fast Formation of Stable Poly(vinyl acetate) Latexes at Low Temperature

Summary: Poly(vinyl acetate) macroinitiators end‐capped by a Co(acac)₂ complex (PVAc–Co(acac)₂), prepared in bulk by cobalt‐mediated radical polymerization (CMRP), are used for the controlled radical polymerization of vinyl acetate in miniemulsion to give high‐molecular‐weight polymers and high monomer conversion. Stable poly(vinyl acetate) latexes with solid contents ranging from 25 to 30 wt.‐% are prepared within unusually short reaction times (∼1 h) at low temperatures (0–30 °C).

SEC chromatograms for the PVAc–Co(acac)₂ macroinitiator and PVAc latex obtained under ultrasonication for 6 min at 0 °C (79% monomer conversion).     

Cobalt‐Mediated Radical Polymerization of Vinyl Acetate and Acrylonitrile in Supercritical Carbon Dioxide

Cobalt‐mediated radical polymerization (CMRP) of vinyl acetate (VAc) is successfully achieved in supercritical carbon dioxide (scCO₂). CMRP of VAc is conducted using an alkyl‐cobalt(III) adduct that is soluble in scCO₂. Kinetics studies coupled to visual observations of the polymerization medium highlight that the melt viscosity and PVAc molar mass (M_n) are key parameters that affect the CMRP in scCO₂. It is noticed that CMRP is controlled for M_n up to 10 000 g mol⁻¹, but loss of control is progressively observed for higher molar masses when PVAc precipitates in the polymerization medium. Low molar mass PVAc macroinitiator, prepared by CMRP in scCO₂, is then successfully used to initiate the acrylonitrile polymerization. PVAc‐b‐PAN block copolymer is collected as a free flowing powder at the end of the process although the dispersity of the copolymer increases with the reaction time. Although optimization is required to decrease the dispersity of the polymer formed, this CMRP process opens new perspectives for macromolecular engineering in scCO₂ without the utilization of fluorinated comonomers or organic solvents.

     

衰减链转移(DT)聚合醋酸乙烯酯的动力学

在醋酸乙烯酯的普通自由基聚合体系中加入少量碘（质量分数为0.57%～0.86%）,用偶氮二异丁腈作引发剂合成聚醋酸乙烯酯,对其聚合反应的动力学及反应机理进行了研究。 考察了碘质量分数对聚合反应速率、聚合物分子量及分子量分布的影响,发现随着碘浓度的增加,聚合物分子量及分子量分布得到更好的控制;对聚合过程进行了核磁跟踪,考察了聚合过程中几种化合物的变化情况,特别是初级自由基与碘生成的加合物A-I（A来自引发剂分裂后产生的自由基）及单体加合物A-Mn-I（M代表单体单元）的变化情况;对聚合物结构作了详细的1H NMR分析,结果表明,聚合过程中分子量随时间延长而逐渐增大,分子量分布随单体转化率增加而变窄,聚合终期,单体转化率达到80%左右时,所得聚合物分子量分布窄（Mw/Mn≤1.41）,且含有碘端基。该方法的自由基聚合具有活性/可控的性质。     

Xanthates designed for the preparation of N‐Vinyl pyrrolidone‐based linear and star architectures via RAFT polymerization

Novel xanthate RAFT agents, RAFT1‐5, designed for the preparation of a range of novel N‐vinyl pyrrolidone‐based polymeric materials with linear and star architectures via RAFT polymerization are reported. Ethyl pyrrolidone moiety was included in the structures of the xanthates as a part of R (RAFT1‐3) or Z group (RAFT4) to evaluate their effect on the polymerization and to impart homogeneity in the resulting products. The xanthates were designed to fragment to give primary (RAFT1), secondary (RAFT2 and 4), and tertiary radicals (RAFT 3) allowing evaluation of their effect on polymerization. RAFT5 was designed to produce polymeric materials with four‐arm architectures. RAFT1 showed comparable characteristics as conventional radical polymerization. RAFT2 and RAFT4 exhibited living/controlled polymerizations, owing to the combination of stable secondary radical species and incorporation of ethyl pyrrolidone moiety as the R and Z group, respectively. RAFT2 and RAFT5 gave first examples of random copolymers of NVP and VAc with linear and four‐arm star architectures, all exhibiting monomodal distributions and narrow dispersity. The four‐arm PVAc star was used as a macroCTA to synthesize amphiphilic four‐arm star PVAc‐block‐PNVP. The TEM investigation showed the formation of spherical micelles with an average diameter of about 60 nm. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 775–786     

