聚乙烯基环己烷-聚乙烯-聚乙烯基环己烷三嵌段共聚物溶液的受限结晶研究

嵌段共聚物由于组分间的化学不相容性而发生微相分离,组装成各种有序的纳米结构,如球、圆柱、层及双连续结构等．半晶型嵌段共聚物由于引入了能结晶的组分,使体系中存在两种相互竞争的过程,即微相分离与结晶,所以能形成更为丰富的有序结构．聚乙烯基环己烷-聚乙烯-聚乙烯基环己烷[Poly(Vinylcyclohexane)-b-poly(ethylene)-b-poly(vinylcyclohexane),     

Synthesis and characterization of poly(vinylcyclohexane) derivatives

Six nearly monodisperse substituted poly(styrene) homopolymers, poly(styrene) (PS), poly(2-methylstyrene) (P2MS), poly(3-methylstyrene) (P3MS), poly(4-methylstyrene) (P4MS), poly(tertiary-butylstyrene) (PtBS), and poly(α-methylstyrene) (FαMS) were anionically polymerized and subsequently saturated using heterogeneous hydrogenation techniques to poly(vinylcyclohexane) (PVCH), poly(2-methylvinylcyclohexane) (P2MVCH), poly(3-methylvinylcyclohexane) (P3MVCH), poly(4-methylvinylcyclohexane) (P4MVCH), and poly(tertiary-butylvinylcyclohexane) (PtBVCH), respectively. In each case, except PαMS, the materials were saturated to > 99% conversion with no chain degradation. PS hydrogenations required the addition of small amounts of tetrahydrofuran to the reaction solvent cyclohexane to enhance miscibility and eliminate large-scale chain degradation. Density gradient and differential scanning calorimetry (DSC) measurements were used to characterize the density and glass transition temperature, T_g, of the unsaturated and saturated polymers. Saturation reduces the density by 3% to 11% and changes T_g substantially. The greatest variation in T_g is obtained with the 3-methyl substituted species where a 63°C increase is observed, while the highest measured T_g is 186°C for P2MVCH. Small-angle neutron scattering (SANS) experiments on binary mixtures of hydrogenous and deuterium labeled PVCH derivatives provided a determination of bulk chain statistics. The statistical segment length is relatively insensitive to vinylcyclohexane ring substitution, except with P3MVCH where a 20% greater value is obtained. ©1995 John Wiley & Sons, Inc.     

Crystallization of tethered polyethylene in confined geometries

Ordered poly(ethylene)‐poly(vinylcyclohexane) (PE‐PVCH) block copolymers are employed to study the crystallization of tethered PE in confined geometries. The high T_g of the PVCH component of these materials forces PE chains to crystallize in well‐defined geometries dictated by the mesophase structure of the block copolymer. Effects of chain tethering on crystallization are examined through comparison of singly‐tethered PE chains in PE‐PVCH (EV) diblocks and doubly‐tethered PE in PVCH‐PE‐PVCH (VEV) triblocks. Crystallinity is independent of the block copolymer mesophase structure in both the EV and VEV systems, although crystallinity in VEV depends on the molecular weight of the PE block of the copolymer. Melting temperature data indicate that spatial confinement reduces crystallite size in EV and VEV, and that the double tethering of PE chains in VEV reduces crystallite size further through topological constraints. Crystal nucleation and growth depend strongly on the type of microstructure in both EV and VEV block copolymers. Differences in the overall rate of crystallization are correlated with the dimensional continuity of the PE microdomains. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37:2053–2068, 1999     

Copolymerization of vinylcyclohexane with ethene and propene using zirconocene catalysts

Vinylcyclohexane (VCH) was copolymerized with ethene and propene using methylaluminoxane‐activated metallocene catalysts. The catalyst precursor for the ethene copolymerization was rac‐ethylenebis(indenyl)ZrCl₂ ( 1 ). Propene copolymerizations were further studied with C_s‐symmetric isopropylidene(cyclopentadienyl)(fluorenyl)ZrCl₂ ( 2 ), C₁‐symmetric ethylene(1‐indenyl‐2‐phenyl‐2‐fluorenyl)ZrCl₂ ( 3 ), and “meso”‐dimethylsilyl[3‐benzylindenyl)(2‐methylbenz[e]indenyl)]ZrCl₂ ( 4 ). Catalyst 1 produced a random ethene–VCH copolymer with very high activity and moderate VCH incorporation. The highest comonomer content in the copolymer was 3.5 mol %. Catalysts 1 and 4 produced poly(propene‐co‐vinylcyclohexane) with moderate to good activities [up to 4900 and 15,400 kg of polymer/(mol of catalyst × h) for 1 and 4 , respectively] under similar reaction conditions but with fairly low comonomer contents (up to 1.0 and 2.0% for 1 and 4 , respectively). Catalysts 2 and 3 , both bearing a fluorenyl moiety, gave propene–VCH copolymers with only negligible amounts of the comonomer. The homopolymerization of VCH was performed with 1 as a reference, and low‐molar‐mass isotactic polyvinylcyclohexane with a low activity was obtained. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6569–6574, 2006     

Polymerization of vinylcyclohexane with ziegler–natta catalyst

Polymerization of vinylcyclohexane (VCHA) with TiCl₃–aluminum alkyl catalysts was investigated. The polymerization rate of VCHA was low due to the branch at the position adjacent to the reacting double bond. The effects of aluminum alkyl on the polymerization and monomer-isomerization were observed; the polymer yield decreased in the following order: (CH₃)₃Al > (i–C₄H₉)₃Al > (C₂H₅)₃Al. Isomerization of VCHA was observed with the TiCl₃–(i–C₄H₉)₃Al and the TiCl₃–(C₂H₅)₃Al catalysts during the polymerization, while with the TiCl₃–(CH₃)₃Al catalyst such isomerization was not observed. Monomer-isomerization copolymerization of VCHA and trans-2-butene took place to give copolymers consisting of VCHA and 1-butene units.     

低密度聚环己基乙烯泡沫的制备

低密度CH聚合物多孔材料是惯性约束聚变(ICF)的重要靶材料,利用热致相分离原理对低密度聚环己基乙烯泡沫的制备进行了研究。首先通过聚苯乙烯(PS)氢化反应制备了聚环己基乙烯(PVCH),经过溶剂选择,确定以环己烷/1,4-二氧六环为溶剂体系,经热致相分离和冷冻干燥技术制备出低密度PVCH泡沫。通过分析溶液浓度对泡沫密度的影响,确定了泡沫密度与聚合物溶液质量浓度之间的关系,在0.04~0.15 g/cm3/sup>范围之内可实现对泡沫密度的有效控制。泡沫孔结构测试结果表明随着密度的增加,平均孔径有升高的趋势,孔径分布趋于单一化,孔径范围为23.63~0.83 μm。