SYNTHESIS OF POLY(ETHYLENE TEREPHTHALATE)-POLYCAPROLACTONE BLOCK COPOLYMER BY DIRECT COPOLYMERIZATION*

Poly(ethylene terephthalate) -polycaprolactone block copolymer (PCL- b-PET) is a polyester withimproved biodegradability. In the present paper, a new direct copolymerization method of ε-caprolactone (ε-CL) and bishydroxyethylene terephthalate (BHET) in the presence of Ti(OBu)_4 was proposed for thesynthesis of PCL-b-PET. The PCL-b-PET copolymer was characterized by IR, GPC and ~1H-NMRtechniques, and the effects of synthesis conditions, such as temperature, reaction time and concentration ofcatalyst on the copolymerization were discussed.     

Synthesis and characterization of biodegradable block copolymers of ϵ-caprolactone and D,L-lactide initiated by potassium poly(ethylene glycol)ate

Poly(D ,L -lactide)–poly(ϵ-caprolactone)–poly(ethylene glycol)–poly(ϵ-caprolactone)–poly(D ,L -lactide) block copolymer (PLA–PCL–PEG–PCL–PLA) was prepared by copolymerization of ϵ-caprolactone (ϵ-CL) and D ,L -lactide (D ,L -LA) initiated by potassium poly(ethylene glycol)ate in THF at 25°C. The copolymers with different composition were synthesized by adjusting the mole ratio of reaction mixture. The resulted copolymers were characterized by ¹H-NMR, ¹³C-NMR, IR, DSC, and GPC. Efforts to prepare copolymers with the corresponding structure of PCL–PLA–PEG–PLA–PCL and D ,L -lactide/ϵ-caprolactone random copolymers were not successful. © 1997 John Wiley & Sons, Inc.     

Polymerization of ε-Caprolactone and its Copolymerization with γ-Butyrolactone using Metal Complexes

Solution polymerization of ε-caprolactone (ε-CL) was performed using four different initiators namely: tin(II) octanoate (Sn(Oct)₂)/ethanolamine, aluminium Schiff's base complex-HAPENAlOⁱPr, lithium diisopropyl amide (LDA) and aluminium isopropoxide. The reaction conditions varied with the initiator used. LDA gave rise to the most rapid polymerization with the highest amount of cyclic species as detected by ¹³C NMR. However, no cyclic species were detected when HAPENAlOⁱPr was used as initiator. The tin(II) octanoate/ethanolamine system lead to an α,ω-dihydroxy-polycaprolactone (PCL). The copolymerization of ε-CL was then performed with the hard to oligomerize γ-butyrolactone using the four initiators. GPC (Gel Permeation Chromatography) analyses showed the formation of copolymers. The highest incorporation of polybutyrolactone (PBL) in the copolymer was obtained using HAPENAlOⁱPr as evidenced by ¹H NMR. ¹³C NMR indicated the presence of pseudoperiodic random copolymers with short blocks of PCL whose block length varied with initiator used. The longest and shortest block length were obtained using Sn(Oct)₂ and HAPENAlOⁱPr respectively as calculated from ¹³C NMR. The reactivity ratios were determined using the Finemann-Ross method at low conversion with HAPENAlOⁱPr as initiator. The values obtained, r_CL = 19.4 and r_BL = 0.11, confirmed the presence of long blocks of CL units in the copolymer.     

Block copolymerization of methylmethacrylate via ATRP method using a macroinitiator produced by ring opening polymerization: Characterization,dielectric properties,and a kinetic investigation

Poly(2-(3-methyl-3-phenylcyclobutyloxirane-co-?-caprolactone) [P(PCBO-co-?-CL)] was synthesized by ring opening polymerization (ROP) of 2-(3-methyl-3-phenylcyclobutyloxirane and ?-caprolactone (?-CL) using benzyl alcohol as the initiator and Sn(Oc)₂ as the catalyst. To produce a macroinitiator from copolymer with hydroxyl end group was carried out reaction of acylation with choloroacetyl chloride. The molecular structures of copolymers were confirmed by FT-IR, ¹H-NMR spectroscopies and gel permeation chromatography (GPC). A kinetic series of methyl methacrylate (MMA) via ATRP method were studied in the presence of this macroinitiator and using CuBr/2,2′-bipyridine (bpy) as catalyst at 110°C. The kinetic study showed that the polymerization proceeded in a controlled way up to high conversions and the number-average molecular weight (M_n) increased depending on time. The thermal properties of copolymers were evaluated by TGA and DSC measurements. The temperature and frequency dependence of dielectric constant (?) and dielectric loss factor (?″) of P[(PCBO-co-?-CL)-b-PMMA] and that of doped with different concentration of EuCl₃ were investigated between the frequency of 100–2000 Hz and temperature range (300–430 K). Also, the ac conductivity has been measured to see the effect of frequency and temperature.     