Copolymerization of N-Vinylcarbazole and Vinyl Acetate via Reversible Addition-Fragmentation Chain Transfer (RAFT) Polymerization

Summary: The reversible addition–fragmentation chain transfer (RAFT) random copolymerization of N-vinylcarbazole (NVC) and vinyl acetate (VAc) was carried out using s-benzyl-o-ethyl dithiocarbonate (BED) as the chain transfer agent and 2,2′-azoisobutyronitrile (AIBN) as the initiator in 1,4-dioxane solution at 70 °C. The polymerization showed the characteristics of ‘living’ free radical polymerization behaviors: first order kinetics, linear relationships between molecular weight and conversion, and narrow polydispersity of the polymers. The reactivity ratios of NVC and VAc were calculated via the Kelen–Tudos (KT) and non-linear error in variable (EVM) methods and showed as r₁ = 1.938 ± 0.191, r₂ = 0.116 ± 0.106. The thermal behavior of the copolymers with different content of NVC and VAc was investigated by DSC and TGA. The results showed that the introduction of a VAc segment into copolymer significantly reduced the T_g of the NVC homopolymers. FT-IR spectra, fluorescence spectra, and cyclic voltammetric behavior of these copolymers were also measured and compared with those of NVC homopolymers. The copolymers showed similar oxidative behavior to the NVC homopolymer. However, there was only one reductive potential peak shown for the copolymers at about 0.058 V.     

Seleno‐containing poly(vinyl acetate) prepared by diselenocarbonates‐mediated controlled free radical polymerizations

The living free radical polymerizations of vinyl acetate (VAc) were successfully achieved in the presence of a novel organic selenium compound (diselenocarbonates), with 2,2′‐azobisisobutyronitrile (AIBN) as the initiator. The living characteristics of the VAc polymerization were confirmed by the linear first‐order kinetic plots and linear increase of molecular weights (M_n) of the polymers with monomer conversions, while keeping the relatively low molecular weight distributions. In addition, the end of the polymers contains selenium element which may be useful in biotechnological and biomedical applications. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3159–3165     

The Preparation of PVAc with Lower PDI Through RATRP in Miniemulsion Polymerization

In this paper, reverse atom transfer radical polymerization (RATRP) was used to prepare polyvinyl acetate (PVAc) with lower polydispersity index (PDI). The different reaction parameters such as ligand, catalyst, and surfactant were studied separately to control the polymerization of VAc. The results show that RATRP is not controlled with bpy as ligand, but it is possible to obtain PVAc with low PDI when PMDETA was used as ligand. The molecular weight and the PDI is 10.71×10⁴ and 1.62 when the molar ratio of AIBN/CuCl₂/PMDETA is 1.5:1:2, the molar ratio of AIBN to VAc is 0.5%, surfactant to deionized water is 10 wt%. The molecular weight and the PDI is 12.81×10⁴ and 1.48 when the molar ratio of AIBN/CuCl₂/PMDETA is 2:1:2. The structure of the polymer and the polymer conversion were investigated through ¹H-NMR and gravity method separately. The molecular weight (Mn) and the polydispersity of the obtained polymers were characterized through gel permeation chromatography (GPC).     

Copper(0)‐mediated radical copolymerization of vinyl acetate and acrylonitrile in DMSO at ambient temperature

In this work, Cu(0)‐mediated radical copolymerization of vinyl acetate (VAc) and acrylonitrile (AN) was explored. The polymerization was carried out at 25°C with 2,2′‐bipyridine as ligand and dimethyl sulfoxide as solvent. The copolymerization proceeded smoothly producing moderately controlled molecular weights at low VAc feed ratios. The high VAc feed ratios generated low polymerization rate and poorly controlled molecular weights. FTIR, ¹H NMR, and differential scanning calorimetry confirmed the successful obtaining of the copolymers. Based on ¹H NMR spectra, the reactivity ratios of VAc and AN were calculated to be 0.003 and 1.605, respectively. This work conveyed the first example for the Cu(0)‐mediated radical polymerization of AN and VAc, wherein VAc cannot be homopolymerized by Cu(0)‐mediated radical polymerization technique. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012