Synthesis and reactivity of a fluorinated N-alkylmaleimide towards free-radical grafting and polymerization reactions

A new fluorinated N-alkylmaleimide, N-(2-pentadecafluoro-n-octanoyloxy)-ethyl)maleimide (FOMI), was synthesized from perfluorooctyl carboxylic acid (FOCA) by reaction of the furan adduct of maleic anhydride (MAH) with ethanolamine and esterification of the resulting alcohol-imide. The reactivity of FOMI in free-radical reactions such as copolymerization with butyl vinyl ether (BVE) and grafting onto olefin copolymers (OCP) was investigated. Copolymerization with 2/1 molar excess BVE yields a copolymer with 63 mol% FOMI in moderate conversion, indicating that homopropagation of the maleimide prevails over comonomer alternation. The thermal stability of FOMI is quite poor, with onset of the pyrolytic loss of the N-perfluoroalkylcarboxyethyl moiety just above 100 °C, similarly to that of FOCA. This restricts the possibilities for direct melt functionalization of OCP with FOMI. To bypass this limitation three distinct approaches were preliminarly investigated. These were respectively based on either direct grafting of FOMI at low temperature, or reaction of a MAH-grafted polyolefin with a low molecular weight amine or amino-terminated oligomer bearing the perfluoroheptyl group. A functionalization degree FD=2% was achieved by solution grafting of a linear very low density polyethylene (VLDPE) with FOMI and Perkadox 16 as the free-radical initiator. The relatively high grafting efficiency was attributed to the growth of some oligomeric FOMI grafts onto the OCP. The alternative routes of post-modification of VLDPE-g-MAH by imidization with an amidoamine obtained by amidation of FOCA with a diamine or an amino-terminated FOMI/BVE oligomer, respectively, were also preliminarly investigated.     

A Comprehensive Review on Controlled Synthesis of Long‐Chain‐Branched Polyolefins: Part 2, Multiple Catalyst Systems and Prepolymer Modification

Long‐chain branching plays an important role in the performance of polyolefins (POs). The existence of a very small amount of long‐chain branches (LCBs), i.e., <1 per 10 000 carbons, can significantly improve processability of the polyolefin materials, which is highly desired for those intractable polyolefins with narrow molecular weight distribution and high degree of crystallinity. Numerous literatures have been published on the controlled synthesis of long‐chain‐branched POs. In the previous paper, the major literatures of single catalyst systems have been summarized. This paper provides a comprehensive review for the binary and multiple catalyst systems and a brief summary of some other methods for the controlled synthesis of long‐chain‐branched POs. The controllability of long‐chain‐branched structures in the various preparation procedures with single or two reactor systems, and in one or two‐step processes, is analyzed and compared in‐depth.

     

An In situ Experimental Study on Solidification Kinetics of Polyolefins: Effect of Cooling Conditions

The solidification kinetics of polyolefins (PO) under three cooling conditions were investigated using an in situ measurement of the temperature decay within the PO resins. The phase-change temperature range of high-density polyethylene (HDPE) was located between 110 and 120°C, and those of low-density polyethylene (LDPE) and polypropylene (PP) were 90–110°C and 100–120°C, respectively. The cooling rate of the liquid-state stage is larger than that of the crystallization stage, primarily owing to the release of the latent heat of crystallization as well as the reduced temperature difference between the sample and cooling medium; they jointly slow down the cooling rate to an extent. The time with respect to phase transformation and its lasting period have close relations to the materials' molecular characteristics (e.g., Mw, MWD, LCB, etc.). Three empirical equations were proposed, and found to be applicable for the cooling analysis of the PO molten materials at relatively low cooling rates prior to crystallization.     

Well‐defined polyolefin/poly(ε‐caprolactone) diblock copolymers: New synthetic strategy and application

A new synthetic strategy, the combination of living polymerization of ylides and ring‐opening polymerization (ROP), was successfully used to obtain well‐defined polymethylene‐b‐poly(ε‐caprolactone) (PM‐b‐PCL) diblock copolymers. Two hydroxyl‐terminated polymethylenes (PM‐OH, M_n= 1800 g mol^?1 (PDI = 1.18) and M_n = 6400 g mol^?1 (PDI = 1.14)) were prepared using living polymerization of dimethylsulfoxonium methylides. Then, such polymers were successfully transformed to PM‐b‐PCL diblock copolymers by using stannous octoate as a catalyst for ROP of ε‐caprolactone. The GPC traces and ¹H NMR of PM‐b‐PCL diblock copolymers indicated the successful extension of PCL segment (M_n of PM‐b‐PCL = 5200–10,300 g mol^?1; PDI = 1.06–1.13). The thermal properties of the double crystalline diblock copolymers were investigated by differential scanning calorimetry (DSC). The results indicated that the incorporation of crystalline segments of PCL chain effectively influence the crystalline process of PM segments. The low‐density polyethylene (LDPE)/PCL and LDPE/polycarbonate (PC) blends were prepared using PM‐b‐PCL as compatibilizer, respectively. The scanning electron microscopy (SEM) observation on the cryofractured surface of such blend polymers indicates that the PM‐b‐PCL diblock copolymers are effective compatibilizers for LDPE/PCL and LDPE/PC blends. Porous films were fabricated via the breath‐figure method using different concentration of PM‐b‐PCL diblock copolymers in CH₂Cl₂ under a static humid condition. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Unsaturation Characterization of Polyolefins by NMR and Thermal Gradient NMR (TGNMR) with a High Temperature Cryoprobe