Benzo-12-crown-4 modified N-heterocyclic carbene for organocatalyst: Synthesis,characterization and degradation of block copolymers of ϵ-caprolactone with L-lactide

A set of poly(L-lactide)-poly(?-caprolactone) diblock copolymers (AB) and poly(L-lactide)-poly(?-caprolactone)-poly(L-lactide) triblock copolymers (ABA) with predictable molecular weights and relatively narrow distributions were synthesized by ring-opening polymerization of successively added ?-caprolactone (?-CL) and L-lactide (LLA) using 4-methyl benzo-12-crown-4 imidazol-2-ylidene as catalyst. The effects of polymerization conditions, such as reaction time, temperature, monomer/catalyst molar ratio and monomer concentration on the copolymerization have been discussed in detail. The resulting copolymers were characterized by ¹H-NMR, ¹³C-NMR, IR, GPC and DSC methods which confirmed the successful synthesis of block copolymers of LLA and ?-CL. Hydrolytic degradation of the polymers showed that the PLLA-PCL-PLLA copolymer exhibited faster degradation as compared with the PCL homopolymer in alkaline medium at 37°C.     

New organic-inorganic nanohybrids via ring opening polymerization of (di)lactones initiated by functionalized polyhedral oligomeric silsesquioxane

The synthesis of new organic-inorganic materials were investigated. Poly(ε-caprolactone) and poly(l, l-lactide) covalently end-capped by a polyhedral oligomeric silsesquioxane (POSS) moiety, leading to new nanohybrid materials, were successfully prepared by coordination-insertion ring opening polymerization (ROP) of ε-caprolactone (ε-CL) and l,l-lactide (l,l-LA) respectively. The reaction was initiated from the primary amine available on aminopropylheptakis(isobutyl)POSS nanoparticles and catalyzed by tin(II) 2-ethylhexanoate (tin octoate, Sn(oct)₂). The covalent grafting of the polyester chains onto the POSS “nanocages” was assessed by selective fractionation experiment, Fourier transform infrared spectroscopy (FTIR) and further confirmed by proton nuclear magnetic resonance (¹H NMR). The polymerization proved to be well controlled as attested by the quite narrow polydispersity indices as determined by size exclusion chromatography (SEC). Furthermore, well-defined semi-crystalline poly(ε-caprolactone)-b-polylactide block copolymer carrying such POSS nanoparticle at one end was successfully synthesized attesting for the very efficient control over the polymerization reaction.     

酶促开环聚合和原子转移自由基聚合制备新型H型嵌段共聚物

在生物酶催化剂Novozyme-435的作用下, 乙二醇引发己内酯(ε-CL)酶促开环聚合, 再用三乙胺作催化剂, 将PCL端羟基与2,2-二氯代乙酰氯反应, 生成四官能度大分子引发剂, 引发甲基丙烯酸环氧丙酯(GMA)的原子转移自由基聚合(ATRP), 合成了H型三嵌段共聚物(PGMA)2-b-PCL-b-(PGMA)2. 嵌段共聚物的结构通过核磁共振和凝胶渗透色谱(GPC)得到了确证, 其多分散性为1.32, 分子量为32000. 通过差热扫描量热法对嵌段共聚物的热性能进行了研究.     

Copolymerisation of ε-caprolactone and trimethylene carbonate catalysed by methanesulfonic acid

The copolymerisation of ε-caprolactone (ε-CL) and trimethylene carbonate (TMC) catalysed by methanesulfonic acid was investigated. Preliminary copolymerisation tests using a monofunctional initiator confirm that the side bidirectional propagation previously detected in the homopolymerisation of TMC is also present in the copolymerisation. The comonomers in the ε-CL/TMC system do not follow first order kinetics. The values of the reactivity ratios obtained by the Kellen–Tüdös method (r_ε-CL = 2.90; r_TMC = 0.62) suggest that random copolymerisation can be achieved, although the copolymer will be richer in ε-CL. Dihydroxyl-telechelic ε-CL/ TMC random copolymers were prepared using a bifunctional initiator. ¹H and ¹³C NMR, SEC and DSC measurements show that the poly(TMC-co-ε-CL) samples presented the expected microstructural characteristics, a unimodal molar-mass distribution and a very narrow polydispersity. Based on these features a novel route for the preparation of block copolyesters with tuned properties, and highly regarded in the development of materials for biomedicine, may be foreseen.     

Polymerization of cyclic acetals. I. Polymerization of 1,3,6-trioxacyclooctane and copolymerization with p-methoxystyrene

The polymerization of 1,3,6-trioxacyclooctane initiated by trityl salts with various counterions in CH₂Cl₂ was investigated. The reaction mixtures and the isolated polymers were analyzed by GPC (double detection—IR and UV at 254 nm),¹H-, and¹³C-NMR spectroscopy. In the early stage of polymerization only oligomers (mainly cyclic) were formed. With longer reaction times, linear polymers (yield 86–94%, M = 70,000–80,000) were obtained. The concentration of each individual oligomer passed through a maximum and decreased, reaching its equilibrium concentration. The time interval necessary to reach the maximum concentration increased with n. The total concentration of the oligomers was 0.2 mol L^?1 regardless of the initiator used. Conditions for polymerization with virtually no termination were found. Addition of p-methoxystyrene to the “living” polyacetals resulted in block copolymers. GPC,¹H- and ¹³C-NMR and acidolytic degradation were used to prove the formation of AB block copolymers. The reactive alkoxycarbenium growing species are responsible for the formation of block polyacetal-polymethoxystyrene copolymer.     

辛酸镁催化L-丙交酯与ε-己内酯共聚及其共聚物结构与性能研究

以无毒性的辛酸镁为催化剂催化L-丙交酯和ε-己内酯本体开环共聚合,制备了一系列不同单体配比的共聚物.首先用1H-NMR跟踪了共聚合单体转化率,显示L-LA聚合速率显著快于ε-CL.用13C-NMR分析共聚物微观结构和计算单体单元平均序列长度(LLLe和LCe),表明聚合过程中酯交换反应导致单元序列结构重新分布.随着反应进行,LLLe急剧下降而LCe逐渐增加后稍有降低,游程数逐渐增大,共聚物无规度提高.反应初期主要是一级酯交换反应,二级酯交换反应导致的CLC序列结构在反应后期才观察到.由Fineman-Ross法计算出L-丙交酯和ε-己内酯的竞聚率分别为rLA=23和rCL=0.22,表明在聚合反应初期L-LA单体优先插入聚合物增长链端,形成LL单元长嵌段结构.共聚物组成显著影响单元序列长度,各序列长度随相应单体加入量增加而增长.二级酯交换系数(TII[CLC])随ε-CL含量增加而增大.对于整个组成范围内,根据竞聚率计算的LLLr值始终要大于聚合产物的LLLe,而LCr计算值小于或接近LCe实验值.因此,共聚物单元序列分布随共聚物投料比和反应时间而改变,趋向于无规分布.以DSC和XRD分析了共聚物热性能和结晶性,表明共聚物结晶性与单元序列长度密切相关.所有共聚物只有一个玻璃化转变温度Tg,符合无规共聚物的Fox方程,说明所得共聚物为无规共聚物,或者说包含有相容性嵌段成分的共聚物.     

Effect of microwave energy on chain propagation of poly(ε-caprolactone) in benzoic acid-initiated ring opening polymerization of ε-caprolactone

Microwave-assisted ring opening polymerization of ε-caprolactone (ε-CL) initiated by benzoic acid was investigated. The molar ratio of ε-CL to benzoic acid was 5, 15 and 25. The mixtures of ε-CL/benzoic acid were heated under microwave irradiation and the temperatures were self-regulated to equilibrium from 204 to 240 °C with microwave power ranging from 340 to 680 W. The polymer chain propagated fast between 160 and 230 °C, within which the higher the temperature, the faster the propagation. However, when the temperature was over 230 °C, the resultant poly-(ε-caprolactone) (PCL) degraded. The advantage of microwave-assisted polymerization was that the propagation of PCL chain was significantly enhanced but the formation of growing center at the beginning stage of the polymerization was greatly inhibited. With this metal-free method, PCL with weight-average molar mass (M_w) over 4×10⁴ g/mol was prepared.     

SYNTHESIS AND POLYMERIZATION OF α-METHACRYLYOXYLETHYLOXYCARBONYLMETHYL-ω-(N,N-DIETHYLDITHIOCARBAMYL)POLYSTYRENE MACROMONOMERS

Polystyrene macromonomers with different molecular weight were prepared by radical polymerization of styrene(St) in benzene using β-methacryloxylethyl 2-N,N-diethyldithiocarbamylacetate (MAEDCA) as a monomer-iniferter.Characterization of the macromonomer by ~1H-NMR showed that the end groups were α-methacrylyoxylethyloxycarbonyl-methyl and ω-(N,N-diethyldithiocarbamyl). The macromonomer was difficult to homopolymerize, but it was easilycopolymerized with methyl methacrylate (MMA) initiated by AIBN to form graft copolymers (PMMA-g-PSt) with PStbranches randomly distributed along the PMMA backbone. Copolymerization reaction and the structure of the graftcopolymers were strongly affected by M_n and concentration of the macromonomer. The composition and M_n of the purified graft copolymer were determined by ~1H-NMR and GPC analysis.     