Summary: It is important to identify the types of unsaturation and to quantify the amount of unsaturation in polyolefins for understanding chain termination mechanisms of polymerization with different catalysts. Unsaturation is also closely related to processibility, weatherability of polyolefin products and the level of antioxidants to be added for stabilizing purposes. However, it can be very challenging to accurately measure samples with a low level of the unsaturation within a reasonable amount of NMR acquisition time, along with some challenging technical issues, such as dynamic range with ¹H NMR. This paper reports a new method to accurately quantify unsaturation by using multi peak presaturation ¹H NMR with a high temperature NMR cryoprobe. The limit of quantification can be less than 1 unsaturation/1,000,000 carbons with about 30 min NMR acquisition. This paper also introduces a new technique, temperature gradient NMR (TGNMR) with or without substrates, to characterize unsaturation distribution directly in NMR tube upon temperature change.     

High Temperature Thermal Gradient Interaction Chromatography (HT-TGIC) for Microstructure Analysis of Polyolefins

Summary: High temperature thermal gradient interaction chromatography (HT-TGIC) is a newly developed technique to analyze comonomer distributions in polyolefins. This paper documents the key differences between crystallization elution fractionation (CEF) and HT-TGIC, and the advantages of using multiple detectors in HT-TGIC to provide comprehensive microstructure characterization. A demonstration of the technique using a specifically designed blend, provides comprehensive data in less than 1.5 hours of analysis time by HT-TGIC. This paper also reports that HT-TGIC has excellent short term repeatability.     

Small‐Molecule Modulation of Soft‐Matter Frank–Kasper Phases: A Method for Adding Function to Form

Incorporation of small amounts of α‐tocopherol (vitamin E) in blends with the cellobiose–triazole‐linked atactic poly(4‐methyl‐1‐pentene) (CB‐aPMP) sugar–polyolefin conjugate can be used to exert external control over thermotropic phase behavior and provide access to non‐canonical soft matter Frank–Kasper A15 and σ phases. These results establish a paradigm that can be used for the further design and development of scalable quantities of soft matter FK phases of increased structural complexity and functional capability.     

聚烯烃弹性体催化剂研究进展

聚烯烃弹性体(POE)是一类有高性能、高附加值的高分子材料,随着其应用领域的不断拓展,在国内外得到迅速发展,国内各大相关企业纷纷投入巨资进行研究开发。作为聚烯烃产业核心技术的催化剂,核心技术目前主要控制在西方公司手中,开发具有自主知识产权的催化剂是当前的POE领域研究热点。为了给国内同行提供参考,课题组结合国内外的研究工作,对目前主流的POE催化剂——限定几何构型茂金属催化剂(CGC) 、桥连双配体结构茂金属和苯氧基亚胺催化剂(FI)的发展历程进行了评述,对近五年这三类催化剂的微观结构、催化活性以及结构与催化性能的关系,特别是催化乙烯/1-辛烯共聚反应的活性以及1-辛烯插入率进行详细的比较,考察了各类不同的有机配体对催化剂催化行为、聚合物组成的影响,揭示了均相催化条件下通过改变配体结构以提高聚合反应温度和1-辛烯插入率的技术方案,本文摘录了67篇文献,涉及到109种催化剂,相信本文的工作对于国内同行设计、合成新型POE催化剂将具有重要的参考作用。     

Amphiphilic Triblock Copolymers Containing Polypropylene as the Middle Block

The synthesis of stereoregular telechelic polypropylene (PP) and their use to access triblock amphiphilic copolymers with the PP block located in the center is described. The strategy consists of selectively copolymerizing propylene and a di-functional co-monomer (1,3-diisopropenylbenzene) to yield a α,ω-substituted polypropylene. Initiation of the copolymerization favors insertion of DIB over propylene; propagation steps favor insertion of propylene. Termination via a chain-transfer reaction yields the terminal unsaturation of the polymer. The telechelic polypropylene is then converted into α,ω-hydroxyl-terminated polypropylene and used as a macroinitiator for the synthesis of triblock copolymers. Water-soluble amphiphilic triblock polymers are also synthesized. The use of catalytic reactions simultaneously provides the stereocontrol of the polypropylene and high productivity (multiple chains of block copolymer per metal center).     

呼吸图法制备聚亚甲基-b-聚甲基丙烯酸甲酯多孔薄膜

首先利用叶立德活性聚合和原子转移活性自由基聚合(ATRP)相结合制备了三个不同链段比的聚亚甲基-b-聚甲基丙烯酸甲酯(PM-b-PMMA)两嵌段聚合物. 接着以它们为原料, 利用静态呼吸图方法在四种不同溶剂中制备了一系列的具有蜂窝状表面的多孔薄膜, 用扫描电子显微镜(SEM)观察了多孔薄膜的形貌. 研究了溶剂、溶液浓度、聚合物链段长度及链段比等因素对多孔薄膜表面孔的大小和分布的影响. 结果表明: 当PM_2k-b-PMMA_2k嵌段聚合物浓度为3 wt%、溶剂为二硫化碳(CS₂)和二氯甲烷(CH₂Cl₂)时, 可以通过静态呼吸图方法制备出孔径为纳米级(520 nm)和微米级(1.1 μm)的较为规整的多孔薄膜. 多孔薄膜表面的孔径随PM-b-PMMA浓度的减小而增大|两嵌段聚合物中两个链段的长度及其链段比的变化对多孔膜表面孔径均产生较大的影响.