Free-radical copolymerization of styrene with N-phenyl maleimide initiated by thiol

2-Methyl–2-undecanethiol was found efficient to initiate the free-radical copolymerization of styrene (St) with N-phenyl maleimide (NPMI) at 40°C. The initial copolymerization rate increases with the increasing of thiol concentration at first, then keeps constant with the further increasing of the thiol concentration. The charge-transfer complex (CTC) formed between St and NPMI was investigated in different solvents by using ¹H-NMR. There is no definite correlation between CTC equilibrium constant, K, and the polarity of the solvent. With the increasing of CTC concentration, both the copolymerization rate and NPMI content in copolymer enhances, indicating the participation of CTC in both initiation and propagation. The monomer reactivity ratios were calculated to be r_NPMI = 0.052 and r_St ? 0.166, showing an alternating tendency for the copolymerization of St with NPMI. The molecular weight approach has shown again the effect of CTC. The function of thiol as a regulator is mitigated due to the involvement of CTC. © 1992 John Wiley & Sons, Inc.     

Synthesis and Characterization of Four-Arm Star Poly(ϵ-caprolactone)-Block-Poly(cyclic-carbonate methacrylate) Copolymers by Combining Ring-Opening Polymerization With Atom Transfer Radical Polymerization

Well-defined four-arm star poly(?-caprolactone)-block-poly(cyclic carbonate methacrylate) (PCL-b-PCCMA) copolymers were synthesized by combining ring-opening polymerization (ROP) with atom transfer radical polymerization (ATRP). First, a four-arm poly(?-caprolactone) (PCL) macroinitiator [(PCL-Br)₄] was prepared by the ROP of ?-CL catalyzed by stannous octoate at 110°C in the presence of pentaerythritol as the tetrafunctional initiator followed by esterification with 2-bromoisobutyryl bromide. The sequential ATRP of CCMA monomer was carried out by using the (PCL-Br)₄ tetrafunctional macroinitiator (MI) and in the presence of CuBr/2, 2′-bipyridyl system in DMF at 80°C with [(MI)]:[CuBr]:[bipyridyl] = 1:1:3 to yield block polymers with controlled molecular weights (M_n (NMR) = 10700 to 27300 g/mol) by varying block lengths and with moderately narrow polydispersities (M_w/M_n = 1.2–1.4). Block copolymers with different PCL: PCCMA copolymer composition such as 50:50, 70:30 and 74:26 were prepared with good yields (48-74%). All these block copolymers were well characterized by NMR, FTIR and GPC and tested their thermal properties by DSC and TGA.     

Synthesis of poly(4-vinylpyridine) and block copoly (4-vinylpyridine-b-styrene) by atom transfer radical polymerization using 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazamacrocyclotetradecane as ligand

Poly(4-vinylpyridine) (P4VP) and block copolymer, poly(4-vinylpyridine-b-styrene) (P4VP-b-PSt) were prepared by atom transfer radical polymerization (ATRP) using 1-phenylethyl chloride as initiator, CuCl and 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazamacrocyclotetradecane (Me₆[14]aneN₄) as catalyst and ligand. The polymerization of 4VP was carried out in 2-propanol at 40 °C. GPC and NMR studies show that the plot of ln([4VP]₀/[4VP]) against the reaction time is linear, and the molecular weight of the resulting P4VP increased linearly with the conversion. Within 3 h, the conversion can reach almost 90%. P4VP-b-PSt amphiphilic block copolymer with low polydispersity index (M_w/M_n ≈ 1.2) is also obtained by ATRP of St in DMF at 110 °C using P4VP-Cl as macroinitiator, CuCl/ Me₆[14]aneN₄ as catalyst.     

ABC triblock polymethacrylates: Group transfer polymerization synthesis of the ABC,ACB, and BAC topological isomers and solution characterization

ABC triblock copolymers of methyl methacrylate (MMA), (dimethylamino)-ethyl methacrylate (DMAEMA), and tetrahydropyranyl methacrylate (THPMA) consisting of 12 units of each type of monomer were synthesized by group transfer polymerization (GTP). These were the three topological isomers with differentblock sequences: DMAEMA₁₂-THPMA₁₂-MMA₁₂, DMAEMA₁₂-MMA₁₂-THPMA₁₂, and THPMA₁₂-DMAEMA₁₂-MMA₁₂. The molecular weights and molecular weight distributions of the copolymers were determined by gel permeation chromatography (GPC) in tetrahydrofuran, and their number-average degrees of polymerization and copolymer compositions were calculated by proton nuclear magnetic resonance spectroscopy (¹H-NMR). These molecular weights and degrees of polymerization corresponded closely to the values expected from the monomer/initiator ratios. The polydispersities were low as expected for GTP, and ranged from 1.09 to 1.25. The three triblocks were chemically modified by converting the THPMA units to methacrylic acid (MAA) units either by thermolysis or acid hydrolysis. The resulting ABC triblock poly-ampholytes were characterized by ¹H-NMR spectroscopy and hydrogen ion titration. Aqueous GPC studies in 1.0M NaCl at pH 8.5 showed that the triblock copolymers form micelles whose size depends on their block sequence. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 617–631, 1998     

Ring-opening polymerization of degradable polyesters

Medium to high molecular weight random copolymers of 1,5-dioxepan-2-one (DXO) and L-lactide (L-LA) or ε-caprolactone (ε-CL) of different compositions have been investigated. Polymerization was conducted in bulk at 110°C using stannous 2-ethylhexanoate as catalyst. Poly(DXO-co-L-LA) is a hydrolysable material with a glass transition temperature (T_g) ranging from −36 up to 58°C depending on the molar composition. The material exhibited crystallinity as long as the amount of DXO did not exceed 50 weight%. Reactivity ratios were determined to r_L-LA=10 and r_DXO=0.1, giving a more blocky structure than expected in a random copolymer. The copolymer between ε-CL and DXO was shown to be a truly random copolymer by ¹³C NMR, as expected from the reactivity ratios, r_DXO=1.6 and r_ε-CL=0.6. T_g of the material was ranging from −64 up to −39°C. The ability of the poly(DXO-co-ε-CL) to crystallize was retained up to a DXO content of 40 weight%. The melting temperature and crystallinity of both copolymers decrease with increasing amount of DXO. Incorporation of semicrystalline comonomers, L-LA or ε-CL, into the amorphous poly(DXO) creates materials with adjustable properties depending on the molar composition.     

Quasiliving Carbocationic Polymerization. XIV. Synthesis of Poly(styrene-b-Isobutylene)

The synthesis of poly(styrene-b-isobutylenes) by the sequential addition of styrene and isobutylene has been accomplished. First a stream of styrene was added to a cumyl chloride/TiCl₄ in nhexane/methylene chloride charge at -50°C under quasiliving conditions. After the polystyrene block has reached a desirable sequence-length (molecular weight), gaseous isobutylene was continuously introduced to the quasiliving polystyrene carbocation until the polyisobutylene block also reached a desirable molecular weight. The M _n versus monomer input plot was uninterrupted and linear over both monomer introduction phases, indicating quasi-living conditions over the entire regime of block copolymer synthesis. The block copolymers have been characterized by selective solvent extraction and GPC, and their compositions determined by ¹H-NMR spectroscopy.     

Cationic polymerization of styrene initiated by phosphorus oxychloride

Cationic polymerization of styrene (St) initiated by phosphorus oxychloride was carried out at 30° in dichloromethane and nitrobenzene. The rate of polymerization was proportional to (POCl₃) and (St)². The degree of polymerization of the polymer decreased with increasing conversion in the range beyond 30% and increased with increasing (St) although it was independent of (POCl₃) in both solvents. The rate and the degree of polymerization were enhanced with increasing dielectric constant of the mixed solvent composed of C₆H₅NO₂, CH₂Cl₂, and benzene. Addition of water revealed a cocatalytic effect in both systems. The molecular weight distribution (MWD) of the polymer was studied.     

A novel route to the synthesis of PP-g-PMMA copolymer via ATRP reaction initiated by Si-Cl bond

The copolymerization of propylene with allyldimethylsilane (ADMS) was carried out with conventional Ziegler-Natta catalyst supported on MgCl₂. The effects of the concentration of ADMS in the feed on the polymerization reaction and copolymer properties were investigated. The resulting copolymer PP-co-ADMS was chlorinated to PP-Si-Cl by refluxing the copolymer with SOCl₂ in benzene. The chlorinated copolymer was used to initiate ATRP of MMA with CuCl/PMDETA as catalyst to produce graft copolymer PP-g-PMMA, which was characterized with ¹H NMR, ¹³C NMR, GPC and DSC. Polymer blend of iPP/PP-g-PMMA/PMMA was prepared and the results shown that PP-g-PMMA was an effective compatilizer.